Acetylene feedstock

FIGURE 17.3 Monomer synthesis chemical flow diagram based on acetylene feedstock. 

Palladium-catalyzed 1,4-diacetoxylation of butadiene is a useful reaction of commercial interest which provides an interesting alternative for the synthesis of butanediol and tetrahydrofuran, previously based on acetylene feedstocks (equation 165). 

Following this seminal discovery, SOHIO successfully commercialized its technology based on a bismuth-molybdenum oxide catalyst in 1960. The SOHIO process has since become the industry leader for acrylonitrile manufacture, with over 90% of the world s production based on this technology. The propylene-based process effectively displaced all the existing technologies for acrylonitrile that were based on acetylene feedstock, a much more expensive feedstock than propylene. This resulted in an explosion in the development of new applications for acrylonitrile stemming from the invention of the novel, lower cost production technology. 

The glass fiber based catalysts containing transition metals in highly dispersed state (mostly, Pt and Pd) were tested in many catalytic reactions, such as deep oxidation of saturated hydrocarbons [1], SO2 oxidation [3], deNOx [8], selective hydrogenation of acetylene feedstock [2 ] etc. Despite of extremely low content of noble metals the GFCs showed high activity and thermal stability, low ignition temperature. 

Feedstocks come mainly from catalytic cracking. The catalyst system is sensitive to contaminants such as dienes and acetylenes or polar compounds such as water, oxygenates, basic nitrogen, organic sulfur, and chlorinated compounds, which usually require upstream treatment. 

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

Although the rapid cost increases and shortages of petroleum-based feedstocks forecast a decade ago have yet to materialize, shift to natural gas or coal may become necessary in the new century. Under such conditions, it is possible that acrylate manufacture via acetylene, as described above, could again become attractive. It appears that condensation of formaldehyde with acetic acid might be preferred. A coal gasification complex readily provides all of the necessary intermediates for manufacture of acrylates (92). 

Although acetylene production in Japan and Eastern Europe is stiU based on the calcium carbide process, the large producers in the United States and Western Europe now rely on hydrocarbons as the feedstock. Now more than 80% of the acetylene produced in the United States and Western Europe is derived from hydrocarbons, mainly natural gas or as a coproduct in the production of ethylene. In Russia about 40% of the acetylene produced is from natural gas. 

Energy source Process designation Feedstock Typical cracked gas concentrations, mol % Acetylene Ethylene ... 

Taking into account the purification losses, the following operating requirements are necessary in order to obtain 100 kg of purified acetylene 200 kg hydrocarbons (feedstock plus quench), 1030 kWh electric energy for the arc, 250 kWh electric energy for the separation unit, and 150 kg steam. 

A considerable amount of carbon is formed in the reactor in an arc process, but this can be gready reduced by using an auxiUary gas as a heat carrier. Hydrogen is a most suitable vehicle because of its abiUty to dissociate into very mobile reactive atoms. This type of processing is referred to as a plasma process and it has been developed to industrial scale, eg, the Hoechst WLP process. A very important feature of a plasma process is its abiUty to produce acetylene from heavy feedstocks (even from cmde oil), without the excessive carbon formation of a straight arc process. The speed of mixing plasma and feedstock is critical (6). 

Farbwerke Hoechst AG and Hbls AG have cooperated in the development of industrial-scale plasma units up to 10,000 kW (7). Yields of acetylene of 40—50 wt % with naphtha feedstock, and about 27 wt % with cmde oil feedstock, have been obtained. Acetylene concentration in the cracked gas is in the 10—15 vol % range. 

Hoechst WHP Process. The Hoechst WLP process uses an electric arc-heated hydrogen plasma at 3500—4000 K it was developed to industrial scale by Farbwerke Hoechst AG (8). Naphtha, or other Hquid hydrocarbon, is injected axially into the hot plasma and 60% of the feedstock is converted to acetylene, ethylene, hydrogen, soot, and other by-products in a residence time of 2—3 milliseconds Additional ethylene may be produced by a secondary injection of naphtha (Table 7, Case A), or by means of radial injection of the naphtha feed (Case B). The oil quenching also removes soot. 

Flame or Partial Combustion Processes. In the combustion or flame processes, the necessary energy is imparted to the feedstock by the partial combustion of the hydrocarbon feed (one-stage process), or by the combustion of residual gas, or any other suitable fuel, and subsequent injection of the cracking stock into the hot combustion gases (two-stage process). A detailed discussion of the kinetics for the pyrolysis of methane for the production of acetylene by partial oxidation, and some conclusions as to reaction mechanism have been given (12). 

