Acetylene from steam-cracking

ACETYLENE MANUFACTURE BY EXTRACTION FROM STEAM-CRACKED C, CUTS... 

Thus, butadiene is first recovered from steam-cracked C4 cuts by solvent extraction, an operation that is sometimes facilitated by preliminary selective hydrogenation of the acetylenic compounds. In a number of applications, the raffinate itself must undergo similar treatment to rid it of residual diolefins. The initial cut, after being debutadienized by hydrogenation, can also serve the same purpose. This also applies to catalytic cracker diluents that are very often directly upgradable, but whose albeit low butadiene content may justify hydrogenation pretreatment for certain uses. 

Acetylene manufacture by extraction from steam-cracked C2 cuts. 322... 

Finally, we would like to mention the selective hydrogenation of acetylenic compounds in propylene and Cl olefinic cuts from steam cracking units. A very efficient process, developped by IFF, uses two trickle-bed reactors in series to obtain polymer grade propylene or a feedstock from which butadiene is selectively extracted (Figure k) k6yh9),... 

The removal of acetylenes and dienes from steam-cracked olefins is a critical step in purification. Selective hydrogenation processes and catalysts have become more important as worldwide olefin production has increased in 1999 to more than 90 million tormes of ethylene and almost 50 million tonnes of propylene. Demand for better catalysts with improved selectivity and longer operating cycles has grown as larger plants are built. Tighter product specifications have also been imposed now that more of the olefins produced are being converted to polyolefins. 

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. 

One approach is to uses solvent extraction with dimethyl formamide (DMF) to remove Cj acetylene and a C, acetylene-propadiene mixture from their steam cracked ethylene and propylene streams. The simple acetylene is sold as welding gas, and the C, stream is sold as starting material for chemical synthesis. 

FIG. 19-13 Noncatalytic gas-phase reactions, (a) Steam cracking of light hydrocarbons in a tubular fired heater, (b) Pebble heater for the fixation of nitrogen from air. (c) Flame reactor for the production of acetylene from hydrocarbon gases or naphthas. [Patton, Grubb, and Stephenson, Pet. Ref. 37(11) 180 (1958).] d Flame reactor for acetylene from light hydrocarbons (BASF), (e) Temperature profiles in a flame reactor for acetylene (Ullmann Encyclopadie der Technischen Chemie, vol. 3, Verlag Chemie, 1973, p. 335). 

The primary source of isoprene today is as a by-product in the production of ethylene via naphtha cracking. A solvent extraction process is employed. Much less isoprene is produced in the crackers than butadiene, so the availability of isoprene is much more limited. Isoprene also may be produced by the catalytic dehydrogenation of amylenes, which are available in C-5 refinery streams. It also can be produced from propylene by a dimerization process, followed by isomerization and steam cracking. A third route involves the use of acetone and acetylene, produced from coal via calcium carbide. The resulting 3-methyl-butyne-3-ol is hydrogenated to methyl butanol and subsequently dehydrogenated to give isoprene. The plants that were built on these last two processes have been shut down, evidently because of the relatively low cost of the extraction route. 

Kureha crude oil steam cracking technology was devdoped jointly with Union Carbide for the manufacture of ethylene (see Section 2.13.4). By operating at very temperature and with very short xomact dmes (0LOO3 to 0.010 s), approximately equal amounts of acetylene and ethylene can be produced from a number of crude oils. This is illustrated by Table 52 for Indonesian and Arabian crudes, cracked in the presence of steam at 2000 in a steam to feed weight rado of about 5, and with residence time of O.OOS s. In these conditions, the temperature at the reactor exit before quench reaches 1150-C. /... 

