Methyl methacrylate acetone-cyanohydrin process

The handling of toxic materials and disposal of ammonium bisulfate have led to the development of alternative methods to produce this acid and the methyl ester. There are two technologies for production from isobutylene now available ammoxidation to methyl methacrylate (the Sohio process), which is then solvolyzed, similar to acetone cyanohydrin, to methyl methacrylate and direct oxidation of isobutylene in two stages via methacrolein [78-85-3] to methacryhc acid, which is then esterified (125). Since direct oxidation avoids the need for HCN and NH, and thus toxic wastes, all new plants have elected to use this technology. Two plants, Oxirane and Rohm and Haas (126), came on-stream in the early 1980s. The Oxirane plant uses the coproduct tert-huty alcohol direcdy rather than dehydrating it first to isobutylene (see Methacrylic acid). 

The only method used in the U.S. for the production of methyl methacrylate is the acetone cyanohydrin process. Acetone cyanohydrin (from the reaction of acetone with hydrogen cyanide) is reacted with sulfuric... 

The price of butanes and butylenes fluctuates seasonally depending on the demand for gasoline in the United States. Since much chemical-product usage is determined by price—performance basis, a shift to development of butylene-based technology may occur. Among the butylenes, demand for isobutylene is likely to increase (and so its price) as more derivatives such as methyl methacrylate and methacrylic acid are produced from isobutylene instead of the conventional acetone cyanohydrin process. 

The most common process used to produce methyl methacrylate ( 0.71/lb) is the acetone cyanohydrin process [36]. Acetone is reacted with hydrogen cyanide and methanol to produce methyl methacrylate ... 

Vinyl compounds are widely used in the industry in manufacture of various resins and polymers and the like. Methacrylic acid and methyl methacrylate are especially attractive as row materials of polymethyl methacrylate that is an important polymer so-called "organic glass." Until a new process consisting of two-step oxidation of isobutylene was commercially practiced in 1982, methyl methacrylate had been produced by the "Acetone Cyanohydrine Process," which uses acetone, hydrogen cyanide, methanol, and sulfuric acid as raw materials. Technical and economical drawbacks of this process have spurred a considerable industrial research effort to develop an alternate route to methacrylic acid and methyl methacrylate. Therefore, many attempts have been focused on the production of these compounds by aldol-type condensation using HCHO. 

Most methyl methacrylate (MMA) is made by the acetone cyanohydrin process. Developed in the 1930s for the production of MMA from acetone, hydrogen cyanide, sulfuric acid, and methanol, it has been improved over the years, but problems inherent in the basic process persist. For example, production of large quantities of ammonium bisulfate by-product and sulfuric acid sludge, as well as difficulty in obtaining low cost sources of... 

Acrylics. Acetone is converted via the intermediate acetone cyanohydrin to the monomer methyl methacrylate (MMA) [80-62-6]. The MMA is polymerized to poly(methyl methacrylate) (PMMA) to make the familiar clear acryUc sheet. PMMA is also used in mol ding and extmsion powders. Hydrolysis of acetone cyanohydrin gives methacrylic acid (MAA), a monomer which goes direcdy into acryUc latexes, carboxylated styrene—butadiene polymers, or ethylene—MAA ionomers. As part of the methacrylic stmcture, acetone is found in the following major end use products acryUc sheet mol ding resins, impact modifiers and processing aids, acryUc film, ABS and polyester resin modifiers, surface coatings, acryUc lacquers, emulsion polymers, petroleum chemicals, and various copolymers (see METHACRYLIC ACID AND DERIVATIVES METHACRYLIC POLYMERS). 

Until 1982, almost all methyl methacrylate produced woddwide was derived from the acetone cyanohydrin (C-3) process. In 1982, Nippon Shokubai Kagaku Kogyo Company introduced an isobutylene-based (C-4) process, which was quickly followed by Mitsubishi Rayon Company in 1983 (66). Japan Methacryhc Monomer Company, a joint venture of Nippon Shokubai and Sumitomo Chemical Company, introduced a C-4-based plant in 1984 (67). Isobutylene processes are less economically attractive in the United States where isobutylene finds use in the synthesis of methyl /i / butyl ether, a pollution-reducing gasoline additive. BASF began operation of an ethylene-based (C-2) plant in Ludwigshafen, Germany, in 1990, but favorable economics appear to be limited to conditions unique to that site. 

