Isobutane main process

THE SELECTIVE OXIDATION OF ISOBUTANE CATALYZED BY POMs MAIN PROCESS FEATURES... 

For H2SO4 and HF catalysts, three main process variables affect alkylate quality temperature olefin space velocity and external isobutane/olefin ratio. 

The photolysis of neopentane has been studied by Lias and Ausloos at 1236 and 1470 A. The two main processes which occur are molecular methane elimination from, and fragmentation of, the excited neopentane. The products of photolysis are methane, isobutene, hydrogen, ethane, and propene, with smaller amounts of isobutane, ethylene, propane, acetylene and 2,2-dimethylbutane. The suggested reactions are... 

This process was originally developed and commercialized by Oxirane (a joint venture company between ARCO Chemical, now Lyondell, and Halcon) and independently by Shell Petrochemical Company. At present, this is one of the main processes for the commercial manufacture of propylene oxide (the other is a variant of the same that starts with isobutane instead of ethylbenzene, and produces propylene oxide together with tert-butyl alcohol, isobutylene, and... 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

In some catalytic processes, it is necessary to avoid carbon-carbon bond cleavage. For example, isobutane is mainly transformed into its lower alkane homologues (hydrogenolysis products) on metal surfaces, while it can be converted more and more selectively into isobutene when the Pt catalysts contain an increasing amount of Sn (selective dehydrogenation process) [131]. 

Figure 14.2 shows the simplified flow sheet of the process, as reported in patents issued to Sumitomo. CO2 is maintained in the recycle loop to act as a ballast component the desired concentration of CO2 is obtained by combustion of CO, while excess CO2 is separated. Methacrolein is separated and recycled to the oxidation reactor. An overall recycle yield of 52% to methacrylic acid is reported, with a recycle conversion of 96% and a per-pass isobutane conversion of 10%. The heat of reaction produced, mainly deriving from the combustion reaction, is recovered as steam. 

Isobutylene supply initially came mainly from the cracked gas streams generated by the cat cracker, plus whatever other units fed gases into the cracked gas plants. The isobutylene market trades very thinly, so when the cracked gas plant supply is insufficient, a producer must turn to a dehydrogenation process for converting isobutane to isobutylene. 

Alkylation A refinery process for producing high-octane components consisting mainly of branched chain paraffins. The process involves combining light olefins with isoparaffins, usually butene and isobutane, in the presence of a strong acid catalyst such as hydrofluoric or sulfuric acid. 

More information is available about orientation, when a second alkyl group is introduced into the aromatic ring, and about relative rates. As might be expected, propene reacts more easily than ethylene [342,346] and isobutene more easily than propene [342]. Normal butenes are sometimes isomerised in the process practically the same product composition, consisting mainly of 2,2,4-trimethylpentane, is obtained in the alkylation of isobutane whether the olefin component is isobutene or 2-butene [339]. In the alkylation of aromatic hydrocarbons, this side reaction is negligible. 

Such reactions can take place predominantly in either the continuous or disperse phase or in both phases or mainly at the interface. Mutual solubilities, distribution coefficients, and the amount of interfadal surface are factors that determine the overall rate of conversion. Stirred tanks with power inputs of 5-10 HP/1000 gal or extraction-type equipment of various kinds are used to enhance mass transfer. Horizontal TFRs usually are impractical unless sufficiently stable emulsions can be formed, but mixing baffles at intervals are helpful if there are strong reasons for using such equipment. Multistage stirred chambers in a single shell are used for example in butene-isobutane alkylation with sulfuric acid catalyst. Other liquid-liquid processes listed in Table 17.1 are numbers 8, 27, 45, 78, and 90. 

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. 

Ethylene is dissolved in isobutane. This ethylene reacts with itself to form polyethylene particles that gradually settle out of solution and are collected in one of six settling legs. Particles pass through a main 8-inch (21 cm) block valve called a DEMCO valve to collect in a chamber. The particles are periodically isolated from the reactor, the volatiles are removed, and the polyethylene is routed to other equipment for further processing. See Figure 5—7, which appeared in OSHA Reports and has been reproduced with the permission of OSHA. 

The input-output structure of the flowsheet is presented in Figure 9.1. Butene (feed rate FA,0) and isobutane (feed rate FB-0) are the raw materials. The butene feed is impure with quite large amounts of propane (FI 0). The main product is the alkylate C8Hi8, at the rate FP. The selectivity of the process is not 100%, therefore heavy products are formed at the rate FR. The inert fed into the process must also leave the plant, the flow including light byproducts that are formed in secondary reactions. Often, significant quantities of n-butane are mixed with the isobutane fresh feed. For this case, development of the flowsheet and the design of the main units is left as an exercise for the reader. 

In the alkylation process, the main reaction involves the olefin and isobutane. In contrast, the secondary reactions consist of olefin polymerization or the reaction between the olefin and C8 paraffins. For this reason, a high concentration of isobutane in the reactor is necessary. In our design the isobutane olefin ratio is 7.3 1, while typical values are in the range 5 1 to 10 1 [7]. Note that the reactants are fed to the process in a nearly stoichiometric proportion, the high excess of isobutane being accomplished by recycling. 

