ON THE EFFECTS OF SYNGAS COMPOSITION AND WATER-GAS-SHIFT REACTION RATE ON FT SYNTHESIS OVER IRON BASED CATALYST IN A SLURRY REACTOR

Water gas shift reaction plays an important role in the Fischer-Tropsch synthesis reaction over iron-based catalysts. A slurry reactor model which accounted for the kinetics of both Fischer-Tropsch synthesis and water gas shift reaction was used to investigate the effects of hydrogen to carbon monoxide ratio, water vapor concentration and reactor temperature on synthesis gas conversion. The model was used to determine optimum concentration of water in the feed gas. For a given reactor temperature, the optimum concentration of water in the feed gas was found to increase with decreasing hydrogen to carbon monoxide ratio. The optimum concentration of water in the feed gas was found to decrease with increasing reactor temperature. Increasing the water gas shift reaction rate improved syngas conversion for low reaction temperatures.     

A Technological Perspective for Catalytic Processes Based on Synthesis Gas

Continuously increasing oil prices, a dwindling supply of indigenous petroleum, and the existence of extensive coal reserves has made the conversion of coal to chemicals and clean-burning fuels an increasingly important part of the national energy programs for a number of industrial nations. In particular, there is a growing interest in the production and use of synthesis gas as a feedstock for the manufacture of fuels and chemicals. Most of the proposed routes are catalytic in nature, and are directed at overcoming the limitations of Fischer-Tropsch chemistry, especially selectivity. Over the past several years, research efforts have led to new selective routes to various fuel fractions; to petrochemical feedstocks including light olefins and various aromatics; to commodity chemicals such as ethylene glycol, ethanol, and acetic acid; and to a number of other fuels and chemicals.     

A Technological Perspective for Catalytic Processes Based on Synthesis Gas

Abstract

Continuously increasing oil prices, a dwindling supply of indigenous petroleum, and the existence of extensive coal reserves has made the conversion of coal to chemicals and clean-burning fuels an increasingly important part of the national energy programs for a number of industrial nations. In particular, there is a growing interest in the production and use of synthesis gas as a feedstock for the manufacture of fuels and chemicals. Most of the proposed routes are catalytic in nature, and are directed at overcoming the limitations of Fischer-Tropsch chemistry, especially selectivity. Over the past several years, research efforts have led to new selective routes to various fuel fractions; to petrochemical feedstocks including light olefins and various aromatics; to commodity chemicals such as ethylene glycol, ethanol, and acetic acid; and to a number of other fuels and chemicals.     

The Catalytic Synthesis of Hydrocarbons from Carbon Monoxide and Hydrogen

The increasing demand for energy, coupled with the uncertainty and expense of crude oil imports, has renewed interest in the production of fuels and chemicals from hydrogen-deficient materials. These energy sources such as coal, residua, oil shale, and tar sands can be gasified with steam and oxygen to produce a gas containing large quantities of carbon monoxide and hydrogen. Once methane is removed from this CO/H₂ mixture it is purified to remove S poisons and then reacted over a catalyst to produce a variety of organic products. The synthesis of hydrocarbon products, with the exception of methane, is commonly referred to as the Fischer-Tropsch synthesis reaction.     

Incorporation of catalytic dehydrogenation into Fischer-Tropsch synthesis of liquid fuels from coal to minimize carbon dioxide emissions

Synthesis gas (syngas) produced from coal typically has hydrogen to carbon monoxide ratios in the range of approximately 0.7-1.1, depending on the gasification method. In order to produce liquid fuels from this syngas by Fischer-Tropsch synthesis (FTS), these ratios must be raised to 2.0 or higher. If this is accomplished by the water-gas shift reaction, the traditional method, large emissions of carbon dioxide are produced. In this paper, it is shown that catalytic dehydrogenation (CDH) of the gaseous C1-C4 products of FT synthesis and recycling of the resulting hydrogen to the syngas feed-stream can increase the H₂/CO ratio to the desired values with little or no production of carbon dioxide. All carbon from the CDH reaction is in the form of a potentially valuable by-product, multi-walled carbon nanotubes (MWCNT). The amounts of hydrogen and MWCNT produced, carbon dioxide emissions avoided, and water saved are calculated for a 50,000 bbl/day FTS-CDH plant and it is demonstrated that the energy balance for the process is favorable. Methods of utilizing the large quantity of MWCNT produced are discussed.     

