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THERMODYNAMICS OF REACTIVE EXTRACTION OF

PROPIONIC ACID

INTRODUCTION

Industrial scale fermentors for production of carboxylic

acids operate in the temperature range of 305 to 313 K.

Thus, reactive extraction process for recovery of these

acids requires an extractant that could operate efficiently

in this operating range. Usually, extraction is an exothermic

process and a decrease in extraction is expected as the

temperature is increased. However, it can be stated that

the decrease in extraction is the function of the extractant

and diluent chosen i.e. the extracting medium. Thus, it

makes the study of temperature effect important when

the process is to be designed. Further, the variation in

climate, feed and bioreactor conditions make the study

 AMIT KESHAV * KAILAS L. WASEWAR ** SHRI CHAND ***

HASAN USLU **** ISMAIL INCI *****

By

 ABSTRACT 

Temperature effect is an important subject of study in the reactive extraction process in view of operating temperature

and back extraction/regeneration step. Usually in industrial scale, for production of carboxylic acids, fermentor operatesin the temperature range of 303 to 313 K. Thus, an extractant can be considered as good, only if it could operate

efficiently in this operating range. The study, thus aims two objectives. (1) To find the effect of temperature on extraction of

the propionic acid (2) Whether temperature swing extraction/regeneration can be employed for recovery of the acid.

Three types of extractants: tri-n-butylphosphate, tri-n-octylamine and Aliquat 336 were used in different diluents and the

thermodynamics of extraction process was discussed in terms of enthalpy and entropy of reaction. Extraction of

 propionic acid using TOA in different diluents resulted in negative values of enthalpy and entropy. Thus, the reactive

extraction process is exothermic in nature and decrease in entropy is obtained. Aliquat 336 in 2-octanol shows the similar

 behavior as TOA in different diluents but the entropy and enthalpy values were lower, thus by suggesting not so high

exothermic nature of the extraction process and not so strong acid Aliquat 336 complexation as acid TOA

complexation. Two departures in the normal trend were observed when Aliquat 336 was used in oleyl alcohol and TBP

was used in MIBK. In both cases an increase in K was observed upto a certain temperature and whereupon a decrease E

was observed. The effect of temperature was correlated in terms of the heat of transfer from organic to aqueous phase

 (  Ä H ). It was found that the higher the  Ä H for a particular diluent, higher is the temperature effect.transfer transfer

 Keywords: Reactive Extraction, Propionic Acid, Thermodynamics, Temperature, Extractants, Diluents.

* Department of Chemical Engineering, National Institute of Technology (NIT) Raipur, Chhattisgarh.

**

 

 Department of Chemical Engineering, Visveswarya National Institute of Technology (VNIT) Nagpur, Maharashtra, India.

*** Department of Chemical Engineering, Indian Institute of Technology (IIT) Roorkee, Uttarakhand,

**** Faculty of Engineering & Architecture , Department of Chemical Engineering, Beykent University,  Ayazaðý köyü, Ýstanbul, Turkey .***** Engineering Faculty, Department of Chemical Engineering, Istanbul University, Avcilar, Istanbul, Turkey.

of temperature effect more important. The study thus aims

two objectives, (i) To find the effect of temperature on

extraction of the acid from fermentation broth (ii) Whether

temperature swing extraction/regeneration can be

employed for recovery of the acid.

Literature Review

Baniel et al. [1,2] studied the effect of temperature on

extraction of citric acid using tridecylamine in petroleum

fractions with alcohol as modifier, in xylene and in

nitrobenzene and observed a sharp decrease of

distribution of acid with temperature. Similar results were

obtained by Wennersten [3] for the extraction of citric acido

by Alamine 336 in a variety of diluents at 25 and 60 C

RESE RCH P PERS

 41i-manager’s Journal o Future Engineering & Technology Vol. No. 2 n , 4   November 2008 - January 2009