EXTRACTION OF POST-TANNING CHEMICALS

FROM LEATHER WASTES

by

G. SENTHILKUMAR ARGOT, B.Tech.

A THESIS

IN

CIVIL ENGINEERING

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

IN

CIVIL ENGINEERING

Approved

Accepted

December, 2000

ACKNOWLEDGMENTS

I wish to thank my conmiittee members Dr. Heyward Ramsey (Chairperson), Dr.

Richard Tock, and Dr. Dennis Shelly for their support in this project. Beyond the project,

I owe Dr. Shelly a great deal more for his guidance as a professional in all the decisions

that I have made as a graduate student for the past 18 months. He will be a role model to

me forever.

I would like to thank Dr. Ramsey for being pafient with me while selecting

courses for each semester, his help as a faculty advisor put me in the right direction such

that I was able to complete my degree in the right pace. I would also like to thank Dr.

Tock for helping me get the ftinding for summer 1999 and for the academic year 1999-

2000. This made my stay in Lubbock a pleasant one without any financial difficulties.

The support of my family has meant a lot to me. Without their blessings, I could

not have succeeded. To my parents go my love and respect—thanks for providing me

with a good education and for standing by me on all the decisions that I have made so far.

I would also like to thank my brother for showing what not to do in more than one way.

Thank you Bobsy.

I wish to thank the Leather Research Institute for sponsoring and providing space

for my projects and for supporting me financially. I wish to thank all those with whom I

have worked in L.R.L, especially Dr. Terry Ervin. I would like to thank someone who

showed me how to be mean and yet retain a healthy friendship. Jill you have been a

11

wonderftil person right from the first day I started working in L.R.L I would like to thank

you for all the help that you have done to me (especially the first aid kit).

I wish to thank Dr. Ramesh Krishnan, and Dr. Sethuraman for their help in

providing me informafion on SFE. I would also like to thank Sada for helping in my

thesis work. I would like to thank Sahu, Thanikai, and Subbu for providing me with

valuable suggestions during my thesis work.

I wish to thank Vasuki for making me realize a few things about life. Thanks a lot

Vasuki. I would also like to thank all my friends in Lubbock especially the guys who

come to play cricket (long live cricket).

Finally, I wish to thank my fiancee for allowing me to pursue my childhood

dream and for bearing with me for the past 2 years. She was always there for me. Her

support, love, and friendship helped through all the rough times. I love you da.

Ill

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACT vi

LIST OF TABLES vii

LIST OF FIGURES viii

CHAPTER

I INTRODUCTION 1 1.1 Problem Identification 1 1.2 Generation of Leather Scrap 3 1.3 Leather Recovery Processes 5 1.4 Objectives 6

n LITERATURE REVIEW 8 2.1 Extracting Techniques 8

2.1.1 Conventional Method 9 2.1.1.1 Extraction of Fatliquor 9

2.1.2 Supercritical Fluid Extraction Technology 10 2.1.2.1 Factors Determining Extractability 13 2.1.2.2 Applications of Supercritical Fluids 16

2.2 Recovery Processes 17

III EXPERIMENTAL PROCEDURES AND PLAN OF WORK 19 3.1 Sample Preparafion 19

3.1.1 Precaution 20 3.2 Extraction of Sample Components 20

3.2.1 One-Step Process 22 3.2.1.1 Optimization of Temperature and Density in SFE... 24 3.2.1.2 Control Experiments 24

3.2.2 Two-Step Process 27 3.2.2.1 Soxhlet Extraction 27 3.2.2.2 Extraction of Residue Using SFE 28

3.2.3 Modifier-Assisted SFE Process 30 3.3 Analysis of Extract 30

3.3.1 Quantification of Extract 30 3.3.2 GC Analysis 31

3.4 Plan of Work 31 3.4.1 Pre-Treatment 31 3.4.2 Experimental Design 32

IV

3.4.3 Two-Step Process 33 3.4.3.1 Removal of Fafliquors by Solvent Exchange

Method 33 3.4.3.2 Removal of Retannins and Dyes and by SFET 33

3.4.4 One-Step Process 35 3.4.4.1 Removal of Post Tanning materials by SFE 35

3.4.5 Analysis 35 3.4.5.1 Gravimetric Analysis 35 3.4.5.2 GC Analysis 35

IV RESULTS AND DISCUSSION 36 4.1 Soxhlet Extraction 36

4.1.1 Extracfion of Soxhlet's Residue 36 4.2 SFE Experiments 39

4.2.1 Effect ofTemperature With Constant Density 39 4.2.2 Effect of Density With Constant Temperature 39 4.2.3 Optimization of Sample Weight 43

4.3 Effect of Modifiers 43 4.4 Comparison of Extraction Techniques 47 4.5 Control Experiment Results 48 4.6 GC Analysis Results 48

V CONCLUSION AND RECOMMENDATION 52 5.1 Conclusion 52 5.2 Recommendation 54

REFERENCES 55

APPENDDC A. SAMPLE PREPARATION 59 B. EXTINCTION FROM POWDERED LEATHER USING SFE 61

ABSTRACT

The disposal of leather scraps produced by the footwear industry is a difficult and

expensive task due to their undesirable and adverse effects on the environment. It will be

profitable for the shoe industry to convert this waste into value added products. This

thesis investigated the feasibility of employing supercritical fluid extraction (SFE)

technique in the pre treatment phase of gelatin extracfion process (Taylors' Process). The

current study had three experimental phases namely sample preparation, extraction of

components from the sample and quantification of the extracted components. Three

methods (one-step process, two-step process and modifier-assisted SFE process) were

used in the extraction of components from leather samples. In the one-step process, the

post-taiming chemicals were extracted using SFE. In the two-step process, Soxhlet

extraction followed by SFE was employed in extracting the post-tanning chemicals.

Preliminary SFE experiments were conducted to determine optimum extracting

conditions for the extraction of post-tanning chemicals from leather scraps. The third

method was similar to one-step process, except that instead of using carbon dioxide as

extracting solvent modified carbon dioxide was used. The modifiers used were methanol

and phenol. This research was able to introduce SFE as an option for extracting post-

tanning chemicals from leather scraps by optimizing the extraction conditions and

comparing the results with conventional Soxhlet extraction technique.

VI

LIST OF TABLES

2.1 Physical Data for Gaseous, Supercritical Fluid, and Liquid States 15

2.2 Comparison of Physical Properties of Supercritical Carbon Dioxide with Liquid Solvents at 25^C 15

3.1 SFE Operating Conditions 25

3.2 Extraction Conditions Tested 26

4.1 Soxhlet Extraction Results 37

4.2 Soxhlet Residue Results under SFE 38

4.3 Effect of Temperature on Quantity of Extract (Constant Density) 40

4.4 Effect of Density on Quantity of Extract 41

4.5 Optimization of Sample Weight 44

4.6 Effect of Phenol as Modifier 45

4.7 Effect of Methanol and Phenol-Methanol as Modifiers 45

4.8 Comparison of Effects of Extraction Techniques for 100 Units of Powdered Leather Scraps 46

4.9 Control Experiment Results 46

A. 1 Moisture Content 60

B. 1 Optimization of Extraction Conditions 62

B.2 Quantity of Post-Tarming Chemicals 63

Vll

LIST OF FIGURES

1.1 Location of Hide Parts 4

2.1 Phase Diagram for Carbon Dioxide (Pressure vs. Temperature) 12

3.1 Extraction Thimble Packed with Sample 21

3.2 Flow Diagram of SFE Unit 23

3.3 Soxhlet Extraction 29

3.4 Plan of Work 34

4.1 Results from GC Analysis (Control) 50

4.2 Results from GC Analysis (Phenol Methanol-Modified Carbon Dioxide) 51

Vlll

CHAPTER I

INTRODUCTION

1.1 Problem Identification

One of the major concems in the footwear industry is the disposal of leather

scraps produced during the manufacture of shoe uppers (Wilford 1999). These solid

wastes are difficult to avoid or reduce due to the nature of tanned leather and the pattem

shapes required for shoe manufacture. Wilford (1999) reported that some 0.4 million

tons of waste leather is produced annually by the footwear industry. Some of these

wastes may be marketable, with small additional cost for further processing or transport,

but the remainder requires disposal. This may be a difficult and expensive task, as the

scraps are often considered undesirable in many environments due to their smell, noxious

nature, or adverse effect on the surrounding land or water. It is vital for the shoe industry

to devise a process that can treat and convert this waste into usable products.

