Methyl methacrylate (MMA) is a specialty monomer for poly methyl methacrylate (PMMA) and the increasing demand for this monomer has motivated industry to develop clean technologies based on renewable resources. The dominant commercial process reacts acetone and hydrogen cyanide to MMA (ACH route) but the intermediates (hydrogen cyanide, and acetone cyanohydrin) are toxic and represent an environmental hazard. Esterification of methacrylic acid (MAA) to MMA is a compelling alternative together with ethylene, propylene, and isobutene/t-butanol as feedstocks. Partially oxidizing isobutane or 2-methyl-1,3-propanediol (2MPDO) over heteropolycompounds to MAA in a single-step is nascent technology to replace current processes. The focus of this review is on catalysts and their role in the development of processes herein described. Indeed, in some cases remarkable catalysts were studied that enabled considerable steps forward in both the advancement of catalysis science and establishing the basis for new technologies. An emblematic example is represented by Keggin-type heteropolycompounds with cesium and vanadium, which are promising catalysts to convert isobutane and 2MPDO to MAA. Renewable sources for the MMA or MAA route include acetone, isobutanol, ethanol, lactic, itaconic, and citric acids. End-of-life PMMA is expected to grow as a future source of MMA.

Catalysis for the synthesis of methacrylic acid and methyl methacrylate

Renewable production of acrylic acid and its derivative: New insights into the aldol condensation route over the vanadium phosphorus oxides

Vapor phase condensation of methyl acetate with formaldehyde to preparing methyl acrylate over cesium supported SBA-15 catalyst

Synthesis of methacrylic acid by aldol condensation of propionic acid with formaldehyde over acid–base bifunctional catalysts

Supported cesium catalysts with various carriers (SiO2, Al2O3, TiO2, MgO) were prepared and characterized by X-ray diffraction, BET nitrogen adsorption-desorption, NH3 and CO2-TPD methods and thermogravimetric analysis. Experimental results showed that the Zr-Mg-Cs/SiO2 catalyst exhibited moderate activity for aldol condensation of methyl propionate with formaldehyde (FA) to produce methyl methacrylate. Though the activity of Zr-Mg-Cs/SiO2 catalyst decreased with the time-on-stream, the deactivated catalyst was completely regenerated by calcination. The catalyst was regenerated 16 times and total operation time was over 500 h, its activity was identical with that of the fresh catalyst.

Synthesis of Methyl Methacrylate by Aldol Condensation of Methyl Propionate with Formaldehyde Over Acid-Base Bifunctional Catalysts

The vapor-phase aldol condensation of propionic acid (PA) with formaldehyde (HCHO) to form methacrylic acid (MAA) was performed with a PA/HCHO molar ratio of 2 using various silica-supported metal phosphate catalysts. In the absence of water, a silica-supported tin phosphate with Sn/Si/P atomic ratio of 1/8/2.3 showed the same level of performance as a silica-supported vanadium phosphate with V/Si/P atomic ratio of 1/8/2.2 did. The one-pass yield of MAA reached 58% based on the HCHO feed. In the presence of water, the performances of almost all catalysts fell. However, the Sn/Si/P catalyst showed a relatively high performance even in the presence of water. The performance is almost identical to that obtained from a silica-supported cesium oxide catalyst.

Akiyo Yoshida

Papers

Production of methacrylic acid by vapor-phase aldol condensation of propionic acid with formaldehyde over silica-supported metal phosphate catalysts