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Process report on modification of Basic chromium sulphate

Process report on

Preparation of Modified Basic chromium sulphate

Submitted toInstitute of Chemical Engineering & Technology

University of Punjab, Lahore

In Partial Fulfillment of the Requirementfor the Degree

Of

Bachelor of Science (Chemical Engineering)Session 2010-14

Submitted by:

Touqeer Nawaz CE-E10-16

Jahanzeb Khalil CE-E10-17

Muhammad Umair CE-E10-14

Syed Ali Hassan CE-E10-18

Supervised by:

Professor Dr. Mehmood Saleem




Dedication

We dedicate our work and utmost efforts to ALLAH almighty the creator of this

universe and most merciful and bounteous, You have always been by my sideguiding me all the way to this destiny & Holy Prophet (PBUH) the cause of thecreation of this universe. Our parents who taught us how to be persevere and bepatient in midst of trials. Our most respected Teachers who built our knowledgefoundations, Our Friends who encouraged and strengthened us and our siblingswho are our supporters and well-wishers.




Acknowledgment

By the Grace of Almighty Allah, the most Merciful, the most Beneficial, I'm

today submitting my report. I have the pearls of my eyes to admire theblessings of the compassionate, omnipotent, the Merciful and thebeneficent Allah who is the entire source of knowledge and wisdom. Due tohis bounteous blessings, I become able to contribute this comprehensiveassignment toward the deep ocean of knowledge. Heart is warm with love andthoughts have turned to the city of knowledge – The Holy Prophet(P.B.U.H) His saying “Learn from to Cradle to Grave” inspired the strongdesire in me to undertake this course of valuable studies. It would obviouslybe injustice not to mention the name of the person involved to make thisassignment possible and helped their utmost to make us understand the

overall nature of the report as of their best knowledge. Despite of the mosthectic schedule,

Pro. Dr. Mehmood Saleem

helped us so much. I'm really grateful to them for clarifying my concepts andmaking me learn from their experience. Whatever I learnt from them willdefinitely help me in my upcoming study and the professional life ahead.




Abstract

Steam economy is very important in every industrial unit as it decreases the

capital and running plant cost and ultimately boosts up the profit index of theindustry.

Tanning bath employed in leather processing units for the tanning of leather

usually constitute of Basic chromium sulphate and normally efficient at elevated

temperatures and consumes a considerable amount of steam. The steam

economy of this process can be improved by enhancing solubility of chromium

sulphate at temperature less than that, at which is being operated for the sake of

better steam economy of leather tanneries.

This report is being classified in five sections, In first part we have described the

Introduction and background of leather tanning. Second section comprises of

Chemistry of chrome tanning, third section consists of all the raw materials

required for preparing modified chrome salt. Fourth section includes methods

available to synthesize basic chromium sulphate. Whereas the final section

ponders lights upon the experimental setup, results, conclusions and

discussions.




Table of Contents

1. Introduction ........................................................................................................ 8

1.1 Background: .................................................................................................... 8

1.2 Vegetable Tanned Leather: ............................................................................. 9

1.3 Aldehyde Tanned Leather: ............................................................................ 10

1.4 Formaldehyde Tanned Leather: .................................................................... 10

1.5 Rose Tanned Leather: ................................................................................... 10

1.6 Syntans: ........................................................................................................ 10

1.7 Alum Tanned Leather: ................................................................................... 11

1.8 Chrome Tanned Leather: .............................................................................. 11

1.9 Position in Pakistan: ...................................................................................... 12

1.10 Literature Review ........................................................................................ 13

2. Chemistry of Tanning ...................................................................................... 14

2.1 Chrome tanning: ............................................................................................ 14

2.2. Mechanism of Chrome Tanning: .................................................................. 15

2.3. Chemistry of Chromium salts: ...................................................................... 17

2.4. Uses and Health hazards: ............................................................................ 17

2.5 Health safety and Environment. .................................................................... 17

3. Raw materials .................................................................................................. 18

3.1 Sodium Dichromate: ...................................................................................... 18

3.2 Sulphuric Acid: .............................................................................................. 19

3.3 Glucose: ........................................................................................................ 20

3.4 Ethylene Glycol: ............................................................................................ 21

4. Preparation methods for modified basic chromium sulphate .......................... 23

4.1. Sugar Reduction Method:............................................................................. 23

4.2. Sulfur Dioxide Reduction Method: ................................................................ 24

4.3. Selection of the Process: .............................................................................. 25

4.4.Modification in product of basic chromium sulphate: .................................... 25

5. Experimental Setup ......................................................................................... 26




5.1 Raw materials. ....................................................................................................................... 26

5.2 Apparatus ............................................................................................................................... 26

5.1.3 Procedure ........................................................................................................................... 27

5.2 Addition of Glycols: ........................................................................................ 27

6. Experimental tests ........................................................................................... 28

6.1.1 Description ......................................................................................................................... 28