Solid waste reduction can be achieved by the following methods: source

reduction, reuse and reprocessing, and land filling. Source reduction is the best method

of waste minimization for any type of pollution. As mentioned, it is difficult to achieve

100 percent use of the leather through source reduction as the property and value of the

leather varies with respect to the location of the tabbed hide. Land filling is the primary

method that is employed to dispose of leather scraps. Altematively, some of the larger

leather scraps generated in shoe manufacturing may be reused in the manufacture of

small leather items like wallets, pouches, and belts or patchwork designs whereas the

shavings and buffing dust can be part of composite materials such as leather boards

(Brown et al. 1996). However, the demand for these products is far less than the supply,

so that large amounts of leather scraps are transported to landfills. One option available

to the shoe industry that would help reduce the disposal of leather scraps in landfills is the

extraction of gelatin and hydrolizable protein from wet blue shavings. This process may

be extended to finished leather scraps.

To reuse finished leather, it is vital to remove the chemicals such as chromium,

retarming agents, fatliquors, and dyes prior to the recovery process. General and

advanced separation techniques that are utilized in other industries like ultrasonic

separation and supercritical fluid technology, may be applicable for the removal of the

post tanning chemicals from the leather scraps, so that the treated scraps can be processed

for the extraction of gelatin.

Gelatin, the most profitable value added byproduct from leather scrap recovery, is

an important commodity used in the manufacture of a wide range of products. Gelatin is

an important ingredient in food, pharmaceuticals, textiles, and in the production of a

variety of other industrial products. The highest quality gelatin is used in the

photographic industry, whereas the food industry makes use of lowest quality edible

gelatin. The pharmaceutical industry uses the industry's established United States

Pharmaceutical grade for its gelatin purchases.

1.2 Generation of Leather Scrap

It is essential to know the different locations on a hide to fiilly understand the

difficulty involved in the pattem cutting used for shoe uppers that contributes to waste

production. A cowhide is divided into the following locations as shown in Figure 1.1.

These locations are known in the business as the belly, butt, shoulder, fore shank, hind

shank, double shoulder, and neck. The location with the highest cutting value in a hide is

the butt region. Leather processed for shoe uppers should be flat and smooth. The grain

surface must not have any defects such as brands, scars, infections, flay-cuts, or sections

affected by putrefaction.

The leather for shoe uppers is cut with a die by laying the die on the leather and

cutting each piece. Definite operational guidelines are utilized by leather industry

workers to guide the cutting operations. Parts of the toe and vamp should be cut from the

butt area whereas heel parts can be cut from bellies and looser areas. Care should be

taken to avoid color differences on the cutout from one side of the piece to the other. All

these factors contribute to the generation of leather scraps while producing shoes. Thus,

the cutting efficiency and the quantity of scrap generated per hide may vary from one

hide to another ranging from 50 percent to nil; the amount per hide carmot be determined

accurately. The scrap produced could be the fiiU hide or small trimmings based on hide

quality.

Tt-_>.S. MIHD

'SWAN

Figure 1.1 Location of Hide Parts (Thorstensen 1993)

1.3 Leather Recovery Processes

The unit operation that produces the maximum amount of scrap leather is the

cutting operation. The leather scraps that are collected are sorted manually based on the

size. The larger scraps (5 ft and above) are usually used in the manufacture of small

goods such as wallets and for patchwork. In some production units, only the ftiU sides

(one half of a hide) are used for the production of small goods, the rest of the scraps are

taken to landfills. The leather scraps are taken to the landfills by a collection agency

whose charges may range up to $1500 per month.

The scraps collected could be reprocessed into value added gelatin. The presence

of post taiming chemicals (retarming agents, fatliquors, and dyes) is a major problem in

the gelatin recovery process. This investigation is a start in developing a profitable

means to produce gelatin from the finished leather wastes by extracting the post tanning

chemicals from leather.

In the manufacture of shoe upper leathers from cowhides, the raw hides are

initially tarmed to wet-blue using an 8% chrome sulfate solution. The wet-blue hide is

then treated with 20 to 25% of retanning agents and 10 to 12% of fatliquors. The

percentage of dye given may vary (2 to 5%) depending on the shade required. Assuming

an ideal condition where all the chemicals are absorbed by the leather, 100 units of

leather scrap will contain 25 units of retarming agent, 12 units of fatliquors, 5 units of

dyes, and 8 units of chrome sulfate. Once the post-tarming chemicals are extracted, the

remaining mass should have at least 50 units of protein for gelatin production.

Based on this, the amount of finished leather scraps available per annum for

disposal can be estimated at 0.2 million tons. If 50% of the available leather scraps are

converted to gelatin, then the yield of gelatin can be estimated to be 33 M lbs. per annum

at the current gelatin extraction efficiency. The lowest quality gelatin is priced at

approximately SI.00 per pound. Thus, the potential of a practical gelatin recovery process

as a viable solution for the leather waste disposal problem of the footwear industry is

high.

Currently there are no commercial-scale extraction processes available for the

removal of post tarming chemicals from leather. In most lab-scale activities, a solvent

exchange method is used for the removal of fatliquors from leather scraps. Another

prospect that posses possibilities for use in leather recovery is the supercritical fluid

extraction technique (SFET). Unlike solvent exchange where fatliquor alone is removed,

SFET has the potential to extract many more post tanning chemicals. This research

explored methods to optimize the parameters of SFET.

1.4 Objectives

The current investigation looked into the possibilities of utilizing supercritical

fluid technology in the extraction of post tanning chemicals from leather scraps. The

primary objective was to produce gelatin through processing to remove the tarming

agents from the finished leather scraps collected following the manufacturing operations.

As there are no established methods available currently for the removal of retanning

agents and dyes, an approach using supercritical fluid was employed and investigated.

The extraction of fatliquors will be compared between the conventional solvent exchange

method and supercritical fluid method. The ultimate aim of the project is the development

of an innovative method for the recovery of gelatin from leather scraps and thereby, to

reduce the amount of land filled solid waste produced by the footwear industries.

CHAPTER II

LITERATURE REVIEW

This chapter revieus the \arious extraction techniques that were used previoush

for the extraction of post tanning chemicals. The review will provide insight into the

de\ elopment of the soh ent exchange method with respect to the extraction of fatliquors

from leather. The theory behind the working principle of SFE and the development of its

application is discussed. Moreover, the literature revie\\ formed the basis from which the

ultimate plan of action for this study was derived. The literature re\ ie\\ substantiated the

non-existence of a commercial method for the extraction of post tanning chemicals from

leather using conventional or SFE techniques and thereby, reiterates the importance of

this stud). Thus, it was necessary to develop and perform a feasibility study to optimize

the parameters of SFE and to determine the efficiencies of SFE and the Soxhlet extraction

methods.

2.1 Extraction Techniques

The principle behind the extraction of a compound or mixtures of substances from

a sample matrix such as leather scraps is to cause the matrix to \ield at least two fractions

of differing properties by using a third component (usually called as an extracting agent)

or by supplying energy (Stahl et al. 1988). The major factor that determines the choice of

separation is whether the sample matrix is homogeneous or heterogeneous. A

heterogeneous matrix can be separated using mechanical operations like filtration,

8

centriftiging, or pressing. To separate a homogeneous matrix, it is essential to know the

differing physico-chemical properties of the individual components in the matrix. In any

solvent exchange method, a mobile liquid solvent is used as an extraction agent, whereas

in supercritical fluid extraction dense gaseous fluids are used.

2.1.1 Conventional Method

The literature review revealed that there are no established methods currently

available for the removal of retanning chemicals and dyes from leather scraps. The

preferred method for lab-scale studies employed for the removal of fatliquors from

leather is the solvent exchange method. Solvent extraction is a traditional extraction

method in which a mobile liquid solvent that is immiscible is introduced into a container

of solid or hquid sample (Sethuraman 1997).

2.1.1.1 Extraction of Fatliquor

Early development work in the extraction of lipids from leather was performed by

Wilson in 1918 (O' Flaherty et al. 1965). The ALCA committee declared that no solvent

has 100 percent removal efficiency in extracting fatliquors from leather (JALCA 1919).

Zimmerman and Pangbom (1951) developed a procedure to extract lipids from chrome

retan upper leather. This method was adapted from that used in extraction of rubber

samples. In this method, the leather sample is placed in a metal thimble present in a

Pyrex siphon cup that is suspended from a coiled block tin condenser. This entire setup

is inserted into a 400 mL wide-mouth Erlenmeyer flask. Sufficient heat is supplied to fill

and empty the siphon cup every 2 to 3 minutes. The total time period for this experiment

ranges from 2 to 24 hours (O' Flaherty et al. 1965). However, the Swiss Association of

Leather Chemists submitted a report favoring the Soxhlet method over the method

suggested by Zimmerman and Pangbom. The Soxhlet extraction is a method used for

continuous extraction of analytes from a solid into an organic solvent. As the flask

containing the solvent is heated, vapors rise in the larger outside tube, enter the water-

cooled condenser, and condense. When the liquid level in the extractor reaches the top of

the bent tube, siphoning action retums the extract-enriched solvent to the flask (Hewlett-

Packard 1990). The completed extraction produces a high-volume dilute solution that

needs to be concentrated prior to evaporation. The committee report claims that the

Soxhlet method is more convenient and that the Zimmerman and Pangbom method gave

no better results (1955). Pre-drying the leather to remove the moisture present in the

leather reduces the contamination of fatty extracts by non-fatty substances (Merrill 1951).

