Grantee Research Project Results
Final Report: Novel Membranes for In-Process Recycling of Hydrocarbon Feedstocks in Oxygen-Oxidation Processes
EPA Contract Number: 68D70023Title: Novel Membranes for In-Process Recycling of Hydrocarbon Feedstocks in Oxygen-Oxidation Processes
Investigators: Wijmans, J. (Hans) G.
Small Business: Membrane Technology and Research Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1997 through March 1, 1998
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1997) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Description:
Oxygen-oxidation processes are used to produce a number of important chemicals by selective catalytic oxidation of hydrocarbons in a reactor. Products include ethylene oxide, propylene oxide, vinyl acetate, and vinyl chloride. All of these processes include an inert gas purge stream from the reactor. This purge stream is required to remove argon, which enters the reactor as a contaminant in the oxygen feed. Because argon does not react, the concentration in the reactor builds up unless it is purged. Currently, the purge gas is flared, resulting in a loss of approximately 450 million lb/yr of the hydrocarbon feedstocks used in these processes in the United States.The membrane separation system developed by Membrane Technology and Research, Inc. (MTR) will improve process economics and reduce air pollution by recovering feedstock. For example, during the production of ethylene oxide, about 16 lb of ethylene are lost in the argon purge stream per ton of ethylene oxide produced. This loss translates into 56 million lb/yr of ethylene (about 1 percent of the ethylene used), at a value of $8.4 million per year. Incineration of the purge stream produces 440 million lb/yr of carbon dioxide plus the accompanying amounts of NOx. These numbers are based on just the production of ethylene oxide, which represents about 15 percent of all chemicals produced by selective oxidation. Clearly, the argon purge represents an important resource recovery and pollution reduction opportunity. In this project, selective membranes were developed to separate the hydrocarbon feedstock from the argon, so that the feedstock can be recycled to the reactor. The value of the recovered hydrocarbon is high, so process payback times of 1?2 years are possible.
Summary/Accomplishments (Outputs/Outcomes):
Ethylene can be separated from argon by using either argon-selective or ethylene-selective membranes; both types were investigated in this project. The conclusion of the Phase I work was that the performance of the argon-selective membranes available at that time, with an argon/ethylene selectivity in the range 1.8?1.6, was not adequate for an economically viable membrane-based process. This redirected the Phase II work towards the development of ethylene-selective membranes. Three types of composite membrane were considered, with selective layers of silicone rubber [poly(dimethylsiloxane)], a polyamide-polyether block copolymer, and poly(propylene oxide-allylglycidylether) [Parel], respectively. The project target was to develop a membrane with an ethylene flux of 360 ? 10-6 cm3(STP)/cm2 s cm Hg, measured with a gas mixture, and an ethylene/argon selectivity of 4. This performance corresponds to the following pure gas permeation properties: an ethylene flux of 450 ? 10-6 cm3(STP)/cm2 s cm Hg and an ethylene/argon selectivity of 5. The Parel membrane, with the highest pure-gas ethylene/argon selectivity of 5.6 compared with 4 for silicone rubber and 5 for the polyamide-polyether copolymer, was selected for optimization. However, during the project period the supplier of Parel discontinued production of that polymer. Therefore, the two alternative ethylene-selective polymers were investigated further. The result was that, despite having a higher ethylene/argon pure-gas selectivity, the polyamide-polyether copolymer had a similar mixed-gas selectivity but lower fluxes than silicone rubber. This led to the final selection of silicone rubber as the preferred material for ethylene-selective membranes.In a separate project, a group of perfluorinated copolymers was identified as having promising selectivities for permanent gases over hydrocarbon vapors. These glassy polymers were evaluated for the ethylene-recovery application described here and were found to have a mixed-gas argon/ethylene selectivity of 4?5 and an argon flux of 20?40 ? 10-6 cm3(STP)/cm2 s cm Hg. These permeation properties are adequate for a commercially viable process.
Conclusions:
A detailed process analysis showed that ethylene-selective as well as argon-selective membranes can be used to economically recover ethylene from the argon purge stream from oxygen-oxidation reactors. Processes based on MTR's ethylene-selective silicone rubber membrane are superior to those using argon-selective membranes and can achieve 80 percent ethylene recovery with a system payback time under 1 year, provided sufficient compressor capacity is available in the plant. If additional compressors are required, the novel perfluorinated, argon-selective glassy membranes could be used to achieve a short payback period.A detailed process analysis showed that the silicone rubber membrane recovers about 80 percent of the ethylene present in the purge stream, resulting in a payback period of less than 2 years. The annual revenue generated (ethylene value minus operating costs) by the membrane system is between $200,000 and $400,000 per year, for a typical ethylene oxide plant. The addition of the membrane system is a simple retrofit. To date, the development of this technology has resulted in the sale of three systems worldwide to recover ethylene from the argon purge stream in ethylene oxide plants.
Supplemental Keywords:
pollution prevention, catalytic oxidation, purge stream, gas, oxidation, ethylene, argon, hydrocarbon., RFA, Scientific Discipline, Air, Toxics, Sustainable Industry/Business, Chemical Engineering, air toxics, cleaner production/pollution prevention, Environmental Chemistry, Sustainable Environment, HAPS, Technology for Sustainable Environment, Civil/Environmental Engineering, Chemistry and Materials Science, EPCRA, Environmental Engineering, ambient air quality, emission control strategies, in-process changes, in-process recycling, air pollutants, cleaner production, environmentally conscious manufacturing, feedstock, hydrocarbon, membrane technology , clean technology, recovered hydrocarbon, emission controls, Propylene oxide, industrial air pollution, membrane process, feedstocks, recycling, hydrocarbons, novel membrames, Ethylene oxide, air emissions, pollution prevention, Vinyl chlorideSBIR Phase II:
Novel Membranes for In-Process Recycling of Hydrocarbon Feedstocks in Oxygen-Oxidation ProcessesThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.