6.1.2 Composition ....................................................................................................................... 28

6.2 Method of Test for Basic Chromium Sulphate (For Tanning) ........................ 29

6.2.1 Determination of moisture ............................................................................................. 29

Apparatus .................................................................................................................................. 29

Procedure .................................................................................................................................. 29

Calculations ............................................................................................................................... 29

6.2.2 Determination of basicity ................................................................................................ 29

6.2.3 Determination of matter insoluble in water................................................................ 30

Apparatus .................................................................................................................................. 30

Procedure .................................................................................................................................. 30

Calculation ................................................................................................................................ 30

6.2.4 Determination of pH ........................................................................................................ 31

Apparatus .................................................................................................................................. 31

Procedure .................................................................................................................................. 31

6.2.5 Test for unreduced chromium ....................................................................................... 31

Reagent ...................................................................................................................................... 31

Procedure .................................................................................................................................. 31

6.3 Conclusions ................................................................................................... 33

Refrences ............................................................................................................ 34




Chapter 1

1. Introduction

1.1 Background:Leather is a durable and flexible material created by the tanning of

animal rawhide and skin, often cattle hide. It can be produced through

manufacturing processes ranging from cottage industry to heavy industry.

Leather is one of the oldest materials used by mankind. Tanning is generally

said to be the first manufacturing process of man on the earth. Leather has

remained and is still the most essential commodity of man. A lot of changes

have occurred in this industry. Due to lack of scientific knowledge and

equipment the earlier tanner had to face a lot of problems. However today,

due to the development of many leather substitutes, the present tanner isfacing even a greater test. Animal Skins and Furs have been prepared prior to

civilization and with primitive methods (for example clothing) and so made

useful. (Coulson)

Preparing animal skins to leather with the addition of tanning agents pre-dates

the Stone Age man (ca.8000 BC). It is evident that the form of fat tanning

http://en.wikipedia.org/wiki/Heavy_industry

http://en.wikipedia.org/wiki/Cottage_industry

http://en.wikipedia.org/wiki/Rawhide_(textile

http://en.wikipedia.org/wiki/Tanning




(Chamois Method) was done in the Neolithic period (ca.6000 BC). Also smoke

tanning over fire and the mineral tanning with alum (White Tanning) are surely

ancient tanning methods. Tanning with botanic agents (Vegetable Tanning) is

known since the Bronze Age (ca.2000 BC), where mainly the bark of the oak

and beech as tanning agents were used. Bark Tanning was traditionally usedduring the medieval period. Out of these basics and through increasing

civilization and knowledge a craft and industry has emerged.

Leather is a product obtained by stabilizing proteins of animal’s skin through

tanning. Animal skin used for tanning is a byproduct of meat industry. Animals

are not killed in the world just for the sake of skin. The flayed skin must be

preserved so that all its leather potential is retained or protected against the

action of microorganisms, autolytic enzymes and chemical hydrolysis. The

skin is protected by reducing the moisture in the hide to 5%. Before the

development of chrome tanning all the leather was treated by vegetable

tanning. After the introduction of chrome tanning all the tanners started to tan

leather by this method

1.2 Vegetable Tanned Leather:Vegetable-tanned leather is tanned using tannins and other ingredients found

in different vegetable matter, such as tree bark prepared in bark

mills, wood, leaves, fruits and roots and other similar sources. It is supple andbrown in color, with the exact shade depending on the mix of chemicals and

the color of the skin. It is the only form of leather suitable for use in leather

carving or stamping. Vegetable-tanned leather is not stable in water; it tends

to discolor, so if left to soak and on drying it will shrink and become less

supple, and harder. In hot water, it will shrink drastically and partly gelatinize,

becoming rigid and eventually brittle. Boiled leather is an example of this,

where the leather has been hardened by being immersed in hot water, or in

boiled wax or similar substances. Historically, it was occasionally used

as armor after hardening, and it has also been used for book binding.Vegetable tanned leathers present unique, recognizable and natural

characteristics while respecting the environment.

http://en.wikipedia.org/wiki/Bark_mill


http://en.wikipedia.org/wiki/Book_binding

http://en.wikipedia.org/wiki/Armour

http://en.wikipedia.org/wiki/Wax

http://en.wikipedia.org/wiki/Boiled_leather

http://en.wikipedia.org/wiki/Root

http://en.wikipedia.org/wiki/Fruit

http://en.wikipedia.org/wiki/Leaf

http://en.wikipedia.org/wiki/Wood




http://en.wikipedia.org/wiki/Tanbark

http://en.wikipedia.org/wiki/Tannin

http://en.wikipedia.org/wiki/Tanning




1.3 Aldehyde Tanned Leather: Aldehyde-tanned leather is tanned using glutaraldehyde or oxazolidine compound.

This is the leather that most tanners refer to as wet-white leather due to its pale

cream or white color. It is the main type of "chrome-free" leather, often seen in

automobiles and shoes for infants.

