Effects of sulfates on the decomposition of cellobiose in supercritical water

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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 400 °C and 30 MPa. When we add extremely small amount of sulfuric acid, i.e. 6.4×10 −5 and 3.2×10 −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. CuSO 4, FeSO 4 and MgSO 4 have been tested. Introducing CuSO 4 into supercritical water and keeping the concentrations between 6.4×10 −5 and 3.2×10 −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 CuSO 4 are three or four times greater than those of pure supercritical water and similar to those of sulfuric acid. For the case of FeSO 4 the conversions are slightly lower than those of CuSO 4 while the selectivities of glucose are comparable to CuSO 4. When MgSO 4 is added to supercritical water, the conversion, yield and selectivity of glucose show relatively lower values than those of CuSO 4 and FeSO 4. 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.