Détermination du potentiel prébiotiques des hémicelluloses de bois résineux / Determining the prebiotic potential of softwood hemicellulose

The objective of this research was to develop novel and applicable methodologies to solve systematically problems along a roadmap of constructing a globally optimum biorefinery design. The roadmap consists of the following problems: (1) synthesis of conceptual biorefinery pathways from given feedstocks and products, (2) screening of the synthesized pathways to identify the most economic pathways, (3) development of a flexible biorefinery configuration, and (4) techno-economic analysis of a detailed biorefinery design. In the synthesis problem, a systems-based "forward-backward" approach was developed. It involves forward synthesis of biomass to possible intermediates and reverse synthesis starting with desired products and identifying necessary species and pathways leading to them. Then, two activities are performed to generate complete biorefinery pathways: matching (if one of the species synthesized in the forward step is also generated by the reverse step) or interception (a task is determined to take a forward-generated species with a reverse-generated species by identifying a known process or by using reaction pathway synthesis to link to two species.) In the screening problem, the Bellman's Principle of Optimality was applied to decompose the optimization problem into sub-problems in which an optimal policy of available technologies was determined for every conversion step. Subsequently, either a linear programming formulation or dynamic programming algorithm was used to determine the optimal pathways. In the configuration design problem, a new class of design problems with flexibility was proposed to build the most profitable plants that operate only when economic efficiency is favored. A new formulation approach with proposed constraints called disjunctive operation mode was also developed to solve the design problems. In the techno-economic analysis for a detailed design of biorefinery, the process producing hydrocarbon fuels from lignocellulose via the carboxylate platform was studied. This analysis employed many state-of-the-art chemical engineering fundamentals and used extensive sources of published data and advanced computing resources to yield reliable conclusions to the analysis. Case studies of alcohol-producing pathways from lignocellulosic biomass were discussed to demonstrate the merits of the proposed approaches in the former three problems. The process was extended to produce hydrocarbon fuels in the last problem.

Secondary sludge is an essential part of biosolids produced through the waste treatment plant of paper mills. Globally paper mills generate around 3.0 million ton of biosolids and in the absence of beneficial applications, the handling and disposal of this residual biomass poses a serious environmental and economic proposition. Secondary paper sludges were investigated in this work for recovery of proteins and their use as wood adhesive. After identifying extracellular polymeric substances as adhesion pre-cursors through analytical techniques, studies were carried out to optimize protein recovery from SS and its comprehensive characterization. A modified physicochemical protocol was developed to recover protein from secondary sludge in substantial quantities. The combined effect of French press and sonication techniques followed by alkali treatment resulted in significant improvement of 44% in the yield of solubilized protein compared to chemical methods. The characterization studies confirmed the presence of common amino acids in recovered sludge protein in significant quantities and heavy metal concentration was reduced after recovery process. The sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed the presence of both low and high molecular weight protein fractions in recovered sludge protein. After establishing the proof-of-concept in the use of recovered sludge protein as wood adhesive, the bonding mechanism of protein adhesives with cellulose substrate was further elucidated in a complementary protein-modification study involving soy protein isolate and its glycinin fractions. The results of this study validated the prevailing bonding theories by proving that surface wetting, protein structure, and type of wood play important role in determining final adhesive strength. Recovered sludge protein was also investigated for its compatibility to formulate hybrid adhesive blends with formaldehyde and bio-based polymers. Apart from chemical cross-linking, the synergy of adhesive blends was evaluated through classical rule-of-mixture. The findings of this study warrants further investigation concerning other potential uses of recovered sludge protein, especially as food supplements and economic implications.

Modern biorefineries provide a framework for the sustainable conversion of biomass to biofuels and biochemicals. In light of the recalcitrance of lignin in woody feedstocks, the native shrub eastern leatherwood is proposed as a model hypolignified species. Xylem tissue of this low-lignin plant contained syringyl-rich lignin that was more easily hydrolysed and did not appear to be localised in the middle lamellae. Also, leatherwood cellulose was less crystalline and the xylan was highly acetylated. While viable low-lignin plants will enable the sustainable utilisation of woody feedstocks, high-value bioproducts are needed to economise future biorefineries. The carbohydrate oxidoreductases galactose oxidase and glucooligosaccharide oxidase were studied for use in the oxidation and derivatisation of plant-derived polysaccharides for the production of such high-value bioproducts. The carbohydrate-binding module of galactose oxidase was necessary for recombinant protein production. Also, a mutant library of glucooligosaccharide oxidase variants was produced to generate enzymes with novel activity.

