Chemical News

Thursday, December 18, 2008

Acrylic & Methacrylic monomers from Alkanes

Current methods for manufacturing acrylic acid, methacrylic acid, and the corresponding nitriles are two-step gas-phase oxidation processes that start with propylene or isobutylene feedstocks.

Alkanes are more readily available and less expensive feedstocks than alkenes; and, according to inventors A. M. Lemonds and D. L. Zolotorofe, it would be more desirable to oxidize alkanes directly to unsaturated carboxylic acids or nitriles in a liquid medium. In addition to specifying solvents and reaction conditions for their liquid-phase process, the inventors describe a long list of molybdenum- and tungsten-based catalysts.

In one example of the process, a perfluoropolyether solvent with negligible vapor pressure is used in the oxidation of propane to acrylic acid. A continuous-flow stirred-tank reactor capable of pressurized operation is completely filled with the solvent, and 30 mL of an insoluble catalyst, an oxide of MoV0.3Te0.23Nb0.37Pd0.01, is placed in a steel basket that is continuously rotated during the reaction. The solvent is heated to 190 °C at atmospheric pressure and a feed gas comprising 7 mol% propane, 14 mol% oxygen, and 79 mol% nitrogen is fed at 10–100 mL/min. Propane conversion is 33.0%, with selectivity to acrylic acid of 45.2%.

At higher pressures (up to 10 atm), conversion is about the same or slightly higher, but selectivities are considerably lower. The inventors do not report how long the reactions are run.

Additional examples are given for lower boiling fluorocarbon solvents—which require higher operating pressures—and for increased feed concentrations. The solvents can be recycled, but it remains to be seen whether the lower feedstock costs offset the higher solvent costs and low conversions and selectivities.
Source: CAS and Rom & Haas