Methanol, reaction with isobutene

It is manufactured by the reaction of isobutene with methanol. The reaction is highly selective and practically any C4 stream containing isobutene can be used as a feedstock... 

Chain-Transfer with anisole. The phenomenon of chain-transfer, especially with aromatic compounds, has been extensively investigated for the polymerisation of styrene, but there is only one such study with isobutene [13]. Isobutene (0.1 mole/l) was polymerised by titanium tetrachloride (3 x 10 3 mole/l) in methylene dichloride with a constant, low, but unknown concentration of water in the presence of anisole (0.02 to 0.15 mole/l) over the temperature range -9° to -90°. The reactions were stopped at 10-20 per cent conversion by the addition of methanol. 

Two recent papers report the main features of the heterogeneously catalysed addition of alcohols to alkenes [364,365]. The reaction proceeds both in the liquid and gas phase [364], and the temperature must be kept well under 150°C with respect to the position of the equilibrium [364], The reactivity of isobutene and 2-methyl-l-butene is much higher than that of propene, 2-butene and 3-methyl-l-butene [364,365]. 2-Methyl-l-butene reacts faster than 2-methyl-2-butene [365]. The reactivity of alcohols with isobutene decreases in the order methanol > ethanol > 1-propanol > 1-butanol [365]. 

MTBE is currently synthesized industrially from methanol and isobutene over an acidic ion-exchange resin, mostly Amberlyst 15 which is in fact a macroreticular cation-exchange resin [1,2]. ETBE which is obtained by reaction of isobutene with ethanol, is also an attractive octane enhancer for gasoline [3]. Although the commercial catalyst is very efficient, it suffers from several drawbacks such as thermal instability, acid leaching from the resin... 

In the isobutane process the f-butanol (TBA) co-product is converted to the gasoline additive, methyl t-butyl ether (MTBE), via dehydration to isobutene and reaction with methanol. The theoretical weight ratio of TBA/PO is 1.32 1 but commercial plants produce 2-3 kg TBA per kg, depending on demand. Because of the very large gasoline pool, marketing 2-3 kg of TBA per kg PO is not a problem. 

The synthesis of MTBE is carried out in the liquid phase over a fixed bed of ion exchange resin in the form. The rate of reaction of isobutene with methanol is much higher than that of the n-butenes (isobutene forms a relatively stable tertiary carbenium ion in the first step), which enables the selective conversion of isobutene in the presence of the M-butenes. In fact, streams with an isobutene content as low as 5% can be converted. 

A problem present in the refinery is that, due to its fast transport in water and low biodegradabUity, MTBE addition to gasoline pool has been banned in some countries (from 2003 in Cahfomia). MTBE is formed by add-catalyzed reaction of isobutene with methanol. Other alcohols could be used to form different oxygenated additives, as discussed below, but the alternative is to use isobutene for conversion into another high octane number component such as isooctane, which could substitute in part the need of the alkylation process and related environmental/safety problems. 

The conventional MTBE synthesis consists of a reaction of isobutene and methanol over an acidic sulfonated cation-exchange catalyst. This reaction is highly selective, equilibrium-limited, and exothermic in nature. Several types of industrial reactors such as tubular reactors, adiabatic reactors with recycle, and catalytic distillation configurations have been utilized to cany out the MTBE synthesis reaction. The factors considered in the optimal design of a MTBE unit include the following items [52]. 

ETBE (ethanol tertiary butyl ether, CgH, 0, density = 760 kg/m, LHV = 36 MJ/kg) is a better ingredient than bioethanol because it is not so volatile, not so corrosive, and has less affinity for water. ETBE-15 fuel is a blend of gasoline with 15% in volume of ETBE. ETBE is obtained by catal5dic reaction of bioethanol with isobutene (45%/55% in weight), noting that isobutene comes from petroleum. The other gasoline-substitute ether, MTBE (methanol tertiary butyl ether, (CH3)3-CO-CH3), is a full petroleum derivate (65% isobutene, 35% methanol). 

The light alkenes (propene, butene and pentene) are important feedstocks for alkylation, oligomerization and the synthesis of ethers (refs. 1,2). MTBE (methyl tert-butyl ether) and TAME (tert-amyl methyl ether) have research octane numbers of 118 and 112 respectively. These premium blend stocks are synthesised by reaction of methanol with isobutene or isopentene (refs. 3,4). The reaction with methanol is selective towards the branched alkenes so that a mixture may be treated and the straight chain alkenes recovered for other processing such as alkylation. 

