Through the use of a metal catalyst, gasification of wet biomass can be accomplished with high levels of carbon conversion to gas at relatively low temperature (350 °C). In a pressurized-water environment (20 MPa), near-total conversion of the organic structure of biomass to gases has been achieved in the presence of a ruthenium metal catalyst. The process is essentially steam reforming, as there is no added oxidizer or reagent other than water. In addition, the gas produced is a medium heating value gas due to the synthesis of high levels of methane, as dictated by thermodynamic equilibrium. While good gas production was demonstrated, biomass trace components caused some processing difficulties in the fixed catalyst bed tubular reactor system used for the catalytic gasification process. Results are described for tests using both bench-scale and scaled-up reactor systems.

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Experimental results are reported for high-pressure liquefaction of high-moisture biomass. The feedstocks included macrocystis kelp, water hyacinths, spent grain from a brewery, grain sorghum field residue and napier grass. The biomass was processed in a batch autoclave as a ten weight percent slurry in water with sodium carbonate catalyst and carbon monoxide gas. Thirty-minute experiments were performed at 350°C with operating pressures ranging from 270 to 340 atmospheres. The oil products were collected by methylene chloride and acetone extractions. Oil yields ranged from 19 to 35 mass percent on a moisture and ash-free basis. The oil products contained from 9.9 to 16.7 percent oxygen with hydrogen to carbon atomic ratios from 1.36 to 1.61. Significant nitrogen content was noted in the oil product from those feedstocks containing nitrogen (kelp, hyacinth, spent grain). Chemical composition analysis by gas chromatography/mass spectrometry demonstrated many similarities between these products and wood-derived oils. The nitrogen components were found to be mainly saturated heterocyclics.Significant progress has been made over the past fifteen years toward the development of processes for direct production of liquid fuels from biomass. Process research has generally progressed along two lines -flash pyrolysis and high-pressure processing. Extensive analysis of the liquid products from these two types of processes has demonstrated the significant process-related differences in product composition. However, the effect of feedstock has received a lesser degree of attention.

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Pacific Northwest Laboratory (PNL) is developing a low-temperature, catalytic process that converts high-moisture biomass feedstocks and other wet organic substances to useful gaseous and liquid fuels. The advantage of this • process is that it works without the need for drying or dewatering the feedstock. Conventional thermal gasification processes, which require temperatures above 750'C and air or oxygen for combustion to supply reaction heat, generally cannot utilize feedstocks with moisture contents above 50 wt%, as the conversion efficiency is greatly reduced as a result of the drying step. For this reason, anaerobic digestion or other bioconversion processes traditionally have been used for gasification of high-moisture feedstocks. However, these processes suffer from slow reaction rates and incomplete carbon conversion. • The PNL high-moisture gasification system, in which thermocatalytic conversion takes place in an aqueous environment, was designed to overcome the problems usually encountered with high-water-content feedstocks. The process uses a reduced nickel catalyst at temperatures as low as 3Sooc and pressures ranging from 2000 to 4000 psig-conditions favoring the formation of methane gas rather than hydrogen and carbon oxides. Tests have produced gases containing up to 55% methane. By comparison, gases produced by conventional thermal gasifiers typically contain only 5% to 15% methane. When compared with anaerobic digestion, the PNL-produced gases contain similar amounts of methane, but the reaction rate is 300 to 400 times faster. Furthermore, carbon conversion is nearly complete, whereas with anaerobic digestion it is only about 50% to 80%. Over 180 tests have been conducted to evaluate the effectiveness of the process on feedstocks defined as high-moisture biomass. These tests also included 11 experiments at liquefaction conditions to determine oil product compositions and yields. All experiments were conducted batchwise in a 1-L, bolted-closure, highpressure autoclave (reactor), with a magnetically coupled stirrer. The reactor and associated sample lines were made of stainless steel to minimize i i i corrosion. The entire system, except for certain valves and the instrumentation, was housed in a 0.25-in.-thick plate steel barricade. Many other safety features were built into the system, including remotely controlled monitoring and sampling procedures.

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Bench-scale reactor tests are under way at Pacific Northwest Laboratory to develop a low temperature, catalytic gasification system. The system, licensed under the trade name Thermochemical Environmental Energy System (TEES®), is designed for to a wide variety of feedstocks ranging from dilute organics in water to waste sludges from food processing. The current research program is focused on the use of a continuous feed, tubular reactor. The catalyst is nickel metal on an inert support. Typical results show that feedstocks such as solutions of 2 percent para-cresol or 5 percent and 10 percent lactose in water or cheese whey can be processed to >99 percent reduction of chemical oxygen demand (COD) at a rate of up to 2 L/hr. The estimated residence time is less than 5 min at 360°C and 3000 psig, not including 1 to 2 min required in the preheating zone of the reactor. The liquid hourly space velocity has been varied from 1.8 to 2.9 L feedstock/L catalyst/hr depending on the feedstock. The product fuel gas contains 40 percent to 55 percent methane, 35 percent to 50 percent carbon dioxide, and 5 percent to 10 percent hydrogen with as much as 2 percent ethane, but less than 0.1 percent ethylene or carbon monoxide, and small amounts of higher hydrocarbons. The byproduct water stream carries residual organics amounting to less than 500 mg/L COD.