DEVELOPMENT OF BIOPOLYMERS AND THEIR MODIFIED FORMS AS SUSTAINABLE SORBENT MATERIALS

The production of ethanol in the biofuels industry requires methods to remove water from mixtures to improve biofuel quality. To address the large energy footprint of conventional distillative separation of biofuels and water, new materials and methods are required to reduce GHG emissions and to develop more sustainable industrial processing. The overall goal of this research focuses on the sorption properties of biopolymers and their modified forms as adsorbents for fractionation of chemical mixtures such as water/ethanol in binary systems. The short term goals of this thesis are related to the synthesis, characterization, and evaluation of the sorption properties of biopolymers and their modified forms. Moreover, a long term goal relates to the development of biopolymer materials with tunable adsorptive properties for the fractionation of binary water-ethanol (W-E) mixtures. Biopolymers such as starch (linear and branched) and cellulose were modified with variable amounts of epichlorohydrin (EPI) as a cross-linker for the enhancement of physicochemical properties related to sorption processes. The characterization of materials included Thermogravimetry Analysis (TGA), Infrared spectroscopy (FT-IR) and NMR spectroscopy. These methods provided support that incorporation of incremental levels of cross-linker with the biopolymers resulted in variable structure and physicochemical properties related to sorption. This thesis describes four leading edge contributions related to the objectives of this study: i) The development of biopolymers and their modified forms for the controlled uptake of ethanol in binary W-E systems, ii) Evaluation of the adsorption properties using dye probes, nitrogen adsorption, and the use of quantitative NMR (qNMR) spectroscopy as a convenient and rapid analytical tool to quantify uptake of both water and ethanol content in binary solvent systems, iii) Evaluation of biomass and its biopolymer components for the fractionation of W-E mixtures, and iv) Evaluation of the role of solvent effects on the adsorption properties of biopolymers. Based on the results herein, the biopolymer adsorbents displayed preferential uptake of water over ethanol in binary W-E solutions. The adsorptive solvent uptake selectivity (Rselectivity; Qm(W)/Qm(E)) of water over ethanol for a given sorbent material requires an understanding of hydration phenomena, biopolymer structure, and textural properties of adsorbent materials. This thesis contributes to a molecular-level understanding of the solvent fractionation properties of biopolymers and their modified forms, along with the development of green strategies for biofuel separation. The isotherm modeling results show that the monolayer adsorption capacity (Qm) of ethanol and water by cellulose biopolymer materials along with its cross-linked forms cover a range (Qm= 1.13−2.44 g/g) of values. The parameters indicate heterogeneous adsorption behaviour, in agreement with the Sips exponential fitting parameter (ns ≠ 1). The Rselectivity values ((Qm(W)/Qm(E)) obtained at saturative conditions are variable (1.10 to 2.03) and further illustrate that cellulose materials display molecular selective solvent fractionation in binary W−E solutions. By comparison, the Qm values for starch and its cross-linked forms varied from 0.01 to 2.70 g·g−1 for water and ethanol in binary mixtures according to the Sips isotherm model. The Rselectivity (Qm (W)/Qm(E)) values of starch-EPI adsorbents for water (W) and ethanol (E) in the binary mixtures range from 3.8 to 80. As well, the isotherm results show that the monolayer adsorption capacity (Qm; g.g−1) of biomass such as miscanthus with water Qm (W) and ethanol Qm (E) fractions were determined by the best-fit Sips model isotherm parameters for raw Miscanthus (Qm (W) =8.93 and Qm (E) =4.15 g.g-1) and pretreated Miscanthus (Qm (W) =4.73 and Qm (E) =3.22, g.g-1). The fractionation properties of Miscanthus revealed variable Rselectivity (Qm(W)/ Qm(E)) values: raw Miscanthus (Rselectivity=3:1); pretreated Miscanthus (Rselectivity = 1.5:1), and lignin isolates (Rselectivity = 1: 5.4). The solvent interactions of biopolymers impact their biodegradability, recyclability and tunable physicochemical properties for various applications that employ composite materials, pharmaceutical delivery systems, paper production, fibers and biofuel production. Studies of the hydration properties of these materials were carried out that include dielectric absorption, Raman spectroscopy and Differential Scanning Calorimetry (DSC) to determine the structural and thermodynamic properties that reveal differences in biopolymer-solvent interactions that depend on the nature of the system