Direct Coal Liquefaction Process Research Articles

Theoretical analysis of hydrogen solubility in direct coal liquefaction solvents

The cyclic hydrogenation technology in a direct coal liquefaction process relies on the dissolved hydrogen of the solvent or oil participating in the hydrogenation reaction. Thus, a theoretical basis for process optimization and reactor design can be established by analyzing the solubility of hydrogen in liquefaction solvents. Experimental studies of hydrogen solubility in liquefaction solvents are challenging due to harsh reaction conditions and complex solvent compositions. In this study, the composition and content of liquefied solvents were analyzed. As model compounds, hexadecane, toluene, naphthalene, tetrahydronaphthalene, and phenanthrene were chosen to represent the liquefied solvents in chain alkanes and monocyclic, bicyclic, and tricyclic aromatic hydrocarbons. The solubility of hydrogen X (mol/mol) in pure solvent components and mixed solvents (alkanes and aromatics mixed in proportion to the chain alkanes + bicyclic aromatic hydrocarbons, bicyclic saturated aromatic hydrocarbons + bicyclic aromatic hydrocarbons, and bicyclic aromatic hydrocarbons + compounds containing heteroatoms composed of mixed components) are determined using Aspen simulation at temperature and pressure conditions of 373–523 K and 2–10 MPa. The results demonstrated that at high temperatures and pressures, the solubility of hydrogen in the solvent increases with the increase in temperature and pressure, with the pressure having a greater impact. Furthermore, the results revealed that hydrogen is more soluble in straight-chain alkanes than in other solvents, and the solubility of eicosanoids reaches a maximum of 0.296. The hydrogen solubility in aromatic ring compounds decreased gradually with an increase in the aromatic ring number. The influence of chain alkanes on the solubility of hydrogen predominates in a mixture of solvents with different mixing ratios of chain alkanes and aromatic hydrocarbons. The solubility of hydrogen in mixed aromatic solvents is less than that in the corresponding single solvents. Hydrogen is less soluble in solvent compounds containing heteroatoms than in compounds without heteroatoms.

Investigation of the mechanism of solvothermal extraction of direct coal liquefaction residue by macromolecular models

Direct coal liquefaction residue (DCLR) is an industrial by-product from the direct coal liquefaction process. It has the unique characteristics of high carbon, high sulfur and high ash content, strong cohesiveness and low softening point, which makes DLCR a potential raw material. However, direct discharge of untreated DCLR can cause severe damage to environment and human body. Thus it is of great importance to utilize DCLR properly. In this study, solvothermal extraction of direct coal liquefaction residue (DCLR)was treated with N-methyl-2-pyrrolidone (NMP) and 1-methyl naphthalene (1-MN). In addition, molecular models of DCLR and two hypercoals (HPC: NMP-HPC, MN-HPC) were built to clarify the extraction mechanism, aiming to provide a technically feasible route to utilize DCLR and investigate the adaptation between extractant and raw materials. The structural parameters were obtained by means of industrial and elemental analysis, 13C NMR, XPS and FTIR. Subsequently, macromolecular structure models were constructed, with simulated molecular formulas C153H108N2O10S, C206H168N6O7 and C278H202N2O13S, respectively. After modifying the macromolecular models by Materials Studio for geometric optimization, annealing dynamics calculation, density simulation and analysis of chemical bonds and charge layout, these models reflected the macromolecular structural characteristics precisely. On the other hand, DCLR model underwent significant changes in functional groups, branched chain length and quantity pre and post solvothermal extraction, indicating that the thermal extraction process was mainly affected by swelling behavior and pyrolysis. Meanwhile the principles of the two extractants were also different.1-MN extraction was a heat-induced relaxation, while NMP extraction was heat & solvent-induced relaxation process. This study will be helpful in expanding the utilization of DCLR and understanding of mechanism of solvothermal extraction on the macromolecular level based on modeling.