Modern biorefineries provide a framework for the sustainable conversion of biomass to biofuels and biochemicals. In light of the recalcitrance of lignin in woody feedstocks, the native shrub eastern leatherwood is proposed as a model hypolignified species. Xylem tissue of this low-lignin plant contained syringyl-rich lignin that was more easily hydrolysed and did not appear to be localised in the middle lamellae. Also, leatherwood cellulose was less crystalline and the xylan was highly acetylated. While viable low-lignin plants will enable the sustainable utilisation of woody feedstocks, high-value bioproducts are needed to economise future biorefineries. The carbohydrate oxidoreductases galactose oxidase and glucooligosaccharide oxidase were studied for use in the oxidation and derivatisation of plant-derived polysaccharides for the production of such high-value bioproducts. The carbohydrate-binding module of galactose oxidase was necessary for recombinant protein production. Also, a mutant library of glucooligosaccharide oxidase variants was produced to generate enzymes with novel activity.

This work focused upon design and operation of biodiesel production facilities in support of the broader goal of developing a strategic approach to the development of biorefineries. Biodiesel production provided an appropriate starting point for these efforts. The work was segregated into two stages. Various feedstocks may be utilized to produce biodiesel, to include virgin vegetable oils and waste cooking oil. With changing prices, supply, and demand of feedstocks, a need exists to consider various feedstock options. The objective of the first stage was to develop a systematic procedure for scheduling and operation of flexible biodiesel plants accommodating a variety of feedstocks. This work employed a holistic approach and combination of process simulation, synthesis, and integration techniques to provide: process simulation of a biodiesel plant for various feedstocks, integration of energy and mass resources, optimization of process design and scheduling, and techno-economic assessment and sensitivity analysis of proposed schemes. An optimization formulation was developed to determine scheduling and operation for various feedstocks and a case study solved to illustrate the merits of the devised procedure. With increasing attention to the environmental impact of discharging greenhouse gases (GHGs), there has been growing public pressure to reduce the carbon footprint associated with fossil fuel use. In this context, one key strategy is substitution of fossil fuels with biofuels such as biodiesel. Design of biodiesel plants has traditionally been conducted based on technical and economic criteria. GHG policies have the potential to significantly alter design of these facilities, selection of feedstocks, and scheduling of multiple feedstocks. The objective of the second stage was to develop a systematic approach to design and scheduling of biodiesel production processes while accounting for the effect of GHG policies. An optimization formulation was developed to maximize profit of the process subject to flowsheet synthesis and performance modeling equations. The carbon footprint is accounted for through a life cycle analysis (LCA). The objective function includes a term reflecting the impact of the LCA of a feedstock and its processing to biodiesel. A multiperiod approach was used and a case study solved with several scenarios of feedstocks and GHG policies.

The first part of the thesis presents a study based on the forest biorefinery concept, which involves converting a pulp mill into a multi-purpose biofuels, biomaterials, and biopower production facility in which these products are produced in an environmentally compatible and sustainable manner. A key challenge in this process is the recovery of lignin from process streams such that it can be utilized in a variety of innovative green chemistry processes The first study examines the fundamental chemical structure of LignoBoost derived lignin recovered from Kraft pulping streams using an acid precipitation/washing methodology. Functional group analysis and molecular weight profiles were determined by nuclear magnetic resonance (NMR) and size exclusion chromatography. These findings gave valuable insight into the physical properties and the determining chemical properties of this currently underutilized, renewable bioresource. The second study is based on the future second generation bioethanol production process, where ethanol produced from lignocellulosic materials will bring about the co-production of significant amounts of under-utilized lignin. The study examines the potential of conventional heterogeneous and novel homogeneous catalysts for the selective cleavage of the aryl-O-aryl and aryl-O-aliphatic linkages of ethanol organosolv lignin to convert it from a low grade fuel to potential fuel precursors or other value added chemicals. The experimental data demonstrated that aryl-O-aryl and aryl-O-aliphatic linkages could be cleaved and the hydrogenated lignin had a decrease in oxygen functionality and the formation of products with lower oxygen content. The second part of this thesis reports the development and optimization of a novel qualitative method for the determination of the various types of hydroxyl groups present in biodiesel production streams. In the first study, the use of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane as a phosphitylation reagent for quantitative ³¹P-NMR analysis of the hydroxyl groups in biodiesel process samples has been developed. Subsequently a characteristic chemical shifts library is developed with model compounds to provide quantitative data on the concentration of biodiesel precursors, intermediates and final product. The last part of this thesis depicts the results of an industrial trial based on the novel biodiesel analytical method developed earlier.

