Sn-silica catalyzes cheese whey to lactic acid in a fluidized bed reactor

Abstract

Worldwide, the dairy industry produces 200 million tons per year of whey. Among the most abundant components of cheese whey is lactose, a low-priced raw material for nutraceuticals, animal feed, and high value products such as lactic acid (LA)., a specialty chemical platform in the pharmaceutical, cosmetic, and in the food industry, and is the precursor to polylactic acid, a biodegradable polymer. Here, we propose a fluidized bed process that atomizes an aqueous lactose solution directly into a catalytic bed operating at 325^∘C to produce LA. We synthesized silica supported Sn catalysts by varying the metal loading (from 0 to 0.1 g g⁻¹ of Sn) and analyzed its physicochemical properties. This research highlights the critical role of Sn as an active site to hydrolyse/isomerize/retro-aldol/dehydrate/crack lactose to lactic acid in a gas phase environment. All catalysts achieved complete conversion. SiO₂ impregnated with 0.1 g g⁻¹ Sn catalyst achieved the maximum lactic acid yield of 23 % at 2 h of the reaction. Lactic acid yield declined thereafter due to coke blocking the active catalytic sites. XPS, Raman and CHN analysis highlighted changes in carbon distribution and evidence of coke accumulation in the spent catalyst. This article brings new findings related to significant challenges related to the continuous operation of a fluidized bed reactor in the conversion of lactose and strategies to mitigate agglomeration and coke formation.