2013生物基化学品 (Biobased Chemicals) 专刊序言

生物基化学品是生物经济和生物制造的核心内容之一。本专刊综述了国内外生物基化学品的重要研究进展,包括：丁二酸、己二酸、乳酸、3-羟基丙酸、葡萄糖二酸、甘油、木糖醇、高级醇、乙烯等生物基化学品的代谢工程和发酵调控,直接利用木质纤维素生产生物基化学品的菌株构建,生物基乳酸的衍生和生物转化技术,生物基化学品的盐析萃取分离纯化技术等。同时,本专刊也包括了国内学者在丁二酸、D-甘露醇、苹果酸、5-氨基乙酰丙酸、1,3-丙二醇和丁醇方面的研究论文。     

微生物菌群发酵生产化学品的研究进展

廉价生物质资源的利用是工业生物技术领域研究的热点,复杂的成分和较多的杂质使传统的单菌发酵方式难以应对,成为产业化的关键问题。文中从微生物菌群的工业应用、微生物菌群发酵与纯种发酵的比较、微生物细胞间的相互作用等方面综述了微生物菌群发酵技术的最新研究进展,并对微生物菌群的设计和应用进行了展望。微生物菌群发酵可以充分利用廉价生物质基质、生产多个产品或减少副产物的生成,在生物基化学品和燃料的生产中将是一种有前景的发酵技术。     

运动发酵单胞菌在生物炼制中的研究进展

以木质纤维素生物质为原料的生物炼制技术已成为全球研发的热点和难点。欧盟国家和美国的中长期生物质能源发展路线图中均将木质纤维素生物炼制技术作为重要目标,但是目前整体水平尚处于中试阶段。我国的纤维素类生物质原料非常丰富,将其转化成燃料乙醇及生物基础化学品等具有较大的潜力,但当前要想实现商业化生产,还面临着很多瓶颈问题亟待解决。缺乏能够同时高效利用纤维素类水解物的发酵菌株,已成为纤维素生物质高效与高值转化的关键制约因素。运动发酵单胞菌是目前唯一一种通过ED途径兼性厌氧发酵葡萄糖的微生物,其独特的代谢途径使其成为构建产乙醇工程菌的优选宿主之一;同时由于该菌具有较高的糖利用效率等优点,也是其他生物基化学品生产的重要候选平台微生物,如山梨醇、葡萄糖酸、丁二酸和异丁醇等。本文从该菌的研究历程、分子生物学基础、菌种改良及该菌在生物能源及生物基化学品等生物炼制体系中的应用研究角度进行了综述,并提出该菌可作为纤维素生物质生物炼制系统的新的重要平台微生物。     

生物基化学品生产合成橡胶技术正在脱颖而出

虽然生物基化学品仍然处于发展阶段,但是生物质原料转化成能源已经是一个成熟的技术,生物基化学品（尤其是生物基异丁烯、生物基丁二烯、生物基异戊二烯和生物基乙烯）生产合成橡胶技术正在脱颍而出。     

我国生物丁醇分离提取技术研究进展

本文概述了目前国内外生物丁醇生产体系中的分离提取技术,包括液液萃取、气提、吸附、精馏和渗透汽化技术等的应用研究现状,详细阐述了上述几种方法在分离提取生物丁醇方面的优势与不足,对各类方法的分离特性和效果进行了比较,并展望了生物丁醇分离提取技术的发展前景。     

生物质原料预处理、组分分离到结构选择性拆分——生物质原料工程学的发展

在石化资源日益匮乏的严峻形势下,生物质将成为未来新一代生物及化工产业的最理想的替代原料.因此,如何使生物质资源成为生物基能源、生物基化学品和生物基材料的通用原料,成为目前世界各国共同关注的焦点和热点.从生物炼制及生物质科学与工程的发展可以看出,原料预处理是实现生物质高效转化的必要手段,而组分分离-定向转化是原料预处理的进一步提升,它可以实现纤维素、半纤维素和木质素的分别转化,但是仍然存在着原子利用率不高、能耗高、工艺路线复杂等问题.鉴于生物质是一个功能大分子体,要使其成为通用原料,应该根据原料结构特点和产物要求,发展结构化功能高值拆分的转化过程,即原料的选择性结构拆分思路.从原料预处理到组分分离,再到选择性结构拆分,实现了原料工程学的发展与逐步成熟,其最终目的是要真正建立以生物质为通用原料的新型工业技术体系和研究平台.     

