problem   solution   benefits   examples   performance   related publications   faqs

Problem: Hydrogen is a valuable commodity in refining and petrochemical processes, which must be economically generated, purchased, or recovered from numerous process streams. The demand for hydrogen is increasing rapidly due to changes in government regulations affecting refiners. (back to top) Solution: PRISM® membrane systems are engineered, designed and fabricated by the Air Products and Chemicals Hydrocarbon Product Supply Team using PRISM hydrogen gas filters. This team evaluates customer needs and supplies a custom-engineered system based on the best demonstrated available technology. When the choice is membrane technology, you can count on PRISM membranes. (back to top) Benefits: Economical recovery of hydrogen. Can operate at high process loop pressures such as 2500 psig. Robust against plant upsets. Small skid footprints. No moving parts means minimal maintenance costs. Easy to install and operate. Note: The brochure is in PDF format. You will need the free Adobe Acrobat Reader to view the brochure. Advanced Prism® Membrane Systems For Cost Effective Gas Separations (4.10M, PDF) (back to top) Examples: Hydrocracker and hydrotreater purge gas FCC off gas Cat reformer off gas H2 recovery in ammonia purge gas H2/CO ratio adjustments CO purification (back to top) Related Publications: Perry, Eli, "Process for the Recovery of Hydrogen from Ammonia Purge Gases," US Patent 4,172,885, Oct. 30, 1979. Graham, Tommy E. and Donald L. MacLean, "Process for Hydrogen Recovery from Ammonia Purge Gases," US Patent 4,180, 552, Dec 25, 1979. Null, Harold R., "Method for Separating Gases," US Patent 4,264,338, April 28, 1981. Posey, Lloyd G., "Processes," US Patent 4,367,135, Jan 4, 1983. Makin, Earle C. and K. Keith Okamoto, "Process for Methanol Production," US Patent 4,181,675, Jan. 1, 1980. MacLean, D.L., D.J. Stookey and T.R. Metzger, "Fundamentals of gas permeation: Here's what the process engineer needs to know to handle a membrane system," Hydrocarbon Processing, August 1983. Stookey, D.J., C.J. Patton, and G.L. Malcolm, "Membranes separate gases selectively," CEP, November 1986. Bollinger, W.A., D.L. MacLean, and R.S. Narayan, "Separation systems for oil refining and production," CEP, October 1982.  (back to top) Frequently Asked Questions: How can I determine if PRISM membranes will provide the separation I need? PRISM membranes will effectively separate hydrogen from carbon monoxide, nitrogen, argon, methane, and heavier hydrocarbon vapors. PRISM membranes are widely used in the petrochemical, ammonia, and refining industries for hydrogen recovery. Optimum design and performance depend on several factors, including feed gas composition, feed pressure, and the required product hydrogen pressure. In addition, there is always a tradeoff between the rate of hydrogen recovery and its purity. To accurately determine the separation and membrane size for your specific application, Air Products uses a proprietary computer model to provide you with a complete heat and material balance. What are the operating limits of the membrane? The membrane can operate over a wide range of pressures and temperatures. The maximum operating temperature is 230°F (110°C). The maximum feed pressure is only limited by the mechanical design pressure of the ANSI flanges on the pressure vessel. The maximum differential pressure across the membrane is dependent on operating temperature and can be as high as 1650 psi (113 bar) at 105°F (40°C) or less for certain applications. Air Products will advise the maximum differential pressure for your application and operating conditions. What pre-conditioning of the feed gas is required? Several factors determine the required pretreatment. A feed heater is usually required to maintain a constant operating temperature and constant membrane performance. If the feed gas may contain entrained liquids, a mist eliminator vessel with a high-efficiency coalescing element is required. A mist eliminator and heater are sufficient pretreatment where the liquid is water or hydrocarbons. If other liquids may be present, Air Products should be consulted for other pretreatment recommendations. Particulate filtration of the feed gas is not required. The design of shell-side–fed PRISM membranes prevents plugging from rust, pipe scale, and other particulates typically found in hydrogen-containing streams. However, a temporary conical strainer is recommended during the commissioning period to remove any weld slag or excessive amounts of debris that may be in new piping. What process controls and instrumentation are required? Air Products will provide a standard Piping and Instrumentation Diagram (P&ID) showing recommended control systems and instruments on the membrane and pretreatment equipment. Air Products can review and approve customized control systems for special applications. The control system will provide turndown over a wide range of feed flow rates, usually to 30% of design or less. What is the life of the membrane? With proper operation and maintenance, the membrane should last for the life of the project. Many PRISM membranes are in operation in hydrogen recovery for more than 15 years. If replacement becomes necessary, the membrane cartridge is easily replaced without need for special tools or expertise. (back to top)