V. P. YADAV et al., Kinetics of Esterification of Ethylene Glycol with Acetic Acid …, Chem. Biochem. Eng. Q. 25 (3) 359–366 (2011) 359 Kinetics of Esterification of Ethylene Glycol with Acetic Acid Using Cation Exchange Resin Catalyst V. P. Yadav,a S. K. Maity,b,* P. Biswas,a and R. K. Singha aDepartment of Chemical Engineering, National Institute of Technology Rourkela, Rourkela-769008, Orissa, India bDepartment of Chemical Engineering, Original scientific paper Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Received: December 8, 2010 Yeddumailaram-502205, Andhra Pradesh, India Accepted: September 18, 2011 The esterification of ethylene glycol with acetic acid was investigated in a batch re- actor in presence of a strongly acidic cation exchange resin, seralite SRC-120, as catalyst in the temperature range of 333 to 363 K. The detailed kinetic study was performed to understand the effect of various process variables such as catalyst loading, ethylene glycol to acetic acid mole ratio, and temperature on conversion of reactants and selec- tivity to products. Further, two different kinetic models, empirical and kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach, were developed to correlate the experimental concentration versus time data. The kinetic parameters of the developed models were then estimated at different temperatures using non-linear regression technique based on modified Levenberg-Marquardt algorithm. The cal- culated results based on the estimated kinetic and equilibrium constants at different tem- peratures were then compared with the experimental values and LHHW-based model was found to fit the experimental data reasonably better compared to empirical kinetic model. The estimated rate constants at different temperatures of LHHW-based model were then used to estimate the activation energy and frequency factor of the rate con- stants. Key words: Reaction kinetics, modeling, ethylene glycol, ethylene glycol di-acetate, cation exchange resin Introduction The esterification process is widely used in in- dustry to produce esters for a wide range of applica- The growing international energy crisis cou- tions such as plasticizers, solvent, perfumery, flavor pled with rising oil prices and increasing awareness chemicals, precursors for pharmaceuticals, agro- of the environment and pollution has intensified the chemicals, and other fine chemicals.3–4 In recent research on renewable fuels derived from biomass. times, several esterification reactions with different The bio-oil produced by the process of biomass py- alcohols and carboxylic acids have been reported in rolysis is nowadays an emerging technology for the open literature using different types of solid acid production of renewable fuels and value-added catalysts such as zeolites (HB, HY, ZSM-5) and cat- chemicals. The bio-oil was first separated into ion exchange resin (Amberlyst 15, Amberlyst 36, aqueous and non-aqueous fractions by the addition Amberlite IRA-120).5–11 of water. The aqueous fraction of bio-oils contain- ing sugars, anhydrosugars, acetic acid, hydroxy- The esterification reactions are known to be cata- acetone, furfural, and small amounts of guaiacols is lyzed by a variety of Lewis or Bronsted acid catalysts. The homogeneous mineral acids such as H SO and a potential source of alkanes (ranging from C1 to 2 4 p-toluenesulphuric acid are however highly corrosive C6) and polyols (ethylene glycol, 1,2-propanediol, 1,4-butanediol etc.).1 The ethylene glycol obtained to process equipment and difficult to separate from from bio-oil fraction can be utilized to produce eth- the reaction mixture.11–13 Moreover, there is an in- ylene glycol mono- and di-acetate suitable for ap- creasing tendency to develop processes that should plication as solvent for coating, paints, and oxygen- meet the requirement of generation of nearly zero ated diesel fuel additives.2 waste. Thus, it would be preferable to use a safer and simpler catalyst possibly in solid state, such as cation *Corresponding author (Dr. Sunil K. Maity): Phone: +91-040-2301-6075; exchange resin. The various types of processes in- Fax: +91-40-2301 6003; E-mail: [email protected] cluding isomerization, dehydration, etherification, 360 V. P. YADAV et al., Kinetics of Esterification of Ethylene Glycol with Acetic Acid …, Chem. Biochem. Eng. Q. 25 (3) 359–366 (2011) acetylation, and esterification have been intensified by the measured volume of ethylene glycol (25 cm3), solid acid catalysts.14–17 kept separately at reaction temperature, was charged The study of esterification of ethylene glycol into the reactor and the reaction started. Samples with acetic acid is however limited in open litera- were withdrawn from reaction mixture at regular ture.18 Schmid et al.19 studied the reaction using intervals after stopping the stirring and allowing the acidic cation-exchange resin, Amberlyst 36, as cata- catalyst to settle. The detailed study