Distribution Of Gaseous Products Research Articles

Catalytic Effects of the Typical Alkali Metal on Gaseous Products Distribution and Char Structure During Co-pyrolysis of Low Rank Coal and Lignocellulosic Biomass

Abstract In order to investigate the influencing mechanism of alkalis on gaseous products distribution and char structure during co-pyrolysis of low rank coal and lignocellulosic biomass, carboxymethylcellulose sodium (CMC) was selected as the typical organic sodium salt. Gaseous products distribution was explored in a drop tube furnace from 800 – 1000 o C under various CMC mass ratio, surface morphology of co-pyrolysis char was examined via scanning electron microscopy technology and fractal dimension analysis, and microcrystalline structure was evaluated using Raman spectra and peak deconvolution. The results indicated that the addition of CMC promoted the yields of H 2 and CO, and the yield of CO 2 was improved due to the content of carboxylate radical in CMC. Quantitative information on co-pyrolysis char surface morphology was obtained from fractal analysis on the SEM images. The fractal dimension of co-pyrolysis char was in range 1.61 to 1.78 and higher than that of coal char, which meant the uniformity of the co-pyrolysis char was promoted by CMC. Peak fitting analysis on the Raman spectra illustrated that the value of A D /A All and A D /A G increased with the mass ratio of CMC, indicated that CMC improved the ordering of char structure. This paper provides an insight on the effects of organic sodium salt on products evolution during co-pyrolysis of coal and biomass.

Investigation on the fast co-pyrolysis of sewage sludge with biomass and the combustion reactivity of residual char

Gaining the valuable fuels from sewage sludge is a promising method. In this work, the fast pyrolysis characteristics of sewage sludge (SS), wheat straw (WS) and their mixtures in different proportions were carried out in a drop-tube reactor. The combustion reactivity of the residual char obtained was investigated in a thermogravimetric analyzer (TGA). Results indicate that SS and WS at different pyrolysis temperatures yielded different characteristic gas compositions and product distributions. The co-pyrolysis of SS with WS showed that there existed a synergistic effect in terms of higher gas and bio-oil yields and lower char yield, especially at the WS adding percentage of 80wt%. The addition of WS to SS increased the carbon content in the SS char and improved char porous structures, resulting in an improvement in the combustion reactivity of the SS char. The research results can be used to promote co-utilization of sewage sludge and biomass.

Effect of potassium organic and inorganic salts on thermal decomposition of reconstituted tobacco sheet

In order to deeply investigate the role of potassium in modifying thermal behavior and burning characteristics of reconstituted tobacco sheet (RTS), electrodialysis (ED) technology was employed at first to remove the main ions in the tobacco extract to reduce interference of endogenous ions. Characterization on thermal behavior of RTS treated with three organic (acetate, malate and citrate) potassium salts and three inorganic (chloride, sulfate and phosphate) potassium salts was then performed using thermogravimetric analyzer coupled with Fourier transforms infrared spectrometer (TG-FTIR) at the heating rate of 20 °C min−1. TG results illustrated that potassium decreased the peak temperature of carbohydrate pyrolysis, retarded the thermal degradation of the major components of RTS and meanwhile promoted the formation of stable char firmly depending on its chemical state. The organic potassium salts had a more significant effect on the process of char oxidation than inorganic ones with a new peak at around 570 °C. Analyses of evolved gaseous products distribution demonstrated a significant reduction of CO and CO2 during carbohydrates pyrolysis in the presence of potassium, especially organic potassium salts. Moreover, the maximum firecone temperature was also measured by Infrared thermography, and it had been found that the burning cone temperature of ED-modified RTS was averagely 13.27 °C higher than that of organic potassium treated RTS but averagely 16.57 °C lower than that of inorganic ones.

