Process development with reaction kinetics

Abstract

Chemical engineering industries perform the basic task of converting raw materials into useful products, which involves reaction and separation. The most complex step, in many instances, is the reaction itself. It may be tedious, time consuming or costly or in some cases all of these. It is obvious that any attempt to improve the reaction step will help the particular industry. Converting batch process into continuous one, reducing the process steps and employing techniques like process intensification are some ways to achieve this. There are several classes of reactions which the industry uses to produce useful products like alcoholysis, aldol condensation, etherification, and esterification etc. newlineEsterification reactions are important and form the backbone of many pharmaceuticals, many speciality chemicals, intermediates and bulk chemical industries as well. Esters are useful for applications in lacquers and varnishes, paints and pigments, flavours and fragrances, as solvents among other important applications. Esterification is equilibrium limited and it is necessary that ways to achieve higher conversion are adopted, while keeping economics in view. This may involve change of catalyst, change of process parameters, using alternate techniques or employing process intensification. Reactive separation (RS) is one such way to improve the performance due to the uniqueness of RS in that it combines reaction and separation in one single vessel. Reactive distillation (RD), reactive extraction (RE) and reactive chromatography (RC) are important candidates of RS. RD is effective for esterification reactions and although it achieves higher conversions, mostly it is heat intensive and hence costly. newlineRE can be attractive only if the right entrainer is selected which offers large separation due to good distribution coefficient. RC, that is reactive chromatography, employs adsorptivity - desorptivity of reactants as well as products, is gaining popularity, of late. newlinexv newlinePacked bed reactors provide an access in the laboratory to check the efficiency of simultaneous reaction and removal of selected compounds from reactive zone by adsorption - desorption. newlineOut of the various catalysts, solid catalysts have gained importance over their liquid counterparts due to reasons like good conversion and high selectivity, ease of separation from reaction mass, possibility to manufacture tailor made catalysts and can be used to employ newer methods like RS. Catalysts like ion exchange resins (IERs), zeolites, clays, metal oxides have been employed in different instances in the past. Especially ion exchange resins are employed in a variety of reactions including esterifications. Mostly acidic IERs are useful for esterifications and basic IERs are useful for other reactions like aldol condensation. newlineThis work has explored two industrially important reactions: newline1. Esterification of propionic acid with isoamyl alcohol to produce isoamyl propionate newlineand newline2. Esterification of butyric acid with methanol to produce methyl butyrate. newlineIsoamyl propionate is used in fragrances, flavours, plasticizers and solvent industry. Initially, batch experiments were performed to obtain the kinetics. Regression was then performed to obtain a kinetic model. Further, in order to make the process continuous, packed bed experiments were performed. For three hours operation 53% and 33% conversion was obtained with the packed bed reactor and batch reactor respectively. The packed bed reactor is advantageous in terms of its increased conversion rate. Continuous nature of process and is less heat sensitive. All these features make the packed bed better option for enhancement of process performance. newlineMethyl butyrate is used in flavours, pesticides, plasticizers, polymerisation monomers, adhesives and solvent industry. Batch experiments were performed initially to obtain the kinetics. Regression was then performed to obtain a kinetic model. Further, in order to make the process continuous, packed bed experiments were performed. The conversion obtained for newlinexvi newlinethis run was ~ 60% in three hours. For the same conditions, the conversion obtained in batch mode for three hours was less (38 %). Thus, it is seen that the process can be made continuous and also that better conversion is obtained.