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Thermal conversion technologies may be the most efficient means of production of transportation fuels from lignocellulosic biomass. In order to increase the viability and improve the carbon emissions profile of pyrolysis biofuels, improvements must be made to the required catalytic upgrading to increase both hydrogen utilization efficiency and final liquid carbon yields. However, no current single catalytic valorization strategy can be optimized to convert the complex mixture of compounds produced upon fast pyrolysis of biomass. Staged thermal fractionation, which entails a series of sequentially increasing temperature steps to decompose biomass, has been proposed as a simple means to create vapor product streams of enhanced purity as compared to fast pyrolysis. In this work, we use analytical pyrolysis to investigate the effects of time and temperature on a thermal step designed to segregate the lignin and cellulose pyrolysis products of a biomass which has been pre-torrefied to remove hemicellulose. At process conditions of 380 °C and 180 s isothermal hold time, a stream containing less than 20% phenolics (carbon basis) was produced, and upon subsequent fast pyrolysis of the residual solid a stream of 81.5% levoglucosan (carbon basis) was produced. The thermal segregation comes at the expense of vapor product carbon yield, but the improvement in catalytic performance may offset these losses.

The catalytic conversion of meta-cresol (3-methylphenol) was investigated over HBeta, Pt/SiO2, and Pt/HBeta catalysts at 400 °C and atmospheric pressure. The acid sites of zeolite HBeta catalyze methyl transfer reactions (isomerization and transalkylation), yielding cresol isomers (para- and ortho-cresol), dimethylphenol (xylenol) isomers, and phenol. Pt alone catalyzes hydrodeoxygenation and hydrogenation reactions, leading to toluene as the major product and methylcyclohexane as the minor product. Bifunctional Pt/HBeta catalyzes both methyl transfer reactions and hydrodeoxygenation reactions at the same time, producing toluene, benzene, and xylenes. The Pt/HBeta catalyst is about 10 times more active than the Pt/SiO2 catalyst toward hydrodeoxygenation, with a turnover frequency (on the basis of Pt only) 3 times higher, highlighting the significant role of acid sites in the metal-catalyzed hydrodeoxygenation reactions of phenolics. While Pt/HBeta and Pt/SiO2 exhibit similar rates of coke formation, the f...

Partial oxidation of ethanol with air was carried out in a pulsed discharge plasma reactor at low temperature and atmospheric pressure. Effects of O 2 :ethanol ratio, ethanol flow rate, and discharge current were investigated. H 2 and CO are the major products (>86%). Increases of O 2 :ethanol ratio promote CO formation at the expense of C 2 hydrocarbons. H 2 selectivity and H 2 + CO selectivity are maximized at O 2 :ethanol ratios of 0.3 and 0.5, respectively. Increases of feed flow rate accompanied by current increases allow the reactor to operate with high throughput. The LHV energy efficiency is increased with increasing feed flow rate, reaching 85% at high ethanol flow rates, conditions that also increase throughput. In contrast to catalytic and homogenous reactions, not all O 2 is consumed at high O 2 :ethanol ratio for the low temperature plasma reaction. A radical reaction pathway of H abstraction from –OH and the α-H in ethanol to form CH 3 CHO followed by C–C scission is proposed. The produced hydrogen rich gas can be potentially used in fuel cells and engines.

The results of catalytic treatment of vapors exiting a g/min pyrolysis unit before product condensation to the liquid phase using a Ru/TiO2 catalyst for oak and switchgrass pyrolysis are reported. The pyrolysis is conducted at 500°C and the catalysis at 400°C at atmospheric pressure with a hydrogen partial pressure of 0.58 atm. It is found that the catalytic treatment provides significant conversion of light oxygenates to larger, less oxygenated, molecules and, simultaneously, bio-oil phenolics are also converted to less oxygenated phenolics with methoxy methyl groups transferred to the ring. The activity of the catalyst gradually diminished with increasing biomass fed to the system. Untreated pyrolysis oil forms a single liquid phase with some tarry material, consistent with the literature, whereas the treated liquid product forms separate oil and aqueous phases, the latter of which is about 80% water. The oil from the treated vapors has a lower initial viscosity with only a small increase upon accelerated aging compared to the untreated product oil, which has a dramatic increase in viscosity after aging. This is indicative of poor oil stability for untreated oil that is further confirmed by large increases in molecular weight, while the treated oil has a small increase in molecular weight after accelerated aging. In an effort to understand compatibility with refinery streams, the solubility of the oils in tetralin was examined. The untreated oil was found to have very limited solubility in tetralin, whereas the treated oil phase was completely soluble except for a small aqueous phase that appeared. There are a number of challenges in developing a high yield process for pyrolysis based conversion of biomass to transportation fuels. The Ru/TiO2 catalyst used here shows promise for conducting multiple types of favorable reactions in the presence of the full spectrum of primary pyrolysis products that creates significant product stability under mild conditions. This could lead to higher liquid yields of stable, refinery compatible, product oil. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2275–2285, 2013

The catalytic conversion of anisole (methoxybenzene), a phenolic model compound representing a thermal conversion product of biomass lignin, to gasoline-range molecules has been investigated over a bifunctional Pt/HBeta catalyst at 400 °C and atmospheric pressure. The product distribution obtained on the bifunctional catalyst was compared with those obtained on monofunctional catalysts (HBeta and Pt/SiO2). This comparison indicates that the acidic function (HBeta) catalyzes the methyl transfer reaction (transalkylation) from methoxyl to the phenolic ring, yielding phenol, cresols, and xylenols as the major products. The metal function catalyzes demethylation, hydrodeoxygenation, and hydrogenation in sequence, resulting in phenol, benzene, and cyclohexane. On the bifunctional catalyst, both methyl transfer and hydrodeoxygenation are achieved at significantly higher rates than over the monofunctional catalysts, leading to the formation of benzene, toluene, and xylenes with lower hydrogen consumption and a significant reduction in carbon losses, in comparison with the metal function alone. In addition, on the bifunctional Pt/HBeta, the rate of deactivation and coke deposition are moderately reduced.

