ETHANOL FROM SOUTHERN HARDWOODS: THE ROLE OF PRESULFONATION IN THE ACID HYDROLYSIS PROCESS

A two-stage acid hydrolysis process is currently used in the production of ethanol from hardwoods. In this process, dilute sulfuric acid in water at high pressure and short residence times hydrolyzes the wood and first stage substrate. The chemical action is particularly impeded in the second stage by the presence of acid condensed lignin.

Presulfonation followed by delignification is proposed using a sulfur dioxide/water sulfuric acid/ethanol treatment step in place of the first stage acid hydrolysis step to alleviate this problem.

Results presented include the effects caused by varying treatment time, sulfur dioxide concentration, temperature and ethanol concentration on the degree of delignification, and, on the recovery of C₅ and C₆ sugars in the hydrolysates. A preliminary economic feasibility analysis is made to determine the impact of improved ethanol yields and lignin by-product values in the production of ethanol from hardwoods.     

Future prospects of delignification pretreatments for the lignocellulosic materials to produce second generation bioethanol

Production of bioethanol is winning support from masses because it is a workable choice to solve the problems associated with the fluctuating prices of crude petroleum oil, climatic change, and reducing non‐renewable fuel reserves. First‐generation biofuels are produced directly from food crops. The biofuel (bioethanol, biodiesel) is ultimately derived from the starch, sugar, animal fats, and vegetable oil that these crops provide. It is important to note that the structure of the biofuel itself does not change between generations, but rather the source from which the fuel is derived changes. Corn, wheat, and sugar cane are the most commonly used first‐generation bioethanol feed stocks. Lignocellulosic materials are used as a feed stock for the production of second‐generation bioethanol. The major production steps are (1) delignification, (2) depolymerisation, and (3) fermentation. Agricultural residues are waste materials produced through the processing of agricultural crops. The main reason to use of these agricultural residues to produce bioethanol is to convert waste to value added products. The main challenges are the low yield of the cellulosic hydrolysis process due to the presence of lignin and hemicellulose with cellulose. Pretreatments of lignocellulosic materials to remove lignin and hemicellulose are the techniques used to enhance the hydrolysis. Present review article comprehensively discusses the different pretreatment methods of delignification for ethanol production. Published literature on pretreatments from 1982 to 2018 has been studied. Perspectives, gaps in studies, and recommendations are given to fully describe implementation of eight prominent pretreatments (milling, pyrolysis, organic solvents, steam explosion, hot water treatments, ozonolysis, enzymatic delignification, and genetic modification) for future research. The energy and environmental features of lignocellulosic materials are elaborated to show a sustainable aspect of second‐generation biofuel. It was felt necessary to discuss the concept of bio refinery to make biofuel production financially more attractive as well because the future prospects of second‐generation biofuel are promising.     

胡麻杆碱性亚硫酸钠—蒽醌法蒸煮脱木素过程的研究及应用

本文分析了胡麻原料的纤维形态,化学组成,着重研究了加麻AS—AQ法蒸煮过程中木素和碳水化合物的溶出规律,并对四种蒸煮方法的成浆质量进行了对比。试验结果表明:AS—AQ法胡庥浆得效高、硬度底、抄片物理强度好、抄纸板达牛皮箱纸板标准。胡麻AS—AQ法纸浆对于生产强韧牛皮箱纸板是适宜的,并有突出的经济效益。     

竹材碱性过氧化氢预处理及其酶水解性能研究

采用碱性过氧化氢（AHP）体系对慈竹进行预处理,研究过氧化氢（H₂O₂）用量对竹材化学组分及酶水解得率的影响。利用X射线衍射（XRD）和傅里叶变换红外光谱仪（FTIR）分析预处理前后物料的物理和化学结构变化,采用二维核磁共振技术研究预处理物料中剩余木质素的化学结构。结果表明：AHP预处理过程中,随着H₂O₂用量（质量分数）的增加,竹材的葡聚糖含量（相对质量百分比）先增加后减少,木聚糖含量基本不变,而木质素含量整体呈减少趋势。AHP预处理能显著提升竹材的酶解效率,在纤维素酶用量为15 FPU/g葡聚糖,H₂O₂用量为7.0%时,预处理竹材的酶水解性能最高,葡聚糖和木聚糖酶水解得率分别为93.9%和100%。研究发现,慈竹木质素脱除率在H₂O₂用量达到2.0%后趋于稳定,为68.8%,继续增加H₂O₂用量,木质素脱除率无明显提升,对预处理竹材中剩余木质素进行2D-HSQC核磁分析,这部分难以脱除的木质素的化学结构为：64%的S单元、33.7%的G单元和61.6%的β——O——4键,其中S/G值为1.90。     

