Acetylene process

Most carbide acetylene processes are wet processes from which hydrated lime, Ca(OH)2, is a by-product. The hydrated lime slurry is allowed to settle in a pond or tank after which the supernatant lime-water can be decanted and reused in the generator. Federal, state, and local legislation restrict the methods of storage and disposal of carbide lime hydrate and it has become increasingly important to find consumers for the by-product. The thickened hydrated lime is marketed for industrial wastewater treatment, neutrali2ation of spent pickling acids, as a soil conditioner in road constmction, and in the production of sand-lime bricks. 

Based on the bench-scale data, two coal-to-acetylene processes were taken to the pilot-plant level. These were the AVCO and Hbls arc-coal processes. The Avco process development centered on identifying fundamental process relationships (29). Preliminary data analysis was simplified by first combining two of three independent variables, power and gas flow, into a single enthalpy term. The variation of the important criteria, specific energy requirements (SER), concentration, and yield with enthalpy are indicated in Figure 12. As the plots show, minimum SER is achieved at an enthalpy of about 5300 kW/(m /s) (2.5 kW/cfm), whereas maximum acetylene concentrations and yield are obtained at about 7400 kW/(m /s) (3.5 kW/cfm). An operating enthalpy between these two values should, therefore, be optimum. Based on the results of this work and the need to demonstrate the process at... 

Alternatives to oxychlorination have also been proposed as part of a balanced VCM plant. In the past, many vinyl chloride manufacturers used a balanced ethylene—acetylene process for a brief period prior to the commercialization of oxychlorination technology. Addition of HCl to acetylene was used instead of ethylene oxychlorination to consume the HCl made in EDC pyrolysis. Since the 1950s, the relative costs of ethylene and acetylene have made this route economically unattractive. Another alternative is HCl oxidation to chlorine, which can subsequently be used in dkect chlorination (131). The SheU-Deacon (132), Kel-Chlor (133), and MT-Chlor (134) processes, as well as a process recently developed at the University of Southern California (135) are among the available commercial HCl oxidation technologies. Each has had very limited industrial appHcation, perhaps because the equiHbrium reaction is incomplete and the mixture of HCl, O2, CI2, and water presents very challenging separation, purification, and handling requkements. HCl oxidation does not compare favorably with oxychlorination because it also requkes twice the dkect chlorination capacity for a balanced vinyl chloride plant. Consequently, it is doubtful that it will ever displace oxychlorination in the production of vinyl chloride by the balanced ethylene process. 

The end product of the acetylene process was a high purity monomer that contained some water-derived impurities such as acetaldehyde but was free of some of the organic impurities such as butadiene, ethylene, and propylene which are often associated with other processes. 

The petrochemical acetylene processes using light petroleum fractions, such as the Wulff, Kureha, and Japanese Geon processes are interesting in a strict economic sense, but according to a published report (20), one of these encountered technical problems in operation. It is believed that the problem was in maintaining the desired 1 1 ratio of acetylene to ethylene (21). 

The synthesis of acetaldehyde by oxidation of ethylene, generally known as the Wacker process, was a major landmark in the application of homogeneous catalysis to industrial organic chemistry. It was also a major step in the displacement of acetylene (made from calcium carbide) as the feedstock for the manufacture of organic chemicals. Acetylene-based acetaldehyde was a major intermediate for production of acetic acid and butyraldehyde. However the cost was high because a large energy input is required to produce acetylene. The acetylene process still survives in a few East European countries and in Switzerland, where low cost acetylene is available. 

M. Sittig, Acetylene Processes and Products, Noyes Development Corp., Park Ridge,... 

Co saturated hydrocarbons are used extensively in the United States, whereas the acetylene process was used almost exclusively in Europe until recently. These processes were extended by the late 1950 s and early 1960 s by a new approach called the Wacker process or the Wacker-Hoechst process, consisting of the liquid phase catalytic oxidation of ethylene to acetaldehyde, as outlined in Table II. 

No comparative economic evaluation of all the known commercial acetaldehyde processes has been described in the literature. Recently, the Wacker process was compared with the acetylene process, using European economic data (29). An economic comparison of the one-stage vs. two-stage Wacker processes, using German wage and material price levels of 1961, is given in Table VIII. 

The economics of this process, compared with the acetylene process, will depend on the ratio of acetylene to ethylene prices per unit weight. This ratio is 2 1 to 3 1, based on recent literature data 11, 29, 38). Although one cannot obtain exact data, prices of 10 cents per lb. for acetylene vs. 5 cents per lb. of ethylene have been quoted. A savings of 28 per metric ton may be obtained using the Wacker process 11, 20). 

It should be emphasized that the development of separation processes has, to a large extent, made possible production of the hydrocarbons from petroleum and natural gas. Large volumes of many of these hydrocarbons are naturally present in the raw materials or in the gases produced by refining operations, and separation is the only problem. For those hydrocarbons requiring special manufacturing processes such as benzene and acetylene, processes for purification are also necessary. Separation process articles are listed under Separation Processes in the bibliography except for those articles which relate to only one compound. 

