Oxidative Lime Pretreatment of Alamo Switchgrass

Previous studies have shown that oxidative lime pretreatment is an effective delignification method that improves the enzymatic digestibility of many biomass feedstocks. The purpose of this work is to determine the recommended oxidative lime pretreatment conditions (reaction temperature, time, pressure, and lime loading) for Alamo switchgrass (Panicum virgatum). Enzymatic hydrolysis of glucan and xylan was used to determine the performance of the 52 studied pretreatment conditions. The recommended condition (110°C, 6.89 bar O₂, 240 min, 0.248 g Ca(OH)₂/g biomass) achieved glucan and xylan overall yields (grams of sugar hydrolyzed/100 g sugar in raw biomass, 15 filter paper units (FPU)/g raw glucan) of 85.9 and 52.2, respectively. In addition, some glucan oligomers (2.6 g glucan recovered/100 g glucan in raw biomass) and significant levels of xylan oligomers (26.0 g xylan recovered/100 g xylan in raw biomass) were recovered from the pretreatment liquor. Combining a decrystallization technique (ball milling) with oxidative lime pretreatment further improved the overall glucan yield to 90.0 (7 FPU/g raw glucan).     

Oxidative Lime Pretreatment of Dacotah Switchgrass

Oxidative lime pretreatment increases the enzymatic digestibility of lignocellulosic biomass primarily by removing lignin. In this study, recommended pretreatment conditions (reaction temperature, oxygen pressure, lime loading, and time) were determined for Dacotah switchgrass. Glucan and xylan overall hydrolysis yields (72 h, 15 FPU/g raw glucan) were measured for 105 different reaction conditions involving three different reactor configurations (very short term, short term, and long term). The short-term reactor was the most productive. At the recommended pretreatment condition (120 °C, 6.89 bar O₂, 240 min), it achieved an overall glucan hydrolysis yield of 85.2 g glucan hydrolyzed/100 g raw glucan and an overall xylan yield of 50.1 g xylan hydrolyzed/100 g raw xylan. At this condition, glucan oligomers (1.80 g glucan recovered/100 g glucan in raw biomass) and xylan oligomers (25.20 g xylan recovered/100 g xylan in raw biomass) were recovered from the pretreatment liquor, which compensate for low pretreatment yields.     

Potential of Potassium Hydroxide Pretreatment of Switchgrass for Fermentable Sugar Production

Chemical pretreatment of lignocellulosic biomass has been extensively investigated for sugar generation and subsequent fuel production. Alkaline pretreatment has emerged as one of the popular chemical pretreatment methods, but most attempts thus far have utilized NaOH for the pretreatment process. This study aimed at investigating the potential of potassium hydroxide (KOH) as a viable alternative alkaline reagent for lignocellulosic pretreatment based on its different reactivity patterns compared to NaOH. Performer switchgrass was pretreated at KOH concentrations of 0.5–2 % for varying treatment times of 6–48 h, 6–24 h, and 0.25–1 h at 21, 50, and 121 °C, respectively. The pretreatments resulted in the highest percent sugar retention of 99.26 % at 0.5 %, 21 °C, 12 h while delignification up to 55.4 % was observed with 2 % KOH, 121 °C, 1 h. Six pretreatment conditions were selected for subsequent enzymatic hydrolysis with Cellic CTec2® for sugar generation. The pretreatment condition of 0.5 % KOH, 24 h, 21 °C was determined to be the most effective as it utilized the least amount of KOH while generating 582.4 mg sugar/g raw biomass for a corresponding percent carbohydrate conversion of 91.8 %.     

Alkali (NaOH) Pretreatment of Switchgrass by Radio Frequency-based Dielectric Heating

