Heather Lorelei Trajano

Naturally occurring and structurally diverse alkene-containing substrates, terpenes, provided a platform for establishing chemo-, regio-, and diastereoselective reactivity in tantalum catalysed hydroaminoalkylation. Naturally derived 1,3-butadienes revealed the unique regio- and diastereoselective (Z)-1,4-addition products accessible from isoprene and β-myrcene by hydroaminoalkylation. Selective terpene functionalisation, within an industrially produced turpentine mixture, demonstrates functionalisation specificity of β-pinene and limonene. Lastly, sesquiterpene functionalisation using β-caryophyllene and humulene provide rare examples of trisubstituted alkene reactivity in hydroaminoalkylation, by leveraging strain-release and stereoelectronic effects to control chemoselectivity. As a result of these reactivity studies using natural substrates, new tools for understanding alkene electronic, strain, and stereoelectronic effects on chemo- and diastereoselectivity outcomes have revealed new mechanistic insights into hydroaminoalkylation.

Hemicelluloses are amorphous polymers of sugar molecules that make up a major fraction of lignocellulosic biomasses. They have applications in the bioenergy, textile, mining, cosmetic, and pharmaceutical industries. Industrial use of hemicellulose often requires that the polymer be hydrolyzed into constituent oligomers and monomers. Traditional models of hemicellulose degradation are kinetic, and usually only appropriate for limited operating regimes and specific species. The study of hemicellulose hydrolysis has yielded substantial data in the literature, enabling a diverse data set to be collected for general and widely applicable machine learning models. In this paper, a dataset containing 1955 experimental data points on batch hemicellulose hydrolysis of hardwood was collected from 71 published papers dated from 1985 to 2019. Three machine learning models (ridge regression, support vector regression and artificial neural networks) are assessed on their ability to predict xylose yield and compared to a kinetic model. Although the performance of ridge regression was unsatisfactory, both support vector regression and artificial neural networks outperformed the simple kinetic model. The artificial neural network outperformed support vector regression, reducing the mean absolute error in predicting soluble xylose yield of test data to 6.18%. The results suggest that machine learning models trained on historical data may be used to supplement experimental data, reducing the number of experiments needed.

Hemicelluloses consume alkali during kraft pulping and dissolve in the black liquor as a low energy fuel. Acidic pre-hydrolysis of softwood chips removes hemicelluloses but preserves cellulose content prior to pulping. This study compared mild pre-hydrolysis (140 °C) kraft pulping with conventional kraft pulping of commercial softwood chips at two H-factors for wood chips with thickness ranging from less than 2 mm to over 6 mm. The chip thickness less than 2 mm increased hemicelluloses oligomer yield and showed little influence on pulp fiber yield. However, the kraft pulp fiber length decreased 5.6%. Kappa number and fiber reject increased dramatically when chip thickness was greater than 6 mm. The detailed compositional analysis of kraft pulp and fiber quality analysis indicate that pre-hydrolysis followed by kraft pulping enhanced delignification with limited reduction of fiber length and width, and increased kinks. Strategic considerations for the integration of pre-hydrolysis into kraft pulping for future biorefineries were outlined.

Previously it was shown that wood chip compression or enzyme impregnation prior to refining reduces energy consumption and improves pulp quality. This work characterizes the effect of different magnitudes and rates of compression on the extent of enzymatic hydrolysis. A laboratory compressor and a controlled uniaxial load set-up were used to apply different compression ratios and compression times to mixed-softwood wood chips. The chips were subsequently subjected to enzymatic hydrolysis with a high-yield exoglucanase preparation to demonstrate changes in cellulose hydrolysis. Enzymatic hydrolysis yield increased with compression ratio but was unaffected by compression time. Increasing compression ratio increased removal of soluble molecules such as sugars and acid-soluble lignin. Microscopy imaging showed increased cell wall buckling and fracturing with increased compression. The morphological changes led to improved enzyme diffusion and resulted in higher available surface area. The improved cellulose hydrolysis is due to changes in wood morphology as well as the removal of extractives.

The adsorption of locust bean gum (LBG) onto Northern Bleached Softwood Kraft (NBSK) pulp improved paper tensile and burst strength and lowered refining energy by strengthening inter-fibre bonding. Adsorption kinetics and isotherms were investigated to develop a fundamental understanding of the adsorption mechanism. The adsorption rate followed pseudo-second-order kinetics and the activation energy was 99.34 kJ·mol⁻¹, suggesting chemisorption. The adsorption rate constant increased rapidly with temperature from 25 to 45 °C (k = 1.93 to 24.03 g·mg⁻¹·min⁻¹), but the amount adsorbed at equilibrium decreased (q_e = 1.91 to 0.48 mg·g⁻¹ o.d. fibre). LBG adsorption to NBSK at 25 °C was consistent with the Langmuir adsorption model for LBG < 2.1 wt% of o.d. fibre, suggesting reversible, homogenous adsorption to a finite number of sites on the fibre surface. Refining to 3000 rev increased the heterogeneity of the NBSK pulp surface leading to multi-layer Freundlich adsorption with adsorption constant n = 5.00, and the equilibrium constant K_f = 2.57 mg·g⁻¹·(mg·L⁻¹)^−1/n at 25 °C. Favorable adsorption conditions for negatively charged LBG were identified: 25 °C for 10 min, low dosage level (< 2 wt%), lightly refined (< 3000 rev) NBSK pulp at low fibre consistency (< 0.5 wt%), high agitation rate (> 150 r.p.m.), acidic or neutral conditions (pH 2–7) without salt addition. Graphic abstract