负载离子液体的生物质炭磺酸催化水解纤维素

纤维素是生物质的主要成分,其水解产物作为平台化合物在能源化工方面具有广泛的用途.绿色、低成本、高效的转化纤维素为平台化合物是目前研究的热点.本文报道了以生物质玉米秸秆、花生壳、核桃壳为原料经700℃碳化150℃磺化后得到生物质炭磺酸,将得到的生物质炭磺酸进行离子液体的负载得到离子液体功能化的生物质炭磺酸催化剂,探讨了时间和温度对制备的催化剂水解纤维素后总还原糖产率的影响,与负载前的生物质炭磺酸进行了对比.结果表明,150℃反应28 h三种催化剂均得到良好的总还原糖产率,相对于生物质炭磺酸总还原糖产率分别提升了13. 9%、16. 4%和14. 7%.循环使用四次后,催化剂依然保持着良好的催化活性.     

纤维素超临界水预处理与水解研究

利用超临界水解工艺进行生物质废弃物(秸秆)能源转化, 使其主要成分纤维素在超临界水中快速水解为低聚糖, 为其进一步葡萄糖转化和乙醇发酵解决技术瓶颈. 其中纤维素在超临界水中的溶解是预处理与水解过程的限速步骤. 研究表明, 反应温度达到380 ℃及以上时, 纤维素可迅速溶解并进行水解, 液化比例可达100%; 在374～386 ℃范围内反应温度对纤维素的转化率有明显作用, 低聚糖和六碳糖的总产率在临界点附近出现最大值. 超临界条件下, 低聚糖和六碳糖转化率在较短反应时间内出现峰值, 而后随反应时间的延长快速下降, 固液比对于纤维素的低聚糖和六碳糖转化也有显著影响. 最优水解条件研究显示, 在380 ℃, 40 mg纤维素/2.5 mL水条件下反应16 s可获得最大的低聚糖产率, 为29.3%, 在380 ℃, 80 mg纤维素/2.5 mL水条件下反应18 s可获得最大的六碳糖产率, 为39.2%.     

微波辅助DMSO/AmimCl复合溶剂预处理玉米秸秆的酶解影响

为了实现玉米秸秆纤维素的高效糖化, 设计利用微波加热辅助的离子液体1-烯丙基-3-甲基咪唑氯盐(AmimCl)/二甲基亚砜(DMSO)复合溶剂生物质预处理体系, 破坏玉米秸秆天然结构, 提高纤维素酶解效率. 研究发现, 15% (w)DMSO, 110℃, 60 min 及4 g 秸秆/100 g 复合溶剂为最适预处理条件. 在此条件下, 秸秆溶解率、提取率可分别达46.6%和22.9%; 提取物纤维素酶解率14 h 可达71.4%, 相较于天然玉米秸秆的20 h 酶解率12.5%有极大提高. 通过XRD,SEM及¹H NMR 分析发现:秸秆预处理后, 提取物纤维素晶型由Ⅰ 型变为Ⅱ 型, 残渣纤维素相对结晶度明显降低, 有利于纤维素酶解的进行, 达到了生物质预处理的目的; 预处理过程中使用的AmimCl 离子液体经简单回收再生, 结构及秸秆溶解性能未发生变化, 可循环使用. 为玉米秸秆生物质预处理提供了一个新的方案.     

烟煤与生物质快速共热解产物特性分析

研究了烟煤(YL)分别与富含半纤维素的玉米芯(CB)和富含木质素的松木屑(SD)快速共热解产物产率和气体组成的变化规律。结果表明,烟煤与生物质共热解组分互相作用,造成共热解气、液、固相产率和气体组成的明显变化,且与生物质种类有关。相对于独立热解过程,玉米芯丰富的半纤维素造成热解水蒸气和CO₂浓度较高,且玉米芯中富含的K元素挥发迁移至煤焦表面,对热解半焦与水蒸气、CO₂的气化反应起到催化作用,反应生成的H₂和富氢组分易与热解生成的自由基结合,抑制自由基之间的缩聚反应,使得共热解气体和液体产率增加,而半焦产率减小。烟煤/松木屑共热解过程中,松木屑中富含的Ca元素在煤焦表面迁移,促进了松木屑热解液体在半焦表面裂解反应,生成CO₂、CO和富氢自由基等轻质组分,造成共热解半焦和液体产率降低而气体产率增加。热解产物半焦、焦油、水蒸气、CO₂之间的气化和裂解反应均产生富氢的次生组分,从而提高了共热解气体中CO和烃类气体产率,降低了H₂产率。     