In bed and downstream hot gas desulphurization during solid fuel gasification: A review

Syngas produced by gasification process of biomass fuels is an environmental friendly alternative to conventional petrochemical fuels for the production of electricity, hydrogen, synthetic transportation biofuels and other chemicals. However, the advanced utilization of syngas is significantly limited due to the contaminants which can seriously deactivate the catalysts used for downstream reaction such as steam reforming methane, Fischer-Tropsch synthesis and corrosion of downstream equipments such as a gas turbine. Among the contaminants, sulphur compounds produced in the gasification process, which are mainly H₂S with small amounts of COS, CS₂ and thiophenes depending on process conditions, must be removed. For biomass feedstock advances are required in the cleanup technologies and processes to upgrade the raw product gas with minimal impact on the overall process efficiency. Hot gas desulphurization (HGD) can improve the overall thermal efficiency due to the elimination of fuel gas cooling and associated heat exchangers. With this aim, the present review paper highlights currently developed methods used for desulphurization of hot gas produced from gasification process of solid fuels. The methods presented here are for both in situ and downstream sulphur capture. Also, the attention is paid to the regeneration of the used materials. In situ sulphur capture is mainly done by using calcium-based sorbents such as limestone and dolomite, whereas downstream sulphur capture is mainly focused on the use of regenerable single, mixed, and supported metal oxides. A comparison is indicated at the end to show the sulphur loading of various materials.     

Review: Microstructured reactors for distributed and renewable production of fuels and electrical energy

The current paper provides an overview of recent and past research activities in the field of microreactors for energy related topics. The main research efforts in this field are currently focussing on fuel processing as hydrogen source, mostly for distributed consumption through fuel cells. Catalyst development, reactor design and testing for reforming and removal of carbon monoxide through water-gas shift, preferential oxidation, selective methanation and membrane separation are therefore under investigation. An increasing number of integrated complete micro fuel processors has been developed for a large variety of fuels, assisted by static and dynamic simulation of these systems. The synthesis of liquid fuels is another emerging topic, namely Fischer-Tropsch synthesis, methanol and dimethylether production from synthesis gas and biodiesel production.     

The Application of Zeolites and Periodic Mesoporous Silicas in the Catalytic Conversion of Synthesis Gas

In the recent years there has been a rising interest in the conversion of remote and abundant natural gas as well as renewable biomass sources into high quality fuels and valuable raw chemicals via synthesis gas (syngas, CO + H₂) as a versatile intermediate. The metal catalysed CO hydrogenation can be selectively directed towards hydrocarbons as precursors of ultra clean liquid fuels (Fischer-Tropsch synthesis) or to added-value products such as light olefins and oxygenates (alcohols, carboxylic acids, ethers, etc.). By taking advantage of their unique and tunable structural and chemical properties, inorganic molecular sieves such as zeolites and periodic mesoporous silicas have been extensively explored as effective components of heterogeneous catalysts for the selective conversion of syngas. Thus, ordered mesoporous silicas (MCM-41, MCM-48, SBA-15) have shown interesting properties as catalytic supports for Co and Fe based Fischer-Tropsch catalysts. Besides, zeolite-entrapped mono and bimetallic clusters have been reported to selectively direct the synthesis towards oxygenates. In this work, the use of the original structural properties of these materials to tailor the dispersion, geometrical location and chemical state of metallic sites leading to heterogeneous catalysts with enhanced activity and selectivity in syngas catalytic routes is reviewed. The introduced peculiarities, benefits and drawbacks of these structured solids in comparison to conventional amorphous supports are also discussed.     