The usage of the Soxhlet apparatus for extracting fatty matters from a wide

variety of materials is followed worldwide. Petroleum ether is the preferred solvent as its

boiling point is about 50''C (O'Flaherty 1965).

2.1.2 Supercritical Fluid Extraction Technology

One of the newest methods used to extract analytes from a sample is the

supercritical fluid extraction process. The state of the fluid above its critical pressure and

critical temperature is called supercritical fluid (Taylor 1996). Supercritical fluids (SF)

possess some unique properties that make them one of the best extracting solvents.

10

Though the density of SF is slightly less than the liquid, the dynamic viscosit> is similar

to that of the normal gas state. Moreover, the diffusion coefficients of SFs are an order of

magnitude ten greater than those of liquids. These characteristics make SFs attracti\ e

soh ents to penetrate into the solid matrix such as leather and carry aw ay the soluble

compounds. The visual disappearance of the gas-liquid boundan, for SFs was first

reported by Baron Cagniard de la Tour (1822). The abilit\ of supercritical fluids to

dissoh e low-vapor-pressure sohd materials was first reported at a meeting of the Royal

Society of London in 1879 (Harmay and Hogarth 18^9).

In the later half of the nineteenth century, supercritical carbon dioxide attracted

considerable attention from researchers. Andrews (1875-1876) carried out an extensive

in\estigation on the phase behavior and critical properties of carbon dioxide. Francis

(1954) presented a quantitative study on the solvent properties of liquid carbon dioxide

with hundreds of compounds. However, the results of this work were general. E\en so.

the data was used to assess the potential of supercritical fluid extraction for many

separations before carr\ing out any experimental work. The commercial process of

decaffeination of green coffee with carbon dioxide (Zosel 1971) provided an incentive for

significant future development in supercritical fluid extraction.

The physical stage of carbon dioxide can be described by a phase diagram as

shown in Figure 2.1. The three Imes describmg the sublimation, melting, and boiling

processes correspond to the gas, liquid, and solid states. Points along the lines represent

the equilibrium between Uvo of the phases. The vapor pressure starts at triple point (TP)

and ends at critical point (CP). Any substance above the critical temperature (Tc) and

11

Pressure (Bars)

TP

400

350

300

250

200

150

100

'••'•50-.. . . .

S o 1 i d

G h T ^

Melting Line

Boiling line

-60 0 30 90

Sublimation line Temperature (Celsius)

Tc31.06degC

Figure 2.1 Phase Diagram For Carbon Dioxide (Pressure vs. Temperature) (Taylor, 1996)

CP = critical point Pc = critical pressure

TP = triple point Tc = critical temperature

12

critical pressure (Pc) can be defined as supercritical fluid (Taylor 1996). Table 2.1

provides a comparison of some of the significant properties of supercritical fluid with

liquids and gases (Taylor 1996).

The advantages of using supercritical fluids for extractions are that they are

inexpensive, contaminant free, and less expensive to dispose of in a safe manner than

organic solvents. The organic solvent-like property of a supercritical fluid with higher

difftisivity, lower viscosity, and lower surface tension provide some advantages for

analytical extractions. The solvating power can be adjusted by changing the density,

pressure, or temperature; or by adding modifiers to the supercritical fluid. A common

modifier used with CO2 is methanol (typically 1 to 10 percent) (Riley 1999). Phenol can

also be used as a modifier. At elevated temperatures, phenol being an organic acid has

the potential to hydrolyze the post tarming chemicals from the collagen matrix thereby

enhancing the efficiency of SFE. The addition of phenol may elevate the boiling curve

and at the same time lower the melting curve.

According to Sethuraman (1997), the following are some of the properties of

carbon dioxide that make it the most popular and appropriate solvent for supercritical

fluid extraction

• Non-toxic and inexpensive,

• Neither combustible nor explosive,

• Harmless to the environment, and

• Commercially available at all purity levels.

13

2.1.2.1 Factors Determining Extractability

According to Taylor (1996), the ability to remove analytes from a matrix depends

to varying degrees on the following factors irrespective of the extraction mode. They are:

• Solubility of an analyte in extracting supercritical fluid,

• Interaction between analyte and matrix,

• Analyte location within the matrix, and

• Porosity of the matrix.

The density of a solvent is one of the important factors governing the extraction of

solutes from the solid matrices. From Figure 2.1, it is apparent that near the critical

region the density of the fluid changes significantly with pressure (Stahl et al. 1988). A

marginal change in pressure near the critical temperature results in substantial variations

of solvent density whereas at reduced temperatures there are barely any changes in the

fluid density. Theoretically, the solubility of a compound in supercritical fluid is

dependent on solvent density and temperature of extraction (Chrastil 1982).

The difftisivity of supercritical fluid is 10 to 100 times lower than that of liquids.

Table 2.2 shows a comparison of physical properties of supercritical carbon dioxide with

liquid solvents at 25^C (Taylor 1996). Difftisivity of supercritical carbon dioxide at a

pressure ranging from 50 to 500 atm varies within 10'"̂ and 10'̂ ^ cmVsec. The value of

viscosity and difftisivity depends on temperature and pressure. Difftisivity increases with

an increase in temperature whereas viscosity decreases.

In the region near the critical point and at high pressures (300 to 400 atm),

changes in viscosity and difftisivity are more pronounced. The low value of surface

14

Table 2.1 Physical Data for Gaseous, Supercritical Fluid, and Liquid States (Taylor 1996)

STATE

GAS

SUPERCRITICAL FLUID (Tc, Tp)

LIQUID

DENSITY (gm/mL)

0.0006-0.002

0.2-0.5

0.6-1.6

DYNAMIC VISCOSITY (gm/cm-sec)

0.0001-.003

0.0001-0.0003

0.002-0.03

DIFFUSION COEFFICIENT

(cm^/sec)

0.1-0.4

0.0007

0.000002-0.00002

Table 2.2 Comparison of Physical Properties of Supercritical Carbon Dioxide with Liquid Solvents at 25^ C (Taylor 1996)

PROPERTY

DENSITY (gm/mL)

KINEMATIC VISCOSITY

(m^-sec)XlO^

DIFFUSIVITY IN BENZOIC ACID

(m^-sec)XlO^

CO2'

0.746

1.00

6.0

n-HEXANE

0.660

4.45

4.0

METHANOL

0.791

6.91

1.8

'200 atm, 55^C

15

tension coupled with the properties such as gas-like difftisivity and viscosity and liquid­

like density allow supercritical fluids to have better penetration into the sample matrix

(Stahl etal. 1988).

In the quantitative extraction of constituents from a matrix the efficient collection

by the trapping device is important for 100% recovery of the analyte. Trapping efficiency

may be influenced by extraction hardware like outlet restrictor; extraction parameters

such as chamber temperature, solvent density and so forth, and high percentages of

certain modifiers. Plugged restrictors may cause low recoveries and unreproducible

results. The presence of large amounts of inorganic sulfur, water, or other highly

extractable matter will plug the restrictor. There are four types of trappings, they are

accumulation of an analyte (1) into an empty bottle, (2) onto an inert solid support, (3)

onto an active solid sorbent, and (4) into a small volume liquid solvent (Taylor 1996).

Recovery of analyte by trapping the analyte onto the inert solid phase (stainless steel

beads) and rinsing with a solvent is more efficient than using a solid sorbent phase. When

modifiers are used it is better to keep the concentration of modifiers used low.

2.1.2.2 Applications of Supercritical Fluids

The removal of caffeine from green coffee beans using supercritical carbon

dioxide as the solvent was the earliest reported commercial application of supercritical

fluid extraction (Zosel 1964). After 1980, supercritical fluid technology advanced in the

fields of biotechnology, environmental control, and chemical engineering. Extraction of

hops, cholesterol from butter, monomers from polymers, and unsaturated fatty acids from

16

fish oils are just some of the applications of supercritical fluids. The impact of using

physico-chemical properties of solvents in numerous industrial applications has been

significant in recent \ears. These applications include remediation of soils, chemical

reactions involving synthesis of polymers and organic chemicals, in-situ deposition of

chemicals, and removal of nicotine from tobacco (Taylor 1996). Selecting organic

compounds from bulk samples, impregnation of chemicals, and analytical techniques are

other examples of the application of supercritical fluid technology (Sethuraman 1997).

