Esteban Chornet

Fractionation of Populus tremuloides at the pilot plant scale : optimization of steam pretreatment conditions using the STAKE II technology

Fractionation of a prototype hardwood, Populus tremuloides, was optimized in a 4 t/h pilot plant STAKE II unit located in Sherbrooke, Quebec. The aim was to find operational zones which maximized the recoveries of hemicelluloses (pentosans), lignin and cellulose. A phenomenological approach, based on the definition of a severity parameter R = t∗exp[T − 100)/14·75] which combines time, t (min), and temperature, T (°C), to express the severity of a given pretreatment, was developed. Performance curves, using the R0 parameter, have been experimentally determined. These indicated that the maximum recovery of pentosans is 65% of the potential at log10Ro = 3·8. Under these conditions, lignin recovery by caustic extraction was about 80% of total lignin. Cellulose was completely recovered at this severity but needed to be bleached to achieve its natural coloration. At severities both greater and smaller than log10Ro = 3·8 pentosans recovery decreased. The cellulose derived from the steam fractionation process was rapidly depolymerized as severity increased, whilst its enzymatic digestibility was close to theoretical at severities beyond log10Ro = 3·2. The results obtained suggest that steam explosion processes are fundamentally hydrolytic in nature.

Catalytic steam reforming of biomass-derived oxygenates: acetic acid and hydroxyacetaldehyde

Abstract Biomass can be pyrolytically converted in high yields (∼ 70 wt.%) into vapors (or oils when condensed) composed mainly of oxygenated organic compounds. Using a fixed-bed microreactor interfaced with a molecular beam mass spectrometer (MBMS), we have been studying the catalytic steam reforming of model oxygen-containing compounds present in biomass pyrolysis vapors. This MBMS sampling system is unique in its rapid, real-time, and universal detection of gaseous and condensible products. In this paper, we present results for steam reforming of acetic acid (HAc) and hydroxyacetaldehyde (HAA), two major products derived from the pyrolysis of carbohydrates in biomass. We propose mechanisms to couple the thermal decomposition and steam reforming reactions of these compounds. Both HAc and HAA undergo rapid thermal decomposition; complete steam reforming of these two model compounds can be achieved with commercial Ni-based catalysts. HAc forms coke on the catalyst surface, which is subsequently gasified by steam. The proposed mechanism for this coke formation involves an adsorbed acetate species that decar☐ylates to form the coke precursor, (CH 1–3 ) abs , and also ketene, a dehydration product of HAc, that decomposes to form (CH 1,2 ) abs . The reforming of HAA by steam does not involve any detectable intermediate and proceeds smoothly to a complete breakdown to CO and H 2 on the catalyst surface.

Phenomenological kinetics of complex systems: the development of a generalized severity parameter and its application to lignocellulosics fractionation

Abstract The modelling of complex reaction systems, either homogeneous or heterogeneous, is possible only when the sequence of all of the elementary steps is established. Few complex reactions have, however, a known and unambiguously determined set of elementary steps. Modelling of such complex systems is essentially phenomenological; thus, the estimated kinetic parameters lack mechanistic meaning and are functions of the ranges of experimental conditions used. Confronted with this situation, industrial applications of such complex reactions have adopted the use of severity factors which try to combine into a single parameter the effect of the different operational variables. In what follows we shall focus on the application of the reaction ordinate to the case of biomass fractionation leading to hemicellulose solubilization. We shall propose a new, generalized severity parameter which accounts for the acid catalyst effect on the extent of reaction. Despite the fact that the kinetics of complex systems are essentially phenomenological, we present here an approach derived from basic kinetic principles.

Inclusion and release of proteins from polysaccharide-based polyion complexes

The notion of a polyelectrolyte complex is well established for the complexation of two polymers one anionic, the other cationic. Electronic microscopy studies have shown the formation of a fibrilar structure. A method for the preparation of polyionic hydrogels from the complexation of chitosan and xanthan is reported. Electronic microscopy studies have shown the formation of a fibrilar structure. Stable hydrogels have been used to immobilize xylanase, lipase and protease. The immobilized xylanase and lipase activity was significantly higher than that of the free enzyme.

Fractionation of Wheat Straw by Steam-Explosion Pretreatment and Alkali Delignification. Cellulose Pulp and Byproducts from Hemicellulose and Lignin

Abstract The fractionation of wheat straw was studied using a two-stage process based on an hydrolytic pretreatment followed by alkali delignification. The hydrolytic pretreatment was performed by steam explosion. Straw was steamed at temperatures comprised between 205 and 230°C for 2 min. The steamed straw was washed with hot water to yield a solution rich in hemicellulose-derived mono- and oligosaccharides. The washed fiber was delignified by alkali at 160°C for 60 min using a NaOH load of 20%. The alkali-soluble lignin was recovered by filtration after acidification of the black liquor. The delignified pulp was screened and bleached to produce viscose-grade cellulose. The optimization of the pretreatment conditions led to the following results at a pretreatment severity of log(R0) = 3.80: yield of viscose-grade cellulose = 70% of the potential; lignin recovery = 70% of the Klason lignin present in the untreated straw; hemicellulose sugars = 55% of the potential, recovered as molasses.

Study of biodegradation behavior of chitosan-xanthan microspheres in simulated physiological media.

