Direct Coal Liquefaction Research Articles

Prediction of direct coal liquefaction residue catalytic gasification based on back propagation neural network

ABSTRACT As an important clean coal technology, direct coal liquefaction generates a large amount of residue while producing oil. Catalytic gasification is an attractive conversion route for direct coal liquefaction residue (DCLR). Due to the complex reaction process affected by many variables, so this paper applies BP neural network which has the advantage of solving nonlinear problems. Firstly, a back propagation (BP) neural network model was established with four inputs (the relative molecular weight of catalyst, the melting point of catalyst, the loading content of catalyst, and the final gasification temperature) and three outputs (the gasification conversion, the maximum gasification rate, and gasification reaction index reaction) to simulate the catalytic gasification of DCLR in CO2 atmosphere. In order to enhance the training speed and the stability of the network, some improvement of BP model were conducted by both additional momentum term and adaptive learning rate, or variable excitation function, and the prediction relative errors of the two models are less than 5%. Finally, the impact degree of factors was investigated by weight analysis based on the BP single-output model, and the result shows that the catalyst type is the most significant among these variables.

Coking behavior and mechanism of direct coal liquefaction residue in coking of coal blending

Direct coal liquefaction residue (DCLR) was directly blended with five coke-making coals for the first time in this study. The effect of DCLR addition on coke quality was investigated. The coking mechanism of DCLR as a binder in blending coals was also elucidated. Results showed that 5% and 10% DCLR addition to blending coal could reduce 8% and 13% high caking property coals respectively without causing any great impairment in cold mechanical strength. Compared with JM (coking coal) and FM (fat coal) asphaltenes, DCLR asphaltene exhibited obvious differences as it contained higher percentages of aromatic CC and aliphatic –CH2– functional groups which could indirectly enhance the caking property of blending coal and improve the cold mechanical strength of coke resulting in cold mechanical strength M13 increasing from 90.31% to 96.77%.The roles of DCLR participating in coking can be summarized in two stages. Firstly, DCLR can fully moisten the surface of coal particles in the early stage of coal pyrolysis (350–380 °C) and suppress the gas escaping from coal particles, resulting in a higher internal pressure. Secondly, internal gas breaks through the metaplast layer and squeezes the sticky metaplast produced by DCLR into holes between coal particles in the key stage of coal pyrolysis (380–450 °C), leading to high quality coke.

Fe3O4 Nanoparticles Supported on Modified Coal toward Catalytic Hydrogenation of Coal to Oil.

Iron-supported catalysts exhibit good catalytic performance in direct coal liquefaction (DCL), but the effect of the carrier on the performance of the composite catalyst is unclear. In this paper, a simple solid-state synthesis strategy for the preparation of coal-loaded Fe3O4 nanoparticles (Fe3O4/Coal) and the hydrochloric acid treatment of coal-loaded Fe3O4 nanoparticles (Fe3O4/Coal-HCl) is presented. The resulting composite was used as a catalyst for DCL. The effects of supports on the structure and performance of iron-supported catalysts have been illustrated. After the acid pretreatment of the catalyst carrier coal, the surface structure and functional groups changed, which affected the aggregation morphology of the Fe3O4 active component. The Fe3O4/Coal-HCl catalyst improved the catalytic performance of DCL with conversion and oil yield of 98.02 and 49.96 wt %, respectively. The result shows that pretreatment can be an effective way to modify the surface of the catalyst carrier coals, thereby further improving the catalytic performance of composites. The iron-based composites prepared by the solid-state route show great potential as supported catalysts in DCL.