Process study and CO2 emission reduction analysis of coal liquefaction residue fluidized bed pyrolysis

The direct coal liquefaction process usually produces a liquefaction residue of about 30% of its coal feed. The effective utilization of the coal liquefaction residue (CLR), which contains about 80% organic matter, is of great significance for improving the oil yield of the direct liquefaction process and reducing the amount of pollution emitted from this oil-containing organic solid waste. In this study, the CLR fluidized bed pyrolysis process was studied through a fluidized bed reactor pyrolysis experiment and steady-state thermal analysis. The characteristics of CLR were first analyzed, and then the pyrolysis experiment was conducted in a fluidized bed reactor system. The experiment results show that the oil yield is 34.81% at 540°C for an ash-free feedstock using a fluidized bed pyrolysis reactor. Based on the pyrolysis experimental data and the Aspen Plus software platform, the fluidized bed pyrolysis reactor, fractionation column, coke burner, gasifier, and other equipment were modeled to compare four different process schemes. CLR pyrolysis is an endothermic reaction, and its heat is usually supplied by coke combustion, which produces significant CO2 emissions. Case studies of the pyrolysis process were performed in detail in order to reduce CO2 emissions. Thermal efficiency, carbon efficiency, solid waste discharge, and CO2 emissions of the different schemes were compared, and a flexible fluidized pyrolysis (FFP) process coupled with water electrolysis was proposed. The introduction of green hydrogen and green oxygen to the process can realize near-complete utilization of carbon and hydrogen elements in the CLR and produce high-quality liquid fuels and syngas (for further chemical synthesis), and this new process can achieve almost near-zero CO2 emission in the entire unit. This process principle can also be applied to the CO2 emission reduction of organic solid waste pyrolysis, catalytic fluid cracking, fluid coking, and so on.

Preparation of hot-pressed coal briquette with the extract from direct coal liquefaction residue

Direct coal liquefaction residue (DCLR) is an industrial by-product from the direct coal liquefaction process. It is harmful to the environment and the human body when directly charged or used due to the high content of sulfur, ash, and polycyclic aromatic hydrocarbons (PAHs). Therefore, it is of great importance to treat and utilize DCLR. In this paper, the thermal extraction method was applied to extract DCLR with N-methylpyrrolidone (NMP), and the hot-pressed coal briquette (HPCB) was prepared with DCLR extract and anthracite powder. DCLR and its extract and residue were characterized by TG, FTIR, and GC-MS. The ash content was decreased from 11.72% to 0.72% and the sulfur content was decreased from 1.72% to 0.09% after thermal extraction. TG analysis shows that the weight loss of the extract was about 30.4% higher than that of the residue during the pyrolysis process, indicating that the extract contained more light components. FTIR analysis shows that the thermal extraction process had strong extraction capacity for aliphatic hydrocarbons and aromatic hydrocarbons, but weak extraction capacity for carboxyl, phenol, or alcohol groups. GCMS shows that 60.6% of the volatile substances in the extract were PAHs, while the residue had only 6.8% of PAHS. It is proven that the residue has been rendered harmless to humans and the environment. Moreover, the HPCB with a compressive strength exceeding 2.5 MPa was prepared by using the DCLR extract as a binder and anthracite powder as a raw material. It has the potential and advantages of being used as a metallurgical raw material.

In-situ catalytic gasification of sodium-rich direct coal liquefaction residue under CO2 atmosphere and kinetic analysis of gasification reaction process