In Situ Reforming of the Volatile by Char during Sewage Sludge Pyrolysis

In this study, the volatile from sewage sludge (SS) pyrolysis is passed through the hot char from the same source in a fixed bed reactor. The reforming effect of the sewage sludge char (SSC) on the quality and energy distribution of liquid and gas products is studied. In comparison to dolomite, SSC presents a better tar-eliminating effect from 450 to 650 °C. The production of combustible products, including CH4, H2, and CO, is significantly increased by both the catalytic cracking on the SSC surface and the volatile–char reaction. After the reforming effect at the pyrolysis temperature of 650 °C, the gas yield is increased from 17.19 to 34.27 wt % and the fraction of combustible components is increased by 54.28 vol %. The quality of the oil is also upgraded by reforming of SSC, with the escalation of the light components, and nitrogen-containing and oxygenated fractions are greatly reduced. When the pyrolysis temperature is fixed at 650 °C and the reforming temperature is increased from 450 to 650 °C, the liquid yield is decreased from 18.76 to 10.67 wt %. In addition, the combustible fraction in the gaseous product is greatly increased. The calculation of the energy distribution indicates that, via the reforming process, a lot more heating value will concentrate on the gas product and the overall high heat value of the pyrolysis volatile and SSC will be significantly promoted.

Petroleum-containing residue processing via co-catalyzed pyrolysis

This paper is devoted to the study of oil-containing residue (oil-slime) pyrolysis process in the presence of cobalt chloride as a catalyst. A mixture consisting of crude oil (20wt.%) and silica (80wt.%) was used as a model substrate. The pyrolysis process carried out at a temperature 500°C in nitrogen atmosphere in the presence of 5wt.% of CoCl2 allowed obtaining an optimal gaseous, liquid and solid product distribution. Moreover the comparison of liquid and solid pyrolysis products composition with those obtained in non-catalytic process was done. It was found that the use of CoCl2 increases the calorific value of both gaseous and liquid products due to the increase in hydrocarbon formation. Pyrolysis solid residue was found to consist of silica particles coated with pyrolysis graphite and can be used as a valuable sorbent.

Pyrolysis and catalytic upgrading of low-rank coal using a NiO/MgO–Al2O3 catalyst

The catalyst NiO/MgO–Al2O3 was prepared by loading magnesium and nickel onto the surface of γ-Al2O3 beads, respectively, and was adapted to in situ upgrade the high temperature pyrolysis vapor derived from coal pyrolysis. The catalyst synthesis process, and structural variation were characterized by the XRD, SEM, and physical adsorption analyzer. In order to examine the catalytic effect on the different nickel loading ratio in the catalysts, the solid–liquid–gas product distribution, variation of gas and components of coal tar were studied by simulated distillation, GC/MS, elemental analysis and so on. The results shows both the tar yield and the content of the light fraction in the tar can be increased by catalytic up grade. The catalyst has a strong ability to convert the heavy component and polycyclic aromatic hydrocarbons in the tar to lower molecular weight components.

Anthracene aquacracking using NiMo/SiO2 catalysts in supercritical water conditions

A series of effective NiMo/SiO2 catalysts for heavy oil upgrading in supercritical water have been developed. Experimental results with anthracene as model compound resembling structures present in heavy oils showed that the catalytic activity as well as the liquid and gas product distributions are governed by catalyst composition. In particular by adjusting the Ni/Mo ratio different physicochemical properties (crystalline phase composition, particle size and catalysts reducibility) are obtained, which have influence on catalytic behavior. A variety of liquid products together with a valuable gas (rich in H2) are produced in this process, which takes place with remarkably low coke deposition on the catalysts. Overall, the results derived from this work confirm the viability of upgrading polyaromatic structures in supercritical water using Ni-Mo catalysts and provides an insight on the main parameters to control in catalyst design.

(Invited) Single Step Direct Electrocatalytic Reduction of CO2 towards CO and Hydrocarbons