of the reac- lyst, and pseudo-homogeneous kinetic model based tion was performed in wide range of temperature on activity was then developed using the measured (333–363 K), catalyst loading (0.5 to 1.5 % (w/v)), thermodynamic properties of ethylene glycol–acetic and acetic acid to ethylene glycol mole ratio (0.66 acid reactive system.20 Suman et al. studied the to 3.13). entrainer-based reactive distillation of ethylene gly- col–acetic acid system using 1,2-dichloroethane Product analysis (EDC) as an entrainer to enhance the conversion of The reaction product containing acetic acid, reactants and selectivity to ethylene glycol di-ace- 2 ethylene glycol, ethylene glycol mono-acetate tate. Considering the importance of the reaction, (EGMA), and ethylene glycol di-acetate (EGDA) the present work was undertaken to study the kinet- were analyzed by gas-liquid chromatography (Che- ics of esterification of ethylene glycol with acetic mito GC 8610) using carbowax column. The GC acid in presence of a commercial cation-exchange equipped with a flame ionization detector (FID) resin catalyst and to develop suitable kinetic models was used for analysis. The column temperature was for its application in design and simulation of reac- programmed with an initial temperature of 333 K tive distillation column. for one minute, increased at a rate of 20 K min–1 up to 473 K, and maintained at 473 K for 2 min. The nitrogen (99.99 % purity) was used as carrier gas. Experimental An FID detector was used at a temperature of Chemicals 523 K. An injector temperature of 523 K was used during the analysis. The moles of water formed in Ethylene glycol and acetic acid (³99 % purity) the reaction were obtained from the overall mole (aldehyde free) were purchased from Merck Spe- balance. Each sample was analyzed three times and cialities Private Limited, Mumbai, India. The average value was taken for further calculation. strongly acidic (hydrogen form) cation-exchange resin, seralite SRC-120 (mesh number = 20–50, ion-exchange capacity = minimum 4.5 meq g–1 dry Results and discussion resin, and pH range = 0–14) was procured from Sisco Research Laboratories Private Limited, Mum- The reaction of ethylene glycol with acetic acid bai, India. in presence of cation-exchange resin proceeds in two consecutive reversible steps as shown in Experimental set-up Scheme 1. In the first step, ethylene glycol reacts with acetic acid to produce EGMA and water. The All kinetic experiments were carried out in EGMA formed in the first step reacts further with batch mode in a 6.5 cm i.d. fully baffled, mecha- acetic acid resulting in the formation of EGDA and nically agitated glass reactor with a volume of water. The term selectivity (S) of the two products, 250 cm3. A six-blade glass disk turbine impeller EGMA and EGDA, used throughout the present with 2.0 cm diameter was used for stirring the reac- article was defined as follows. tion mixture. The impeller was kept at a height of 1.5 cm from reactor bottom. The reactor was kept moles of EGMA formed S (%) =×100 in a constant temperature water bath whose temper- EGMA mole of AA reacted ature was controlled within ±1 K. The reaction mix- ture was well agitated with the help of a mechanical 2´ moles of EGDA formed =× stirrer. To avoid the vaporization loss of reaction S EGDA (%) 100 mixture, reactor setup was equipped with a con- mole of AA reacted denser. Effect of stirring speed Experimental procedure To determine the role of mass transfer resistan- In a typical experimental run, about 75 cm3 of ces, the effect of agitation speed on the conversion acetic acid with known amount of catalyst (say 1 g) of ethylene glycol was studied. The stirring speed was charged into the reactor and kept well stirred was varied in the range of 1000–2000 rev min–1. until steady-state temperature was reached. Then The strongly acidic cation-exchange resin (seralite V. P. YADAV et al., Kinetics of Esterification of Ethylene Glycol with Acetic Acid …, Chem. Biochem. Eng. Q. 25 (3) 359–366 (2011) 361 Scheme 1. SRC-120) of 1.5 % (w/v) was used in each test. The variation of conversion of ethylene glycol was found to be negligible with speed of agitation as shown in Fig. 1. The external mass transfer resis- tance factors were therefore unimportant. There- fore, all other experiments were performed at a safe stirring speed of 1500 rev min–1. Fig. 2 – Effect of temperature on conversion of ethylene glycol. Conditions: catalyst loading = 1.5 % (w/v); acetic acid to ethylene glycol mole ratio = 3.13; stirring speed = 1500 rpm. Table 1 – Effect of temperature on selectivity to EGDAa Selectivity/% to EGDA Temperature/K at different reaction time Fig. 1 – Effect of speed of agitation on conversion of ethyl- 30 min 60 min 120 min ene glycol. Conditions: Acetic acid to ethylene gly- col mole ratio = 3.13; temperature = 333 K; cata- 333 42.7 48.8 56.2 lyst loading = 1.5 % (w/v); matching reaction time = 5 min.