Cyanohydrins are used primarily as intermediates in the production of other chemicals. Manufacture of methyl methacrylate, used to make acrylic mol ding resins and clear sheet, eg, Plexiglas acrylic sheet, from acetone cyanohydrin is the most economically important cyanohydrin process (see Methacrylic polymers). Cyanohydrins are also used as solvents in appHcations including fiber-spinning and metals refining. Cyanohydrins and derivatives reportedly act as antiknock agents in fuel oil and motor fuels and serve as electrolytes in electrolytic capacitors. 

One of the most important appHcations of this process is that of methyl methacrylate manufacture. In this process (81), acetone cyanohydrin is treated with sulfuric acid at 100°C, affording the corresponding methacrylamide sulfate which is esterified with methanol. After purification, methyl methacrylate (99.8% purity) is obtained in a yield of ca 85%. 

A plant produced methyl methacrylate by reacting hydrogen cyanide with acetone to produce acetone cyanohydrin followed by further processing to produce methyl methacrylate. The hydrogen cyanide was produced at another site and was transported to the methyl methacrylate plant by railcar. A hydrogen cyanide plant was subsequently installed at the methyl methacrylate plant site to eliminate the need for shipping hydrogen cyanide or acetone cyanohydrin. 

Inhibitors are introduced al specific points in the process to prevent polymerization Sulfuric acid serves as catalyst in a combined hydrolysis-esterilieaiion of methacrylamide sulfate to a mixture of methyl methacrylate and methacrylic acid. Conversion of methacrylamide sulfate to methyl methacrylate can be carried out using a variety of procedures for die recovery of crude methyl methacrylate and fur separation of methanol and methacrylic acid for recycling. A schematic of the overall process is given in Figure I. The overall yield based on acetone cyanohydrin is approximately 90D Most of Ihe world supply of MMA is still produced by this process. 

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

The traditional acetone cyanohydrin (ACH) process is the most widely used in Europe and North America, while other processes are more often used in Asia. In the ACH process (Figure 2.63), acetone and hydrogen cyanide react to yield acetone cyanohydrin the latter is then reacted with an excess of concentrated sulfuric add to form methacrylamide sulfate. In a later stage, methacrylamide is treated with excess aqueous methanol the amide is hydrolyzed and esterified, with formation of a mixture of methyl methacrylate and methacrylic acid. The ACH process offers economical advantages, especially in Europe, where large plants are in use - most of them have been in operation for decades. The process also suffers from drawbacks that have been the driving forces for the development of alternative technologies. 

The ACH process has been improved by Mitsubishi Gas [332]. Acetone cyanohydrin is first hydrolyzed to 2-hydroxyisobutylamide with a Mn02 catalyst the amide is then reacted with methyl formate to produce the methyl ester of 2-hydroxyisobutyric acid, with co-production of formamide (this reaction is catalyzed by sodium meth-oxide). The ester is finally dehydrated with an Na-Y zeolite to methyl methacrylate. Formamide is converted into cyanhydric acid, which is used to produce acetone cyanohydrin by reaction with acetone. The process is elegant, since it avoids the co-production of ammonium bisulfate, and no net income of HCN is present. However, there are many synthesis steps, and a high energy consumption. 

The process flowsheet is given in Figure 4.4 [38]. Acetone and hydrogen cyanide are reacted in a strong base. Sulfuric acid is used to neutralize excess alkali to prevent the decomposition of the cyanohydrin then sodium sulfate is filtered out and the unreacted HCN and acetone are recycled by distillation. The cyanohydrin is hydrolyzed with sulfuric acid to form methacrylamide sulfate. The methacrylamide sulfate reacts with methanol to form methyl methacrylate and ammonium bisulfate. Distillation removes methyl methacrylate and unreacted methanol which is recycled. Water extraction is used to remove any excess methanol and the monomer is purified to 99.8% in a rerun tower. This is the only process used in United States to produce methyl methacrylate [39]. 

Acryclic acid is obtained by the catalytic oxidation of propylene and acrylates (methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate...) by alcohol esterification of the acid. The preparation of methacrylic acid involves the acidic hydrolysis of acetone cyanohydrin and methyl methacrylate is obtained by a similar process involving the methanolysis of acetone cyanohydrin. 

