Jianguo Li

Enhancing hemicelluloses removal from a softwood sulfite pulp.

Hemicelluloses removal is highly desirable in many biomass processes, including the pretreatment steps of the bioconversion for ethanol production, production of high-quality dissolving pulps. In this study, a sequential treatment consisting of pulp fractionation, followed by caustic treatment to remove hemicelluloses from a softwood sulfite pulp, was investigated. The long-fiber fraction obtained after pulp fractionation, had a lower hemicelluloses content and smaller specific surface area, but larger pore diameter than the short-fiber fraction. The fiber fractions were subsequently treated in a cold caustic extraction (CCE) or hot caustic extraction (HCE). Results showed that hemicelluloses removal in the long-fiber fraction was more pronounced than the short-fiber fraction in both CCE and HCE processes. Other parameters, such as hemicelluloses removal selectivity, yield were studied. The underlying explanations were given.

Changes of cellulose accessibility to cellulase due to fiber hornification and its impact on enzymatic viscosity control of dissolving pulp

This study was to determine the effect of fiber hornification on the viscosity decrease of prehydrolysis kraft-based dissolving pulp using a commercial endoglucanase-rich cellulase. Three pulp samples, namely never-dried (ND), air-dried (AD) and oven-dried (OD), were used. The results showed that the enzymatic performance in the viscosity decrease was affected by the fiber history: the ND sample showed the strongest viscosity drop, followed by the AD sample, and the lowest was obtained from the OD sample. These results were explained by the concept of cellulose accessibility to cellulase (CAC), which decreased with the increasing degrees of hornification (DH) in the order of ND, AD and OD samples. The CAC of the samples and the cellulase adsorption on the samples were highly correlated to the DH, which consequently influenced the enzymatic treatment efficiency in viscosity control. The kinetics of the viscosity decrease during the cellulase treatment, showed an initial rapid phase, followed by a slow phase.

Mechanical pretreatment improving hemicelluloses removal from cellulosic fibers during cold caustic extraction

Hemicelluloses removal is a prerequisite for the production of high-quality cellulose (also known as dissolving pulp), and further recovery and utilization of hemicelluloses, which can be considered as a typical Integrated Forest Biorefinery concept. In this paper, a process of combined mechanical refining and cold caustic extraction (CCE), which was applied to a softwood sulfite sample, was investigated. The results showed that the hemicelluloses removal efficiency and selectivity were higher for the combined treatment than that for the CCE alone. The combined treatment can thus decrease the alkali concentration (from 8% to 4%) to achieve a similar hemicelluloses removal. The improved results were due to the fact that the mechanical refining resulted in increases in pore volume and diameter, water retention value (WRV) and specific surface area (SSA), all of which can make positive contributions to the hemicelluloses removal in the subsequent CCE process.

Combination of mechanical, alkaline and enzymatic treatments to upgrade paper-grade pulp to dissolving pulp with high reactivity.

A modified process consisting of an initial mechanical refining (R) followed by a low-alkali (5.5% NaOH) cold caustic extraction (CCE) and finally an endoglucanase (EG) treatment (R-5.5%CCE-EG) was investigated for upgrading paper-grade pulp to dissolving pulp. Results showed that compared to the conventional process (9%CCE-EG), the modified process can decrease the alkali concentration (from 9% to 5.5%) to achieve a similar hemicelluloses removal while simultaneously enhancing the Fock reactivity (from 62.2% to 81.0%). The improved results were due to the fact that the mechanical refining resulted in favorable fiber morphological changes, including increased pore volume/size, water retention value and specific surface area. Consequently, the hemicelluloses removal was enhanced even under the subsequent low-alkali CCE condition. A synergic effect of refining, low alkali concentration and enzymatic activation was responsible for the higher reactivity of resulting dissolving pulp.

Comparison of acid sulfite (AS)- and prehydrolysis kraft (PHK)-based dissolving pulps

The processability and quality of viscose are mainly influenced by the properties of dissolving pulps. Acid sulfite (AS) and prehydrolysis kraft (PHK) are the main commercial processes for the production of dissolving pulps. In this paper, the properties of dissolving pulps obtained from the AS and PHK processes, with respect to purity, molecular weight distribution (MWD), porosity, surface area, accessibility and reactivity, were comparatively evaluated. The results indicated that the PHK pulps had higher α-cellulose, lower S10/S18 content, and narrower MWD than the AS pulps, which can be ascribed to the different reaction mechanisms in the acid and alkaline pulping processes. The traditional parameters (S10/S18, α-cellulose and intrinsic viscosity) were insufficient to evaluate the pulp quality when comparing with dissolving pulps from different pulping processes. The Fock reactivity and the Chinese filterability tests were applied to evaluate their end-use properties in the rayon production process. The AS pulps had better accessibility than the PHK pulps (larger pore size and volume and thinner primary wall), supporting the conclusion that the AS samples exhibited higher reactivity that the PHK samples. The results from the Fock reactivity and Chinese filterability corresponded well.

