Cracking, thermal butane

As indicated in Table 4, large-scale recovery of natural gas Hquid (NGL) occurs in relatively few countries. This recovery is almost always associated with the production of ethylene (qv) by thermal cracking. Some propane also is used for cracking, but most of it is used as LPG, which usually contains butanes as well. Propane and ethane also are produced in significant amounts as by-products, along with methane, in various refinery processes, eg, catalytic cracking, cmde distillation, etc (see Petroleum). They either are burned as refinery fuel or are processed to produce LPG and/or cracking feedstock for ethylene production. 

Reactions of /l-Butane. The most important industrial reactions of / -butane are vapor-phase oxidation to form maleic anhydride (qv), thermal cracking to produce ethylene (qv), Hquid-phase oxidation to produce acetic acid (qv) and oxygenated by-products, and isomerization to form isobutane. 

Thermal Cracking. / -Butane is used in steam crackers as a part of the mainly ethane—propane feedstream. Roughly 0.333—0.4 kg ethylene is produced per kilogram / -butane. Primary bv-pioducts include propylene (50 57 kg/100 kg ethylene), butadiene (7-8.5 kg/100 kg), butylenes (5-20 kg/WO kg) and aromatics (6 kg/ToO kg). 

Production of maleic anhydride by oxidation of / -butane represents one of butane s largest markets. Butane and LPG are also used as feedstocks for ethylene production by thermal cracking. A relatively new use for butane of growing importance is isomerization to isobutane, followed by dehydrogenation to isobutylene for use in MTBE synthesis. Smaller chemical uses include production of acetic acid and by-products. Methyl ethyl ketone (MEK) is the principal by-product, though small amounts of formic, propionic, and butyric acid are also produced. / -Butane is also used as a solvent in Hquid—Hquid extraction of heavy oils in a deasphalting process. 

About 35% of total U.S. LPG consumption is as chemical feedstock for petrochemicals and polymer iatermediates. The manufacture of polyethylene, polypropylene, and poly(vinyl chloride) requires huge volumes of ethylene (qv) and propylene which, ia the United States, are produced by thermal cracking/dehydrogenation of propane, butane, and ethane (see Olefin polymers Vinyl polymers). 

Butadiene. Although butadiene was produced in the United States in the eady 1920s, it was not until the start of Wodd War 11 that significant quantities were produced to meet the war effort. A number of processes were investigated as part of the American Synthetic Rubber Program. Catalytic dehydrogenation of / -butenes and / -butanes (Houdry process) and thermal cracking of petroleum hydrocarbons were chosen (12). 

Thermal Cracking. Heavy petroleum fractions such as resid are thermally cracked in delayed cokers or flexicokers (44,56,57). The main products from the process are petroleum coke and off-gas which contain light olefins and butylenes. This stream also contains a considerable amount of butane. Process conditions for the flexicoker are more severe than for the delayed coker, about 550°C versus 450°C. Both are operated at low pressures, around 300—600 kPa (43—87 psi). Flexicokers produce much more linear butenes, particularly 2-butene, than delayed cokers and about half the amount of isobutylene (Table 7). This is attributed to high severity of operation for the flexicoker (43). 

Thermal cracking takes place without a catalyst at temperatures up to 900 °C. The exact processes are complex, although they undoubtedly involve radical reactions. The high-temperature reaction conditions cause spontaneous homolytic breaking of C-C and C-H bonds, with resultant formation of smaller fragments. We might imagine, for instance, that a molecule of butane... 

Under certain conditions the product from the thermal cracking of butane has the wt% composition given in the table. Find the mols of product per mol of butane converted. 

Butadiene, used for the production of elastomers, is produced by the catalytic thermal cracking of butane and as a by-product of other cracking reactions. 

Feed stock for the first sulfuric acid alkylation units consisted mainly of butylenes and isobutane obtained originally from thermal cracking and later from catalytic cracking processes. Isobutane was derived from refinery sources and from natural gasoline processing. Isomerization of normal butane to make isobutane was also quite prevalent. Later the olefinic part of the feed stock was expanded to include propylene and amylenes in some cases. When ethylene was required in large quantities for the production of ethylbenzene, propane and butanes were cracked, and later naphtha and gas oils were cracked. This was especially practiced in European countries where the cracking of propane has not been economic. 

The analysis of the product gas, calculated to a hydrogen-free basis, is shown in Table II. The high percentage of methane and the predominance of n-butane and n-pentane over the branched compounds suggest that they were produced by a thermal cracking reaction with hydrogenation of the olefins. 

Mol, Visser, and Boelhouwer 741 subjected 1,2-dimethyl-butane (ring structure of the suggested transition state for disproportionation of propylene) to rhenium oxide-alumina catalyst under conditions which propylene gives high disproportionation conversions. This compound was stable only at high temperatures (730 °C), where thermal cracking occurred, were olefins found. 

Ethylene is a key building block for the petrochemical industry. It is usually made by thermally cracking gases—ethane, propane, butane, or a mixture of these—as they exist in refinery off-gases. When gas feedstocks are scarce or expensive, naphthas and even whole... 

Higher hydrocarbons. Thermal cracking of higher hydrocarbons is believed to occur with Rice-Herzfeld-type mechanisms [45,46], Of course, with more carbon atoms in the molecule, more free radicals of different carbon numbers appear and produce a greater variety of products. As a still relatively simple example, the network of principal steps in cracking of n-butane is [47,48] ... 

Rates of thermal cracking are first-order in good approximation for propane, butane and still higher hydrocarbons [21], This is remarkable because chain mechanisms with initiation by break-up of a reactant normally result in reaction orders of one half or one-and-a-half, depending on which radical is consumed by termination. First-order behavior can result from "mixed" termination, which, however, can in most cases be ruled out as dominant mechanism (see Section 9.3). A more probable explanation is a combination of effects that key hydrocarbon radicals participate in several steps of different molecularities, that some steps are reversible, and that some unimolecular ones require collision partners. 

Examples include the hydrogen-bromide reaction, thermal cracking of ethane and n-butane, oxidation of cyclohexane, and the hydrogen-oxygen reaction. 

Fuel Gas yield Thermal vs. Catalytic Cracking. A higher ratio of fuel gas/iso-butane was found in the case of the MR, which is to be expected with a relatively low catalyst volume fraction and longer residence time of the hydrocarbons in the reactor (see Table I). With increasing catalyst fraction (or conversion) the ratio decreases due to the formation of more iso-butane. A reduction in contact time will also result in a lower ratio, because fewer thermal cracking reactions will take place. 

Butadiene, a substance used industrially to make polymers, is prepared by thermal cracking of butane over a chromium oxide/aluminum oxide catalyst, but this procedure is of little use in the laboratory. 

Thermal cracking of ethane, propane, butane, naphthas, gas oils, and/or vacuum gas oils is the main process employed for the production of ethylene and propylene butadiene and benzene, toluene, and xylenes (BTX) are also produced. Thermal cracking of these hydrocarbons is also called pyrolysis of hydrocarbons. Ethylene is the organic chemical produced worldwide in the largest amoimts and has been called keystone to the petrochemical industry. This technology is well documented in the literature. Somewhat similar thermal cracking processes are used to produce vinyl chloride monomer (VCM) from ethylene dichloride (EDQ, styrene from ethylbenzene, and allyl chloride from propylene dichloride (PDC). Production of charcoal and coke from wood and coal is actually a pyrolysis process, but it is not discussed here. 

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