Keiichi Koda

Conversion of Technical Lignins to Amphiphilic Derivatives with High Surface Activity

Abstract To make use of technical lignins as a nonionic polymeric surfactant, we have already reported the modification of acetic acid lignin (AL) to amphiphilic derivatives by polyoxyethylation using two types of polyethylene glycol (PEG) with diglycidyl (PEGDE) and monoglycidyl (EPEG) groups.[ 1 ] Kraft lignin (KL) was converted to amphiphiles in a similar manner. The resultant KL derivatives also indicated high surface activity. Polyethylene glycol with long alkyl chain was introduced to AL, KL, and lignosulfonate (LS) to prepare surfactants of high performance, using dodecyloxy-polyethylene glycol glycidyl ether (DAEO). The resultant DAEO-derivatives showed lower critical micelle concentration by 2–4 orders of magnitude than the corresponding PEGDE- and EPEG-derivatives. The DAEO-derivatives from LS showed better dispersibility for gypsum paste, one of cement components, than LS.

Preparation of Novel Lignin-Based Cement Dispersants from Isolated Lignins

Abstract Lignin-based amphiphiles were prepared from the waste liquors of softwood and hardwood kraft pulpings (SKLliq and HKLliq, respectively) and their isolated lignins (SKL and HKL, respectively) by a reaction with several epoxylated polyethylene glycol analogues: polyethylene glycol diglycidylether (PEGDE), its monoglycidyl ether (EPEG), and dodecyloxypolyethylene glycol glycidyl ether (DAEO). The effect of these amphiphiles on cement dispersity was examined at 6°C and 20°C. Generally, only half the amount of EPEG- and PEGDE-series (e.g., 0.4%) was required to achieve the same cement dispersibility (e.g., Γp value of 2) compared to lignosulfonate (LS) (e.g., 0.8%). DAEO-lignin derivatives with the highest surface activity did not show cement dispersibility, suggesting no correlation between cement dispersibility and surface activity of the amphiphiles. Thus, together with the test of bending strength, it was found that the amphiphiles prepared from isolated lignins and EPEG were promising cement dispersants, which were available even in the wintertime without losing mechanical strength.

Improvement of Mechanical Properties of Softwood Lignin-Based Carbon Fibers

Abstract PEG-lignin fibers obtained by a solvolysis pulping of Japanese cedar with polyethylene glycol (PEG) 400 were successfully converted into defective-free, infusible fibers as a precursor for carbon fibers (CFs) by chemical curing followed by oxidative thermostabilization. The curing was performed by immersing PEG-lignin fibers in an aqueous mixed solution of hexamethylenetetramine (60 g/L) and hydrochloric acid (3 M) at 85°C for 1 h, resulting in the formation of crosslinkages between lignin molecules through methylene groups. These cured fibers were completely thermostabilized upon heating up to 250°C at a heating rate of 2°C/min under an air atmosphere. Finally, the thermostabilized fibers were carbonized to yield CFs, which showed about 1.5 times the tensile strength of our CFs previously prepared.

Interference of Carbohydrates in the Determination of the Methoxyl Content of Lignin in Woody Samples

Abstract To evaluate the effect of the presence of carbohydrates on the determination of the methoxyl content of lignin, the mechanism of acid‐catalyzed reaction of lignin methoxyl groups with iodide ion to form methyl iodide was evaluated using carbohydrate and lignin model compounds. Not only the iodide concentration but also the acid concentration was found to significantly affect the rate of formation of methyl iodide. This fact and Hammett plots of the relative reaction rates observed for several model compounds suggest an SN2cA reaction mechanism for methyl iodide formation. Carbohydrates interfered with the rate of formation of methyl iodide, probably by acting as Lewis bases. Interestingly, the study also revealed that a certain amount of methyl iodide could arise from carbohydrates even when the carbohydrates did not contain methoxyl groups as potential precursors to methyl iodide. These sources of error were significant when methoxyl content was determined for samples with low lignin content.

Formation of methyl iodide from methoxyl-free compounds by hydriodic acid treatment

Methoxyl groups (including methyl esters, methyl ethers, and methanol) react with hydriodic acid to produce methyl iodide. This reaction is applied for the determination of methoxyl groups in lignin. Gran suggested that glucose and other carbohydrates give rise to “apparent” methoxyl contents on use of the reaction although the formation of methyl iodide was not confirmed. In our recent study, however, methyl iodide was detected by gas chromatography (GC) in the reaction mixture of α-cellulose with hydriodic acid. As the reason for the formation of methyl iodide from α-cellulose, two possibilities were suspected. One possibility was that α-cellulose was contaminated with methoxylcontaining compounds. Another possibility was that methyl iodide was produced by an unknown mechanism from methoxyl-free compounds. In the present study, these possibilities were examined by the use of carbohydrates as methoxyl-free compounds and the effect of these compounds on the determination of methoxyl group content in lignin was evaluated. Materials and methods

Preparation of electrode for electric double layer capacitor from electrospun lignin fibers