In the field of leather technology, degreasing experiments were carried out using

supercritical fluid technolog>'. Another interesting potential use of supercritical fluid

technology for the leather industry is the extraction of metal ions from a protein substrate

(Addy 1999). Meyer and Kleibohmer (1997) compared the efficiency of supercritical

fluid extraction over conventional extraction methods. In their experiment,

pentachlorophenol present in leather and wood was extracted by SFE with in situ

derivatization.

2.2 Recovery Processes

Different processes for the treatment of tannery wastes such as recovery of

chrome shavings have been reported. The wet-blue shavings have also been treated with

enzymes for the recovery of chromium and hydrolyzed proteins (Taylor et al. 1992,

1993). Leather w astes can be processed for the recovery of gelatin, hydrolyzed protein,

and chromium (Brown et al. 1994, Taylor et al. 1994). The gelatin recovery process from

chrome shavings consists of an initial pepsin treatment (Taylor et al. 1995, 1998). The

17

leather waste is then treated by 10 %> magnesium oxide introduced at 76°C to stimulate

protein hydrolysis (Arcot et al. 2000). The suggested process time is 3 hours for a typical

extraction.

MgO maintains a pH of 8 to 9 in aqueous solution since it is a self-buffering

chemical compound. Taylor et al. (1998) and Cabeza et al. (1998 a, b) have documented

the mechanism of the reactions involved in the literature. The gelatin recovered is

isolated from the aqueous extract by filtration, de-ionization, and lyophylization (Taylor

et al. 1986, 1999). In the separation of gelatin from chrome cake, a cross flow filter can

be replaced by a centriftige (Shelly 1999).

A process economic study demonstrated that the two-step treatment of chrome

shavings has the potential for ftiture industrial applications (Cabeza et al. 1998). Taylor

et al. (1999) has demonstrated improvements in the process chemistry in a study. In the

U.S., 55.9 miUion lb of gelatin are imported annually (U.S. Department of Commerce

1998). Currently, the price of gelatin ranges from less than $1.00/lb for a low quality

inedible gelatin to $15.00/lb for a photographic grade gelatin (Shelly et al. 1999). Hence

the development of a process to produce gelatin from waste scrap leather should find a

ready market.

18

CHAPTER III

EXPERIMENTAL PROCEDURES AND PLAN OF WORK

The three experimental phases developed in this research were:

a. Sample preparation,

b. Extraction of components from the sample, and

c. Quantification of the extracted components.

This chapter present the experimental procedures followed, the instruments used for

extraction and analysis, and illustrations depicting the experimental setup.

3.1 Sample Preparation

The material used in this research was a milled (Fritsch mill) and dried form of

leather. The material was obtained from the production unit of Red Wing Shoes. Five

hundred grams of this leather was powdered in a cutting mill and then dried in a Precision

gravity convection oven.

The first step in the sample preparation was to dry the milled sample. The amount

of moisture present in the leather was measured using a gravimetric difference. A set of

five samples each weighing approximately five grams were placed in a ceramic crucible

(weight of the crucible already noted) and dried at 120° C for 20 hours. Then the cmcibles

were cooled in desiccators and weighed (Appendix A.l). All the samples used in the

experiment were used on a dry weight basis.

19

To ensure uniform distribution of the dried powder and to fill the void volume in

the thimble, celite was used as an extender. The sample was loaded in the thimble as

shown in Figure 3.1. The following procedure was adopted in preparing samples for all

the experiments.

a. An empty sample cup was weighed and the weight recorded.

b. A small quantity of sample ranging from 0.25 g to 0.5 g was placed in the cup.

c. Filter papers were cut to size and placed on the both sides of the thimble (Figure 3.1).

d. The sample was mixed with the extender in the ratio of approximately 1:2,

respectively, and added to the thimble.

e. The empty space inside the thimble was filled with celite.

3.1.1 Precaution

During sample preparation, the following precautions were followed to avoid

problems with clogging in the supercritical fluid extractor.

• Insure that the sample was not compressed,

• Do not overload the system, and

• Keep the sealing surfaces clean, and if necessary, clean them before securing the cap.

3.2 Extraction of Sample Components

As discussed in the previous chapter, the experimental stages involve the

extraction of the components from the sample utilizing three different techniques. A

conventional Soxhlet extraction apparatus and a HP 7680A supercritical fluid extractor

20

BxmAcnoNcsx THIMBLE CAP

SSFRIT

FILTER PAPER

LEATHER SAMPLE WITH CELITE

SSWALL

FILTER PAPER

Figure 3.1 Extraction Thimble packed with Sample (Hewlett-Packard 1990)

21

were used to extract the components from the leather sample. The experiments were

either duplicated or triplicated to provide an estimate of the repeatability of the

experimental parameter being measured. The following sections describe the

instrumentation and the procedures involved in this step.

3.2.1 One-Step Process

In the one-step process, a supercritical fluid extractor (SFE) was used. The SFE

apparatus (model HP 7680A) is a laboratory-scale unit that extracts chemicals from solid

and semisolid samples using solvents in their supercritical state. Carbon dioxide was

selected as the solvent, since it is non-toxic, inexpensive, harmless to the environment,

and commercially available at all purity levels.

A flow diagram of a SFE unit is shown in Figure 3.2. The extraction fluid was

pressurized to the necessary level using a high-pressure pump, and was then passed

through a heater in order to reach the desired temperature. The fluid then entered the

extraction chamber (thimble) that controls the temperature of extraction. At the specified

pressure and temperature, the supercritical fluid enters the thimble and dissolves the

extractable material. The fluid is then released from the extracted components when the

pressure of the fluid exiting the chamber is reduced while passing through a nozzle. The

extracted compounds are collected in a stainless steel trap.

This SFE was controlled by a HP Vectra PC based computer using HP

Chemstation software. In order to operate an SFE, several steps must be followed. For a

specific application, the set points were preset to the desired values and stored as a

22

rgh-pressLire

Pump

V-'.;;' ; ^ '

. A , / ^ . » - . ' . rr

ExL '̂action t!u;d 1 check valves ^

Extraction fluid select valves

1

CO,

i

rulse (iamper

Cv5T):5SSu're

PfBfiOZIjS

II..::

Prevatve f:l!er

/ / 3

M I X

A Mix 3

Pressure isciaton

valve

pressure Transducer

i Cham&e/

Preheaters 1

I

Tray ^ with ; viais U

To v.a3:=

R.nse solvent

Rinse puT.p ic-ve inlet valve

Ripse solvent select vaives

Bypass va!ve

Chamt>er valve

Figure 3.2 Flow Diagram of SFE Unit (Hewlett-Packard 1990)

23

method file. Moreover, instructions for the set up are given in the HP 7680 manual. The

methods and the sequence of steps performed can be saved for ftiture reference. Table 3.1

shows the operating conditions of the SFE unit used in this study.

3.2.1.1 Optimization ofTemperature and Density in SFE

Because the parameters involved in the extraction of post tarming chemicals from

leather waste were not known, preliminary SFE experiments were conducted to

determine optimum extraction conditions. The variables investigated were density,

temperature, pressure, and initial weight of sample. Pressure is dependent on the density

of carbon dioxide and temperature of the extracting chamber. Therefore, the experiments

were conducted by varying one parameter and keeping the others constant. A set of four

experiments per parameter was performed to determine the optimum solvent density and

chamber temperature. All the experiments were duplicated to check the repeatability of

the experiments. Samples of 0.5 grams were used in all the experiments prior to

optimization of an initial weight. The extraction conditions that were tested are the cells

that are checked in Table 3.2.

3.2.1.2 Control Experiments

To determine the reliability of the SFE apparatus, both standard and blank

experiments were used. The thimble was packed only with celite during the blank run

and then with 10 mg of paraffin for the standard runs. Optimized extraction conditions

were used to run both the blank and the standard.

24

Table 3.1 SFE Operating Conditions (Hewlett-Packard 1990)

CONDITION RANGE

Flow rate of CO2

Density of CO2

Chamber temperature

Extraction pressure

Extraction time

0.5 - 4.0 ml/min

0.25 - 0.95 g/ml

40-150°C

77 - 383 bar

0.00 - 300.00 min

25

Table 3.2 Extraction Conditions Tested.

