Butane isomerisation

The aim of the present work was the investigation of the catalytic reactivity of different salts (K, NH4, Cs ) of H3PW12O40 and H4SiWi2O40 with various compositions in continuous liquid phase alkylation and its comparison with n-butane isomerisation reaction in gas phase. 

In Fig. 9 we sketch two process routes to isobutene. Starting from n-butane, isomerisation to isobutane is followed by dehydrogenation to isobutene. Both process steps have been widely operated commercially. The second step involves a capital intensive dehydrogenation reaction. Because of the intensity large plants are called for (economy of scale). An alternative and in principle less capital-intensive route is the skeletal isomerisation of n-butenes to isobutene. Previously this was not economically attractive because of the limited lifetime of the catalyst and the limited yield of isobutene. The latter drawbacks were due to the high temperatures applied previously (>400°C) and the related fast coke formation. 

Carbon monoxide has been widely used to characterise the hydroxyl groups of solid acids, since its interaction with acidic protons modifies the strength of the C-O bond.I Analysis by IR spectroscopy is a tool of choice to obtain information on the surface of the catalyst. CO acts as a basic probe and according to previous studies, its complexation with Lewis acid sites (LAS) decreases the acidity and consequently, the activity of the catalyst in n-butane isomerization. However, it is uncertain if the interaction of CO with LAS is the main origin of catalyst deactivation, since n-butane isomerisation is also inhibited by CO in the absence of LAS. 

SSITKA has contributed much to our understanding of many surface catalyzed reactions. To date, the reactions that have been studied by SSITKA are summarized in Table 1. Although most of the published work is presented in Table 1, not all the references for different reactions utilizing SSITKA have been reported, due to space limitations. Effects of temperature, reactant partial pressure, and promotion have also been explored using SSITKA. SSITKA has been used to determine the cause of deactivation for n-butane isomerisation on sulfated zirconia, and the... 

Kim et successfully showed that for n-butane isomerisation on sul-fated zirconia, deactivation was due to a decrease in site activity and a blockage of active sites. The initial loss in activity was caused by the loss of the most active sites. The less active sites deactivated slower and had more of a relative impact on the isomerisation reaction at later TOS. 

Sulfated zirconia (SZ) is a well-known solid acid catalyst that has been widely studied in the past 15 years. SZ is a very strong acid catalyst and is active for n-butane isomerisation even at room temperature. Many parameters have been found to impact the catal dic activity of SZ, such as catalyst preparation and pretreatment, which affect the sulfur content, the concentration of Lewis and Bronsted acid sites, and other characteristics. However, the deactivation of SZ during n-butane isomerisation can be severe. 

The present paper is an attempt to unravel a rather confused aspect of cationoid polymerisations. This concerns the phenomenon comprised in the term monomer complexation of the growing cation . The idea seems to have occurred for the first time in the work of Fontana and Kidder on the polymerisation of propene by AlBr3 and HBr in w-butane [3]. The kinetics indicated a reaction of zero order with respect to monomer, M to explain this, it was assumed that the growing end of the chain, written as a carbenium ion, Pn+, is complexed with M and that the rate-determining growth step is an isomerisation of this complex ... 

The tppts process has been commercialised by Ruhrchemie (now Celanese), after the initial work conducted by workers at Rhone-Poulenc, for the production of butanal from propene. Since 1995 Hoechst (now Celanese) also operates a hydroformylation plant for 1-butene. The partly isomerised, unconverted butenes are not recycled but sent to a reactor containing a cobalt catalyst. The two-phase process is not suited for higher alkenes because of the... 

With palladium—alumina, the products of the reaction of but-l-yne with deuterium [189] were but-l-ene, 99.1% frans-but-2-ene, 0.2% cis-but-2-ene, 0.2% n-butane, 0.5%, until at least 75% of the but-l-yne had reacted. But-l-ene hydrogenation and hydroisomerisation were observed to occur when all the but-l-yne had reacted. The formation of but-2-ene as an initial product was postulated as being the result of a slow isomerisation of but-l-yne to absorbed buta-1 2-diene... 

