Novel adsorption based purification processes
Abstract
New adsorption based hybrid processes are developed for the purification or separation of both gas and liquid feed mixtures. The hybrid PSA-TSA supercycle combines pressure swing regeneration with thermal regeneration and provides synergistic advantage for certain cases. This hybrid cycle consists of a number of Skarstrom type PSA cycles (with low purge/feed ratio) followed by thermal regeneration. The PSA cycles reach cyclic steady state but are always in the start-up mode, although supercycle as a whole does reach cyclic steady state. When applied to a model system of moisture removal from N2 streams, the supercycle is more than twice as productive as TSA for a required N 2 purity of 1 ppmv water vapor from a feed of 40,000 ppmv water vapor. The supercycle is particularly useful for purifying feeds that contain high concentrations of strongly adsorbing impurities. Further, new adsorptive solvent vapor recovery TSA processes are developed that use hot N2 instead of steam. This ‘TSA with N2 ’ process is applied for the recovery of isopropyl alcohol (IPA) vapor from air. IPA feed concentration (in air) cannot exceed 5000 ppmv (1/4 lower explosion limit for IPA) and the air purity has been arbitrarily set at 100 ppmv IPA. The ‘TSA with N2’ process recovers IPA and recycles the N2. Makeup is approximately 2 % of the total N2 required. The ‘TSA with N2’ process is compared to normal steam regeneration which uses downstream azeotropic distillation unit to separate IPA from water. The steam regeneration overall annualized cost is ∼19 % greater than that for ‘TSA with N2 process. The ‘TSA with N2 ’ is particularly useful for the removal and recovery of the solvent vapors that form homogeneous azeotropes with water. Finally, distillation-adsorption hybrids are developed for high purity IPA (99.9999 mol % IPA) production from dilute IPA-water liquid feeds (10 mol % IPA). These hybrids use adsorptive processes like PSA and TSA after distillation. The distillate vapor is fed to TSA (the distillation-TSA hybrid) or PSA (the distillation-PSA hybrid). The TSA in distillation-TSA uses hot N2 as the regenerating agent while the PSA uses product vapor purge (IPA-rich) at 0.2 atm. An azeotropic distillation unit using cyclohexane to recover IPA is also designed. The distillation-PSA hybrid is the most economical with the azeotropic distillation process costing almost twice and the distillation-TSA costing three times that for the distillation-PSA hybrid.
Degree
Ph.D.
Advisors
Wankat, Purdue University.
Subject Area
Chemical engineering
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