Viscosity control and reactivity improvements of cellulose fibers by cellulase treatment

AbstractnCellulase treatment for decreasing viscosity of cellulose (dissolving pulp) is a promising approach to reduce the use of toxic chemicals, such as hypochlorite in the dissolving pulp manufacturing process. In this study, the use of an endoglucanase-rich cellulase to replace the hypochlorite for this purpose and its improvements of the Fock reactivity were investigated. The results showed that at a given viscosity level, the replacement of hypochlorite treatment with a cellulase treatment in the bleach plant under otherwise the same conditions led to a higher Fock reactivity (72.0 vs 46.7xa0%). These results were due to the enzymatic peeling/etching mechanism, which partially peeled the primary wall of the fibers, thus improving the accessibility of fibers. The improved accessibility of the enzymatic treated pulp was supported by the positive fiber morphological changes determined, based on the SEM, BET and WRV methods. The alkali solubility results further supported the conclusion.

Enhanced removal of hemicelluloses from cellulosic fibers by poly(ethylene glycol) during alkali treatment

Enhancing removal of hemicelluloses from cellulosic fibers is of decisive importance for producing high-purity cellulose. In this study, poly(ethylene glycol) (PEG) was added to a cold caustic extraction (CCE) process to promote removal of hemicelluloses from a softwood sulfite dissolving pulp. The content of hemicelluloses was considerably decreased from 11.4xa0% in the original sample to 5.3xa0% in the PEG/CCE-treated sample under the studied conditions. This positive result of PEG addition can be explained by (1) improved inward penetration and diffusion of NaOH into the fiber structure and outward diffusion of hemicelluloses from the fiber structure to the bulk phase, and (2) enhanced fiber swelling due to inclusion of PEG in the fiber walls and improved NaOH diffusion. Moreover, the effects of PEG/CCE treatment on the distribution of hemicelluloses in the fiber walls and the molecular weight of the residual hemicelluloses in the resulting pulp were investigated.

Kinetics and mechanism of hemicelluloses removal from cellulosic fibers during the cold caustic extraction process

The effective separation of hemicelluloses and cellulose is desirable for the production of high-purity cellulose, which is a sustainable raw material for many value-added applications. For this purpose, the kinetics and mechanism of hemicelluloses removal from the cold caustic extraction (CCE) were investigated in the present study. The hemicelluloses removal process consists of: 1) the bulk phase, characteristic of significant hemicelluloses removal; 2) the transition phase, hemicelluloses transferring from the inner to the outer region of the fiber wall, with negligible overall hemicelluloses removal; 3) the residual phase, presenting a weak but continuing hemicelluloses removal. Furthermore, the enzymatic peeling method was adopted to study the fundamentals of hemicelluloses removal. The results showed that the molecular weight of hemicelluloses is the main parameter governing their diffusion/dissolution processes, and that the low molecular weight hemicelluloses are preferentially removed.

Cellulase pretreatment for enhancing cold caustic extraction-based separation of hemicelluloses and cellulose from cellulosic fibers

The effective separations of cellulose and hemicelluloses from cellulosic fibers are the prerequisite for creating high-value to the abundant and green cellulose materials. In this study, the process concept of cellulase pretreatment, followed by a cold caustic extraction (CCE) was investigated for a softwood sulfite pulp. The results showed that the cellulase pretreatment led to favorable fiber morphological changes, including the increases of the specific surface area (SSA), pore volume and diameter, and the water retention value (WVR). These changes can induce more pronounced fiber swelling in the subsequent CCE process so that the hemicelluloses removal is enhanced. After the cellulase pretreatment (cellulase dosage of 1u202fmg/g) and CCE process, the cellulose purity was as high as 97.49%, while the hemicelluloses removal selectivity reached 76.42%.

A new approach to improve dissolving pulp properties: spraying cellulase on rewetted pulp at a high fiber consistency

Cellulase treatment is a promising technology that will increase the reactivity of a prehydrolysis kraft (PHK) dissolving pulp. In this study, a cellulase solution was sprayed onto rewetted pulp at a very high consistency (about 60%) to increase its Fock reactivity with high efficiency and low cost. This novel and facile approach is based on favorable cellulose adsorption onto pulp fibers and high cellulose concentration at the reaction sites. Consequently, the enzymatic reactions towards cellulose fibers are more effective, thus a higher enzymatic performance in comparison with the conventional process. With the cellulase spraying technique under the conditions of 60% fiber consistency and 1.5xa0mg/g cellulase dosage at 12xa0h, the Fock reactivity of a PHK dissolving pulp increased from 51.22 to 82.64% with acceptable viscosity (469xa0mL/g). Herein, the proposed cellulase spraying technology is flexible and readily implementable in practice.Graphical abstract