The Synthesis of Methacrylic Acid - Essay Example

A SYNTHESIS OF METHACRYLIC ACID Brief Information on Methacrylic Acid With elements of carbon, hydrogen and oxygen, Methacrylic Acid (MAA) has as its structural formula CH2=C(CH3)COOH (see Barbalace) or C(4)H(6)O(2) (see OSHA for more technical or, rather, chemical details). It is colorless liquid with an acrid or repulsive odor. MAA is used as an internal and external intermediate in the chemical industry for the production of methacrylic acid esters and as a co-monomer in different types of polymers (OECD SIDS). Specifically, methacrylic acid is an element for the production of resin and plastics. In cosmetics, MAA at concentration between fifty (50) and eighty-eight (88) per cent is used to pre-treat the nail and maximize the adhesion between the nail and artificial nail extender (see Andersen). As commercial product, MAA is always made to contain inhibitor to prevent polymerization. Exposure to traces of hydrochloric acid or heat is a primary condition that contributes to its instability. Likewise, exposure to light and air should be avoided to foil possible polymerization, which – if it happens inside tightly sealed containers – may result to violent rupture (of container) (see OSHA). MAA is incompatible with oxidizing agents such as peroxides, amines, strong bases, elevated temperatures, or hydrochloric acid (HCL). Contact between MAA and any of these may cause reactions to transpire (OSHA; Barbalace). In cases of fire involving methacrylic acid, toxic gases (such as carbon monoxide) – a hazardous decomposition product – may be released. Human exposure to MAA may be through inhalation, ingestion, eye or skin contact and absorption through the skin. Possible effects on humans are on the eyes, skin and immune system (ACGIH). Medical case reports involving MAA often involve children (see Andersen). These cases are about ingestion including drooling, gagging and vomiting. Children who were exposed to methacrylic acid as a result of accidental spills caused first and second degree burns to the eyes, face, hands, arms and chest. The workers – e.g., acrylic acid resin workers – who are exposed to up to 113 ppm (parts per million) MAA are sensitized, exhibiting skin toxicity and severe corneal burn (ACGIH). As to its effect to animals, MAA is absorbable by the mucous membranes of the lungs, the gastrointestinal tract and the skin, from which it is distributed to all major tissues. Acute toxicity symptoms may include severe gastric irritation, gasping, labored perspiration, prostration and hematuria. In one short-term study involving rats, it was shown that exposure to methacrylic acid at 1300 ppm (parts per million) showed nose and eye irritation and weight loss. To other animals as well, MAA is an ocular toxicant; specifically to the skin of rabbits and guinea pigs, methacrylic acid is corrosive – that is, an exposure of 3 minutes may cause severe erythema and slight to moderate edema while 15 minutes to 24 hours can cause marked to severe discoloration, slight to severe subcutaneous hemorrhages, necrosis, ulcerations, severe erythema, edema and concave eschar (see Andersen). Possible Production Routes of Methacrylic Acid Industrially, methacrylic acid may have a limited use in the production of homo- and co-polymers for application as sizing and finishing agents; but MAA and its derivatives – and methyl ester is the most frequently used derivative – have an opulent array of chemistries and are very widely used in commercial applications as monomers for the production of various types of polymer artifact (Wilczynski & Juliette). For one, MAA is submitted to esterification with methanol en route to production of methyl-methacrylate that is ordinarily polymerized to form poly(methyl methacrylate). “This polymer, because of its hardness and clarity, is used as cast and extruded sheet for glazing materials, biomedical appliances, surface coatings, and optical products” (Rase, 288). In the United States of America, this polymer is placed under the trade names ‘Plexiglas’ and ‘Lucite’ (Rase). In addition, MAA and its esters are widely used in the production too of specifically “acrylic sheet, molding products, coatings and impact modifiers, and in applications that include use in detergent builders, rheology modifiers, oil additives, solvent-less inks, paints, polishes and coatings” (Dicosimo et al.). In fact, figures show that in 