The hydrogenation of buta-1 2-diene appears to have received relatively little attention. Over palladium—alumina at room temperature, the products of the gas phase hydrogenation were c/s-but-2-ene, 52% but-l-ene, 40% frans-but-2-ene, 7% and n-butane, 1% [189]. Some isomerisation of the buta-1 2-diene to but-2-yne (10%) together with traces of but-l-yne and buta-1 3-diene was also observed. A similar butene distribution (namely, cis-but-2-ene 52%, but-l-ene 45% and frans-but-2-ene 3%) was observed in the liquid phase hydrogenation over palladium [186]. 

The deactivation functions for the isomerisation reactions of n-hexane were shown to be exponential functions of the coke content. The deactivation constant, the parameter of these functions, did not differ significantly for the various isomerisation reactions leading to tertiary carbenium ions. The deactivation constant for the isomerisation to 2,2-di-Me-butane, formed out of a secondary carbenium ion, was larger. 

Direct dehydroisomerisation (DHI) of n-butane into isobutene over bifunctional zeolite-based catalysts represents a potential new route for the generation of isobutene utilising cheap n-butane feedstock. Isobutene is used worldwide for production of methyl tert-butyl ether (MTBE) and polyisobutylene. It is currently obtained via extraction from refinery/cracker C4 streams or via conversions of isobutane (in one step) or n-butane (in two steps).1,2 Isobutene can also be produced via the isomerisation of n-butenes,3 although there is no evidence that this is practised commercially.2,3... 

The main objective of the present work was to investigate the possibilities of direct (and selective) n-butane dehydroisomerisation into isobutene over Ga-containing zeolites. Another objective was to evaluate the role played by Ga and acid sites in this reaction. For this work such medium pore zeolites, as ferrierite (FER) and theta-1, were chosen because of their superior performance in n-butene isomerisation reaction.3,7 The modifying metal, Ga, was chosen due to the known high dehydrogenation activity of Ga-ZSM-5 catalysts in propane and n-butane conversions. 10 However, Ga-ZSM-5 catalysts were not used in this study because of their high aromatisation activity,8,9 which would not allow to stop the reaction at the stage of formation and isomerisation of butenes. 

Investigation of n-butane conversion over H-forms of the ferrierite and theta-1 zeolites demonstrated that the isobutene selectivities were similar (and low) for these catalysts. The maximum selectivities (7-8 %) were obtained at low n-butane conversions (5-10 %) and decreased with increasing conversion of n-butane due to olefin interconversion and aromatisation reactions. Isobutene was in equilibrium with the other butene isomers due to the high isomerisation activity of the parent zeolites. The maximum selectivity to butenes, which was observed at low conversions, was around 20 %. This value reflects a moderate contribution of the dehydrogenation steps in n-butane transformation over H-forms of the ferrierite and theta-1 zeolites and indicates an important role of the n-butane protolytic cracking steps over these two catalysts. 

Thus, an operation able to crack butane would be able to lift propylene yields if the increased amounts of isobutane were to be fed into the system. This could be by either isobutane purchases or isomerisation of n-butane feedstock. This gives a gas cracking operation some flexibility in altering the ethylene/propylene split which is otherwise difficult with gaseous feedstock. 

The heats of combustion of n-butane and isobutane are — 688.0 and — 686.3 kcal., respectively, at 25 C. Calculate the heat of formation of each of these isomers from its elements, and also the heat of isomerisation, i.e., iv-butane — isobutane, at 25 C. 

Iso-butane/n-butane ratios are close to e< librium values as conversion decreases to zero and iso-butene is never more than 50% of the total C4 olefins (the equilibrium value at 400°C) suggesting that the butenes are close to equilibrium. There is scsne uncertainty because 1-butene is not detected but, since at equilibrium only around 10% of the butenes is present as l-butene at 400°C, this is probably due to difficulty in detection. These C results suggest that iso C4 and iso-C4 are not extensively produced by cracking of oligcmers and this view is supported by the absence of C7+ material in the product stream. Since the isomerisation of the n-C4 carbenium ion is energetically unfavourable it afpears that consideration ould be... 

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