Switching from fossil based to renewable power generation requires the installation of large overcapacities of wind and solar due to their intermittency. Storage or conversion possibilities are essential due the volatility of electricity. Economic feasibility is difficult when considering the low fossil energy carrier prices and the physical efficiency limitations of the processes. Therefore, we choose to focus on high volume chemical feedstock such as Ethylene or CO, where the chemical value exceeds by far its pure heating value. Electrocatalyts facilitate the conversion of CO2 to valuable base chemical feedstocks – for selectivity improvements substantial advances in electrode design are required. Depending on the electro catalytic system, CO2 can be electrochemically reduced to carbon monoxide (CO), methane (CH4), ethylene (C2H4) and various other hydrocarbons even in aqueous media. CO could be obtained with faradic efficiencies over 90% at current densities exceeding the industrial necessary level of 100 mA/cm² with a total energy efficiency approaching 50%. Ethylene is more challenging due the highly complex reduction process involving 12 electrons and 8 protons. Faradic efficiencies up to 57% for ethylene at current densities above 150 mA/cm² could be obtained using in-situ-deposited nano-structured copper based electrocatalysts. In many experiments we observed a large gap in the sum of the current efficiencies of gaseous products to 100% FE. It is well known, that the electro-reduction of CO2 also yields liquid products. This gap could be fully closed by detailed analysis of the electrolyte revealing a strongly pronounced formation of ethanol (> 20% FE) accompanied by wide range of C1-C3 alcohols, carboxylates and ketones in yields up to ~ 5%. To the best of our knowledge, the here reported faradaic efficiencies for ethanol above 20% in a current density regime above 150mA/cm2 have been unpresent in the literature so far. In addition time resolved parallel analysis of the gaseous and liquid product distribution revealed striking relationships between different species i.e. the parallel formation of ethylene and ethanol. Figure 1

Conversion of the waste rapeseed oil by aerosol gliding arc discharge-assisted pyrolysis

The aerosol gliding arc discharge-assisted pyrolysis was firstly proposed to convert the waste rapeseed oil. The arc motions in pure argon gas and oil mixture discharge were compared at different total flow rate. Calculated by FLUENT software, the average flow velocity distribution along the axis direction was obtained, ranging from 8 m/s at the arc initiated gap to 0.5 m/s at the exit. The distribution of gaseous products was investigated under the effect of applied voltage and pyrolysis temperature, which indicated 74% of waste oil was converted into gaseous products at applied voltage of 10 kV and pyrolysis temperature of 800 °C, respectively. Selectivity of gaseous products (CO, H2 and C2 hydrocarbons) exhibited different sensitivity to variation of operating conditions. Optical images were captured to record the evolution of deposited carbon on copper substrate under different temperatures, while the Raman spectroscopy implied that well-organized graphitized structure was formed at rotating gliding arc regime as well as the copper surface.

Seasonal and diurnal dynamics of physicochemical parameters and gas production in vertical water column of a eutrophic pond

Small and shallow water bodies often exhibit high rates of biogeochemical activities, yet have not received much attention. Here we test the hypothesis that there is strong diurnal stratification of physicochemical characteristics in a hyper-eutrophic pond, which would lead to a heterogeneous distribution of gas production via biological processes along vertical profile of water column. Accordingly, we focused on quantifying the seasonal and diurnal dynamics of nutrients (NO3−, NH4+, total dissolved nitrogen TDN, PO43−, total dissolved phosphorus TDP), physicochemical environment factors (DO, pH, light intensity, Chlorophyll-a) and gas emission (N2, N2O, O2, CH4) in the vertical profile of an ultra-eutrophic pond located at the subtropical climate zone, China. The strong and persistent stratification of several parameters at the resolution of centimeters along vertical profile of water was observed in summer and autumn. Interestingly, the surface water and sediment–water interface produced much more gas than the middle layers of water column. The quantity and composition of gas collected from the surface water were greatly affected by O2 production, which followed the diurnal cycle of sunlight intensity. Other biological processes, e.g. nitrification and/or denitrification, may also have contributed to the heterogeneous gas production as high N2 and N2O fluxes were detected in the surface layer and sediment–water interface. CH4 production was mainly from the sediment–water interface, especially in summer when the bottom layer developed very low DO concentrations due to strong stratification. Our results demonstrate that besides the unexpectedly long and strong thermal and physicochemical stratification, the shallow eutrophic pond can undergo significant vertical heterogeneity of gas emission due to the strong diurnal stratification of these physicochemical parameters.

Hydrogen production from tea waste

Hydrogen production from biomass is gaining more attention due to the depletion of fossil fuel sources. Tea waste as an agricultural waste is a promising feedstock in order to obtain hydrogen-rich gas via gasification.In this study, tea waste was gasified at 450, 650, 850 °C and 1 atm in an updraft gasifier using K2CO3 and air as catalyst and gasification agent, respectively. Effect of catalyst ratio (0, 10, 20, 30, 40, 60 wt.%) (catalyst/biomass), temperature (450, 650 and 850 °C) and reaction time (10, 15, 20 min) on product gas distribution was investigated. Composition of gas product was determined by micro gas chromatography system. Suitable gasification conditions were determined as 20% catalyst, 850 °C temperature and 15 min reaction time.

