Pressure-swing adsorption product purity/recovery

Air Products and Chemicals, Inc. has been selected to supply a hydrocarbon and nitrogen recovery system for a new polyethylene manufacturing plant in Baytown, TX. The plant will be owned by Chevron Phillips Chemical Company and Solvay Polymers, Inc. The recovery system uses partial condensation in conjunction with Air Products pressure swing adsorption technology to recover hydrocarbons in the polyolefin plants, and recycle nitrogen with a purity of greater than 99%55. 

The third process used in the production of carbon dioxide is pressure swing adsorption. The feed gas usually contains approximately 20 percent carbon dioxide, 70 percent hydrogen, and the remainder methane, carbon monoxide, nitrogen, and water. The feed gas is typically under a pressure of 125 100 psig at temperatures of 80-120°F. The carbon dioxide and water are strongly adsorbed in the adsorb beds and the residual gas stream is depressurized for further recovery. The adsorber vessel is then evacuated through vacuum blowers where the carbon dioxide, which has been adsorbed by the bed, is released at purities of essentially 99+ percent pure. 

Pressure swing adsorption processes are also designed to produce high-purity (99.95+ %) H2 products from refinery-off gases containing H2 (65-90%) and C1-C5 hydrocarbon impurities with high H2 recoveries ( 86+ %). Silica gel and activated carbons are used as adsorbents. 

Cyclic adsorption processes Two examples (a) thermal swing adsorption -maximization of total adsorption efficiency and minimization of consumption rate of regeneration energy, and (b) rapid pressure swing adsorption -maximization of both purity and recovery of the desired product for RPSA. Modified Sum of Weighted Objective Function (SWOF) method Modified SWOF method is superior to the conventional SWOF as it was able to find the non-convex part of the Pareto-optimal set. Ko and Moon (2002)... 

A fuel gas long situation also provides the opportunity to recover valuable products from the fuel gas. For example, a refinery plant might consider recovery of hydrogen from a hydroprocessing gas source. Options for H2 recovery include pressure swing adsorption (PSA) and membrane systems based on the H2 purity requirement. Alternatively, ethane and ethylene could be recovered from certain fuel... 

Pressure swing adsorption (PSA) utilizes molecular sieves to selectively remove hydrocarbons and other impurities to produce a high purity hydrogen stream. The greater the pressure swing (between the high pressure of adsorption and the low pressure of desorption), the greater the unit capacity and product recovery. 

Figure 7.23 Oxygen production rate and oxygen recovery as a function of product purity for rapid pressure swing adsorption process (source Sircar and Hanley 1995).

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