The Preparation and Application of Environmentally Benign Titanium Pillared Clay Catalyst for Esterification of Ethanol and Acetic Acid

Abstract

Aims: The study is aimed to develop an indigenous heterogeneous based catalyst and evaluate kinetic mechanism for the synthesis of ethyl acetate by esterification of acetic acid and ethanol. Study Design: Batch reactor system. Place and Duration of Study: Department of Pure and Industrial Chemistry, Faculty of Science, University of Port Harcourt, Rivers State. Nigeria. The study was carried out between February to August, 2011. Methodology: A sample of the natural clay was collected from the open clay deposit in Ezinachi, Okigwe Local Government Area, Imo state, Nigeria. The clay sample was washed and dried under sunshine for two days. Titanium pillared bentonite was produced by modification of natural bentonite clay using titanium pillaring solution at 500ᶿC. X-Ray diffraction (XRD), Fourier Transform Infra-Red (FTIR) and BET gas sorption analysis were employed to characterize the pillared material. Esterification reactions were carried out in a batch mode using a three-necked round bottom glass flask of 250 ml capacity fitted with a reflux condenser and mercury in glass thermometer to monitor the temperature. Heating and stirring was achieved using a magnetic hot plate with a stirrer. Pre-determined amount of acetic acid (for 1:1, 2:1, 3:1, 4:1 acid: alcohol mole ratio) and the clay catalyst were charged into the reactor and heated to 90 ±0.5ºC. After the desired temperature has been reached, a known amount of ethanol preheated separately using heating mantle was added into the reactor. About 2 ml of the reaction mixture was taken immediately using Pasteur pipette and titrated against 0.1 M NaOH solution using phenolphthalein indicator. All the experimental runs were designed by varying the amount of the catalyst, the acid to alcohol mole ratios, and the reaction period to obtain various kinetic parameters while keeping the temperature constant for all the runs. Results: The result revealed that significant improvement on physicochemical characteristics of the bentonite samples occurred as a result of pillaring. The results obtained revealed that the conversion of acetic acid was dependent on the catalyst weight, reaction time and mole ratio. The maximum conversion of acetic acid was obtained for mole ratio (acid: alcohol) of 2:1 with optimum catalyst weight of 2.0g at a reaction temperature of 368K and 90 minutes time on-stream. The pillared clay material was shown to be more active in the conversion of acetic acid than the unpillared counterparts. Kinetics studies revealed that the esterification reaction is second-order and follows the single step Eley-Rideal reaction mechanism. Conclusion: The esterification results showed that the conversion of acetic acid increased as a result of pillaring than the zero and unpillared catalyst. The mechanism involves a nucleophilic attack between adsorbed acetic acid and unadsorbed or competitively adsorbed ethanol to give ethyl-acetate and water. This research has demonstrated that titanium pillared clay has potential for esterification and trans-esterification of carboxylic acids.