Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2001-07-18
2003-05-27
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S920000, C062S931000
Reexamination Certificate
active
06568206
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to cryogenic processes for recovering hydrogen and/or carbon monoxide from gas mixtures containing those and possibly other components, and in particular to such cryogenic processes which use hydrogen rejection membranes.
Syngas is a gaseous mixture consisting primarily of hydrogen (H
2
) and carbon monoxide (CO) which, depending upon the level of purity, may contain relatively small amounts of argon, nitrogen, methane and other trace hydrocarbon impurities. The primary uses of syngas are in the synthesis of methanol (requiring a hydrogen:carbon monoxide molar ratio of 2:1) and in reactions to produce oxo-alcohols (requiring a hydrogen:carbon monoxide molar ratio of at least 1:1). For many applications, it is necessary to control the relative proportions of hydrogen and carbon monoxide. This is achieved by, for example, cryogenically separating crude syngas into separate hydrogen-rich and carbon monoxide-rich streams and then combining those streams in the appropriate molar ratio to produce the required syngas composition. In addition to various syngas ratio adjustment applications, it is often desirable to extract and purify significant quantities of carbon monoxide and/or hydrogen from similar crude syngas feed streams. These carbon monoxide and/or hydrogen production processes can also be achieved through cryogenically separating the crude syngas into separate hydrogen-rich and carbon monoxide-rich streams before further purification and/or blending as appropriate. The level of impurities, especially methane and other hydrocarbons, in the crude syngas usually also is reduced during the cryogenic separation.
Existing technologies for the cryogenic processes that recover hydrogen and carbon monoxide use various methods of refrigeration that are relatively expensive and inefficient. Many of the difficulties with the existing technologies relate to the inherent nature of those methods of refrigeration. There are two main methods for providing refrigeration for processes with lower levels of H
2
production when an external refrigerant is not available. The first method is to partially condense the H
2
—CO syngas feed and turbo-expand all or part of the H
2
-rich fraction that is not condensed from the syngas feed. This is often inefficient because of the large amount of refrigeration required to partially condense the feed stream when it contains significant quantities of H
2
. The second method is to use a membrane system to reject the excess H
2
upstream of the cryogenic system and rely on the Joule-Thompson (J-T) refrigeration resulting from the lower pressure flashing of the cold feed stream. Although there are numerous variations on this method, the refrigeration from the feed stream J-T expansion is not always sufficient to operate the overall system.
There are several existing membrane integration schemes for cryogenic process cycles to produce carbon monoxide, hydrogen, and/or syngas. All of these processes have several features in common. All of the processes typically start with a crude syngas feed stream containing primarily hydrogen and carbon monoxide with lower levels of N
2
, Ar,CH
4
, and other trace hydrocarbon impurities. The syngas feed stream typically is passed over a semi-permeable membrane to remove varying levels of excess H
2
while the H
2
-rich permeate typically is blended with fuel or taken as product at this point. The CO-enriched retentate stream typically is then cooled and partially condensed to partially separate most of the heavier components from the hydrogen. Any non-condensed remaining H
2
-rich stream may be washed with a condensed fluid, such as CH4, to remove further impurities in what commonly are known as CH
4
-wash cycles. In these wash cycles, the process refrigeration is most commonly provided by a pure carbon monoxide recycle system integrated with a carbon monoxide product compressor. In cycles without the wash step, commonly referred to as partial condensation cycles, the H
2
-rich stream is commonly expanded in a turbo-expander for refrigeration before it leaves the cryogenic part of the plant as a crude hydrogen product. This second crude hydrogen product is often further purified by pressure swing adsorption (PSA) and is sometimes compressed to final delivery pressure.
The remaining heavier liquid is then separated in one or more columns to remove the residual hydrogen, CH
4
, and optionally any other relevant impurities. The purified carbon monoxide is then rewarmed and typically leaves the cryogenic part of the plant as low pressure carbon monoxide product. This carbon monoxide stream is often compressed to final delivery pressure with part of the carbon monoxide stream sometimes compressed and returned to the cryogenic system to provide column reflux or as a heat pumping fluid.
There are numerous examples of this general purification scheme with various different methods of membrane integration disclosed in the patent literature. Some of these examples are discussed below.
U.S. Pat. No. 4,548,618 (Linde, et al.) discloses a membrane and cryogenic process integration for H
2
removal and purification of light gases with a normal boiling point of less than 120° K. Here, H
2
is removed from the feed to the cryogenic system by the membrane. The H
2
-lean stream is then fed to the cyogenic system and is itself expanded to provide refrigeration for the process. The H
2
-rich permeate stream does not even enter the cyrogenic system and is discharged as byproduct.
U.S. Pat. No. 4,654,063 (Auvil, et al.) discloses integration of a membrane system with a non-membrane separation system (specifically including the case of a cryogenic system) to recover H
2
from a feed gas mixture. Here, the membrane is used to remove H
2
from the feed to the non-membrane separator and/or to take an H
2
-enriched stream from the non-membrane separator unit and remove H
2
before recycling the subsequent H
2
-lean stream to the non-membrane separator. The H
2
-rich permeate streams in all of the embodiments are subsequently discharged as a product stream with optional compression.
EP 0359 629 (Gauthier, et al.) discloses generation of a H
2
/CO syngas from a feed with excess H
2
. This feed is passed through a permeator to adjust the H
2
/CO ratio by removing some H
2
before at least a portion of the adjusted syngas is subsequently fed to a cryogenic system for the production of H
2
and CO. The H
2
-rich permeate stream is directly discharged from the membrane as a byproduct.
JP 63-247582 (Tomisaka) discloses a process to separate CO from a predominantly CO and H
2
feed which is passed to a membrane system immediately upstream of a cryogenic system to raise the concentration of CO in the gas fed to the cryogenic system. Here the refrigeration for the process is provided by a combination of J-T refrigeration from the feed stream and a supplemental liquid nitrogen (LIN) stream. The H
2
-rich permeate from the membrane is used for regeneration of adsorption based CO
2
and H
2
O removal beds.
DE 43 25 513 (Fabian) describes a process for recovery of a high purity CO product stream and a H
2
product stream using a membrane integrated with a cryogenic partial condensation cycle. An intermediate syngas stream is passed through a membrane to remove H
2
before the stream is recycled to the cryogenic system to recover and purify the CO product. The H
2
-rich permeate is then discharged from the process as H
2
product. The claimed benefit relative to a condensation cycle without a membrane is the elimination of the cold heat exchanger and H
2
expansion refrigeration system. Fabian's work is clearly focused on situations where there is sufficient J-T refrigeration in the feed stream to completely drive the overall separation process.
EP 0 968 959 (Billy) also discloses an integrated membrane and cryogenic process. Here the membrane rejects H
2
from a CO/H
2
stream produced at cryogenic conditions. The H
2
-depleted non-permeate stream is compressed and recycled back to the cryogenic syste
Air Products and Chemicals Inc.
Capossela Ronald
Chase Geoffrey L.
LandOfFree
Cryogenic hydrogen and carbon monoxide production with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cryogenic hydrogen and carbon monoxide production with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cryogenic hydrogen and carbon monoxide production with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3013099