Process Chemistry and Design Alternatives for Converting Dilute Acetic Acid to Esters in Reactive Distillation

Abstract

This work explores the recovery of acetic acid aqueous solution with different acid concentrations. Instead of separating acid from water using azeotropic distillation, acetic acid is converted to acetate via esterification. Two questions then arise. First, what is a better choice of alcohol (e.g., ranging from methanol to pentanol, C 1 -C 5 ) for the esterification? This is a solvent selection problem. Second, what is the more economical process flowsheet (e.g., a stand-alone reactive distillation versus a pretreatment unit followed by a reactive distillation)? For the solvent selection problem, an earlier study [Tang et al., AIChE J. 2005, 51, 1683-1699 has indicated that the esterifications using methanol or pentanol is much more economical as compared to other choices (e.g., ethanol, 2-propanol, or butanol). Quantitative analysis reveals that the production of methyl acetate (from methanol and acetic acid) is not tolerant to acid concentration variation, and a very-high-purity acid feed is needed to achieve product specification. Thus, methanol is ruled out for esterification and pentanol is selected to convert acid to the ester. Next, a systematic design procedure is taken to design the process flowsheets and the total annual cost (TAC) is used to discriminate between different flowsheets, with and without pretreatment unit. A range of acetic acid concentration is explored, varying from 100 wt %, to 75 wt %, to 50 wt %, and then to 30 wt %. The TAC analysis shows that a stand-alone reactive distillation is more economical than the flowsheet with a pretreatment unit.

Experimental methods in chemical engineering: Process simulation

“…Process simulation discriminates between process alternatives (design: 246 articles), which comprises modelling (187 articles) and determines the dimensions of unit operations like separation (126), including distillation (137 articles) (reactive and extractive), heat integration (33), and dehydration (26). Hung et al, [ 27 ] for example, demonstrated that recovering dilute acetic acid water solutions (between 30‐70% by mass of acid) with amyl alcohols among C 1 ‐C 5 minimizes the total annual cost (TAC), without any stream pretreatment. Pirola et al [ 28 ] simulated an extractive distillation column employing p‐xylene as entrainer to maximize acetic acid recovery.…”

Reactive Distillation: An Interesting Intensification Process Technology

“…Esterification and hydrolysis are widely studied in literature, with heterogeneous catalysis (Lai et al, 2007;Hung et al, 2006;Arpornwichanop et al, Huang et al, 2005). The main lack in these studies is about the technology ensuring resin stability in trays.…”

Phase equilibria for reactive distillation of diethyl succinate. Part II: Systems diethyl succinate+ethyl acetate+water and diethyl succinate+acetic acid+water

“…Also, RD provides advantages over traditional processes to upgrade fermentation products as recognized since early 1900s [1]. This method has been successfully applied for esterification of solutions with acetic acid [2][3][4][5][6][7][8][9][10][11][12][13], lactic acid [14,15], and citric acid [16,17].…”