1999, the world capacity for methyl methacrylate (MMA was about 24,000,000 tons per year. Of this volume, 780,000 per year was needed in the United States of America, 440,000 for Western Europe, and 460,000 for Japan. The largest worldwideproducer of MMA in 2000 was Ineos, producing a total of 540,000 tons per year (cf. Weissermel, Arpe & Lindley 283). First described in its polymeric form in 1880 (Engelhorn et al. 70), methacrylic acid was initially obtained in the form of its ethyl ester with the treatment of phosphorus pentachloride with oxyisobutyric ester (Frankland 12). However, it has become more readily obtained by boiling citra- or meso-brompyrotartaric acids with alkalis – a process which crystallizes MAA in prisms. When fused with an alkali, propionic acid is formed; while sodium amalgam causes MAA’s reduction into isobutyric acid (Engelhorn et al.). Since 1930’s, there have been a number of production routes to MAA; and, all of which require various types of catalysts in order to promote the separate steps involved (Wilczynski & Juliette). At least, in the past years, the predominant manufacturing route to the two simplest methacrylates remains through the conversion of acetonecyanohydrin (ACH) in sulfuric acid to methacrylamide and by either hydrolysis to MAA or esterification with methanol to give methyl methacrylate (MMA) (see Wilczynski & Juliette). The ACH route – which remains the feedstock of all methacrylic acid derivatives particularly in the United States of America and the Western Europe (Weissermel, Arpe & Lindley 284) -- produces MAA by base-catalyzed reaction of acetone with hydrogen cyanide. This is followed by reaction with sulfuric acid in order to produce methacrylamide sulfate. The process’ final stage is a combined hydrolysis-esterification of the sulfate with methanol to methyl methacrylate and methacrylic acid. In the same process, methacrylic acid and methanol are recycled (Rase 288). It was the Rohm and Hass and ICI in the 1930’s that first industrially manufacture MMA from acetone. They were eventually followed by Degussa, DuPont, and Rheinpreussen. Their very first step to manufacture ACH consisted of base-catalyzed addition of HCN to acetone below 400C. Used generally in the liquid phase, the catalysts that these manufacturing companies used were alkali, metal hydroxides, carbonates and/or basic ion-exchangers. Markedly, the selectivity to ACH is 92-99% (based on HCN) and more than 90% (based on acetone). ACH is then reacted with 98% H2SO4 at 80-1400C to form methacrylic acid amide sulfate. Methacrylic acid amide sulfate is eventually converted into methyl methacrylate and NH4HSO4 by reacting with methanol at about 800C, or at 100-1500C under pressure. Now, the over-all selectivity to methyl methacrylate is measly about 77% (based on acetone). Mitsubishi Gas Chemical (MGC) has come up with a new development by intending to avoid the disadvantages of NH4HSO4 co-products. MGC partially hydrolyzes cyanohydrin to α-hydroxyisobutyr-amide, which is successively reacted with methyl formate so as to give the methyl ester and the formamide (Weissermel, Arpe & Lindley 284). In the 1960’s, according to the Process Economics Program (PEP) Report No. 11, which was “concerned primarily with the production of methyl methacrylate (MMA),” there was at the time various processes that were application to production of both methacrylic acid and MMA. These processes were the “acetone cyanodhydrin process, the dinitrogen tetroxide oxidation of isobutylene, the vapor-phase air oxidation of isobutylene, … the catalytic methyl acetylene process, … the isobutylene ammoxidation process, the saturated ester process, the formaldehyde-propionate condensation process, and the dehydrochloronation process.” Minor updates in the design of the ACH process for methyl methacrylate marked the 1970’s (see PEP Report No. 11A). These updates were in the form of the extension of the scope of the acetone cyanohydrin (ACH) process “to include the manufacture of hydrogen cyanide and the decomposition of the ammonium acid sulfate by-product.” The process routes, too, of direct oxidation of isobutylene and the production and hydrolysis of methacrylonitrile were updated, with the latter process made to include the integrated production of methacrylonitrile. PEP Report No. 11A finally notes that the trade literature of the 1970’s was showing a high level of activity in isobutylene oxidation, but