Density Temperature (° C)

(g/mL) 40 50 60 70

0.3 X X X

X

0.5

0.7 X

0.9 X

26

3.2.2 Two-Step Process

In this phase, the first step involved extraction of leather sample utilizing the

Soxhlet extraction technique and a solvent. Then the residue, which remained after the

Soxhlet extraction, was subjected to the SFE process. Fatliquors are traditionally

extracted in laboratory-scale units using organic solvents in an experimental setup called

the Soxhlet apparatus. A base-case Soxhlet extraction was necessary in order to compare

the performance of SFE. Hence, the Soxhlet extraction process was conducted to:

• Extract the fatliquors present in the leather sample,

• Determine the performance of the SFE relative to Soxhlet extraction for

removal of fatliquors, and

• Determine the presence of components other than the fatliquors that were

extracted by SFE.

3.2.2.1 Soxhlet Extraction

The sample preparation for this process varies slightly from that used previously,

since in place of celite, it was necessary to use sea sand as filling agent. The purpose of

adding a filling agent is to increase the draining capacity of the solvent. Fatliquor is

highly soluble in petroleum ether. Moreover, the boiling point of petroleum ether is at 40

to 50° C, which is suitable for extraction using the Soxhlet apparatus. The duration of the

Soxhlet extraction range from 1 to 72 hours (Hewlett-Packard 1990). In this experiment,

the extraction was performed for 4 hours. Although the hardware required for a Soxhlet

extraction is relatively simple, extreme care must be taken to prevent contaminants of the

27

extract and to minimize any losses that might occur during sample transfer and solvent

exchange.

The Soxhlet apparatus was arranged as shown in Figure 3.3. The sample was

placed in a thimble (cellulose or ceramic) inside the extractor. The extractor was

connected to a flask containing the solvent and a condenser was fitted to the top of the

extractor. As the solvent boils, its vapor passes through a bypass arm to reach the

condenser where it condenses and then drips over the sample in the thimble. Once the

solvent level in the extractor reaches the top of the siphon arm, the solvent and the extract

are siphoned back into the lower flask. The extraction produces a high-volume, dilute

solution of solvent extract that usually requires concentration prior to quantification.

A sample size of 3.0 grams of dried leather powder was used for each experiment

and the extraction was carried out for approximately 4 hours. The extract was collected as

a solution and concentrated by partial evaporation of the petroleum ether. The experiment

was replicated three times.

3.2.2.2 Extraction of Residue Using SFE

The residue from Soxhlet extraction was subjected to SFE under the optimized

extraction conditions. The same procedures as described in section 3.2.1 were followed.

The residue was allowed to dry in a convection hood for 24 hours to ensure that the

extracted sample was devoid of solvent prior to loading in the SFE thimble.

28

Condcr.sef-

Exl/aclw-

Thfmble-

n

Solvent Heater-

Figure 3.3 Soxhlet Extraction (Hewlett-Packard 1990)

29

3.2.3 Modifier-Assisted SFE Process

This process is similar to the one-step process, except that instead of using carbon

dioxide as the extracting solvent, phenol-modified carbon dioxide was used. The

percentage of phenol added varies from 3 to 7 percent of the weight of sample taken. The

rest of the experiment is the same as the one-step process given in section 3.2.1.

Optimized extraction conditions were used. Phenol was added to the thimble along with

the sample prior to filling the thimble with celite.

A control experiment was performed by taking 30 mg of phenol mixed with twice

the amount of celite in the thimble, to quantify the amount of phenol being extracted by

the SF under the optimized conditions. The empty space in the thimble was filled with

celite.

3.3 Analysis of Extract

3.3.1 Quantification of Extract

Extract quantification was determined from gravimetric analysis. The samples

were weighed in a Mettler Toledo weighing apparatus that is sensitive to mass charges of

10""̂ g. The method followed for analysis was:

• The empty vials were weighed and this weight was recorded,

• The vial with the solvent and the extract was placed in rotary vacuum evaporator to

remove the solvent,

• The vial with the extract was weighed and recorded, and

30

• The difference in weight between the first measurement and the last gives the weight

of the extract.

3.3.2 GC Analysis

Gas chromatography (GC) is widely used for identification and quantification of

chemical compound especially volatile analytes. In this investigation, GC was primarily

used to ascertain the presence of volatile extracted components.

The extract from the final experiment (phenol-methanol-modified extraction) was

analyzed using GC. The column used for the experiment was a DB5 30 m by 0.25 mm

fused silica capillary column. The classic semi-volatile temperature gradient was used.

The initial temperature was set at 75°C, since this is greater than the boiling point of

tetrahydroftiron (THF). The boiling point of THF is 66°C. Isothermal conditions were

maintained for 2 minutes after injection. Then the temperature was increased to 150°C at

15°C per minute and then to 230°C at 20°C per minute. A final 5-minute isothermal step

at 230^C completed the elution condition.

3.4 Plan of Work

3.4.1 Pre-Treatment

Leather scraps are cut into strips of random size and then powdered by milling in

a cutting mill. The powdered leather product that results from the milling operation was

used as the sample material for the experiments. Care was taken while powdering the

scraps, since the leather strips can clog the cutting mill. To avoid this, the size of the

31

strips was restricted to pieces of 3 cm by 1 cm, and the cutting mill was never

overloaded.

3.4.2 Experimental Design

This study investigated the feasibility of using the supercritical fluid extraction

process to remove post-tanning chemicals from leather samples. Two methods of

removal were examined; a two-step process and a one-step process. In the two-step

process, the fafliquors are removed in the first step using a solvent exchange method.

The residual product is then processed using a supercritical fluid extraction technique

(SFET) to remove the retarmin agents and dyes.

In the second method, a single-step process, the powdered leather sample were to

be subjected to the supercritical fluid extraction technique to remove the fatliquors,

retarmins, and dyes all in one step. The amount extracted was calculated using a

gravimetric difference method. The difference between the weights from extracts from

the one step process and the value obtained from the second step in the two-step process

gave an identification of the fatliquors extracted in the single step process. This value

was used to compare the efficiency of the supercritical extraction technique with the

solvent exchange method. Moreover, a modified liquid carbon dioxide was used to check

the possibility of enhancing the extractability of the post tarming chemicals.

In all the methods pertaining to the super critical fluid extraction technique, a

supercritical fluid extraction (SFE) grade of carbon dioxide was used as the extracting

32

solvent. A batch process was used for the supercritical fluid extraction experiment. The

procedure that was followed in the extraction process is shown in Figure 3.4.

3.4.3 Two-Step Process

3.4.3.1 Removal of Fafliquors by Solvent Exchange Method

In this phase, a 3 g sample of powdered leather is placed in a thimble and mixed

with approximately 2 g of sea sand to enhance the draining of solvent. This mixture was

dried at 125°C in an oven for 1 hour. The dried sample is then treated with 100 mL of

petroleum ether by Soxhlet extraction for at least 4 hrs to remove the fatliquor. The

amount of fatliquors extracted was calculated using a gravimetric difference approach.

3.4.3.2 Removal of Retannins and Dyes by SFET

A sample of leather that was extracted with Soxhlet procedure was subjected to

supercritical fluid extraction using the supercritical grade carbon dioxide as the solvent.

This procedure was intended for the removal of retarming and dyes. The assumption

made here is that the fatliquors were completely removed in the previous step. The mass

of retanning material and dyes extracted by the SFE step was calculated using a

gravimetric difference technique. This experiment will seek to optimize the working

conditions for SFE grade carbon dioxide in supercritical fluid extraction.

33

DRIED LEATHER POWDER

Two-Step Process

SOXHLET EXTRACTION

One-Step Process >

Figure 3.4 Plan of Work

34

3.4.4 One-Step Process

3.4.4.1 Removal of Post-Tanning Materials by SFE

The powdered leather samples are subjected to supercritical fluid extraction

directly using SFE-grade carbon dioxide. The conditions used in the second step of the

first method were used as a reference to optimize working conditions for the SFE-grade

carbon dioxide. The effect of modifiers used to enhance the extractability of the

powdered sample was tested using phenol, methanol, and a combination of phenol and

methanol, respectively.

3.4.5 Analysis

3.4.5.1 Gravimetric Analysis

In all the above experiments, the samples were analyzed employing a gravimetric

difference technique. Here the initial and final weights (dry weight) of the sample were

determined. The difference between these two masses gave the total mass of chemical

removed from the sample.

3.4.5.2 GC Analysis

The extract samples obtained from the SFE were analyzed using GC. The extract

from the control as well as the experiment were analyzed to check the presence of

additional peaks that confirm the extraction of additional compounds from finished

leather powder by SFE.

35

CHAPTER IV

RESULTS AND DISCUSSION

The objective of this research was to investigate the feasibility of employing

supercritical fluid as a primary extraction technique for the extraction of post tanning

chemicals from leather scraps generated in the production of shoes. To study the

efficiency of SFE, it was essential to establish a basis for comparison. In this regard, the

Soxhlet extraction technique (section 3.2.2.1), which is a conventional sample extraction

method, was used as a reference method.

