Bimodal hydrogen manufacture

Details Bimodal hydrogen manufacture Bimodal hydrogen manufacture

2001-01-22

2003-07-29

Langel, Wayne A. (Department: 1754)

Chemistry of inorganic compounds

Nitrogen or compound thereof

Ammonia or ammonium hydroxide

C422S186220, C423S648100, C423S652000

Reexamination Certificate

active

06599491

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed generally to a process for making hydrogen by steam reforming a lower alkanol, e.g., methanol, and more particularly to a bimodally operable plant wherein in a first mode of operation the plant manufactures hydrogen and methanol by initially steam reforming a hydrocarbon feed, and in a second mode of operation the plant manufactures hydrogen by steam reforming a hydrocarbon or lower alkanol feed.
BACKGROUND OF THE INVENTION
The manufacture of hydrogen from methanol using a methanol reforming catalyst alone or in conjunction with a hydrogen-generating shift reactor is known in the art. Representative references disclosing this and similar processes include U.S. Pat. No. 4,175,115 to Ball et al (Ball); U.S. Pat. No. 4,316,880 to Jockel et al (Jockel); U.S. Pat. No. 4,780,300 to Yokoyama et al (Yokoyama) and U.S. Pat. No. 6,171,574 B1 to Juda et al (Juda), each of which is hereby incorporated herein by reference.
Ball discloses the production of synthesis gas by contacting methanol in the vapor phase with a catalyst that is a supported Group VIII metal. The metal may be used alone or in combination with one or more other metals from Groups I to VIII, excluding binary combinations of copper and nickel. Anhydrous methanol is preferably used since the presence of water makes the efficient production of a carbon monoxide and hydrogen mixture much more difficult. On the other hand, the methanol may be diluted with carbon monoxide, carbon dioxide or hydrogen. The feed may be diluted with recycle of carbon monoxide and hydrogen.
Jockel discloses a process for producing carbon monoxide and hydrogen by contacting methanol vapor with an indirectly heated zinc containing catalyst. The carbon monoxide is separated from the hydrogen by using adsorbers containing zeolite-type molecular sieves that allow the hydrogen to permeate through and sorbs the carbon monoxide. Water is minimized in the methanol to not in excess of 20 percent by weight to minimize the carbon dioxide content in the effluent.
Yokoyama discloses a process for reforming methanol by cracking 100 moles of methanol in admixture with 1 to 99 moles of water, thereby obtaining a gas containing hydrogen and carbon monoxide. Therefore, less than stoichiometric quantities of water are used. The process is preferably carried out using a catalyst that consists of a carrier comprising copper and chromium oxides with or without magnesium oxide and/or barium oxide and a catalytic component of nickel oxide or a mixture of nickel oxide and a basic oxide.
Juda discloses catalytic steam reforming of methanol and similar fuels to generate hydrogen. The hydrogen is purified by its permeation through a selective membrane. These two processes are linked by bounding a longitudinal tortuous flow path of a methanol reformate by a thin palladium-bearing membrane. The methanol reformate contains hydrogen, oxides of carbon, steam and methanol. The flow path contains a turbulence inducing material, in one case the methanol reforming catalyst crushed to a uniform sieve size.
The manufacture of hydrogen from a hydrocarbon, e.g., natural gas, using a hydrocarbon reforming catalyst is also known in the art. Representative references disclosing this and similar processes include U.S. Pat. Nos. 5,653,774 to Bhattacharyya et al (Bhattacharyya); 5,855,815 to Park et al (Park); 6,048,508 to Dummersdorf et al (Dummersdorf);
Bhattacharyya discloses a nickel containing reforming catalyst and a process using same wherein a hydrocarbyl compound, e.g. natural gas, is reformed using an oxygen-containing compound, e.g., molecular oxygen or carbon dioxide. Steam may be added when carbon dioxide is used to reduce coking of the catalyst so that deactivation does not occur. The amount of water as steam is preferably about 10 to 50 percent of the feed gases.
Park discloses a process for producing synthesis gas containing carbon monoxide and hydrogen from the reduction of carbon dioxide with natural gas or a lower hydrocarbon having methane as the main component and oxygen and steam over a catalyst. The catalyst is composed of nickel and, as promoters, alkali metal and alkaline earth metal component supported on silicon-containing support. The support has a high surface area and may be a zeolite, silica, silicate or silica-alumina which are stable under the reaction conditions disclosed therein. The objective of the process is to produce a synthesis gas having a low ratio of hydrogen to carbon monoxide from carbon dioxide and hydrocarbon by using inexpensive Ni catalyst.
Dummersdorf discloses a process for simultaneously obtaining pure carbon monoxide and pure hydrogen in a steam reformer plant for hydrogen or ammonia generation. Natural gas is fed to the steam reformer plant that has a primary reformer, a secondary reformer and down stream thereof, a CO conversion stage. A portion of the syngas stream discharged from the second reformer is treated to remove the carbon monoxide and a major portion of the steam contained therein to produce a pure CO stream. The thus treated syngas stream is combined with the remaining portion of the syngas stream discharged from the second reformer prior to entering the CO conversion stage, which is a hydrogen-generating shift reactor, wherein the carbon monoxide and water are converted into carbon dioxide and hydrogen.
The primary raw materials for methanol manufacture are, of course, carbon monoxide and hydrogen. In the typical methanol plant, natural gas or another hydrocarbon is reformed with steam and/or carbon dioxide to generate a syngas containing carbon dioxide, carbon monoxide and hydrogen. The syngas is supplied to a methanol synthesis unit to convert the carbon dioxide and hydrogen therein into methanol.
Market conditions, from time to time in various localities, can result in relatively low methanol prices (an oversupply) and/or high natural gas prices (a shortage) that can make methanol manufacture unprofitable. Operators of existing methanol manufacturing facilities can be faced with the decision of whether or not to continue the unprofitable manufacture of methanol in the hope that product prices will eventually rebound and/or raw material prices will drop to profitable levels. The present invention addresses a way of modifying an existing unprofitable methanol plant to make it more profitable when methanol prices are low and/or natural gas prices are high. The present invention also addresses a way of building a new plant with two modes of operation—one with a hydrocarbon feed and the other with an imported methanol feed.
As far as applicant is aware, there is no disclosure in the prior art for modifying existing methanol plants, including methanol/ammonia plants, to switch from methanol production in one mode to producing hydrogen in another mode when hydrogen becomes a more valuable product than methanol. Further, as far as applicant is aware, there is no disclosure in the prior art for modifying existing methanol plants, particularly the steam reformers thereof to reform either a hydrocarbon or a lower alkanol, e.g. methanol, using a hydrocarbon reforming catalyst with the optional presence of carbon dioxide, carbon monoxide, steam or a combination thereof.
SUMMARY OF THE INVENTION
The present invention involves the discovery that the large capital costs associated with hydrogen generation in a new hydrogen plant can be significantly reduced or largely eliminated by converting an existing methanol or methanol/ammonia plant to make hydrogen and/or ammonia. The present invention is equally applicable to a new plant wherein the syngas producing portion of the plant accepts either a hydrocarbon feed, e.g., natural gas, or a lower alkanol feed, preferably a C
1
-C
3
alkanol feed, e.g., a methanol feed. The steam reformer is built or modified to accept either a natural gas feed or an imported methanol feed and to optionally have one or more additional feeds of carbon dioxide, carbon monoxide, steam or various combinations thereof. Depending on the mode of operation, the re

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