Hydrogen production from catalytic gasification of cellulose in supercritical water

Interests in large-scale use of biomass for energy and in hydrogen are motivated largely by global environmental issues. Cellulose and sawdust were gasified in supercritical water to produce hydrogen-rich gas in this paper, and Ru/C, Pd/C, CeO₂ paticles, nano-CeO₂ and nano-(CeZr)_xO₂ were selected as catalysts. The experimental results showed that the catalytic activities were Ru/C > Pd/C > nano-(CeZr)_xO₂ > nano-CeO₂ > CeO₂ particle in turn. Low-concentration sodium carboxymethylcellulose (CMC) (2–3 wt.%) was mixed with particulate biomass and water to form a uniform and stable viscous paste which can be efficiently gasified. The 10 wt.% cellulose or sawdust with CMC can be gasified near completely with Ru/C catalyst to produce 2–4 g hydrogen yield and 11–15 g potential hydrogen yield per 100 g feedstock at the condition of 500 °C, 27 MPa, 20 min residence time in supercritical water.     

Hydrogen production by oxidative methanol reforming with various oxidants over Cu-based catalysts

In order to improve the start-up property of a small hydrogen producer with a micro methanol reformer, oxidative methanol reforming (OMR) with various oxidants over copper-based catalysts was examined. The addition of Fe to a Cu/ZnO/Al₂O₃ catalyst resulted in higher catalyst durability, with a slight improvement in catalytic activity, for OMR with air. However, the addition of larger amounts of Fe inhibited further improvement of catalytic performance, possibly due to the formation of less active CuFe₂O₄ spinel in the catalyst. The production of hydrogen by OMR with hydrogen peroxide as an alternative oxidant, which has the potential to provide concentrated hydrogen without nitrogen dilution, was also considered. It was found that hydrogen peroxide is an effective oxidant for OMR over copper-based catalysts due to its ability to suppress CO formation and its improving effect on methanol conversion.     

Hydrogen production by biomass gasification in supercritical water: A systematic experimental and analytical study

Hydrogen production from biomass gasification in supercritical water is a new technology, which was developed in last two decades. Biomass energy of low quality can be converted to hydrogen energy of high quality by supercritical water gasification. Particularly, supercritical water gasification is an elegant way of wet biomass utilization. Up to now, many important progresses have been made in supercritical water gasification technology by the studies of researchers around the world. Since 1997, supercritical water gasification, which include reaction system, rule of biomass gasification and theory, have been studied in State Key Laboratory of Multiphase Flow in Power Engineering of Xi’an Jiaotong University. In this paper, we summarize the results from systematic experimental and analytical study on biomass gasification in supercritical water in our laboratory. Also, the development status and future prospect on supercritical water gasification is evaluated.     

Applicability of sub- and supercritical water hydrolysis of woody biomass to produce monomeric sugars for cellulosic bioethanol fermentation

In this study two woody biomasses, poplar and pitch pine wood, were treated with sub- and supercritical water (SCW) at temperature of 325–425 °C, at pressure of 220 ± 10 atm and residence time of 60 s, respectively, to develop a time saving and efficient conversion process for the production of fermentable sugars from woody biomasses using supercritical water system. Cellulose/hemicellulose was easily hydrolyzed during SCW treatment into monomeric sugars with the total yield of 7.3% and 8.2% based on the oven dried weight of poplar and pitch pine, respectively. Total yield of the monomeric sugars was increased about threefolds to 23.0% and 25.1% in the presence of 0.05% of hydrochloric acid. Model experiment confirmed that glucose and xylose were readily converted into low molecular weight compounds during SCW hydrolysis. According to GC/MS analysis main compounds converted from glucose and xylose by SCW were identified to 5-hydroxymethyl furfural and 4-oxo-5-methoxy-2-penten-5-olide, respectively.     

