Investigation on hydrogen production by catalytic steam reforming of maize stalk fast pyrolysis bio-oil

Hydrogen production via catalytic steam reforming of maize stalk fast pyrolysis bio-oil over the nickel/alumina supported catalysts promoted with cerium was studied using a laboratory scale fixed bed coupled with Fourier transform infrared spectroscopy/thermal conductivity detection analysis (FTIR/TCD). The effects of nickel loading, reaction temperature, water to carbon molar ratio (WCMR) and bio-oil weight hourly space velocity (W_bHSV) on hydrogen production were investigated. The highest hydrogen yield of 71.4% was obtained over the 14.9%Ni-2.0%Ce/A1₂O₃ catalyst under the reforming conditions of temperature = 900 °C, WCMR = 6 and W_bHSV = 12 h⁻¹. Increasing reaction temperature from 600 to 900 °C resulted in the significant increase of hydrogen yield. The hydrogen yield was significantly enhanced by increasing the WCMR from 1 to 3, whereas it increased slightly by further increasing WCMR. The hydrogen yield decreased with the increase of W_bHSV. Meanwhile, the coke deposition percentage changed little with increasing W_bHSV up to 12 h⁻¹ and then it increased by 4.5% with the further increase of W_bHSV from 12 to 24 h⁻¹.     

Biomass to bio-ethanol: The evaluation of hybrid Pennisetum used as raw material for bio-ethanol production compared with corn stalk by steam explosion joint use of mild chemicals

The second generation biomass to bio-ethanol production is of growing interest. Energy crop were becoming important for second generation biomass to bio-ethanol production for their growth advantages. Hybrid Pennisetum as a new hybrid energy crop was selected as a model to compare with corn stalk. As pre-treatment methods, steam explosion and its combined action with dilute sulfuric acid, bisulfite, and mixed dilute acid and bisulfite were selected. The enzymatic hydrolysis demonstrated that the cellulose conversion is a strong function of the pre-treatment method applied, with corn stalk providing slightly better results. With dilute acid steam explosion (DA-SE), conversions were 67.6% and 54.5% for corn stalk and pennisetum, respectively. This can be attributed to the higher Cr. I of pennisetum (65.03%) than of corn stalk (54.05%). The cell lumen of pretreated pennisetum was smaller than for corn stalk as shown in SEM photos, meaning there was a substantially higher enzyme accessible surface and porosity in pennisetum, thus responsible for the higher cellulase adsorption of pretreated pennisetum. DA-SE was the most effective pre-treatment method, but the inhibitors' concentration was higher than in other methods. Combined dilute acid and bisulfite can moderately remove hemicelluloses and lignin. Cr. I values, lignin content, accessible surface and porosity were supplied the energy crop evaluation standards for bio-ethanol production.     

The steam explosion pretreatment and enzymatic hydrolysis of wheat bran

This article focused on the saccharification of wheat bran with steam explosion pretreatment and enzymatic hydrolysis. Wheat bran was pretreated with steam explosion to improve saccharification with enzymatic hydrolysis, and a maximum reducing sugar yield reached 194.6 mg/g (dry), which was about 63% higher than that of the wheat bran without pretreatment. Electronic microscope scanning and infrared spectroscopy showed that steam explosion with low pressure destroyed the structure and promoted the enzymatic hydrolysis of wheat bran effectively. Further, higher pressure produced harmful substances to hinder the saccharification and subsequent fermentation rather than increase saccharification ability of blasting bran.     

Screening of steam explosion conditions for glucose production from non-impregnated wheat straw

The conversion of wheat straw to fermentable sugar for bioethanol production typically involves a thermal pretreatment step, followed by enzymatic hydrolysis. In this study we have investigated the effect of steam explosion parameters on wheat straw digestibility using a newly designed steam explosion unit and a process without acid impregnation. The wheat straw was steam pretreated using 18 different conditions in the temperature range of 170-220 °C and the resulting material was used directly (i.e. without washing) for enzymatic hydrolysis and fermentation in either a separate hydrolysis and fermentation (SHF)-type or a simultaneous saccharification and fermentation (SSF)-type set-up. Maximum glucose yields upon enzymatic hydrolysis were obtained after pretreatment at 210 °C for 10 min and yields were similar at harsher conditions. Xylose yields increased with temperature and residence time up to 190 °C, but decreased at harsher pretreatment conditions since these led to xylan degradation and concomitant production of furfural. In an SHF-type set-up ethanol formation did not follow enzymatic glucose release and was inversely correlated with furfural levels. An SFF-type set-up displayed a straightforward correlation between the expected amount of released glucose and the ethanol yields. The highest saccharification yields corresponded to about 90% of the cellulose in the substrate. Overall, this study shows that steam explosion without an acid catalyst is a good pretreatment method for saccharification of wheat straw. Optimal steam explosion conditions need to be a compromise between sugar accessibility and sugar degradation.     