Ionic liquids for coal dissolution, extraction and liquefaction

AbstractCoal is the most abundant fossil fuel. Direct combustion of low‐ and medium‐rank coals causes alarming environmental impacts. Therefore, it is crucial for coal to undergo pretreatments before its efficient utilization [such as coal to liquid (CTL) processes]. Conventional pretreatment methods suffer from several limitations including the use of volatile organic solvents, environmental hazards, strong reaction conditions (e.g. high temperature and pressure), consumption of large quantities of nonrecoverable chemicals (e.g. bases used in aqueous alkaline digestion), or being only effective for specific coals. On the other hand, coal pretreatment by nonvolatile ionic liquids (ILs) could lead to partial coal dissolution/swelling and structure disruption, which is a critical step before coal liquefaction, hydrogenation, pyrolysis or the inhibition of oxidation/combustion. In addition, ILs are suitable solvents for extracting sulfur compounds from coal, asphaltenes from Direct Coal Liquefaction Residues (DCLR) and phenolic compounds from coal tar. This review will discuss these aspects of coal pretreatments by ILs, and identify how ILs could lead to a cleaner and more efficient utilization of coal resources. © 2020 Society of Chemical Industry

Effect of Swelling Treatment by Organic Solvent on the Structure and Pyrolysis Performance of the Direct Coal Liquefaction Residue

Five organic solvents, N-methyl-2-pyrrolidone (NMP), cyclohexanone (CYC), N,N-dimethyl­formamide (DMF), acetonitrile (ACN), and toluene (TOL) were used to treat Shenhua direct coal liquefaction residue (DCLR) by swelling processes. The treated residues were characterized by swelling degree (Q), SEM, FTIR, TG-DTG, and Py-GC/MS methods. The effect of swelling treatment on the swelling properties, surface morphology, functional group distribution, and pyrolysis performance of the residues was investigated. Swelling results showed that the swelling effect with different solvents on each residue was different and that the swelling degree of the residue treated by NMP was high, 2.4. Swelling treatment could significantly change the surface morphology and pore structure of DCLR, resulting in the increase of pores in the residue. FTIR spectra proposed that swelling treatment could effectively break the hydrogen bonds in residue and change the abundance of oxygen-containing functional groups. TG-DTG profiles demonstrated that the swelling procedure could increase the weight loss and pyrolysis rate of the residue, and the pyrolysis activation energy in high-temperature region (≥360 °C) was obviously reduced, while the energy in the low-temperature region (120–360 °C) was increased. Py-GC/MS proposed that the swelling pretreatment could change the pyrolysis product distribution of the residue, with the species of the products decreased, and that ketones and arenes compounds were the main products.

Effects of Direct Coal Liquefaction Residue Additions on Low-Rank Pulverized Coal during Co-Pyrolysis

This study examined the co-pyrolysis characteristics of low-rank coal (SJC) and direct coal liquefaction residue (DCLR) through thermogravimetric analysis coupled with Fourier transform infrared spectrometry. It also investigated the influences of different mass fractions of DCLR to SJC on the co-pyrolysis characteristics and release regulation of gas phase components. Results showed that with increasing DCLR content, coke yield initially decreased and then increased, but tar and gas yield reversed. Different addition of DCLR changed the composition of the pyrolysis gas in various degrees, and reduced the content of-OH and nitrogen compounds in coke. The H2 content in the gas gradually increased. When 40% DCLR was added, the maximum tar yield was 22.79%, and the maximum H2 yield was 37.12%. At 60% DCLR, the lowest semi-coke yield was 65.01%, and the highest gas yield was 14.65%. The co-pyrolysis of SJC and DCLR can be divided into three stages. The first was the dry degassing stage, during which the adsorbed gas and small-molecule gas were removed on the coal surface at room temperature to 350 °C. The second stage (350 °C–650 °C) was the intense pyrolysis reaction stage, during which a large number of volatiles were obtained. The substantial weight loss rate peak appeared around 450 °C. The weight loss rate of pyrolysis gradually increased with increasing DCLR dosage. The co-pyrolysis of SJC and DCLR was not a simple sum between SJC and DCLR, which indicated a synergistic effect in the co-pyrolysis. The synergistic effect between SJC and DCLR enhances the interaction between free-radical fragments, thereby increasing the yield of pyrolysis tar. The third stage was the shrinkage of semi-coke from 650 °C to the end of the reaction. The polycondensation reaction between free-radical fragments to form solid coke with higher aromaticity, and H2 released.

