Isoamylene process

One can react methanol with the tertiary olefins having five c irbon atoms (isoamylenes). This process increases the octane number of FCC olefinic C5 fractions, in order to reduce the concentration of olefins and to increase gasoline production. 

Some isopentane is dehydrogenated to isoamylene and converted, by processes analogous to those which produce methyl /-butyl ether [1634-04-4] (MTBE) to /-amyl methyl ether [994-05-8] (TAME), which is used as a fuel octane enhancer like MTBE. The amount of TAME which the market can absorb depends mostly on its price relative to MTBE, ethyl /-butyl ether [637-92-3] (ETBE), and ethanol, the other important oxygenated fuel additives. 

Commercially, sulfonic acid ion-exchange resins are used in fixed-bed reactors to make these tertiary alkyl ethers (14). Since the reaction is very selective to tertiary olefins and also reversible, a two-step procedure is also used to recover commercially pure tertiary olefins from mixed olefin process streams. The corresponding tertiary alkyl ether is produced in the olefin mixture and then easily separated from the unreacted olefins by simple fractionation. The reaction is then reversed in a second step to make a commercially pure tertiary olefin, usually isobutylene or isoamylene. 

The isoprene monomer is not readily available from direct cracking processes. Several routes are employed for its synthesis. One route begins with the extraction of isoamylene fractions from catalytically cracked gasoline streams. Isoprene is produced by subsequent catalytic dehydrogenation. 

Similar to the processes used in the manufacture of 1,3-butadiene, isoprene can be prepared from isopentane, isoamylenes, or a mixed isoC5 feed.172 176 177 The Shell process177 dehydrogenates isoamylenes to isoprene in the presence of steam with 85% selectivity at 35% conversion, over a Fe203—K2CO3—Cr2Oj catalyst at 600°C. 

A number of new processes exploiting metathesis have been developed by Phillips. A novel way to manufacture lubricating oils has been demonstrated.145 The basic reaction is self-metathesis of 1-octene or 1-decene to produce Ci4-C28 internal alkenes. The branched hydrocarbons formed after dimerization and hydrogenation may be utilized as lubricating oils. Metathetical cleavage of isobutylene with propylene or 2-butenes to isoamylenes has a potential in isoprene manufacture.136,146 High isoamylene yields can be achieved by further metathesis of C6+ byproducts with ethylene and propylene. Dehydrogenation to isoprene is already practiced in the transformation of isoamylenes of FCC C5 olefin cuts. 

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. 

Application To produce butadiene from butane or mixed butane/ butylenes isoprene from isopentane or mixed isopentane/isoamylenes using the Catadiene process. 

Another source of isoamylenes is obtained by dismutation of the dedienized C4 cut using a technique derived from that of PhilUps (Triols process), in the first step, using the C4 cut. isobutene and 2-butenes react with each other to yield isopentenes and propylene. The propylene reacts in turn with the isobutene to produce an additional quantity of isopentenes and ethylene. The ethylene, by reacting with isohexenes, heavy by-products of the conversion of 1-buiene and isobutene, regenerates the initial reactants in a second step. 

Supplemental processes which can be operated in conjunction with alkylation and/or sulfuric acid production can influence the overall economics. Examples are (1) the integration of normal butane-to-isobutane isomerization with alkylation, utilizing common fractionation equipment and (2), utilizing 65% sulfuric acid extraction of isobutylene or isoamylene from olefins fed to alkylation, justified by monetary return on sale of the high purity iso-olefin as a petrochemical feedstock, which reduces quantity of alkylate produced and reduces isobutane required while producing still higher quality alkylate with sulfuric acid catalyst. 

Figure 3.34 shows a schematic of the Ethermax process by Hiils AG and UOP [61]. Feed for the process includes methanol or ethanol and hydrocarbon streams containing reactive tertiary olefins such as isoamylene and isobutylene. Typical hydrocarbon streams are FCC light gasoline, steam cracker C4 hydrocarbons, or product from a butane dehydrogenation unit. In the production of MTBE, the feed first passes through an optional water wash system (1) to remove resin contaminants. The majority of the reaction is carried out in a... 

Various industrial companies have developed a metathesis process for the production of 2-methylbut-2-ene (isoamylene), which can be used to make isoprene via oxidative dehydrogenation. It is produced via cross-metathesis of isobutene and but-2-ene reaction (8). Cross-metathesis can also be carried out with propene instead of but-2-ene, or a mixture of the two. 

Technology for a number of applications of olefin metathesis has been developed (, fO At Phillips, potential processes for producing isoamylenes for polyisoprene synthesis and long-chain linear olefins from propylene have been through pilot plant development. In the area of specialty petrochemicals, potential industrial applications include the preparation of numerous olefins and diolefins. High selectivities can be achieved by selection of catalyst and process conditions. The development of new classes of catalysts allows the metathesis of certain functional olefins (, 14). The metathesis of alkynes is also feasible (15) ... 

Isoprene (2-methylbuta-1,3-diene) is produced mainly by the dehydrogenation of isoamylenes (2-methylbutenes) or isopentane (2-methylbutane), in processes similar to those used in the U.S.A. for butadiene manufacture. 

Various industrial companies have developed a process for the production of isoamylene (2-methyl but-2-ene), which is a precursor of isoprene (obtained by oxidative dehydrogenation). It can be produced by cross-metathesis of isobutene with but-2-ene or propene ... 

Three processes are associated with production of olefins. One process is designed to convert natural gas or raw methanol to ethylene, propylene, and butane. The second process is designed to produce isobutylene and isoamylene feedstocks from hydrocarbon feedstock. This material is used in production of ethers, polymerization, and linear olefins for alkylation. The third process selectively converts gas oil feedstocks into high-octane gasoline and distillate, and C2-C5 olefins. 

Flow rates of isoamylene fraction, methanol and TAME fraction are measured using tensiometer balances, and reflux and distillate flow rates using a Coriolis-type flowmeter. The samples are analysed off line. Process data, such as temperatures, flows, levels and pressures are stored and visualised by a monitoring system based on microprocessor controller MSC68. This gives a way to identify steady states in the column. 

Several operational parameters have been varied and their influence on the process performance has been analysed. In particular, the feed rate has been changed in the range between 25 and 45 kg/h, the molar feed ratio of methanol/isoamylenes between 0.9 and 1.45 and the reflux ratio between 1 and 2. 

---