水热条件下酸催化氧化木质纤维生物质制取乙酸

木质纤维基生物质是一类新的能够生产液体燃料和化学品的可再生资源. 本文研究了木质纤维生物质在水热条件下, 以少量无机酸作为酸催化剂, 氧气作为氧化剂(2.0 MPa), 经过"一锅两步法"转化成乙酸的反应. 以玉米秸秆作为反应原料时, 最高可以获得21.3 wt%的乙酸, 占据整个液体产物质量比例的84.6% (选择性). 同时, 将反应推广到玉米芯, 甘蔗渣, 竹子, 杨木和松木等多种生物质原料的转化, 同样取得了较高的乙酸产率. 最后, 我们对木质纤维生物质转化到乙酸的反应过程进行了研究. 研究表明木质纤维生物质中的碳水化合物六碳糖是乙酸的主要来源, 六碳糖经过脱水和水解生成乙酰丙酸中间体, 乙酰丙酸在氧化条件下断裂C-C键生成乙酸.     

钾元素对生物质主要组分热解特性的影响

采用热重-红外联用仪对松木及生物质主要化学组分半纤维素、纤维素、木质素的热解特性及钾元素对其热解特性的影响进行了研究.结果表明,半纤维素、纤维素、木质素发生热解的主要温度分别为200~350 ℃、300~365 ℃和200~600 ℃;半纤维热解产物中CO、CO₂较多;纤维素热解产物中LG和醛酮类化合物最多;木质素热解主要形成固体产物,气体中CH₄相对含量较高.三种组分共热解过程中发生相互作用使热解温度提高、固体产物增加,气体中CO增加而CH₄减少.添加K₂CO₃后半纤维素和纤维素热解温度区间向低温方向移动,固体产率提高.K对纤维素作用最明显,CO、CO₂气体与固体产物产率明显增加,醛酮类和酸类物质的产率降低;木质素受K影响相对较小,热解固体产物略有增加,挥发分中H₂O和羰基物质增加;三组分共热解减弱了钾元素的催化作用.     

超临界水中钾对甲醛降解过程影响的研究

为掌握生物质中钾对生物质超临界水降解过程的影响,选择生物质气化转化过程中生成的重要小分子中间产物甲醛作为研究对象,研究不同工艺条件下(反应温度400～650℃、压力23～29 MPa、停留时间4～12 s),单一钾成分(KHCO₃/K₂CO₃/KCl)或混合钾成分(KHCO₃、K₂CO₃、KCl)对甲醛超临界水降解气体产物的影响。结果表明,KHCO₃、K₂CO₃、KCl、混合钾均降低了气体产物中CO的体积分数,提高了CO₂的体积分数,但KCl的影响程度弱于其他三种钾成分。此外,由于不同钾成分均不利于气体产物中CO和H₂体积分数的提高,从而使得气体产物的热值降低。KHCO₃、K₂CO₃、KCl、混合钾均降低了H₂、CO、CO₂的产率以及气化率,其对H₂产率以及气化率的抑制程度从大到小依次为:混合钾、KHCO₃、K₂CO₃、KCl,且提高反应温度、延长反应停留时间时抑制气体生成的作用相对越明显。而当反应压力改变时,钾成分对H₂产率及气化率的影响程度变化较小。较高反应温度、较高反应压力、较长停留时间时,混合钾中各成分出现协同作用,明显抑制了气体产物的生成。     