1.4 Formaldehyde Tanned Leather:Formaldehyde tanning (being phased out due to its danger to workers and the

sensitivity of many people to formaldehyde is another method of aldehyde

tanning. Brain-tanned leathers fall into this category and are exceptionally

water absorbent.

Brain tanned leathers are made by a labor-intensive process which uses

emulsified oils, often those of animal brains. They are known for their

exceptional softness and their ability to be washed.

Chamois leather also falls into the category of aldehyde tanning and, like

brain tanning, produces highly water-absorbent leather. Chamois leather is

made by using oils (traditionally cod oil) that oxidize easily to produce the

aldehydes that tan the leather to make the fabric the color it is.

1.5 Rose Tanned Leather:Rose tanned leather is a variation of vegetable oil tanning and brain tanning,

where pure rose otto replaces the vegetable oil and emulsified oils. It has

been called the most valuable leather on earth, but this is mostly due to the

high cost of rose otto and its labor-intensive tanning process.

1.6 Syntans:Synthetic-tanned leather is tanned using aromatic polymers such as

the Novolac or Neradol types (syntans, contraction for synthetic tannins). This

leather is white in color and was invented when vegetable tannins were in

short supply during the Second World War. Melamine and other amino-

functional resins fall into this category as well. Urea-formaldehyde resins were

http://en.wikipedia.org/wiki/Urea

http://en.wikipedia.org/wiki/Melamine

http://en.wikipedia.org/wiki/Second_World_War

http://en.wikipedia.org/wiki/Novolac

http://en.wikipedia.org/wiki/Polymer

http://en.wikipedia.org/wiki/Rose_oil

http://en.wikipedia.org/wiki/Formaldehyde

http://en.wikipedia.org/wiki/Oxazolidine

http://en.wikipedia.org/wiki/Glutaraldehyde




also used in this tanning method until dissatisfaction about the formation of

free formaldehyde was realized.

1.7 Alum Tanned Leather : Alum-tanned leather is transformed using aluminum salts mixed with a variety

of binders and protein sources, such as flour and egg yolk. Alum-tanned

leather is technically not tanned, as tannic acid is not used, and the resulting

material will revert to rawhide if soaked in water long enough to remove the

alum salts. Very light shades of leather are possible using this process.

1.8 Chrome Tanned Leather :Chrome-tanned leather, invented in 1858, is tanned using chromium

sulfate and other salts of chromium. It is more supple and pliable than

vegetable-tanned leather and does not discolor or lose shape as dr astically in

water as vegetable-tanned. It is also known as wet-blue for its color derived

from the chromium.

After 1900 Chrome Tanning with Chrome Salts was the most important

tanning method, due to the shorter time requirement as compared to the Bark

Tanning method which can last up to 15 months.

The first concept of chrome tanned leather is attributed to Knap who

discovered in 1858 that the basic chromium compound can convert animal

hide into leather. But he failed to realize the commercial possibilities of his

discovery. In 1884 augustus Schultz, a dye man planted a two bath method of

chrome tanning process in which sodium dichromate is reduced in the skin to

form chrome tanning compound. This proved to be the revolutionary change

in the leather industry. The two bath method was replaced by one bath

method in 1893. Maton dannis used this process which was original process

used by Knap. In indo Pak this process was first used in Madras in 1913.Chrome tanning developed rapidly in first half of the century as its greatly

speeds up the tanning operation and increases strength.

http://en.wikipedia.org/wiki/Chromium_sulfate


http://en.wikipedia.org/wiki/Chromium



http://en.wikipedia.org/wiki/Protein

http://en.wikipedia.org/wiki/Salt

http://en.wikipedia.org/wiki/Aluminium




1.9 Position in Pakistan:Tanning industry of the undivided indo Pak gain encouragement in the

Second World War when the export of raw hide became practically

impossible. At that time fifty tanneries were organized. Majority of these werein Kanpur, Calcutta and Madras. On division if India and Pakistan, Pakistan

was left without any recognized tannery, though it had a very rich production

of raw hide and skin. At that time Pakistan was primarily a raw hide and skin

exporting country. A very few mechanical tanneries were operating at that

time. Leather is prepared by both vegetable and chrome tanning methods.

Pakistan Tanners Association (PTA) was established in late 50s. PTA is now

functioning as a renowned trade body duly licensed by the Ministry of

Commerce under Trade Organizations Ordinance/Rules 2007, registered with

the Security & Exchange Commission of Pakistan and a bonafide member ofthe Federation of Pakistan Chambers of Commerce & Industry. It is the 2nd

largest export earning sector representing highly dynamic and value added

industry in leather and leather products besides being job oriented sector. The

industry employs about 500,000 people directly, producing fine quality

finished leather for export as well as for home consumption. It contributes 5%

of GDP and 5.4% to the overall export earnings of the country and is

considered to be the most significant sector which plays viable role in

revamping economic spectrum of the country.