Due to attractive features, such as low mineral matter content and strong reactivity, sodium-rich coals are viewed as suitable raw materials for direct coal liquefaction technology. After direct coal liquefaction process, the inherent sodium species in sodium-rich coals will be enriched in direct coal liquefaction residue. In this work, to provide potential guidance for better utilization of sodium-rich direct coal liquefaction residue, catalytic effects of the inherent sodium species on gasification reactivity of sodium-rich direct coal liquefaction residue and kinetic analysis of gasification reaction process were investigated in detail. The results show that inherent sodium species has obvious catalytic effects on gasification of sodium-rich direct coal liquefaction residue. Compared with that for demineralized direct coal liquefaction residue, the time for sodium-rich direct coal liquefaction residue to be completely gasified at 1000 °C and 1100 °C was shortened by 82% and 70%, respectively. With the increase of gasification temperature, CO2 gasification reactivity of all types of direct coal liquefaction residue was enhanced. For instance, gasification reactivity indexes (R0.5) of sodium-rich direct coal liquefaction residue are 0.06 min−1, 0.15 min−1, and 0.23 min−1 at 900 °C, 1000 °C, and 1100 °C, respectively. Kinetic analyses indicate that linear correlation coefficients obtained by homogeneous model and shrinking core model are on high levels and they are closely related with gasification temperature and residue type. According to calculation of homogeneous model and shrinking core model, activation energies of demineralized direct coal liquefaction residue are 78.60 kJ/mol and 73.73 kJ/mol, respectively. In contrast, the corresponding activation energies of sodium-rich direct coal liquefaction residue are 75.42 kJ/mol and 71.55 kJ/mol, which proves that activation energy required for gasification of direct coal liquefaction residue can be reduced by the inherent sodium species. To conclude, catalytic coal gasification may be potentially efficient to process sodium-rich direct coal liquefaction residue.

Techno-economic analysis of a solar thermochemical cycle-based direct coal liquefaction system for low-carbon oil production

Direct coal liquefaction turns solid coal into transportable liquid fuel with a high energy conversion efficiency of nearly 60%. However, the hydrogen used in the direct coal liquefaction process mainly comes from coal gasification units, and gasification coal consumption accounts for about 30% of the total coal consumption. The authors of this article have proposed a solar thermochemical cycle-based direct coal liquefaction system and conducted a corresponding thermodynamic analysis. In this work, the economic feasibility, environmental impact, and the influence of key factors (coal price, oil price, carbon tax) for the industrial-scale low-carbon oil production system are analyzed. Compared with the traditional direct coal liquefaction system, the total coal consumption of the new system is reduced by ∼40%. Under low carbon constraints, the economics of the new system is comparable to that of the traditional one with a lower solar thermochemical hydrogen production cost (<13–16 yuan/kg H2). With the help of the solar thermochemical hydrogen production process, CO2 emissions of the new system can be reduced by 63%. Moreover, the solar thermochemical cycle could generate additional pure oxygen and profits. The methodology and results can provide important references for coal-to-liquid technology with high efficiency and low carbon emissions.

Structural changes of Zhundong coal matrix induced by thermal treatment and its effects on oil yield in direct coal liquefaction

Sodium-rich coals are suitable raw materials for direct coal liquefaction (DCL). However, sodium species in coals, especially exchangeable ones, can significantly reduce oil yield. In this work, to increase oil yield in direct liquefaction of sodium-rich coals, a feasible method using organic solvents to pretreat sodium-rich coals is proposed. Initially, sodium-rich coal was thermally treated with tetralin or 1-methylnaphtalene. Then, raw coal and all the treated coals were liquefied under the same conditions to evaluate the effects of thermal treatment on structural changes of coal molecules and oil yield. The results show that surface areas of the treated coals increased to 7.86 m2/g at most, which was favorable for combination between hydrogen and coal molecules during the DCL process. More importantly, the content of hydrogen in the treated coals was 0.95 wt% higher than that of raw coal on average, suggesting that treated coals could be later liquefied at mild conditions. Raman spectra demonstrated that during thermal treatment with tetralin, small aromatic ring systems in raw coal were prehydrogenated and transformed into nonaromatic systems. The pre-hydrogenation of the coal matrix definitely contributes to the increase in oil yield. In view of sodium species distribution in the treated coals, it is proved that tetralin can promote the transformation of exchangeable sodium species into other chemical forms more easily than 1-methylnaphtalene, which implies that tetralin has more positive effects on the increase of oil yield. Compared with that of raw coal, oil yields in direct liquefaction of the samples treated by tetralin increase by 14.0 to 15.1 wt% (daf).

