Development of large-scale applications in organic solvent nanofiltration and pervaporation for chemical and refining processes

Abstract

New membrane, modules, and systems are under development for large-scale organic/organic separations. Practical applications are envisioned in the refining, chemical, pharmaceutical, and polymer industries. A large-scale organic solvent nanofiltration (OSN) process is MAX-DEWAX™ for solvent recovery in lube dewaxing. A commercial installation has been in operation since 1998 at a feed rate of 5800 m 3/day (36,000 barrels/day). A pervaporation process, S-Brane™, is also available for comparable large-scale operations. S-Brane selectively removes sulfur containing hydrocarbon molecules from fluidized catalytic cracking (FCC) and other naphtha streams. A 300 barrels/day demonstration plant has been run on-stream using FCC light and intermediate cat naphthas. S-Brane reduces the overall capital and operating cost for clean fuel compliance, and also provides a means for preserving octane value in hydrotreating based technology. There are several key steps in the development of a robust membrane process that can be moved from lab-scale to pilot plant trials to a demonstration unit on-line at a refinery. These steps expand in complexity and size as process development moves forward. Both MAX-DEWAX and S-Brane are presented as examples of applications that have moved through this progression. Since these processes are large-scale and relatively low capital cost compared to conventional technologies, gains in yield, quality, or energy savings are found to offer significant economic benefits. Experimentally, it appears that high-pressure nanofiltration and low-pressure pervaporation are governed by the principles found in solution-diffusion models. Data taken in OSN mode is used to estimate pervaporation performance. Choice of membrane operating systems is dependent on the composition of the feed stream and the required product quality. In some cases, the high throughput for OSN outweighs the higher selectivities gained in pervaporation, since OSN is inherently a lower cost process to operate. Further investigations of new applications include toluene recovery from a toluene disproportionation unit, lowering benzene levels in gasoline feedstocks to <1%, and integration of membrane separation with aromatics reformer or distillation operations.