Measurement of coal pyrolysis reaction heat by empirical baseline method

ABSTRACT Pyrolysis can be considered as the initial stage or/and paralleling part of coal combustion, gasification, and direct liquefaction, and pyrolysis itself constitutes one of the fundamental technologies in coal conversion. Reaction heat of coal pyrolysis is an important thermodynamic parameter used in reactor design, mechanism study, and energy efficiency assessment. In this study, thermogravimetric & differential scanning calorimetry technique (TG-DSC) was exploited to determine and plot the total heat flux curve along with pyrolysis temperature of Shenmu coal sample, and the varying curves of heat flux baselines in different reaction areas were analyzed and discriminated by empirical method, then the coal pyrolysis reaction heat was figured out. Moreover, the effects of primary test parameters on coal pyrolysis reaction heat were investigated. Results show that during the measurement rational settings including open crucible, ca. 15 mg sample amounts and – 0.074 mm particle size and 80 ml/min carrier gas flows could eliminate both internal and external diffusion effects and help to reduce secondary reactions of coal pyrolysis and heat resistance. When the heating rate increases from 3°C/min to 20°C/min, the total pyrolysis reaction heat of Shenmu coal sample shows an upward trend. Low hysteresis effect of heat transfer and high resolution of heat effect could be observed when the heating rate is 5°C/min, and the reaction heat measured is −12985 J/g, which can objectively express the reaction heat of coal pyrolysis. It could be concluded that coal pyrolysis reaction heat can be conveniently measured by the empirical baseline method with TG-DSC technique.

Rutting resistance of direct coal liquefaction residue (DCLR) modified asphalt mixture under variable loads over a wide temperature range

This research aims to investigate the rutting resistance of Direct Coal Liquefaction Residue (DCLR) modified asphalt mixture under variable loads over a wide temperature range. The SK-90 asphalt mixture and Styrene-Butadiene-Styrene (SBS) modified asphalt mixture were selected as comparisons. The rutting resistance of these three mixtures was studied by the rutting test with temperature of 30–70 °C under variable loads of 0.7–1.0 MPa. Meanwhile, the double factor variance analysis was performed to study the effect of temperature and load on the rutting resistance of mixtures, and the radar analysis was applied for comprehensive evaluation on the rutting resistance as well. The results demonstrate that the rutting resistance of mixtures presents a negative linear correlation with the load or the temperature. Comparing load, the temperature shows a more significant influence on the resistance to rutting of mixtures. Under the coupling effect of temperature and load, the DCLR modified asphalt mixture had higher values of Va, Vb, WL and WT than the other two mixtures. Therefore, among these three mixtures, the DCLR modified asphalt mixture owns the best stable rutting resistance, which gives the least sensitivity and dependence on the temperature and load.

Development of a skeletal surrogate mechanism for emulating combustion characteristics of diesel from direct coal liquefaction

A surrogate describing the oxidation characteristics of Diesel from direct coal liquefaction (DDCL) was proposed in this work. n-dodecane and decalin were chosen as representative species of alkane and cycloalkane hydrocarbons in DDCL according to compositional analysis results. A proportion of 24.6% n-dodecane and 75.4% decalin by mole was determined by emulating real DDCL properties including Cetane number (CN), Hydrogen-Carbon (H/C) ratio, lower heating value (LHV) and density. Sub-mechanisms of n-dodecane and decalin were constructed on top of a detailed C0C6 core mechanism and then sensitivity analysis was used to eliminate unimportant species and reactions. The final version of the skeletal DDCL surrogate mechanism consists of 131 species and 461 reactions. The skeletal mechanism was extensively validated against experimental data including ignition delay times, species concentration profiles and laminar flame speeds for each pure component. Furthermore, diesel engine experiments fueled with DDCL were conducted and the corresponding 3-D CFD simulation results show that the present skeletal mechanism gives reliable performance for combustion behavior as well as NOx and CO emissions predictions, indicating the proposed mechanism can be applied for modeling DDCL in practical engine applications.