The conversion of furfural (FAL) and 2-methylpentanal (MPAL) under hydrogen has been studied over silica-supported monometallic Pd and bimetallic Pd–Cu catalysts. At low space times, the conversion of MPAL yields primarily pentane (decarbonylation), but at higher space times, di-methylpentyl ether (etherification) becomes the main product. Upon addition of Cu, both the overall activity and the decarbonylation selectivity decrease while the selectivity to hydrogenation and etherification increases. In contrast to MPAL, the conversion of FAL shows no etherification products at any space time in the temperature range 210–250 °C but only produces furan via decarbonylation. It is proposed that the presence of the aromatic ring in the furfural molecule has a marked effect in inhibiting the formation of the alkoxide surface intermediate, which is required in the etherification reaction. Density Functional Theory (DFT) calculations of furfural and 2-methyl pentanal have been conducted to gain a better understanding of the differences in the molecule–surface interactions between the aldehydes and the Pd and Pd–Cu surfaces. The reaction mechanisms and the resulting selectivity towards the possible reaction paths (hydrogenation/etherification/decarbonylation) are discussed in terms of the relative stability of the η2-(C,O) and acyl surface species occurring on the different metal surfaces.

Sodium (1–10 wt.%)-promoted 1 wt.% Pt/TiO2 catalysts were prepared by a co-impregnation method and tested for the water gas shift (WGS) reaction under differential reaction conditions. Significantly higher intrinsic activity is achieved with 2–4 wt.% Na addition, when 2–4 layers of NaOx are deposited on the support and the Pt particles are partially covered by NaOx, with moderate surface basicity and exposed Pt surface areas. In addition to the physical coverage, XPS data suggest that interactions between Pt and NaOx may occur by Pt electron donation to O in NaOx through Pt–O–Na. The strong metal–promoter interactions provide highly active sites for the WGS reaction at the periphery of the Pt–NaOx interface and also inhibit Pt particles from sintering. Optimal 4 wt.% Na (Na/Pt = 34) improves the intrinsic reaction rate and turnover frequency of Pt/TiO2 at 300 °C by 8 and 11 times, respectively, and appears to be significantly higher than reported in the literature. The catalysts were characterized by X-ray diffraction, N2 adsorption, CO chemisorption, transmission electron microscopy, H2 temperature-programmed reduction, CO2 temperature-programmed desorption, and X-ray photoelectron spectroscopy.

Vapor phase condensation reactions of propanal were investigated over CexZr1−xO2 mixed oxides as a model reaction to produce gasoline range molecules from short aldehydes found in bio-oil mixtures. Several operating parameters were investigated. These included the type of carrier gas used (H2 or He) and the incorporation of acids and water in the feed. Propanal is converted to higher carbon chain oxygenates on CexZr1−xO2 by two pathways, aldol condensation and ketonization. The major products of these condensation reactions include 3-pentanone, 2-methyl-2-pentenal, 2-methylpentanal, 3-heptanone and 4-methyl-3-heptanone. It is proposed that the primary intermediate for the ketonization path is a surface carboxylate. The presence of acids in the feed inhibits the aldol condensation pathway by competitive adsorption that reduces the aldehyde conversion. Water also promotes ketonization and inhibits aldol condensation by increasing the concentration of surface hydroxyl groups that enhance the formation of surface carboxylates with the aldehyde. Hydrogen enhances cracking and production of light oxygenates and hydrocarbons. The light oxygenates may in turn be reincorporated into the reaction path, giving secondary products. However, the hydrocarbons do not react further. Analysis of the fresh and spent catalysts by XPS showed varying degrees of reduction of the oxide under different operating conditions that were consistent with the reaction results. Changing the proportion of the parent oxides showed that increased Zr favored formation of aldol products while increased Ce favored ketonization. This occurs by shifting the balance of the acid–base properties of the active sites. © 2010 Elsevier B.V. All rights reserved.

