Hydrogen recovery from ammonia purge streams

Hydrogen recovery from ammonia purge streams... 

Hydrogen Hydrogen recovery was the first large commercial membrane gas separation. Polysulfone fiber membranes became available in 1980 at a time when H9 needs were rising, and these novel membranes qiiickly came to dominate the market. Applications include recovery of H9 from ammonia purge gas, and extraction of H9 from petroleum crackiug streams. Hydrogen once diverted to low-quahty fuel use is now recovered to become ammonia, or is used to desulfurize fuel, etc. H9 is the fast gas. 

Metal Hydride Process for Ammonia Purge Gas, The metal hydride process will be illustrated using the case of hydrogen recovery from an ammonia purge gas stream generated during ammonia manufacture. 

The first widespread commercial application of membrane separations is to use hollow-fiber membrane separators for hydrogen recovery from processes, ammonia plants and petrochemical purge streams, and H2/CO ratio adjustment in synthesis gas (Gardner et al., 1977 Bollinger et al., 1984 Koros and Mahajan, 2000). The reported ideal hydrogen selectivities with respect to different gases, such as CO2, CO, N2, and CH4, appear to be reasonable, ranging from 170 for H2/CH4 to 6.75 for H2/CO2. The operation of these permeators, however, is restricted to low temperatures because of the polymeric material used for the synthesis of hollow fibers. 

Within a relatively short period after their commercialization, membranes for gas separation have been utilized in a wide variety of applications. Among these applications are recovery of hydrogen from purge streams such as encountered in ammonia plants, retrofit chemical plants and from hydroprocessors in refineries. Membrane systems have been introduced into oil fields for C02 recovery from well-head gas in enhanced oil recovery, and they have been used to separate oxygen from nitrogen in air. Also, they have been utilized in combination with other recovery systems, such as cryogenic and adsorption, to both reduce cost and increase efficiency. 

Copper Recovery. The purge stream of clear liquid from Step 2 is neutralized with ammonia, and then treated with iron and hydrogen sulfide to recover dissolved copper for recycle to the process. 

Hydrogen and helium have relatively small molecular sizes compared to other gases and exhibit high selectivity ratios in glassy polymers. Applications can be found in the recovery of H2 from purge gas streams in ammonia synthesis, petroleum refineries and methanol synthesis. 

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