Room-Temperature Solid-State Preparation of CoFe2O4@Coal Composites and Their Catalytic Performance in Direct Coal Liquefaction

Iron-based catalysts are promising catalysts in the direct coal liquefaction (DCL) process as they are inexpensive and environmentally friendly. However, most such iron-based catalysts show relatively low activity in coal conversion and oil yield. Common techniques for the synthesis of these catalysts with excellent catalytic performance remain a substantial challenge. We present a simple solid-state synthesis strategy for preparing CoFe2O4 nanoparticles and CoFe2O4 nanoparticles supported on coal (CoFe2O4@coal) composites for DCL. The obtained bimetallic oxide CoFe2O4 nanoparticles show an enhanced catalytic performance in the DCL compared with monometallic components Fe2O3 and Co(OH)2 nanoparticles. The synergistic effect between Co and Fe of CoFe2O4 nanoparticles promotes the catalytic hydrogenation of coal during the DCL process. Moreover, the catalytic performance of CoFe2O4 nanoparticles is further improved when they are loaded on the coal. The conversion, oil yield, liquefaction degree, and gas yield of Dahuangshan lignite are 99.44, 56.01, 82.18 and 19.30 wt %, respectively, with the CoFe2O4@coal composites involved. The smaller particle size and high dispersion of CoFe2O4 supported on coal are of great benefit to full contact between coal and active components. The in-situ solid-state synthesis with coal as support shows great potential to prepare effective iron-based catalysts toward DCL in practice.

Recycling Molybdenum from Direct Coal Liquefaction Residue: A New Approach to Enhance Recycling Efficiency

In this paper, direct coal liquefaction residue was prepared from Shen-dong coal, and the solubility of the residue in five organic solvents was studied. Then, an experimental device was set up to recover molybdenum (Mo) compounds from the direct coal liquefaction residue after extraction, and the influences of sublimation temperature and duration on recycling efficiency were examined. The recycled Mo-based products were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and a thermal analyzer. The results reveal that the optimum extraction conditions were obtained through ultrasonic extraction with a quinoline solvent and the highest recycling efficiency occurred for sublimation at 900 °C for 30 min. The recycled products are identified to be α-MoO3 crystals. Moreover, the α-MoO3 crystal is thermally stable before the temperature reaches its melting point.

Five-stage sequential extraction of Hefeng coal and direct liquefaction performance of the extraction residue

Ultrasonic-assisted extraction (UAE) and direct liquefaction of the corresponding residue were conducted on an acid-washed ashless Hefeng bituminous coal (HBCAW). Petroleum ether (PE), carbon disulfide (CDS), methanol (MeOH), acetone and isometric CDS/acetone mixture (IMCDSAM) were used to sequentially extract HBCAW via UAE to obtain extracts (E1–E5). Gas chromatograph/mass spectrometer (GC–MS) analysis showed that most of the free molecules were extracted in the first two stages, and E1 and E2 were mainly consisted of aliphatics and alkanes. PE presented a strong extraction ability for the low polar compounds, and the average molecular weight of E2 was higher than E1. While E3 is more varied containing more complex molecules than E1 and E2. IMCDSAM was more favorable for the diffusion and dissolution of alcohols. Direct liquefaction performance suggested that the oil yields of Hefeng bituminous coal (HBC), HBCAW and the fifth stage extraction raffinate (ER5) were 66.00%, 63.57% and 44.11%, respectively, and that the conversion of ER5 was only 69.67%, much lower than HBC and HBCAW (82.75% and 82.68%). Higher yield of gaseous product for ER5 might be resulted from the looser coal structure by UAE process, resulting in more small molecules during the direct coal liquefaction.