Sustainable waste treatment and lignin development strategies targeted for biorefineries will benefit industry, consumers, and the environment. This dissertation demonstrates the feasibility of a novel biochemical pathway capable of converting sugars and lignin sourced from biorefinery waste streams into microbial oils suitable for biodiesel, cosmetic, and biopharmaceutical applications. This biochemical pathway also presents interesting avenues for the commercial production of higher-value intermediate metabolites such as catechol, protocatechuate, pyruvate, and succinate. Alternatively, this dissertation also demonstrates a unique polymerization strategy for lignin that can be adopted towards the production of green polymeric biomaterials. Overall, these strategies jointly present intriguing routes for lignin valorization.

This work integrates perennial feedstock yield modeling using climate model data from current and future climate scenarios, land use datasets, transportation network data sets, Geographic Information Systems (GIS) tools, and Mixed integer linear programming (MILP) optimization models to examine biorefinery network designs in the southeastern United States from an overall systems perspective. Both deterministic and stochastic cases are modeled. Findings indicate that the high transportation costs incurred by biorefinery networks resulting from the need to transport harvested biomass from harvest location to processing facilities can be mitigated by performing initial processing steps in small scale mobile units at the cost of increased unit production costs associated with operating at smaller scales. Indeed, it can be financially advantageous to move the processing units instead of the harvested biomass, particularly when considering a 10-year planning period (typical switchgrass stand life). In this case, the mobile processing supply chain configuration provides added flexibility to respond to year-to-year variation in the geographic distribution of switchgrass yields. In order to capture the effects of variation in switchgrass yields and incorporate it in optimization models, yield modeling was conducted for both current and future climate scenarios. (In general profits are lower in future climate scenarios). Thus, both the effects of annual variation in weather patterns and varying climate scenarios on optimization model decisions can be observed.

This thesis reports the rheological properties of algae slurries as a function of cell concentration for three microalgae species: Nannochloris sp.,Chlorella vulgaris, and Phaeodactylum tricornutum. Rheological properties ofalgae slurries have a direct impact on the agitation and pumping power requirements as well as process design for producing algal biofuels. This study measures the rheological properties of eight diff erent concentrations of each species ranging from 0.5 to 80 kg dry biomass/m³. Strain-controlled steady rate sweep tests were performed for each sample with an ARES-TA rheometer using a double wall couette cup and bob attachment. Shear rates ranged from 5 - 270 s⁻¹, corresponding to typical expected conditions. The results showed that Nannochloris sp. slurry behaved as a Newtonian fluid for concentrations up to 20 kg/m³. Samples with concentrations above 40 kg/m³ behaved as a shear thinning non-Newtonian fluid. The effective viscosity increased with increased biomass concentration for a maximum value of 3.3x10⁻³ Pa-s. Similarly, C. vulgaris slurry behaved as a Newtonian fluid with concentrations of up to 40 kg/m³, above which it displayed a shear thinning non-Newtonianf behavior and a maximum eff ective viscosity of 3.5x10⁻² Pa-s. On the other hand, P. tricornutum slurry demonstrated solely Newtonian fluid behavior, with the dynamic viscosity increasing with increasing biomass concentration for a maximum value of 3.2x10⁻³ Pa-s. The maximum observed e ffective viscosity occurred at a concentration of 80 kg/m³ for all three species. Moreover, an energy analysis was performed where a non-dimensional bioenergy transport e ffectiveness was de termined as the ratio of the energy content of the transported algae biomass to the sum of the required pumping power and the harvesting power. The results show that the increase in major losses due to increase in viscosity was overcompensated by the increase in the transported biomass energy. Also, cultivating a more concentrated slurry requires less dewatering power and is the preferred option. The largest bioenergy transport eff ectiveness was observed for the slurries with the largest initial dry biomass concentrations. Finally, the relative viscosity of algae slurries was modeled using a Kelvin-Voit based model for dilute and concentrated viscoelastic par- ticle suspensions. The model, which depends primarily on the packing factor of the algae species, agrees with the measured viscosity with an average error of 18%, while the concentrated particle suspension model was slightly more accurate than the dilute suspension model. / text