Catalytic conversion of glycerol to gasoline-range alkyl-aromatics has been investigated on a series of zeolites (HZSM-5, HY, Mordenite, and HZSM-22) at 300−400 °C and atmospheric pressure or 2 MPa. Although propenal (acrolein) is the major primary glycerol dehydration product over all zeolites, the pore structure of the zeolite plays a significant role on the final product distribution. The major products over one-dimensional zeolites Mordenite and HZSM-22 are oxygenates (propenal, acetol, and heavy oxygenates) without aromatic formation. HZSM-22 is suitable for the production of acrolein with 86% yield at 100% glycerol conversion. However, it is found that glycerol can be converted to high yields of alkyl-aromatics, mainly C8−C10 over three-dimensional HY and HZSM-5. A longer contact time, higher temperatures, and higher pressures favor the formation of aromatics, with a maximum yield of 60% over HZSM-5. A two-bed configuration with a deoxygenation/hydrogenation catalyst (Pd/ZnO) as the first bed and HZ...

article i nfo The conversion of propanal on large (2-5 µm) and small (0.2-0.5 µm) crystallite HZSM-5 at 400 °C and atmospheric pressure has been studied. Improved catalyst stability was observed on small crystallites due to faster removal of products with the shorter diffusion path length, reducing the formation of coke precursors. As previously shown, C9 aromatics are the initial aromatics produced from propanal via aldol condensation followed by cyclization and these have less opportunity to crack to lighter aromatics on the small crystallites. Thus, a higher ratio of C9/(C8+C7) aromatics was observed on the small crystallites. The main isomer of the C8 aromatic products observed on small crystallites was the initial cracking product of the C9 aromatics, and thermodynamically preferred, meta-xylene, while the shape-selective preferred para-xylene was the predominant product on large crystallites. The higher internal diffusion rate of the para isomer results in greater shape selectivity with the longer path of the large crystallite zeolite. It is concluded that the use of smaller crystallite HZSM-5 improves results for production of alkyl aromatics from light oxygenates at mild conditions that may prove useful for bio-oil upgrading.

Conversion of anisole, a typical component of bio-oil, was studied over an HZSM-5 zeolite at varying space times (W/F), reaction temperatures, type of carrier gas, and concentration of water in the feed. Several bimolecular and unimolecular reactions are proposed to explain the evolution of products observed. The bimolecular reactions include the following transalkylation reactions: (a) anisoles to phenol and methylanisole; (b) phenol and methylanisole to cresols; (c) phenol and anisole to cresol and phenol; (d) methylanisole and cresol to phenol and xylenol. A pseudo first-order kinetic model based on these bimolecular reactions was found to describe well the observed product distribution as a function of W/F. It is observed that shape selectivity effects prevail over electrophilic substitution and thermodynamic equilibrium effects in the formation of methylanisole isomers. However, the opposite is true for the distribution of cresol isomers. The kinetic analysis indicates that the contribution of unimolecular reactions such as isomerization is much lower than that of bimolecular reactions. The carrier gas composition was found to have a moderate effect on catalyst activity. When H2 was used as a carrier, catalyst stability showed a moderate improvement in comparison to the runs under He. However, a remarkable increase in catalytic activity was observed upon the addition of water in the feed.

Dialkyl ethers have been selectively produced from etherification of aldehydes and alcohols on supported Pd catalysts. A yield of 79% ether with a selectivity of 90% was observed when feeding 2-methylpentanal with 2-methylpentanol at a molar ratio 1:1 at 125 ◦ C. Cross etherification of n-butanol with 2-methylpentanal shows a much higher rate than that observed when the alcohol or aldehyde is fed alone. This enhanced activity is in line with the catalyst requirement for large ensembles that allow surface alkoxide species next to 2 adsorbed aldehydes. Etherification when only aldehyde or alcohol is fed arises predominantly due to aldehyde–alcohol inter-conversion to produce the necessary co-reactant. The ether yield at the same reaction conditions decreases with metal loading in the order 16 > 10 > 3 wt.% Pd. Increasing reduction temperature also increases ether yield. It is apparent that etherification is highly sensitive to metal particle morphology, consistent with needing ensembles that accommodate the two adjacent adsorption sites.

The reactivities of propanal and propylene have been compared over HSZM-5 zeolites (Si/Al = 45 and 25). Propanal is found to be much more reactive than propylene and to form mostly 2-methyl-2-pentenal and C9 aromatics as early products in the reaction network. Propylene, in contrast, requires more severe conditions to form C6 and C7 aromatics. It is proposed that propanal undergoes acid-catalyzed aldol condensation to form 2-methyl-2-pentenal. This dimer undergoes further condensation to form the aldol trimer, which subsequently dehydrates and cyclizes into C9 aromatics. In contrast, it is well known that propylene, like other olefins, undergoes aromatization via oligomerization and formation of a hydrocarbon pool. While in the conversion of propanal, propylene is also produced, it appears that it does not play a major role in the formation of aromatics under conditions of shorter space times and lower temperatures, at which propanal produces aromatics in significant amounts.

Conversion of propanal to gasoline-range molecules was investigated over a series of HZSM-5 catalysts with controlled mesoporosity generated by desilication. Characterization of the structure of the solid by powder X-ray diffraction (XRD), scanning electronic microscopy (SEM), ammonia and isopropylamine temperature programmed desorption (TPD), and n-butane diffusivity measurements confirmed the development of various degrees of mesoporosity in the zeolites. This structural modification seems to have little influence on Bronsted acid density. The catalyst stability was improved upon desilication due to an increase in coke tolerance. The product distribution of the propanal conversion was found to vary with the severity of the desilication. Increasing the extent of desilication gradually reduced the aromatization and cracking reactions, due to a reduction in the fraction of micropores and in the diffusion path length. Mildly desilicated samples were found to exhibit the best stability on stream and inhibited coke formation.

