High-pressure liquefaction

Liquefaction of wet biomass streams is done by hydrothermal processes at elevated pressures. The feed stocks for these high pressure liquefaction processes are slurries of biomass particles and water. Feeding these slurries into the high pressure equipment, at reasonable costs, is an important hurdle in the process development. For example, the reported operating conditions for high pressure liquefaction are in the range 280-360 °C and 90-250 bar [25, 26]. Under these conditions, biomass is converted, in a complex sequence of chemical reactions, into various compounds. Upon cooling, the reactor effluent consists of three... 

One modification of the Claude cycle that has been used extensively in high-pressure liquefaction plants for air is the Heylandt cycle. In this cycle, the first warm heat exchanger in Fig. 5a has been eliminated, permitting the inlet of the expander to operate with ambient temperature... 

Directly liquefying biomass (liquefaction) by, for example, high temperature pyrolysis or high pressure liquefaction. 

The liquefaction of solid biomass followed by hydrotreating is viewed as an attractive route to the production of petroleum like liquid fuels [1], While liquefaction processes (e.g. high pressure liquefaction or fast pyrolysis) have already been demonstrated at a relatively large scale [2], the hydroprocessing step still requires development and demonstration. 

At Pacific Northwest Laboratory we have been testing the use of high-moisture biomass (marine and fresh-water biomass, post-harvest field residues and food processing wastes) in a thermochemical conversion system to produce useful fuels. Although the main focus of the work (19) has been gasification (catalytic production of methane) we have also performed a limited number of tests under high-pressure liquefaction conditions. 

Two types of biomass-derived oils have been studied at PNL. The first type of oil is produced by high pressure liquefaction at relatively long residence times. Oils identified as TR7 and TR12 in Table I were produced by this type of process at the Albany, Oregon Biomass Liquefaction Experimental Facility. These highly viscous oils consist primarily of substituted phenols and naphthols (1-2). The other type of oil is produced by low-pressure, flash pyrolysis at somewhat higher temperature and very short residence times. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

Concentration of Rare Gas Crudes. The distillation of air is classically carried out in the double-column and auxihary equipment of Figure 5. Dry, C02-free air, chilled to partial liquefaction by heat exchange, is introduced into the lower nitrogen or high pressure column. This unit is typically... 

Direct-Liquefaction Kinetics All direct-liquefac tion processes consist of three basic steps (1) coal slurrying in a vehicle solvent, (2) coal dissolution under high pressure and temperature, and (3) transfer of hydrogen to the dissolved coal. However, the specific reac tion pathways and associated kinetics are not known in detail. Overall reaction schemes and semiempirical relationships have been generated by the individual process developers, but apphcations are process specific and limited to the range of the specific data bases. More extensive research into liquefaction kinetics has been conducted on the laboratory scale, and these results are discussed below. 

Expansion turbines are related in many design features to the centrifugal compressor. The key exception being that the turbine receives a high pressure gas for expansion and power recovery to a lower pressure and is usually accompanied by the recovery of the energy from the expansion. For example, applications can be (1) air separation plants (2) natural gas expansion and liquefaction (for gas let-down in pipeline transmission to replace throttle valves where no... 

Methane may be liquefied under very high pressures and low temperatures. Liquefaction of natural gas (methane), allows its transportation to long distances through cryogenic tankers. 

Liquefaction of coal involves the extraction of carbon by solvents at high pressures and at temperatures up to about 500 C, followed by separation of the extract, which is then hydrogenated in the presence of a catalyst to yield hydrocarbon oils. The corrosion conditions are not regarded as severe. 

CCDC built a continuous short residence time coal liquefaction unit with throughput of about 4.5 kg/hr of coal. The SRC unit consisted of a short residence time reactor constructed from 53.3 m of high pressure tubing having an ID of 0.516 or... 

Failure of hexylpyrene as the liquefaction solvent may be due to the easy dealkylation (13) or high carbonization reactivity probably catalyzed by coals. Transalkylation for coal-liquefaction may require the acid-catalyst (14) or high pressure (15). 

A number of the assumptions used in the BET theory have been questioned for real samples [6]. One assumption states that all adsorption sites are energetically equivalent, which is not the case for normal samples. The BET model ignores lateral adsorbate interactions on the surface, and it also assumes that the heat of adsorption for the second layer and above is equal to the heat of liquefaction. This assumption is not valid at high pressures and is the reason for using adsorbate pressures less than 0.35. In spite of these concerns, the BET method has proven to be an accurate representation of surface area for the majority of samples [9,10]. 

---