There are about 800 tanneries in the country, 213 Members currently

registered with Pakistan Tanners Association from all over the country are

actively engaged in manufacturing and fully geared-up towards promoting

export of quality finished leather and leather products on modern pattern as

per international demand and are playing their positive role in earning much

needed foreign exchange by invigorating country’s export volume. They are

courageously prepared to meet the challenges of WTO regime and other

global pressures with quality consciousness and full sense of responsibilities

to uphold the impeccable image of leather industry within the ambit of nationalpolicies, rules & regulations and international conditionality.

The superb quality of Pakistani Leather & Leather Products is exported all

over the world fetching sizeable foreign exchange. PTA has been organizing a

number of International Fairs every year for participation of its interested

member exporters to display their eye catching leather & leather products.




The export of Leather & Leather Products is progressing gradually in terms of

Value, Quantity and Unit Price of the leather articles. The main buyers of

Pakistani Leather & Leather Products are Hong Kong, Italy, China Korea,

Vietnam, Germany, Turkey, India, South Africa, Spain, Japan, France &

Indonesia.

1.10 Literature ReviewThis report examines the effect of change in solubility of basic chromium sulphate at

room temperature. A detailed study on this topic was required as basic chromium

sulphate is used in leather industry for tanning purposes as a high quality tanning agent.

The process which is being employed at industry requires the temperature of tanning

bath to be at 70 degree Celsius.

Herbert B. Guynn studied from United States worked on this topic and found certain

chemicals which can enhance the solubility of basic chromium sulphate at room

temperature. The objective was achieved by in the process if manufacture of basic

chromium sulphate which is soluble in cold water by evaporating aqueous solution andadding at least one glycol. The addition of glycols may take place before the chromium

salt solutions are adjusted to the desired basicity or just before the solution is

dehydrated. Glycols used in this process are mono or poly glycols provided they are

soluble in water. Preferred mono glycols are those which have 2 to 4 carbon atoms.

Preferred compounds are ethylene glycol, 1-2 propylene glycol, 1-2 Butylene glycol.

Particular examples of poly glycols are ethylene di glycol, ethylene tri glycol, And tri

propylene glycol. No change in the tanning efficiency of the chrome tanning was

observed as compare to the un modified basic chromium sulphate. The chrome tanning

agent prepared by this method can be used in conjunction with vegetable and synthetic

tanning agent just same as the un modified agent. The technical advance is the that

much better liquid exhaustion is achieved even in cold water due to improved solubility

of agent and the waste liquor obtained from the process contains much less chromium




Chapter 2

2. Chemistry of TanningTanning may be defined as the treatment of hides and skin to preserve and

convert them into useful articles of commerce. It is the process of treating skins

of animals to produce leather, which is more durable and less susceptible to

decomposition. Tanning leather involves a process which permanently alters the

protein structure of skin. Before tanning, the skins are unhaired, degreased,

desalted and soaked in water over a period of 6 hours to 2 days. To prevent

damage of the skin by bacterial growth during the soaking period, Biocides,

typically dithiocarbamates are used. Vegetable, chrome and most other tanning

methods yield useable leathers from tanning process alone. (Heidemann, 1982)

2.1 Chrome tanning:

In chrome tanning the reaction with the chromium salts give a very stable hide

fiber which is very resistant to bacterial attack and to high temperatures. Without

further processing, however, chrome tanned leather doesn’t have many of the

qualities desired for useful articles.




Chrome tanning must be used in conjunction with the additional processes

dyeing, fat liquoring and perhaps vegetable re-tanning to produce useable

leather articles.

The major advantages of chrome tanning are high speed, low cost light colour

and excellent preservation of hide protein. Chrome tanning took its place in

commercial world shortly after its discovery and became the most common way

of tanning light leathers and shoe upper leathers.

The original patent of Schultz was based on a two bath tannage. In the two bath

system, the skins are treated with an acid dichromate solution and later in the

process the dichromate is reduced to green trivalent state. The two bath chrometanning method has continued to be popular for some types of skins, though it

has been considerable modified for the modern production. (Gustavson, 1956)

2.2. Mechanism of Chrome Tanning:Commercial chrome tanning is always done by one bath process. This is based

on the reaction between hide and trivalent chromium salts usually a basic

chromium sulphate. Chromium sulphate has long been regarded as the most

efficient and effective tanning agent. Chromium(III) compounds of the sort used

in tanning are significantly less toxic than hexavalent chromium. Chromium(III)

sulfate dissolves to give the hexaaquachromium(III) cation, [Cr(H2O)6]3+, which at

higher pH undergoes processes called olation to give polychromium(III)

compounds that are active in tanning, being the cross-linking of the collagen

subunits. The chemistry of [Cr(H2O)6]3+ is more complex in the tanning bath

rather than in water due to the presence of a variety of ligands. Some ligands

include the sulfate anion, the collagen's carboxyl groups, amine groups from the

side chains of the amino acids as well as "masking agents." Masking agents




are carboxylic acids, such as acetic acid, used to suppress formation of

polychromium (III) chains. Masking agents allow the tanner to further increase

the pH to increase collagen's reactivity without inhibiting the penetration of the

chromium (III) complexes.