玉米芯酸水解残渣的热解特性

在热重分析仪和管式炉热解装置上对玉米芯酸水解残渣（简称残渣）的热解过程进行了研究,并利用气相色谱（GC）,气相色谱-质谱联用(GC-MS)和扫描电镜(SEM)对热解产物进行了分析。热重分析结果表明,残渣的热裂解主要发生在280℃~ 450℃,仅在340.7℃有一个明显的失重峰。管式炉热解实验表明, 随着热解终温的升高,残渣的气相产物产率明显增加,而固相和液相产物产率均有所下降。GC分析结果表明,H₂和CH₄的产率随着热解终温的升高而升高,CO₂产率呈现下降趋势; 与玉米芯热解气相产物相比,残渣热解CO、H₂和CH₄的产率较高,CO₂产率较低。GC-MS结果表明,残渣热解焦油的主要成分为酚类物质和多环芳烃。SEM结果表明,随着热解终温的升高,残渣热解焦炭的表面结构趋于有序化。     

Polyethylene glycol radical-initiated aerobic propargylic oxidation in dense carbon dioxide

The selective aerobic oxidation of alkynes to correspondingα,β-acetylenic ketones was achieved in polyethylene glycol/dense CO₂/O₂ biphasic system without any catalyst or additive.The effects of reaction parameters,e.g.temperature,CO₂ pressure,PEG molecular weight and loading on the reaction were carefully examined.Moreover,various substrates worked well in the presence of PEG 1000 under 5 MPa of CO₂ and 2 MPa of O₂ at 100℃for 12 to 24 h and acceptable yield and selectivity could be obtained in most cases.Preliminary mechanistic investigations were also discussed.     

垃圾衍生燃料热解半焦气化过程中HCl与H2S析出规律

通过水平管式气化炉和化学吸收法,对比研究了矿化垃圾热解半焦（ARC）和常规垃圾热解半焦（NRC）在水蒸气和CO₂气化过程中腐蚀性气体（HCl和H₂S）的析出特性,考察了气化温度、气化介质类型和流量对腐蚀性气体析出特性的影响。当气化温度升至950℃,ARC在水蒸气气化过程中的碳气化率、HCl和H₂S产率分别为66.1%、100%和74.9%,而其在CO₂气化过程中的碳气化率、HCl和H₂S产率分别为77.8%、100%和2.9%;NRC在水蒸气气化过程中的碳气化率、HCl和H₂S产率分别为98.8%、100%和53.7%,而其在CO₂气化过程中的碳气化率、HCl和H₂S产率分别为100%、96.2%和10.3%。以NRC为原料,考察了水蒸气和CO₂流量对其HCl和CO₂析出特性的影响。NRC的HCl和H₂S产率均随水蒸气流量增加而增加,但当水碳比大于等于3.3时,其促进作用不再明显。NRC的HCl产率随CO₂流量的增加而增加,而H₂S产率随CO₂流量的增加而减小。     

Effect of Alkali Pretreatment on the Structural Properties and Enzymatic Hydrolysis of Corn Cob

An effective alkali pretreatment which affects the structural properties of cellulose (corn cob) has been studied. The pretreatment of corn cob was carried out with different combinations of alkali at varying temperatures. The most effective pretreatment of corn cob was achieved with 1?% alkali at 50?°C in 4?h. The crystallinity index (CrI) and specific surface area (SSA) of untreated corn cob was 39?% and 0.52?m²/g wherein after alkali pretreatment CrI decreased to 15?% and SSA increased to 3.32?m²/g. The fungal organism was identified as Penicillium pinophilum on the basis of ITS sequence. At 5?% substrate concentration using a complete cellulase from Penicillium pinophilum the hydrolysis of untreated corn cob with 5, 10 and 20 FPU/g enzyme loadings were 11?%, 13?% and 16?%, whereas after alkali treatment the hydrolysis increased to 78?%, 90?% and 100?%, respectively. Further hydrolytic potential of commercial cellulases viz. Accellerase? 1,000, Palkofeel-30 and Palkocel-40 were investigated under similar conditions.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Optimization of SO2-catalyzed steam pretreatment of corn fiber for ethanol production