Isobutene is present in refinery streams. Especially C4 fractions from catalytic cracking are used. Such streams consist mainly of n-butenes, isobutene and butadiene, and generally the butadiene is first removed by extraction. For the purpose of MTBE manufacture the amount of C4 (and C3) olefins in catalytic cracking can be enhanced by adding a few percent of the shape-selective, medium-pore zeolite ZSM-5 to the FCC catalyst (see Fig. 2.23), which is based on zeolite Y (large pore). Two routes lead from n-butane to isobutene (see Fig. 2.24) the isomerization/dehydrogenation pathway (upper route) is industrially practised. Finally, isobutene is also industrially obtained by dehydration of f-butyl alcohol, formed in the Halcon process (isobutane/propene to f-butyl alcohol/ propene oxide). The latter process has been mentioned as an alternative for the SMPO process (see Section 2.7). 

For the experiments in which the first-step reaction products of isobutylene were employedt reactions between high molecular weight olefins and isobutane were of major importance. Presumably a first step in the overall process was the protonation of the heavier olefins to form heavier isoalkyl cations. These cations apparently fragmented to a large extent to form mainly... 

The isomerization of open-chain alkanes with more than six carbon atoms gives isobutane as the main product, together with disproportionated materials, even though the reaction proceeds by the monomolecular pathway [144]. On the other hand, for cyclic alkanes the monomolecular process with preservation of the cyclic structure seems to be the most probable, judging from the results for cyclohexane. The absence of isobutane in the products indicates that the reaction path does not involve open-chain intermediate species. Therefore, it is of interest to try cycloalkanes larger than cyclohexane for clarification of the reaction mechanism along with the catalytic action of S04/Zr02. 

The alkylation of isobutane with C4 olefins using solid acid catalysts has become a growing research field during recent years. The main reason is that the currently used processes in industry have the HF or H2SO4 acids as catalysts, both of them being very difficult of being handled or disposed of they also present severe problems for the environment. However, in spite of an important research effort carried out both by industrial (1-4) and academic (5) laboratories, it has been very difficult to solve the major problem that the solid acid catalysts present, which is the fast deactivation due to the coke deposition. 

The economic data concerning the production of isobutane by vapor phase n-butane isomerization, with and without recycling of unconverted n-butane, and concerning the production of isobutene by dehydrogenation, by the three main current industrial processes, are given in Table 6.5 a. The corresponding feed and product compositions are given in Table 6.5 b. 

The current industrial production of methylmethacrylate by the acetone-cyanohydrin process suffers from a number of drawbacks, which make it environmentally unfriendly. In particular, it makes use of a very toxic reactant (HCN) and intermediate (acetone cyanohydrin), and coproduces large amounts of impure ammonium sulphate, contaminated with organic compounds. Among the several alternative synthetic routes which have been proposed, particularly interesting from both the practical and scientific points of view is the single-step oxidation of isobutane to methacrylic acid, intermediate in the synthesis of methylmethacrylate. Several industrial companies have studied this reaction (and the selective oxidation of propane to acrylic acid, as well), and it has been established that the most active and selective catalysts are those which are based on Keggin-type polyoxometalates (POM s), containing phosphorus and molybdenum as the main components [1-18]. 

An important aspect of this reaction is that the processes claimed in all patents make use of fuel-rich conditions, thus with sub-stoichiometric oxygen [1-5]. Under these conditions the conversion of isobutane is necessarily low (in the best cases, not higher than 25%), and therefore recycle of the unconverted reactant becomes necessary. It has been proposed that the reason for this is that the catalyst is selective only provided molybdenum in the POM can be kept at an average reduced state lower than that typical of the calcined POM [17], This can be obtained only provided a reducing, hydrocarbon-rich gas-phase is employed as the feedstock to the reactor. Some authors have reported catalyst preparations which lead to the development of reduced compounds that perform better than POMs prepared conventionally [10,12,13]. However, in all cases very few indications are given about the possibility of maintaining these performances for prolonged lifetimes. Indeed, the main question is whether... 

Depending on the feed composition, Saipem offers different possible processing schemes. In a typical configuration, the feed is sent to the first column (1) where the heavy hydrocarbons (mainly n-butane and butene-2) are removed as the bottom stream. In the second column, (2) the butene-1 is recovered at the bottom and the light ends (mainly isobutane) are removed as overhead stream. 

During World War II, the great demand for aircraft fuel necessitated the production of large quantities of isobutane, a basic raw material in the production of high octane aviation gasoline. (See chapter on Alkylation of Alkanes. ) Various processes have been developed for the isomerization of n-butane to isobutane all of them employed aluminum chloride-hydrogen chloride as catalyst. The difference between the various processes consisted either in the method of introduction of aluminum chloride to the reaction zone, the catalyst support, or the state of the catalyst. The following summary describes some of the main features of the various processes which were developed ... 

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