Regenerative pyrolysis processing is very versatile it can handle varied feedstocks and produce a range of ethylene to acetylene. The acetylene content of the cracked gases is high and this assists purification. On the other hand, the plant is relatively expensive and requires considerable maintenance because of the wear and tear on the refractory of cycHc operation. 

The quantity of coproduct acetylene produced is sensitive to both the feedstock and the severity of the cracking process. Naphtha, for example, is cracked at the most severe conditions and thus produces appreciable acetylene up to 2.5 wt % of the ethylene content. On the other hand, gas oil must be processed at lower temperature to limit coking and thus produces less acetylene. Two industry trends are resulting in increased acetylene output (/) the ethylene plant capacity has more than doubled, and (2) furnace operating conditions of higher temperature and shorter residence times have increased the cracking severity. 

Acetylene Absorption. The gaseous feedstock containing the hydrocarbons is introduced into the acetylene absorption tower at a pressure... 

Coal, considered a soHd hydrocarbon with a generic formula of CHq g, was explored by numerous workers (24—31) as a feedstock for the production of acetylene. Initially, the motivation for this work was to expand the market for the use of coal in the chemical process industry, and later when it was projected that the cost of ethylene would increase appreciably if pretroleum resources were depleted or constrained. 

Much more important is the hydrogenation product of butynediol, 1,4-butanediol [110-63-4]. The intermediate 2-butene-l,4-diol is also commercially available but has found few uses. 1,4-Butanediol, however, is used widely in polyurethanes and is of increasing interest for the preparation of thermoplastic polyesters, especially the terephthalate. Butanediol is also used as the starting material for a further series of chemicals including tetrahydrofuran, y-butyrolactone, 2-pyrrohdinone, A/-methylpyrrohdinone, and A/-vinylpyrrohdinone (see Acetylene-DERIVED chemicals). The 1,4-butanediol market essentially represents the only growing demand for acetylene as a feedstock. This demand is reported (34) as growing from 54,000 metric tons of acetylene in 1989 to a projected level of 88,000 metric tons in 1994. 

United States. The demand for acetylene generally peaked between 1965 and 1970, then declined dramatically until the early 1980s, and has been slowly increasing at between 2 and 4% per year since. The dramatic decline was related to increased availabiHty of low cost ethylene, an alternative feedstock for many chemicals, and the recent increase is due to the modest growth of acetylenic chemicals, particularly 1,4-butanediol. 

It is difficult to indicate a representative price for acetylene because it is generally produced either for captive use or on contract. The price seems to be dictated mainly by the price movement of ethylene, often a coproduct as well as an alternative feedstock competing with acetylene. That is, in 1981 when ethylene was 0.55 per kg, acetylene was 1.12 per kg and when in 1987 the price of ethylene dropped to 0.31 per kg, acetylene dropped to 0.68 per kg. 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

When natural gas is used as a feedstock to produce thermal blacks, the reaction is endothermic. In order to maintain the reaction, the reactor has to be kept at about 1300°C. When acetylene is used as the feedstock to produce acetylene blacks, the reaction is exothermic, and the reaction can be mn at a temperature between 800 and 1000°C. 

The production process or the feedstock is sometimes reflected ia the name of the product such as lamp black, acetylene black, bone black, furnace black, or thermal black. The reason for the variety of processes used to produce carbon blacks is that there exists a unique link between the manufactuting process and the performance features of carbon black. 

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

Although a small fraction of the world s vinyl chloride capacity is stiU based on acetylene or mixed actylene—ethylene feedstocks, nearly all production is conducted by the balanced process based on ethylene and chlorine (75). The reactions for each of the component processes are shown in equations 1—3 and the overall reaction is given by equation 4 ... 

Acetjiene has found use as a feedstock for production of chlorinated solvents by reaction with hydrogen chloride or chlorine (6). However, because of safety concerns and the lower price of other feedstock hydrocarbons, very Htfle acetylene is used to produce chlorinated hydrocarbons in the United States (see Acetylene-derived chemicals). 

Tetrachloroethane is produced by direct chlorination or oxychlorination utilizing ethylene as a feedstock. In most cases, 1,1,2,2-tetrachloroethane is not isolated, but immediately thermally cracked at 454°C to give the desired trichloroethylene and tetrachloroethylene products (122). A two-stage chlorination of 1,2-dichloroethane to give 1,1,2,2-tetrachloroethane has been patented (126). High purity 1,1,2,2-tetrachloroethane is made by chlorinating acetylene. 

The first U.S. plant for acrylonitrile manufacture used an ethylene cyanohydrin feedstock. This was the primary route for acrylonitrile manufacture until the acetylene-based process began to replace it in 1953 (40). Maximum use of ethylene cyanohydrin to produce acrylonitrile occurred in 1963. Acrylonitrile (qv) has not been produced by this route since 1970. 

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