Paraffin reactions

Mobil s High Temperature Isomerization (MHTI) process, which was introduced in 1981, uses Pt on an acidic ZSM-5 zeoHte catalyst to isomerize the xylenes and hydrodealkylate EB to benzene and ethane (126). This process is particularly suited for unextracted feeds containing Cg aHphatics, because this catalyst is capable of cracking them to light paraffins. Reaction occurs in the vapor phase to produce a PX concentration slightly higher than equiHbrium, ie, 102—104% of equiHbrium. EB conversion is about 40—65%, with xylene losses of about 2%. Reaction conditions ate temperature of 427—460°C, pressure of 1480—1825 kPa, WHSV of 10—12, and a H2/hydtocatbon molar ratio of 1.5—2 1. Compared to the MVPI process, the MHTI process has lower xylene losses and lower formation of heavy aromatics. 

In the n-paraffin reactions, let us suggest that the reaction scheme shown in Figure 6 satisfies most of the observations. The solid lines represent reactions that have been observed, while the dashed lines are proposed reactions involving products whose steady state concentrations are too small to be measured with our analytical equipment. 

In contrast with readsorption reactions, which broaden the carbon number distribution of FT synthesis products, cracking reactions narrow such distributions, within the constraints imposed by the random nature of C—C bond cleavage in carbenium ion reactions of large olefins. Cracking of n-paraffins can also occur on intrapellet acid sites, but acid-catalyzed paraffin reactions are much slower than those of corresponding olefins of equal size. As in all secondary reactions, cracking sites are used most efficiently when... 

The role of the collisional deactivation of excited sulfur atoms in paraffin reactions (as well as in the COS-olefin systems) has been convincingly demonstrated in separate studies with added inert gases. The data given in Table II show that large excess of CO2 completely suppresses the formation of the propyl mercaptans in the propane reaction by collisional quenching of S( Z)) atoms,... 

C. Selectivity in Polystep Paraffin Reactions 1. Isomerization Selectivity... 

Nitration and sulfonation of aromatics, Diels-Alder condensation, polyethylene, molecular complexes, CO-paraffin reaction, detergents, etc. 

Cracking into two paraffins (reaction 3) and decomposition into carbon and hydrogen (reaction 4) can also occur to an appreciable extent in the same temperature range as the conversion to aromatics. 

Olefin Alkylation of Paraffins. Reactions involving parafiSns and olefins may be represented as follows ... 

For paraffins, the ratio of yields of penultimate and interior -H radicals is 20% higher than expected from the abundance of the corresponding C-H bonds (this was observed using both by the product analysis [111] and EPR [112]). Since the C-H bond dissociation energies for carbon-2 bonds are higher than those for interior carbon atoms, this preference cannot be explained through the abstraction by H atoms. One way to explain the observed preference is to assume the occurrence of reaction (4) it is known that in low-temperature solid paraffins reaction (1) yields mainly terminal and penultimate radicals [114]. In addition to the -H radicals, paraffins exhibit high yield of radicals formed upon C-C scissions, preferably for interior carbon atoms [3]. 

Reactions of Paraffins. Paraffin reactions, particularly reactions of lighter paraffins, are the most difficult reactions to effect in reforming. For that reason, the ability to convert paraffins selectively is of primary importance in reforming. 

Hydrocracking of Paraffins. An additional acid-catalyzed paraffin reaction is cracking to lighter products, thus removing them from the liquid product. Octane is improved through the removal of low octane paraffinic species from the liquid product by their conversion to gaseous, lower molecular weight paraffins. 

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