Experimental study on sooting characteristics of a direct coal liquefaction derived jet fuel and its blend with RP-3 jet fuel

Alternative jet fuel from direct coal liquefaction (DCL) process is of critical importance to meet the energy goals of both military and civil aviation. Soot emission is a critical issue for the promotion of airworthiness certification process of jet fuels. In this work, a systematic evaluation of sooting characteristics is conducted for the DCL derived jet fuel together with RP-3 jet fuel and their 50/50 blend. Experiments are performed in a shock tube facility at conditions of 3.0 bar, 1700 to 2300 K and equivalence ratios of 5, 20, and infinity (pyrolysis) diluted in argon. The effect of pressure on sooting characteristics of the DCL derived jet fuel is also investigated. Soot induction time and soot yield are obtained by measuring the soot-induced laser extinction signal. The effects of temperature, pressure and equivalence ratio on soot induction times and soot yields are then systematically analyzed. Detailed comparisons of the soot induction times and soot yields are performed. This work provides quantitative experimental data set of soot formation properties for alternative jet fuels that can be used for combustion kinetic model development and validation. The experimental data is also valuable for the airworthiness certification process of the DCL derived jet fuels.

Dissolution behavior of hydrogen in the model recycle solvent of mild direct coal liquefaction

Direct coal liquefaction (DCL) at mild conditions (about 693 K and less than 10 MPa) is an important and efficient way for the conversion of coal to high value-added chemicals and fuel oil. In the process of DCL, the pre‑hydrogenation of a recycle solvent is an important step and the recycle solvent is always heated from low temperatures to high temperatures. So, it important to study the dissolution behavior and the migration of hydrogen in the recycle solvent for DCL processes, especially for mild DCL processes. First, physical solubility of hydrogen in a model recycle solvent of naphthalene and 1,2,3,4-tetrahydronaphthalene was measured, and the Henry's constants at different temperatures were obtained. Then, the chemical solubility of hydrogen (chemical bonded hydrogen via hydrogenation of naphthalene to 1,2,3,4-tetrahydronaphthalene) in the recycle solvent was measured simultaneously. The equilibrium constants of the hydrogenation reaction at different temperatures were obtained. Finally, through the physical solubility of hydrogen and chemical solubility of hydrogen, the dissolution and migration of hydrogen in the recycle solvent were analyzed. When the temperature is increased, the physical solubility of hydrogen increases, the chemical solubility of hydrogen decreases, the total solubility of hydrogen decreases due to the dominant contribution of chemical solubility of hydrogen, and interestingly a small part of hydrogen released from 1,2,3,4-tetrahydronaphthalene is transferred to physical solubility. When the pressure is increased, the chemical solubility of hydrogen, the physical solubility of hydrogen and the total solubility of hydrogen all increase

In-situ impregnation of β-FeOOH on coal by solid-state reaction toward direct coal liquefaction

Herein, β-FeOOH nanoparticles supported on coal (β-FeOOH@C) were prepared by a solid-state in-situ impregnation and tested for the direct coal liquefaction (DCL) process. The β-FeOOH nanoparticles with ~10–50 nm were uniformly loaded over coal through a solid-state reaction among ferrous chloride, sodium hydroxide and coal. The obtained β-FeOOH@C solid showed enhanced catalytic performance for DCL compared with unsupported β-FeOOH nanoparticles. The conversion and oil yield achieved by β-FeOOH@C were 92.88 and 48.78% in the catalytic liquefaction of Dahuangshan lignite. The solid-state in-situ impregnation with coal as support shows great potential to prepare effective iron-based catalysts toward practical DCL.