Pulping Catalysts in Trees

Abstract

Several hardwood and softwood trees were analyzed for anthraqui-none-type components. Wood samples were reduced to a small size and extracted with an organic solvent; the extracts were then concentrated and analyzed by gas chromatography-mass spectroscopy. Low levels of AQ and anthrone components were detected using a sensitive selected-ion monitoring technique. Ten out of seventeen hardwood samples examined contained AQ-type components; however, the levels were typically below ～6 ppm. Such components were not observed for the few softwood samples that were examined. The AQs were more concentrated in the heart-wood of teak than in the sapwood. Extraction of cottonwood with an organic solvent had little effect on the ease of pulping of the wood.     

Ionic Liquid-Based Molecular Oxygen Oxidation of Eucalyptus Kraft Lignin to Obtain a Suite of Monomeric Aromatic By-Products

The oxidative degradation of eucalyptus kraft lignin as a function of an oxygen-enriched ionic liquid (IL) medium was investigated as part of a fundamental study to examine its capacity to degrade lignin into a suite of potentially valuable by-products relative to a standard sodium hydroxide solution (control). The variables of temperature, oxygen pressure, reaction time, and catalyst on the aromatic monomer products were controlled, whereas it was found that the yields of various aromatic monomer products were significantly improved when ionic liquid was used as the solvent instead of sodium hydroxide solution. These yields increased more substantially when a mixture of ionic liquid and sodium hydroxide was exploited as the reaction solvent. A quantity of 105.3 mg/g aromatic monomer products can be obtained at a temperature of 150°C, reaction time of two hours, and oxygen pressure of 6 MPa using CuO as the catalyst. In addition to the formation of aromatic monomer products, there were a number of other fascinating functional group and chemical linkage changes observed in the lignin macromolecule within the IL-based reaction system.     

杂多酸(盐)——氧脱木素的新型催化剂

概述了杂多酸 (盐 )的结构和催化性能 ,并展望了杂多酸 (盐 )应用于纸浆脱木素的应用前景     

提高硫酸盐竹浆氧脱木素选择性的研究

研究了在氧脱木素过程中添加不同的助剂、改变助剂的用量以及在氧脱木素前进行预处理等方法提高硫酸盐竹浆氧脱木素选择性．结果表明：在氧脱木素过程中添加表面活性剂能提高脱木素效率,但会加剧碳水化合物的降解;木聚糖酶预处理对提高竹浆氧脱木素选择性有一定的帮助,但效果不明显;而蒽醌磺酸钠、磷钨酸及氧脱木素前采用HNO3／NaNO3预处理能显著氧脱木素效率．     

Low energy steam explosion treatment of plant biomass

The rational operational condition for maximizing the pretreatment effect on plant biomass while minimizing heat required was investigated. Eucalyptus globulus chips were used to evaluate the operational method for the most efficient conversion of plant biomass into useful materials by steam explosion. The energy consumption required to carry out the steam explosion was calculated by considering the mass balances of the water, the wood component, and the heat balance in the steam explosion apparatus. The energy consumption increased significantly with the increase of steam pressure and steaming time, and decreased rapidly with increase of the thickness of the heat‐insulating material in the steam explosion apparatus. The amount of methanol‐soluble lignin, a low molecular weight lignin, was measured experimentally under various operational conditions such as steam pressure and steaming time. The steam explosion at the steam pressure of 3.9 MPa and steaming time of 1.1 min was the most effective method for maximizing the delignification with low energy consumption. © 2001 Society of Chemical Industry     

Effect of Counter Cation on Alkaline Reaction of β-O-4-Type Substructure in Lignin

This study aimed to clarify the effects of counter cations on the alkaline-induced β-O-4 bond cleavage and further reactions of β-O-4-type substructures in lignin. For this purpose, a non-phenolic β-O-4-type lignin model compound, the erythro isomer of 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (veratrylglycerol-β-guaiacyl ether), was treated in a 100% water solution or an aqueous methanol, ethanol, or 1,4-dioxane solution containing LiOH, NaOH, or CsOH as an alkaline source at 150?°C. The rates of β-O-4 bond cleavage were in the order of CsOH?>?NaOH?>?LiOH in all solvents. This order can rationally be attributed to the strength of the interactions between HO^– and the counter cations. Because Cs⁺ has the lowest positive charge density among the counter cations and hence interacts with HO^– most weakly, HO^– can exert its reactivity most actively in the reactions using CsOH. We also discuss how the counter cations affect the profile of reaction products.