1.0. Introduction 4044 2.0. Biomass Chemistry and Growth Rates 4047 2.1. Lignocellulose and Starch-Based Plants 4047 2.2. Triglyceride-Producing Plants 4049 2.3. Algae 4050 2.4. Terpenes and Rubber-Producing Plants 4052 3.0. Biomass Gasification 4052 3.1. Gasification Chemistry 4052 3.2. Gasification Reactors 4054 3.3. Supercritical Gasification 4054 3.4. Solar Gasification 4055 3.5. Gas Conditioning 4055 4.0. Syn-Gas Utilization 4056 4.1. Hydrogen Production by Water−Gas Shift Reaction 4056

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Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering.

Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.

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Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies

Hydrothermal liquefaction of biomass: A review of subcritical water technologies

This paper is a review of the developments in the field of catalytic hydroprocessing of biomass-derived liquefaction conversion products (bio-oil) over the past 25 years. Work has been underway, primarily in the U.S. and Europe, in catalytic hydrotreating and hydrocracking of bio-oil in both batch-fed and continuous-flow bench-scale reactor systems. A range of heterogeneous catalyst materials have been tested, including conventional sulfided catalysts developed for petroleum hydroprocessing and precious metal catalysts. The important processing differences have been identified, which required adjustments to conventional hydroprocessing as applied to petroleum feedstocks. This application of hydroprocessing is seen as an extension of petroleum processing and system requirements are not far outside the range of conventional hydroprocessing. The technology is still under development but can play a significant role in supplementing increasingly expensive petroleum.

Historical Developments in Hydroprocessing Bio-oils

Water near or above its critical point (374 C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this new attention is driven by the search for more green or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution prevention. Interest in doing chemistry in SCW is not entirely new, however. There has been much previous research in this area with applications in synthetic fuels production, biomass processing, waste treatment, materials synthesis, and geochemistry. Water near its critical point possesses properties very different from those of ambient liquid water. The dielectric constant is much lower, and the number and persistence of hydrogen bonds are both diminished. As a result, high-temperature water behaves like many organic solvents in that organic compounds enjoy high solubilities in near-critical water and complete miscibility with SCW. Moreover, gases are also miscible in SCW so employing a SCW reaction environment provides an opportunity to conduct chemistry in a single fluid phase that would otherwise occur in a multiphase system under more conventional conditions. The paper discusses the use of supercritical water in the following reactions:more » hydrogenation/dehydrogenation; C-C bond formation; rearrangements; hydration/dehydration; elimination; hydrolysis; partial oxidation; H-D exchange; decomposition; and oxidation.« less

Organic Chemical Reactions in Supercritical Water.

A liquid water processing environment was used at 20 MPa and 350 C to convert organic compounds to methane and carbon dioxide in the presence of catalysts. This paper describes the evaluation of various types of base and noble metal catalysts and numerous support compositions for the process. The feedstock used in these tests was a mixture of p-cresol and water. Nickel, ruthenium, and rhodium were identified as active metals for the reaction. Other metals from groups VIII, VIB, IB, and IIB were inactive or readily oxidized and lost activity. Stable supports in the processing environment included [alpha]-alumina and zirconia. Silica and titania did not react chemically, but the tablet forms lost their physical integrity. Alumina forms, other than [alpha]-alumina, reacted with water to form boehmite ([gamma]-AlOOH) with significant loss of surface area and physical strength.

Chemical processing in high-pressure aqueous environments. 2. Development of catalysts for gasification

A high-pressure (20 MPa) and high-temperature (350 o C) liquid water processing environment was used to treat various wastewaters and model compounds. Organics were converted to methane and carbon dioxide in the presence of a fixed bed of nickel or ruthenium catalyst. Nitrates were destroyed by reaction with methanol in the presence of a nickel catalyst. Noncatalytic hydrolysis of carbon tetrachloride and chloroform was also demonstrated. Three scales of continuous-flow reactors were used in these tests. Extended tests to demonstrate catalyst lifetimes were also performed. Several examples of test results with actual industrial waste streams showed that this process can be effectively used with appropriate catalysts to clean wastewater and recover waste organics as useful fuel gas

Chemical processing in high-pressure aqueous environments; 4: Continuous-flow reactor process development experiments for organics destruction

A high-pressure (20 MPa) and high-temperature (350 C) liquid water processing environment was used to treat various wastewaters and model compounds. Organics were converted to methane and carbon dioxide in the presence of catalysts. Functional types included hydrocarbons, both aliphatic and aromatic; phenolics and other oxygenates; chlorinated hydrocarbon solvents; and sodium salts of organic acids. Tests with aqueous nickel ion showed negligible catalytic activity. Noncatalytic hydrolysis of sodium cyanide, carbon tetrachloride, and chloroform was also demonstrated. Ammonium destruction was proven by reaction with nitrate at these processing conditions. Several examples of test results with actual industrial waste streams showed that this process can be effectively used with catalysts to clean wastewater and recover waste organics as useful fuel gas.

Chemical Processing in high-pressure aqueous environments. 3. Batch reactor process development experiments for organics destruction

Use of high-temperature pressurized liquid water has been investigated as a reaction medium for conducting chemical reactions and conversion. Results of these studies have demonstrated that high-temperature pressurized liquid water, especially in the presence of suitable catalysts, has unique chemical and physical properties. An overview of fundamental investigations and processing considerations in this environment is presented including details regarding the effects of temperature, pressure, and catalysis. The reactivities of various feedstocks tested are discussed along with the development and scale-up of high-pressure reactor systems used to investigate the process chemistry and engineering. Several new processing concepts were developed for gasification, destruction, and gas processing based on these findings. Most of the research has centered on catalytic processing for the production of liquid and gaseous fuels from biomass and wastes at lower temperatures and higher pressures than conventionally used. Other studies have investigated new methods for carrying out chemical reactions, separations, and the destruction of hazardous organic materials. All of this research has in common the use of high-pressure, water systems operating at below and above critical conditions.

Chemical processing in high-pressure aqueous environments. 1. Historical perspective and continuing developments

A combination of fundamental and applied process research at Pacific Northwest National Laboratory resulted in the development of several new processing concepts. These concepts have in common the use of high-temperature pressurized water as a unique reaction medium for carrying out chemical reactions. Typical operating conditions of these processes range from 300 to 360 °C and have pressures to above 200 bar. Investigation of the process chemistry and engineering for these new processing concepts required the development and scale-up of several high-pressure reactor systems which are described. Several new processes involving catalysts and the distinctive properties of pressurized water were patented as part of this effort. These processes, which are at various stages of development, address a broad mix of energy and environmentally related problems. Chemical processing in a high-temperature liquid water environment remains a relatively untapped area for commercial application.

L.J. Sealock

Papers

Chemical processing in high-pressure aqueous environments. 2. Development of catalysts for gasification

Chemical processing in high-pressure aqueous environments; 4: Continuous-flow reactor process development experiments for organics destruction

Chemical Processing in high-pressure aqueous environments. 3. Batch reactor process development experiments for organics destruction

Chemical processing in high-pressure aqueous environments. 1. Historical perspective and continuing developments

Chemical processing in high-pressure aqueous environments. 5. New processing concepts