Reaction rates were measured in the absence of MTBE in a thermostated packed-bed reactor. The reactor was fed with pure isobutene (IB) and methanol (MeOH), with a molar ratio IB/MeOH (Ri/a) between 0.5 and 2. It was operated isothermically in a differential regime, in the absence of mass transfer control. The experiments were carried out at four different temperatures in the range 318-363 K, and the pressure was kept at 1.6 MPa to assure that all the compounds involved in the reaction are in the liquid state. The sulfonic macroporous resin with a styrene-divinylbenzene matrix Bayer K2631 was used as the catalyst. The reactor inlet and outlet were analyzed by a gas chromatograph with a FID detector. Reaction rates were determined from these compositions at the steady state. 

Uhde GmbH Ethers—MTBE C, -cuts from steam cracker and FCC units with isobutene contents range from 12% to 30% Catalytic additive reaction for isobutene and methanol 5 NA... 

After the above discussion on RD of ideal ternary mixtures, in this section two nonideal ternary systems are considered. These are the heterogeneously catalyzed syntheses of the fuel ethers MTBE (methyl tert-butyl ether) and TAME (fert-amyl methyl ether) by etherification of methanol with isobutene or isoamlyenes respectively. Both reaction systems have enormous industrial importance because of the outstanding antiknock properties of MTBE and TAME as gasoline components. 

The framework substitution of Mn(II) is responsible for a variety of phenomena (1) the high selectivity of the MnAPSO-34 toward formation of ethane in the reaction of methanol conversion (231), (2) the catalytic activity of MnAPO-5 in oligomerization of propane (232) and the catalytic activity of MnAPSO-44 in methanol dehydration (233), (3) the high yields in the production of isobutene and isobutene over MnAPSO-11 (234), (4) a sensor ability of MnAPO-5 to detect small molecules as CO, CO2, N,2 and H2O at room temperature (235), (5) MnAPO-5 registered to give 11% yield of p-IPEB and 5.8% yield of m-IPEB at 350°C in isopropylation of ethylbenzene with 2-propanol (236), and (6) cyclohexane (RH) reactions with O2 on MnAPO-5, where the oxidation rates are determined to be proportional to the number of redox-active Mn centers (237) The measurements by H2-O2 reduction-oxidation cycles indicate that these species act as active sites for kinetically relevant elementary steps in alkane oxidation catalytic cycles. 

Felthouse and Mills (321) report the amination of methyl ferf-butyl ether (MTBE) and isobutene to fert-butylamine using alumino- and borosilicate pentasil molecular sieve catalysts. The ether and alkene amination reactions were found to proceed preferentially under SCF conditions at temperatures on the order of 330°C and pressures greater than 193 bar. The smdy showed that MTBE can be used as a substitute raw material for terf-butylamine manufacture, but MTBE decomposition products of isobutene, methanol, and methanol conversion products are produced that require a more complicated product separation process than with isobutene as the only C4 substrate. 

The numbers of acid sites as determined by a titration method were 0.3, 0.2 and 2.0 m mol g for the silica gel modified by methods I, II, and III, respectively. The order of the catalytic activities of the three catalysts for both dehydration of isopropyl alcohol and the reaction of isobutene with methanol was in agreement with the order of the number of acid sites. 

MTBE is produced by reacting methanol with isobutene. Isobutene is contained in the C4 stream from steam crackers and from fluid catalytic cracking m the crude oil-refining process. However, isobutene has been in short supply in many locations. The use of raw materials other than isobutene for MTBE production has been actively sought. Figure 2 describes the reaction network for MTBE production. Isobutene can be made by dehydration of i-butyl alcohol, isomerization of -butenes [73], and isomerization and dehydrogenation of n-butane [74, 75]. t-Butanol can also react with methanol to form MTBE over acid alumina, silica, clay, or zeolite in one step [7678]. t-Butanol is readily available by oxidation of isobutane or, in the future, from syngas. The C4 fraction from the methanol-to-olefins process may be used for MTBE production, and the C5 fraction may be used to make TAME. It is also conceivable that these... 

So-called centre cracking produces a C4-C5 olefin fraction which rapidly isomerises to isobutene and isoamylene. These products were converted to methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME) by reaction with methanol to produce octane-enhancing additives for use in reformulated gasoline. Propane and n-butane are also produced. Fresh ZSM-5 also cracks paraffins imtil the acid site density decreases. Eventually, olefin cracking activity dechnes but isomerization activity is retained. Regular addition of fresh ZSM-5 is therefore required to maintain the shape-selective activity. 

