Hydrothermal gasification of glucose and starch in a batch and continuous reactor

Abstract

A batch reactor was used for the gasification of glucose and starch as carbohydrate model compounds. The effects of H2O in various states (low-pressure hot compressed water (LP-HCW, 300 °C and 10 MPa), high-pressure hot compressed water (HP-HCW, 360 °C and 20 MPa), high-temperature steam (HTS, 400 °C and 10 MPa), and supercritical water (SCW, 400 °C and 25 MPa)), as well as reaction time (10, 30, and 60 min), sample concentration (10, 20, and 30 wt%), and catalyst (mixture of Ca(OH)2 and Na2CO3) on gas production were investigated in the hydrothermal gasification. In addition, using a continuous reactor, the hydrothermal gasification of glucose was examined with LP-HCW (200 °C and 5 MPa), HP-HCW (200 °C and 25 MPa), HTS (600 °C, 5 MPa), and SCW (600 °C, 25 MPa) in order to study the productions of gases and tar, and the mass balance. The reaction temperature affected gasification considerably, but pressure had little effect. In the batch experiments, the characteristics of the produced gases were almost identical after a reaction time of 10 min, and addition of Ca(OH)2 and Na2CO3 as catalysts in a molar ratio of 7:3 led to selective production of H2 in the SCW gasification of 10 wt% glucose for 30 min. In a continuous experiment under the SCW conditions, the conversion efficiency of glucose to gas was 26% and the composition of the produced gas was 29 vol% CO, 23 vol% H2, and 16 vol% CH4. Under the hydrothermal conditions, glucose was mainly converted to char and suspended components of high-molecular-weight compounds such as fat, whereas starch was mainly converted to gas and liquid.