Collagen is characterized by a high content of glycine, proline,

and hydroxyproline, usually in the repeat -gly-pro-hypro-gly-. These residues give

rise to collagen's helical structure. Collagen's high content of hydroxyproline

allows for significant cross-linking by hydrogen bonding within the helical

structure. Ionized carboxyl groups (RCO2-) are formed by hydrolysis of the

collagen by the action of hydroxide. This conversion occurs during the liming

process, before introduction of the tanning agent (chromium salts). The ionized

carboxyl groups coordinate as ligands to the chromium(III) centers of the oxo-

hydroxide clusters.

In the typical one bath process the hides or skins are in a pickled state at a pH of

3 or when the chrome tanning materials are introduced.

At these low pH values, the affinity of chrome tanning salts for the protein is

moderate allowing penetration of the chrome tanning salt or agent into the hide.

After proper penetration and initial absorption of some of the chrome salts have

been achieved, the pH is raised. This brings about in both the chromium salts

and the protein and causes reaction between them. When the reaction is

completed, the leather is said to be full chrome tanned.

The chemistry of chrome tanning process is complicated and involves several

simultaneous competing reactions. (Heidemann, Ullmann's Encyclopedia of

Industrial Chemistry, 2005)




2.3. Chemistry of Chromium salts:Chromium tanning salts have a valency of +3. They are soluble in strong acids

but will usually precipitate as chromium hydroxide or hydrated chromium oxide,

pH value slightly above 4. They react with a number of organic materials to form

coloured soluble salts at higher pH values, and they will precipitate soluble

protein. (Greenwood, 1997)

2.4. Uses and Health hazards:Chromium was first used to make chromium chemicals in about 1800 to 1860

and was first employed as a refractory in France in about 1879. Intensified use ofchromium metal in steel started about 1908 to 1912. These three applications;

chemical, refractory and metallurgical constitute the main usage of chromium

today.

2.5 Health safety and Environment. Acute effects of chromates are mainly on the skin and mucous menrane, and

have been observed in workers for 150 years. The breathing of dusts or mists

containing chromium VI compounds leads to ulceration and eventual perforation

of the cartilaginous portion of the nasal septum.

In additional to these effects, chromates may produce ulcers when a cut or

abrasion in the skin is contaminated. If sufficient chromate is brought into contact

with skin lesions, fatalities may result. Dermatitis and allergic reactions may

result from prolonged exposure of skin to chromate. In the majority of workers

dermatitis results only from prolonged exposure




Chapter 3

3. Raw materialsThe essential raw materials required for the production of Basic Chromium

Sulphate includes:

Sodium Dichromate

Sulphuric Acid

Glucose

Ethylene Glycol

3.1 Sodium Dichromate:Molecular formula of sodium dichromate is Na2Cr2O7.2H20 which have

molecular weight of 298.05, forms deliquescent, orange reddish monoclinic

crystals. The dehydrate loses water when it is heated to high temperature,

transforming into anhydrous salt.

Colour Bright red

Solubility in water 73g/100 mL at 25 degree C

Density 2.52 g/cm3




Sodium Dichromate is manufactured in hydrated form by fluxing chrome iron ore

with lime and sodium carbonate, the resultant sodium chromate is reacted with

Sulphuric acid which converts it into sodium dichromate which is crystallized from

water as reddish orange monoclinic crystals.

Industrially Sodium dichromate find its applications in the manufacturing of

CHROMOSOLE, pigments, chromic acid and Basic Chromium sulphate. Sodium

dichromate find its enormous applications in Leather tanneries, the present

production of this product is ………. Which is very limited and most of the

demand is fulfilled through imports.

3.2 Sulphuric Acid:The increase and expansion in the industrial production in Pakistan has

necessitated rising quantum of sulphuric acid consumption. Industrial sub sector

uses relatively significant amounts of sulphuric acid in the country which includes

Fertilizers, Aluminum sulphate, Leather tanning, and Storage batteries etc.

Leather industry employs excess amount of sulphuric acid for the

preparation of sodium dichromate and basic chromium sulphate.

Molar mass 98.079 g/mole

Density 1.84 g/cm3

Melting point 10 degree C

Solubility in water Miscible

Acidity 1.99

Melting point 356.7 degree C

Odor Odourless

Table 3. 1 Characteristics of sodium dichromate




Viscosity 26.7 cP

Table 3. 2 Characteristics of Sulphuric acid

There are more than 12 manufacturing units of sulphuric acid across the country

producing acid. Production capacity of the units stood at ….. approximately.

