Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-12-22
2003-09-02
Smith, Duane (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C096S004000, C096S014000
Reexamination Certificate
active
06613125
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to recovery and utilization of hydrogen gas from synthesis gas.
BACKGROUND OF THE INVENTION
The production of synthesis gas from the solid and liquid carbonaceous fuels, especially coal, coke, and liquid hydrocarbon feeds, has been utilized for a considerable period of time and has recently undergone significant improvements due to the increased energy demand and the need for clean utilization of otherwise low value carbonaceous material. Synthesis gas may be produced by heating carbonaceous fuels with reactive gases, such as air or oxygen, often in the presence of steam in a gasification reactor to obtain the synthesis gas which is withdrawn from the gasification reactor.
Synthesis gas mixtures comprise carbon monoxide and hydrogen. Hydrogen is a commercially important reactant for hydrogenation reactions. The synthesis gas can also be used to generate power from otherwise environmentally unacceptable fuel sources, and as a source of feed gas for the synthesis of hydrocarbons, oxygen-containing organic compounds or ammonia.
Other materials often found in the synthesis gas include hydrogen sulfide, carbon dioxide, anmmonia, cyanides, and particulates in the form of carbon and trace metals. The extent of the contaminants in the feed is determined by the type of feed and the particular gasification process utilized as well as the operating conditions. In any event, the removal of these contaminants is critical to make gasification a viable process. As the product gas is discharged from the gasifier, it is usually subjected to a cooling and cleaning operation involving a scrubbing technique wherein the gas is introduced into a scrubber and contacted with a water spray which cools the gas and removes particulates and ionic constituents from the synthesis gas. The initially cooled gas may then be treated to desulfurize the gas prior to utilization of the synthesis gas.
When the most desired product is hydrogen, the synthesis gas from the gasifier is advantageously further processed by water-shifting, also called steam reforming, using catalyst to form hydrogen from carbon monoxide as shown below:
H
2
O+CO→H
2
+CO
2
The water shift process, or steam reforming, converts water and carbon monoxide to hydrogen and carbon dioxide. The shift process is described in, for example, U.S. Pat. No. 5,472,986, the disclosure of which is incorporated herein by reference.
The hydrogen gas is often used in subsequent refining processes, particularly hydrotreating. For many applications, especially for hydrotreating hydrocarbons, the hydrogen is required at higher purity than is available in synthesis gas or even water shifted synthesis gas, and at pressures between about 1000 psi (47.9 kPa) and about 3000 psi (143.6 kPa). The shifted or unshifted synthesis gas must therefore be purified to meet product specifications. In addition, the purified gas may need to be further compressed.
Relatively pure hydrogen at high pressure can be obtained from synthesis gas via the pressure swing absorption process. This method is expensive and requires significant capital outlay. What is needed is an efficient and cost effective method of extracting a relatively pure high pressure hydrogen stream from synthesis gas.
SUMMARY OF THE INVENTION
The present invention is a process to recover a high pressure hydrogen rich gas stream from synthesis gas. The synthesis gas is provided at a temperature between about 10° C. and about 100° C. The synthesis gas is passed along a membrane at high pressure, typically between about 800 psi (38.3 kPa) and about 1600 psi (76.6 kPa), more typically between about 800 psi (38.3 kPa) and about 1200 psi (57.5 kPa). A hydrogen enriched gas permeates through the membrane. The permeate experiences a substantial pressure drop of between about 500 psi (23.9 KPa) to 700 psi (33.5 kPa) as it passes through the membrane. The pressure of the hydrogen-depleted non-permeate gas is unchanged by the membrane. The non-permeate gas pressure is advantageously reduced to between about 200 psi (9.58 kpa) and about 500 psi (23.0 kPa) for use in a combustion turbine by expanding the gas in an expander. The hydrogen-rich permeate is advantageously compressed to between about 800 psi (38.3 kPa) and 3000 psi (143.6 kPa) for use in subsequent operations, i.e., for use in hydrotreating of crude oil. The non-permeate gas is advantageously expanded in a manner to provide energy which is used to compress the permeate gas. It is preferred that an expander be directly coupled with a compressor.
DETAILED DESCRIPTION OF THE INVENTION
The invention involves the integration of oil refining and gasification, and more particularly the integration of solvent deasphalting, gasification, and hydrotreating. A deasphalted oil is typically separated from a heavy crude through solvent extraction. The bottoms from the extraction, the asphaltenes, are low value hydrocarbonaceous material. Such material may be advantageously gasified to generate hydrogen, power, steam, and synthesis gas for chemical production.
The deasphalted oil can easily be broken down into high-value diesel oil in a fluidized catalytic cracking unit. The deasphalted oil generally contains significant quantities of sulfur- and nitrogen-containing compounds. This deasphalted oil may also contain long chain hydrocarbons. To meet environmental regulations and product specifications, as well as to extend the life of the catalyst, the fluidized catalytic cracking unit feed, i.e., the deasphalted oil, is hydrotreated first to remove sulfur components.
Hydrotreating advantageously utilizes hydrogen that is generated by the gasification unit. This invention concerns a new configuration for the integration of gasification and hydrotreating that is more cost effective that conventional hydrotreating processes.
The integration of gasification and hydrotreating employs a process to recover a high pressure hydrogen rich gas stream from synthesis gas. The hydrogen rich gas stream can also be used for many other purposes. A commercially important use is hydrotreating, also called hydrocracking, of liquid hydrocarbons.
Hydrogen is extracted from synthesis gas using a membrane. A membrane allows small molecules like hydrogen to pass through (permeate) while the larger molecules (CO
2
, CO) do not permeate. Membranes are a cost effective alternative to a pressure swing absorption unit. However, the membranes have two flaws. They make a large non-permeate steam that must be utilized economically for the process to be cost effective. The membranes reduce the pressure of the product hydrogen so it has to be compressed prior to use. For example, the product hydrogen pressure when purified using a membrane is substantially lower than is required by hydrotreaters. Therefore, hydrogen compressors have been added at significant capital and operating cost. This hydrogen so extracted is make-up hydrogen for the hydrotreater. The hydrogen reacts with the hydrocarbon mixture.
As used herein, the term “synthesis gas” refers to gases comprising both hydrogen gas and carbon monoxide gas. The mole ratio of hydrogen to carbon monoxide may, but need not necessarily, be about one to one. There are often some inerts in the synthesis gas, particularly nitrogen and carbon dioxide. There are often other contaminants present, such as hydrogen sulfide and COS.
The synthesis gas is prepared by partially burning a hydrocarbonaceous fuel and oxygen in a reactor, often in the presence of steam, in proportions producing a mixture containing carbon monoxide and hydrogen in the reactor.
The term “hydrocarbonaceous” as used herein to describe various suitable feedstocks is intended to include gaseous, liquid, and solid hydrocarbons, carbonaceous materials, and mixtures thereof. In fact, substantially any combustible carbon-containing organic material, or slurries thereof, may be included within the definition of the term “hydrocarbonaceous”. Solid, gaseous, and liquid feeds may be mixed and used simultaneously; and these may include paraffinic, olefin
Johnson Kay Anderson
Wallace Paul S.
Greene Jason M.
Howrey Simon Arnold & White , LLP
Smith Duane
Texaco Inc.
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