乳酸预浸渍对小麦秸秆蒸汽爆破预处理效果的影响

相比未乳酸预浸,小麦秸秆经1.0%乳酸预浸后在较低的汽爆温度下就能有效提高纤维素的酶水解性。绝大部分半纤维素在汽爆预处理过程中转化为单糖,且不会产生更多的发酵抑制物。试验结果表明,小麦秸秆经乳酸预浸后汽爆预处理的最佳温度为190℃,其酶水解可获得最高的葡萄糖产量,为29.4 g/100 g原料;同步糖化发酵结束后的乙醇浓度达到25.3 g/L,产率为15.6 g/100 g原料,相比未乳酸预浸小麦秸秆,均有一定程度提高。     

Solar enriched methane production by steam reforming process: Reactor design

A novel hybrid plant for a mixture of methane and hydrogen (enriched methane) production from a steam reforming reactor whose heat duty is supplied by a molten salt stream heated up by a concentrating solar power (CSP) plant developed by ENEA is here presented. By this way, a hydrogen stream, mixed with natural gas, is produced from solar energy by a consolidated production method as the steam reforming process and by a pre-commercial technology as molten salts parabolic mirrors solar plant. After the hydrogen production plant, the residual heat stored in molten salt stream is used to produce electricity and the plant is co-generative (hydrogen + electricity).The heat-exchanger-shaped reactor is dimensioned by a design tool developed in MatLab environment. A reactor 3.5 m long and with a diameter of 2″ is the most efficient in terms of methane conversion (14.8%) and catalyst efficiency (4.7 Nm³/h of hydrogen produced per kg_cat).     

Hydrogen from ethanol by steam iron process in fixed bed reactor

This research is devoted to the use of ethanol (i.e. bio-ethanol) in the combined production and purification of hydrogen by redox processes. The process has been studied in a single lab scale fixed bed reactor. Iron oxides, apart from their remarked redox behavior, exert an important catalytic role allowing the complete decomposition of ethanol at temperatures in the range from 625 to 750 °C. The resulting gas stream (mainly H₂ and CO) reduces the solid to metallic iron. During a subsequent oxidation with steam, the solid can be regenerated to magnetite producing high purity hydrogen (suitable to be used in PEM fuel cells). Even though small amounts of coke are deposited during the reduction step, this is barely gasified by steam during the oxidation step (detection of CO_x in concentrations lower than 1 ppm). Influence of parameters like temperature, ethanol partial pressure and alternate cycles' effect has been studied in order to maximize the production of pure hydrogen.     

蒸汽爆破预处理中影响酶解效果因素的研究

为提高秸秆蒸汽爆破预处理制乙醇的酶解率及经济效益,研究了蒸汽爆破预处理过程中影响酶解效果的物料温度、喷爆出口直径、汽爆次数等因素,以寻找提高酶解效率的方法。试验结果显示,物料温度对酶解效果有显著影响,在不破坏纤维素结构且不产生酶解抑制物的前提下,温度越高越有利于水解;在不致堵塞喷爆口的前提下,喷爆出口直径越小酶解效果越好;汽爆次数对于酶解物料预处理效果有着显著的积极影响。     

无外加催化剂条件下甜高粱渣汽爆预处理研究

甜高粱茎秆压榨提汁后产生的残渣是生产纤维素乙醇的优良原料。预处理是纤维素乙醇生产过程的关键环节之一。文章对甜高粱压榨剩余残渣进行了无外加催化剂的汽爆预处理研究,通过比较不同反应条件下的预处理效果、发酵抑制物糠醛的生成,及残渣水解效果,确定了最佳预处理工艺:压力为2.4 MPa,时间为120 s,在此条件下,预处理后残渣中纤维素含量达到44.71%,纤维素水解率为82.72%,而在预处理过程中糠醛产生量为1.62 mg/g,对后期酵母发酵影响小。     