Ferrites as redox catalysts for chemical looping processes

Spinel ferrites can accommodate oxygen vacancies in their structure and reversibly exchange oxygen with the environment at high temperatures, depending on the partial pressure of oxygen. Therefore their use in Chemical Looping Combustion (CLC) is being studied intensively. In the present work the use of ferrites with the general formula of MeFe2O4 (Me=Mn, Ni, Zn, Co, Cu) as oxygen carriers or potentially reactive supports for oxygen carriers in Chemical Looping Combustion is explored. Polycrystalline ferrite samples are prepared using the conventional ceramic technology of “solid-state reaction”. The performance of the prepared materials is evaluated at a fixed-bed laboratory scale pulse reaction unit. During the fuel oxidation step, methane pulses are injected over the ferrite powder while subsequent oxidation of the solid is performed with gaseous oxygen. The performance of the candidate materials is ranked by comparing the amount of oxygen per mole solid (δ) that can be delivered reversibly to the fuel which corresponds to the Oxygen Transfer Capacity of the different ferrite materials as well as the methane conversion during the fuel oxidation step and the gaseous product distribution. The stability of the materials during multiple reduction–oxidation cycles is evaluated during 5–10 subsequent cycles, each of which is comprised of an activation–regeneration and a solid oxidation step. All the examined ferrites have the ability to deliver their lattice oxygen to a fuel and to some extend regain it in the presence of air. Cu ferrites are very active in CH4 oxidation with maximum conversion higher than 95%, while Zn and Ni ferrites are also highly ranked with methane conversion reaching up to 90% and 78% respectively, however they deactivate very fast after redox cycles. Mn ferrites present relatively low activity (∼30%), while Co ferrites present moderate methane conversion, approximately 68% but remarkable stability during subsequent redox cycles. Cu-, Co- and Ni-ferrites can deliver higher amounts of lattice O, compared to Mn ferrite. The structural and morphological stability of the materials after the multiple redox cycles is examined by X-ray diffraction and SEM–EDS analysis.

H2 production from catalytic steam reforming of n-propanol over ruthenium and ruthenium-nickel bimetallic catalysts supported on ceria-alumina oxides with different ceria loadings

Catalytic steam reforming of n-propanol was investigated over ruthenium and ruthenium-nickel bimetallic catalysts supported on ceria-alumina oxides with different ceria loading (0–10% CeO2 wt/wt). Catalysts were characterized by BET surface area analysis, powder X-ray diffraction, temperature programmed reduction and energy dispersive X-ray analysis with scanning electron microscopy. Steam reforming activity was tested in a fixed bed tubular flow reactor at 450 or 500 °C using a feed of n-propanol/water mixture at a molar ratio of 1:12 and a constant liquid feed rate of 0.1 ml min−1. The effluent gas was monitored by GC/TCD and the evolution of the rate of hydrogen formation and the product gas distribution as a function of time was studied. Calcination in air after the impregnation with RuCl3 was found to reduce ruthenium dispersion and lower steam reforming activity. Both high metal loading and sufficient ceria promotion are essential for active and stable performance. Otherwise, dehydration reaction dominates and catalyst deactivation became severe. Catalysts with 3 wt% Ru, 10 wt% Ni and 3 or 10 wt % ceria were found to be very reactive and stable at both 450 and 500 °C.

