Effects of sulfates on the decomposition of cellobiose in supercritical water

The decomposition of cellobiose in supercritical water (SCW) with and without sulfates has been performed using a continuous reaction apparatus. For the reactions in pure supercritical water the conversions of cellobiose increase from 36.7 to 59.3% while the selectivities of glucose decrease from 19.9 to 12.8% by changing residence time between 0.05 and 0.15 s at 400degreesC and 30 MPa. When we add extremely small amount of sulfuric acid, i.e. 6.4 x 10(-5) and 3.2 x 10(-4) mol/l, to supercritical water, the conversions of cellobiose reach high values between 54.2 and 93.9% and the selectivities of glucose show 35.4-73.5%. In order to investigate the effects of metal sulfate on the decomposition of cellobiose several metal sulfates, i-e. CuSO4, FeSO4 and MgSO4 have been tested. Introducing CuSO4 into supercritical water and keeping the concentrations between 6.4 x 10(-5) and 3.2 x 10(-4) mol/l, the conversions of cellobiose increase from 49.1 to 96.7% and the selectivities of glucose vary between 25.3 and 62.5% with residence time. The glucose selectivities of CuSO4 are three or four times greater than those of pure supercritical water and similar to those of sulfuric acid. For the case of FeSO4 the conversions are slightly lower than those of CuSO4 while the selectivities of glucose are comparable to CuSO4. When MgSO4 is added to supercritical water, the conversion, yield and selectivity of glucose show relatively lower values than those of CuSO4 and FeSO4. Although the catalytic activities of metal sulfates are somewhat different, it is evident that high glucose yields may be obtained in a very short reaction time, e.g. 0.05-0.15 s, by employing extremely small amount of metal sulfates. From the product distribution it has been found that the hydrolysis path through the glucose/fructose gives larger effects than the pyrolysis paths through intermediate products, i.e. glycosyl-erythrose/glycolaldehyde and glycosyl-glycolaldehyde/erythrose, for the decomposition of cellobiose in supercritical water when metal sulfates are used as catalysts. (C) 2003 Elsevier B.V. All rights reserved.