Microspheres of a polyelectrolyte complex hydrogel were prepared from chitosan and xanthan after interaction between the two polyionic polymers. Their biodegradation was studied vs. chitosan. Simulated gastric fluid (SGF, pH 1.2) and intestinal fluid (SIF, pH 7.5) both as biodegradation media and phosphate buffered saline (PBS, pH 7.4) as a negative control were used. The degradation studies were performed at 37 degrees C at 240 rpm permanent stirring to mimic the physiologic conditions. High performance liquid chromatography (HPLC) was carried out to quantify the chitosan degradation products using glucosamine (GA) and N-acetyl-D-glucosamine (N-Ac-GA) as references. The peaks area integration method was used to determine the amount of each degradation product as a function of incubation time in the media. The effect of the media on the morphological structure of microspheres was assessed by scanning electron microscopy. From HPLC studies, it appeared that in SGF and SIF the major degradation products were glucosamine (GA) and N-acetyl-D-glucosamine (NAc-GA). In the first 15 days, oligochitosan fractions were released from the complex, whereas N-acetyl-D-glucosamine was detected in the media after this period. The degradation kinetics were assessed by the measurement of the cumulative degradation products, which showed faster degradation of chitosan than the complex in SGF and SIF. SEM micrographs showed an enhancement of microsphere porosity as a function of incubation time in the simulated physiological media. Our results suggest a better control of the degradation kinetics when chitosan is complexed to xanthan.

Recovery of a solvolytic lignin: Effects of spent liquor/acid volume ratio, acid concentration and temperature☆

Abstract A lignin has been isolated from a prototype hardwood, Populus deltoides, by organosolv delignification using ethylene glycol, followed by dilute acidification of the spent black liquor. Various approaches for product separation are described. It was found that separation of the product slurry was best achieved if suction filtered whilst hot (> 100°C). The effects of temperature, volume ratio of black liquor/acidic aqueous solution, and acid concentration for precipitation of the lignin are discussed. Optimum conditions, in terms of yields, filterability, texture and color of the lignin were found to be: temperature range 50–60°C, liquor/acid volume ratio 1:3 and an acid concentration of 0·05%wt aqueous hydrochloric acid. The glycol lignin so isolated was soluble or partly soluble in a number of organic solvents. Gel permeation chromatography showed the weight average molecular weight to be 4762 g/mole with a polydispersity of 4·8 and the elution profile indicated a significant proportion of this lignin consists of a low molecular weight material. 13C NMR spectroscopy suggested that some cleavage of β-aryl ether linkages during the solvolysis process had occurred. This lignin seems to be rich in aliphatic hydroxyl groups and syringyl units. The presence of a strong signal at low field in the aliphatic region of the NMR spectrum suggests its origin from the solvent due to a possible ‘lignin-solvent interaction’ that occurred during the delignification step. Electron microscopy showed the lignin to exist as aggregates of mostly spherical particles of size range 0·5–2·5 μm.

A rapid method for the determination of the degree of N-acetylation of chitin-chitosan samples by acid hydrolysis and HPLC

Abstract A simple and rapid method for the quantitative determination of N -acetyl groups in chitin-chitosan samples consists of an acid hydrolysis conducted at high temperature with a mixture of sulfuric and oxalic acids. The acetic acid formed is determined by spectrophotometry at 210 nm after separation from the reaction mixture by HPLC. The method is valid for the entire range of degrees of acetylation and the results compare fairly to those of other techniques.

Analytical methodology for biomass pretreatment. Part 2: Characterization of the filtrates and cumulative product distribution as a function of treatment severity

Abstract Populus deltoides was pretreated using an aqueous/steam thermo-mechanical process in which shear forces were applied to medium consistency slurries by rapid passage through homogenizing valves. As a consequence of the treatment the biomass material was partially solubilized. In a previous paper (Bouchard, J., Nguyen, T. S., Chornet, E. & Overend, R. P. (1990). Analytical methodology for biomass pretreatment. Part 1: Solid residues. Biomass , 23 (4) 243–261), the characterization of the solids was discussed. The present paper concerns the characterization of the water-soluble fractions by standard, thermal (DSC) and spectroscopic (DRIFT) methods. The results are discussed in terms of the effect of the severity of the treatment on the chemical structure of the soluble wood polymers. A comparative evaluation between steam explosion and aqueous processes on the importance of the autohydrolysis concept and the role played by acetic acid is presented.

Chemisorption of hydrogen on iron

Abstract The flash desorption technique has been used to study adsorption and desorption of hydrogen on very clean, reproducible surfaces of polycrystalline iron. Preparation of the surfaces was achieved by extensive outgassing in vacuo, followed by hydrogen reduction and finally by argon ion bombardment and annealing in ultrahigh vacuum. The experimental results strongly suggest the presence of a single phase of chemisorbed hydrogen atoms at 298 °K, which recombine upon desorption following a second order rate equation. For the clean iron surface, the activation energy for desorption is about 20.3 kcal mole−1, and this energy remains nearly constant up to a surface coverage of about 0.2 × 1015 H-atoms cm−2, decreasing thereafter with coverage. As surface coverage changes, both the preexponential factor of the desorption kinetic rate constant and the activation energy change, and, furthermore, they display the usual “compensation effect” interdependence. Equilibrium data for the iron-hydrogen system, indicate that the adsorbed species is mobile, behaving as an ideal two-dimensional gas up to a coverage of 0.2 × 1015 H-atoms cm−2. At higher adsorbed amounts, lateral interactions between adsorbed species cause a departure from ideality. The initial rates of adsorption of hydrogen are consistent with an activated complex that requires about 0.5 kcal mole−1 for its formation.