4.1 Soxhlet Extraction

Combinations of three Soxhlet extractions were performed, using petroleum ether

as the solvent. The results of these extractions are summarized in Table 4.1, which lists

the amount of fatliquor extracted per gram of dried leather powder. The average amount

of fatliquor extracted was 64 mg/g of powdered leather sample.

4.1.1 Extraction of Soxhlet Residue

The previously extracted leather from the Soxhlet's extraction was subjected to

supercritical fluid extraction under optimized conditions (sections 4.2.1 and 4.2.2). The

appropriate weights were noted and are tabulated in Table 4.2. According to the

observations, 3.1 mg/g of extract was obtained from the Soxhlet extracted leather. This

suggests that the SFE may be a more efficient extraction process than the Soxhlet's

36

Table 4.1 Soxhlet Extraction Results

Weight of Weight of Percentage Amount Extracted

Sample (g) Extract (g) Extracted (%) per g of Sample (mg)

2.601 0.1827 7̂ 02 702

2.5752 0.1568 6.09 60.9

2.5856 0.1603 6.20 62.0

37

Table 4.2 Soxhlet Residue Results under SFE

Weight of Weight of Extract Avg. Weight Amount Extracted

Sample (g) (mg) (mg) per g of sample (mg)

035 To

1.1 3.1

0.35 1.2

38

extraction technique. It has been claimed that Soxhlet's extraction is one of the best

methods for the extraction of fafliquors from leather (O' Flaherty et al. 1965).

4.2 SFE Experiments

4.2.1 Effect of Temperature with Constant Density

Four experiments, each with different temperature and a constant carbon dioxide

density of 0.3 g/mL were conducted. The results of the experiment are shown in Table

4.3. It is apparent that the amount of components extracted was low. This could be

because of the analytical nature of the SFE procedure such that the SFE was able to trap

only minimum amount of extract. Figure 4.1, a plot of the data from Table 4.3, shows

that as the temperature increases the extracting capacity of the solvent may peak at 60° C.

The optimum temperature with the best extraction results was 60° C. The increase in

extraction capacity is due to the increase in pressure. As the system pressure increases

the SF acts more like a liquid and exhibits higher solubility. Therefore, carbon dioxide

was able to dissolve more of the extractable material.

4.2.2 Effect of Density with Constant Temperature

Four experiments, with different carbon dioxide densities varying from 0.3 to 0.9

g/mL, were conducted. Table 3.1 shows that the maximum pressure that HP 7680 SFE

instrument can handle is 383 bars. At a solvent density of 0.9 g/mL and 60°C the pressure

increases beyond 383 bars. Therefore, a constant chamber temperature of 40°C was

selected to remain within the instrumentation limitations. The results of the experiment

39

Table 4.3 Effect ofTemperature on Quantity of Extract (Constant Density)

Sample. No Chamber Temperature Pressure Avg. Weight of

(degree C) (bar) Extract (mg)

i 40 81 0

2 50 91 0

3 60 101 0.85

4 70 111 0.65

40

Table 4.4 Effect of Density on Quantity of Extract (40° C Constant Temperature)

Sample. No Density of CO2 Pressure Avg. Weight of Extract

(g/mL) (bar) (mg)

i 03 81 0

2 05 91 1.0

3 0.7 115 1.6

4 0.9 281 4.5

41

are shown in Table 4.4. From these data, we see that the rate of increase of chamber

pressure with respect to density of carbon dioxide is higher than the results obtained by

varying the chamber temperature. Figure 4.2 is a plot of density versus quantity of

components extracted. The amount of components extracted by increasing the density of

the SF is more than the amount extracted with the rise in temperature. The optimum

density was the value at which the maximum extract amount was produced (i.e., 0.9

g/mL).

From the above experiments, we have determined the apparent optimum

extraction conditions are a solvent density of 0.9 g/mL and a temperature of 60°C. The

maximum density that carbon dioxide can reach in this SFE instrument is 0.95 g/mL. It

is better, therefore, to use the highest possible density. Since at higher densities, a

supercritical fluid acts much more like a liquid, thereby increasing the dissolving capacity

of carbon dioxide. As the temperature increases beyond 54°C (at a density of 0.9 g/mL),

the pressure exceeds the instrument limit, 383 bars. Therefore, the optimum temperature

was set at 40°C that produces a 281 bar pressure at 0.9 g/mL.

The optimization experiments demonstrate that pressure dramatically influences

the dissolving capacity of the supercritical fluid. Since pressure increases more with

increasing density of carbon dioxide than with increases in chamber temperature, it is

better to keep the carbon dioxide density high and the temperature low to operate within

overall pressure limitations. In addition, by keeping the chamber temperature low, we

can prevent the loss of any volatile compounds that the leather may have. The optimum

temperature for SFE is lower than the temperature used in the Soxhlet extraction. This

42

shows that there may be a chance of losing volatile material that could e\ aporate above

50° C in Soxhlet extraction. If such material exists, the SFE extraction would be

preferred over Soxhlet extraction.

4.2.3 Optimization of Sample Weight

After optimizing the extraction conditions, the effect of sample weight on the SFE

effectiveness was investigated. This is an important variable as initial w eight of the

sample is used to determine the efficiency of the extraction. Since the capacity of the SFE

test apparatus is not generally known, it w as essential to determine the optimum amount

of sample the SFE instrument and method can handle. Three different sample weights

were used, 500 mg, 350 mg, and 250 mg. The amount of extract obtained for each of

these trials is shown in Table 4.5. The 350 mg initial sample mass yielded the greatest

extraction efficiency, under optimum temperature and density conditions, with the

Hewlett Packard 7680 SFE instrument.

4.3 Effect of Modifiers

The leather samples were extracted using "modified" carbon dioxide with an "in-

situ" modification technique. The modifiers were phenol (at 3% and 5% of sample

weight), methanol (2 mL), and a combination of phenol (3%) and methanol (2 mL). The

extraction was carried out under optimized conditions (i.e.. 40°C). The results are

recorded in Table 4.6.

43

Table 4.5 Optimization of Sample Weight

Sample. No Initial Weight of Sample Avg. Weight of Extract

(g) (mg)

i 0̂ 5 4̂ 5

2 0.25 3.1

3 035 6.9

44

Table 4.6 Effect of Phenol as Modifier

Exp. \ o . % Of Phenol Weight of Extract Ave. Weight of Extract

(%) (mg) (mg)

la. 3 10.2

lb 3 10.0 11.8

Ic. 3 15.2

2a 5 12.4

13.05

2b 5 13.-

Table 4.7 Effects of Methanol and Phenol-Methanol as Modifiers

Exp. Amount of Modifiers Weight of Extract Avg. Weight

Xo. Phenol (%) Methanol (ml) (mg) of Extract (mg)

i l 3 2 8̂ 0

lb 3 2 8.1 7.77

Ic. 3 2 7.2

2^ ~- 2 SA

7.85

2b - 2 ".3

45

Table 4.8 Comparison of Effects of Extraction Techniques for 100 units of Powdered Leather Scraps. _ ^

Extraction Technique Weight of extract per 100 units

1. Soxhlet Extraction and SFE 6.75

2. Supercritical Fluid extraction

a. Carbon dioxide 1.97

b. Methanol modified 2.24

c. Phenol modified 3,78

d. Methanol and phenol modified 2.22

Table 4.9 Control Experiment Results

Experiment Weight of Paraffin (mg) Weight of Extract (mg)

Standard lOO 6̂ 0

Blank 0 0

46

From Table 4.6, it is clear that the quantity of extract increases with the addition

of phenol as a modifier. The extract weight from SFE using only carbon dioxide differs

by 7 mg over the extract weight from SFE using modified carbon dioxide. Table 4.7

shows that the amount extracted from SFE employing phenol- methanol-modified carbon

dioxide as the extracting solvent was same as the amount extracted by using methanol-

modified carbon dioxide as extracting solvent. There was no significant increase in the

methanol-modified extract when compared to the phenol-modified extract.

The pattern of results obtained from this in-situ modification experiments shows

that a phenol-modified extraction gives better results than the methanol and phenol

methanol-modified extraction procedure. No significant effect on the weight of extract

was noted by varying the percentage of phenol used for modification. Triplicate runs of

both the phenol-modified extraction and phenol methanol-modified extraction processes

were performed showing the repeatability of the experiment (Table 4.7, experiment

numbers la, lb, Ic, and 2a, and 2b). From the concordant values recorded, it can be

safely assumed that the experimental procedure is consistent. These experiments proved

that by using modified carbon dioxide and an in-situ extracting technique, the extraction

efficiency of the SFE approach could be increased.