The first system is the production of MTBE from the reaction of methanol with isobutene. The second is the production of ETBE from the reaction of ethanol with isobutene. 

Smith, J.D., J.D. DeSain, and C.A. Taatjes (2002b), Infrared laser absorption measurements of HCl(v = 1) production in reactions of Cl atoms with isobutene, methanol, acetaldehyde, and toluene at 295 K, Chem. Phys. Lett., 366, 417 25. 

Alkenes are scavengers that are able to differentiate between carbenes (cycloaddition) and carbocations (electrophilic addition). The reactions of phenyl-carbene (117) with equimolar mixtures of methanol and alkenes afforded phenylcyclopropanes (120) and benzyl methyl ether (121) as the major products (Scheme 24).51 Electrophilic addition of the benzyl cation (118) to alkenes, leading to 122 and 123 by way of 119, was a minor route (ca. 6%). Isobutene and enol ethers gave similar results. The overall contribution of 118 must be more than 6% as (part of) the ether 121 also originates from 118. Alcohols and enol ethers react with diarylcarbenium ions at about the same rates (ca. 109 M-1 s-1), somewhat faster than alkenes (ca. 108 M-1 s-1).52 By extrapolation, diffusion-controlled rates and indiscriminate reactions are expected for the free (solvated) benzyl cation (118). In support of this notion, the product distributions in Scheme 24 only respond slightly to the nature of the n bond (alkene vs. enol ether). The formation of free benzyl cations from phenylcarbene and methanol is thus estimated to be in the range of 10-15%. However, the major route to the benzyl ether 121, whether by ion-pair collapse or by way of an ylide, cannot be identified. 

The phenyl tellurium tribromide can be prepared in situ from diphenyl ditellurium and bromine. Olefins thus far investigated include isobutene, (E)- and (Z) -butene, 1 -hexene, 2-methyl-l-pentene, 1-octene, (E)- and (Z)-4-octene, 1-decene, phenylethene, 1-phenyl-I-methylethene, cyclopentene, cyclohexene, cycloheptene, and cyclooctene. Most of the reactions were carried out with phenyl tellurium tribromide in methanol. 

Photochemically generated trimethylsilylphenylsilylene also adds to the carbon-carbon double bonds of many types of olefins (54). Thus, the photolysis of a hexane solution of tris(trimethylsilyl)phenylsilane (20) in the presence of isobutene by irradiation with a low-pressure mercury lamp produces, after subsequent treatment of the photolysis mixture with methanol, fert-butylphenyI(trimethylsilyl)methoxysilane in 52% yield, as the sole insertion product. Direct evidence for the formation of 1-trimeth-ylsilyl-l-phenyl-2,2-dimethyl-l-silacyclopropane in this photolysis can be obtained by NMR spectroscopic analysis of the reaction mixture. 

Isobutene was condensed at —78°C into a graduated cylinder under nitrogen, and 12 ml were transferred into a reaction vessel containing 1 g of tri-n-octylaluminum. The mixture was stirred for 30 minutes at —78°C and then transferred to a second reaction vessel. It was then treated with 48 rml of 0.05M l,2-bis(9-bora-l,2,3,4,5,6,7,8-octafluorofluorenyl)-3,4,5,6-tetrafluorobenzene dissolved in toluene, which resulted in an uncontrolled, exothermic polymerization accompanied by rapid gelation of the solution. The mixture was quenched with 1 ml of 0.2M NaOCHs in methanol. The volatiles were removed and the residue washed with methanol then dissolved in hexane. The solution was filtered, concentrated, and the product isolated. Reaction scoping results are provided in Table 1. 

This is an endothennic conversion, which takes place in the gas phase between 150 and 300 C (preferably at about 275 C), at a pressure as low as possible, but suffident to recover the isobutene in the l uid phase by cooling with water, namely about 0.6. 10 Pa absolute. To avoid dehydration side reactions, operations are conducted in the presence of steam, with a typical H2O/MTBE mole ratio at the reactor inlet of 5/1. As in the steam cracking ofhydrocarbons, this procedure serves to reduce the partial pressure of the components and to fedlitate the production of isobutene and methanoL... 

Often isomerization reactions are highly two-way (reversible). For example, the isomerization of 1-butene to isobutene is an important step in the production of methyl tertiary butyl ether (MTBE), a common oxygenated additive in gasoline used to lower emissions. MTBE is produced by reacting isobutene with methanol ... 

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