Dehydration of isopropanol

Rouge, A., Spoetzl, B., Gebauer, K., Sghenk, R., Renken, a., MicroChannel reactors for fast periodic operation the catalytic dehydration of isopropanol,... 

The selective separation of water from aqueous solutions of isopropanol or the dehydration of isopropanol can be carried out with different membranes, which contain polar groups, either in the backbone or as pendent moieties. For the dehydration of such a mixture, poly(vinyl alcohol) (PVA) and PVA-based membranes have been used extensively. PVA is the primary material from which the commercial membranes are fabricated and has been studied intensively for pervaporation because of its excellent film forming, high hydrophilicity due to -OH groups as pendant moieties, and chemical-resistant properties. On the contrary, PVA has poor stability at higher water concentrations, and hence selectivity decreases remarkably. 

Another approach to enhance separation performance of membrane for dehydration of isopropanol is the modification of PVA membranes in gaseous plasma [30], The modification of membrane properties in nitrogen plasma environment lead to increase in selectivity by about 1477 at 25 °C such increase in the selectivity is justified by an increase of cross-linking on membrane surface provoked by plasma treatment. 

Ai and Suzuki [5,9] investigated the combination V2Os—P2Os. The acidity was measured indirectly by the activity for dehydration of isopropanol and was shown to decrease with increasing P2Os content. The activity for the oxidation of butene-1 and butadiene to maleic acid anhydride decreased accordingly. It was shown that the adsorption equilibrium constant of the olefin on the catalyst also decreased in the same way. 

The effects of post-synthesis alumination on purely siliceous MCM-41 material with A1(NC>3)3 on acidity have been studied by FTIR, NH3-TPD, and IPA decomposition reaction. The FTIR results of pyridine absorption show that both Lewis and Bronsted acid sites are increased by the post-modification. The amount of NH3 adsorbed on the alumina-modified MCM-41 samples increases with the loading of Al onto the surface of MCM-41. Due to the improved acidity, the alumina-modified MCM-41 materials show considerably higher catalytic activity for dehydration of isopropanol than purely siliceous MCM-41. In addition, XRD and N2 adsorption results show that all MCM-41 samples maintained their uniform hexagonal mesoporous structure well after they have been subjected to post-synthesis alumination with the loading of Al species on Si-MCM-41 varied from 0.1 wt. % up to 10 wt. % (calculated based on AI2O3). 

Table 2 shows the conversion of isopropanol to propylene over PSM and AMM samples. The reactivity of isopropanol on PSM is very low due to the lack of acid sites on PSM. The conversion is less than 1% at temperatures lower than 200 °C and only 10% at 250°C. However, all AMM samples show considerable activities for the dehydration of isopropanol to propylene. Having only 0.1 wt.% loading of AI2O3 on the sample, the conversion of isopropanol on AMM-0.1 reaches 79.6 % at 200°C and reaches complete conversion at 250°C. With the increase of A1 content, the catalytic activity is found to be increased. The conversion of isopropanol at 200°C is over 90% on AMM-1 and 100% on AMM-5 and AMM-10. 

Post-synthesis alumination using A1(N03)3 as the precursor improves the acidity of siliceous MCM-41 materials significantly. FTIR results show that both Bronsted and Lewis acid sites are increased upon alumination. The number of acid sites increases with the Al content on MCM-41. NH3-TPD reveals the mild strength of these created acid sites. Due to the improved acidity, the catalytic activity for dehydration of isopropanol to propylene over these alumina-modified MCM-41 materials is considerably promoted by post-synthesis alumination. The results of XRD and N2 adsorption show that the enhancement of acidity for siliceous MCM-41 by postsynthesis alumination does not cause any serious structural deformation of the resulting material. 

With the introduction of microreactors, transient reactor operations became interesting due to their low internal reactor volume and, thus, fast dynamic behavior. In 1999, Liauw et al. presented a periodically changing flow to prevent coke development on the catalyst and to remove inhibitory reactants in an IMM microchan-nel reactor [58]. This work was preceded by Emig in 1997, of the same group, who presented a fixed-bed reactor with periodically reversed flow [59]. In 2001, Rouge et al. [14] presented the catalytic dehydration of isopropanol in an IMM microreactor. 

Using nearly straight-pore alumina membrane plates as both a separator and a catalyst, Fumeaux et al. [1987] demonstrated the dehydration of isopropanol to form propene and hydrogenolysis of ethane to make methane. No quantitative information, however, was provided for the conversion or yield of the associated reactions. 

Van HV, Vanden AL, Buekenhoudt A, Dotremont C, and Ley sen R. Economic comparison between azeotropic distillation and different hybrid systems combining distillation with pervaporation for the dehydration of isopropanol. Sep. Purific. Tech. 2004 37(l) 33-49. 

The results in Figures 1 and 2 could have important bearing on the observed catalytic behavior of this system. The diffusivity of propene, the product of the acid-catalyzed dehydration of isopropanol, is seen to be more than one order of magnitude larger than that of acetone, the product of the base-catalyzed reaction. If both reactions occur in parallel, the difference in product diffusivities could lead to a transport-promoted output of the acid-catalyzed product if the process is diffusion limited. 

