Dehydrogenation isobutane

3 Isobutane Dehydrogenation. - The pore size distributions of fresh and spent sulfided nickel catalysts were determined by a standard nitrogen desorption technique. Two catalysts with different pore size distribution were coked during the dehydrogenation of isobutane The pore volume was measured as a 

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The various sources of isobutylene are C streams from fluid catalytic crackers, olefin steam crackers, isobutane dehydrogenation units, and isobutylene produced by Arco as a coproduct with propylene oxide. Isobutylene concentrations (weight basis) are 12 to 15% from fluid catalytic crackers, 45% from olefin steam crackers, 45 to 55% from isobutane dehydrogenation, and high purity isobutylene coproduced with propylene oxide. The etherification unit should be designed for the specific feedstock that will be processed. 

New aluminophosphate oxynitrides solid basic catalysts have been synthesised by activation under ammonia of an AIPO4 precursor. When the nitrogen content increases, XPS points out two types of nitrogen phosphorus bonding. The conversions in Knoevenagel condensation are related to the surface nitrogen content. Platinum supported on aluminophosphate oxynitride is an active catalyst for isobutane dehydrogenation. 

Figure 4 shows the evolution of the initial conversion versus temperature at a space velocity of 0.03 h l. The equilibrium conversion of isobutane to isobutene is 100% in our conditions. An increase of the conversion with temperature up to 773-823 K is observed. When metals were added, we also noted a large increase in isobutane dehydrogenation. Table 2 gives initial isobutane conversions, isobutene selectivities and yields of the reaction at 823 K for the three tested samples. 

Catalytic testings have been performed using the same rig and a conventional fixed-bed placed in the inner volume of the tubular membrane. The catalyst for isobutane dehydrogenation [9] was a Pt-based solid and sweep gas was used as indicated in Fig. 2. For propane oxidative dehydrogenation a V-Mg-0 mixed oxide [10] was used and the membrane separates oxygen and propane (the hydrocarbon being introduced in the inner part of the reactor). 

Most of the results have been already partly presented in [9] (isobutane dehydrogenation) and [10] (propane oxidative dehydrogenation). Let us recall that the membrane presented in this paper has been associated with a fixed bed catalyst placed within the tube. 

In the isobutane dehydrogenation the catalytic membrane reactor allows a conversion which is twice the one observed in a conventional reactor operating under similar feed, catalyst and temperature conditions (and for which the performance corresponds to the one calculated from thermodynamics) [9]. 

Figure 3.37 Activity and selectivity in the reaction of isobutane dehydrogenation to isobutene with nanoparticles of Pt/silica (a) and with Pt/Sn bimetallic nanoparticles/silica obtained via the organometallic route (b).

There are two major uses of isobutane. Dehydrogenation to isobutylene is a large use. The isobutylene is then converted into the gasoline additive methyl /-butyl ether. Isobutane is also oxidized to the hydroperoxide and then reacted with propylene to give propylene oxide and /-butyl alcohol. The /-butyl alcohol can be used as a gasoline additive, or dehydrated to isobutylene. See Chapter 8, Section 5. 

Puurunen et al. have investigated the effect of surface nitridation of y-AI2O3 supports by the atomic layer deposition process on the activity of chromium catalysts for isobutane dehydrogenation. Nitridation was observed to suppress activity and it was argued that oxide ions were more active for the dissociation of isobutane. 

This case is an example of the situation for which a large amount of information at the molecular level can be extracted about the investigated Pt/Sn-containing materials on the basis of analyses of experimental results. It was possible to identify factors that control the nature and the strength of the interaction of the important transition state with a specific catalytic site. A summary of the analyses of isobutane dehydrogenation on Pt/Sn-containing catalysts is provided next. 

Kinetic Parameters for the Horiuti-Polanyi Reaction Scheme for Isobutane Dehydrogenation and Isobutylene Hydrogenation... 

Fig. 4. Rectification plot for isobutane dehydrogenation and isobutylene hydrogenation kinetic data over Pt/Sn/Si02. Adapted from (38).

The paraffins dehydrogenation on platinum-alumina catalysts proceeds with constant rate up to some time-on-stream after which a slow deactivation of the catalysts takes place Since relative changes of the catalyst activity ( characterized by reaction rate) are proportional to relative amounts of the deposited coke it can suppose that coke formation is the main reason of deactivation. Deactivation can be related with an attainment of a threshold in coke concentration (Co) on catalysts. The threshold amounts are 1.8 wt.% for A-I, 6,8% and 2.2% for A-II and A-IXI catalysts respectively. The isobutane dehydrogenation in non-stationary region (C > Co) is described by the following kinetic equation ... 

Recent results on isobutane dehydrogenation have been reported, and a conventional reactor has been compared with membrane reactors consisting of a fixed-bed Pt-based catalyst and different types of membrane [51]. In the case of a mesoporous y-AKOi membrane (similar to those used in several studies reported in the literature), the observed increase in conversion could be fully accounted for simply by the decrease in the partial pressures due to the complete mixing of reactants, products and sweep gas. When a permselective ultramicroporous zeolite membrane is used, this mixing is prevented the increase in conversion (% 70%) can be attributed to the selective permeation of hydrogen shifting the equilibrium. 

ABB Lummus Global Isobutylene Isobutane Dehydrogenation in cyclic-fixed bed reactor yields 57% to 61 % per pass 14 1992... 

Other separation methods have also led to developments, without necessarily culmi Dating in plant construction. Thus, Hoechst has proposed esterification, or, more precisely, passage through t-butylacetate, and Union Carbide has proposed adsorption on molecular sieves. Butenes isomerization, isobutane dehydrogenation, and c-butyl alcohol dehydration (4i C0 Chemicat) offer complementary methods for synthesizing isobutene. 

Figure 13. Transition structure of the isobutane dehydrogenation reaction in chabazite.

Weckhuysen, B.M., Verberckmoes, A.A., Debaere, J., Ooms, K., Langhans, 1. and Schoonheydt, R.A. (2000) In situ UV-Vis diffuse reflectance spectroscopy-on line activity measurements of supported chromium oxide catalysts relating isobutane dehydrogenation activity with Cr-spedation via experimental design. Journal of Molecular Catalysis A Chemical, 151 (1-2), 115-31. 

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