Isobutene, from 1-butene

In the case of propylene and 1,3-butadiene the lifetimes can be readily evaluated from the trends in Figures 1 and 2. In doing this, it is assumed that sufficient energy is removed in a single collision to prevent decomposition of the hot molecule. The values obtained in this manner are given in Table I. For isobutene and butene-1 approximate values... 

Laboratory development of Triolefin Process technology for synthesizing isoamylene, an intermediate in polyisoprene production, was reported by Banks and Regier 571. Isoamylene purity of 92 per cent and isoamylene yield of 1.0 pounds per pound of isobutene converted were obtained with feeds containing isobutene, propylene, and n-butenes. Isobutene converted to C6+ byproduct was recovered by cleaving the C6+ material with ethylene or propylene to yield butenes and pentenes. Process for producing isoprene from butene streams is the subject of a patent issued to McGrath and Williams 1011. 

Alkylate is a gasoline blending component with exceptional antiknock properties, which seems to avoid the legislative pressure. Alkylate consists exclusively of isoalkanes and is obtained from the C3-C4 cut of the FCC units. In many instances, isobutene from the C3-C4 fraction is transformed selectively with methanol into methyl tert-butyl ether (MTBE). Therefore, a mixture of 1-butene and 2-butene is used for alkylation purposes. The other reactant is isobutane. The major constituents of the alkylate are 2,2,3-, 2,2,4-, 2,3,3- and 2,3,4-trimethyl pentane (TMP). Besides, the alkylate contains other C8 isoalkanes, such as dimethyl hexane (DMH), 3-ethyl 2-methyl pentane, methyl heptane and ethyl hexane, and even isoalkanes with carbon numbers that are not multiples of 4. 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

With trimers, he observed that 75-83 percent of the trimer depolyalky-lated. He rationalized further that dimers could behave similarly this is a moot point, because yields of alkylate from butene monomers and dimers are identical when the alkylate formed during chain termination is considered. It was observed (Phillips Petroleum Comp>any, 1946) that Isobutene-butene copolymer yielded alkylate identical to that from the monomers. 

Fig. 2. Conversion from butene to isobutene, at 430°C,(1-butene 5 ml/min, Nz 50 ml/min, Cat=2g) over catalysts AS2, ASM and ASM3 compared with alumina [14].

In polar solvents the excited state of sufficiently electron deficient arenes will accept an electron from donors. The fates of the radical ion pairs produced include formation of products of addition to the arene ring. A new example of this mode of reactivity is the photochemical reaction of 1,4-dicyanonaphthalene with benzyl methyl ether in acetonitrile. This yields stereoisomers of the addition product (120). The reaction most likely involves electron transfer from the ether to the naphthalene excited state and subsequent ionisation of a proton from the benzyl ether radical cation. This produces a benzyl ether radical which adds to the naphthalene derivative. An analogous sequence is proposed to explain the photochemical formation of (121)-(124) from ultra-violet light irradiated solutions of naphthalene-1,2-dicarboxylic acid anhydride in methanolic benzene or acetonitrile containing isobutene, 2-butene or 2-methyl-2-butene. Here it is suggested that the alkene radical cation, formed by electron transfer to the excited state of the naphthalene, is attacked by methanol deprotonation... 

Fig. 5.1. Chromatograms of products of catalytic cracking (A) without reactor and (B) with reactor. Sorbent, 11% quinoline on refractory brick temperature, 25 C column length, 10.5 m. Peaks 1 = propane 2 = propylene 3 = isobutane 4 = n-butane 5 = isobutene 6 = butene-1 7 = rmns-butene-2 8 = cis-butene-2 9 = isopentane 10 = 3-methylbutene-l 11 = n-pentane 12 = pentene-1 13 = 2,2-dimethylbutene 14 = 2-methylbutene-l 15 = tnms-pentene-2 16 = cfsi)entene-2 17 = 2-methyl-butene-2 18 = 2,3-dimethylbutane 19 = 2-methylpentane 20 = 3-methylpentane 21 = 3-methylpen-tene-1 22 = 4-methylpentene-l 23 = c -4-methylpentene-2 24 = cyclopentane 25 = 2,3-dimethyl-butene-1 26 = fmns-4-methylpentene-2 27 = w-hexane 28 = cyclopentene 29 = 2-methylpentene-l 30 = hexene-1 31 = 2,4-dimethylpentane 32 = cis-hexene-3 33 = tnms-hexene-3 34 = 2-ethylbu-tene-1 35 = trans-hexene-2 36 = methylcyclopentane 37 = cis-methylpentene-2 38 = 2-methylpen-tene-2 39 = pisns-3-methylpentene-2 40 = methylcyclopentene-4 41 = 4-methylcyclopentene 42 = cw-3-methylpentene-2 43 = 2,3-dimethylpentane 44 = 2-methylheptane 45 = 2,3-dimethylbutene-2 46 = methylheptane 47 = cyclohexane 48 = C, olefin. Reprinted with permission from ref. 1.