At present the industry is completely dependent on imported sulphur.

However, recovery of sulphur from gaseous phase has shown some

improvement.

The important Sulphuric Acid suppliers in Pakistan are:

1. Atta Chemicals PVT,LTD

2. A.I.K International exports

3. Akber Ali and sons

4. Acid Chemical industries PVT,LTD

5. Amber Chemicals industries PVT,LTD

6. Crescent Chemicals LTD

7. Exide Pakistan LTD (alibaba.com international, 1999-2014)

3.3 Glucose:

Glucose is used as a reducing agent for the reduction of sodium dichromate tobasic chromium sulphate. Sugar can also be used as reducing agent, however

glucose is more preferred over sugar if it is from impurities so that it yields finer

product.

When glucose acts as a reducing agent, it has an aldehyde group or is capable

of forming one in solution through isomerism. Glucose exists in several different

molecular structures, Reducing monosaccharides include glucose,

Glyceraldehyde and galactose. Many disaccharides have also reducing form ,

however sucrose and trehalose are non reducing disaccharides

In Glucose, polymers such as starch and starch derivatives like glucose syrup,

maltodextrin and dextrin the macromolecule begins with reducing sugar, a free

aldehyde. More hydrolysed starch contains more reducing sugars present in

these starch derivatives is called dextrose equivalent.




At present there are two major producers of glucose, M/S glaxo

laboratories and Rafhan maize products Ltd.

3.4 Ethylene Glycol:Ethylene glycol is an odourless, colourless, syrupy, sweet-tasting liquid. Ethylene

glycol is only weakly toxic, but cases of poisonings are not uncommon. The

major application of ethylene glycol is as a medium for convective heat transfer in

automobiles and liquid cooled computers. Pure ethylene glycol has a specific

heat capacity about one half of the water.

In 2009, almost 85% of the mono-ethylene glycol (MEG) consumed worldwide

went into the production of polyethylene terephthalate (PET), which in turn was

converted into fibers and bottles. Another 10% was consumed in antifreeze and5.5% in other uses. In 2009, 69% of the MEG consumed worldwide was in Asia,

followed by 13% in North America and 8% in western Europe.

About 6.7billion kilograms are produced annually.

Density 1.1132 g/cm3

Melting point 260K

Boiling point 470K

Solubility in water Miscible

Viscosity 1.61 X 10^-2 Ns/m2

Main hazards It is extremely harmful to pets andchildren, if ingested get medical helpimmediately

Flash point 111 degree C

Table 3. 3 Characteristics of ethylene glycol

The main Ethylene glycol suppliers in Pakistan are:

1. International Petrochemicals PVT,LTD




2. Venus Corporation

3. Azwaah Associates

4. Pak Euroasia Chemicals (online shopping, 1999-2014)




Chapter 4

4. Preparation methods for modified

basic chromium sulphateThere are normally two methods which are used for the production of basic

chromium sulphate.

Sugar Reduction Method

Sulfur Dioxide Reduction Method

4.1. Sugar Reduction Method:Both chromium sulphate and Basic chromium sulphate have been produced in

Japan since about 1950, by reduction of Sodium dichromate with glucose. (IARC,

1980a). Sodium dichromate is reduced with molasses or glucose in the presence

of sulfuric acid. This is known as organic reduction. (COPSON, 1956)

Sodium dichromate solution is added in agitated resistant tank. Sugar and

stoichiometric amount of sulfuric acid are required for reduction. The reduction of

Cr (VI) to Cr (III) is an exothermic reaction. The rate of reduction of Cr(VI) by

organic reductants like glucose/molasses would depend on many factors,

including the concentration of reagents.




The faster the rate of addition of glucose, on one hand influence the temperature

of reaction medium, and on the other, give rise to reductant/oxidant ratio. This

can be expected to lead to formation of increased organic acid intermediates

rather than the conversion of glucose into CO2.

The general reaction that takes place during the reduction of dichromate by

glucose is

4Na2Cr 2O7+12H2SO4+C6H1206 8Cr(0H)SO4+4Na2SO4+14H2O+6CO2 (4.1)

However, in case of sugar/glucose reduction organic intermediates such as

formic acid, oxalic acid, glyoxalic acids, carbon dioxide and other precursors of

humic acids have been reported. These organic intermediates are capable of

forming complexes with the metal ion by substitution of aquo or sulphato group.

However, this method is costly but in most tanning systems sugar is used for the

reduction of dichromate.

In this method the dichromate is dissolved in water, sulfuric acid is added and

solution of glucose or glucose added slowly. An excess of glucose is necessary

since the oxidation is not complete and some oxidation products remain in the

solution. (B. chandrasekaran, January 1999)

4.2. Sulfur Dioxide Reduction Method:The production of basic chromium sulphate is based on a chemical reaction in

which hexavalent chromium (+6 oxidation state) in the form of sodium dichromate

is reduced to trivalent state (+3) by sulfur dioxide.

