Obtenção de ésteres de cadeia curta, média e longa com lipases imobilizadas em reações multicompetitivas: estudo preliminar de viabilidade técnico-econômica

Abstract

Biocatalysis can be an advantageous alternative for obtaining industrially relevant esters. However, the adoption of biocatalysis for this application faces both economic (high cost) and technological challenges in the synthesis of short-chain esters – high concentrations of short-chain acids and alcohols can generate inhibition or inactivation of the biocatalyst. To achieve feasibility in the biocatalytic synthesis of short-chain esters, this project proposed the synthesis of short-, medium- and long-chain esters simultaneously in the same medium (multicompetitive system) without the need for solvents. Lipases are specific to the type of reaction and can catalyze esterifications with substrates of different chain sizes. A multicompetitive reaction system containing acetic (C2), capric (C10) and oleic (C18) acids reacting simultaneously with ethanol (C2) and n-octanol (C8) to obtain ethyl and octyl esters was evaluated in syntheses catalyzed by commercial biocatalysts: Novozym 435 (Candida antarctica lipase B immobilized onto acrylic resin), Lipozyme RM IM (Rhizomucor miehei lipase immobilized onto anionic resin), and Lipozyme TL IM (Thermomyces lanuginosus lipase immobilized onto silica). The multicompetitive reaction system catalyzed by Novozym 435 at 50 °C and equimolar conditions achieved 88.8% conversion of acids to esters after 4 h in a shaken flask. This result is higher than the obtained in the individual syntheses (1 acid and 1 alcohol) of the shorter chain esters studied (ethyl acetate and octyl acetate) in the same reaction conditions. This demonstrates that the mixture of short-chain reagents with of long and hydrophobic ones promotes the same effects of solvents in the synthesis – reduction of the high concentration of inhibitors, acidity and overall hydrophilicity of the medium. Volumetric productivity and catalytic productivity calculations indicated that the multicompetitive system reaction shows process metrics equal to or higher than the individual syntheses studied. Process improvement included the design and study of a prototype bubble column reactor, aiming to increase conversion, reduce reaction time and increase the biocatalyst reuse. A result of 95,3% conversion was achieved in 3 h of reaction in the bubble-column reactor prototype, adopting acids:alcohols molar ratio 1:2, biocatalyst loading 1.3% (w/w total substrates). Conversions close to 90% were achieved using acids:alcohols molar ratio 1:1.3 in only 2 h; in this condition, the same biocatalyst loading can be reused 13 times, resulting in a high catalytic productivity (878,8 kg of product per kg of biocatalyst). The obtained data was used as input for process design and simulation using SuperPro Designer v.13 software, for preliminary technical-economic study. The base-case was a 6000 tons year-1 esters production plant, isolatedly for commercialization. The simulation output indicated a CAPEX of USD 30,5 million for installation of the plant and an annual OPEX of USD 37,5 million for operation, obtaining a positive net present value of USD 90,5 million over 15 years project lifespan and a payback time of 1.8 years, which is considered economically feasible for the chemical industry. Considering the volumetric productivity and catalytic productivity of the process in this scenario, the cost of the biocatalyst (Novozym 435) corresponded to only 13,2% of the annual operating costs. The biocatalytic production of ethyl and octyl esters in a multicompetitive system is more advantageous than their production by individual reactions between a single acid and a single alcohol catalyzed by immobilized lipase, indicating an economically viable and sustainable technology that can be used to obtain other esters.