clarifies that during this decade no commercial plant was in operation following the process of isobutylene oxidation. In the ‘80’s, there had been proposals to replace the established route for making methyl methacrylate from acetone, hydrogen, cyanide and methanol. This is accounted for the “continued growth in markets for methacrylate polymers for acrylic sheets and acrylic coatings (leading) to increased demand for the monomers, chiefly methyl methacrylate … (and) specialty methacrylate ester made from methacrylic acid” (PEP Report No. 11B). It was observed during this period that the acetone cyanohydrin route is rendered deficient by its production of acidic wastes. And, hence, it was proposed that the newer processes “avoid these wastes and may also offer lower capital investment, lower production costs, and direct production of methacrylic acid.” Expectedly, in the same decade, several new methyl methacrylate processes were brought to fore and evaluated (on the bases of their process description and cost estimates). These “processes begin with isobutylene, t-butanol, or mixed butylenes, and produce methacrylic acid via methacrolein … (Another) process is based on production of methyl methacrylate from ethylene, carbon monoxide, methanol and formaldehyde via methyl propionate.” It was said that these “processes appear to have about the same production costs as the acetonecyanohydrin route. The … processes that produce a methacrolein intermediate are markedly superior economically to the acetonecyanohydrin route, on the basis of new plant construction and current raw material costs.” PEP Report No. 11C – which was released in 1984 – notes that “for the last fifteen years, processes have been developed to supplant the established process for making methyl methacrylate from acetone, hydrogen, cyanide and methanol.” Accordingly, the ACH route is negatively associated with acidic waste production; and, hence, repeating PEP Report No. 11B, it holds that the proposed newer processes intended to avoid these wastes and offer lower costs. Since 1970’s, then, “a methyl methacrylate process based on a C-4 feedstock has been commercialized in Japan.” This process is reportedly involving oxidation of a t-butanol feed to methacrolein and methacrylic acid in two stages, and then followed by esterification of the acid to methyl methacrylate. In 2003, Chauhan et al. presented their invention involving “a process for preparing 2-hydroxyisobutyric acid from acetonecyanohydrin (ACH) with specificity and at high conversion.” These scientists has prescribed the following steps: (a) contacting acetone cyanohydrin in a suitable aqueous reaction mixture with a catalyst characterized by nitrilase activity, or by nitrile hydratase and amidase activities; and (b) isolating the 2-hydroxyisobutyric acid produced in (the first step) as the acid or corresponding salt. Through this process, MMA is obtained by dehydrating the acid produced in (step a), and isolating the acid or corresponding salt. This invention is reportedly making use of enzyme catalysts “in the forms of microbial cells, permeabilized microbial cells, one or more cell components of a microbial cell extract, and partially purified enzyme(s) or purified enzyme(s).” In whatever form, the enzyme catalyst may be rendered immobilized in or on a soluble or insoluble support. In the last day of the same year, a process for the “hydrolysis of methacrylonitril to MAA … in high yield and at high concentration with high specificity” was patented for Dicosimo et al. Robert Dicosimo and his companions noted that while several manufacturing processes to produce methacrylic acid already exist, the hydrolysis of methacrylamite sulfate (produced from ACH) accounts for the majority of current commercial production worldwide. They report that, in this process, “approximately 1.6 kg of sulfuric acid is required to produce 1 kg of MAA through methacrylamide sulfate.” But precisely to do away with sulfuric acid recycle and regeneration – together with the concern about the significant energy resources required – alternative processes needed to be honed for commercial purposes. Thus, they come to suggest the production route of MMA “via the ammoxidation of isobutylene to give methacrylonitrile, which is then hydrolyzed to methacrylamide by treatment with one equivalent of sulfuric acid. The methacylamide can be hydrolyzed to methacrylic acid under conditions