Syngas production through gasification and cleanup for downstream applications — Recent developments

In the present paper various gasification technologies/gasifiers and syngas cleaning options are critically reviewed keeping in view various types of feedstocks and various downstream applications of syngas such as power generation, chemicals and hydrogen production, liquid fuels production and synthetic natural gas (SNG) production. Recent developments on gasification technologies including fixed bed dry bottom (FBDB) gasification, power high temperature Winkler (PHTW) gasification, catalytic steam gasification, transport reactor gasifier as well as syngas cleanup technique including hot gas filter and warm cleaning are discussed. Techno-economic analysis of various gasifiers as well as syngas cleaning processes along with the world scenario of syngas production and its various downstream applications is also discussed.     

Fischer-Tropsch合成中的CO活化机理

Fischer—Tropsch(F—T)合成是将煤炭、天然气和生物质等含碳资源间接转化为液体燃料的关键工艺步骤,深入了解其反应机理,对于完善F-T合成催化剂设计以及优化其工业操作条件具有重要的理论价值．对近年来有关F—T合成中关键的CO活化机理研究进行了总结和评述,着重介绍了不同过渡金属元素对CO的吸附和活化性质,并就金属晶面与CO的相互作用、催化助剂的影响以及F—T合成反应中与H2的共吸附作用等方面进行分析,为进一步的研究工作提供理     

A new gas to liquids (GTL) or gas to ethylene (GTE) technology

Natural gas is a clean-burning and abundant energy resource, but much of it resides in locations remote from an economic means of transporting it to market. A logical solution for the problem would be to liquefy the natural gas, but this option requires very low temperatures and involves considerable costs. Another solution is to convert the natural gas into hydrocarbon liquids using chemical processing. Fischer-Tropsch technology converts the natural gas into “syngas” (a mixture of carbon monoxide and hydrogen) followed by reaction to liquid fuels. Unfortunately, Fischer-Tropsch technology is expensive.

At Texas A&M University, a research team has conceived a radically new process for converting natural gas into hydrocarbon liquids. It is a “direct” conversion method that does not require producing syngas. The process is essentially three reaction steps and two separation steps to produce hydrocarbon liquids. The process consists of two reaction steps and one separation step to produce ethylene. The process can operate economically with natural gas flows of as low as 300 kSCMD up to any desired capacity.

It is possible to use the GTL technology essentially anywhere natural gas exists from offshore platforms to relatively uninhabited onshore sites. This technology offers an alternative to flaring natural gas when pipelines do not exist. The liquids can be transported in liquid pipelines or in trucks or in tankers. Thus, it offers the opportunity to monetize a resource as well as to reduce undesirable emissions into the atmosphere. The GTE technology is more nearly suited to a location near an existing chemical industry that requires ethylene and/or hydrogen.

SynFuels International Inc. has licensed the technology to commercialize it, and the company has constructed a pilot plant capable of processing 3 kMCMD. The cost of a commercial 300 kSCMD plant should be in the US$ 50–75 million range. The cost of the liquids should be about US$ 25–28 per barrel. Of course, larger capacity plants would require a larger investment but produce a less expensive product.     

Hydrogen/carbon monoxide separation with cellulose acetate membranes

Hydrogen/carbon monoxide ratio adjustment is of fundamental interest to the petrochemical and energy industries for the production of C₁ chemicals. Cellulose acetate membranes have been found to be effective for this service and can offer improvements over other gas purification techniques in several respects including reduced capital and operating costs. Membrane and cryogenic processes are compared for the specific case of manufacture of a 1/1 H₂/CO syngas for oxoalcohol production. A particular advantage of the membrane process is its flexibility. This has benefited a recently installed facility for the Central Research Institute of the Electrical Power Institute of Japan for variable adjustment of the hydrogen to carbon monoxide ratio at a test facility demonstrating coal gasification/ gas turbine power production. Design and operating details of this facility are discussed. The membrane process may also be used to produce a pure CO product. The performance of polysulphone and cellulose acetate are compared for this application.     

