Acetylene Production

Beginning in the middle of the twentieth century alternative methods of acetylene production became practical One of these is based on the dehydrogenation of ethylene... 

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. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

Worldwide, approximately 180, 000 t/yr acetylene product is recovered as a by-product within olefin plants. This source of acetylene is expected to increase as plant capacity and furnace temperature increase. The recovery may include compression and transfer of the acetylene product via pipelines directly to the downstream consumer. 

Ethylene Stripping. The acetylene absorber bottom product is routed to the ethylene stripper, which operates at low pressure. In the bottom part of this tower the loaded solvent is stripped by heat input according to the purity specifications of the acetylene product. A lean DMF fraction is routed to the top of the upper part for selective absorption of acetylene. This feature reduces the acetylene content in the recycle gas to its minimum (typically 1%). The overhead gas fraction is recycled to the cracked gas compression of the olefin plant for the recovery of the ethylene. 

In the United States, the acetylene production exceeded 450, 000 t/yr between 1963 and 1970, but then declined until it hit a minimum production level below 150, 000 t/yr in 1982. Of this production, about 40,000 t were dedicated to industrial use, ie, welding, etc. Thus only slightly more than 100,000 t were produced for the chemical process industry. Figure 14 illustrates the 17-year decline in acetylene production and indicates the reduced derivative demand to which the accumulated decline is attributed (37). 

In 1984, acetylene production received a significant influx with the increase of capacity at the Borden Co. plant in Geismar, Louisiana. This influx provided an additional 33,000 t/yr, which were absorbed by the vinyl chloride monomer (VCM) and acetylenic chemicals market. Acetylene demand has... 

Japan and China. During the 1980s, acetylene demand in Japan suffered a significant decline. Chemical use declined from over 100,000 to 42,000 t, acetylene black production declined from 20,000 to less than 10,000 t, and industrial use went from 42,000 to 30,000 t. Thus, based on 1990 estimates, Japan has an excess capacity for acetylene production with capabiUties for 247, 000 t/yr and a demand of only 82,000 t. 

Very Htde data are readily available on China s supply and demand situation. It is known, however, that they rely almost entirely on calcium carbidey for acetylene production and that there are numerous low capacity plants, a situation that is probably not too different from that of Japan. 

Calcium Carbide and its Derivatives. Although hydrocarbon-based acetylene production has become mote important, eady manufacture of acetylene was based on manufacture of the iatermediate, calcium carbide [73-20-7J, CaC2. This ionic acetyUde is produced by reaction of lime and carbon ia electric-arc furnaces (16). 

Fabiano et al. (1999) describe an explosion in the loading section of an Italian acetylene production plant in which the installed flame arresters did not stop a detonation. The arresters were deflagration type and the arrester elements were vessels packed with silica gel and aluminum plates (Fabiano 1999). It was concluded that the flame arresters used were not suitable for dealing safely with the excess pressures resulting from an acetylene decomposition, and may not have been in the proper location to stop the detonation. 

Acetylene production. Hydrogen is produced as a by-product in the production of acetylene by high-temperature thermal cracking in a plasma arc process. In a simplified form,... 

Dehydrophenol 20i is a tautomeric form of carbene la, and a [1,3]-H migration should in principal interconvert these species. However, under the conditions of matrix isolation the benzynes 201—1 are thermally and photochemically stable towards rearrangement to the corresponding carbenes. UV irradiation of 20i results in a ring-opening and formation of so far unidentified acetylenic products. 

As shown in Scheme 7-21, an equimolar mixture of dimethylzinc and the coside chain vinyl lithium is treated sequentially with siloxyl-2-cyclopentenone and the propargylic iodide in the presence of HMPA. The desired product 79 is formed with 71% yield.12 The acetylenic product is a common intermediate for the general synthesis of naturally occurring PGs. 

Primary propargylic formates decarboxylate in the presence of Pd(acac)2 and Bu3P at room temperature to give mainly allenic products (Eq. 9.115) [91]. Initial formation of a propargylic palladium complex, which rearranges to the more stable allenylpalladium species, accounts for this transformation. Under similar conditions, a terminal allenyl formate afforded a 99 1 mixture of allene and acetylene product (Eq. 9.116) [91]. However, a mixture of enyne elimination products was formed when a secondary propargylic carbonate was treated with a palladium catalyst (Eq. 9.117). 

A total of sixteen German scientists worked at the Louisiana, Missouri plant, five in coal hydrogenation, two in Fischer-Tropsch, eight in oil shale, one in acetylene production. 

Fluoride ion promoted cleavage of propynylsilanes and subsequent reaction of the carbanion with carbonyl compounds produces allenic compounds. The reaction with formaldehyde and pivaldehyde fails, but both the allenic and acetylenic products are obtained from the reaction with acrolein and benzaldehyde [49]. Allylsilanes react with carbonyl compounds to produce but-3-en-l-ols [50],... 

The product distribution from the two types of anions is also very different. PropargyUde anions derivatize to give acetylenic products exclusively (except when steric interactions favour the aUenic products), while allenic anions with unhindered derivatizing agents give both aUenic and acetylenic structures " " " . 

Approximately 80% of acetylene production is used in chemical synthesis. In the United States approximately 100,000 tons are used annually. Acetylene saw much wider use in the past, especially in Germany where it was widely used as in chemical synthesis. During recent decades, greater use of ethylene as a chemical feedstock and the development of more economical chemical production methods that eliminate acetylene has reduced acetylenes use in the chemical industry. Since 2000, use in the United States has decreased by approximately... 

A shift from allenes to acetylenic products formed from acetylenic alcohols in which trifluoro-methyl groups are replaced by difluoromethyl groups can be explained in terms of lowering the positive character of the terminal acetylenic carbon atom, thus retarding the nucleophilic attack of fluorine at this position.56... 

Table III shows that gaseous product from the irradiation of less than 10 micron coal (micronized) showed higher methane and lower acetylene than coal from the cube. Other particle sizes will have to be investigated to determine if particle size is a parameter for maximum acetylene production.

Since the substitution reaction succeeded so well with olefins, the obvious extension to acetylenes was tried. Of course, only terminal acetylenes could be used if an acetylenic product was to be formed. This reaction has been found to occur but probably not by a mechanism analogous to the reaction of olefins (43,44). It was found that the more acidic acetylene phenylacetylene reacted with bromobenzene in the presence of triethylamine and a bisphos-phine-palladium complex to form diphenylacetylene, while the less acidic acetylene, 1-hexyne did not react appreciably under the same conditions. The reaction did occur when the more basic amine piperidine was used instead of triethylamine, however (43). Both reactions occur with sodium methoxide as the base (44). It therefore appears that the acetylide anion is reacting with the catalyst and that a reductive elimination of the disubstituted acetylene is... 

The acetylene substitution reaction proceeds much more rapidly than the related olefin reaction. The acetylene products and starting materials also undergo side reactions such as polymerization concurrently with the substitution. The best yields are obtained when the reactants are diluted with a large excess of amine, or carried out at lower temperatures in methanol with sodium methoxide as the base. Vinylacetylene derivatives can also be prepared by this reaction starting with vinylic halides. For example, ( )-methyl 3-bromo-2-methylpropenoate and r-butylacetylene react in 2 hours at 100° to form the expected vinylacetylene derivative in 59% yield ... 

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