Fio. 21. Catalytic activities of cadmium-aluminosilicate catalysts for dehydration of isopropanol versus amounts of cadmium in the catalysts. Reaction pressure, 1 atm reaction temperature, 200° G/W, 8.6 hr 1.7 molar ratio of nitrogen to feed , for catalyst prepared by cation-exchange method A, for catalyst prepared by impregnation method. 

Fig. 2.43 Flow sheet of an extractive distillation for the dehydration of isopropanol...

Mixtures. Part IF. Dehydration of Isopropanol by Diffusion Distillation, Chem. Eng. Process, 20, 265-270 (1986b). 

From the thermodynamic and kinetic standpoints, dehydrogenation is favoured by an increase in temperature. At 325 C and atmospheric pressure, the theoretical conversion reaches nearly 98 per cent It should be practically total at 525°C. In fact a number of side reactions occur aUhese temperatures, including the dehydration of isopropanol to propylene. 

Sulfonated polysiloxanes have been tested in a variety of reactions. A typical reaction used to compare the acid strength of these catalysts with that of other solid acids is dehydration of isopropanol to yield propene [3]. The splitting of ethers, especially MTBE, at temperatures up to 200 °C has also been successfully demonstrated [14]. 

Propane formation occurs through a three-step process with hydrogenation of acetone on the platinum sites, dehydration of isopropanol on the acid sites and hydrogenation of propene on the platinum sites. 2-Methylpentane being a primary product results probably from propene dimerisation on the acid sites followed by hydrogenation. 

Permeation (4) Gas or liquid Forced flow through semipermeable membrane Membrane Dehydration of Isopropanol, Vol. 9, p. 284... 

Membrane separations involve the selective solubility in a thin polymeric membrane of a component in a mixture and/or the selective diffusion of that component through the membrane. In reverse osmosis (3) applications, which entail recovery of a solvent from dissolved solutes such as in desalination of brackish or polluted water, pressures sufficient to overcome both osmotic pressure and pressure drop through the membrane must be applied. In permeation (4), osmotic pressure effects are negligible and the upstream side of the membrane can be a gas or liquid mixture. Sometimes a phase transition is involved as in the process for dehydration of isopropanol shown in Fig. 1.8. In addition, polymeric liquid surfactant and immobilized-solvent membranes have been used. 

Only a few years after the existence of active centers was first postulated, Dohse and coworkers in 1930 ( ) determined the site density by what amounts to determining the number of chemisorbed reactant molecules when the reaction is zero order. For isopropanol dehydration over alumina they found a site density— asji min their alumina had a normal surface area—of about 10 cm. In 1937 Kubokawa ( ) used a poisoning method, measuring the amount of mercuric ion which inhibited > 2 decomposition over platinum black. Balandin and Vasser i rg obtained in 1946 ( ) a site density of the order of 10 cm for the dehydration of isopropanol over a mixed oxide of zinc and alumina. 

PI materials have been used for the dehydration of water/alcohol mixtures by the pervaporation method.P84 co-PI hollow fibers and zeolite filled P84 CO-PI membranes " have been used for the pervaporation dehydration of isopropanol. In addition, P84 co-PI based dual-layer hollow fiber membranes serve for the dehydration of tetrafluoropropanol. ... 

R. Liu, X. Qiao, and T.-S. Chung. The development of high performance P84 co-polyimide hollow fibers for pervaporation dehydration of isopropanol. Chem. Eng. ScL, 60(23) 6674-6686, December 2005. 

X. Qiao, T.-S. Chung, and R. Rajagopalan. Zeolite filled P84co-polyimide membranes for dehydration of isopropanol through pervaporation process. Chem. Eng. ScL, 61(20) 6816-6825, October 2006. 

CS and PVA blend membranes were fabricated to use for pervaporation dehydration of isopropanol aqueous solution [92]. The total flux increased with the CS content in the membrane. The membrane with CS/PVA 3 1 ratio acted as the best pervaporation performance with high flux and excellent selectivity. 

Sajjan et al. [97] prepared pervaporation membranes using sodium alginate and CS-wrapped MWCNTs for the dehydration of isopropanol. An increase of CS-wrapped MWCNTs content in the membrane matrix resulted in increased permeation flnx and selectivity. The membrane containing 2 mass% of CS-wrapped MWCNTs showed the highest separation selectivity of 6419 with a flux of 21.76 x 10" kg/m h at 30°C for 10 mass% of water in the feed. 

Sajjan, A. M., Jeevan Kumar, B. K., Kittur, A. A., and Kariduraganavar, M. Y. 2013. Novel approach for the development of pervaporation membranes using sodium alginate and chitosan-wrapped multiwalled carbon nanotubes for the dehydration of isopropanol. J. Membr. Sci. 425-426 77-88. 

Qiao X, Chung TS, Pramoda K. Fabrication and characterization of BTDA-TDI/MDl (P84) co-polyimide membranes for the pervaporation dehydration of isopropanol. J Membr Sci 2005 ... 

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