similar to those used in the acetonecynanohydrin-based process.” Dicosimo et al. further noted that “microbial catalysts capable of hydrolyzing methacrylonitrile to MAA … do not produce the undesirable ammonium sulfate waste stream that results when using sulfuric acid.” An example of these microbial catalysts is “Rhodococcus rhodochrous J1 nitrilla, which is used to yield … methacrylic acid from … methacrylonitrille. This enzyme exhibited marked inhibition when the acrylonitrile concentration was higher than 200mM, and the conversion rate of methcrylonitrile to MAA was low when compared to acrylic production.” Dicosimo et al. notes that US Patent No. 5135858 is already about the use of nitrilase enzyme from Rhodococcus for the transformation of methacrylonitrile to methacrylic acid. Likewise, US Patent Nos. 5998180 and 6162624 are disclosing about “the use of Rhodococcus nitrilase enzyme for the hydrolysis of methacrylonitrile to methacrylic acid, where the nitrilase enzymes each have a Km of 500µM or below and a Ki of at least 100mM.” However, when the two Rhodococcus isolates as catalysts for ammonium acrylate production – that is, one with only a nitrilase activity, and one with only a combination of nitrile hydratase and amidase activities – are compared, Dicosimo notes that the conclusion was that “the catalyst having a combination of nitrile hydratase and amidase activities was less preferred due to (the following three reasons): (a) difficulty in inducing the two enzymes in the required ratio, (b) susceptibility of the two enzymes (nitrile hydratase and amidase) to deactivation by acrylonitrile, and (c) inhibition of the two enzymes by the respective products.” Precisely for this reason, Dicosimo et al. held that “developing an industrial process using microbial catalysts having nitrilase or nitrile hydratase/amidase activities to efficiently manufacture acrylic and methacrylic acid has proved difficult.” In addition, “many methods using enzyme catalysts to prepare acrylic acid or methacrylic acid from the corresponding nitrites do not produce and accumulate a product at a sufficiently high concentration to meet commercial needs, or are subject to enzyme inactivation (requiring a low concentration of nitrile over the course of the reaction) or product inhibition during the course of the reaction.” Thus, Dicosimo et al. pinpointed that “the problem to be solved continues to be the lack of facile microbial catalysts to convert acrylonitrile or methacrylonitrile to the corresponding acids in a process characterized by high yield, high concentration, and high selectivity, and with the added advantages of low temperature and energy requirements and low waste production when compared to known chemical methods of nitrile hydrolosis.” To solve this specifically perceived problem, Dicosimo et al.’s invention “provides a process for the hydrolysis of … methacrylonitrile to methacrylic acid in high yield and at high concentration with high specificity.” And, they in effect prescribed the following steps: “(a) contacting … methacrylonitrile in a suitable aqueous reaction mixture with a catalyst characterized by nitrile hydratase and amidase activities of Comamonas testosterone 5-MGAM-4D (ATCC 55744) to produce the corresponding carboxylic acid; and (b) isolating the acrylic acid or methacrylic acid produced in (step a) as the acid or corresponding salt.” A variant of the invention makes use as a catalyst of “nitrile hydratase and amidase activities of Comamonas testosterone 5-MGAM-4D in the form of intact of microbial cells, permeabilized microbial cells, one or more cell components of a microbial cell extract, and partially-purified enzyme(s), or purified enzyme(s).” Wilczynski & Juliette likewise mentions about a separate ACH process which – in contrast to the preceding – does not involve sulfuric acid. Accordingly, this route begins with catalyzed hydration of ACH to hydroxyisobutyramide; then, it is followed by esterification and dehydration steps to MMA. This route is reportedly having an added benefit of recycling HCN as a raw material. Very recently, too, Weissermel, Arpe & Lindley (285) mentions about a “new process that is currently being developed in a pilot plant” involving a separate dehydration of the methyl ester that gives methyl methacrylate and formamide and finally yielding hydrogen cyanide. Considering its being in still in period of development, such process technology