Nowadays, due to the depletion of fossil raw materials in the world, the chemical industry is focusing on renewable resources as feedstocks to develop high added value products. In this way, carbohydrates from biomass are seen as a suitable feedstock for many useful chemicals. Lactic acid is a chemical compound with a wide range of applications in many industrial fields: food industry, textile and pharmaceutical industries… It can be also used for medical purposes or as a raw material for different compounds and the main market demand is in the production of polylactic acid.
We are studying the production of lactic acid from D-glucose, D-fructose and sucrose in Hot Compressed Water (HCW) using alkaline aqueous solutions. The experimental set-up and the flow diagram can be seen in Fig. 1.
The reaction from sucrose consists in two steps: first, sucrose is converted into its two monomers (D-glucose and D-fructose) by a hydrolysis process and then, lactic acid is produced using sodium hydroxide aqueous solutions. A possible reaction pathway for the conversion of sucrose into lactic acid is shown in Scheme 1.
Temperature has been studied in the range 20-175 ºC, with NaOH concentrations from 0.1 to 2 M, and autogenous pressure, with values up to 9 bar. In order to maximize the lactic acid yield and study the effect of the different operational variables (temperature, NaOH concentration and time), the RSM Box-Behnken approach will be used. The reaction from sucrose succeeded in a selectivity to lactic acid about 65% and a conversion of this reagent equal to 90% after 45 minutes when the NaOH concentration was 1 M and the reaction took place at 150 ºC.