Radio-frequency (RF)-based dielectric heating was used in the alkali (NaOH) pretreatment of switchgrass to enhance its enzymatic digestibility. Due to the unique features of RF heating (i.e., volumetric heat transfer, deep heat penetration of the samples, etc.), switchgrass could be treated on a large scale, high solid content, and uniform temperature profile. At 20% solid content, RF-assisted alkali pretreatment (at 0.1 g NaOH/g biomass loading and 90°C) resulted in a higher xylose yield than the conventional heating pretreatment. The enzymatic hydrolysis of RF-treated solids led to a higher glucose yield than the corresponding value obtained from conventional heating treatment. When the solid content exceeded 25%, conventional heating could not handle this high-solid sample due to the loss of fluidity, poor mixing, and heating transfer of the samples. As a result, there was a significantly lower sugar yield, but the sugar yield of the RF-based pretreatment process was still maintained at high levels. Furthermore, the optimal particle size and alkali loading in the RF pretreatment was determined as 0.25–0.50 mm and 0.25 g NaOH/g biomass, respectively. At alkali loading of 0.20–0.25 g NaOH/g biomass, heating temperature of 90^oC, and solid content of 20%, the glucose, xylose, and total sugar yield from the combined RF pretreatment and the enzymatic hydrolysis were 25.3, 21.2, and 46.5 g/g biomass, respectively.     

Structural Characterization and Comparison of Switchgrass Ball-milled Lignin Before and After Dilute Acid Pretreatment

To reduce the recalcitrance and enhance enzymatic activity, dilute H₂SO₄ pretreatment was carried out on Alamo switchgrass (Panicum virgatum). Ball-milled lignin was isolated from switchgrass before and after pretreatment. Its structure was characterized by ¹³C, HSQC, and ³¹P NMR spectroscopy. It was confirmed that ball-milled switchgrass lignin is of HGS type with a considerable amount of p-coumarate and felurate esters of lignin. The major ball-milled lignin interunit was the β-O-4 linkage, and a minor amount of phenylcoumarin, resinol, and spirodienone units were also present. As a result of the acid pretreatment, there was 36% decrease of β-O-4 linkage observed. In addition to these changes, the S/G ratio decreases from 0.80 to 0.53.     

Pilot-Scale Fermentation of Aqueous-Ammonia-Soaked Switchgrass

Aqueous-ammonia-steeped switchgrass was subject to simultaneous saccharification and fermentation (SSF) in two pilot-scale bioreactors (50- and 350-L working volume). Switchgrass was pretreated by soaking in ammonium hydroxide (30%) with solid to liquid ratio of 5 L ammonium hydroxide per kilogram dry switchgrass for 5 days in 75-L steeping vessels without agitation at ambient temperatures (15 to 33 °C). SSF of the pretreated biomass was carried out using Saccharomyces cerevisiae (D₅A) at approximately 2% glucan and 77 filter paper units per gram cellulose enzyme loading (Spezyme CP). The 50-L fermentation was carried out aseptically, whereas the 350-L fermentation was semiaseptic. The percentage of maximum theoretical ethanol yields achieved was 73% in the 50-L reactor and 52–74% in the 350-L reactor due to the difference in asepsis. The 350-L fermentation was contaminated by acid-producing bacteria (lactic and acetic acid concentrations approaching 10 g/L), and this resulted in lower ethanol production. Despite this problem, the pilot-scale SSF of aqueous-ammonia-pretreated switchgrass has shown promising results similar to laboratory-scale experiments. This work demonstrates challenges in pilot-scale fermentations with material handling, aseptic conditions, and bacterial contamination for cellulosic fermentations to biofuels.     

Aqueous Ammonia Soaking of Switchgrass Followed by Simultaneous Saccharification and Fermentation

Simultaneous saccharification and fermentation (SSF) of switchgrass was performed following aqueous ammonia pretreatment. Switchgrass was soaked in aqueous ammonium hydroxide (30%) with different liquid–solid ratios (5 and 10 ml/g) for either 5 or 10 days. The pretreatment was carried out at atmospheric conditions without agitation. A 40–50% delignification (Klason lignin basis) was achieved, whereas cellulose content remained unchanged and hemicellulose content decreased by approximately 50%. The Sacccharomyces cerevisiae (D₅A)-mediated SSF of ammonia-treated switchgrass was investigated at two glucan loadings (3 and 6%) and three enzyme loadings (26, 38.5, and 77 FPU/g cellulose), using Spezyme CP. The percentage of maximum theoretical ethanol yield achieved was 72. Liquid–solid ratio and steeping time affected lignin removal slightly, but did not cause a significant change in overall ethanol conversion yields at sufficiently high enzyme loadings. These results suggest that ammonia steeping may be an effective method of pretreatment for lignocellulosic feedstocks.     