Bio-ethanol reforming was studied using a plasma-catalytic reactor for hydrogen production at low temperature and atmospheric pressure without diluent gas or external heating. The plasma applied was a DC pulse discharge (corona) plasma. The water gas shift (WGS) catalyst was put just below the cathode electrode. The discharge generated heat was effectively used for feed vaporization and the WGS reaction. The large amounts of CO (∼30%) in the H 2 rich gas formed in plasma reforming of ethanol (H 2 O/ethanol = 6) was successfully reduced to ∼0.8% when a Pt/TiO 2 and Pt–Re/TiO 2 stacked bed were used for in situ WGS catalysis with a gas hourly space velocity up to 12,000 cm 3 g −1 h −1 . The resultant gases contain ∼73% H 2 and ∼23% CO 2 , with small amounts of CO, CH 4 , and C 2 H 6 , that is suitable for H 2 fuel cell use after residual CO removal. Stability tests with daily startup–shutdown showed both plasma and catalyst are stable. The plasma-catalytic system is promising for low CO content H 2 production, and could be extended to other applications.

Platinum, palladium, and copper catalysts supported on precipitated silica have been studied for the hydrodeoxygenation and hydrogenation of 2-methyl-2-pentenal in the 200–400 °C temperature range. The activity follows the order Pt > Pd > Cu. It has been found that at low temperatures, Pt and Pd are primarily active for the hydrogenation of the C C bond to make 2-methyl-pentanal, with some decarbonylation, yielding n -pentane and CO as products. Decarbonylation increases at higher temperatures. Cu catalyzes hydrogenation of both C C and C O bonds. In both cases, the initial products are further hydrogenated to form 2-methyl-pentanol at higher space times. At higher temperatures on Cu, the hydrogenolysis of 2-methyl-pentanol takes place, giving 2-methyl-pentane (and H 2 O) as the dominant product while no decarbonylation is observed.

Na promoted Pt/TiO2 catalysts have been studied under high severity, near equilibrium, conditions for use as a single stage WGS catalyst. Addition of 3 wt% Na to a 1 wt% Pt/TiO2 catalyst has been found to improve water gas shift activity significantly compared to Pt/TiO2, Pt/CeO2, and Pt–Re/TiO2 catalysts. This catalyst is stable when the reaction temperature is higher than 250 °C. Deactivation occurred when the reaction temperature was lower than 250 °C, however, returning the temperature to higher than 250 °C fully recovered activity. TEM observations revealed that addition of Na inhibited Pt particle sintering. These results suggest that Na promoted Pt/TiO2 is a promising single stage water gas shift catalyst for small scale hydrogen production.

Thermal conversion of biomass is a rapid, low-cost way to produce a dense liquid product, known as bio-oil, that can be refined to transportation fuels. However, utilization of bio-oil is challenging due to its chemical complexity, acidity, and instability – all results of the intricate nature of biomass. A clear understanding of how biomass properties impact yield and composition of thermal products will provide guidance to optimize both biomass and conditions for thermal conversion. To aid elucidation of these associations, we first describe biomass polymers, including phenolics, polysaccharides, acetyl groups, and inorganic ions, and the chemical interactions among them. We then discuss evidence for three roles (i.e., models) for biomass components in the formation of liquid pyrolysis products: (1) as direct sources, (2) as catalysts, and (3) as indirect factors whereby chemical interactions among components and/or cell wall structural features impact thermal conversion products. We highlight associations that might be utilized to optimize biomass content prior to pyrolysis, though a more detailed characterization is required to understand indirect effects. In combination with high-throughput biomass characterization techniques, this knowledge will enable identification of biomass particularly suited for biofuel production and can also guide genetic engineering of bioenergy crops to improve biomass features.

Methane conversion using a low temperature plasma generated by an ac corona discharge has recently been extensively studied. Different products can be produced: C2, C3, H2, CO, CO2 and coke. The understanding of the role of temperature has been limited. This paper discusses the use of an IR thermal imaging and measurement system to study the effects of temperature on the stability and carbon formation in low temperature ac plasma conversion of methane. Three types of coke are observed during the methane conversion process using plasma generated by an ac corona discharge under various conditions. The first type of coke is dark brown and powder coke. The second type of coke is dark greenish and forms a soft coating. The third type is coke filaments, which strongly affects the discharge stability by quickly connecting the two electrodes. In the partial oxidation or steam reforming of methane, the temperature is generally less than 300 °C under normal experimental conditions. Increasing the feed temperature in the steam reforming of methane increases the reactor temperature, causing the formation of coke filaments when the water concentration is not high enough. Therefore, feeding liquid water at room temperature into the reactor helps improve the stability.

