RECOVERY OF PROPIONIC ACID FROM AN AQUEOUS STREAM BY

REACTIVEEXTRACTION: EFFECT OF

DILUENTS

INDEX

• Details• Introduction about Propionic acid• Reactive extraction• Theory• Experiment• Result and Discussion• Conclusion

DETAILS

Process used :- reactive extraction Compound :- Propionic acid Extractant used :- Tri-n-Butyl Phosphate(TBP) Diluent used :-

1. n- heptane

2. Petroleum ether

3. Toluene Analysis factors:-

1. distribution coefficient

2. Equilibrium complexation constant

3. Loading ratio

4. Extraction efficiency

INTRODUCTION ABOUT PROPIONIC ACID…

• Propionic acid is a very important carboxylic acid

,used for animal feed preservation, manufacture of

antiarthritic drugs, perfumes and flavors,

plasticizers, mould preventives in silage and hay and

as a solvent.• Propionic acid is industrially produced by the

petrochemical route . However, since the prices of

the petrochemical products are continuously

increasing , alternative means of propionic acid

production was looked for. Fermentation technology

emerges as the best alternative.

• Conventionally, propionic acid is extracted from

fermentation broth by calcium salt precipitation.• For the recovery of propionic acid by reactive

extraction, common organic solvents such as

ketones and alcohols show a low distribution

ratio because of the high affinity of acid for

water. Thus physical extraction with conventional

solvents is not an efficient method for recovery of

propionic acid.

REACTIVE EXTRACTION…

• Reactive extraction is a effective technique for the recovery of carboxylic acid from dilute aqueous solutions.

• It requires a proper combination of extractant and Diluent which provides higher capacity and selectivity.

• It enhances the recovery by intensifying the separation through simultaneous reaction and extraction and provides advantages of high selectivity and fractional recovery.

• Diluent is usually added along with the extractant to

enhance its physical properties by providing general

solvation and affect the extraction power of the

extractant by providing specific interaction. • The Diluent may consist of one or more components,

inert or active.• When Gu et al. studied the reactive extraction of

propionic acid using Alamine 304-1 in 2-octanol,

1-dodecanol and Withohol 85 NF as diluents at various

amine concentrations (0–100%) , he found extraction to

be maximum at amine concentration between 20–40%.

• The high polarity of the phosphoryl group in tributyl

phosphate (TBP) enables it to act as a strong Lewis

base and as a result it can form acid base complex when

contacted with propionic acid. • The study the extraction of propionic acid

using TBP in n-heptane, petroleum ether and toluene

was done . The distribution of propionic acid between

water and TBP dissolved in various diluents and a

comparison with the extraction capacity of pure Diluent

alone were studied at isothermal conditions.

THEORY…

• The recovery of propionic acid using TBP is

by the formation of a complex via the interfacial

reaction and can be represented as below. As the

propionic acid–TBP complex is formed, it is

rapidly extracted into the organic phase.

HAaq + pSorg (HA.Sp)org

The extraction constant and

the number of reacting

molecules of extractant are

computed by applying the

law of mass action that is the

ratio between concentrations

of reactant molecules and

concentration of the product

species, according to

the general equation of

interaction between the

extractant and the extracted

species as:

• Ks =[(HA).(S)p]org

/[HA]aq [S]p org

• KD is defined as the ratio of total (analytical)

concentration of acid in all its forms (by partition,

dimmers and as complexes) in organic phase and total

(analytical) concentration of all its existing forms

(dissociated and undissociated) in aqueous raffinate.

KD includes the effects like ionic strength, nature of

ion concentration of H+ etc. of solution constituents.• The dissociation of the acid in the aqueous phase is given

as:

Distribution coefficient of the acid by chemical extraction can be defined agiven, where ν is the volume fraction of diluent and [HA]org

diluent is the acid extracted into the organic phase by diluent alone. The overall distribution coefficient is evaluated as the function of extraction constant and the number of reacting species as:

It is well known that carboxylic acid dissociates in aqueous solution. Under the experimental condition that pH of the aqueous solution was smaller than pKa of the acid ,the effect of the acid dissociation was negligibly small. Thus the plot of log ( KD

overall - νKDdiluent ) versus log[S]org would yield a straight line

with the slope of p and the intercept of log(KS) from where KS can be obtained. The extent to which the extractant is loaded with propionic acid is expressed as the overall loading factor (Zt).