提高丁醇萃取发酵耦联生产改良型生物柴油过程中萃余液回用效率的研究

利用少量廉价的萃取剂一正辛醇（正辛醇／萃余液体积比0．2：1）对萃余液中的丁醇进行萃取,萃余液中56％的残余丁醇可被回收,总丁醇得率提高了38％。萃余液经活性炭（3％,w／v）处理后,在100％回用拌料条件下一批次发酵能够正常进行。萃取发酵条件下,反复全回用萃余液5次,萃取发酵性能可以保持稳定。为丁醇萃取发酵耦联生产改良型生物柴油过程中萃余液的全回用提供了一种新型、低成本和绿色环保的方法。     

2，3-丁二醇的发酵及盐析分离工艺

采用克雷伯氏菌（Klebsiella pneumoniae CICC 10011）发酵生产2,3-丁二醇,并对2,3-丁二醇的盐析分离工艺进行了考察。通过实验确定了以葡萄糖为底物微氧批式流加发酵的条件,发酵液中2,3-丁二醇和3-羟基丁酮的质量浓度分别为90．98g/L和12．40g/L,2,3-丁二醇的摩尔转化率为82．7％,生产强度达到2．1g/（L·h）。对发酵液中2,3-丁二醇的盐析分离研究表明,K2HPO4和K3PO4对2,3-丁二醇的盐析效果优于K2CO3。当发酵液浓缩70％后,加入质量分数为45％的K,HPO4,2,3-丁二醇的分配系数达到9．10,回收率为79．37％;上相中2,3-丁二醇的质量浓度达到420g／L;此时3-羟基丁酮的分配系数和回收率分别为11．9和83．48％。     

生物炼制是一个多学科交叉的前沿方向

1982年．生物炼制的概念在《science》上首次被提出。生物炼制．就是说以生物质为基础的化学工业也必须打破原来用生物质单纯生产单一产品的传统观念．充分利用原料中的每一种组分,将其分别转化为不同的产品．实现原料充分利用、产品价值最大化和土地利用效率最大化。目前．生物炼制已经成为世界各国研究的热点．主要内容包括生物材料、生物基化学品、生物能源、生物基原料、生物炼制平台技术等。     

2016生物基材料专刊序言

生物基材料,是利用谷物、豆科、秸秆、竹木粉等可再生生物质为原料制造的新型材料和化学品等,包括生物合成、生物加工、生物炼制过程获得的生物醇、有机酸、烷烃、烯烃等基础生物基化学品,也包括生物基塑料、生物基纤维、糖工程产品、生物基橡胶以及生物质热塑性加工得到塑料材料等。生物基材料由于其绿色、环境友好、资源节约等特点,正逐步成为引领当代世界科技创新和经济发展的又一个新的主导产业。本期专刊报道了生物基材料总体发展情况,介绍了生物基纤维、聚羟基烷酸酯、可生物降解地膜、生物基聚酰胺、蛋白医用生物材料、生物基聚氨酯、聚乳酸改性与加工等几个方面行业状况及其研究进展。     

Separation of bio‐based chemicals from fermentation broths by salting‐out extraction

The possibility of creating a biorefinery using inexpensive biomass has attracted a great deal of attention, which is mainly focused on the improvement of strains and fermentation, whereas few resources have been spent on downstream processing. Bio‐based chemical downstream processing can become a bottleneck in industrial production because so many impurities are introduced into the fermentation broth. This review introduces a technique referred to as salting‐out extraction, which is based on the partition difference between chemicals in two phases consisting of salts and polymers or hydrophilic solvents, hydrophobic solvents, and amphipathic chemicals. The effects of solvents and salts on the formation of two phases were discussed, as was the use of this method to recover bio‐based chemicals. This review focused on the separation of hydrophilic chemicals (1,3‐propanediol, 2,3‐butanediol, acetoin, and lactic acid) from fermentation broths. Diols could be recovered at a high yield from fermentation broths without pretreatment especially with a hydrophilic solvent‐based system, whereas the recovery of organic acids was slightly lower. Most of the impurities (cells and proteins) were removed during the same step. Extractive fermentations were also used for polymer‐based aqueous two‐phase systems.     