4.4 Comparison of Extraction Techniques

The results from all the extraction techniques were summarized for 100 units of

initial sample weight and compared in Table 4.8. From Table 4.8, it is clear that the

Soxhlet extraction followed by SFE produced the best result. In the second method that

47

is, employing only SFE technique the best result was from phenol-modified extraction.

The variation in extract weight between Soxhlet extraction and SFE in Table 4.8 is due to

the difference in the initial weight of the leather sample used in the actual experiments. In

Soxhlet extraction the initial weight of the powdered leather was 2.6 g whereas for SFE it

was 0.35 g. The actual initial weight of leather sample in Soxhlet extraction is almost 100

times more than the actual initial weight of leather sample in SFE. Therefore, it can be

assumed that by employing a SFE instrument that could process a higher initial mass of

powdered leather sample a better result can be obtained.

4.5 Control Experiment Results

The values obtained from control experiments are given in Table 4.8. According

to Table 4.8, the standard experiment was able to recover 60 percent of paraffin (spiking

material). The blank did not recover any material suggesting that the experiment was

true positive The control and blank experiments performed were able to show that the

extract obtained from the experiment using SFE was from the leather sample. Thus, any

possibility that the extracted materials were contaminated was eliminated. This is

important as the weight of sample used and the material recovered was both low.

4.6 GC Analysis Results

The results of the GC analysis are shown in Figures 4.3 and 4.4. In each extract,

we would expect a minimum of three peaks. The first peak ensemble (2.21 and 3.1 min

from Figure 4.3 and from Figure 4.4) is most likely the sample solvent, tetrahydroftiran.

48

The next volatile component would likely be phenol (melting point 45' C) and can be

found at 11.85 min (Figure 4.3) and 11.88 min (Figure 4.4), respectively. The peaks at

6.08 min (Figure 4.3) and 5.86 min (Figure 4.4) are probably the inhibitor/preservative in

tetrahydroftiran. Approaching 19 min in Figure 4.4, we see an ensemble of somewhat

non-volatile components that are not present in the control (Figure 4.3). From this, we

can confirm the feasibility of using SFE for extracting post-tanning chemicals from

leather scraps.

The extraction of material from the Soxhlet residue as found in this study implies

that either the fatliquors that the Soxhlet method was not able remove was extracted or

some other material such as retanning agent or dyes were extracted by SFE. These

encouraging results and the results from GC analysis suggest that SFE, under suitable

conditions, may be effective in the removal of post tanning chemicals from finished

leather.

49

^ !

>>t i

I

1

^ }

"t-'SaMHoj r 4

/

i>—V^

•r M

^ •••••T-

<* 9 -y . - - •••.•.• -:^-*—-"--f»—-«

:« «• - ' • ' - - V

•5M

f j i W

~"T

« ^73K^>;^^

F

« •*.• «

Figure 4.1 Results from GC Analysis (Control)

50

kA^}^r

: )

ih

.1!

ii

kn^y iiM-

3 us

t ;g t s 3( » •« %

Figure 4 2 Results from GC Analysis (Phenol Methanol-Modified Carbon Dioxide)

51

CHAPTER V

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

The primary purpose of this investigation was to develop extraction techniques

for the removal of post tanning chemicals from finished leather scraps. A literature

review was performed, and no extraction methods for the removal of post tanning

chemicals such as retanning agents and dyes were found to have been previously

performed. The extraction of fatliquors has been demonstrated in the past using the

Soxhlet extraction technique. The supercritical fluid technique has been used in the field

of leather technology for other purposes such as enhancing the penetration of chemicals

and dyes in leather. The application of supercritical fluids as an extraction technique for

the removal of post tanning chemicals and dyes has not been performed previously.

The objectives of this thesis were to: (1) introduce supercritical fluid technology

as a method for extracting post-tanning chemicals from leather scraps, (2) postulate the

optimum extracting conditions for removal of post tanning chemicals using supercritical

fluid from a bench scale setup, (3) compare the conventional solvent exchange extraction

of fatliquors and supercritical fluid extraction method, and (4) suggest a method for the

efficient disposal of sohd waste produced by the footwear industries. The results of the

research are summarized in the following conclusions.

1. To introduce the supercritical fluid technique as an option for extracting post-

tanning chemicals, the feasibility of employing a supercritical fluid was

52

examined using a laboratory setup. The powdered leather was treated by

supercritical carbon dioxide and the extracts obtained in the process effluent

were analyzed using gas chromatography. The GC results from the leather

samples, when compared to the test control results, show the presence of a

non-volatile component at about 19 min. From this, we can confirm the

feasibility of using SFE for extracting post-tanning chemicals from leather

scraps.

2. The extracting conditions on a laboratory basis were optimized by comparing

the weight of components extracted from powdered leather at different

extracting conditions. Two parameters, chamber temperature and solvent

density, were optimized by changing one parameter while the other remained

constant. Eight experiments were conducted, four by changing the chamber

temperature and four by altering the solvent density. The optimized

conditions for this test situation were at a chamber temperature of 40°C, a

chamber pressure of 281 bars, and a density of carbon dioxide at 0.9 g/ml.

3. The extractability of the Soxhlet extraction process was compared with

supercritical fluid extraction. The leather residue from the Soxhlet extraction

procedure was treated under supercritical conditions using supercritical carbon

dioxide. The results indicate that supercritical fluid extraction technique was

able to extract some 1.1 mg of components from the leather residue. This

shows that supercritical fluid extraction may potentially extract a greater

number of compounds than the conventional solvent extraction technique.

53

4. The results from this work suggest that the SFE method can be used as an

extracting technique for the removal of post tanning chemicals. The residue

from this stage can then be treated for the production of gelatin with pepsin

for 8 hrs followed by 10% magnesium oxide for 3 hrs at 76°C (Taylor's

Process). Thus, this study was able to initiate the development of an

innovative means for the disposal of leather scraps produced in the footwear

industry by conversion to value added gelatin.

5.2 Recommendations

The results from this research show the feasibility of using SFE for removal of

post-tanning chemicals from finished leather scraps. Future research work can be focused

on

• Increasing the efficiency of SFE by using modified carbon dioxide.

• Performing an ultrasonic-aided supercritical fluid extraction in order to

increase the extraction efficiency.

• Conducting a bench-scale experiment to extract the post tanning chemicals

and to produce gelatin. The extracted components could be analyzed using

mass spectrograph to identify the component.

• Optimizing extraction conditions at the pilot plant scale.

54

REFERENCES

Addy, V. 1999. "Supercritical Fluids- A Future Technology for the Leather Industry'̂ '̂ Leather, pp. 32-33.

Andrews, T 1875-1876. "The Bakerian Lecture- On the Gaseous State of Matter." Proceedings of the Research Society of London. Vol.24, pp. 455.

Arcot, S., Shelly, D. C , and Tock, R. W. 2000. " Process Optimization Study of the Magnesium Oxide Digestion of Wetblue Waste." Presented in the 96 Annual Meeting of the American Leather Chemists Association.

Brown, E. M., Taylor, M. M., and Thompson, C. J. 1994. "Molecular Size and Conformation of Protein Recovered from Chrome Shavings." Journal of American Leather Chemists Association. Vol. 89. pp. 214-219.

Brown, E. M., Taylor, M. M., and G. L., Manner, W N. 1996. "Production of Potential Uses of Co-Products from Solid Tannery Waste." Journal of American Leather Chemists Association. Vol. 91. pp. 270-275.

Cabeza, L. F., Taylor, M. M., DeMaio, G. L., Manner, W. N., Brown, E. M., Carrio, R., Celma, P. J., and Cot, J. 1998. "Processing of Leather Waste: Pilot Scale Studies on Chrome Shavings. Part II. Purification of Chrome Cake Tanning Trials." Journal of American Leather Chemists Association. Vol. 93. pp. 83-98.

Cabeza, L. F., McAloon, A. J., Yee, W. C, Taylor, M. M., Marmer, W. N., and Brown, E. M. 1998. "Process Simulation and Cost Estimation of Treatment of Chromium-Containing Leather Waste." Journal of American Leather Chemists Association. Vol. 93. pp. 299-315.

Chrastil. J. 1982. "Solubility of Solids and Liquids in Supercritical Gases." Journal of Physical Chemistry. Vol. 86. pp 3016-3021.

Committee Report. 1955. The Determination of Extractable Fat in Leather." Journal of American Leather Chemists Association. Vol. 50. pp. 524.

de la Tour, C. 1822. "Effect Obtained by Simultaneous AppHcation of Heat and Pressure on certain liquids." Analytical Chemistry. Vol. 22. pp. 410.