EXPERIMENT…

MATERIALS

• TBP ,a phosphorous bonded oxygen donor, is a light colorless liquid with

the molecular weight of 266.32 g/mol and density of 0.92 g/cm3. • Propionic acid (99%) and the diluents petroleum ether, n-heptane, toluene

are of technical grade and were used without pretreatment. • Distilled water was used to prepare the solutions of various concentrations

of propionic acid solutions. • NaOH was used for the titration is of analytical grade • Oxalic acid (99.8%) was used, for the standardization of the NaOH.• Phenolphthalein solution (pH range 8.2–10.0) was used as an indicator for

titration . • The range of pH of feed solutions for the experiment was 2.65–3.14 at 305

K.• The initial TBP concentrations in the range 0.37–1.65 kmol/m3 (10–40%)

and the initial aqueous acid concentrations range ([HA]o) of 0.05– 0.4

kmol/m3 were used.

METHODS• The extraction experiments were performed using a temperature-controlled

water bath shaker at room temperature. • Equal volumes (25 cm3) of aqueous and organic phases were shaken for 12

h and then left to settle for at least 2 h at a fixed temperature (305 K) and

atmospheric pressure (101.2 kPa). • Aqueous phase pH was measured by an Orion 3 star pH benchtop (Thermo

Electro). • Aqueous phase acid concentration was determined by titration with NaOH

by a UV spectrophotometer (λ = 230) and by HPLC. (High pressure liquid

chromatography ). The column used was C-18.• The results of the above methods were comparable. The acid content in the

organic phase was determined with a mass balance.

Results And Discussion:Organophosphorous compounds are• Effective extractants• Chemically stable• Higher distribution coeff than carbon-bonded oxygen bearing extractants.

• Thus TBP, an organophosphorous compound, was selected because of low water coextraction(4.67 mass %) and very low solubility in the aqueous phase(0.039 mass%)

• TBP contain =P(O)OH group which has a marked tendency towards an intermolecular hydrogen bonding. Due to the presence of both electron donor and electron acceptor group in =P(O)OH grouping, it undergoes specific interactions like self association and molecular complex formation with diluents or other solutes.

The extraction equilibria of propionic acid by diluents(physical) and extractant-diluent combination (chemical) were studied. The physical extraction using n-heptane, petroleum ether and toluene is shown in fig below. The regression equations for the physical extraction equilibrium of propionic acid in three diluents is represented

The coefficients of [HA]2aq and [HA]aq provides the value of partition and

dimerization coefficient . It can be seen that the distribution coefficient decreases with the increase in the molecular weight of the diluents. But the miscibility of solvent and water increases with decreasing molecular weight.

Table on the next page shows the influence of organic solvent and organic phase concentration of TBP on the distribution coefficient of propionic acid.

It can be seen that maximum KD values were found for the extactant concentration of 20-40%

The maximum removal of propionic acid was for 0.05kmol/m3 propionic acid solution with 40%(1.65 kmol/m3) TBP in toluene.

• The influence of extractant concentration on degree of extraction is give by

E% = KDoverall *100 / (1 + KD

overall )

• The degree of extraction was found to increase with increasing the concentration of TBP from 0.37 to 1.65 kmol/m3 in various diluents.

• The equilibrium complexation constants for the extraction using TBP in different diluents are listed in the above table.

• The comparison clearly shows that the maximum KS values are obtained for the case of TBP-toluene, suggesting it the best system out of the three for the recovery of propionic acid.

• Different approaches have been used to quantify the effects on diluents on the (1:1) complexation. Both partition and self association constants are strongly dependent on the nature of the diluents i.e the thermodynamic activity of the species taking part in the organic phase equilibria is changed when one diluent is replaced by other. The effect of diluent on the partition and self association constants was explained by specific interactions only between the organophosphorous monomeric species and the diluents; those interactions are higher and lower than the partition coeff and self association constants should be, respectively.

Complexing formula of (1:1) propionic acid and TBP complex

Conclusion

• Fermentation being an energy efficient technolgy, it suffers from the disadvantages of acid production is low concentration and difficult separation and purification of the acid.

• Reactive extraction is most successful recovery methods with the advantage of providing high capacity and selectivity.

• Diluents improve the solvation and complex stabilty. Of the different diluents used, toluene was found to give a higher distribution coefficient, equilibrium complexation constants and loading anf extraction efficiency, thus indication it as f best solvent for propionic acid recovery.

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