Combined Decarbonization of Electrical Energy Generation and Production of Synthetic Fuels by Renewable Energies and Fossil Fuels

Power generation from renewable energy sources and fossil fuels are integrated into one system. A combination of technologies in the form of a carbon capture utilization (CCU)-combined power station is proposed. The technology is based on energy generation from fossil fuels by a coal power plant with CO₂ recovery from exhaust gases, and pyrolysis of natural gas to hydrogen and carbon, completed by reverse water-gas shift for the conversion of CO₂ to CO, which will react with hydrogen in a Fischer-Tropsch synthesis for synthetic diesel. The carbon from the pyrolysis can replace other fossil carbon or can be sequestered. This technology offers significant CO₂ savings compared to the current state of technology and makes an environmentally friendly use of fossil fuels for electricity and fuel sectors possible.     

NOx reduction from a large bore natural gas engine via reformed natural gas prechamber fueling optimization

Lean combustion is a standard approach used to reduce NO_x emissions in large bore (35–56 cm) stationary natural gas engines. However, at lean operating points, combustion instabilities and misfires give rise to high total hydrocarbon (THC) and carbon monoxide (CO) emissions. To counteract this effect, precombustion chamber (PCC) technology is employed to allow engine operation at an overall lean equivalence ratio while mitigating the rise of THC and CO caused by combustion instability and misfires. A PCC is a small chamber, typically 1–2% of the clearance volume. A separate fuel line supplies gaseous fuel to the PCC and a standard spark plug ignites the slightly rich mixture (equivalence ratio 1.1–1.2) in the PCC. The ignited PCC mixture enters the main combustion chamber as a high energy flame jet, igniting the lean mixture in the main chamber. Typically, natural gas fuels both the main chamber and the PCC. In the current research, a mixture of reformed natural gas (syngas) and natural gas fuels the PCC. Syngas is a broad term that refers to a synthetic gaseous fuel. In this case, syngas specifically denotes a mixture of hydrogen, carbon monoxide, nitrogen, and methane generated in a natural gas reformer. Syngas has a faster flame speed and a wider equivalence ratio range of operation than methane. Fueling the PCC with Syngas reduces combustion instabilities and misfires. This extends the overall engine lean limit, enabling further NO_x reductions.Research results presented are aimed at quantifying the benefits of syngas PCC fueling. A model is developed to calculate the equivalence ratio in the PCC for different mixtures and flowrates of fuel. An electronic injection valve is used to supply the PCC with syngas. The delivery pressure, injection timing, and flow rate are varied to optimize PCC equivalence ratio. The experimental results show that supplying the PCC with 100% syngas improves combustion stability by 21% compared to natural gas PCC fueling. A comparison at equivalent combustion stability operating points between 100% syngas and natural gas shows an 87% reduction in NO_x emissions for 100% syngas PCC fueling compared to natural gas PCC fueling.     

Iron sulfate/sulfur-catalyzed liquefaction of Wandoan coal using syngas–water as a hydrogen source

Water-soluble iron sulfate/sulfur-catalyzed coal liquefaction using three kinds of hydrogen sources including syngas–water has been investigated. The liquefaction of Wandoan coal, an Australian subbituminous, with iron sulfate/sulfur as a catalyst precursor using syngas–water or carbon monoxide–water afforded higher coal conversions and oil yields than those using pressurized hydrogen gas. The pretreatment at relatively low temperature (200°C) was indispensable to achieve the high coal conversion. In the two-staged liquefaction (400°C, 60 min+425°C, 60 min), the use of syngas–water as a hydrogen source afforded higher coal conversion of 90.1% together with a high oil yield of 46.2% than those using pure hydrogen, and almost comparable to those using carbon monoxide–water, indicating the presence of synergistic effects of two hydrogen sources. At the early stage of the reaction, the contribution of carbon monoxide–water was predominant, whereas hydrogen gas significantly took effect at the latter stage. The XRD and XPS study revealed the formation of pyrrhotite, a possible active species, covered with a small amount of sulfate species.     

