Butane cracking selectivity

In later work by Haag and Dessau product selectivity data were provided for n-butane cracking at 426-523 °C over HZSM-5 with Si/Ah = 70 [90]. The selectivity results at 496 °C and 1-10 kPa for n-butane were extrapolated to zero percent conversion in Table 13.6 to be able to identify the primary products and to assess the decomposition pattern of the n-butyl carbonium ion. Similar selectivities to methane and propylene implied, as expected, that the decomposition of the car-... 

Dilute fluorine gas (0-20%) can be used to treat zeolites at near-ambient temperature and pressure. Most of the resulting materials retain very high crystallinity even after 600°C postcalcination for two hours. Both framework infrared spectra and X-ray powder diffraction patterns clearly show structural dealumination and stabilization. The hydrophobic nature of the fluorine-treated and 600sC-calcined material is shown by a low water adsorption capacity and selective adsorption of n-butanol from a 1 vol.% n-butanol-water solution. Fluorination also changes the catalytic activity of the zeolite as measured by an n-butane cracking method. 

Figure 5. Product selectivity for n-butane cracking over (a) hydrothermally-treated sample H3, and (b) AHFS-treated sample FS9.363. The reaction products are methane (0), ethane and ethene (A), propane (O), isobutane (b), but-l-ene ( ) and but-2-ene (a).

The transformation of n-butane over the Ga and Zn modified ZSM-5 catalysts produced similar aromatic hydrocarbons and gaseous products as over H-ZSM-5. Ethyl benzene was the only aromatic which was not formed with the proton form catalyst. Ga-H-ZSM-5 and Zn-H-ZSM-5 exhibited higher catalytic activity and selectivity to aromatics than the H-ZSM-5 catalyst The amount of cracking products formed for Ga- and Zn- modified catalysts were smaller than for ZSM-5 in its proton form. Toluene constituted almost 50 % of the aromatics formed while benzene, xylenes and ethylbenzene formed the rest The conversion of n-butane and selectivity to aromatic hydrocarbons increased with increasing temperature. The effect of temperature on n-butane conversion and aromatic selectivity over the catalysts is given in Figures 4 and 5. The product selectivity obtained from the transformation of n-butane over the H-ZSM-5, Ga-H-ZSM-5 and Zn-H-ZSM-5 catalysts at 803 K is given in Table 1. 

Table IX. Maximum n-Butane Cracking Values (kA) for Selected MeAPO Molecular Sieves...

Hydrogenolysis reactions over Ir single crystals and supported catalysts have also been shown to be structure sensitive [M, M and M] In particular, it was found that the reactivity tracked the concentration of low-coordination surface sites. Figure A3.10.22 shows ethane selectivity (selectivity is reported here because both ethane and methane are products of butane cracking) for -butane hydrogenolysis over Ir(l 11) and the reconstructed surface Ir(l 10)-(1 x 2), as well as two supported Ir catalysts. There are clear selectivity differences between the two Ir surfaces, with Ir(l 10)-(1 x 2) having approximately three times the ethane selectivity of Ir(l 11). There is also a similarity seen between the ethane selectivity on small Ir particles and Ir (110)-(1 X 2), and between the ethane selectivity on large Ir particles and Ir(l 11). 

Lead Photo KBR s SCORE (Selective Cracking Optimum REcovery) technology is used at the Olefins Plant of Saudi Kayan Petrochemical Complex (A project of SABIC) in Al Jubail, Kingdom of Saudi Arabia. The photo shows the ethane/ butane cracking furnaces, which are part of this 1.35 million tpy cracker scheduled to startup in second quarter 2010. Photo courtesy of Saudi Kayan. 

The effect of cationic EFAL species on catalytic activity, has been shown by comparing steam stabilized and zeolite Y dealuminated by (KH4)2SiFj treatment. While Creighton et al. (100) found the same selectivity, Beyerlain et al. (101) show that clean framework "fresh" zeolite Y dealuminated by (NH4)2SiFs, gave a lower i-butane cracking activity that the same sample after mildly steamed. 