details have not yet been disclosed. For now, recent works on MAA are observably focusing on its three other manufacturing routes. These alternative routes have either already reached or are still approaching commercialization. These substitute modes of manufacturing MAA include processes based on any of the following: ethylene (C-2), propylene (C-3), methylacetylene (C-3), or isobutylene (C-4) feedstock (Wilczynski & Juliette; see also Weissermel, Arpe & Lindley 285). The ethylene-based routes to MAA typically involve formaldehyde condensation on either a proprionaldehyde or propionic acid intermediate (Wilczynski & Juliette), and the propylene-based routes ordinarily involve isobutyric acid or isobytyraldehyde intermediates (Wilczynski & Juliette). BASF, in West Germany, announced a route that it developed to methyl methacrylate which begins with even smaller building blocks in the form of ethylene and carbon monoxide. A BASF-plant capable of 80 MM-1b/yr production capacity was expected to be operational before 1990. Oxidation and ammoxidation of isobutylene give rise to different derivatives of methacrylic acid (family). “Oxidation of isobutylene to methacrylic acid produces a significant value-added incentive. It can be brought about by means of nitric oxices and nitric acid in the present of V2O3 catalyst in the liquid phase, although the yield is only 50-60%” (Szmant 339). In 1988, Mitsubishi Rayon announced a production route starting with TBA and letting methyl methacrylate (MMA) represent a new improvement on the direct oxidation of isobutylene. For this, Mitsubishi Rayon erected a 120MM-1b/yr plant. Another competitive production route that was developed included the acid-catalyzed hydrocarbonylation of propylene, in the presence of water or methanol, which yields either MAA or MMA on dehydrogenation of the isobutyric intermediates (Szmant). Said to be the most selective over-all, the methylacetylene-based process involves carbon monoxide and methanol. A single reaction involving the two leads unswervingly to MMA (Wilczynski & Juliette). The isobutylene-based routes involve oxidation processes to reach the methacrylate backbone. Often, it passes through methacrolein as an intermediate (Wilczynski & Juliette). Steam cracking is the major source of C-4 fractions. Characteristically, all of these fractions have close boiling points (1,3 butadiene, isobutene, 1-butene and other butanes), and must be separated by means other than distillation. Once butadiene is removed by solvent extraction, isobutene, together with its tertiary carbocation intermediates, are hydrated to tert-butyl alcohol and readily separated from C-4 raffinate. Note that reversible is the aforementioned reaction, that is, dehydration can be implemented after separation to yield a pure stream of isobutene. Dehydration is an important step in the production of MTBE, which requires an isobutene feed; but, tert-butyl alcohol can also be used directly in the methlacryltic-acid process (See Rase, 288). Still according to Weissermel, Arpe & Lindley (285), to offset the inadequacies of the above-mentioned process, a two-step oxidation process with N2O4 in which the α-hydroxyisobutyric acid formed initially eliminates water to give methacrylic acid called the Escambia process, was ventured into. Unfortunately, however, explosions occurred during industrial operation of the Escambia route. And, thus, this route was discontinued. Notwithstanding, several firms in Japan have developed a two-step oxidation of isobutene that preferentially goes through tert-butanol as the primary intermediate. In this process, isobutene, generally in mixtures with n-butenes and butane (C4 raffinate), is hydrated almost quantitatively to tert-butanol in the liquid phase with an acid catalyst such as an ion exchange resin. Then, this is followed by the heterogeneously catalyzed oxidation to methacrolein at 4200C and 1-3 bar using a promoted Mo/Fe/Ni catalyst system. The convesion of tert-butanol and the selectivity to methacrolein are both 94% (Weissermel, Arpe, & Lindley 285). In the second oxidation step, to maintain the catalyst lifetime and selectivity, the methacrolein is first absorbed in water under pressure and freed from by-products by distillation (Weissermel, Arpe & Lindley 286). Japan Methacrylic Monomer Co. has developed another variant method – called tandem oxidation -- allowing the oxidation to take place without