Tomoaki Minowa

Oil production from algal cells of Dunaliella tertiolecta by direct thermochemical liquefaction

Algal cells of Dunaliella tertiolecta with a moisture content of 78.4 wt% were converted directly into oil by thermochemical liquefaction at around 300°C and 10 MPa. The oil yield was about 37% on an organic basis. The oil obtained at a reaction temperature of 340°C and holding time of 60 min had a viscosity of 150–330 mPas and a calorific value of 36 kJ g−1, comparable to those of fuel oil.

Recovery of liquid fuel from hydrocarbon-rich microalgae by thermochemical liquefaction

Liquefaction of Botryococcus braunii, a colony-forming microalga, with high moisture content was performed with or without sodium carbonate as a catalyst for conversion into liquid fuel and recovery of hydrocarbons. A greater amount of oil than the content of hydrocarbons in B. braunii (50 wt% db) was obtained, in a yield of 57–64 wt% at 300 °C. The oil was equivalent in quality to petroleum oil. The recovery of hydrocarbons was a maximum (>95%) at 300 °C.

Cellulose decomposition in hot-compressed water with alkali or nickel catalyst

Abstract Cellulose, a major component of woody biomass, was reacted in hot-compressed water using a sodium carbonate catalyst, a reduced nickel catalyst or no catalyst at different reaction temperatures from 200 to 350°C. The reaction mixture was separated into oil, gases, residue and aqueous phase to discuss the reaction mechanism based on the product distribution. Hydrolysis can play an important role in forming glucose/oligomer, and the obtained glucose/oligomer can decompose quickly to non-glucose aqueous products, oil, char and gases. Under the catalyst-free condition, the interpretation of the observation led to a simplified reaction scheme, which produced finally char and gases through oil as intermediates. With regard to the alkali catalyst, the observation suggested a role of the alkali catalyst in inhibiting the formation of char from oil (stabilization of oil); resulting in oil production. On the other hand, the nickel catalyst could catalyze the steam reforming reaction of aqueous products as intermediates and the methanation reaction.

Wet disk milling pretreatment without sulfuric acid for enzymatic hydrolysis of rice straw

Rice straw has recently attracted interest in Japan as a potential source of raw material for ethanol production. Wet disk milling, a continuous pretreatment to enhance the enzymatic digestibility of rice straw, was compared with conventional ball milling and hot-compressed water treatment. Pretreated rice straw was evaluated by enzymatic hydrolysis using Acremonium cellulase and characterized by X-ray diffraction and scanning electron microscopy. Glucose and xylose yields by wet disk milling, ball milling, and hot-compressed water treatment were 78.5% and 41.5%, 89.4% and 54.3%, and 70.3% and 88.6%, respectively. Wet disk milling and hot-compressed water treatment increased sugar yields without decreasing their crystallinity. The feature size of the wet disk milled rice straw was similar to that of hot-compressed water-treated rice straw. The energy consumption of wet disk milling was lower than that of other pretreatments. Thus, wet disk milling is an economical, practical pretreatment for the enzymatic hydrolysis of lignocellulosic biomass, especially herbaceous biomass such as rice straw.

Hydrogen production from biomass by catalytic gasification in hot compressed water

Cellulose, a major component of woody biomass, was gasified to hydrogen rich gas using a reduced nickel catalyst in hot-compressed water of around 350 °C and 18 MPa. During the gasification, steam reforming and methanation can occur, and the methanation was prevented at subcritical condition. The reaction model and the catalyst are described.

Oil production from garbage by thermochemical liquefaction

Abstract Garbage was converted directly into oil by thermochemical liquefaction for the recovery of energy in the form of liquid fuel. The garbage with a moisture content of about 90 wt% was prepared by mixing cabbage, boiled rice, boiled and dried sardine, butter, and the shell of short-necked clam. The mixture was heated under pressurized nitrogen at 250°, 300°, or 340°C for 0.1, 0.5, or 2 h, with or without sodium carbonate as a catalyst (0 or 4% on a dry solid basis). Oil yield and its properties strongly depended on catalyst addition and reaction temperature, while holding time showed no marked effect. Oil was obtained in the highest yield of 27.6% on an organic basis under the following conditions: catalyst addition, 4 wt%; temperature, 340°C; pressure, 18 MPa; and holding time, 0.5 h. The oil had a calorific value of 36 MJ kg−1 and a viscosity of 53,000 mPas at 50°C. Its carbon content, hydrogen content, nitrogen content and oxygen content were 73.6, 9.1, 4.6 and 12.7%, respectively.