A batch reactor was employed to steam explode corn fiber at various degrees of severity to evaluate the potential of using this feedstock as part of an enzymatically mediated cellulose-to-ethanol process. Severity was controlled by altering temperature (150–230°C), residence time (1–9 min), and SO₂ concentration (0–6% [w/w] dry matter). The effects of varying the different parameters were assessed by response surface modeling. The results indicated that maximum sugar yields (hemicellulose-derived water soluble, and cellulose-derived following enzymatic hydrolysis) were recovered from corn fiber pretreated at 190°C for 5 minutes after exposure to 3% SO₂. Sequential SO₂-catalyzed steam explosion and enzymatic hydrolysis resulted in a conversion efficiency of 81% of the combined original hemicellulose and cellulose in the corn fiber to monomeric sugars. An additional posthydrolysis step performed on water soluble hemicellulose stream increased the concentration of sugars available for fermentation by 10%, resulting in the high conversion efficiency of 91%. Saccharomyces cerevisiae was able to ferment the resultant corn fiber hydrolysates, perhydrolysate, and liquid fraction from the posthydrolysis steps to 89, 94, and 85% of theoretical ethanol conversion, respectively. It was apparent that all of the parameters investigated during the steam explosion pretreatment had a significant effect on sugar recovery, inhibitory formation, enzymatic conversion efficiency, and fermentation capacity of the yeast.     

Chemical pretreatments of corn stover for enhancing enzymatic digestibility

Corn stover, the most abundant agricultural residue in Hungary, is a potential raw material for the production of fuel ethanol as a result of its high content of carbohydrates, but a pretreatment is required for its efficient hydrolysis. In this article, we describe the results using various chemicals such as dilute H₂SO₄, HCl, and NaOH separately as well as consecutively under relative mild conditions (120°C, 1h). Pretreatment with 5% H₂SO₄ or 5% HCl solubilized 85% of the hemicellulose fraction, but the enzymatic conversion of pretreated materials increased only two times compared to the untreated corn stover. Applying acidic pretreatment following a 1-d soaking in base achieved enzymatic conversion that was nearly the theoretical maximum (95.7%). Pretreatment with 10% NaOH decreased the lignin fraction >95%, increased the enzymatic conversion more than four times, and gave a 79.4% enzymatic conversion. However, by increasing the reaction time, the enzymatic degradability could also be increased significantly, using a less concentrated base. When the time of pretreatment was increased three times (0.5% NaOH at 120°C), the amount of total released sugars was 47.9 g from 100 g (dry matter) of untreated corn stover.     

Cellulose solvent-based pretreatment for corn stover and avicel: concentrated phosphoric acid versus ionic liquid [BMIM]Cl

Since cellulose accessibility has become more recognized as the major substrate characteristic limiting hydrolysis rates and glucan digestibilities, cellulose solvent-based lignocellulose pretreatments have gained attention. In this study, we employed cellulose solvent- and organic solvent-based lignocellulose fractionation using two cellulose solvents: concentrated phosphoric acid [~85?% (w/w) H₃PO₄] and an ionic liquid Butyl-3-methylimidazolium chloride ([BMIM]Cl). Enzymatic glucan digestibilities of concentrated phosphoric acid- and [BMIM]Cl-pretreated corn stover were 96 and 55?% after 72?h at five filter paper units of cellulase per gram of glucan, respectively. Regenerated amorphous cellulose by concentrated phosphoric acid and [BMIM]Cl had digestibilities of 100 and 92?%, respectively. Our results suggested that differences in enzymatic glucan digestibilities of concentrated phosphoric acid- and [BMIM]Cl-pretreated corn stover were attributed to combinatory factors. These results provide insights into mechanisms of cellulose solvent-based pretreatment and effects of residual cellulose solvents and lignin on enzymatic cellulose hydrolysis.     

Pretreatment of Corn Stover Silage with Fe(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> for Fermentable Sugar Production

Corn stover silage is an attractive raw material for the production of biofuels and chemicals due to its high content of carbohydrates and easy degradability. The effects of Fe(NO₃)₃ pretreatment conditions on sugar yields were investigated for corn stover silage. In addition, a combined severity factor was used to evaluate the effect of pretreatment conditions on the concentration of total sugars and inhibitors. Optimum pretreatment condition was obtained at 150 °C for 10 min with 0.05 M Fe(NO₃)₃, at which the yields of soluble xylose and glucose in liquid achieved 91.80% of initial xylose, 96.74% of initial arabinose and 19.09% of initial glucose, respectively, meanwhile, 91.84% of initial xylose, 98.24% of initial arabinose, and 19.91% of initial glucose were removed. In addition, a severity analysis showed that the maximum sugar concentration of 33.48 g/l was achieved at combined severity parameter value of 0.62, while the inhibitor concentration was only 0.03 g/l. Fe(NO₃)₃ is an effective catalyst to enhance hemicellulose hydrolysis in corn stover silage, the yields of monomeric xylose in the liquid fraction reached as high as 91.06% of initial xylose and 96.22% of initial arabinose, respectively.     

