2- Butenes from steam cracking

IFP Process for 1-Butene from Ethylene. 1-Butene is widely used as a comonomer in the production of polyethylene, accounting for over 107,000 t in 1992 and 40% of the total comonomer used. About 60% of the 1-butene produced comes from steam cracking and fluid catalytic cracker effluents (10). This 1-butene is typically produced from by-product raffinate from methyl tert-huty ether production. The recovery of 1-butene from these streams is typically expensive and requires the use of large plants to be economical. Institut Francais du Petrole (IFP) has developed and patented the Alphabutol process which produces 1-butene by selectively dimerizing ethylene. 

Butadiene is obtained mainly as a coproduct with other light olefins from steam cracking units for ethylene production. Other sources of butadiene are the catalytic dehydrogenation of butanes and butenes, and dehydration of 1,4-butanediol. Butadiene is a colorless gas with a mild aromatic odor. Its specific gravity is 0.6211 at 20°C and its boiling temperature is -4.4°C. The U.S. production of butadiene reached 4.1 billion pounds in 1997 and it was the 36th highest-volume chemical. ... 

Besides ethylene and propylene, the steam cracking of naphtha and catalytic cracking in the refinery produce appreciable amounts of C4 compounds. This C4 stream includes butane, isobutane, 1-butene (butylene), cis- and trans-2-hutene, isobutene (isobutylene), and butadiene. The C4 hydrocarbons can be used to alkylate gasoline. Of these, only butadiene and isobutylene appear in the top 50 chemicals as separate pure chemicals. The other C4 hydrocarbons have specific uses but are not as important as butadiene and isobutylene. A typical composition of a C4 stream from steam cracking of naphtha is given in Table 8.3. 

Refineries that have access to isobutylene streams from steam cracking may face the problem that the existing alkylation and possibly catalytic condensation units cannot take the normal butenes which are contained in the pyrolysis stream. 

Union Carbide has proposed adsorption on molecular sieves to separate isobutene, particularly from steam-cracked C4 cuts. This is the Oleftn-Siv process, which simultaneously produces 1-butene, and is discussed in greater detail in Section 3.13J.A. 

Manufacturing processes today employ petroleum raw materials. In Europe and Japan, butadiene is obtained entirely by extraction from steam-cracked C4 cuts (see Section 3,1.2). In the United States, it is also produced by the dehydrogenation of butane and particularly of butenes contained in C4 cuts from catalytic cracking. 

The -butene feed was supplied by the dehydrogenation of n-butane and the plant began the trend to develop oxidation processes using aliphatic petrochemical hydrocarbons. The main incentive, of course, was to use surplus C4 hydrocarbon from steam cracking. This not only used a cheap by-product gas, but the reaction was less complicated because the straight-chain C4 molecule contained fewer carbon atoms tlm aromatic benzene. 

Butadiene production from these dehydrogenation processes did not continue beyond the 1960s, as butadiene from steam cracking of naphtha became available. Later, however, from about 1990, as butadiene and butene shortages developed, several commercial processes were revived. 

Properly speaking, steam cracking is not a refining process. A key petrochemical process, it has the purpose of producing ethylene, propylene, butadiene, butenes and aromatics (BTX) mainly from light fractions of crude oil (LPG, naphthas), but also from heavy fractions hydrotreated or not (paraffinic vacuum distillates, residue from hydrocracking HOC). 

Aliphatic C-5—C-6. Aliphatic feedstreams are typically composed of C-5 and C-6 paraffins, olefins, and diolefins, the main reactive components being piperylenes cis-[1574-41 -0] and /n j -l,3-pentadiene [2004-70-8f). Other main compounds iaclude substituted C-5 and C-6 olefins such as cyclopentene [142-29-OJ, 2-methyl-2-butene [513-35-9] and 2-methyl-2-pentene [625-27-4J. Isoprene and cyclopentadiene maybe present ia small to moderate quaatities (2—10%). Most steam cracking operatioas are desigaed to remove and purify isoprene from the C-5—C-6 fraction for applications ia mbbers and thermoplastic elastomers. Cyclopentadiene is typically dimerized to dicyclopentadiene (DCPD) and removed from C-5 olefin—diolefin feedstreams duriag fractionation (19). 