Anhydrous sodium dichromate powder is reduced by burner gas. Burner gas

contains 9% sulfur dioxide. The sodium dichromate is dissolved in water to make

a strong solution which is pumped continuously over reaction towers filled with

ceramic packings where it reacts with sulfur dioxide bearing gas. Although thereaction is exothermic, steam injection is required to maintain the temperature

and hence the reaction rate. The product is 100% reduced to +3 oxidation state

and has a basicity of 33%. The chemical reaction involved is:

Na2Cr 2O7+3SO2+H2O Cr 2(OH)SO4+Na2SO4 (4.2)




This compound is still freely water soluble. The sodium sulphate shown on the

right hand side of the equation is part of the product and is normally not

separated, and merely remains an inert diluent. (simpson, 1996)

An excess of sulfur dioxide is required to ensure the chromium is fully reduced to

the +3 oxidation state. A second reaction tower is used to remove the residual

sulfur dioxide. The above reaction is carried out in a steam heated vessel.

4.3. Selection of the Process:Sulfur dioxide reduction method is costly method as compared to sugar reduction

method but it gives better quality of the product.

In sugar reduction method it was not sure that the reduction is complete or not. In

case of S02 reduction method the product may be dried using spray tower and

the spray drier has not necessarily anti corrosive lining.

In sulfur dioxide absorption method the sodium dichromate solution should be

between the range of 10-15% concentration but in sugar reduction case the

restriction of concentration is not taken into consideration. (Udy, 1956)

4.4.Modification in product of basicchromium sulphate:

When basic chromium sulphate that is water soluble at high temperature which is

produced by sugar or sulfur dioxide reduction method is prepared then we add

specific glycol into our basic chromium sulphate product. By the addition of glycol

into product the basic chromium sulphate becomes soluble in water at room

temperature. This is the modified form of basic chromium sulphate.

The modified form of basic chromium sulphate can be dried into spray drier and

can be stored as solid dry product. (Hans- Joachin Nebel, July 5th, 1974)




Chapter 5

5. Experimental Setup

5.1 Raw materials.Basic Chromium sulphate was prepared in the laboratory by sugar reduction

method. The raw materials are given below.

Glucose

Sulphuric acid

Sodium dichromate

Water (utility)

5.2 Apparatus

For making chromium sulphate from sugar reduction

method we need following apparatus

4 beakers (500 ml)

2 beakers (100 ml)

Stirrer

Figure 1 Raw materials




2 petri dishes

Thermometer

Pipette

Burette

5.1.3 ProcedureBasic Chromium sulphate was produced in laboratory by dissolving 100g of

green powdered Sodium Dichromate in 150 cm3 water in beaker followed by

constant stirring.

When it was completely mixed in water to

produce homogenous solution, 25g Glucose as

reducing agent was added. 50ml of 98% Sulphuric

acid was taken in measuring cylinder and was

introduced drop by drop in chromium sulphate

solution. This reaction was highly exothermic,

Beaker was placed in ice bath in order to control

the temperature to 40°C. From the reaction flask,

solution was taken in sample bottle and analysis

was carried out to determine basicity.

5.2 Addition of Glycols:The purpose of the whole process was to enhance the solubility of basic

chromium sulphate in water at room temperature. In beginning different

chemicals were tested and the solubility was initially checked by physical

methods. It was found that the basic chromium sulphate was fairly soluble in

water when we used glycols preferably poly glycols

Added Glycol Solubility

Ethylene glycol Sparingly soluble

Di ethylene glycol Fairly soluble

Tri ethylene glycol Fairly soluble

Table5. 1 solubility of glycols

Figure 2 Exothermic reaction b/Sulphuric acid and sodium

dichromate




Chapter 6

6. Experimental testsIn order to check the quality and the to meet the requirement of the tanning

process we performed certain tests on modified basic chromium sulphate. The

requirement for performing these tests is listed below.

6.1.1 Description

Basic chromium sulphate shall be in the form of flakes or powder. 5 percent

aqueous solution of basic chromium sulphate shall be transparent and optically

clear. A solution is to be considered as optically clear if a bright object is clearly

visible through 5-cm thick layer and if a 1-cm layer in a beaker placed on black

glass or a paper appears black and not opalescent when viewed from above in a

good light.

6.1.2 Composition

The material shall comply with the requirements of the process and should be of

the of the required quality and characteristics




6.2 Method of Test for Basic Chromium

Sulphate (For Tanning)Unless specified otherwise, pure chemicals and distilled water shall be used in

tests.

NOTE- ‘Pure chemicals’ shall mean chemicals that do not contain impurities

which affect the results of analysis.

6.2.1 Determination of moisture

Apparatus

Air Oven with thermostatic control capable of maintaining 105 ± 2°C.