Industrially, MTBE is synthesized from methanol and C4 cuts, mainly containing isobutene, 1 -butene, n-butane, cis-, trans-2-butene and isobutane. The involved reaction is the addition of methanol (MeOH) to isobutene (IB) to form MTBE. Both reactants are relatively cheap and the reaction can be carried out under mild conditions (313-363 K and 1.6 MPa). Reactor feed contains IB and MeOH in a molar ratio IBiMeOH 1 1.1 to minimize the extent of side-reactions and to achieve very high IB conversions, because chemical equilibrium is shifted to the product formation. 

Such a sequence explains, for instance, the formation of the same secondary ozonide from cis or trani-stilbene, and the isolation of the secondary ozonide of isobutene from the ozonolysis of 2,3-dimethyl-2-butene in the presence of formaldehyde -, viz-... 

Monomer Synthesis. Isobutylene is mainly produced from cracked petroleum gases. The cracked gases are passed through sulfuric acid of specific strength so that isobutylene is selectively absorbed and thus separated from butene-1. In this isobutylene synthesis from petroleum, care must be taken to ensure that sulfur compounds are completely removed, since they are poisons toward polymerization catalysts. This danger does not arise when isobutene is obtained by water elimination from isobutanol on passing over AI2O3. 

Isobutene, the main feedstock, is obtained in the form of raffinate from steam crackers, which make up an estimated 40% of MTBE feedstock throughout the world. Isobutene in the form of butene-butane fractions from fluid catalytic crackers represents 28% of MTBE feedstocks isobutene from dehydrogenation of isobutane represents 12% of MTBE feedstocks and isobutene by dehydration of tert-butanol represents 36% of MTBE feedstocks. The Butamer process is often used for the primary butane isomerization, while the Catofln and Olefex processes are commonly used for the isobutane dehydrogenation. 

Figure 4.36. Formation of isobutene from n-butene through a tertiary carbon on coke aromatics ].

The barriers for formation of ethylene, propene, 2-butene and isobutene from the alkoxy HPW states were calculated to be 114, 93.7, 87.8 and 64 kJ/mol, respectively, as compared with the value of 83 kJ/mol for propene over chabazite. Cleavage of the alkoxide bond initiates consecutive reaction steps necessary for many hydrocarbon conversion reactions. 

Butenes are usually obtained from Crack C via naphtha steam cracking (Scheme 4.4) [31]. After the removal of butadiene and isobutene from the crude stream, the so-called Raffinate II contains 1-butene, cis/trans-2-hutene, and the isomeric butanes. Alternatively, it has been produced for a subsequent hydroformylation by dehydrogenation of n-butane on a Cr on alumina... 

Butadiene, isobutene, and butenes (1-butene, cis-2-butene, and traws-2-butene) are isolated from the C4 cut of the steam cracker in a sequence of separation units that is depicted in Figure 5.3.6. In the first step, butadiene (representing roughly 50% of the cracker C4 cut) is isolated from the other C4 components by an extractive... 