Hydrogen production from methanol by oxidative steam reforming carried out in a membrane reactor

The aim of this work is to study from an experimental point of view the oxidative steam reforming of methanol by investigating the behaviour of a dense Pd/Ag membrane reactor (MR) in terms of methanol conversion as well as hydrogen production. The main parameters considered are the operating temperature and the O₂/CH₃OH feed ratio. This is a pioneer work in the application of MR to this kind of reaction, whose goal should be to produce a CO-free hydrogen stream suitable for hydrogen fuel cell applications. The experimental results show that the MR gives methanol conversions higher than traditional reactors (TRs) at each temperature investigated, confirming the good potential of the membrane reactor device for this interesting reaction system.     

Hydrogen production from CO2 reforming of methane over high pressure H2O2 modified different semi-cokes

H₂O₂ was used under different temperatures and pressures to activate three kinds of different semi-cokes. FTIR, BET, SEM and Boehm titration were used to analyze properties of the semi-cokes surfaces, finding that catalytic activities of these semi-cokes after modification by high temperature and high pressure H₂O₂ were improved. FTIR shows that the characteristic infrared absorption peak of functional groups on the semi-cokes surface does not change, but the absorption peak intensity of some functional groups is increased. The strength of OH absorption peak of Hongce lignite (HCL) semi-coke at 3444 cm⁻¹, carboxyl CO at 1598 cm⁻¹, aliphatic ether, cyclic ether and other organic functional groups at 1023 cm⁻¹ in the modified Shenmu bituminous(SMB) semi-coke and Jincheng anthracite (JCA) semi-coke are increased significantly. BET finds that the specific surface area and pore volume of three semi-cokes are increased after modification. Boehm titration shows that the basic functional group content in semi-coke is increased after modification, and the net alkali content is increased significantly. Compared with the raw semi-coke, SEM shows that the surface of semi-coke modified with H₂O₂ becomes rough. Modified JCA semi-coke surface pitted with holes, modified HCL and SMB semi-coke surface present porous.     

Hydrogen production from used lubricating oils

Used lubricating oils (lube oils) are generated throughout the year and collected in central locations in many communities. Disposing lube oil in an improper manner contaminates environment to a great degree. Used lube oil can be valuable as a re-refined lubricant or as an energy source. Lube oil is a complex mixture of aliphatic and polycyclic hydrocarbons formulated to withstand high service temperatures in internal combustion engines. Both synthetic and mineral oils contain a high concentration of hydrogen (about 13–14 wt%). At the Florida Solar Energy Center, we have developed a process that converts lube oils to hydrogen and other valuable low molecular weight hydrocarbons. The lube oil reformation experiments were carried out using several commercially available dehydrogenation catalysts at a range of reactor temperatures and pressures, residence times and steam to carbon ratios. In this paper, the data obtained to date and the results are presented and discussed.     

Hydrogen production by oxidative methanol reforming on Pd/ZnO catalyst: effects of Pd loading

Catalytic performances of Pd/ZnO in oxidative methanol reforming reaction were studied as a function of Pd loading. It was confirmed that the formation of Pd–Zn alloy is essential to the selective production of hydrogen. High active Pd/ZnO, comparable to commercial Cu-Zn catalyst, was obtained with higher Pd loading. Selectivity of the reaction was greatly increased by increasing Pd loading on ZnO. At higher Pd loadings (>5%), co-precipitation was superior to impregnation for the catalyst preparation. The catalytic performances were also discussed based on results from X-ray diffraction (XRD) characterization.     

Hydrogen production from raw bioethanol over Rh/MgAl2O4 catalyst: Impact of impurities: Heavy alcohol, aldehyde, ester, acid and amine

The effect of various impurities added in a pure ethanol + water mixture was studied. The impurities chosen were acetic acid, diethylamine, butanol, butanal, ethyl acetate and diethylether. It was shown that the addition of diethylamine or butanal increases the ethanol conversion, compared to that obtained with a pure ethanol + water mixture, without changing the product selectivity. In the presence of the other impurities, butanol, ethylether and ethyl acetate, a strong deactivation of the catalyst with a decreased ethanol conversion was observed. Moreover, the selectivity in hydrogen was also strongly decreased, whereas an increase in intermediate products especially ethylene was observed. The deactivation was explained in terms of coke deposition at the catalyst surface. The poisoning effect induced by the presence of impurities can be classified in the following increasing order: diethylamine  butanal < no impurity < acetic acid < butanol < diethylether  ethyl acetate.     

