Biomass, such as wood, can be converted directly into heavy oil by thermochemical liquefaction in the liquid water of high temperature and high pressure (about 300 °C and 100 atm) in the presence of alkali catalyst without any reducing gas. This process has merits that no reducing gas, such as hydrogen and carbon monoxide, is needed and no drying process of feedstocks is required. Especially, drying process needs much heating energy due to the large latent heat of the vaporization of water. Since biomass usually has high moisture content, the thermochemical liquefaction, which needs no drying process, is favor in the terms of energy consumption; leading a promising methods for the conversion of biomass.

Recentry, the using of an enormous amount of fossil fuel has caused global environmental problems, such as acid rain and global warming. Biomass has been focused on as an alternative resource, since it is a renewable, carbon neutral, and low sulfur resource. Energy utilization of biomass, however, compares with the utilization for food, fertilizer, fiber, flame, and so on. In future, energy plantation of biomass is proposed, and biomass wastes and unutilized biomass are used for energy in near future. The authors have applied the thermochemical liquefaction to many biomass wastes and unutilized biomass, and clarified their reaction characteristics on the thermochemical liquefaction. In this report, we describe the liquefaction of each feedstocks, and summarize the relationship between the properties of feedstocks and the reaction characteristics, effects of the operating conditions, and so on.

This report consists of four chapters. In the first chapter, the conversion methods of biomass for energy is reviewed. Then, the reaction of the thermochemical liquefaction and history of the studies in the field are reviewed. Finally, the background and purpose of the study are described.

In the second chapter, many kinds of biomass were liquefied under different reaction conditions to clarify the oil yield, product distribution, and the properties of the obtained oil.

The liquefaction of four kinds of ethanol fermentation stillage was carried out, and the oil could be obtained from all stillage. The maximum oil yields for the stillage of sweet potato, barley, rice, and buckwheat were roughly 30, 40, 50 and 60 wt%, respectively, on an organic basis under the optimum operating conditions. The effects of the operating parameters were clarified on the oil yield, its properties, by-products distribution, and so on. The effect of the catalyst depended on the kind of stillage; the stillage of sweet potato and barley required the catalyst loading, but the stillage of rice and buckwheat no need. The reaction temperature showed the strong effect on the oil yield, increasing reaction temperature tended to increase the oil yield. No effect of operating pressure was observed. On the other hand, the effect of holding time depended on the reaction temperature. The properties of the oil and the distribution of by-products were also discussed.

The model garbage as an urban organic waste was made according to the literatures data, and its liquefaction was carried out. The effects of the catalyst loading, the reaction temperature and the holding time were examined according on the variance analysis. It was statistically clear that the catalyst loading and the reaction temperature showed independently the strong effect, while the effect of the holding time depended on the reaction temperature.

Among biomass, microalgae usually have a higher photosynthetic efficiency than other biomass such as trees, and they have been focused on as an energy resource in future. The liquefaction of Dunaliella tertiolecta, a kind of microalgae, was carried out. The oil comparable to the heavy oil of petroleum was obtained in the yield of about 38 wt%. Although the effects of the operating parameters were examined according on the variance analysis, no effect was observed for all parameters. This result showed that Dunaliella tersiolecta was attractive as a feedstock for the liquefaction.

The water hyacinth proliferates rapidly and obstructs river navigation frequently. It fixes large quantities of nitrogen and phosphorus and neutralizes eutrophic lakes and rivers. The liquefaction of the water hyacinth was carried out to clarify the behavior of nitrogen and phosphorus during the reaction. A half of the nitrogen in the feedstock was soluble in the water phase and the phosphorus was mostly present in char-like products.

The liquefaction of bark was carried out by a steam-explosion method and an autoclave method. An increase in the lignin content reduced the oil yield, and increased the char yield. In the steam-explosion method, the oil yield was higher and the char yield was lower. Although lignin produces char by condensation and repolymerization, the steam explosion tends to retard the reaction.

In the third chapter, the thermochemical liquefaction was summarized based on the results of the second chapter and the literatures.

The estimated methods of the heating value of the obtained oil was discussed, and the empirical equation was proposed based on the oxygen contents. Then, the properties of the obtained oil were discussed, and some oils were comparable to the heavy oil of petroleum; these oils can be used directly as an alternative heavy oil. The relationship between the oil yield and its properties showed statistically that the oil with high heating value and low viscosity was obtained in the high yield, while the oil with low heating value and high viscosity was obtained in the low yield. Biomass feedstocks were able to be classified statistically to three groups; the suitable biomass for the liquefaction, the unsuitable biomass, and the middle biomass. From the relationship between the biomass properties and the oil properties, evidently the crude fat affected the oil yield and its properties.

The energy consumption ratio (ECR) was proposed as indication of energy balance for the liquefaction process. In case of the suitable biomass for the liquefaction, ECR showed that the liquefaction process was a net energy producer, but, in case of the unsuitable biomass, it was a energy consumer, and the improvements were needed in the term of the energy balance. The effect of the moisture content, which affects strongly the ECR, was examined. The moisture content of 60 wt% was a low limit for the liquefaction, and the highest energy efficient was obtained at the moisture content of 60 wt%. The low moisture content, however, reduces the fluidity of feedstocks; causing the problem of handling of the feedstock. Therefore, the reducing the moisture content, keeping the fluidity, is needed technically in terms of energy balance.

The catalytic effect of the alkali was discussed. The biomass with high crude fat content or high ash content required no catalyst loading. The role of the crude fat as a stabilizer of intermediates was considered to suppress the polymerization, and it was considered that the ash shows the catalytic effect.

The effects of the reaction temperature and the holding time were discussed on the oil yield, its properties, ECR, the operating pressure, and by-products. With regard to these operating parameters, more evaluation is needed in the standpoints of total system, and so on.

In the forth chapter, the future works were described. The thermochemical liquefaction can be applied widely to many biomass feedstocks, and energy can be recovered in the form of the oil. Since the reaction characteristics are depended strongly on the kinds of biomass feedstocks, basically experimental data of the liquefaction for the other biomass is needed. The R & D of the liquefaction process on the demonstration stage is also needed; treatment of by-products, use of obtained oil, environmental and economical evaluation, total system, and so on. In addition, upgrading of the oil, improvement of the reaction, and clarification of the reaction mechanism are also needed.