Francis, A. W. 1954. "Ternary Systems of Liquid Carbon Dioxide." Journal of Physical Chemistry. Vol. 58. pp. 1099.

55

Hannay, J. B., and Hogarth, J. 1879. "On the Solubility of Solids in Gases.' Proceedings of Royal Society of London. Vol. 29. pp. 324.

Hewlett-Packard. 1990. FIP 7680A SFE Manual, Edition 1. Wilmington, Delaware: Hewlett-Packard.

JALCA Committee Report. 1919. Journal of American Leather Chemists Association. Vol. 14. pp. 140-178.

Merrill, H. B. 1951. "Does Chloroform Extract Tannin from Vegetable Leather?" Journal of American Leather Chemists Association. Vol. 46. pp. 609.

Meyer, A., Kleibohmer, W. 1997. "Comparison of Supercritical Fluid Extraction with in situ Derivatization and Conventional Extraction Methods for the Analysis of Pentachlorophenol in Wood and Leather." Journal of Chromatographic Science. Vol. 35. pp. 165-168.

O' Flaherty, F., Roddy, W. T., and Lollar, R. M. 1965. The Chemistry and Technology of Leather Volume IV-Evaluation of Leather. Reinhold Publishing Corporation, New York.

Riley, R. G. 1999. "Supercritical Fluid Extraction." http://www.pnl.gov/WEBTECH/voclsfe.html.

Riley, R. G. 2000. Personal Communication. Pacific Northwest Laboratory, Richland, Wa.

Sethuraman, R. 1997 "Supercritical Extraction of Capsaicin from Peppers." Ph. D. Dissertation, Texas Tech University, Lubbock, TX.

Shelly, D. C. 1999. Personal Communication. Texas Tech University.

Shelly, D. C, Cabeza, L. F., Ortkiese. S. A. 1999. "Operational, Regulatory and Economic Considerations for Recovering a U.S.P.- Grade Gelatin from Wet-Blue Wastes." Journal American Leather Chemists Association Vol. 94. pp. 48-54.

Stahl, E., Quirin, K. W., and Gerard. D. 1988. "Dense Gases for Extraction and Refining." Springer-Verlag, Berlin, Germany.

Taylor, L. T. 1996. Supercritical Fluid Extraction-Techniques in Analytical Chemistry. John Wiley and Sons, Inc, New York.

56

Taylor, M. M., Diefendorff, E.J., Phillips, J. G., Fearheller, S. H., and Bailev. D. G. 1986. "Wet Process Technology I. Determination of Precision for Various .Analytical Procedures." Journal of American Leather Chemists Association. Vol. 81. pp. 4-18.

Taylor, M. M., Diefendorff, E.J., Marmer, W. N., and Na. G. C. 1992. "Enzymatic Processing of Materials Containing Chromium and Protein.' U. S. Patent 5,094,946.

Taylor, M. M., Diefendorff, E.J., Marmer, W. N., and Brown, E. M 1993. "Enzymatic Processing of Materials Containing Chromium and Protein." U. S. Patent 5,271,912.

Taylor, M. M., Diefendorff, E.J., Marmer, W N., and Brown, E. M. 1994. "Effect of Various Alkalinity Inducing Agents on Chemical and Physical Properties of Protein Products Isolated from Chromium-Containing Leather Waste." Journal of American Leather Chemists Association. Vol. 89. pp. 221-228.

Taylor, M. M., Diefendorff, E.J., Marmer, W. N., and Brown, E. M 1995. "Effect of Deionization on Physical Properties of Gelable Protein Products Recovered from Sohd Tannery Waste." Journal of American Leather Chemists Association. \'ol. 90. pp. 365-374.

Taylor, M. M., Cabeza, L. F., Marmer, W N., Brown, E. M , and Kolomaznik, K. 1998. "Functional properties of Hydrolysis Products from Collagen." Journal of American Leather Chemists Association. Vol. 93. pp. 40-50.

Taylor, M. M., Cabeza, L. F., DeMaio, G. L., Marmer. W. N., Brown, E. M., Carrio, R., Celma, P. J., and Cot, J. 1998. "Processing of Leather Waste: Pilot Scale Studies on Chrome Shavings. Part I. Isolation and Characterization of Protein Products and Separation of Chrome Cake." Journal of American Leather Chemists Association. Vol. 93. pp. 61-82.

Taylor, M. M., Cabeza, L. F., Marmer, W N., and Brown, E. M. 1999. "Uses of Commercial Trypsin Preparations in Treatment of Solid Chromium Containing Tannery Waste." 95^ Annual Meeting of American Leather Chemists Association.

Thorstensen, T. C. 1993. Practical Leather Technology. Krieger Publishing Company, Melbourne, FL.

U.S. Department of Commerce. 1998. "U.S. Domestic ExportsAmports." www.ita.doc.gov/industry/otea/Trade-Detail/Latest-December/Exports/index.html.

57

Wilford, A. 1999. "Waste in the Shoe Industry-Consequences for the Leather Industry." Journal of the Society of Leather Technologists and Chemists \'ol. 83 pp. 84-86.

Zimmerman, E. W., and Pangbom, E. F. 1951. "Determination of Grease in Leather." Journal of American Leather Chemists Association. \'ol. 46. pp. 342

Zosel, K. 1964. German Patent 1,493,190.

Zosel, K. 1971. French Patent 2,079,261.

58

APPENDIX A

SAMPLE PREPARATION

59

Table A. 1 Moisture Content

S. No

1

2

3

4

5

Weight of Sample

(g)

5.06

5.06

5.00

5.04

5.03

Moisture Content

(g)

0.48

0.60

0.59

0.41

0.44

Average:

Percentage

Moisture (%)

9.49

11.86

11.80

8.13

8.75

10.01

60

APPENDIX B

EXTRACTION FROM POWDERED LEATHER USING SFE

61

Table B. 1 Optimization of Extraction Conditions

Batch ld#

1A 18

2A , B 3A, B 4A , B 5A, B 6A , B 7A, B 8A, B

C02 Density

g/ml

0.6 0.62 0 3 0.3 0.3 0.3 0.5 0.7 0.9

Pressure

bar

97 105 81 91 101 111 91 115 281

Chamber Temp.

40 42 40 50 60 70 40 40 40

Flow Rate

ml/min

1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2

Equ. Time

min

2 2 2 2 2 2 2 2 2

Extraction

min

5 5.5 5 5 5 5 5 5 5

Thimble Vol.

Swept ml

1.3 1.4 2.6 2.6 2.6 2.6 1.6 1.1 0.9

62

Table B.2 Quantity of Post-Tanning Chemicals

Batch Id #

1

2

3

4

5

6

7

8 9

10

11 12

13

14

15

16

17

18

Sample #

A B A B A B A B A B A B A B A B A A B A B A

A B A B A B A B C A B A B C

Wt of Empty Vial

(10'mg) 2.6012 2.6033 2.6116 2.5695 2.5887 2.6114 2.6038 2.6023 2.5714 2.6035 2.5985 2.5755 2.5874 2.6066 2.6439 2.5991 2.6168 2.6449 2.5681 2.6012 2.6027 2.6144

2.6214 2.574

2.5845 2.5743 2.6255 2.6458 2.5783 2.5798 2.6324 2.5964 2.5979 2.6277 2.6459 2.6214

Wt after Extraction (10'mg) 2.6043 2.6043 2.6116 2.5695 2.5887 2.6114 2.6047 2.6031 2.5719 2.6043 2.5999 2.5761 2.589

2.6082 2.6474 2.6037 2.6229 2.6482 2.571

2.6093 2.6074 2.6456

2.6215 2.575

2.6002 2.5751 2.6407 2.6532 2.5885 2.5898 2.6476 2.6048 2.6052 2.6357 2.6540 2.6286

Wt of sample Extracted

(mg) 3.1 1.0 0 0 0 0

0.9 0.8 0.5 0.8 1.4 0.6 1.6 1.6 3.5 4.6 6.1 3.3 2.9 8.1 4.7 31.2

1.0 1.0 15.7 8.0 12.4 13.7 10.2 10.0 15.2 8.4 7.3 8.0 8.1 7.2

Avg.Wt Extracted

(mg) 0.00205

0

0

0.85

0.65

1.0

1.6

4.05

6.1 3.1

6.4

31.2

1.0

8.25

13.05

11.8

7.85

0.0078

Remarks

optimization of extracting Conditions

Control-std optimization of sample

weight It It

Control-phenol Soxhlet Residue

3% Phenol M M

5% phenol 1 1 I I

3% phenol It II

I I I I

Methanol Modified Phenol & Methanol Modified

63

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