Pyrolysis of oil shale by solid heat carrier in an innovative moving bed with internals

This article reports a new moving bed with particularly designed side and central channels as its internals for small-size oil shale pyrolysis by solid heat carrier. The bed is called moving bed with internals (MBI), and the solid heat carrier is shale ash from industrial Fushun retorting furnace. The pyrolysis was tested by varying the temperature of solid heat carrier, thickness of particle bed between the side and central channels, and ash-to-shale mass blending ratio in terms of the oil and gas product distribution and qualities. The shale oil yield is close to 90% of the Fischer Assay yield, and of the produced oil over 70wt.% is gasoline and diesel and its dust content is only about 0.1wt.%. The highest shale oil yield occurs at the pyrolysis temperature of 495°C. The shale oil yield decreases with increasing particle bed thickness due to the increased shale oil cracking over shale ash in the prolonged residence time of volatile products inside the particle bed. Mechanism analysis shows that the central channel in the MBI directs the pyrolysis products to flow from the annulus to center of the particle bed, and this makes the moving bed as a filtration layer that considerably reduces the dust content in the produced oil. Meanwhile, this lateral flow greatly shortens the time of secondary reactions occurring to the pyrolysis products so that MBI could be applied to small-size oil shale to produce shale oil with high yield and high quality.

Experimental and modeling study of thermal and catalytic cracking of n-decane

Catalytic cracking of n-decane over a platinum/lanthanum–alumina coated stainless steel tube is experimentally studied to obtain the product distributions and gas yield at a pressure of 1atm and different temperatures 600, 650 and 700°C. The results reveal that the higher the cracking temperature is, the higher the gas yield will be. A detailed micro-kinetic model for cracking of n-decane over a platinum/lanthanum–alumina catalyst is developed to simulate the gaseous product distribution and gas yield. In high temperature catalytic cracking systems, the interactions of gas-phase and surface reactions are very significant phenomena. Thus, the model contains a detailed gas-phase pyrolysis kinetic model along with a surface kinetic model for n-decane cracking over a platinum/alumina catalyst. The gas-phase pyrolysis kinetic model contains 304 species, 1104 reactions and the surface kinetic model contains 52 adsorbed chemical species and 218 reactions. The modeling results of the gaseous product distribution and gas yield are acceptable compared with experimental results. In order to evaluate the contribution of thermal cracking in catalytic cracking, simulation of thermal cracking of n-decane is performed by using the gas-phase pyrolysis kinetic model. The simulation results show that the contribution of thermal cracking in catalytic cracking is increasing with temperature increasing. This work provides insight at the molecular level for the kinetic process of n-decane cracking over a platinum/lanthanum–alumina catalyst.

Conversion of cassava rhizome using an in-situ catalytic drop tube reactor for fuel gas generation

The air-gasification of cassava rhizome mixed with Ni/α-Al2O3 catalyst in a drop tube reactor for production of fuel gas was carried out in this work. The conversion was performed at different temperatures from 873 to 1073 K, equivalence ratio (ER) of 0.2–0.6, and semi-continuous feeding of raw material for 30 min. Gas yields, cold gas efficiency (CGE) and lower heating value of fuel gas (LHV) were compared with non-catalytic cases. Generally, higher temperature and ER significantly improved the performance of cassava rhizome gasification. Similar for both of non-catalytic and catalytic cases, at optimum temperature of 1073 K and ER of 0.6, the maximum gas yields were closed to 80% while yields of char and tar were kept minimal at 4% and 11%, respectively. Addition of prepared catalysts resulted in greater CGE and LHV of 92% and 8.6 MJ/N m3, respectively, comparing to the non-catalytic case of 61% and 6.36 MJ/N m3, respectively. Moreover, the measured gas distribution data were comparable with the result obtained from thermodynamics conversion model based on minimization of Gibbs free energy of product gases using elemental composition of cassava rhizome (C3.13H5.2O3.52N0.03S0.04.) constrained by mass and energy balances for the system. As a result, the gas product distribution and characteristics obtained from this experimental implied its suitability for heat and power applications.

Gaseous organic emissions during air gasification of woody waste: effect of bed agglomeration/defluidization

This study investigated the effects of temperature and the use of additives on the distribution of gaseous products (H2, CO, CO2, and CH4) and organic pollutants (BTEX and PAHs) during the fluidized bed gasification of woody waste in bed agglomeration/defluidization processes. The results indicated that the hydrogen content increased with an increase in temperature. However, the concentrations of CO, CO2, and CH4 decreased. Moreover, the concentrations of BTEX were significantly influenced by temperature, but the concentrations of PAHs were stable at approximately 100,000μg/Nm3. On the other hand, the addition of CaO and Al2O3 enhanced the production of hydrogen. Then, the emission concentrations of both organics increased with time and decreased with the occurrence of agglomeration. The PAH emission increased dramatically when only SiO2 was present, but PAHs were adsorbed when CaO and Al2O3 were added during the defluidization process.

