Pedram Fatehi

Separation of lignocellulosic materials by combined processes of pre-hydrolysis and ethanol extraction.

In this paper, we proposed a new modification for an ethanol-based pulping process, which would consist of the pre-hydrolysis (pre-extraction) of wood chips for removing hemicelluloses; the ethanol extraction of pre-hydrolyzed wood chips for removing lignin; and the post purification of cellulose, leading to the production of pure cellulose. We also experimentally evaluated the separation of hemicelluloses from the pre-hydrolysis liquor (PHL) obtained from a pulp mill. To remove lignin from the PHL, it was acidified to a pH of 2, which resulted in 47% lignin precipitation. The lignin separation from the acidified PHL was further improved via adding polyethylene oxide and poly aluminum chloride or adding ethyl acetate. To recover the hemicelluloses from the acidified PHL, ethanol was added to the acidified PHL with a volumetric ratio of 4 to 1. The isolated lignin and hemicelluloses were characterized by a Fourier transform infrared spectroscopy (FTIR) and a gas permeation chromatography (GPC).

A combined acidification/PEO flocculation process to improve the lignin removal from the pre-hydrolysis liquor of kraft-based dissolving pulp production process

The presence of lignin impairs the utilization of the hemicelluloses dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this paper, a novel process was developed by combining the acidification and poly ethylene oxide (PEO) flocculation concepts to improve the lignin removal. The results showed that the lignin removal was improved by the addition of PEO to the acidified PHL, particularly at a low pH of 1.5. The main mechanisms involved are the lignin/PEO complex formation and the bridging of the formed complexes. This hypothesis was supported by the turbidity, FTIR and particle size measurements. Interestingly, the hemicelluloses removal from the acidification/PEO flocculation was marginal, which would be beneficial for the down-stream ethanol production from the PHL. Additionally, a process flow diagram was proposed that incorporates this new concept into the existing configuration of kraft-based dissolving pulp production process.

Recent advancements in the production of hydroxymethylfurfural

Lignocellulosic materials can be utilized in the production of platform chemicals such as hydroxymethylfurfural (HMF). HMF production has been investigated in various aqueous, solvent, biphasic and ionic liquid systems. Aqueous medium usually suffers from a low HMF yield (usually 50 to 60% while using fructose as feedstock) due to the production of by-products and the decomposition of HMF. A higher HMF production was achieved by applying biphasic systems, however, these systems face some technical challenges including solvent recovery, process complexity and environmental issues, which prevent its practical implementations at industrial scales. The unique properties of ionic liquids (IL)s make them promising solvents for producing HMF from polysaccharides. In this review, the effects of various parameters such as catalysts, solvents, and process conditions on the production of HMF from various lignocellulosic feedstocks as well as systems developed for purifying HMF after production are discussed. Generally, the yield of HMF production in the IL systems was higher than 80% when fructose was used as the raw material, but was less than 50% when cellulose or other polysaccharides were used. However, the IL system is complicated and has a challenging recovery process. The proposed IL systems are also not environmentally friendly. The main emphasis of this paper is on the industrial applicability of proposed processes for producing HMF.

Removal of inhibitors from pre-hydrolysis liquor of kraft-based dissolving pulp production process using adsorption and flocculation processes.

A process for removing inhibitors from pre-hydrolysis liquor (PHL) of a kraft-based dissolving pulp production process by adsorption and flocculation, and the characteristics of this process were studied. In this process, industrially produced PHL was treated with unmodified and oxidized activated carbon as an absorbent and polydiallyldimethylammonium chloride (PDADMAC) as a flocculant. The overall removal of lignin and furfural in the developed process was 83.3% and 100%, respectively, while that of hemicelluloses was 32.7%. These results confirmed that the developed process can remove inhibitors from PHL prior to producing value-added products, e.g. ethanol and xylitol via fermentation.

Production and Application of Lignosulfonates and Sulfonated Lignin

Lignin is the largest reservoir of aromatic compounds on earth and has great potential to be used in many industrial applications. Alternative methods to produce lignosulfonates from spent sulfite pulping liquors and kraft lignin from black liquor of kraft pulping process are critically reviewed herein. Furthermore, options to increase the sulfonate contents of lignin-based products are outlined and the industrial attractiveness of them is evaluated. This evaluation includes sulfonation and sulfomethylation of lignin. To increase the sulfomethylation efficiency of lignin, various scenarios, including hydrolysis, oxidation, and hydroxymethylation, were compared. The application of sulfonated lignin-based products is assessed and the impact of the properties of these products on the characteristics of their end-use application is critically evaluated. Sulfonated lignin-based products have been used as dispersants in cement admixtures and dye solutions more than other applications, and their molecular weight and degree of sulfonation were crucial in determining their efficiency. The use of lignin-based sulfonated products in composites may result in an increase in the hydrophilicity of some composites, but the sulfonated products may need to be desulfonated with an alkali and/or oxygen prior to their use in composites. To be used as a flocculant, sulfonated lignin-based products may need to be cross-linked to increase their molecular weight. The challenges associated with the use of lignin-based products in these applications are comprehensively discussed herein.