烃类在超临界水中的化学转化

超临界水是一种新型反应介质,烃类在超临界水中化学转化效率高。对烃类在超临界水反应制氢气、重油改质和合成含氧化合物方面的研究进展进行了综述,同时简要介绍了各种技术产生的背景,对研究重点进行了必要评述,展望了该领域的发展前景。     

Hydrogen production by the partial oxidation and steam reforming of tar from hot coke oven gas

Hot coke oven gas (COG) with a temperature of about 1050 K was produced from a test unit for coke production, the capacity of which was 80 kg of coal. The COG was introduced into an experimental unit with a tar converter where oxygen and steam were injected. Over 98% of the total carbon in the hot COG was partially oxidized, reformed with steam and converted to hydrogen and CO. About 1 Nm³/h of hydrogen was continuously produced for 5 h in this experiment. The experimental results suggest that three to five times the amount of hydrogen and CO that were present in the original COG could be recovered by this technology, utilizing the heat of the hot COG for the reaction. The feasibility study showed that hydrogen can be produced by this technology at a lower cost and higher efficiency than by the separation of cold COG.     

Hydrogen production from oxidative steam reforming of ethanol in a palladium-silver alloy composite membrane reactor

In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd-Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. An ethanol-water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2, 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn-Cu commercial catalyst (MDC-3). The reaction temperatures were set at 593-723 K and the pressures at 3-10 atm. The hydrogen flux in the permeation side increased proportionately with increasing pressure; however, it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd-Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO₂ increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same.     

Hydrogen production from partial oxidation and reforming of DME

Hydrogen production from partial oxidation and reforming of dimethyl ether (DME) was investigated with a fixed bed continuous-flow reactor. H₂ yield of over 90% was obtained with 100% DME conversion at 700 °C over Pt/Al₂O₃+Ni–MgO dual catalyst bed, while keeping CH₄ yield at low level. Such results indicated that partial oxidation and reforming of DME to produce hydrogen at high temperature is possible and effective.     

Hydrogen production from propane in Rh-impregnated metallic microchannel reactors and alumina foams

Rh-impregnated alumina foams and metallic microchannel reactors have been studied for production of hydrogen-rich syngas through short contact time catalytic partial oxidation (POX) and oxidative steam reforming (OSR) of propane. Effects of temperature and residence time have been compared for the two catalytic systems. Temperature profiles obtained along the central axis were valuable in understanding the different behaviour of the reactor systems. Gas phase ignition occurs in front of the metallic monolith at furnace temperatures above 700 °C, leading to lower hydrogen selectivity. Lowering the residence time below 10 ms for the microchannel monolith increases the syngas selectivity. This probably due to quenching of the gas phase reactions at high linear gas velocity, and suggests that microchannel reactors have potential for isolating kinetic effects and minimising gas phase contributions. The Rh/Al₂O₃ foam systems show higher initial syngas selectivity than the Rh-impregnated microchannel reactors, but deactivate rapidly upon temperature cycling, especially when steam is added as a reactant.     

Catalytic hydrogen production from 2-propanol in supercritical water: Comparison of some metal catalysts

The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, and in order to improve the hydrogen yield or selectivity, activities of various catalysts are evaluated. In this study, hydrogen production from 2-propanol over Ni/Al₂O₃ and Fe–Cr catalysts was investigated in supercritical water. The experiments were carried out in the temperature range of 400–600 °C and in the reaction time range of 10–30 s, under a pressure of 25 MPa. The hydrogen yields and selectivities of Ni/Al₂O₃ and Fe–Cr used in this study, and those of Pt/Al₂O₃ and Ru/Al₂O₃ used in our previous work were compared. The hydrogen contents of the gaseous products obtained by using Ni/Al₂O₃ and Fe–Cr were measured as 62 mol% and 70 mol%, respectively, at low temperatures and reaction times. However, the hydrogen yields remained in low levels when compared with that of Pt/Al₂O₃ used in previous study. Pt/Al₂O₃ was established to be the most effective and selective catalyst for hydrogen production. During the catalytic gasification of a 0.5 M solution of 2-propanol, hydrogen content up to 96 mol% and hydrogen yield of 1.05 mol/mol 2-propanol were obtained.     