F-T合成反应机理的研究

对F-T合成反应机理的发展过程,应用范围及研究前景进行了系统综述,着重总结了近期提出的机理模型,讨论了各种反应机理的合理性和欠缺处,并分析了链引发,链增长和链终止在反应机理中的作用,列举了支持各反应机理的直接实验事实。     

The Use of Methane‐Containing Syngas in a Solid Oxide Fuel Cell: A Comparison of Kinetic Models and a Performance Evaluation

The nickel‐based anodes of solid oxide fuel cells (SOFCs) can catalytically reform hydrocarbons, which make natural gas, gasification syngas, etc., become potential fuels in addition to hydrogen. SR and water–gas shift (WGS) often occur inside SOFCs when operated on these fuels. Their reaction rates affect the partial pressures of hydrogen and carbon monoxide, the local temperatures and the related Nernst voltages. Consequently, the reaction rates affect the electrochemical reactions in the fuel cell. Three different kinetic models were used to characterize methane SR in a tubular SOFC; the results of each model were evaluated and compared. The polarizations of the fuel cell results of these models were validated against experimental data. The performance of a fuel cell operated with different fuels and based on a selected kinetic model was further studied in terms of the anode oxygen partial pressure, the thermo‐electrochemical distribution, and the system level performance.     

Evaluation of the economic and environmental impact of combining dry reforming with steam reforming of methane

Lately, there has been considerable interest in the development of more efficient processes to generate syngas, an intermediate in the production of fuels and chemicals, including methanol, dimethyl ether, ethylene, propylene and Fischer–Tropsch fuels. Steam methane reforming (SMR) is the most widely applied method of producing syngas from natural gas. Dry reforming of methane (DRM) is a process that uses waste carbon dioxide to produce syngas from natural gas. Dry reforming alone has not yet been implemented commercially; however, a combination of steam methane reforming and dry reforming of methane (SMR + DRM) has been used in industry for several years.     

Generation of fuel from CO2 saturated liquids using a p-Si nanowire ‖ n-TiO2 nanotube array photoelectrochemical cell

Light-driven, electrically biased pn junction photoelectrochemical (PEC) cells immersed in an electrolyte of CO(2) saturated 1.0 M NaHCO(3) are investigated for use in generating hydrocarbon fuels. The PEC photocathode is comprised of p-type Si nanowire arrays, with and without copper sensitization, while the photoanode is comprised of n-type TiO(2) nanotube array films. Under band gap illumination, the PEC cells convert CO(2) into hydrocarbon fuels, such as methane, along with carbon monoxide and substantial rates of hydrogen generation due to water photoelectrolysis. In addition to traces of C3-C4 hydrocarbons, methane and ethylene were formed at the combined rate of 201.5 nM/cm(2)-hr at an applied potential of -1.5 V vs. Ag/AgCl. The described technique provides a unique approach, utilizing earth abundant materials, for the photocatalytic reduction of CO(2) with subsequent generation of higher order hydrocarbons and syngas constituents of carbon monoxide and hydrogen.     

Automotive fuels from biomass via gasification

There exists already a market of bio-automotive fuels i.e. bioethanol and biodiesel produced from food crops in many countries. From the viewpoint of economics, environment, land use, water use and chemical fertilizer use, however, there is a strong preference for the use of woody biomass and various forest/agricultural residues as the feedstock. Thus, the production of 2nd generation of bio-automotive fuels i.e. synthetic fuels such as methanol, ethanol, DME, FT-diesel, SNG and hydrogen through biomass gasification seems promising. The technology of producing synthetic fuels is well established based on fossil fuels. For biomass, however, it is fairly new and the technology is under development. Starting from the present market of the 1st generation bio-automotive fuels, this paper is trying to review the technology development of the 2nd generation bio-automotive fuels from syngas platform. The production of syngas is emphasized which suggests appropriate gasifier design for a high quality syngas production. A number of bio-automotive fuel demonstration plant will be presented, which gives the state of the art in the development of BTS (biomass to synthetic fuels) technologies. It can be concluded that the 2nd generation bio-automotive fuels are on the way to a breakthrough in the transport markets of industrial countries especially for those countries with a strong forest industry.