In the acetylene process, methane is first converted acetylene by par tial Oxidation. 

Acetaldehyde can be produced by the partial oxidation of ethanol and the direct oxidation of ethylene. The predominant commercial process, however, is the direct liquid phase oxidation of ethylene. As with many other ethylene-based petrochemicals, acetaldehyde was first produced commercially from acetylene. The acetylene process was developed in Germany more than 70 years ago and was still practiced until the mid-1970s when the high cost and scarcity of acetylene forced it into obsolescence. Another early route to acetaldehyde was based on ethanol. Ethyl alcohol can be either oxidized or alternatively dehydrogenated to acetaldehyde. Site-... 

Figure 77. Flow diagram of the old Huls acetylene process...

The acetylene process was developed in Germany in the early 1940s to supply the synthetic rubber industry [19]. Acetylene is reacted with hydrogen cyanide in an aqueous medium in the presence of catalytic amounts of cuprous chloride. The reaction is maintained at 80 90°C at a pressure of 1-2 atm. The reaction is highly exothermic forming a gaseous reactor effluent. This crude product is water-scrubbed and the pure acrylonitrile product is recovered from the resultant 1-3% aqueous solution by fractional distillation. The major drawbacks of this process are the large number of by-products formed by hydration, the loss of catalyst activity from hydrolysis reactions, and the buildup of ammonium chloride and tars. 

The acetylene process is a particular form of the thermal process because acetylene thermally decomposes at about 800°C in an exothermic reaction. Once the reaction is started, the acetylene decomposition reaction autogenously provides the energy required for the cracking of acetylene to carbon followed by the synthesis of the carbon black ... 

The reaction produces temperatures exceeding 2,500°C at the carbon black surface. The carbon black formation takes place in the temperature region below 2,0(X)°C above 2,000°C a partial graphitization occurs. The Shawinigan process is a typical example of an acetylene process. ... 

Due to the relatively low temperature of the flame, soldering can be performed using simple propane/air burners. The oxy-acetylene process, however, maybe a better option for more demanding soldering tasks. 

Braze welding (see Fig. 2.35) uses filler metals such as brass or bronze, which are not distributed in the joint by capillary action. The benefits of the flexible oxy-acetylene process make this a frequent choice here. Braze welding produces very strong joints in steel and copper. It is widely used to repair cast parts. 

Carbon black is favorable as a support material not only because of its high surface area and electronic properties, but it is also abundant, chemically inert, and environmental friendly (Bleda-Martinez et al., 2007). Carbon blacks are typically used as supports which are manufactured by the pyrolysis of hydrocarbons or oil fractions using oil furnaces or acetylene processes. Some of the most common carbon blacks used for platinum deposition in PEMFC catalysts are synthesized using the furnace method where the input materials are burned with hmited air at about 1400°C (Dowlapalli et al., 2006). Vulcan XC-72 and Black Pearl 2000 represent these types of carbon blacks. These carbon blacks are easily made and abundant making them popular choices for carbon black supports for Pt/C catalysts (Cameron et al., 1990). 

Carbon black can be produced using several methods, including the lampblack, channel black, thermal black, and acetylene processes. However, the vast majority - over 90% - of today s carbon black is manufactured using the oil furnace process, a highly efficient method that permits rigid control of chemical and physical properties. The oil furnace process yields carbon black in fluffy or low-density powder form. Many grades are subsequently converted to pellets (beads) for ease of handling. 

Now there are at least six chloroprene plants worldwide. All but one of these plants produce chloroprene from butadiene. However, there is one remaining plant that produces chloroprene monomer using the original acetylene process as shown in Figure 4.27. 

Figure 4.27 Chloroprene monomer produoed by the original acetylene process Standard Classifications...

The "acetylene process", used until the 1960s for making chloroprene, starts out by joining two acetylene molecules, and then adds HCl to the joined intermediate across the triple bond to convert it to chloroprene as shown here ... 

This "acetylene process" has been replaced by a process which adds CI2 to one of the double bonds in 1,3-butadiene instead, and subsequent elimination produces HCl instead, as well as chloroprene. 

Acetylene still is a preferred raw material for some products, but it has been largely supplanted by ethylene for many others. Chemicals once produced from acetylene by processes now considered outdated include vinyl chloride, vinyl acetate, acetaldehyde, acrylonitrile, neoprene, and chlorinated solvents. In 1990, an improved, carbide-based acetylene process was being implemented to supply raw material for chemical processes. This may make acetylene more competitive with ethylene as a raw material. 

From the very beginning up to the 1960s, chloroprene was produced by the older energy-intensive acetylene process using acetylene, derived from calcium carbide [3]. The acetylene process had the additional disadvantage of high investment costs because of the difficulty of controlling the conversion of acetylene into chloroprene. The modern butadiene process, which is now used by nearly all chloroprene producers, is based on the readily available butadiene [3]. 

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