purification of the material from the first step. In this process, “the oxidation to methacrylic acid takes place in the presence of steam at about 3000C and 2-3 bar over oxides of Mo, P, Sb, and W, or of Mo, P, and V, with a conversion of 89% and a selectivity of more than 96%. Then, the acid is extracted from the aqueous phase, purified by distillation, and esterified with methanol” (Weissermel, Arpe & Lindley). In addition to Japan Methacrylic Monomer Co., other plants using this technology are the Kyodo Monomer, Mitsubishi Rayon and Japan Catalytic/Sumitomo Chemical in Japan. Recently, interest has developed in an isobutene or tertbutyl alcohol route (to MAA) similar to the flourishing acrylic acid process for partial oxidation of propane. In Japan, for instance, it is said that apparently viable processes have already been implemented (Rase 288). According to Weissermel, Arpe & Lindley (285), the C-4 basis is especially used in Japan and that “detailed experiments have shown that it is possible to oxidize isobutene directly (single-step process) to methacrylic acid.” This process (in Japan) starts off with inexpensive isobutene, isobutyraldehyde and proppionaldehyde that are produced in the ACH route, and actually avoids formation of the NH4HSO4. Nonetheless, “the selectivity is low to be economical; the oxidation of the intermediate methacrolein to methacrylic acid is particularly critical, and the result is in (observably) in contrast to the oxidation of propene to acrylic acid.” A second possible synthetic pathway to methacrylic acid and its derivatives, not based on acetone, is the ammoxidation of isobutene. Asahi Chemical uses this technology in a plant in Japan… In the second process not based on acetone, isobytyraldehyde is first oxidized with air or O2 to isobutyric acid. The next step, the formal dehydrogenation to methacrylic acid, can be conducted as an oxydehydrogenation in the presence of O2… This reaction can be carried out with homogenous catalysis using HBr (Eastman Kodak) at 160-1750C or in the presence of a Bi-Fe catalyst (Cyanamid) at 250-2600C” (Weissermel, Arpe, & Lindley, 286). In the United States of America, after the introduction of MTBE (methyl tert-butyl ether) as gasoline additive, the demand for isobutene and tert-butyl alcohol as feedstock for the more profitable MTBE production has risen exponentially. However, in 2000, the state of California was restricting the use of MTBE (see Rase 288). References: ACGIH. Industrial Ventilation – A Manual of Recommended Practice. 21st Ed. Cincinnati: American Conference of Governmental Industrial Hygienists, 1992. Andersen, Alan. “Final Report on the Safety Assessment of Methacrylic Acid.” International Journal of Toxicology. 2005. 13 April 2009. . Barbalace, Kenneth. “Chemical Database – Methacrylic Acid.” EnvironmentalChemistry.com. 1995 – 2009. 10 April 2009. . Chauhan, Sarita et al. “Method for Producing 2-Hydroxyisobutyric Acid and Methacrylic Acid from Acetone Cyanohydrin”. World Intellectual Property Organization WO/2003/066815. 14 August, 2003. Clayton, G. & Clayton, F. Patty’s Industrial Hygiene and Toxicology. 3rd Revised Edition. New York: John Wiley and Sons, 1981. Dicosimo, Robert et al. “Method for Producing Methacrylic Acid Acrylic Acid with a Combination of Enzyme Catalysts”. United States Patent 6670158. 30 December, 2003. Engelhorn, F. et al. Annalen. 1880, 200. Frankland, Edward. Annalen. 1865, 136. “Methacryllic Acid and Methacrylic Esters”. Process Economics Program Report 11. May 1966. 16 April, 2009. . “Methacrylic Acid and Methacrylic Esters.” Process Economics Program Report 11A. May 1974. 16 April, 2009 . “Methacrylic Acid and Methacrylic Esters”. Process Economics Program Report 11B. July 1980. 16 April, 2009. . “Methacrylic Acid and Methacrylic Esters”. Process Economics Program Report 11C. September 1984. 16 April, 2009 . OECD SIDS. “Methacrylic Acid.” 2001. 10 April 2009. . OSHA.”Methacrylic Acid.” 13 April 2009. . Rase, Howard. Handbook of Commercial Catalysts: Heterogeneous Catalysts. Boca Raton (Florida): CRC Press, 2000. Szmant, Herman. Organizing Building Blocks of the Chemical Industry. New Jersey: John Wiley and Sons, 1989. Weissermel, Klaus, Arpe, Hans-Juergen, & Lindley, Charlet. Industrial Organic Chemistry (4th Ed.). Berlin: Wiley-VCH, 2003. Wilczynski, Robert & Juliette, Jamie Jerrick. “Methacrylic Acid and Derivatives.” Wiley Inter-Science. 14 March 2003. . Read More