Enhanced enzymatic hydrolysis of poplar bark by combined use of gamma ray and dilute acid for bioethanol production

Pretreatment of poplar bark with a combination of sulfuric acid (3%, w/w, H₂SO₄) and gamma irradiation (0–1000 kGy) was performed in an attempt to enhance enzymatic hydrolysis for bioethanol production. The yields of reducing sugar were slightly increased with an increasing irradiation dose, ranging from 35.4% to 51.5%, with a 56.1% reducing sugar yield observed after dilute acid pretreatment. These results clearly showed that soluble sugars were released faster and to a greater extent in dilute acid-pretreated poplar bark than in gamma irradiation-pretreated bark. When combined pretreatment was carried out, a drastic increase in reducing sugar yield (83.1%) was found compared with individual pretreatment, indicating the possibility of increasing the convertibility of poplar bark following combined pretreatment. These findings are likely associated with cellulose crystallinity, lignin modification, and removal of hemicelluloses.     

Direct conversion of corn cob to formic and acetic acids over nano oxide catalysts

Considering energy shortage, large molecules in corn cob and easy separation of solid catalysts, nano oxides are used to transform corn cob into useful chemicals. Because of the microcrystals, nano oxides offer enough accessible sites for cellulose, hemicellulose and monosaccharide from corn cob hydrolysis and oxidant. Chemical conversion of corn cob to organic acids is investigated over nano ceria, alumina, titania and zirconia under various atmospheres. Liquid products are mainly formic and acetic acids. A small amount of other compounds, such as D-xylose,D-glucose, arabinose and xylitol are also detected simultaneously. The yield of organic acids reaches 25%–29% over the nano oxide of ceria,zirconia and alumina with 3 h reaction time under 453 K and 1.2 MPa O2. The unique and fast conversion of corn cob is directly approached over the nano oxides. The results are comparative to those of biofermentation and offer an alternative method in chemically catalytic conversion of corn cob to useful chemicals in a one-pot chemical process.     

Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility

Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million to fcorn stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40% of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time, and pH during steam pretreatment. The best conditions (200°C, 5 min, 2% H₂SO₄) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated material. However, steam pretreatment at 190°C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars, 56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the glucose to ethanol efficiently.     

Oxidative lime pretreatment of high-lignin biomass

Lime (Ca[OH]₂) and oxygen (O₂) were used to enhance the enzymatic digestibility of two kinds of high-lignin biomass: poplar wood and newspaper. The recommended pretreatment conditions for poplar wood are 150°C, 6 h, 0.1 g of Ca(OH)₂/g of dry biomass, 9 mL of water/g of dry biomass, 14.0 bar absolute oxygen, and a particle size of −10 mesh. Under these conditions, the 3-d reducing sugar yield of poplar wood using a cellulase loading of 5 filter paper units (FPU)/g of raw dry biomass increased from 62 to 565 mg of eq. glucose/g of raw dry biomass, and the 3-d total sugar (glucose + xylose) conversion increased from 6 to 77% of raw total sugars. At high cellulase loadings (e.g., 75 FPU/g of raw dry biomass), the 3-d total sugar conversion reached 97%. In a trial run with newspaper, using conditions of 140°C, 3 h, 0.3 g of Ca(OH)₂/g of dry biomass, 16 mL of water/g of dry biomass, and 7.1 bar absolute oxygen, the 3-d reducing sugar yield using a cellulase loading of 5 FPU/g of raw dry biomass increased from 240 to 565 mg of eq. glucose/g of raw dry biomass. A material balance study on poplar wood shows that oxidative lime pretreatment solubilized 38% of total biomass, including 78% of lignin and 49% of xylan; no glucan was removed. Ash increased because calcium was incorporated into biomass during the pretreatment. After oxidative lime pretreatment, about 21% of added lime could be recovered by CO₂ carbonation.