The Application of Ultrasound in the Enzymatic Hydrolysis of Switchgrass

In a series of experiments, untreated and ammonium hydroxide pretreated Klenow lowland variety switchgrasses are converted to reducing sugars using low-frequency (20 kHz) ultrasound and commercially available cellulase enzyme. Results from experiments using untreated and pretreated switchgrasses with and without ultrasound are presented and discussed. In untreated switchgrass experiments, the combination of ultrasound and enzymes resulted in an increase of 7.5% in reducing sugars compared to experiments using just enzymes. In experiments using ammonium hydroxide pretreated switchgrass, the combination of ultrasound and enzymes resulted in an increase of 9.3% in reducing sugars compared to experiments using just enzymes. Experimental evidence indicates that there is a synergistic effect from the combination of ultrasound and enzymes which lowers the diffusion-limiting barrier to enzyme/substrate binding and results in an increase in reaction rate. Scanning electron microscopic images provide evidence that ultrasound-induced pitting increases substrate surface area and affects reaction rate and yield.     

Switchgrass PviCAD1: Understanding Residues Important for Substrate Preferences and Activity

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step in monolignol biosynthesis. Although plants contain numerous genes coding for CADs, only one or two CADs appear to have a primary physiological role in lignin biosynthesis. Much of this distinction appears to reside in a few key residues that permit reasonable catalytic rates on monolignal substrates. Here, several mutant proteins were generated using switchgrass wild type (WT) PviCAD1 as a template to understand the role of some of these key residues, including a proton shuttling HL duo in the active site. Mutated proteins displayed lowered or limited activity on cinnamylaldehydes and exhibited altered kinetic properties compared to the WT enzyme, suggesting that key residues important for efficient catalysis had been identified. We have also shown that a sorghum ortholog containing EW, instead of HL in its active site, displayed negligible activity against monolignals. These results indicate that lignifying CADs require a specific set of key residues for efficient activity against monolignals.     

顺序注射-样品预处理模块系统-电热原子吸收法测定海水中痕量铜

将样品预处理模块与自动化顺序注射系统相结合,建立了未经稀释的海水中痕量铜的分离富集方法。铜-PDC螯合物在样品预处理模块中被吸附在聚四氟乙烯微珠填充柱上,用少量甲醇洗脱后,将洗脱液引入电热原子吸收中测定。进样体积为1.0mL时,富集倍率为20,检出限为0.015μg/L,采样频率为26次/h,线性范围为0.05~1.00μg/L,相对标准偏差(RSD)为1.8%(0.50μg/L)。利用本方法分离富集并测定了标准海水样品NASS-5及近海水样中的铜含量,并进行了加标回收实验。     

木质纤维素的预处理及其酶解

从木质纤维素制取燃料乙醇,主要包括原料预处理、酶水解糖化及酒精发酵三个部分.通过前二步获得较高还原糖总量是提高乙醇得率的关键.预处理技术及工艺直接影响酶解效果,而酶水解是一个涉及多因素变化的复杂异相动力学过程.本文主要针对这两部分的国内外研究现状作一论述,并提出该领域目前所面临的问题及发展前景.     

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%.     

Extraction of Proteins from Switchgrass Using Aqueous Ammonia within an Integrated Biorefinery

Switchgrass (Panicum vergatum) is a potential feedstock for future cellulosic biorefineries. Such a feedstock may also provide protein, most likely for use as an animal feed. In this paper, we present a potential scheme for integrating fiber processing with extractions to obtain both sugar and protein products from switchgrass pretreated using Ammonia Fiber Expansion (AFEX). Solutions of 3% aqueous ammonia at pH 10.5 provided optimal extraction of proteins. Addition of the nonionic surfactant Tween-80 improved protein recovery for AFEX-treated materials. It was determined that an extraction following AFEX solubilized approximately 40% of the protein, while a subsequent hydrolysis solubilized much of the remaining protein while producing 325 g sugar per kg biomass. The remaining insoluble residue contained very little protein or ash, making it ideal for heat and power production. In contrast, an extraction following hydrolysis solubilized only 68% of the original protein in the biomass, while obtaining slightly higher sugar yields.     