Analysis of oil derived from liquefaction of Botryococcus Braunii

Abstract Botryococcus braunii is a colonial green microalga that produces and accumulates oily hydrocarbons called botryococcenes (36% based on organics). It was reported that more oil was obtained than hydrocarbons in B. braunii when thermochemical liquefaction was applied to B. braunii for recovery of botryococcenes. In this paper, the properties of oil obtained by thermochemical liquefaction are clarified. The liquefied oil of B. braunii was fractionated into three fractions by silica gel column chromatography and analyzed to determine its composition. The yields of the three fractions based on organics were 5% of lower molecular weight hydrocarbons (MW, 197–281), 27.2% of botryococcenes (MW, 438–572) and 22.2% of polar substances (MW, 867–2209). The maximum recovery (78%) of botryococcenes in the liquefied oil was achieved at 200°C with the use of a catalyst.

Thermochemical Liquidization and Anaerobic Treatment of Kitchen Garbage

The pretreatment effect of thermochemical liquidization for anaerobic digestion of kitchen garbage was studied. Model kitchen garbage (dry matter: 11.3%) was thermochemically liquidized at 175°C and 4 MPa with 1 h of holding time. The liquidized garbage was separated into a solid fraction (12.2 wt%) and filtrate (82.9 wt%). The filtrate was anaerobically digested at added volatile solid (VS) concentrations of 1.8–1.9 g/l in a batch system. The biogas yield from the filtrate after 4 d of digestion was 311 ml/g-added VS and the digestion ratio was 67%. The anaerobic treatment of the filtrate indicated fast digestion compared with mechanically disrupted garbage. The diluted supernatant was continuously anaerobically digested by the upflow anaerobic sludge blanket (UASB) method. The range of digestion ratios was 74–75% at an added TOC concentration of 17.0 g/l and an added TOC amount of 1.8–2.8 mg/cm3-granule·d. The solid fraction was suggested to be easily processed to refuse derived fuel, based on its low moisture content. The energy balance of the liquidization and anaerobic digestion treatment process was initially analyzed to be better than direct incineration.

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga itself was studied. The growth of Chlorella vulgaris in 75-300-fold diluted recovered solution containing phosphate, magnesium ions and micro-elements was comparable to that in the standard culture medium. It was suggested that C. vulgaris could use ammonium in the recovered solution as its nitrogen source and at the same time could provide a source of biomass which was recycled via gasification.

Methane production from cellulose by catalytic gasification

A water slurry of cellulose was directly gasified into methane using reduced nickel on kieselguhr and sodium carbonate as catalysts at 400 °C under pressure (about 13 MPa) for 1 h. In the absence of the catalysts, cellulose at about 20 wt% was converted into the gas which consisted mainly of carbon dioxide. Cellulose at about 40 wt% was converted into a char-like-material (residue), and 40 wt% was lost due to the formation of water promoted by the carbon balance (more than 90 %) and by the mole ratio (about 2) of hydrogen loss to oxygen loss. With increasing load of reduced nickel (from 0 to 20 wt% of the cellulose), the yield of residue and production of water decreased linearly (from 40 to 10 wt%) and gas yield increased linearly (from 20 to 80 wt%). The methane yield increased by the reduced nickel and mole ratio of CH4/CO2 approached unity with increasing load of reduced nickel. Reduced nickel would thus appear to catalyze the formation of methane and carbon dioxide through reaction of carbon and water. Sodium carbonate increased methane yield in the presence of reduced nickel, although the yield was negligible when sodium carbonate alone was added.