Pyrolysis of proteins in the presence of active inorganic solids

Analytical studies on the effect of active solids on the pyrolytic behavior of biomass components have been conducted principally to lignin and cellulose. Proteins have been less investigated, nevertheless they may constitute an abundant fraction of some biomass feedstock (e.g. algae). Here the pyrolytic behaviour of proteins in the presence of CaO and zeolite H-ZSM-5 was investigated by off-line analytical pyrolysis utilising bovine serum albumin (BSA) as model protein. Pyrolysis products evolved at 700 °C were analysed by GC-MS and the yields of main 2,5-diketopiperazines (DKP, cyclic dipeptides) were determined by internal standardisation. Active solids at 1/1 ratio with respect to BSA did not affect markedly the pyrolysate composition which was dominated by thermal fragmentation products of the side chain of aromatic amino acids and lower levels of DKPs. At higher ratios (9/1) zeolite induced aromatisation and alkylation with the formation of polyaromatic hydrocarbons (PAHs) and methylated phenols and indoles. The formation of DKPs, among which cyclo(Pro-Leu) was the most abundant, was favoured by catalytic pyrolysis. The yields of DKP increased from about 1‰ from untreated BSA to 5 ‰ in the presence of zeolite.