The pattern of commercial production of 1,3-butadiene parallels the overall development of the petrochemical industry. Since its discovery via pyrolysis of various organic materials, butadiene has been manufactured from acetylene as weU as ethanol, both via butanediols (1,3- and 1,4-) as intermediates (see Acetylene-DERIVED chemicals). On a global basis, the importance of these processes has decreased substantially because of the increasing production of butadiene from petroleum sources. China and India stiU convert ethanol to butadiene using the two-step process while Poland and the former USSR use a one-step process (229,230). In the past butadiene also was produced by the dehydrogenation of / -butane and oxydehydrogenation of / -butenes. However, butadiene is now primarily produced as a by-product in the steam cracking of hydrocarbon streams to produce ethylene. Except under market dislocation situations, butadiene is almost exclusively manufactured by this process in the United States, Western Europe, and Japan. 

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. ... 

Butadiene is mainly obtained as a byproduct from the steam cracking of hydrocarbons and from catalytic cracking. These two sources account for over 90% of butadiene demand. The remainder comes from dehydrogenation of n-butane or n-butene streams (Chapter 3). The 1998 U.S. production of butadiene was approximately 4 billion pounds, and it was the 36th highest-volume chemical. Worldwide butadiene capacity was nearly 20 billion pounds. 

Small olefins, notably ethylene (ethene), propene, and butene, form the building blocks of the petrochemical industry. These molecules originate among others from the FCC process, but they are also manufactured by the steam cracking of naphtha. A wealth of reactions is based on olefins. As examples, we discuss here the epoxida-tion of ethylene and the partial oxidation of propylene, as well as the polymerization of ethylene and propylene. 

Dehydrogenation ofTertiary Amylenes. The starting material here is a CB fraction which is cut from catalytic cracking of petroleum. Two of the tertiary amylene isomers, 2-methyl-l-butene and 2-methyl-2-butene, are recovered in high purity by formation of methyl tertiary butyl ether and cracking of this to produce primarily 2-methyl-2-butene. The amylenes are mixed with steam and dehydrogenated over a catalyst. The crude isoprene can be purified by conventional or extractive distillation. 

Butylenes are four-carbon monoolefins that are produced by various hydrocarbon processes, principally catalytic cracking at refineries and steam cracking at olefins plants. These processes yield isomeric mixtures of 1-butene, cis- and tra s-butene-2, and isobutylene. Derivatives of butylenes range from polygas chemicals and methyl t-butyl ether, where crude butylenes streams may be used, to polybutene-1 and LLDPE, which require high-purity 1-butene. In 1997, the estimated consumption of butylenes (in billions of pounds) was alkylation, 32.0 MTBE, 12.0 other, including polygas and fuel uses, 0.5. 

Favored at high temperature and low pressure, it is closely related to the manufacture of butadiene from butenes or the primary dehydrogenation observed in the steam cracking of hydrocarbon feedstocks. 

Separadon of butenes from C4 cuts produced by steam cracking and catalytic cracking... 

Only the first five methods are of direct interest to industry. About 50% of butene-1 is produced from refinery and steam cracking operations. The remainder is obtained as alpha olefin co-product. The United States and European countries are the major sources for butene-1 in the world market. The breakdown of the 1993 global butene-1 production capacities is presented in Table 1. 

Derivation Absorption of butene from cracking petroleum or natural gas in sulfuric acid with subsequent hydrolysis by steam. 

A mixture of butenes and steam is to be thermally (noncatalytically) cracked in a tubular-flow reactor at a constant temperature of 1200°F and a constant pressure of 1.0 atm. Although the feed consists of a number of different butenes and the products vary from coke to butadiene, the rate of reaction may be adequately represented by the first-order mechanism... 

In practice, the Bayer process (Fig. 8.7), which has not yet been industrialized, starts with a steam-cracked C cut, for example, from which the butadiene and isobutene are extracted, and which therefore consists of about 20 per cent weight butanes and 80 per cent weight n-butenes. The butanes behave as a diluent The unit has three sections ... 

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