Salting-out extraction and crystallization of succinic acid from fermentation broths

In this study, salting-out extraction (SOE) and crystallization were combined to recover succinic acid from fermentation broths. Of the different SOE systems investigated, the system consisting of organic solvents and acidic salts appeared to be more favorable. A system using acetone and ammonium sulfate was investigated to determine the effect of phase composition and pH. The highest partition coefficient (8.64) and yield of succinic acid (90.05%) were obtained by a system composed of 30% (w/w) acetone and 20% (w/w) ammonium sulfate at a pH of 3.0. Additionally, 99.03% of cells, 90.82% of soluble proteins, and 94.89% of glucose could be simultaneously removed from the fermentation broths. Interestingly, nearly 40% of the pigment was removed using the single-step salting-out extraction process. The analysis of the effect of pH on salting-out extraction indicates that a pH lower than the pK of succinic acid is beneficial for the recovery of succinic acid in an SOE system. Crystallization was performed for the purification of succinic acid at 4 °C and pH 2.0. By combining salting-out extraction with crystallization, an identical total yield (65%) and a higher purity (97%) of succinic acid were obtained using a synthetic fermentation broth compared with the actual fermentation broth (65% and 91%, respectively).     

1,3-丙二醇发酵液后提取技术研究进展

1,3-丙二醇是一种重要的化工原料,以甘油或葡萄糖为原料发酵法制备1,3-丙二醇具有原料可再生、反应条件温和等优点,是近年来国内外的研究热点。由微生物发酵获得的1,3-丙二醇发酵液是含多种强极性的醇及盐类的稀溶液,这使得采用传统的分离方法难以经济、有效地的将1,3-丙二醇从发酵液中纯化出来,后提取过程成为发酵法工业化生产1,3-丙二醇的瓶颈。1,3-丙二醇后提取过程主要包括微生物菌体等高分子物质的去除,盐的去除、回收,有机物的纯化和水的去除。以下对应用于以上分离过程的技术的研究进展进行讨论,提出在该领域应该重视的发展方向。     

Development of Suitable Solvent System for Downstream Processing of Biopolymer Pullulan Using Response Surface Methodology

Downstream processing is an important aspect of all biotechnological processes and has significant implications on quality and yield of the final product. Several solvents were examined for their efficacy on pullulan precipitation from fermentation broth. Interactions among four selected solvents and their effect on pullulan yield were studied using response surface methodology. A polynomial model was developed using D-optimal design and three contour plots were generated by performing 20 different experiments and the model was validated by performing optimization experiments. The results indicated that lower concentration of ethanol in combination with the other three solvents has resulted in higher yield of polymer from fermentation broth and the optimized solvent system was able to recover 1.44 times more pullulan as compared to the conventional ethanolic precipitation method. These observations may help in enhancing efficiency of pullulan recovery from fermentation broth and also result in reduced cost of production for the final product.     

Measuring oxygen diffusion coefficients with polarographic oxygen electrodes. II. Fermentation Media

Fermentation media consist of a large number of chemicals which composition undergoes alteration during the course of fermentations. In consequence, the conventional methods and correlations for gas diffusion coefficient measurement and prediction cannot be easily applied to such systems. Oxygen diffusion coefficients have been measured in simulated chemical systems as well as in complex solutions of nutrient broth, using the polarographic technique introduced in a previous article. It is identified that sugars and salts are the major factors influencing oxygen diffusion coefficients in these aqueous fermentation media. The effect of salts on oxygen diffusion coefficients in electrolyte solutions has been found to be well correlated with the square root of total ionic strength of electrolyte solutions. The individual effect of glucose and its combined effect with salts are explored in order to reach rational correlations capable of predicting oxygen diffusion coefficients in synthetic fermentation media. For aqueous solutions of glucose plus salts, it is observed that the log-additive relationship can be used to account for the combined effect. Finally, a linear correlation has been established in measuring oxygen diffusion coefficients in aqueous solutions having different concentrations of nutrient broth.     

Downstream separation and purification of bio-based alpha-ketoglutaric acid from post-fermentation broth using a multi-stage membrane process

In this study, a multi-stage membrane process, assisted by vacuum evaporation and crystallization, for recovery of bio-based alpha-ketoglutaric acid from the actual post-fermentation broth was designed and investigated. In the first part of this study, pre-treatment of crude fermentation broth (centrifugation-ultrafiltration-nanofiltration) was carried out to remove biomass, proteins, sugars, part of inorganic ions and color compounds. The commercial ceramic UF membrane (15 kDa) and nanofiltration ceramic membrane (200 Da or 450 Da) were applied. Electrodialysis with a bipolar membrane was proposed for separation of ionic compounds and simultaneous electro-acidification to the acid form. During bipolar membrane electrodialysis carried out under acidic conditions, it was possible to remove close to 90 % of alpha-ketoglutaric acid. Moreover, the migration of other acids present in the fermentation broth (lactic and acetic) was significantly limited. The calculated specific energy consumption was low and equal to 0.6 kW h/kg. The final purification using crystallization assisted vacuum evaporation allowed obtaining alpha-ketoglutaric acid in solid form. Analysis of the final product showed that the proposed method of alpha-ketoglutaric acid recovery gives the acid of high purity equal to 94.8 %. Furthermore, the presented results have practical relevance and may in future be the basis for the development of separation technologies of alpha-ketoglutaric acid from the fermentation broth on industrial scale.     

