Microwave-assisted conversions of biomass into valuable compounds

This study contains two major topics including 1.) non-thermal atmospheric pressure plasma and ozone pretreatment assisted hydrolysis of biomass, and 2.) microwave-assisted one-pot conversion of tapioca starch to valuable compounds For the evaluation of non-thermal atmospheric pressure plasma (NTAP) pretreatment, cellulose powder was directly pretreated under NTAP generated by dielectric barrier discharge (DBD) with the frequency and voltage of 11 kHz and 6 kV respectively. The effect of NTAP pretreatment time (5-10 min) on hydrolysis was investigated. The diluted-acid hydrolysis of 10-min NTAP pretreated cellulose resulted in a 3% higher glucose yield than the native cellulose. However, the DBD reactor could not perform for a longer time than 10 min due to reactor damage caused by the heat accumulation. In the meantime, the hydrolysis parameters including the reaction temperature (100 to 170 °C), the acid concentration (0 to 1 M), and acid types (HCl and HNO3) were investigated. The maximum glucose yield of 70.5 %, 81.2 %, and 53.1 % were obtained from the hydrolysis of cellulose (1M HCl, 130 °C), starch (0.1M HCl, 150 °C), and sugarcane bagasse (1M HCl, 130 °C) for 15 min, respectively.For the evaluation of ozone pretreatment generated by NTAP, cellulose, and sugarcane bagasse powder were pretreated for 0 to 180 min then hydrolyzed by 1M HCl at 150 °C for 15 min. The pretreatment aimed to decrease the percent of crystallinity and increase the glucose yield from hydrolysis. The percent of crystallinity of cellulose decreased from 62 % to 47 % and the glucose yield increased from 18% to 26% after the pretreatment time of 60 min then slightly changed. For sugarcane bagasse, the percent of crystallinity decreased from 53 % to 46 % and the glucose yield increased from 8.9% to 16% after the pretreatment time of 120 min then slightly changed. Moreover, Fourier-transform infrared spectroscopy (FTIR) showed the change in chemical functional groups of the sample after the pretreatment, the lower peak intensity at the wavelength of 1160 and 900 cm-1 associated with the cleavage of β-1,4-glycosidic linkage in the cellulose, the lower peak intensity at the wavelength of 1030 cm-1 associated with the delignification, and the lower of the broad peak (3000 and 3600 cm-1) associated with the weaker intramolecular hydrogen bonding of cellulose. For the one-pot conversion of starch to 5-(hydroxyl methyl) furfural (5-HMF) using solid catalysts, such as commercial metal oxides (TiO2 and ZrO2), and metal-phosphates supported on alumina (NiPO4/γAl2O3, CuPO4/γAl2O3, and CoPO4/γAl2O3). The examined catalysts possess the acid and base properties confirmed by the ammonium and carbon dioxide temperature-programmed desorption (NH3-, and CO2-TPD) which are essential to promote 1.) hydrolysis of starch to glucose, 2.) isomerization of glucose to fructose, and 3.) dehydration of fructose to 5-HMF. The effect of reaction temperature (150 to 220 °C), reaction time (5 to 30 min), catalyst loading (catalyst to substrate ratio of 1:10 to 2:1) was investigated. This study obtained 29.4 mol% HMF from a reaction condition: starch = 1 g, 500 mg TiO2, 10 mL RO, 220 °C, and 15 min, and here is the first time to report using metal-phosphates supported on alumina (NiPO4/γAl2O3, CuPO4/γAl2O3, and CoPO4/γAl2O3), 49.54 mol% HMF obtained from a reaction condition: starch = 100 mg, 10 mg NiPO4/γAl2O3, 1 mL RO, 220 °C, and 15 min. Moreover, the recyclability tests were conducted, TiO2 and NiPO4/γAl2O3 can be used up to 5 cycles without advance separation and catalyst compensation while the HMF yields remained acceptable.