TG–MS analysis of thermal behavior and gaseous emissions during co-combustion of straw with municipal sewage sludge

The thermal behavior and gas product distribution during combustion of straw (wheat straw, corn stalks, and cotton stalks), municipal sewage sludge (MSS), and their blends were investigated by thermogravimetry–mass spectroscopy. The experiments were conducted with various blending ratios and temperatures ranging from 323 to 1,173 K. Addition of MSS decreased the combustion performance of the straw. The reactions between wheat straw and corn stalks with MSS proceeded more easily than that of cotton stalks. Significant interactions were observed between the straw and MSS at the char combustion stage. Gaseous species (CO2, SO2, NH3, HCN, and NO) were mainly produced at temperatures of 523–873 K at which most of the mass loss occurred. Higher MSS proportions in the blends resulted in lower emissions peaks for CO2, NH3, HCN, and NO except for SO2. To ensure combustion performance and mitigate problematic gaseous emissions, the proportion of MSS added to the blends should be <30 mass%.

The impact of diffusion type on multiscale discrete fracture model numerical simulation for shale gas

The development of unconventional gas reservoirs represents totally distinctive characteristics as compared with the conventional reservoirs. The complex pore structure in shale reservoir determines its special flow mechanism, which can be divided into several categories according to the size and type of pores- non Darcy flow, gas slippage, adsorption-desorption and gas diffusion effect. Based on the gas molecules diffusion form in porous media and combining with the multi-scale distribution structural characteristics of shale gas reservoirs, the shale gas diffusion mechanisms in the shale reservoir space including the diffusion of dissolved gases in the organic kerogen and the diffusion of free gas in the nanopores are analyzed in this paper. Meanwhile, the diffusion in the nanopores consists of Knudsen diffusion (KN ≥ 10), Fick diffusion (KN ≤ 0.1) and transition diffusion (0.1 < KN < 10) according to the Knudsen (KN) number.In this work, we set up new mathematical models for shale gas flow in matrix and fracture networks, and also for their mass transfer in between without neglecting its varying-scale nature following the concept of discrete fracture network (DFN). In addition, we also investigate the different diffusion mechanisms' influences on the production and pressure in the tight shale gas reservoir. Ultimately, concluding that the gas diffusion mechanisms in micro-and nano-scale matrix block have a greater impact on the distribution of shale gas production (especially the production at early time) and reservoir pressure.

Influence of TiN coating on products distribution for hydrocarbon fuel cracking under high temperature and pressure

To understand the cracking behavior of hydrocarbon fuels when a passivation coating covers the metal substrate, the pyrolysis of n-hexane, cyclohexane and benzene in uncoated and titanium nitride (TiN) coated stainless steel 304 (SS304) continuous tubular reactors (3mm diameter, 700mm long) under high temperature and pressure were studied. The TiN coating was prepared on the inner surface of SS304 tubes by atmospheric pressure chemical vapor deposition (APCVD) using TiCl4-H2-N2 system. The solid, liquid and gaseous products distribution of the pyrolysis of n-hexane, cyclohexane and benzene for bare and TiN-coated tubes were analyzed and discussed. The results show that the influence of TiN coating on hydrocarbon fuels cracking is not a simple effect of promotion or inhibition. As a whole, the TiN coating has little effects on the distribution of the gas products for n-hexane cracking, but has great influence on that of cyclohexane and benzene cracking. For the liquid products distribution, the mass fractions of alkane for bare tubes reduce compared with those for TiN-coated tubes, while the alkene contents are higher than those for TiN-coated tubes. Moreover, the morphologies of carbon deposits are mainly filamentous and spherical on the inner surface of SS304 tubes, but no morphologies of carbon deposits are observed on TiN-coated tubes surface after thermal cracking of hydrocarbon fuels. Meanwhile, the amount and carbon deposition rate of cokes deposited in the system for TiN-coated tubes are higher than those of bare tubes, regardless of the hydrocarbon fuels are n-hexane, cyclohexane and benzene.