Dehydroisomerization Of N-butane Research Articles

An Integrated Membrane Process for Butenes Production

Iso-butene is an important material for the production of chemicals and polymers. It can take part in various chemical reactions, such as hydrogenation, oxidation and other additions owing to the presence of a reactive double bond. It is usually obtained as a by-product of a petroleum refinery, by Fluidized Catalytic Cracking (FCC) of naphtha or gas-oil. However, an interesting alternative to iso-butene production is n-butane dehydroisomerization, which allows the direct conversion of n-butane via dehydrogenation and successive isomerization. In this work, a simulation analysis of an integrated membrane system is proposed for the production and recovery of butenes. The dehydroisomerization of n-butane to iso-butene takes place in a membrane reactor where the hydrogen is removed from the reaction side with a Pd/Ag alloys membrane. Afterwards, the retentate and permeate post-processing is performed in membrane separation units for butenes concentration and recovery. Four different process schemes are developed. The performance of each membrane unit is analyzed by appropriately developed performance maps, to identify the operating conditions windows and the membrane permeation properties required to maximize the recovery of the iso-butene produced. An analysis of integrated systems showed a yield of butenes higher than the other reaction products with high butenes recovery in the gas separation section, with values of molar concentration between 75% and 80%.

Dehydroisomerization of n-butane over Cr/SiO2

Abstract The catalytic activity and selectivity of CrOx/SiO2 for the dehydroisomerization of n-butane were studied at 550 °C and 1 atm. Influence of chromia concentration and chromia precursor on the oxidation state, activity and selectivity were investigated. The catalysts were characterized by X-ray diffraction (XRD), TGA and temperatures programmed reduction (TPR). The isomerization activity linearly increased with increasing acidity and Cr loading. The addition of chromium precursors in complex form decreased the initial activity in dehydroisomerization of n-butane and but increased the selectivity of butenes. Catalyst, which had the highest acidity and lowest crystallite size, was the most active in isomerization reaction. The highest selectivity and yield of butenes achieved was 92% and 5.5%, respectively.

Comparative catalytic studies on the conversion of 1-butene and n-butane to isobutene over MCM-22 and ITQ-2 zeolites

The catalytic properties of H-MCM-22 and Pt-MCM-22 for the skeletal isomerization of 1-butene and the dehydroisomerization of n-butane were compared with those obtained from their delaminated derivatives, H-ITQ-2 and Pt-ITQ-2. The overall results of our study strongly suggests that the desired 1-butene and n-butane conversions to isobutene in steady state occur mainly near the pore mouth inlets of the sinusoidal 10-ring channels retained in both of MCM-22 and ITQ-2 and inside this intralayer void space, respectively, which may be attributed to the unique geometric constraints imposed by the two-dimensionality of the pore system with a suitable degree of ellipticity of 10-ring channels. Whereas coke formation on the sinusoidal channels during the 1-butene skeletal isomerization can occur in such a way as to make most of the intrachannel Brønsted acid sites less available for nonselective dimerization-cracking reactions, it appears that the presence of H 2 in the n-butane dehydroisomerization stream would prevent extensive coke buildup, thereby allowing pore diffusion of reactants and products even in steady state.

Dehydroisomerization of n-butane over H-Y zeolite supported Pt and Pt,Sn catalysts

The direct one-step conversion of n-butane to isobutene was investigated over H-Y zeolite supported platinum and platinum-tin catalysts. Catalytic results over monometallic Pt catalysts showed that dispersion of Pt mainly affects the selectivity towards reaction products, larger Pt ensembles resulting in a higher degree of cracking/hydrogenolysis reactions and consequently to a lower n-butenes and isobutene formation. Addition of tin has been found to significantly improve both the selectivity to isobutene and the resistance to deactivation of the catalytic system. On the basis of characterization results (H 2 chemisorption, NH 3-TPD, FT-IR of adsorbed CO) the higher isobutene selectivity of Pt,Sn catalysts have been accounted for a dilution effect of Pt ensembles induced by the second metal which inhibits hydrogenolysis reactions, requiring several contiguous Pt sites, and enhances the selectivity for the dehydrogenation reaction that can instead proceed over smaller metal ensembles. The improved stability of Pt,Sn catalysts has been related to the lower surface acidity of the system in the presence of Sn, which results in a reduced formation of carbonaceous deposits responsible for catalysts deactivation.

Mn-Containing AlPO-11 and SAPO-11 Catalysts for Simultaneous Isomerization and Dehydrogenation of n-Butane

MnAPO-11 and MnAPSO-11 were synthesized hydrothermally, and supported Mn-AlPO-11 and Mn-SAPO-11 were also prepared for comparison. Characterization results showed that there were differences in acidity and reducibility caused by the different incorporation methods of manganese. The manganese species in the samples also weakened the metallic properties of the palladium particles when the latter was added into the catalysts. Catalytic testing results for dehydroisomerization of n-butane indicated that incorporation of manganese increased the selectivity toward isomerization products. The highest isobutene selectivity (34.86%) could be obtained over a Pd/MnAPO-11 catalyst. When a combined catalyst system containing Pd/SAPO-11 and MnAPSO-11 was used in a single bed of two layers, the isobutene selectivity could be greatly improved, as compared to the single catalyst alone.

Direct Conversion of n-Butane to Isobutene over Pt–MCM22

MCM22 is a very active and selective catalyst for the skeletal isomerization of butene. At temperatures up to 775 K, Pt–MCM22 gives good results in the dehydroisomerization of n-butane, achieving higher yields of isobutene than does Pt–ZSM5. Most notably, the formation of cracking products is low. Alternatively, MCM22 can also be used as an isomerization catalyst in combination with Pt–ZSM5 in order to increase the yield of isobutene in dehydro-isomerization. A disadvantage of the MCM22 materials, however, is their moderate stability, especially at higher temperatures. During calcination/reduction of Pt–MCM22 partial dealumination of the framework occurs, leading to enhanced deactivation by coking.