Kinetic modelling of low temperature direct coal liquefaction: Consideration of dynamic catalyst activity

A kinetic model for direct coal liquefaction at low temperature in the presence of a magnetite nano-catalyst was developed. The model took into account the iron oxide catalyst transformation into its active state as well as the process of reactive dissolution of coal at the reduced temperatures. The validity of the model was tested by performing a regression on experimentally obtained data for the direct coal liquefaction process. The experiments were performed in a high-pressure batch reactor, with medium to low ranking coal, using synthesised magnetite nano-catalysts and within the temperature range of 240 °C to 320 °C. This temperature range is known to be below that required for thermolysis of the coal. The model was able to qualitatively capture the general trends of the experimental data. The regression indicated that the depolymerisation reactions of the dissolved moieties directly into key products occur more rapidly than the reactions of key product groups, which is a typical occurrence in lower rank coals.

Residues characteristics and structural evolution of Naomaohu coal during a mild direct liquefaction process

Direct coal liquefaction (DCL) is an important way of coal conversion and is important to the global energy industry. In this paper, a typical liquefied coal–Naomaohu coal (NMHC)–was liquefied under mild conditions (400 °C, initial H2 pressure of 3 MPa), and a NMHC conversion of 90.6% was obtained with an oil+gas yield of 65.1%. In the DCL process, the solid particles of coal and its residues are not only reactants but also carriers of catalysts of DCL. To study the structural characteristics of these residues, the reaction mixture was extracted with n-hexane and tetrahydrofuran (THF), separately, yielding n-hexane insoluble residues (ReHEIS) and THF insoluble residues (ReTHFIS). Several patterns of the reaction progresses were identified. First, the particle sizes of ReHEIS and ReTHFIS have a decreasing trend, and the particle surface becomes loose and porous while raw coal has a relatively flat surface. Second, most of the aliphatic structure and some small aromatic compounds can gradually split off from coal skeleton structure, and the condensation degree of aromatic clusters in residues increases with the aromatic condensation degree of ReTHFIS being higher than that of ReHEIS. Third, the contents of carbonyl carbon and oxygen-attached carbon decrease while methylene chain and side chain of aromatic clusters are broken. Lastly, the aromatic structure of ReTHFIS becomes regular, and the graphitization degree increases, while the pyrolysis rate slows down. These results of element analysis show that the H/C of ReHEIS is larger than that of ReTHFIS, which implies that preasphaltene and asphaltene are relatively rich in hydrogen.

Kinetic study of CO 2 gasification on coal char and extraction residue char from direct coal liquefaction

Extraction residue (ER) is, in this study, considered as an insoluble portion derived from a novel extraction process with direct coal liquefaction residue, which is the byproduct from 1000 kton/y direct coal liquefaction and oil production process in Ordos, China. ER mostly consists of unreacted coal and minerals, spent catalyst, and solvent. It is considered as a hazardous waste in China. Gasification is a promising way to employ ER, as the carbon resource contained in it could be adequately utilized, so strongly reducing the environmental impact of this material. In this paper, a kinetic study is carried out concerning CO2 gasification (in thermobalance) of ER char, coal char, and their blends. The results show that, at temperatures ranging from 1123 to 1323 K, the reactivity of ER char is much larger than that of coal char, and the reactivity of ER/coal char blends increases when the ER fraction increases, consistently resulting in between the reactivities shown by ER char and coal char alone. The partial pressure of CO2 promotes the reactivity of all samples. BET surface area resulted three times larger for ER char vs coal char, while pore surface area and pore volume were four times larger. Moreover, the relevant parameters of the random pore model for CO2 gasification of ER char, coal char, and their blend #2 (with 20% ER) were obtained; the activation energy resulted 210.6, 240.5, and 232.8 kJ/mol, and the reaction order 0.30, 0.45, and 0.40, respectively.