Recovery of lignocelluloses from pre-hydrolysis liquor in the lime kiln of kraft-based dissolving pulp production process by adsorption to lime mud

Dissolved lignocelluloses from the pre-hydrolysis liquor (PHL) of kraft-based dissolving pulp production process were recovered by adsorption to lime mud produced in the causticizing plant of the kraft process. The adsorption of lignocelluloses was a fast process, and could be completed within one hour. The addition of polydiallyldimethylammonium chloride (PDADMAC) significantly increased the amounts of adsorbed lignin and hemicelluloses, which more than doubled at the PDADMAC dosage of 0.1% (based on the weight of PHL). The measured heating values of the adsorbed lignocelluloses indicate that adsorption of lignocelluloses to lime mud may result in the energy saving of the lime kiln. The process proposed in this study could also be adapted to decrease inhibitor concentrations (lignin and acetic acid) if the dissolved hemicelluloses in the PHL were used to produce value-added products, e.g., ethanol, xylitol, based on the fermentation process.

Application of hemicelluloses precipitated via ethanol treatment of pre-hydrolysis liquor in high-yield pulp.

Hemicelluloses in industrially produced pre-hydrolysis liquor (PHL) were precipitated with ethanol. These PHL-derived hemicelluloses (PHL-EH) and a commercial, pure birch wood xylan sample (powder form) (BWX) were bleached using chlorine dioxide (D(0) and D(1)) and hydrogen peroxide (Ep) in the D(0)EpD(1) sequence, and the chemical compositions, molecular weights and charge densities of the treated samples were assessed. When applied to high-yield pulp (HYP) at 50 mg/g, 26 and 20 mg/g of the bleached PHL-EH and BWX, respectively, were adsorbed without significantly affecting paper properties. These results suggest that semi-bleached hemicelluloses could be used to increase the basis weight of paper products. Furthermore, an integrated process was proposed that converts the kraft-based dissolving pulp production process into a biorefinery unit with dissolving pulp, bleached hemicelluloses and lignin as main products.

Adsorption of lignocelluloses of model pre-hydrolysis liquor on activated carbon.

The main objective of this work was to study the adsorption behavior of various components dissolved in the pre-hydrolysis of kraft process on activated carbon. In this work, model prehydrolysis liquor (PHL) solutions (MPHL)s were prepared via mixing various commercially available monosugars, xylan, lignin and furfural; and their adsorption performance on activated carbon (AC) was investigated. In singular (one component) MPHL/AC systems, furfural had the maximum and xylose had the minimum adsorption, and the adsorption of monosugars was basically similar on AC. Also, polydiallyldimethylammonium chloride (PDADMAC) was added (0.5 g/l) to singular xylan or lignin MPHL/AC system, which increased the lignin and xylan adsorptions to 350 and 190 mg/g on AC, respectively.

Recent advancements in various steps of ethanol, butanol, and isobutanol productions from woody materials

In this review, the recent advancements and technical challenges associated with the production of ethanol, butanol, and isobutanol via bioconversion routes from celluloses of woody materials are reviewed. Physicochemical processes, e.g. steam explosion, seem to be the most viable process for pretreating woody materials. Although enzymatic hydrolysis is selective, it is rather a slow process. Acid hydrolysis is a relatively fast process with a high yield, but it produces inhibitory compounds of fermentation, which necessitates a detoxification process before the fermentation. Presently, the major challenges in the production of ethanol, butanol, and isobutanol via biological conversions are the rather low production yield and the sensitivity of microorganisms to the presence of inhibitors and products in fermentation media. In this study, the recent advancements in the applications of Saccharomyces cerevisiae, Clostridium acetobutylicum, and Corynebacterium glutamicum, the most promising microorganisms, for ethanol, butanol, and isobutanol production are also discussed.

Water soluble kraft lignin–acrylic acid copolymer: synthesis and characterization

Lignin produced in the kraft pulping process is insoluble in water at neutral pH, which limits its application in industry. In this paper, kraft lignin (KL) was copolymerized with acrylic acid (AA) in an aqueous solution to produce a water soluble lignin-based copolymer. The copolymerization was carried out using K2S2O8–Na2S2O3 as the initiator under alkaline aqueous conditions, and the influence of the reaction parameters, i.e. initiator dosage, reaction time and temperature, mole ratio of acrylic acid to lignin and reaction concentration, on resultant lignin copolymers were investigated. The mechanism of copolymerization of kraft lignin with acrylic acid was also discussed in this work. The resultant lignin copolymer was characterized by Fourier Transform Infrared (FTIR) spectrophotometry and Nuclear Magnetic Resonance (NMR). The successful copolymerization of AA and KL was confirmed by the new absorption peak of carboxyl anions in the FTIR spectrum and new peaks in the 1H-NMR spectrum. At optimal conditions, the charge density and molecular weight of lignin copolymer reached 1.86 meq g−1 and 46 421 g mol−1, respectively, and the solubility of lignin after reaction was increased from 1.80 g L−1 to 100 g L−1 at neutral pH.