Cryogenic distillation process

The cmde product from the gasifier contains CO2 and H2S, which must be removed before the gas can be used to produce chemicals. The Rectisol process is used to remove these contaminants from the gas. This is accompHshed by scmbbing the product with cold methanol which dissolves the CO2 and H2S and lets the H2 and CO pass through the scmbber. The H2S is sent to a Claus sulfur plant where over 99.7% of the sulfur in the coal feed is recovered in the form of elemental sulfur. A portion of the clean H2 and CO are separated in a cryogenic distillation process. The main product from the cryogenic distillation is a purified CO stream for use in the acetic anhydride process. The remaining CO and hydrogen are used in the methanol plant. 

Finally, it is possible to obtain a pure hydrogen stream through several techniques, such as PSA, cryogenic distillation or membrane separation. PSA and cryogenic distillation processes are commercially available separation techniques [14]. 

Figure 7.5 Conventional cryogenic distillation process for an olefin/paraffin process (Adapted from Ref. [35]).

In the cryogenic partial condensation process, the feed gas is cooled to 85 K, which condenses the bulk of the carbon monoxide and methane. Uncondensed hydrogen-rich gas is cooled further to 70 K to liquefy additional carbon monoxide. These liquid fractions are degassed and then warmed to obtain high-purity carbon monoxide gas. A cryogenic distillation process can produce ul-trapure carbon monoxide. 

Krypton and Xenon are valuable gases present in very low concentrations in air. U.S. 6,662,593 assigned to Air Products describes a cryogenic distillation process for air separation with recovery of a stream concentrated in Kypton and Xenon. What would be the cost of producing purified Krypton and Xenon by this method Consider reactive methods for separating Krypton and Xenon from the concentrated stream as well as the methods suggested in the patent. 

In all of the cryogenic distillation processes oxygen is produced in the low pressure column at slightly above 1 bar pressure. As a result, it is frequently necessary to compress the product prior to its use in downstream applica-... 

The cryogenic distillation process has been summarized by Bohnenstingl et al. (1976) ... 

Oxygen is not only one of the most important molecules for life but also one of the most widely used chemicals in the world for industrial and medical applications. Traditionally, the industrial separation of O2 from the air involves the extremely energy-consuming cryogenic distillation processes. Aerobic organisms can selectively take up O2 from the air at ambient temperature and pressures with the assistance of oxygen-transport metallopro-teins, such as hemoglobin, hemerythrin, or hemocyanin. ... 

The cryogenic distillation process is usually carried out at very low temperature. It uses the difference in the boiling temperatures of the feed components to effect the separation and this process consumes a considerable amount of energy (Hinchliffe and Porter, 2000). 

The separation of nitrogen from natural gas reHes on the differences between the boiling points of nitrogen (77.4 K) and methane (91.7 K) and involves the cryogenic distillation of a feed stream that has been preconditioned to very low levels of carbon dioxide, water vapor, and other constituents that would form soHds at the low processing temperatures. 

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

An enrichment is defined as a separation process that results in the increase in concentration of one or mote species in one product stream and the depletion of the same species in the other product stream. Neither high purity not high recovery of any components is achieved. Gas enrichment can be accompHshed with a wide variety of separation methods including, for example, physical absorption, molecular sieve adsorption, equiHbrium adsorption, cryogenic distillation, condensation, and membrane permeation. 

Most refinery/petrochemical processes produce ethylene that contains trace amounts of acetylene, which is difficult to remove even with cryogenic distillation. Frequently it is necessary to lower the acetylene concentration from several hundreds ppm to < 10 ppm in order to avoid poisoning catalysts used in subsequent ethylene consuming processes, such as polymeri2ation to polyethylene. This can be accompHshed with catalytic hydrogenation according to the equation. 

Cryogenic distillation has been used extensively ia the processiag of natural gas for nitrogen removal and for helium recovery (22—23). Two basic processes are now used for nitrogen rejection from natural gas— the single-column heat-pumped process and the double-column process. Eadier processes utilized multistage flash columns for helium recovery from natural gas (24). 

The Ryan-Holmes distillation process uses cryogenic distillation to remove acid gases from a gas stream. This process is applied to remove COi for LPG separation or where it is desired to produce COt at high pressure for reservoir injection. This complicated process is beyond the scope of this book. 

Competing Processes Membranes are not the only way to make these separations, neither are they generally the dominant way. In many applications, membranes compete with cryogenic distillation and with pressure-swing adsorption in others, physical absorption is the dominant method. The growth rate for membrane capacity is higher than that for any competitor. 

Ryan-Holmes A cryogenic extractive distillation process using liquid carbon dioxide, in which a light hydrocarbon is added in order to suppress the freezing of the carbon dioxide. Licensed by Process Systems International nine licenses had been granted by 1992. 

All commercial processes involve either separation of nitrogen from air by cryogenic distillation or combustion of air with natural gas to remove oxygen. In the former process, air is liquefied and the liquid air is subjected to fractional distillation to separate its components. 

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