Pretreatment and enzymatic saccharification of corn fiber

Corn fiber consists of about 20% starch, 14% cellulose, and 35% hemicellulose, and has the potential to serve as a low-cost feedstock for production of fuel ethanol. Several pretreatments (hot water, alkali, and dilute, acid) and enzymatic saccharification procedures were evaluated for the conversion of corn fiber starch, cellulose, and hemicellulose to monomeric sugars. Hot water pretreatment (121°C, 1 h) facilitated the enzymatic sacch arification of starch and cellulose but not hemicellulose. Hydrolysis of corn fiber pretreated with alkali un dersimilar conditions by enzymatic means gave similar results. Hemicellulose and starch components were converted to monomeric sugars by dilute H₂SO₄ pretreatment (0.5–1.0%, v/v) at 121°C. Based on these findings, a method for pretreatment and enzymatic saccharification of corn fiber is presented. It in volves the pretreatment of corn fiber (15% solid, w/v) with dilute acid (0.5% H₂SO₄, v/v) at 121°C for 1 h, neutralization to pH 5.0, then saccharification of the pretreated corn fiber material with commercial cellulase and β-glucosidase preparations The yield of monomeric sugars from corn fiber was typically 85–100% of the theoretical yield. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Big and little Meccano

The emergence of the mechanical bond during the past 25 years is giving chemistry a fillip in more ways than one. While its arrival on the scene is already impacting materials science and molecular nanotechnology, it is providing a new lease of life to chemical synthesis where mechanical bond formation occurs as a consequence of the all-important templation orchestrated by molecular recognition and self-assembly. The way in which covalent bond formation activates noncovalent bonding interactions, switching on molecular recognition that leads to self-assembly, and the template-directed synthesis of mechanically interlocked molecules—of which the so-called catenanes and rotaxanes may be regarded as the prototypes—has introduced a level of integration into chemical synthesis that has not previously been attained jointly at the supramolecular and molecular levels. The challenge now is to carry this level of integration during molecular synthesis beyond relatively small molecules into the realms of precisely functionalized extended molecular structures and superstructures that perform functions in a collective manner as the key sources of instruction, activation, and performance in multi-component integrated circuits and devices. These forays into organic chemistry by a scientific nomad are traced through thick and thin from the Athens of the North to the Windy City by Lake Michigan with interludes on the edge of the Canadian Shield beside Lake Ontario, in the Socialist Republic of South Yorkshire, on the Plains of Cheshire beside the Wirral, in the Midlands in the Heartland of Albion, and in the City of Angels beside the Peaceful Sea.     

Plasma-Assisted Pretreatment of Wheat Straw

O₃ generated in a plasma at atmospheric pressure and room temperature, fed with dried air (or oxygen-enriched dried air), has been used for the degradation of lignin in wheat straw to optimize the enzymatic hydrolysis and to get more fermentable sugars. A fixed bed reactor was used combined with a CO₂ detector and an online technique for O₃ measurement in the fed and exhaust gas allowing continuous measurement of the consumption of O₃. This rendered it possible for us to determine the progress of the pretreatment in real time (online analysis). The process time can be adjusted to produce wheat straw with desired lignin content because of the online analysis. The O₃ consumption of wheat straw and its polymeric components, i.e., cellulose, hemicellulose, and lignin, as well as a mixture of these, dry as well as with 50% water, were studied. Furthermore, the process parameters dry matter content and milled particle size (the extent to which the wheat straw was milled) were investigated and optimized. The developed methodology offered the advantage of a simple and relatively fast (0.5–2 h) pretreatment allowing a dry matter concentration of 45–60%. FTIR measurements did not suggest any structural effects on cellulose and hemicellulose by the O₃ treatment. The cost and the energy consumption for lignin degradation of 100 g of wheat straw were calculated.     

Sequential trapping of dichlorocarbene and dichlorocarbonyl ylides

The thermal decomposition of phenyl (bromodichloromethyl)-mercury in the presence of aryl aldehydes and dimethyl acetylenedicarboxylate leads to the formation of dimethyl 2-halo-5-arylfuran-3, 4-dicarboxylates by selective trapping of the intermediate dihalocarbonyl ylides.     

Pretreatment of Polymer-Supported Pd-Co and Its Catalytic Activity

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