Abstract Lignin-based activated carbon fibers (ACFs) were prepared by electrospinning of hardwood acetic acid lignin (HW-AAL) solution followed by thermostabilization, carbonization, and steam activation. The thermostabilization process was able to be remarkably shortened from 38 h to 3 h with hexamethylenetetramine (hexamine) in binary solvents, AcOH/CCl4 (8/2), when compared with conventional thermostabilization processes. The resultant ACFs possessed higher specific surface area (2185 m2 g-1) than those from commercial activated carbon and electrospun lignin fibers without hexamine. These ACFs also exhibited good electrical capacitance (133.3 F g-1 at a current density of 1 A g-1) as electrodes of electric double layer capacitor (EDLC) are efficient not only due to their large surfaces area but also due to their porous structure with well-developed micropores (diameter: 0.5–1.3 nm). High energy density and power density of this EDLC (42 Wh kg-1 and 91 kW kg-1, respectively) were also achieved.

Amphipathic lignin derivatives to accelerate simultaneous saccharification and fermentation of unbleached softwood pulp for bioethanol production.

Amphipathic lignin derivatives (A-LDs) were already demonstrated to improve enzymatic saccharification of lignocellulose. Based on this knowledge, two kinds of A-LDs prepared from black liquor of soda pulping of Japanese cedar were applied to a fed-batch simultaneous saccharification and fermentation (SSF) process for unbleached soda pulp of Japanese cedar to produce bioethanol. Both lignin derivatives slightly accelerated yeast fermentation of glucose but not inhibited it. In addition, ethanol yields based on the theoretical maximum ethanol production in the fed-batch SSF process was increased from 49% without A-LDs to 64% in the presence of A-LDs.

Optimization of simultaneous saccharification and fermentation conditions with amphipathic lignin derivatives for concentrated bioethanol production

Amphipathic lignin derivatives (A-LDs) prepared from the black liquor of soda pulping of Japanese cedar are strong accelerators for bioethanol production under a fed-batch simultaneous enzymatic saccharification and fermentation (SSF) process. To improve the bioethanol production concentration, conditions such as reaction temperature, stirring program, and A-LDs loadings were optimized in both small scale and large scale fed-batch SSF. The fed-batch SSF in the presence of 3.0g/L A-LDs at 38°C gave the maximum ethanol production and a high enzyme recovery rate. Furthermore, a jar-fermenter equipped with a powerful mechanical stirrer was designed for 1.5L-scale fed-batch SSF to achieve rigorous mixing during high substrate loading. Finally, the 1.5L fed-batch SSF with a substrate loading of 30% (w/v) produced a high ethanol concentration of 87.9g/L in the presence of A-LDs under optimized conditions.

Preparation of electric double layer capacitors (EDLCs) from two types of electrospun lignin fibers

Abstract Electrodes has been prepared for application in an electric double layer capacitor (EDLC) based on polyethylene glycol lignin (PEGL) and soda lignin (SL) derived from cedar wood. Fibers with a diameter of 23 μm were prepared by direct melt electrospinning of PEGL. Much finer fibers of 3.6 μm diameter were obtained by dry electrospinning of 70% PEGL in a dimethyl formamide (DMF) solution at 145°C. The dry electrospinning of SL alone in an alkaline aqueous solution was not achievable, but this was possible of a mixture of SL and polyethylene glycol (Mw=500 000) at a ratio of 99/1, which resulted in thin SL fibers with a diameter of 0.85 μm. These fibers were converted into activated carbon fibers (ACFs) by thermostabilization, carbonization, and steam activation. The specific Brunauer, Emmett and Teller (BET) surface areas of the resulting PEGL-ACFs and SL-ACFs were 1880 m2 g-1 and 1411 m2 g-1, respectively. PEGL-ACFs electrodes with an organic electrolyte exhibited an impedance of 1.6 Ω and a specific capacitance of 92.6 F g-1 at a scan rate of 1 A g-1, and the SL-ACFs electrodes had an impedance and specific capacitance of 4.5 Ω and 55.6 F g-1, respectively.

Enzymatic Saccharification of Soda Pulp from Sago Starch Waste Using Sago Lignin-Based Amphipathic Derivatives

Abstract The aim of this research is to develop an enzymatic saccharification process of sago starch waste, with a small charge of cellulase. The waste contained a significant amount of residual starch, which was recovered as glucose by mild acid hydrolysis. The starch-free residue was subjected to soda-anthraquinone pulping to yield soda pulp and soda lignin. The lignin was converted to amphipathic lignin derivatives by the reaction with epoxylated polyethylene glycol analogues. The pulp was hydrolyzed with cellulase (Genencor GC220), with the amphipathic derivatives, to yield glucose. The lignin derivative-assisted, enzymatic saccharification was repeatedly conducted by reusing cellulase recovered by ultrafiltration from saccharification media. Saccharification efficiency with the derivatives was maintained at a high level even after the fourth run of saccharification, while the efficiency was remarkably decreased by repeated use of cellulase without additive. Thus, the amphipathic sago lignin derivatives enabled repeated use of cellulase for saccharification of sago starch waste.