Thermal decomposition of model compound of algal biomass

Abstract

This contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self‐condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO2 and –OH, respectively, from the –COOH group attached to the α‐carbon. The molecular channel for deamination involves cleavage of NH2 from α‐carbon of leucine. The activation energies for direct elimination of CO2, NH3, and H2O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical‐prompted pathways, systematically require lower energy barriers, in reference to closed‐shell reaction corridors. Detailed computations at the CBS‐QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas‐phase reactions, within the context of a plug‐flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed‐phase leucine. Among notable N‐containing species, the model predicts the prevailing of NH3 over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self‐condensation reactions of leucine in the gas phase.

Predicting the Decomposition Mechanism of the Serine α-Amino Acid in the Gas Phase and Condensed Media

“…The decarboxylation and deamination channels entail activation barriers of 282.1 (TSM2) and 273.9 kJ/mol (TSM3), respectively. These values are in accord with analogous values previously computed for leucine at 299.5 and 278.8 kJ/mol, respectively, computed at the CBS-QB3 . It is unlikely that these two channels will significantly participate in the initial degradation of the Ser compound.…”

“…For instance, deamination reactions are prominent in the case of energy crops and lignocellulose when compared to sludge and microalgae. We have illustrated in a previous study that the formation of the experimentally major observed products from pyrolysis of leucine amino acid takes place via bimolecular reactions . Such reactions typically occur in the condensed medium prior to evaporation.…”

Density functional theory-based investigation of HCN and NH3 formation mechanisms during phenylalanine pyrolysis

“…The potential barriers of this path (304.85 and 256.46 kJ mol À1 ) are similar to those observed for leucine. 37 The initial reaction step is ratedetermining, and the energy barrier is not high, which further conrms that path VII-1 plays an important role in Phe pyrolysis.…”

Removal of highly dispersive microspheres from wastewater using modified spirulina hetero-coagulation and their application in flame retardancy

“…18,19 Spirulina is a marine algal of arthrospira platensis with naturally intact three-dimensional helical structure demonstrating its desirable feasibility and efficiency in contaminant removal. [20][21][22] As an example, Doke's work showed that by using a spirulina strain they managed to remove up to 95% of biochemical oxygen demand, 52% of nitrate, and 76% of phosphate, while reducing the bacterial count up to75%. 23 As mentioned above, due to emulsifiers adhered to fluororesin microspheres, it is not possible for fluororesin microspheres to coagulate completely.…”