Glyphosate production via carbon-catalyzed oxidation of N-(phosphonomethyl)glycine (PMIDA) in a trickle bed reactor offers numerous potential advantages over multiphase batch or continuous slurry reactors, including improved selectivity control and lower catalyst and capital costs. The slurry processes suffer reaction yield losses to non-catalytic methylation of glyphosate and over-oxidation of glyphosate, which is an intermediate in a series of oxidation reactions. In addition, the slurry processes face challenges with catalyst recovery and recycle as well as costs associated with high carbon catalyst unit ratios.<br/>We have developed and patented continuous fixed bed technology for this reaction step. A key component of this development is selection of a carbon catalyst that provides maximum glyphosate yield subject to several process constraints, including bed pressure drop, reactant solubility, and reaction temperature. A simple conceptual model of a strongly pore diffusion-limited system teaches that the fixed bed approach requires a reduced carbon catalyst activity relative to that typically used in a slurry process in order to selectively make glyphosate at higher temperatures, where the reactant solubility is greatly enhanced. Using a batch recycle trickle bed reactor, we have demonstrated significant differences in performance between several alternative carbons, characterizing these differences in a model of the apparent reaction kinetics. In comparing carbons from a variety of sources, such as wood, peat, and coal, we have found that the best alternative means for comparing alternative carbons is to compare rates of hydrogen peroxide decomposition, suggesting that the active sites for the PMIDA oxidation reaction are identical to or correlated with the active sites for hydrogen peroxide decomposition.

Oxidation of N-(phosphonomethyl)glycine to glyphosate in a trickle bed reactor

251st National Meeting (2016)

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