Second generation biofuels are produced from plant biomass (e.g., agricultural waste) by enzymatic degradation of cellulose fibers into sugars and subsequent fermentation to ethanol. The high demand for cellulolytic enzymes makes the biomass conversion costly. Recently, Mackenzie and Francis<sup>1</sup> suggested an enzyme recovery procedure based on the properties of Poly(N-isopropylacrylamide) [Poly(NIPAm)] to reduce the price of biofuel production. Enzyme recovery relies on the thermosensibility of Poly(NIPAm) that undergoes a phase transition in aqueous solution when the temperature is increased. Below the lower critical solution temperature (LCST ≈ 305K), linear polymer chains are soluble in water, adopting a coiled shape; above the LCST, Poly(NIPAm) becomes insoluble and precipitates in a compact globular shape. The enzymes, covalently attached to the polymer, were recovered at the end of the reaction by precipitation upon heating and then reused in another cycle of cellulose degradation. Experiments show that the Poly(NIPAm) LCST phase transition depends on molecular properties of the polymer, such as molecular weight, tacticity and polymer concentration. Therefore, a full understanding of these polymer properties at the atomic level is required for process optimization and cost reduction. In the present work, we employ comprehensive molecular dynamics simulations of single Poly(NIPAm) chains in water to analyze polymer molecular properties with the aim of improving the degradation yields of cellulose to ethanol. First results from the molecular dynamics simulations above the LCST revealed already 20% fewer water molecules than do results from the simulations below the LCST, explaining the temperature dependence of the employed precipitation at the atomic level. Ongoing simulations seek to adjust polymer properties to optimal process control.

Usage of Poly(NIPAm) in the biofuel production

249th National Meeting (2015)

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