Process for production of methacrylic acid

#This invention generally relates to improved high yield production processes for methacrylic acid (“MAA”) and methacrylate esters, such as methyl methacrylate (“MMA”). More particularly, according to a preferred embodiment, the present invention relates to an improved process for the high yield production of substantially pure MAA that is at least 95% pure.

#Methacrylic acid (“MAA”) and methacrylate esters such as methyl methacrylate and butyl methacrylate are used in a wide variety of applications. Typical end-use applications include: acrylic plastic sheeting; molding resins; polyvinyl chloride modifiers; processing aids; acrylic lacquers; floor polishes; sealants; auto transmission fluids; crankcase oil modifiers; automotive coatings; ion exchange resins; cement modifiers; water treatment polymers; electronic adhesives; metal coatings; and acrylic fibers. MAA and methacrylate esters are especially prized in these applications and others because of the hardness they impart to the products in which they are used. They also enhance chemical stability and light stability, as well as ultraviolet radiation resistance, when used in certain products. Therefore, MAA and methacrylate esters are often used in applications requiring resins of excellent transparency, strength, and outdoor durability. The MAA and methacrylate ester market is extremely cost-sensitive; thus, any improvement in process yield, however slight, can result in significant cost-savings.

#Although other feedstocks, including various C4-based feedstocks, may be used, the most common feedstock for the production of MAA and methacrylate esters has been acetone cyanohydrin (“ACH”).

#A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

#FIG. 1 is a process flow diagram providing an overview of the process of the present invention.

#FIG. 2 is a process flow diagram illustrating one embodiment of the present invention wherein both the hydrolysis and cracking systems have been integrated.

#FIG. 1 is a process flow diagram generally providing an overview of the process of the present invention as indicated at 10. There are five basic steps in the process of making MAA and methacrylate esters, namely, hydrolysis, cracking, reaction, separation, and purification. These steps for the MAA process are shown at 12, 18, 22, 26, and 30, respectively, in FIG. 1. These steps for methacrylate esters are shown at 32, 38, 42, 46, and 50, respectively, in FIG. 1. Although only one methacrylate ester train is illustrated in FIG. 1 along side the methacrylic acid train, it is within the scope of the present invention that multiple methacrylate ester trains may be advantageously employed in the methods provided by the present invention. For instance, an ethyl methacrylate train can be employed as well as a methyl methacrylate train with the methacrylic acid train.

#The first stage of producing either MAA or methacrylate esters from ACH involves hydrolysis of the ACH in a hydrolysis system; the general chemistry of the hydrolysis process for both MAA and methacrylate esters may be very similar. Shown at 12 and 32 in FIG. 1 is hydrolysis of the ACH in a hydrolysis system to produce a hydrolysis mixture that contains α-sulfatoisobutyramide (“SIBAM”) and α-hydroxyisobutyramide (“HIBAM”). ACH and an excess of sulfuric acid are fed into hydrolysis reactor 12. It is preferable to use ACH that has low levels of water and other impurities in the hydrolysis step. The sulfuric acid serves as both a specific reactant and a solvent for the reaction. Using sulfuric acid at concentrations of greater than 95% is also preferred. In an alternative embodiment, oleum or a combination of sulfuric acid and oleum may be used in place of sulfuric acid. Either hydrolysis system may contain a single reactor or multiple reactors connected in series and may also employ one or more reactant addition points.

#In the hydrolysis reaction, anhydrous conditions are preferred to minimize the formation of HIBAM, which is more difficult than SIBAM to convert to methacrylamide (MAM).