Biogas production from reed biomass: Effect of pretreatment using different steam explosion conditions

Biogas production often competes with food and feed production for the raw materials and cropland required for cultivation. Common reed offers an alternative source of biomass for biogas production, alleviating this conflict. Effective microbiological conversion of this type of lignocellulosic biomass requires a pretreatment process. This study aims to determine the specific methane yields of steam-exploded reed as well as to identify how pretreatment conditions influence its physico-chemical characteristics. For this purpose, reed was pretreated with steam explosion at severity factors ranging from 2.47 to 4.83. The effects on methane yields were analyzed in batch experiments. Scanning electron microscopy (SEM) images were captured and detailed chemical analyses of the substrates carried out. Results show that the digestibility of reed biomass improved remarkably after pretreatment. Compared to the untreated sample, steam explosion increased the specific methane yield up to 89% after pretreatment at 200 °C for 15 min. However, methane yield decreased under harsher conditions, which may be due to the formation of degradation compounds during the pretreatment.     

生物质水蒸气气化利用过程数学模型的建立

分析了甘蔗渣的水蒸气气化过程,基于气化过程的物料平衡和化学平衡关系,建立了一种生物质气化过程的数学模型。用该模型模拟计算甘蔗渣在水蒸气氛围下气化后的气体成分,计算结果与试验数据基本相符,尤其在温度950℃之后,计算值和测量值更接近。以甘蔗渣和木薯渣为例,研究该气化模型的特性。甘蔗渣和木薯渣水蒸气气化的最佳水蒸气/燃料值(S/B)分别为0.3和0.2。气化气组分和气化效果随温度和S/B变化的结果表明:提高温度有利于气化反应的进行,提高S/B,可以增加气体产率,气体热值有所降低。     

碱和双氧水预处理玉米秸秆的试验研究

研究了在5%NaOH中加入不同质量分数的双氧水时,对玉米秸秆的预处理效果;在预处理后的玉米秸秆中加入纤维素酶,考察此时酶解还原糖得率随预处理程度的变化;对浸泡时间、双氧水浓度、固液比3个因素进行单因素试验。试验结果表明,质量分数为2.5%的浓度下,糖得率最大;在2.5%H2O2浸泡24 h,固液比对酶解糖化几乎没有影响;当浸泡时间为24,72,96 h时,糖得率相差甚微。设计正交试验对预处理的条件进行优化,分析预处理玉米秸秆的各因素,以木质素去除率为基准参数,得到水解木质纤维素的适宜预处理条件:5%NaOH下加入质量分数为2.5%的双氧水,浸泡时间为72 h,固液比为1∶20。预处理后木质素的去除率为61.52%;加入纤维素酶酶解,还原糖得率为39.30%。     

Effect of microwave irradiation pretreatment of cow dung compost on bio-hydrogen process from corn stalk by dark fermentation

The bio-hydrogen production potential from corn stalk was significantly affected by microwave irradiation pretreatment of cow dung compost in batch tests. The maximum hydrogen yield of 144.3 ml/g-corn stalk and hydrogen production rate of 3.6 ml/g-corn stalk h⁻¹ were observed using the pretreated compost by microwave radiation of 1.5 min at fixed Na₂CO₃ dosage of 800 mg/l, Fe dosage of 400 mg/l, substrate concentration of 20 g/l, which increased about 99.6% and 85.2% compared with that of the control. The effects of microwave irradiation on microbial characteristics were further discussed by Atomic Force Microscope (AFM), determination of protein content and PCR-DGGE. The four dominant hydrogen-producing strains had been isolated and confirmed to be Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus subtilis and Enterococcus faecium, respectively. The diversity and symbiosis relations of the mixed bacteria were also observed in fermentation hydrogen production process.     