Coal and waste direct liquefaction, using glycerol, polyethylene waste and waste tyres pyrolysis oil. Optimisation of liquids yield by response surface methodology

Coal and waste direct liquefaction was carried out to decrease the hydrocarbons production negative bearing to environment. The wastes studied were glycerol, polyethylene waste and waste tyres pyrolysis oil. Glycerol and waste tyres pyrolysis oil were blended with tetralin and used as solvent for coal direct liquefaction (T = 350–450 °C; N2; waste:tetralin at different weight ratios). Glycerol may be considered as a waste from the production of fatty acid methyl esters (FAME). Waste tyres pyrolysis oil showed to be a good hydrogen donor solvent. Solid polyethylene wastes were mixed with coal and used in coal co-liquefaction tests, which showed to be a good option to produce liquid hydrocarbons for fuels or raw materials for chemical industry. Although liquids yield using waste tyres pyrolysis oil or glycerol were high, respectively 62% wt. and 51% wt., the use of polyethylene allowed increasing them to 80% wt. Different experimental conditions were studied, namely: experimental temperature, run time, solvent type and composition and hydrogen initial pressure. The effect of commercial catalysts on co-liquefaction was also studied and the results obtained were compared with those obtained with coal impregnated with Fe or Mo (1% wt./coal). Response surface methodology (RSM) was used to predict the influence of the main experimental conditions studied on product yields. This methodology resulted to be a good one to predict coal liquefaction and co-liquefaction products yields, as predicted values were similar to experimental data. In addition, RSM approach led to the selection of tetralin as solvent and to the use of coal impregnated with 1% of Mo, as liquids yield increased up to 96% wt.

Desulfurization Performances of Activated Coke Prepared from Fine Blue-Coke

Activated coke was prepared by CO2 activation using solid waste fine blue-coke as main raw material and coal direct liquefaction residue (DCLR) as binder. The activated coke was characterized by BET, XRD, and infrared analysis. The flue gas desulfurization experiment was carried out with a fixed bed reactor and activated coke as the adsorbent. The experimental results show that coal direct liquefaction residue pyrolysis process will produce a large number of cohesive colloids, further increasing the strength of the activated coke. BET analysis shows that there is abundant microporous structure in the activated coke, infrared analysis shows that the activated coke contains abundant surface functional groups, and XRD shows that the crystallization degree of the activated coke is high. At lower temperature, SO2 and O2 have competitive adsorption on the surface of activated coke, if the concentration of water vapor is too high, a water film will be formed on the surface of activated coke, which will hinder the adsorption of SO2 by activated coke. The initial concentration of SO2 is 700 ppm, the adsorption temperature is 80 °C, the oxygen concentration is 9%, and the concentration of water vapor is 8%. The removal of SO2 by activated coke is better, and the desulfurization rate reaches 97%.

Behaviors of hydrogen bonds formed by lignite and aromatic solvents in direct coal liquefaction: Combination analysis of density functional theory and experimental methods

Hydrogen bonds play a crucial role in thermal conversion of low rank coal, especially direct coal liquefaction (DCL) because of their wealthy abundance and great influence on generation of light products. Relative distribution of hydrogen bonds was evaluated with in-situ diffuse reflectance infrared Fourier transformation (DRIFT), while visualization analysis of hydrogen bonds (OH-π in particular) between coal and solvents were performed using density functional theory (DFT) and reduced density gradient (RDG) analysis. In terms of their effects, DCL experiments of demineralized Yunnan lignite (DeYN) with/without addition of benzene at 200, 250 and 300 °C were carried out, and oxygen-containing functional groups were investigated by solid-state 13C NMR and in-situ DRIFT. Relative content of OH-π hydrogen bonds increased with temperature rising. Benzene is the stronger hydrogen bonds acceptor compared to tetralin (THN). Conclusions drawn from DCL experiments are consistent with DFT calculations. To be specific, benzene with mass concentration of 2% promotes cleavage of O–H bonds, carboxyl groups and the generation of aryl ether bonds, and the differences caused by benzene are intensified when DCL temperature rises.

