Continuous catalytic esterification using a solid acid activated carbon monolith: Comparison of granular and monolith forms with a commercial catalyst

2-hydroxyisobutyric acid (2-HIBA) is a significant platform chemical for the synthesis of various products and has been produced fermentatively. Recently, the esters of 2-HIBA have gained interest for applications in fragrances and as low-toxic solvents. In this study, solid acid (sulfonated) wood-based activated carbon granular (sGAC) and monolith (sACM) catalysts were employed for the continuous esterification of 2-hydroxyisobuytric acid with ethanol. The effect of reaction conditions, including pressure and feed flow rate (Ql) on ester (ethyl 2-hydroxyi-sobutyrate) space-time yield (STY), ester yield, and selectivity, were determined. A higher STY of 96 g Lcat-1h- 1 (341 g kg cat-1h-1) and selectivity of 76 % was achieved with the sACM compared to the sGAC (87 g Lcat-1h- 1, 60 %) at 150 degrees C, 300 psig, and 3 mL min-1 (18.5-20 min contact time). At optimum pressure (300 psig) and temperature (150 degrees C for sGAC and sACM; maximum of 120 degrees C for Amberlyst), and in time-on-stream studies, 2-HIBA turnover frequency and ester selectivity were higher for sGAC and sACM over Amberlyst-15. The solid acid carbon monolith is a promising catalyst for the continuous catalytic upgrading of biobased organic acids.