In a context of energy transition and the fight against global warming, the production of 2nd generation ethanol seems a very promising way to reduce our dependence on fossil fuels. Three key steps are needed to produce this biofuel: pretreatment disrupts the lignocellulosic matrix to make cellulose more accessible to enzymes; enzymatic hydrolysis produces fermentable sugars; finally, the fermentation transforms the latter into ethanol.
The pretreatment by steam explosion, considered by the industry as the most effective, involves two stages - an acidic cooking and then an explosive trigger causing the mechanical bursting of the lignocellulosic substrate - in order to make the cellulose more reactive to enzymatic hydrolysis. This thesis aims to better understand the physicochemical effects of this pretreatment by relying in particular on experimental discrimination of chemical phenomena (depolymerization reactions) and physical phenomena (explosive relaxation) as well as on a multi-technical and multi-scales characterization of biomass obtained after pretreatment. The objective is also to determine the main characteristics of the biomass causing the reactivity differences observed during the enzymatic hydrolysis step and to explain the impact of the steam explosion pretreatment on the physicochemical properties and therefore on reactivity.
December 4, 2018 - Fluid Mechanics, Energy, Processes Ph.D. title
Study of the impact of autohydrolysis on wood components and on delignification processes to produce pure cellulose.
This study is a part of a large project which aim is to convert a pulp mill into a fully integrated biorefinery by adding an autohydrolysis step to remove and valorize hemicelluloses prior to cooking. This thesis’s goal is to study the impact of adding an autohydrolysis step on wood components and on the subsequent delignification and bleaching processes applied to this wood to produce pure cellulose. Wood components were analyzed before and after autohydrolysis. In particular it was shown that autohydrolysis increases the amount of free phenolic groups, and lowers the involvement of lignin in lignin carbohydrates complexes. A new NMR method using Dynamic Nuclear Polarization was performed directly on milled wood to look at wood components structure without extraction’s steps to avoid chemical modifications.
The second part describes the test of pulp processes (alkaline cooking, oxygen delignification and bleaching) on autohydrolysed wood chips. It showed that the addition of this autohydrolysis step improves delignification during cooking to such an extent that soda cooking alone is possible and efficient. Oxygen delignification was also improved. Two bleaching sequences with or without chlorinated compounds (ECF and TCF) were applied and compared, and it was concluded that sustainable bleaching without any chlorinated reagents is feasible. Finally, evaluation of bleached pulp properties demonstrated that viscose application can be targeted. Indeed, pulp had high purity cellulose content, adequate polymerization degree and high brightness and brightness stability.
The original feature of this thesis is the use of nanocellulose for limiting two security paper defects: corner folds, also called “dog-ears”, and crumpling. These defects, principally caused by daily handling of these high added value documents, are responsible for a decrease of paper visual and mechanical quality and constitute an economic loss.
Nanocellulose can be divided into two different families: cellulose nanofibrils and cellulose nanocrystals. Cellulose nanofibrils are long and flexible materials with the ability to entangle and form a network strongly maintained by hydrogen bonds. Cellulose nanocrystals are short and rigid materials whose outstanding mechanical properties make them good candidates for reinforcement in a polymer matrix.
In this study, two strategies are proposed to incorporate these two kinds of nanocellulose in the security paper process. Finally, these approaches have been performed at pilot and industrial scales with positive results, which allowed deposition of patents on the topic.
The decrease of the recovered paper collection quality and the accumulation of dissolved substances in process water affect the deinking line efficiency and contaminate more and more the liquid effluents. In this context the LGP2 has developed an innovative deinking process, the ozone reactive flotation, to chemically degrade dissolved pollutants in parallel with ink removal.
To better understand the mechanisms involved, air and ozone/oxygen flotation trials have been conducted on three model contaminants selected in a preliminary bibliographic review, in a two-phase gas/liquid system, in the absence of fibers. Experiments have been carried out on two instrumented laboratory pilots: a bubble column operating only with air for the study of the hydrodynamics of the reactor (bubbles size and distribution, gas hold-up) in the presence of dissolved contaminants, and a second one, similar in its conception but built using materials resistant to corrosive gas, dedicated to the study of the oxidation reactions with ozone.
The evaluation of the hydrodynamics related to gas flow and injection system selected, studied with air but supposed to be the same with ozone/oxygen gas mixture, shows that the bubble size, with or without contaminants, is optimal for an efficient flotation process. The study of ozone mass transfer and reactivity with the three model contaminants, for several temperatures and ozone concentrations, leads to the calculation of kinetic constants and shows that the contaminants, depending on their nature, have been oxidized or depolymerized. Although the COD of the treated solutions does not decrease a lot after the ozone reactive flotation, the effluent quality has been improved in terms of biodegradability since contaminants are partially degraded.
The overall objective of the study was to produce bioethanol from lignocellulosic biomass by using free and immobilized xylanase, cellulase and β-1, 3-glucanase.
Specifically, this study was focused on the isolation of Trichoderma citrinoviride strain AUKAR04 able to produce xylanase (55,000 IU/gds), cellulase (385 IU/gds) and β-1, 3-glucanase (695 IU/gds) in solid state fermentation. Then the free enzymes were biochemically characterized depend on effect of pH, temperature and metal ion concentration and corresponding kinetic parameters were determined. Then the enzymes were subjected to two types of immobilization using carrier-free co-immobilization (combi-CLEAs) method or bifunctionalized magnetic nanoparticles (ISN-CLEAs) with higher thermal stability, extended reusability and good storage stability.
Liquid ammonia pretreatment removed 40% of lignin from the biomass and retained 95% of glucan, 65% of xylan and 41% of arabinan in sugarcane bagasse (SCB). SCB was enzymatically hydrolyzed and converted to 87 % glucose from cellulose and 74% of xylose, 64% of arabinose from the hemicelluloses which is remarkably higher than the activity of the free enzymes.
Chemical and structural analysis of SCB was done by ATR-FTIR, TGA and XRD. FTIR result showed a successful pretreatment of the SCB raw material. It showed that hemicelluloses and cellulose are partially depolymerized by the action of xylanase, cellulase and β-1,3-glucanase in ISN-CLEAs. TGA studies showed that the thermal stability of the ammonia pretreated and enzymatically treated samples have improved remarkably. XRD results showed that the crystallinity index of the ISN-CLEAs treated SCB increased to 61.3±1% when compared to the ammonia-treated SCB. Mono-culture fermentation using Saccharomyces cerevisiae LGP2Y1 utilized SCB hydrolysate containing 103.8 g/L of glucose and produced 42 g/L ethanol in 36 h of fermentation. The overall metabolic yield achieved was about 79% of theoretical yield. Co-culture fermentation using Saccharomyces cerevisiae LGP2Y1 and Candida utilis ATCC 22023 utilized SCB hydrolysate containing 107.6 g/L of glucose and 41.5 g/L xylose and produced 65 g/L ethanol in 42 h of fermentation. The overall metabolic yield in co-culture fermentation achieved was about 88 % of the theoretical yield.