Catalytic hydrogenation of amino acids and polyhydroxyalkanoates

Aqueous phase hydrogenation of L-alanine (L-(+)-2-amino-propanoic acid) to L-alaninol (L-(+)-2-amino-propanol) was performed in a three-phase, stirred batch reactor. Under optimal conditions selectivities over 97% with 93% alanine conversion and >99 ee% was achieved. Observed side products included ammonia, ethylamine, and isopropylamine. The catalyst used for this hydrogenation was 5 wt% ruthenium on carbon.; Calculations using standard engineering correlations showed that mass transfer through the gas-liquid and liquid-solid films and intra-particle mass transfer did not limit the rate of conversion. The absence of mass transfer limitations allowed for the derivation of a kinetic model. Conditions within the following experimental matrix were used for kinetic model parameter estimation: alanine feed concentration from 0.22 to 0.46 M, phosphoric acid feed concentration from 0 to 1.2 M, temperatures from 90 to 150°C, hydrogen pressures from 5 to 13 MPa H2, and 1 to 2 grams catalyst per 100 grams feed. A complete kinetic model was developed that predicts reaction trajectories to an 8% error between predicted and experimental data. Modeling results showed that the activation energy for the surface reaction step was 81.5 kJ/mol. The model predicted the observed dependences on hydrogen pressure, temperature, and ionic solution structure.; Hydrogenations have also been performed on biobased polymers PHB (poly-3-hydroxybutanoic acid) and PLA (polylactic acid; 2-hydroxypropanoic acid). These reactions occurred through a two step process of hydrolysis of polymer chains to monomer and soluble short chained oligomers followed by hydrogenation to alcohol product. PHB was found to be only slightly reactive toward hydrogenation. PLA, on the other hand, was easily converted to propylene glycol (PG) at 150°C and 1000 psi HZ over a 5% Ru/C catalyst.