Ethylene thermal alkylation

The main products formed by the catalytic alkylation of isobutane with ethylene (HC1—AICI3, 25-35°C) are 2,3-dimethylbutane and 2-methylpentane with smaller amounts of ethane and trimethylpentanes.13 Alkylation of isobutane with propylene (HC1—AICI3, — 30°C) yields 2,3- and 2,4-dimethylpentane as the main products and propane and trimethylpentanes as byproducts.14 This is in sharp contrast with product distributions of thermal alkylation that gives mainly 2,2-dimethylbutane (alkylation with ethylene)15 and 2,2-dimethylpentane (alkylation with propylene).16... 

Thermal alkylation was never a totally successful commercial process because of the severe operating conditions required. The reaction was carried out in a heater coil with temperatures of 900°-975°F, pressures in the range of 3000-5000 psig, and contact times of 2-7 seconds (16). Polymerization of the olefins occurred readily under these conditions, and low olefin concentrations had to be used to minimize undesirable side reactions. Ethylene could be alkylated more readily than the higher molecular weight olefins, and either normal butane or isobutane could react with the olefin. In general, the yields and quality of the product were not equal to those obtained with catalytic alkylation. 

The thermal alkylation of ethylene-isobutane mixtures at high pressures in the gas phase has been studied in the presence and absence of HCl, and it has been found that HCl can (a) dramatically increase the total yield of alkylate, (b) increase the fraction of the alkylate which is C6 rather than C8> and (c) both increase and decrease the ratio of 2-methyl pentane to 2J2-dimethylbutane in the C6 fraction of the alkylate, this latter depending on the amount of HCl used. All of these effects can be explained readily in terms of the generally accepted free radical mechanism of thermal alkylation, provided one assumes that HCl acts as a catalyst for those reaction steps that involve transfer of a hydrogen atom between a free radical and a hydrocarbon. 

While it has been less generally recognized, there are free radical reaction systems in which hydrogen atom transfer between radicals is not rate controlling but does control the selectivity with which the various possible reaction products are formed. This chapter is a study of the effect of HCl on such a reaction system, the thermal alkylation of ethylene. (The effect of HCl upon this reaction was first disclosed in one of the authors patents (4). Several years after this disclosure, Schmerling (6) published a paper which, though differing in many details, showed... 

Thus, it would appear that catalyzing the thermal alkylation with HC1 might achieve the same result as operation at high isobutane-to-ethylene ratio. 

To study the relative ease with which various hydrocarbons undergo thermal alkylation with ethylene, a mixture of propane, normal butane, isobutane, and neopentane (9.2 mol % each), 4.6 mol % C2H4, and 17 mol % HC1 were reacted at 399°C and at an initial pressure of 177 atm for 1 hr. The yields of the alkylation products (nC5Hi0 and iC5H10 from C3H6 nC6Hi4 and 3-methyl pentane from nC4Hi0 2-methyl pentane and 2,2-dimethyl butane from isobutane and 2,2-dimethyl pentane from neopentane) were measured and are shown in Table I on a relative basis. 

Thermal alkylation occurs readily with ethylene, less readily with propene and n-butylenes, and with difficulty with isobutylene. (As wiU be shown, the reverse is true in catalytic alkylation.) The reaction of propane with propene at 505° and 6300 p.s.i. yielded a liquid product containing 18.0% 2,3-dimethylbutane, 17.7% 2-methylpentane, and 5.4% n-hexane. An even higher pressure, 8000 p.s.i. was required for the reaction of isobutylene with isobutane at 486° the liquid product, whose yield was only 10-20% of that obtained when ethylene w as used, contained 34.0% octanes but also 32.7% octenes. 

Thermal Alkylation. Whereas sulfuric acid alkylation operates most successfully on isobutylene, the butenes, and propylene, thermal alkylation acts most readily on ethylene followed by propylene, butenes, and... 

Acetal Resins. Acetal resins (qv) are poly (methylene oxide) or polyformaldehyde homopolymers and formaldehyde [50-00-0] copolymeri2ed with ahphatic oxides such as ethylene oxide (42). The homopolymer resin polyoxymethylene [9002-81-7] (POM) is produced by the anionic catalytic polymeri2ation of formaldehyde. For thermal stabiUty, the resin is endcapped with an acyl or alkyl function. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

Alkylation in the petroleum industry, a process by which an olefin (e.g., ethylene) is combined with a branched-chain hydrocarbon (e.g., isobutane) alkylation may be accomplished as a thermal or a catalytic reaction. 