The next step in the cracker C4 treatment is the isolation of isobutene from Raffinate 1. To realize this step. Raffinate 1 is reacted with water or methanol to form tert-butanol or methyl-iert-butyl ether, respectively. Ahematively, Raffinate 1 can be treated with an acid catalyst to convert isobutene selectively into isooctene, an important fuel additive. All Raffinate 1 treatment processes have in common that isobutene reacts selectively from the mixture to form a compound of significantly lower vapor pressure. Thus, in the subsequent distillation process, the isobutene adduct is the low boiling component and remains at the bottom of the distillation column while the remaining C4-compounds can be isolated at the top. The obtained distillate is called Raffinate 2 and consists typically of 45% 1-butene, 30% 2-butenes, 19% butanes, 6% isobutane, and traces of 1,3-butadiene. Raffinate 2 can be applied as feedstock for a distillation unit that isolates 1-butene from the mixture for copolymerization apphcations. Alternatively, Raffinate 2 can be fed into a dimerization unit where either a homogeneous (Dimersol-process) or a heterogeneous Ni-catalyst (Octol process) converts the butenes into Cg dimers. Unconverted feedstock of this unit is called Raffinate 3. It typically contains around 70% butane and isobutane and 30% of remaining linear butenes. Raffinate 3 is recycled to the cracker to serve their as an addition to the cracker feed. 

The dry products from the drying unit are first separated in the C2/C3+ spUtter. The C2-fraction contains hydrogen, acetylene, ethene, and ethane. The C3+-fraction contains propyne, propene, propane, the C4 products (butadiene, isobutene, n-butenes, butane), and the C5+ fraction, which is unified with the pygas collected from the cooling and compression units. 

The C3+-fraction of the C2 /C3+ splitter enters the C3/C4+ splitter that separates propane, propene, propadiene, and propyne from all heavier products. The C3 stream undergoes a selective hydrogenation step in a fixed bed reactor that converts propyne and propadiene mainly into propene. Propene and propane are separated in a very similar way as ethane/ethene. Again, distillation columns with more than 100 trays are applied, making these separation units very costly in investment and energy consumption. The bottom fraction of the C3/C4+ splitter is transferred to C4/C5+ splitter. The C4 fraction leaving this column at the top contains mainly butadiene, isobutene, 1-butene, 2-butene, and butane. The further use of this crack-C4 mixture is described in detail in Section 5.3. 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

Olefin Separation. Olefin-containing streams are separated either by the OlefinSiv process (Union Carbide Corp.) separating / -butenes from isobutenes in the vapor phase, or the Olex process (Universal Oil Product) a Hquid-phase process. 

In commercial extraction operations, the fractions that contain butadiene, isobutene, and 1- and 2-butenes usually first go through a butadiene extraction unit in which the butadiene is removed. This may be followed by isobutylene removal via reaction between isobutylene and methanol to form methyl /-butyl ether [1634-04-4] (MTBE). The butenes are then distilled from the MTBE. 1-Butene may then be separated from 2-butene by distillation. 

Figure 2-1 shows the two processes for the separation of n-butenes from isobutene. ... 

The three isomers constituting n-hutenes are 1-hutene, cis-2-hutene, and trans-2-hutene. This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene (Chapter 2). The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same intermediates and hence the same products. Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis-and trans-2-butene mixture. Each stream produces specific chemicals. Approximately 70% of 1-butene is used as a comonomer with ethylene to produce linear low-density polyethylene (LLDPE). Another use of 1-butene is for the synthesis of butylene oxide. The rest is used with the 2-butenes to produce other chemicals. n-Butene could also be isomerized to isobutene. ... 

Upon examining the data for the reactions of all four butene isomers (Fig. 37), the most striking observation is that the data for all four isomers are quite similar, except that there is no YH2 formed from isobutene. In addition, the branching ratios for each isomer are similar, except that 4>ych2 OyCiHe, is approximately a factor of two greater for isobutene than for the other isomers, and for propene, YCH2 is a much more important channel than is YH2 (Fig. 40), a situation that is exactly the opposite to that for the butene reactions (Fig. 37). 

Because hydrogen can easily be removed from a reaction stream, many dehydrogenations have been studied. These include dehydrogenation of methane to carbon,326 ethane to ethene,327,328 propane to propene,329 n-butane to butenes,330 isobutane to isobutene,331,332 cyclohexane to benzene,332-334 meth-ylcyclohexane to toluene 335 n-heptane to toluene,336 methanol to formaldehyde,330 and ethanol to acetaldehyde.337... 

---