The interest in natural gas utilization has increased tremendously over the last decade. Natural gas is being looked at as an energy source, as well as a basis for the production of many chemicals. New technologies are needed for smaller scale, remote and niche applications to match many natural gas resources that will not be suitable for large-scale production of distillate products via syngas. Low temperature plasma reactors have been shown to be an effective method for the conversion of methane, and under some conditions have low power consumption. The advantage of low temperature processing potentially reduces the energy intensity of the process and therefore the cost. The feed reactants for this study consist of methane, hydrogen, and oxygen (less than 2.5%). For the dc plasma reactor using NaOH-treated Y-zeolite, the primary products are acetylene, hydrogen, and small amounts of carbon monoxide. However, recent efforts have focused on the in situ selective hydrogenation of the acetylene to ethylene. Palladium on a supported catalyst is commonly used in industry for the selective hydrogenation of small amounts of acetylene in the purification of ethylene produced in crackers. The addition of palladium to the NaOH-treated Y-zeolite maintains the same methane conversion (20–60%), but allows for the selective hydrogenation of the acetylene to ethylene. The catalyst is most selective around 45 °C, where it produces an ethylene to ethane ratio of about 4–1 with no acetylene. The addition of silver to the Pd–Y-zeolite serves two functions. It increases the ethylene to ethane ratio from 4 to at least 7, and as high as 11. In addition, the temperature at which the high ethylene to ethane ratio achieved is shifted to higher temperatures as well as extended over a wider temperature range. Ethylene yields as high as 30% and hydrogen yields as high as 40% have been obtained without attempting to optimize these yields; and it is expected, based on preliminary results, that higher yields can be obtained.

An experimental study of synthesis gas production from simultaneous steam reforming and partial oxidation of methane using an ac corona discharge was conducted. The benefits of the combination of the two reactions reduce the pure oxygen requirement in the system and increase the thermal efficiency by transferring heat between the exothermic and endothermic reactions. The results show that the addition of water vapor greatly enhanced the conversions of methane and oxygen and improved the energy efficiency in an oxygen-lean system. The energy consumed to convert a methane molecule decreased dramatically from 68 to 13 eV/mc with an increase in the percentage of water vapor from 0 to 50% at a CH4/O2 ratio of 5. At the conditions studied, input power had more influence on the methane and oxygen conversions than applied frequency.

In this study, synthesis gas production in an AC electric gas discharge of methane and air mixtures at room temperature and ambient pressure was investigated. The objective of this work was to understand how the CH4/O2 feed mole ratio, ethane added, diluent gas, residence time, input power, applied frequency, and waveform, affected methane and oxygen conversions, product selectivities, and specific energy consumption. Methane and oxygen conversions increased with input power but decreased with increasing CH4/O2 feed mole ratio, flow rate, and gap distance. The experiments were performed at the frequency and power in the range of 200-700 Hz and 8-14 W, respectively, while the residence times were varied from 0.06 to 0.46 s. This study confirms that active oxygen is an important factor in enhancing methane conversion and energy efficiency in a discharge reactor. Ethane is the primary product that forms at short residence times and low energies. Methane conversion dropped dramatically but oxygen conversion increased with addition of ethane to the feed gas. Sinusoidal and square waveforms gave negligibly different results. Current was constant with varying CH4/O2 ratio and flow rate, but increased with increasing power and with decreasing gap distance and frequency. It was shown that the best condition was at 300 Hz and at the highest power used in each condition, since the maximum methane and oxygen conversions and synthesis gas selectivity as well as lowest specific energy consumption were found both with and without ethane in the feed gas. The minimum specific energy consumption, found at 300 Hz, were 21 and 14 eV/mc for the CH4/air system and the CH4/air/C2H6 system, respectively. When studying the effect of residence time by varying the flow rate, the minimum energy consumption of 21 eV/mc was found at 0.12 and 0.23 s. For any given input power or frequency, the CH4/air system had a higher specific energy consumption than the CH4/air/C2H6 system. Less energy was consumed to convert methane under the plasma environment with nitrogen as a diluent compared to helium, indicative of a third body effect.

The independent evaluation of catalyst activity and stability during the catalytic pyrolysis of biomass is challenging because of the nature of the reaction system and rapid catalyst deactivation that force the use of excess catalyst. In this contribution we use a modified pyroprobe system in which pulses of pyrolysis vapors are converted over a series of HZSM-5 catalysts in a separate fixed-bed reactor controlled independently. Both the reactor-bed temperature and the Si/Al ratio of the zeolite are varied to evaluate catalyst activity and deactivation rates independently both on a constant surface area and constant acid site basis. Results show that there is an optimum catalyst-bed temperature for the production of aromatics, above which the production of light gases increases and that of aromatics decrease. Zeolites with lower Si/Al ratios give comparable initial rates for aromatics production, but far more rapid catalyst deactivation rates than those with higher Si/Al ratios.

The present work discusses the direct oxidative conversion of methane to organic oxygenates (methanol, formaldehyde, methyl formate, and formic acid) using a dielectric barrier discharge (DBD) reactor. The DBD reactor can be considered an analog to a catalytic reactor because, just as with the catalytic reactor, the DBD reactor reduces the required temperature and pressure needed for reactions to occur within it as well as control product selectivity. In this study, the effects of changing the electrical properties within a methane–oxygen DBD system were investigated. Increasing the gas gap from 4.0 to 12.0 mm caused the reduced electric field to decrease from 30 to 18 V/cm/Torr, which resulted in a shift in the product distribution from organic oxygenate liquids to ethane and acetylene. The effects of temperature on product selectivity were also studied through the use of a water jacket. Lowering the temperature of water within the water jacket from 75 to 28°C resulted in a 54% increase in organic oxygenate selectivity and a 56% decrease in CO x selectivity.

