(610f) High Performance Composite Membrane for Olefin/Paraffin Separation

Zhong Tang, Bo Lu, Xiaojuan Hu, Kristy Pham, Xueliang Dong, Lin-feng Li

Bettergy Corp., Peekskill, NY 10566

Abstract

Bettergy Corp. is developing a novel, robust, olefin/paraffin membrane separation technology with high selectivity and flux and excellent stability. The membrane can be used as a more efficient replacement for the energy-intensive cryo-distillation processes that are currently being used. Bettergy’s membrane can meet the stringent performance and cost requirements for olefin/paraffin separation, significantly reducing the cost of olefin production. Light olefins such as ethylene and propylene are produced in great quantities in petrochemical plants worldwide. The global light olefins market size was 178.6 million tons in 2008 and is expected to reach 267.9 million tons in 2020. In the United States, ethylene and propylene are the most commonly produced light olefins, with yearly production exceeding 25 million tons for ethylene and 16 million tons for propylene, respectively, representing a market over $50 billion. [1] An important process in the manufacture of olefins is large-scale separation of the olefin from corresponding paraffin. In the petrochemical industry, this separation is carried out by cryo-distillation, which is highly energy-intensive due to the cryogenic temperatures required for the process. [2]Membrane separation for olefin/paraffin mixtures offers an appealing energy-efficient alternative to the cryo-distillation process.

There have been previous attempts to develop membranes for olefin/paraffin separation. Although substantial effort has been dedicated in developing a high flux, high selectivity olefin separation membrane, the state-of-the-art membrane cannot meet the stringent requirements of real life olefin/paraffin separation. Technical barriers include (1) a trade-off between selectivity and flux; (2) poor stability especially under the practical operating environment; (3) fouling or poisoning in the presence of contaminants (olefin, alkynes, dienes, olefin sulfide, and other sulfur species); and (4) high cost of the membranes. Given the significant costs associated with current olefin/paraffin separation technologies, the membrane technology developed by Bettergy has the potential to find a huge market in olefin/paraffin separation. Bettergy estimates that by utilizing its novel membrane technology to replace current cryo-distillation process, the cost of production can be reduced significantly, with the potential for savings of tens of billions of dollars annually on a global basis.

Bettergy has experimentally proved that our unique composite membrane can separate propylene/propane gas mixture achieving propylene selectivity of ~ 50-100, and propylene permeance up to 0.1-1.0×10^-8 mol/m².s.Pa. The membrane has exhibited very stable performance during more than 1500 hours of test. A comparison of the membrane performance between Bettergy’s novel composite membrane and several kinds of other membranes reported in the literature shows that Bettergy’s membrane exhibits the best performance in terms of selectivity to propylene, permeance. In addition, this composite membrane shows excellent stability, can be fabricated in spiral-wound module with low cost.

The simulation of propylene/propane membrane separation has been performed. Only a one-stage membrane process is considered in this work. The feed gas – propylene 88.0% and propane 12.0%, target permeate propylene purity – 99.5%, feed rate – 1000 lb/hr. The trans-membrane pressure is set to 325 psi and operation temperature is 28^oC. Results show that in order to meet the target permeate propylene concentration of 99.5%, the maximum propylene recovery rate possible is about 72%. The membrane area required for this operation with feed rate of 1000 lb/hr is about 500 m².

Bettergy has a number of patents based on this membrane technology that have been either granted or pending. [3]The scale-up modules are also being developed and showing reproducible performance. Bettergy is actively seeking industrial partners to conduct pilot plant testing and further commercialize this advanced membrane technology.