ProcedureTransfer about 1 g of basic chromium sulphate into a tared wide mouth weighing

bottle and weigh accurately. Dry at about 105 +2°C in an air oven for three to

four hours. Cool in a desiccator for about 20 minutes and weigh again accurately.

Repeat the process of drying and weighing until two weightings at an interval of

1h do not differ by more than 2 mg. NOTE - If the weight of the dried material is

found to increase on longer drying, then the lowest weight found shall be taken.

Calculations

Moisture, percent by mass = [(W1- W2)x 100]/W1

where

W1= mass in g of the material taken for the test, and

W2= mass in g of the material after drying.

6.2.2 Determination of basicityBasicity of chrome salt is defined as the percentage of total chrome which is

combined with the hydroxyl groups, that is,

percentage basicity = (Cr combined with OH x 100)/Total chromium

It may be calculated as follows:




If V ml of 0.1 N titrant is required in the chromium titration and V2 ml of 0.1 N

sodium hydroxide solution for a similar volume in the acid titration, then percent

Basicity = {(V1—V2) x 100}/V1

Therefore, in this method firstly the amount of chromium in the basic

chrome sulphate is determined and then the amount of sulphate combined

with chromium is determined. From this the percentage basicity is calculated

6.2.3 Determination of matter insoluble in water

Apparatus

Steam-Bath

Vacuum Oven with thermostatic control capable of maintaining 100°C.

Procedure

Dissolve 10 g of the basic chrome sulphate in 1 000 ml of water at 27 ± 2°C

within a period of 30 minutes. Filter through a dry filter paper, Whatman No. 42 or

equivalent, into a dry beaker. Discarding the first 20-25 ml of filtrate, measure out

250 ml of the filtratein another beaker or better, in a dish and evaporate on a

steambath. Dry the residue at 100 ± 2°C in a vacuum oven, cool in a desiccatorfor about 20 minutes and weigh accurately. Repeat the process of drying and

weighing until two weighings at an interval of one hour do not differ by more than

2 mg.

Calculation

Calculate matter insoluble in water, percent by mass as given below:

Matter insoluble in water, percent by mass 100 – (40 W + M)

Where

W = mass in g of the residue left after evaporating 250 ml of the solution, and

M= moisture percent by mass.




6.2.4 Determination of pH

Apparatus

pH Meter- with glass electrode.

ProcedureDissolve about 15 g of basic chrome sulphate in 250 ml water at 27 ± 2°C to give

a concentration ofabout 1 percent chromium. Measure the pH of the solution

immediately by using a suitable pH meter.

NOTE - The pH of chrome liquors depend not only on the concentration but on

ageing, temperature of preparation or dilution. For results to have any

comparative value, the strength of the solution should be the same and should

be prepared in an identicaltemperature and the pH should be measured

immediately after the preparation of the solution.

6.2.5 Test for unreduced chromium

Reagent

Ammonium Hydroxide Solution

Dilute Hydrochloric Acid - 0.1 N.

Potassium Iodide Solution - 10 percent (w/v),

Starch Solution -see A-4.2.8.

Procedure

Transfer a measured volume of basic chromium sulphate solution containing

about 1 g of chromium per litre to a 250-ml conical flask. Add sufficient amount of

ammonium hydroxide solutionto precipitate all chromium as hydroxide. Filter and

add to the filtrate hydrochloric acidto acidify the solution. Add 10 ml of potassium

iodide solution. Allow the flask to stand for about 10 minutes in the dark. Add

starch solution. To pass the test there shall be no change in colour of the solutionon addition of starch solution.




Sr no Characteristics Results

1 Moisture, % by mass

2 Free sulphate ( as Na2S04),% by mass

3 Basicity (%)

4 Chromium (as Cr2O3), % bymass

5 Matter insoluble in water, %by mass

6 pH of aqueous solution

Table 6. 1 Results of difference tests




6.3 Conclusions



Refrences

1. Thomas C. Thorstensen: Practical leather technology 1969, Van

Nostrand Reinhold company

2. J.M Coulson & J.F. Richardson: Chemical Engineering volume

11, 3rd edition,1983, Pergamon Press.

3. William L. Jolly: Synthetic Inorganic Chemistry, 1960, Prentice Hall

Inc.

4. Mc Cabe & Smith: Unit operation of Chemical Engineering , 3rd ed,

1976, Mc graw hill book company

5. David M. Himmelblau: Basic principles and Calculations inChemical Engineering ,5

th ed, 1992, Prentice hall Inc.

6. Norris Sherve: Chemical process industries , Mc Graw hill book

company N.Y.

7. Marvin J. Udy: Chemistry of chromium and its compound vol 1,

1956, Reinhold publishing cooperation N.Y

8. Chromium Sulphate tanning powder: CW Harland and Jenny

Simpson , 1996

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