Purifying hydrogen process

In the early 1990s, processes were developed for the production of 1,4-butanediol and y-butyrolactone by gas-phase catalytic hydrogenation of maleic anhydride (131—134). Succinic anhydride is obtained as a partial hydrogenation by-product in these processes. It can be recycled to complete the hydrogenation to the desired products, or be separated and purified. This process could in the future become a significant commercial route for succinic anhydride. 

Also, the CL aqueous solution may be hydrogenated at 60°C in the presence of 20% sodium hydroxide and 50% palladium absorbed on carbon to provide caprolactam of very high purity after distillation. Treatment with an ion exchange resin before or after the oxidation or hydrogenation process also improves the quality of the CL obtained after distillation. CL has also been purified by treatment with alkali and formaldehyde followed by fractional distillation to remove aromatic amines and other products. 

Modern SMR plants (Figure 2.5b) incorporate a PSA unit for purifying hydrogen from C02, CO, and CH4 impurities (moisture is preliminarily removed from the process gas). The PSA unit consists of multiple (parallel) adsorption beds, most commonly filled with molecular sieves of suitable pore size it operates at the pressure of about 20 atm. The PSA off-gas is composed of (mol%) C02—55, H2—27, CH4—14, CO—3, N2—0.4, and some water vapor [11] and is burned as a fuel in the primary reformer furnace. Generally, SMR plants with PSA need only a HT-WGS stage, which may somewhat simplify the process. 

Amine Guard A process for extracting acid gases from refinery streams by scrubbing with an alkanolamine. Many such processes have been developed, this one was developed by the Union Carbide Corp. and uses monoethanolamine. It has been used to purify hydrogen produced by steam reforming. In 1990, over 375 units were operating. 

Hydrogen Polybed PSA A version of the Polybed process, for purifying hydrogen from various industrial processes. Developed by the Union Carbide Corporation in 1975 and now licensed by UOP. More than 400 units were operating worldwide in 1992. 

HYSEC A process for purifying hydrogen from coke-oven gas by PSA, developed by Mitsubishi Kakoki Kaisha and the Kansai Coke Chemicals Company. 

In some applications water-gas-shift (WGS) is coupled with other reactions. For example, the steam reforming of methane to produce hydrogen is one example where both the forward and reverse reaction may be involved. However, this reaction is accomplished at high temperatures and the reaction is usually considered to be at equilibrium at the high temperatures used. In the following these high temperature processes will not be covered only those instances where the WGS reaction is the dominant reaction that is used to produce and/or purify hydrogen is considered. 

The annealing process was experimentally optimized using Silane in Ar [3% Silane in 97% nltra-high pnrity (UHP) Ar)]. Initial experiments were conducted with palladium-purified hydrogen as the carrier gas. Unfortunately, this method... 

Byproduct Hydrogen. Large volumes of byproduct hydrogen are generated from a variety of production processes. Some of these processes are listed in Reference 40. Some of the processes that can be used to obtain purified hydrogen are summarized below. 

After the hydrogen is purified, it is ready for use in a refinery hydrogenation process. In an ammonia plant, the hydrogen-nitrogen mix is sent to an ammonia converter (Figure 4.7), which requires a start-up heater. Since the material in the heater will be exposed to hydrogen only for a short period, the time dependent curves in API 941 should be consulted when selecting an alloy for the heater tubes. 

SHP [Selective Hydrogenation Process] A process for purifying 1-butene by selective hydrogenation of C4 streams in petroleum refineries. A heterogeneous palladium catalyst is used. Developed in Hiils and used in 1989 in Germany, the United States, and Japan. The licensing rights were acquired by UOP in 1991. 

High olefin yields due to the very small (less than 0.1 second) reaction times in the pyrolysis furnace unit. Process handles feeds ranging from ethane to vacuum gas oils. Provides ultra-purified hydrogen stream for catalytic conversion. Generates excess high pressure steam for use elsewhere in a multi-purpose plant. 

The production of one ton of ammonia requires a mixture of 2400 m" of highly purified hydrogen and 800 m- of highly purified nitrogen (at 0°C and 1000 mbar). It is produced using different processes depending upon the raw materials utilized. 

The reforming process (as applied to a hydrocarbon or alcohol) yields a product stream that consists predominantly of hydrogen, carbon monoxide, carbon dioxide, water, unconverted feedstock, and trace by-products. This product stream mixture, called reformate, is unsuitable for direct use in low-temperature PEMFC and AFC, and some trace by-products (notably organosulfur compounds) will poison both high-temperature fuel cells and low-temperature fuel cells. A membrane for separating and purifying hydrogen from reformate must also be chemically compatible with the compounds in the reformate stream. 

Zhu, D. Simulation of a PSA process for purifying hydrogen from reforming gas by using an equilibrium model, lianranqi Huagong, 1998, 23, 36 (in Chinese). 

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