Hydrogen production by steam reforming of bio-oil/bio-ethanol mixtures in a continuous thermal-catalytic process

The feasibility of the steam reforming of bio-oil aqueous fraction and bio-ethanol mixtures has been studied in a continuous process with two in-line steps: thermal step at 300 °C (for the controlled deposition of pyrolytic lignin during the heating of the bio-oil/bio-ethanol feed) followed by steam reforming in a fluidized bed reactor on a Ni/α-Al₂O₃ catalyst. The effect of bio-ethanol content in the feed has been analyzed in both the thermal and reforming steps, and the suitable range of operating conditions (temperature and space-time) has been determined for obtaining a high and steady hydrogen yield. Higher ethanol content in the mixture feed improves the reaction indices and reduces coke deposition. Operating conditions of 700 °C and space-times higher than 0.23 g_catalyst h (g_bio-oil+EtOH)⁻¹ are suitable for attaining almost fully conversion of oxygenates (bio-oil and ethanol) and hydrogen yields above 93%, with low catalyst deactivation.     

Storage and separation of hydrogen with the metal steam process

The chemical reaction of metals and metal oxides with steam at elevated temperatures produces pure hydrogen. Therefore certain metals can be used as gas purification and hydrogen storage material. Storage and transport of metals are basic operations, free from safety issues and hydrogen is produced on demand whenever it is needed by passing steam over the solid reactant.     

油泥与玉米秸秆混合成型燃料工艺参数优化

为解决大庆当地典型废弃资源利用的问题,选择大庆地区丰富的玉米秸秆作为试验主要原料和大庆油田废弃油泥作为试验辅助原料,以油泥添加比例、混合原料含水率、成型压力作为影响因子,以成型燃料的发热量、松弛密度、抗跌碎性、抗变形性作为评价指标,优化混合成型燃料的工艺参数。结果表明,混合原料含水率受油泥添加比例的影响很小,当工艺参数分别为油泥添加比例5%~10%,混合原料含水率10%~12%,成型压力25~30 MPa时,成型燃料的物理品质特性良好。该研究可为确定混合成型燃料的工艺参数提供理论依据,同时可为油泥的资源化利用寻求新方向。     

国产200MW汽轮机低真空掉闸事故的分析及处理

凝汽器真空下降是汽轮机运行中常见的典型故障之一，针对一起国产200MW机组因低真空造成的掉闸事故进行了分析，总结了真空泄漏调查的方法及处理措施，为同类机组的真空严密性治理提供参考，具有一定的推广意义。     

Evaluation of the economic impact of hydrogen production by methane decomposition with steam reforming of methane process

There has been considerable interest in the development of more efficient processes to generate hydrogen. Currently, steam methane reforming (SMR) is the most widely applied route for producing hydrogen from natural gas. Researchers worldwide have been working to invent more efficient routes to produce hydrogen. One of the routes is thermocatalytic decomposition of methane (TCDM) - a process that decomposes methane thermally to produce hydrogen from natural gas. TCDM has not yet been commercialized. However, the aim of this work was to conduct an economic and environmental analysis to determine whether the TCDM process is competitive with the more popular SMR process. The results indicate that the TCDM process has a lower carbon footprint. Further research on TCDM catalysts could make this process economically competitive with steam methane reforming.     

Exergoenvironmental analysis of a steam methane reforming process for hydrogen production

Steam methane reforming (SMR) is one of the most promising processes for hydrogen production. Several studies have demonstrated its advantages from the economic viewpoint. Nowadays process development is based on technical and economical aspects; however, in the near future, the environmental impact will play a significant role in the design of such processes. In this paper, an SMR process is studied from the viewpoint of overall environmental impact, using an exergoenvironmental analysis. This analysis presents the combination of exergy analysis and life cycle assessment. Components where chemical reactions occur are the most important plant components from the exergoenvironmental point of view, because, in general, there is a high environmental impact associated with these components. This is mainly caused by the exergy destruction within the components, and this in turn is mainly due to the chemical reactions. The obtained results show that the largest potential for reducing the overall environmental impact is associated with the combustion reactor, the steam reformer, the hydrogen separation unit and the major heat exchangers. The environmental impact in these components can mainly be reduced by improving their exergetic efficiency. A sensitivity analysis for some important exergoenvironmental variables is also presented in the paper.     

Controllability study of an ethanol steam reforming process for hydrogen production

A system for ethanol steam reforming and purification of carbon monoxide (CO) designed to feed a PEM fuel cell has been modelled. From the model, we study the sensitivity and controllability emphasizing the study of the influence of the temperature on the output variables of interest. The results of the study of controllability are used for the identification of the best control structures.