Analysis of distillate product in the direct coal liquefaction of a Chinese bituminous coal

Analysis of distillate product in the direct coal liquefaction of a Chinese bituminous coal

Preparation of polyacrylonitrile based carbon nanofibers by electrospinning with different additives from direct coal liquefaction residue

Direct coal liquefaction residue is of valuable materials for preparation of carbon materials due to its high carbon content and aromatic structures. In this work, extract, extraction residue, and oxidized extraction residue from direct coal liquefaction residue were employed as additives for preparation of polyacrylonitrile based carbon nanofibers by electrospinning, followed by air stabilization and carbonization processes. The results show that the additives were evenly dispersed in the carbon nanofibers, and the diameters of nanofibers were smaller than that pure polyacrylonitrile based carbon nanofibers. After the extraction residue was pretreated with hydrogen peroxide, the morphology of nanofibers became more smooth and uniform.

Investment in carbon dioxide capture and storage combined with enhanced water recovery

Carbon dioxide capture and storage combined with enhanced deep saline water recovery (CCS-EWR) is a potential approach to mitigate climate change. However, its investment has been a dilemma due to high costs and various uncertainties. In this study, a trinomial tree modelling-based real options approach is constructed to assess the investment in CCS-EWR retrofitting for direct coal liquefaction in China from the investor perspective. In this approach, the uncertainties in CO2 prices, capital subsidies, water resource fees, the residual lifetime of direct coal liquefaction plants, electricity prices, CO2 and freshwater transport distance, and the amount of certified emission reductions (CERs) are considered. The results show that the critical CER price for CCS-EWR retrofits is 7.15 Chinese yuan per ton (CNY/ton) higher than that (141.95 CNY/ton) for CCS retrofits. However, the exemption from water resource fees for freshwater recovered from saline water and a subsidy of 26% of the capital cost are sufficient to eliminate the negative impact of enhanced deep saline water recovery (EWR) on the investment economy of CCS-EWR. In addition, when the residual lifetime is less than 14 years, CCS-EWR projects are still unable to achieve profitability, even with flexible management and decision making; therefore, investors should abandon CCS-EWR investments. On the whole, the investment feasibility for CCS-EWR technology is not optimistic despite access to preferential policies from the government. It is necessary to establish a carbon market with a high and stable CER price.

Flow properties of ash and slag under co-gasification of coal and extract residue of direct coal liquefaction residue

Efficient utilization of the extraction residue (ER) of direct coal liquefaction residue is a bottle neck for the efficiency of direct coal liquefaction process. The co-gasification of the ER and coal is a promising way for large-scale utilization of ER. Flow properties of the feedstock including ash fusibility and slag viscosity are important parameters for the gasification process. To optimize co-gasification of the ER and coal, the ash fusibility and slag viscosity behavior of ER and coal under gasification conditions were studied. The results show that the ash fusion temperatures (AFTs) of the blending were lowered with the increasing blending ratio of ER due to the high content of calcium and iron in ER. The content of quartz and anorthite in the blended ashes decreased with the increasing ER blending ratio. The slag viscosities at high temperatures also decreased as the blending ratio of ER increased. The high content of calcium and iron in ER resulted in the decrease in the slag polymerization degree because of the break of Si-O structure and transformation from [AlO4]5− to [AlO6]9−. Besides, the slag presented the behavior of a crystalline slag when the ER blending ratio was increased up to 25% for the formation of anorthite during cooling. For the entrained flow gasification, the ER addition can effectively lower the operation temperature of the gasifiers, improve the gasification efficiency and avoid the slag tapping problems. The optimal ER addition should be in the range of 10–20%, and the corresponding tapping temperature was 1258–1575 °C.

Influence of the Direct Coal Liquefaction Residue on the Fusion Characteristics of Jincheng Coal with a High Ash Fusion Temperature

Nowadays, entrained flow bed gasification technology is the foundation of the modern coal chemical industry, while its liquid slag discharge process generally requires the flow temperature (FT) of ...