As part of the same study selectivity data were provided at 10-100 kPa partial pressures of n-butane at 0-17% conversion over HZSM-5 [90]. With increase in pressure and conversion secondary reactions started to occur. These results are also summarized in Table 13.6. The lowered selectivity to hydrogen, methane and ethane was attributed to increasingly less favorable conditions for monomolecular cracking. The dramatic increase in selectivity to propane which was absent at zero conversion, along with decrease in propylene was considered as signature for bimolecular cracking. More specifically, it was suggested that hydride transfer... 

C4 Hydrorefining. The main components of typical C4 raw cuts of steam crackers are butanes (4-6%), butenes (40-65%), and 1,3-butadiene (30-50%). Additionally, they contain vinylacetylene and 1-butyne (up to 5%) and also some methylacetylene and propadiene. Selective hydrogenations are applied to transform vinylacetylene to 1,3-butadiene in the C4 raw cut or the acetylenic cut (which is a fraction recovered by solvent extraction containing 20-40% vinylacetylene), and to hydrogenate residual 1,3-butadiene in butene cuts. Hydrogenating vinylacetylene in these cracked products increases 1,3-butadiene recovery ratio and improves purity necessary for polymerization.308... 

Table 7 shows the yield distribution of the C4 isomers from different feedstocks with specific processing schemes. The largest yield of butylenes comes from the refineries processing middle distillates and from olefins plants cracking naphtha. The refinery product contains 35 to 65% butanes olefins plants, 3 to 5%. Catalyst type and operating severity determine the selectivity of the C4 isomer distribution (41) in the refinery process stream. Processes that parallel fluid catalytic cracking to produce butylenes and propylene from heavy cmde oil fractions are under development (42). 

Some of the many solvents that have been examined for certain hydrocarbon separations are listed in Table 13.8 part (c) for n-butane and butene-2 separations includes data showing that addition of some water to the solvent enhances the selectivity. The diolefins butadiene and isoprene are available commercially as byproducts of cracking operations and are mixed with other close-boiling saturated, olefinic and acetylenic hydrocarbons, often as many as 10-20 different ones. The most widely used extractive... 

Table III gives a range of the possible feedstocks that can be used to produce ethylene and the kinds and amounts of by-products that can be made from them. For our purposes we have selected a constant basis of 1 billion lbs/year ethylene production. The feedstocks illustrated in Table III include ethane, propane, n-butane, a full range naphtha, a light gas oil, and a heavy gas oil. The yields reflect high severity conditions with recycle cracking of ethane in all cases. For propane feed, propane recycle cracking has been included as well.

Figure 3. Selectivity to gases, Cl + C2, Gasoline, Diesel, Coke and Butene/Butane ratio of samples USY-1 ( ) and U1F-25 ( ) in gas-oil cracking.

The dehydrogenation process feed can be refinery streams from the catalytic cracking processes. This mixed C4 stream typically contains less than 20 percent n-butenes. For use in dehydrogenation, however, it should be concentrated to 80-95 percent. The isobutylene generally is removed first by a selective extraction-hydration process. The n-butenes in the raffinate are then separated from the butanes by an extractive distillation. The catalytic dehydrogenation of n-butenes to 1,3-butadiene is carried out in the presence of steam at high temperature (>600°C) and... 

Should MTBE be banned, what would be the logical replacement(s) There are several options available. Several refiners opted to build MTBE capacity and avoid purchasing the ether on the open market. MTBE units were an option to use the facility s isobutylenes. Several licensed processes can be used to convert existing MTBE units. Kvaerner and Lyondell Chemical Co. offer technologies to convert an MTBE unit to produce iso-octane, as shown in Fig. 18.27.12 Snamprogetti SpA and CDTECH also have an iso-octene/iso-octane process. These processes can use various feedstocks such as pure iso-butane, steam-cracked C4 raffinate, 50/50 iso-butane/iso-butene feeds, and FCC butane-butane streams. The process selectively dimerizes C4 olefins to iso-octene and then hydrogenates the iso-octene (di-iso-butene) into iso-octane. The processes were developed to provide an alternative to MTBE. The dimerization reactor uses a catalyst similar to that for MTBE processes thus, the MTBE reactor can easily be converted to... 

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