This study of methane conversion involves the use of a glass dielectric interposed between metal electrodes and applies kilovolt AC voltage and 118-W power with frequencies in the range of 173−264 Hz. The geometry of the system is cylindrical, with gas flowing axially in the annulus between two electrodes. The partial oxidation reactions in this configuration produce methanol, formaldehyde, formic acid, methyl formate, ethane, hydrogen, water, carbon monoxide, and carbon dioxide. The outer electrode is maintained at a low temperature (12 or 15 °C), allowing the organic oxygenates to condense on the plate itself inside the reactor. The results show, through residence-time experiments, that methane and oxygen react to form methanol, which further reacts to form formaldehyde, methyl formate, and formic acid. Increasing the gas gap from 4.0 to 12.0 mm decreases the reduced electric field from 30 to 18 V/(cm Torr), which results in a shift in the product distribution from organic oxygenate products to ethane, ...

This study on the partial oxidation of methane in a silent electric discharge uses an annular reactor consisting of two metal electrodes separated by a gas gap and a glass dielectric covering the outer surface of the inner electrode. The reactor operates at 7000 V and 26−178 W of AC power. The frequency ranges from 100 to 200 Hz. The organic liquid oxygenates formed from the partial oxidation of methane are principally methanol, formaldehyde, methyl formate, and formic acid. This study showed that, when the oxygen partial pressure became limited in the reaction zone, the energy efficiency of the system significantly decreased. It was also shown that, with a recycle, as opposed to without, the selectivity for organic liquids was enhanced by 12%, whereas the COx selectivity decreased by 19% because the recycle had a short per-pass residence time with removal of organic liquid oxygenate products via a condenser. Finally, experimental simulations of reactors in series with intermediate oxygen additions obtain...

Zeolites are an important class of industrial catalyst. In this investigation, the application of zeolites for plasma catalytic methane conversion (PCMC) to higher hydrocarbons at very low gas temperatures (room temperature to 200°C) has been addressed. Zeolites NaY, HY, NaX, NaA, Linde Type 5A and Na-ZSM-5 have been tested for the application in PCMC. The products contain C2 hydrocarbons (acetylene, ethane and ethylene), other carbon species including carbon deposits and trace C+3 hydrocarbons, and syngas (H2+CO), depending upon co-reactant or dilution gases added to the feed. A streamer corona discharge, a cold plasma phenomenon, has been found to be the most effective and efficient at inducing plasma catalytic activity over zeolites. The order of the zeolites tested from good to poor for sustaining the desired streamer discharges is NaY,NaOH treated Y>HY>NaX>NaA>Linde Type 5A>Na-ZSM-5 . Oxygen, carbon dioxide, hydrogen (with or without oxygen added in a small amount), steam and nitrogen have been tested as co-reactants or dilution gases for PCMC over zeolites. Experimental results showed that the selectivity to higher hydrocarbons decreases in the order H2>H2+O2>H2O>N2>N2+O2>CO2>O2, while the methane conversion decreases in the order N2+O2>N2>O2>CO2>H2+O2>H2O>H2. All the co-reactants tested here, except hydrogen, can induce high methane conversions during plasma catalytic reactions. Small amounts of oxygen added to hydrogen can improve significantly the plasma reactivity of hydrogen over zeolites. This has led to a very selective net production of hydrogen and higher hydrocarbons (especially acetylene).

The effects of plasma chemistry on the conversion of methane were studied using a dielectric barrier discharge reactor at ambient temperatures. A dielectric barrier discharge reactor generates a nonequilibrium plasma when a sufficiently high voltage is applied across the reactor`s electrodes. Methane molecules are activated at this temperature and coupled to form C{sub 2} hydrocarbons, higher hydrocarbons, and hydrogen. The study on the effect of voltage, residence time and third bodies on methane conversion and product selectivity shows that methane conversion initially increases with increasing voltage and residence time above the breakdown voltage, and product selectivities are essentially independent of the voltage. Production of hydrogen during the reaction limits olefin production. Methane conversion also increases when helium and ethane are in the feed stream. Helium and ethane both appear to be more easily activated than methane and enhance methane activation and conversion.

This methane conversion work studies a plasma reaction system for the production of organic oxygenates. The reactor consists of a glass dielectric interposed between the metal electrodes and a flowing gas stream through which kilovolt ac power with frequencies in the range of 100−200 Hz is applied. The geometry for this amounts to an annular system in which gas flows axially between the electrodes, with one electrode covered by a glass plate. The effect of the glass dielectric is to distribute the microdischarges across the entire electrode area and limit the duration of each microdischarge. The partial oxidation studies in this configuration produce methanol and other oxygenates (formaldehyde, formic acid, methyl formate). Selectivities for these products combined amount to 50−65%. These are the primary products when oxygen is included in the feed to the reactor. Thus far, experiments with low methane conversions have been conducted (up to around 25%) to minimize liquid condensation in the reactor. Bypro...

The storage of natural gas in other light hydrocarbons is one procedure for automotive natural gas usage that reduces the requirement of high-pressure or cryogenic storage. Model solutions of methane in n-butane, propane, and a liquefied-bottled-gas mixture were simulated using the Benedict-Webb-Rubin-Starling equation of state to determine the pressures necessary to maintain a liquid phase with perturbations in both temperature ({minus}1 C to 38 C) and mole fraction (50 to 80 mol% methane). Methane storage in these liquid solutions is between 45 and 93% of an equal tank volume of compressed natural gas (CNG) at 21 MPa and 15 C. The simulation results indicate that solutions of this type contain 40 to 67% of the energy of gasoline at pressures that range from 60 to 40% that of CNG at 21 MPa and 15 C.