The utilization of polar polymers and novel N-alkyl-4-(N, N -dialklamino)pyridinium sedts as stable phase transfer catalysts for nucleophilic aromatic substitution are reported. Polar polymers such as poly (ethylene glycol) or polyvinylpyrrolidone are thermally stable, but provide only slow rates. The dialkylaminopyridininium salts are very active catalysts, and are up to 100 times more stable than tetrabutylammonium bromide, allowing recovery and reuse of catalyst. The utilization of b is-dialkylaminopypridinium salts for phase-transfer catalyzed nucleophilic substitution by bisphenoxides leads to enhanced rates, and the requirement of less catalyst. Experimental details are provided. 

Alkylation, In petrochemicals, any reaction involving the thermal or catalytic addition of an olefin to a branch-chain hydrocarbon or aromatic hydrocarbon. The most notable example in petrochemicals is the addition of ethylene or propylene to benzene to produce ethylbenzene or isopropyl benzene (cumene). Other examples include the production of detergent alkylates. 

Reactions conducted in molten quaternary phosphonium salts require no other solvent (199). This material serves as both promoter and reaction medium. Care must be exercised in choosing the salt in such a reaction, since any decomposition could lead to products such as trialkylphosphines and alkyl halides which are expected to be deleterious to catalyst performance. Tetrabutylphosphonium bromide is reported to provide a stable catalyst medium which can be recycled (199, 200), but other related salts show evidence of thermal decomposition during catalytic reactions. Experiments in tetrabutylphosphonium acetate, for example, are found to produce large amounts of methyl and ethylene glycol acetate esters (199). 

The use of thermal and catalytic cracking processes for the production of high-octane motor gasolines is accompanied by the production of quantities of light hydrocarbons such as ethylene, propylene, butene, and isobutane. These materials are satisfactory gasoline components octane-wise, but their vapor pressures are so high that only a portion of butanes can actually be blended into gasoline. Alkylation is one of several processes available for the utilization of these excess hydrocarbons. 

Successful catalytic alkylation of isobutane with ethylene has been accomplished in one commercial installation using aluminum chloride catalyst (I). The chief product of the reaction is 2,3-dime thy lbutane, a hydrocarbon having very high aviation octane ratings. Ethylene has also been alkylated with isobutane in a thermal process to give 2,2-dimethylbutane as the chief product component (6). When sulfuric or hydrofluoric acid alkylation with ethylene is attempted, the ethylene forms a strong bond with the acid, and fails to react with isobutane. The net result is the formation of little or no product, accompanied by excessive catalyst deterioration. 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

These monomers are also produced by an oxidative process in which the alkanols are added directly lo ethylene and Ihe alkyl ethers are thermally decomposed to produce hydrogen and the alkyl vinyl ethers. 

The conventional resinsulfonic acids such as sulfonated polystyrenes (Dowex-50, Amberlite IR-112, and Permutit Q) are of moderate acidity with limited thermal stability. Therefore, they can be used only to catalyze alkylation of relatively reactive aromatic compounds (like phenol) with alkenes, alcohols, and alkyl halides. Nafion-H, however, has been found to be a suitable superacid catalyst in the 110-190°C temperature range to alkylate benzene with ethylene (vide infra) 16 Furthermore, various solid acid catalysts (ZSM-5, zeolite /3, MCM-22) are applied in industrial ethylbenzene technologies in the vapor phase.177... 

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. 

Because of the large excess of ethylene present in the growth reactor, the reverse reaction is insignificant. Ethylene reacts with dialkyl aluminum hydride much more rapidly than does the terminal olefin, and any alkyl group thermally displaced is replaced by an ethyl group. However, terminal olefin present in the growth reactor can react with trialkylaluminum compounds. The a-olefin inserts between the aluminum-carbon bond just as ethylene does in a normal growth process. 

The growth reaction is carried out below 130°C to prevent the alkyl decomposition or thermal displacement (13) described earlier. Ethylene pressure is maintained at approximately 1600 psig. Temperature, pressure, and residence time are adjusted to obtain the desired extent of chain growth or "m-value. Excess ethylene is flashed from the trialkylaluminum product or "growth product and recycled. 

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