Hydrothermal electrolysis reactions of glycerol were investigated under various operating conditions to determine the effects of applied DC current, electrolysis time, and alkali concentration on the decomposition mechanism of glycerol. In addition, intermediate products were identified, possible reaction schemes for both hydrothermal electrolysis and hydrothermal degradation of glycerol based on experimental data were clarified, and detailed product analysis was conducted using high performance liquid chromatography (HPLC), gas chromatography with a flame ionization detector (GC-FID), and gas chromatography with a thermal conductivity detector (GC-TCD). For the present study, a continuous flow reactor equipped with titanium electrodes (as cathode and anode), an electric furnace, a heater, a pump, a heat exchanger, a back pressure regulator, and DC supply was used. The main gaseous product was hydrogen, whereas glycolaldehyde, lactic acid, and formic acid were the main liquid products. Results indicate that greater than 92% of the glycerol could be decomposed under optimum conditions by hydrothermal electrolysis using the continuous flow reactor.
Recently, there has been a rising interest for the disposal of biorelated components that cannot be treated easily by biological processes. Because of the development of biodiesel production, the production of by-products such as crude glycerol has increased dramatically. Presently, in many biodiesel plants with low capacity, the aqueous phase containing produced/left glycerol, which is an important molecule in the context of renewable biomass resources to provide hydrogen energy and chemical intermediates, methanol and salts as by-products, is discharged as wastewater. In this manner, both environmental pollution and economical losses are created. Therefore, we developed a new hydrothermal electrolysis system, by which these organics can be converted into value added chemicals, under high-temperature and high-pressure aqueous conditions. In this study, hydrothermal electrolysis reactions of glycerol with an alkali were investigated systematically to determine the intermediate products and current efficiency. We next studied the effects of electricity loading on the molecular transformation of glycerol through the comparison of the product distribution obtained by hydrothermal electrolysis with that by hydrothermal degradation under alkaline conditions. As a gaseous product, hydrogen gas was generated, whereas lactic acid was produced as the main liquid product. The yield of lactic acid increased to 34.7% at 280°C with 50 mM NaOH after 90 min reaction time.
Hydrothermal conversion of waste hazelnut shell in hot compressed water, green and environmentally friendly medium, was investigated under different operating conditions to clarify the effects of reaction temperature, reaction time, acid concentration and acid kind (H 2 SO 4 and H 3 PO 4 ) on the production of value-added chemicals with high temperature/high pressure autoclave. In literature, to our best knowledge, there is no study about the production of levulinic acid, as a high value chemical, from waste hazelnut shell in hot-compressed water without using any mineral and heterogeneous catalyst. Hydrothermal reactions were conducted at 150-280°C for reaction times of 15 to 120 min with various H 2 SO 4 and H 3 PO 4 concentrations varying from 0 to 125 mM. The detailed liquid product species were identified with High Performance Liquid Chromatography (HPLC) and gaseous products were analyzed by Gas Chromatography with a Thermal Conductivity Detector (GC-TCD). The main identified liquid compounds were levulinic acid, acetic acid and furfural while carbon dioxide and carbon monoxide were the major gaseous products. Increasing the reaction temperature (280°C) and reaction time (120 min) resulted in a significant increment on the conversion (65.40%) as well as levulinic acid yield (13.05%). The production of levulinic acid was enhanced with H 2 SO 4 addition; whereas treatments with H 3 PO 4 improved the furfural production.
In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30-120 min of reaction time at temperature range of 170-230°C. As a proton donor H 2 SO 4 was used at concentrations of 1-50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC-MS) were used. A fractional factorial design with 2-level of four factors; reaction time, temperature, H 2 SO 4 concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200°C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230°C, 120 min., 2 A, 50 mM H 2 SO 4 ).
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