The homogeneous and catalytic oxidative coupling of methane (OCM) for converting methane directly into higher hydrocarbons has been the subject of a large body of research. The present study on conversion of methane in dc corona discharge packed bed reactors may significantly improve the process economics. Experimental investigations have been conducted in which all the reactive gases pass through a catalyst bed which is situated within the corona-induced plasma zone. In this study, a typical OCM catalyst, Sr/La{sub 2}O{sub 3}, was used to investigate experimentally the corona discharge OCM reactions. Experiments were conducted over a wide range of temperatures (823--1,023 K) and input powers (0--6 W) with both positive and negative corona processes. Compared to the catalytic process in the absence of corona discharge, the corona discharge results in higher methane conversion and larger yield of C{sub 2} products even at temperatures at which there is no C{sub 2} activity for the catalyst alone. The methane conversion and C{sub 2} yield increase with O{sub 2} partial pressure during the corona-enhanced catalytic reactions, while the selectivity decreases slightly with increasing O{sub 2} partial pressure. Compared to results obtained in the absence of corona discharges, methane conversion in the presence of themore » dc corona was nearly five times larger and the selectivity for C{sub 2} over eight times higher at 853 K. A great enhancement in catalytic activity has also been achieved at a temperature at which the catalyst alone shows no C{sub 2} activity. The conversion at higher temperature (more than 953 K) is limited by the poor corona performance and the availability of active oxygen species.« less

The oxidative coupling of methane (OCM) is being actively studied for the production of higher hydrocarbons from natural gas. The present study concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by ac or dc corona discharges. Methyl radicals are formed by reaction with negatively-charged oxygen species created in the corona discharge. The selectivity to products ethane and ethylene is affected by electrode polarity, frequency, and oxygen partial pressure in the feed. Higher C2 yields were obtained with the ac corona. All the ac corona discharges are initiated at room temperature (i.e., no oven or other heat source is used), and the temperature increases to 300−500 °C due to the exothermic reactions and the discharge itself. The largest C2 yield is 21% with 43.3% methane conversion and 48.3% C2 selectivity at a flowrate of 100 cm3/min when the ac corona is at 30 Hz, 5 kV (rms) input power was used. The methane conversion may be improved to more than 50%...

This paper reports on a detailed free-radical kinetic model that has been developed to represent the pyrolysis of n-butane and has been used to study the role of pressure on the pyrolysis. THe temperature range covered is from 200 to 600{degrees}C with pressures from 1 to 1000 atm. Simulations were conducted for isothermal, isobaric, homogeneous systems with pure n-butane as the initial reactant. At high temperature, increasing the pressure increases the decomposition rate of butane, as well as increasing the breadth of the carbon number distribution and decreasing the olefins content. Model results agree well with the literature. At low temperature, the rate of decomposition of butane is inhibited by increasing pressures until relatively high pressures, above 100 atm, when the rate increases with higher pressures. Increased pressures at lower temperatures also favor larger products and fewer olefins, but different mechanistic pathways control the decomposition.

Continuous vinyl acetate emulsion polymerization was carried out by using a mixed surfactant system of “Aerosol” OT (AOT) and sodium dodecyl sulfate (SDS). It is well known that the AOT reduces surface tension considerably and has stronger monomer solubilization power than SDS. In this work, particular attention is given to observe the effects of the mixed surfactant on the molecular weights and polydispersities. In comparison with experiments using only SDS, the particle size appears similar, in the range of 190–280 nm. The conversion increased substantially to the 70% range from the 50% level observed with only SDS. All experiments were conducted at 60°C with a mean residence time of 30 min. The total surfactant concentration was maintained at 0.03 mol/L water for all experiments. It was found that once some AOT was included in the surfactant, the behavior was very similar to that observed with only AOT. The number average molecular weights were found to decrease substantially while the polydispersity increases dramatically to about 12. It is believed that AOT may act as a significant chain transfer agent in the polymerization.

The dc plasma catalytic system is very effective in the conversion of methane to hydrogen, acetylene, and carbon monoxide. Reducing the cross sectional area of the reactor decreased the amount of gas that was bypassing the streamer discharges resulting in an increase in methane conversion. Single pass methane conversions as high as 68% and hydrogen, acetylene, and carbon monoxide yields of 52%, 47%, and 21%, respectively, have been achieved. High hydrogen yields can be achieved under different conditions. The highest conversions were obtained with an oxygen concentration of 2% and a residence time of 2.6 seconds. Further work needs to be done to reduce the energy cost. The projected cost of hydrogen may be met by increasing conversion and the throughput of methane while maintaining similar power requirements. This could be accomplished by further minimizing bypassing to increase the overall efficiency of the plasma zone.

