Solvothermal treatment of starch for the production of glucose and maltooligosaccharides

Starch was hydrothermally degraded without any additives over the temperature range from 453 to 563 K at a constant pressure of 10 MPa and the fluid residence times up to 6 min in a semi-batch reactor to produce glucose and maltooligosaccharides. The effects of reaction temperature, flow rate of hot water and residence time of water-soluble components on the product distribution in the solvothermal degradation of starch were investigated. Even at the lowest reaction temperature studied, the loaded starch was partially degraded and dissolved within 8 min by contacting high-temperature and high-pressure water in a semi-batch reactor. By installing a plug-flow reactor at the exit of the first reactor to increase and control precisely the residence time, the maximum glucose yield of 43.8% on the carbon weight basis of the starting material was obtained at 3.64 min and 513 K. The comparison of yields of glucose and 5-hydroxymethyl furfural (HMF), which is a major secondary product, indicates that adjusting the residence time was the most effective to increase the glucose yield and to suppress the 5-HMF production.