Methyl methacrylate monomer, which is polymerized in large quantities in commercial practice to give the clear resinous compositions sold as Lucite and Plexiglas, is prepared from acetone cyanohydrin by a process involving dehydration and hydrolysis of the nitrile to methacrylamide, followed by aicoholysis of the amide. 

Several other types of hydrocarboxylations and hydroesterifications have been conducted with rates and selectivity that are appropriate for the synthesis of fine chemicals and commodity chemicals. One target for hydroesterification has been methyl methacrylate, the monomer of polyfmethyl methacrylate), which is the polymer often called "acrylic". It is estimated that 2.1 million metric tons of methyl methacrylate was produced in 2005. Much of this material is produced from acetone cyanohydrin, but two alternative routes could involve catalytic carbonylation. The first route would involve the hydroesterification of methylacetylene, and this chemistry relates to the original route to methyl methacrylate by carbonylation of methylacetylene using nickel carbonyl as catalyst. The second route involves the sequence of ethylene hydoesterification, aldol addition of the resulting ester to formaldehyde, and dehydration. This sequence comprises Lucite s new "Alpha" process and is shown in Equation 17.33. The route to methyl methacrylate by hydrocarboxylation of ethylene produces water as the only byproduct. 

Synthesis of methyl methacrylate is fundamental to the production of the transparent plastic polymethyl methacrylate (PMMA), and is estimated at over two million metric tons per year. The monomer is most commonly synthesized via the well-established Acetone Cyanohydrin (ACN) process, as shown below, based on easily available raw materials such as, acetone, hydrogen cyanide, methanol and sulfuric acid. Reaction of acetone and hydrogen cyanide yields acetone cyanohydrin as an intermediate, which is then reacted with excess amount of concentrated sulfuric acid, followed by thermal cracking to form methacrylamide sulfate. The methacrylamide sulfate intermediate is then further hydrolyzed and esterified with aqueous methanol to form methyl methacrylate. 

Methyl methacrylate (MMA) is by far the most important methacrylic ester monomer, accounting for 90% of the volume of methacrylic ester monomers. Polyfmethyl methacrylate) (PMMA) was first synthesized in 1928 in various laboratories, and was first brought to market in 1933 by Rohm Haas Co. under the trademark Plexiglas. ICI then reformed Rohm s method and commercialized MMA in 1937 by the acetone cyanohydrine (ACH) process,[l] which is still the most widely adopted technique even today. The world production capacity of PMMA has almost doubled in the past fifteen years, and overall global PMMA production capacity accounts for six hundred and fifty thousand tons per year. [3] It is predicted that starting from 2010, the demand for PMMA will rise by 3-5% annually and the demand of MMA is expected to steadily grow in the future.[3]... 

Various esters of methacrylic acid are commercially available but methyl methacrylate is by far the most important. The ester can be made from free methacrylic acid but the standard method is from acetone cyanohydrin without isolation of intermediates, (cf.. Section 6.2.2). In a typical process, acetone cyanohydrin is treated with concentrated sulphuric acid at lOO C to form methacrylamide sulphate which is fed directly into aqueous methanol. The methyl methacrylate is separated by steam distillation and purified by distillation. 

HCN is the precursor to sodium cyanide and potassium cyanide, which are used mainly in mining. Via the intermediacy of cyanohydrins, a variety of useful organic compounds are prepared from HCN including the monomer methyl methacrylate, from acetone, the amino acid methionine, via the Strecker synthesis, and the chelating agents EDTA and NTA. Via the hydrocyanation process, HCN is added to butadiene to give adiponitrile, a precursor to Nylon 66. 

Methacrylic acid can also be produced by a variety of processes including oxidation of ethylene, propylene, and isobutylene. The most common commercial process for making methacrylic acid is the acetone cyanohydrin (ACN) process. The feedstocks for this process are acetone, hydrogen cyanide, and sulfuric acid. The acetone and HCN are reacted under alkaline conditions to produce the cyanohydrin. Reaction of the cyanohydrin with sulfuric acid ultimately produces methacrylamide sulfate, hydrolysis of which produces methacrylic acid. Methyl methacrylate can be made either by esterifying the acid or directly by reacting the amide sulfate with methanol. 

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