超临界水条件下生物质气化制氢

生物质制氢是农业废弃物资源化利用的一项很有发展前途的技术。介绍了超临界水条件下生物质的气化制氢技术,论述了温度、压力、停留时间以及反应器对气化产物组成及气化制氢效果的影响,着重阐述了催化剂的影响。分析了目前超临界水气化制氢在有机废弃物资源化应用中存在的主要问题,并展望了超临界水气化制氢的研究前景。     

Hydrogen Production from Ethanol Steam Reforming Over Supported Cobalt Catalysts

Hydrogen production was carried out via ethanol steam reforming over supported cobalt catalysts. Wet incipient impregnation method was used to support cobalt on ZrO₂, CeO₂ and CeZrO₄ followed by pre-reduction with H₂ up to 677 °C to attain supported cobalt catalysts. It was found that the non-noble metal based 10 wt.% Co/CeZrO₄ is an efficient catalyst to achieve ethanol conversion of 100% and hydrogen yield of 82% (4.9 mol H₂/mol ethanol) at 450 °C, which is superior to 0.5 wt.% Rh/Al₂O₃. The pre-reduction process is required to activate supported cobalt catalysts for high H₂ yield of ethanol steam reforming. In addition, support effect is found significant for cobalt during ethanol steam reforming. 10% Co/CeO₂ gave high H₂ selectivity while suffered low conversion due to the poor thermal stability. In contrast to CeO₂, 10 wt.% Co/ZrO₂ achieved high conversion while suffered lower H₂ yield due to the production of methane. The synergistic effect of ZrO₂ and CeO₂ to promote high ethanol conversion while suppress methanation was observed when CeZrO₄ was used as a support for cobalt. This synergistic effect of CeZrO₄ support leads to a high hydrogen yield at low temperature for 10 wt.% Co/CeZrO₄ catalyst. Under the high weight hourly space velocity (WHSV) of ethanol (2.5 h⁻¹), the hydrogen yield over 10 wt.% Co/CeZrO₄ was found to gradually decrease to 70% of its initial value in 6 h possibly due to the coke formation on the catalyst.     

Corrosion control methods in supercritical water oxidation and gasification processes

Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).     

Hydrogen production via dry reforming of butanol: Thermodynamic analysis

Dry reforming of butanol for hydrogen production has been studied by Gibbs free energy minimization method. The calculation results showed that the formation of hydrogen and carbon monoxide was through a multi-step pathway via the dehydrogenation, dehydration, decomposition and carbon dioxide reforming of butanol. The optimum conditions for hydrogen production are identified: reaction temperatures between 1150 and 1200 K and carbon dioxide-to-butanol molar ratios between 3.5 and 4.0 at 1 atm. Under the above conditions, 100% conversion of butanol, 34.91-37.98% concentration of hydrogen and 57.34−57.87% concentration of carbon monoxide could be achieved in the absence of coke formation. The butanol dry reforming with carbon dioxide is suitable for providing fuels for Solid Oxide Fuel Cell (SOFC). The coke-formed and coke-free regions are found, which are useful in guiding the search for suitable catalysts for the reaction.     

Hydrogen Production by Steam Reforming of Ethanol on Potassium-Doped 12CaO · 7Al2O3 Catalyst

The performance of hydrogen production from steam reforming of ethanol were investigated by using the K-doped 12CaO · 7Al₂ O₃ catalyst (defined as C12A7–O⁻/x%K). The conversion of ethanol and hydrogen yield over C12A7–O⁻/x%K catalyst mainly depended on the temperature, K-doping amount, steam-to-carbon ratios (S/C) and contact time (W/F). In order to identify the catalyst’s characteristic and active species on the catalyst’s surface, Brunauer-Emmett-Teller (BET) surface area, CO₂ temperature programmed desorption (CO₂TPD), X-ray diffraction (XRD), Fourier transform infrared (FT–IR) and X-ray photoelectron spectroscopy (XPS) were carried out. Based on the characterization, it was found that active oxygen species and doped potassium play important roles in steam reforming of ethanol over C12A7–O⁻/27.3%K catalyst.