Water extraction of pyrolysis oil: the first step for the recovery of renewable chemicals

The interest in biomass as a source of renewable energy and chemicals has been increasing in keeping up with the transition to a sustainable bio-based economy. An important initial step of chemicals recovery from biomass-derived pyrolysis oil is water extraction where most of polar compounds are isolated in the aqueous phase. This study was done to investigate the effects of stirring rate and water-to-oil ratio on the extraction capability (distribution coefficient and yield), water content, and atomic composition of both aqueous and organic phases. The results show that the stirring rate above 300 rpm has no influence on the equilibrium. Increasing the water-to-oil ratio dilutes the aqueous phase without changing the atomic distribution. Forest residue-derived pyrolysis oil should be extracted at a water-to-oil ratio of 0.65-0.7, whereas pine-derived pyrolysis oil is preferably extracted at the lowest feasible water-to-oil ratio where complete phase separation occurs, which is 0.5 in this study.     

Aqueous two-phase extraction of 2,3-butanediol from fermentation broths using an ethanol/ammonium sulfate system

Separation of 2,3-butanediol from the fermentation broth is a difficult task that has become a bottleneck in industrial production. Aqueous two-phase systems composed of hydrophilic solvents and inorganic salts could be used to extract 2,3-butanediol from fermentation broth. The ethanol/ammonium sulfate system was investigated in detail, including phase diagram, effect of phase composition on partition, removal of cells and biomacromolecules from the broths and recycling of ammonium sulfate. The highest partition coefficient (7.10) and recovery of 2,3-butanediol (91.7%) were obtained by a system composed of 32% (w/w) ethanol and 16% (w/w) ammonium sulfate. The maximum selective coefficient of 2,3-butanediol to glucose was 30.74 in the experimental range. In addition, cells and proteins could be simultaneously removed from the fermentation broth. The removal ratio of cells and proteins reached 99.7% and 91.2%, respectively. The recovery of ammonium sulfate in the bottom phase reached 97.14% when two volumes of methanol were added to the salt-rich phase.     

Achievements and perspectives to overcome the poor solvent resistance in acetone and butanol-producing microorganisms

Anaerobic bacteria such as the solventogenic clostridia can ferment a wide range of carbon sources (e.g., glucose, galactose, cellobiose, mannose, xylose, and arabinose) to produce carboxylic acids (acetic and butyric) and solvents such as acetone, butanol, and ethanol (ABE). The fermentation process typically proceeds in two phases (acidogenic and solventogenic) in a batch mode. Poor solvent resistance by the solventogenic clostridia and other fermenting microorganisms is a major limiting factor in the profitability of ABE production by fermentation. The toxic effect of solvents, especially butanol, limits the concentration of these solvents in the fermentation broth, limiting solvent yields and adding to the cost of solvent recovery from dilute solutions. The accepted dogma is that toxicity in the ABE fermentation is due to chaotropic effects of butanol on the cell membranes of the fermenting microorganisms, which poses a challenge for the biotechnological whole-cell bio-production of butanol. This mini-review is focused on (1) the effects of solvents on inhibition of cell metabolism (nutrient transport, ion transport, and energy metabolism); (2) cell membrane fluidity, death, and solvent tolerance associated with the ability of cells to tolerate high concentrations of solvents without significant loss of cell function; and (3) strategies for overcoming poor solvent resistance in acetone and butanol-producing microorganisms.     

Repeated use of yeast biomass in ethanol fermentation of juniper berry sugars

Summary The object of this study was to establish the possibility of using the yeast biomass separated from the fermentation broth at the end of ethanol fermentation of juniper berry sugars as an inoculum in successive batch fermentation processes. A part of the fermentation broth (10% v/v) and a suspension of yeast biomass (separated from the same broth) into the water extract of juniper berries (2 g of wet yeast biomass per liter of water extract) were used as inocula. It was shown that the suspension of yeast biomass could be used as inoculum in successive batch processes without negative effects on the kinetics and ethanol yield, but with positive effects on the capacity and economy of the bioprocess. The addition of ammonium salts at optimum levels did not affect the final ethanol concentrations (4.3–4.4% v/v), but enhanced the specific rate of ethanol production, thus reducing the process duration by about five times.