In the steam cracking of hydrocarbons, a small portion of the hydrocarbon feed gases decomposes to produce coke that accumulates on the interior walls of the coils in the radiant zone and on the inner surfaces of the transferline exchanger (TLX). Albright et identified three mechanisms for coke formation. Mechanism 1 involves metal-catalyzed reactions in which metal carbides are intermediate compounds and for which iron and nickel are catalysts. The resulting filamentous coke often contains iron or nickel positioned primarily at the tips of the filaments. This filamenteous coke acts as excellent collection sites for coke formed by mechanisms 2 and 3. Mechanism 2 results in the formation of tar droplets in the gas phase, often from aromatics. These aromatics are often produced by trimerization and other reactions involving acetylene. Some, but not all, of these droplets collect... 

As in steam cracking, a large number of by-products is produced. Some of them result from the consecutive reactions of the chlorination of vinyl chloride and of its derivatives obtained by dehydrochlorination (tri-, tetra-, pentachloroethane, perchloro-ethane, di-, trichloroethylene. perchloroethyleneX and the others from the hydrochlorination of vinyl chloride il.l-dichloroethane), while others result from decomposition reactions (acetylene, cokei or conversion of impurities initially present (hydrocarbons such as ethylene, butadiene and benzene, chlorinated derivatives such as chloroprene, methyl and ethyl Chlorides, chloroform, carbon tetrachloride, eta, and hydrogen) ... 

C4 cuts from catalytic cracking contain little butadiene and acetylenic compounds. Hence they can be used directly for isobutene separation processes, but require prior hydrogenation to obtain 1-butene. By contrast, steam cracked effluents must systematically undergo hydrogenation pretreatmcnL This is necessary to eliminate the compounds liable to cause highly exothermic side-polymerizations, and to form gums that disturb the operation of the catalyst systems, solvents and adsorbents used in steps designed to produce the different C4 olefins. 

The overproduction of ethylene in certain geographic areas and, all things considered, the strong demand for acetylene at its high price level, could normally justify its recovery from the steam-cracked C3 cut for economic reasons. Given the slight differences in boiling points between the constituents of these effluents, and the pronounced tendency displayed by acetylenic compounds lo polymerize, this separation cannot be achieved by simple distillation or even superfractionation. A feasible alternative is solvent extraction, particularly with dimethylform amide. 

Ethylene. The largest potential chemical market for n-butanc is in steam cracking to ethylene and coproducts. n-Butane is a supplemental feedstock for olefin plants and has accounted for 1 to 4 percent of total ethylene production for most years since 1970. It can be used at up to 10 to 15 percent of the total feed in ethane/propane crackers with no major modifications. n-Butane also can be used as a supplemental feed at as high as 20 to 30 percent in hea y naphtha crackers. The consumption of C s has fluctuated considerably from year to year since 1970, depending on the relative price of butane and other feedstocks. The yield of ethylene is only 36 to 40 percent, with the other products including methane, propylene, ethane, butadiene, acetylene, and butylenes. About 1 to 2 billion lb of butane are consumed annually to produce ethylene. 

A typical ethane cracker has several identical pyrolysis furnaces in which fresh ethane feed and recycled ethane are cracked with steam as a diluent. Figure 3-12 is a block diagram for ethylene from ethane. The outlet temperature is usually in the 800°C range. The furnace effluent is quenched in a heat exchanger and further cooled by direct contact in a water quench tower where steam is condensed and recycled to the pyrolysis furnace. After the cracked gas is treated to remove acid gases, hydrogen and methane are separated from the pyrolysis products in the demethanizer. The effluent is then treated to remove acetylene, and ethylene is separated from ethane and heavier in the ethylene fractionator. The bottom fraction is separated in the deethanizer into ethane and fraction. Ethane is then recycled to the pyrolysis furnace. 

Application Increase the value of steam cracker C4 cuts via low-temperature selective hydrogenation and hydroisomerization catalysis. Several options exist removal of ethyl and vinyl acetylenes to facilitate butadiene extraction processing downstream conversion of 1, 3 butadiene to maximize 1-butene or 2-butene production production of high-purity isobutylene from crude C4 cuts total C4 cut hydrogenation and total hydrogenation of combined C3/C4 and C4C5 cuts for recycle to cracking furnaces or LPG production. 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

---