Effects of potassium on hydrothermal carbonization of sorghum bagasse.

Hydrothermal carbonization (HTC) reacts with biomass in water at a high temperature and pressure to produce hydrochar with a higher heating value (HHV) and lower ash content than dry torrefaction. The high potassium content in biomass can promote thermochemical conversion; however, it lowers the melting temperature of the ash, causing slugging and fouling. Therefore, this study, investigated the effect of potassium on the HTC of sorghum bagasse by comparing the removal of potassium by washing with the addition of K2CO3. Consequently, the ash content was the highest in the potassium-added hydrochar and was 3.81% at a reaction time of 2 h. Elemental analysis showed that the lower the potassium content, the higher the carbon content, and the hydrochar with potassium removed by water washing at a reaction time of 3 h had the highest carbon content at 68.3%. Fourier transform infrared spectrometer showed dehydration and decarboxylation reactions due to HTC, but no significant differences were observed between the potassium concentrations. The mass yield decreased with increasing potassium content, and was 27.2% for the potassium-added hydrochar after 3 h. This trend was more pronounced with increasing reaction temperature. On the other hand, HHV was not affected by the potassium content. Therefore, the energy yield was similar to the weight yield. Thermal gravimetry and derivative thermal gravimetry (TG-DTG) analysis showed that higher potassium tended to accelerate the decomposition of lignin and decrease the oxidation temperature.

Investigation into the combustion kinetics and spontaneous ignition of sweet sorghum as energy resource.

This study investigated the combustion kinetics and spontaneous ignition of sweet sorghum using thermogravimetric analysis and the Frank-Kamenetskii theory. The aim was to determine the proper operating conditions for a direct combustion reactor and predict the safe ambient temperature limits for given silo designs. Oxidative heating rates of 2, 5, and 10 °C/min were set up. Graphical observation shows that combustion was composed of two different stages representing the overlapping processes of pyrolysis and char oxidation, at 131-336 °C and 336-475 °C, respectively. Samples were found to ignite at 215 °C and were extinguished at 433 °C. Different heating rates shifted combustion characteristics to higher temperatures and increased reactivity for ignition and combustion indices up to 12 and 10 times higher. The Friedman method determined the apparent activation energies representing the combustion reaction by 132.91 kJ/mol. Regarding spontaneous ignition, the temperature safe limits were predicted to be 83-84 °C and 84-87 °C for cylindrical and box silos with diameter and height of 15 and 10 m, respectively. Calculations of silos were designed within the limits of certain dimension ratios.

Effect of wood biomass components on self-heating.

Biomass may ignite due to biological oxidation and chemical oxidation. If this phenomenon (spontaneous ignition) is controlled, it would be possible to produce biochar at a lower cost without the need for an external heat resource. We investigated if self-heating could be controlled by using sawdust and bark chips. When sawdust and bark chips were used under controlled conditions, the bark chips temperature increased to the torrefaction temperature. The ash content of bark chips was ~ 2%d.b. higher than that of sawdust; consequently, the inorganic substances contained in the bark chips might affect the self-heating. Self-heating was suppressed when inorganic substances were removed by washing with water. Therefore, the inorganic substances in the biomass might have affected self-heating. The inorganic element contents of the bark chips were measured by inductively coupled plasma optical emission spectrometry before and after washing. The potassium content of the bark chips was reduced remarkably by washing, and there was a possible influence of potassium on self-heating. Finally, the effect of moisture content on self-heating was investigated to obtain stable reactivity. Thus, at a moisture content of 40%w.b., a steady self-heating behavior may be realized.

High-cell density culture of poly(lactate-co-3-hydroxybutyrate)-producing Escherichia coli by using glucose/xylose-switching fed-batch jar fermentation.

Poly(lactate-co-3-hydroxybutyrate) [P(LA-co-3HB)] is produced in engineered Escherichia coli harboring the genes encoding an LA-polymerizing enzyme (LPE) and monomer-supplying enzymes. In this study, high cell-density fed-batch jar fermentation was developed using xylose and/or glucose as the carbon source. Fed-batch fermentation was initially performed with 20 g/L sugar during the batch phase for 24 h, and subsequent sugar feeding from 24 to 86 h. The feeding rate was increased in a stepwise manner. When xylose alone was used for cultivation, the cells produced the polymer at 11.6 g/L, which was higher than the 4.3 g/L obtained using glucose as the sole carbon source. However, in the first 24 h the growth in the glucose culture was greater than in the xylose culture. Based on these results, glucose was used for cell growth (at the initial stage) and xylose was used for polymer production (at the feeding stage). As expected, in the glucose/xylose switching fermentation method, polymer production was significantly enhanced, eventually reaching 26.7 g/L. The enhanced polymer production obtained by using xylose was presumably due to overflow metabolism. In fact, during xylose feeding, acetic acid excretion was greater than that in case of the glucose grown culture, suggesting the channeling of the metabolic flux from acetyl-CoA towards polymer production over into the tricarboxylic acid cycle in the xylose-fed cultures. Therefore, this sequential glucose/xylose feed strategy is potentially useful for production of acetyl-CoA derived compounds in E. coli.

Enhanced production of lactate-based polyesters in Escherichia coli from a mixture of glucose and xylose by Mlc-mediated catabolite derepression.

Lignocellulose-utilizing biorefinery is a promising strategy for the sustainable production of value-added products such as bio-based polymers. Simultaneous consumption of glucose and xylose in Escherichia coli was achieved by overexpression of the gene encoding Mlc, a multiple regulator of glucose and xylose uptake. This catabolite derepression gave the enhancement in the production of poly (15 mol% lactate-co-3-hydroxybutyrate), up to 65% from 50% (wild-type strain) in the cellular contents, of the Mlc-overexpressing strain of E. coli on a mixture of glucose and xylose as carbon sources. Microscopic analysis indicated that the Mlc-overexpressing strain showed the enlargement of cell volume in the presence and absence of polymer production, consequently making an expanded volumetric space available for enhanced polymer accumulation. The enhanced polymer production by the catabolite derepression was also reproducible using the biomass, Miscanthus×giganteus (hybrid Miscanthus), which was cultivated in the farm of Hokkaido University.

Simultaneous hydrolysis-esterification of wet microalgal lipid using acid.

This research demonstrated hydrolysis of wet microalgal lipid and esterification of free fatty acid (FFA) using acid in one-step process. The investigation of simultaneous hydrolysis-esterification (SHE) of wet microalgal lipid was conducted by using L27 orthogonal design and the effects of water content, volume of sulphuric acid, volume of methanol, temperature and time on SHE were examined. As a result, water content was found to be the most effective factor. The effects of various parameters on fatty acid methyl ester (FAME) content and equilibrium relation between FAME and FFA were also examined under water content 80%. Equimolar amounts of sulphuric acid and hydrochloric acid showed similar results. This method has great potential in terms of biodiesel production from microalgae since no organic solvents are used.

Hydrolysis for direct esterification of lipids from wet microalgae.

Hydrolysis of lipids from microalgae under high water content was investigated as a pretreatment of direct esterification. Results indicated that the hydrolysis process reduced the inhibition by water in FAME production; in addition, FAME obtained by esterification of hydrolysates was increased by 181.7% compared to FAME obtained by direct transesterification under the same amount of water content (80%). This method has great potential in terms of biodiesel production from microalgae since it uses no organic solvent, reduces the drying cost and lowers the operating cost compared to any other traditional method.