Publisher Summary This chapter discusses the combined dry and steam reforming of methane using the non-equilibrium plasma generated by an AC discharge. In the low temperature plasma combination of steam and dry reforming, H, OH, and O radicals help activate more methane molecules and increasing hydrogen abstraction from hydrocarbon species, prolonging the chain reactions. The O and OH radicals also help convert carbon to carbon oxides, preventing the hydrogenation of coke to produce methane and removing solid carbon from the discharge space. As a result, methane conversion in the combined steam and dry reforming of methane are much higher than that in the pure methane discharge or in the steam reforming discharge under similar experimental conditions. The results show a significant reduction in power consumption over either steam or dry reforming on their own. At the same consumed power, higher conversion is observed than in steam reforming alone, despite further dilution of methane. The lowest power consumption is 8eV per molecule of C converted, which is 50% lower than observed in combined steam reforming with partial oxidation of methane. An investigation of the bottom electrode configuration suggests an improvement to produce more H2 and CO which can further reduce energy consumption to an estimated 5eV per molecule of H2 produced, if the water gas shift reaction is taken into account. In addition, net production of CO2 is lowered from such a process and the requirement for CO2 removal from natural gas may be eliminated.

This paper describes a technology which provides a method for the storage of natural gas, primarily for vehicular use, as a liquid solution with other hydrocarbons at ambient temperatures which achieves an energy storage density (on a volumetric basis) up to about 80% of gasoline. The solution is stored at pressures of about 2000 psig and provides approximately 3 times the storage density of compressed natural gas. Various operating scenarios may include differing hydrocarbon solvents, such as propane, LPG, or butanes, and different required storage temperatures, with lower temperatures allowing higher volume fractions of methane. With this technology, the low storage density of CNG and the very low storage temperatures of LNG are both overcome, thus dramatically improving the technical feasibility of large scale commercialization of natural gas powered vehicles.

Plasma reactors have been found to be an effective technique for the activation of methane, the major component of natural gas, at low temperatures. The electric discharges produce energetic electrons that excite and decompose the feed gas molecules. Therefore, reactions are accomplished with relatively low power requirements. The catalyst, NaOH treated X and Y zeolite, enhances the production of electrons and the formation of methane radicals. Methane and hydrogen with oxygen as an additive are used as the feed mixture. Acetylene is the major product with hydrogen and carbon monoxide as by-products. However, the addition of metals to the catalyst can hydrogenate the acetylene to ethylene and ethane.

This report summarizes the conditions and results of this multifaceted program. Detailed experimental descriptions and results and discussion can be found in the publications cited in the Appendix. The goal of this project is the development of novel, economical, processes for the conversion of natural gas to more valuable projects such as synthesis gas or direct conversion to methanol, ethylene and other organic oxygenates or higher hydrocarbons. The methodologies of the project are to investigate and develop low temperature electric discharges and electric discharge-enhanced catalysis for carrying out these conversions. With the electric discharge-enhanced conversion, the operating temperatures are expected to be far below those currently required for such processes as oxidative coupling, thereby allowing for a higher degree of catalytic selectivity while maintaining high activity. In the case of low temperature discharges, the conversion is carried out at ambient temperature, trading high temperature thermal energy for electric energy as the driving force for conversion. The low operating temperatures remove thermodynamic constraints on the product distribution due to the non-equilibrium nature of the low temperature plasma. This also removes the requirements of large thermal masses that need very large-scale operation to maximize efficiency that is the characteristic of current technologies,more » including high temperature plasma processes. This potentially allows much smaller scale processes to be efficient. Additionally, a gas conversion process that is electrically driven provides an internal use for excess power generated by proposed Fischer Tropsch gas-to-liquids processes and can increase their internal thermal efficiency and reduce capital costs. This project has studied three primary types of low temperature plasma reactor and operating conditions. The organization of this program is shown schematically in the report. Typical small scale laboratory reactor systems were developed that used mass flow controllers for feed gas mixture delivery and GC and MS analysis of products. The range of operation included flow rates from a few sccm to a few hundred sccm with residence times from less than a tenth of a second to about 30 minutes. Temperatures used were generally from ambient to 100 C, but were from as low as about 0 to a high of 800 C. Pressures were generally atmospheric, but for most of the configurations pressures up to 3 atmosphered were also used.« less

In this study, temperature programmed CO2 desorption, a two-step plasma catalytic methane conversion (PCMC), and temperature programmed oxidation of carbonaceous species were carried out to investigate the interactions between the plasma and heterogeneous catalysts. The experiments demonstrated that NaOH treated Y, NaY and NaX zeolites, which have significant basicity, stabilize sustained streamer corona discharges at low temperatures leading to better and longer lived PCMC. The experiments also confirmed that the basicity, polarity and reactivity of zeolites may be increased by the plasma leading to improved behavior for PCMC. TPO of carbonaceous deposits show that NaX, NaY, NaA and 5A zeolites generate less coke and it is oxidized below about 650 K, while NaZSM-5 generates significantly more coke which oxidizes at higher temperature. This more refractory coke appears to destabilize the plasma leading to arcing and poorer PCMC performance. A two-step PCMC in which methane is adsorbed without plasma and then the plasma is generated with co-reactants but without methane in the gas phase showed that active plasma species interacting with the catalyst surface are necessary for the selective production of higher hydrocarbons.

The MCM-41 family of surfactant templated materials were used as model mesoporous sorbents for storage of light hydrocarbon vapors, by utilizing the phenomenon of capillary condensation. The experimental data show that, because of the fine tunability of MCM-41 type materials (mesopore diameter was controlled between 20 and 40 Å), the onset of capillary condensation can be controlled, and from here the point of achieving liquid-like fluid density in the pores. Such a unique characteristic makes the MCM-41 family of materials a potential media for sorptive fractionation.