Super hard asphalt (SHA) from direct coal liquefaction process as pavement material

Super hard asphalt (SHA) as a black and solid material at ambient temperature is a byproduct of direct coal liquefaction process, which mainly generates clean liquid fuels from coal and is one of the clean-coal technologies. Firstly this paper introduced how the SHA is produced, its physical properties, chemical compositions, as well as its influence to the environment. Then, the opportunities and challenges of using SHA as pavement material were discussed, including three challenges and three corresponding technologies. Lastly, the progresses for SHA based asphalts were illustrated, in which two asphalt modifiers (SHA-N and SHA-S) were produced from SHA using in-situ micro crosslink technology. Then two SHA-based modified asphalts were manufactured at an industrial scale. The performance grades were classified as PG 82–22, which present excellent high and low temperature performance. Thereafter one 1.2 km test road was paved by the road pavement asphalt using the SHA-N-based modified asphalt under AC-13C gradation as the top layer of G110 national highway in Yinchuan. The other 0.9 km test road was paved using the SHA-S modified asphalt under AC-20 gradation in the middle layer of G69 expressway in Chongqing. The field data shows that the performance of asphalt mixtures and pavements after paving is excellent. The long-term performance of the test roads will be followed.

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.

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.

Room-temperature extraction of direct coal liquefaction residue by liquefied dimethyl ether

Direct coal liquefaction residue (DCLR) is the main byproduct during the direct coal liquefaction process. The efficient recovery of organic components from DCLR at low temperatures is beneficial for improving the economy and reducing energy consumption and environmental pollution. Here, DCLR was extracted using liquefied dimethyl ether (DME), acetone, and hexane as the solvents. Compared with the other two solvent Soxhlet extraction, the DME extraction process was performed at room temperature with the shortest extraction time, the lowest energy consumption, and the highest extraction yield (16.2%). Owing to the high carbon contents, low sulfur and oxygen contents, and low ash contents (<0.1%), the extracts obtained using liquefied DME and acetone naturally became the feedstock of carbon materials. Based on the results of the gas chromatography-mass spectrometry analysis, the extracts obtained using the three different solvents had similar compositions in light compounds and were abundant in polycyclic aromatic hydrocarbons with two-, three-, four-, five-, and six-membered benzene rings, indicating that all three DCLR extracts are potential raw materials for preparing high value-added carbon materials. Furthermore, the molecular composition analysis revealed that the room-temperature extraction using liquefied DME was as good as high-temperature Soxhlet extraction using acetone, considering the similarity of their compositions in high molecular weight species and the considerably higher efficiency than that of high-temperature Soxhlet extraction using hexane. Due to the low energy consumption, short extraction time, high extraction yield, and high performance of the extract, liquefied DME is an efficient and economic solvent for extracting DCLR.

The factors on metallic iron crystallization from slag of direct coal liquefaction residue SiO2-Al2O3-Fe2O3-CaO-MgO-TiO2-Na2O-K2O system in the entrained flow gasification condition

The gasification of direct coal liquefaction residue (DCLR) enhances the overall economy of the direct coal liquefaction process. However, the DCLR ash is rich in iron due to pyrite as the catalyst during liquefaction. Coal blending plan with DCLR for gasification should consider the possibility of metallic iron crystallization and agglomeration ahead of suitable viscosity range. In this study, the iron behavior in the DCLR slag in the gasification condition was discussed by the thermodynamic modelling of SiO2-Al2O3-Fe2O3-CaO-MgO-TiO2-Na2O-K2O. Results show that the metallic iron forms only in the dry feed entrained flow gasifier for the high content of reducing gases. The metallic iron crystallizes when Fe2+ of the liquid phase fails to be stabilized by -Si-O. The competition reaction with -Si-O between Ca2+ and Fe2+ and the formation of calcium aluminum-silicate also contribute the metallic iron crystallization. In the gasification condition, the metallic iron crystallization can be inhibited by decreasing the iron content/α value (α = CaO/(SiO2 + Al2O3), mass ratio) or by increasing S/A (S/A = SiO2/Al2O3, mass ratio) of DCLR ash. Finally, the DCLR blends with 3.5 wt% sand/8.0 wt% mullite/50.0 wt% Dalai Nur coal/90.0 wt% Duolun coal is the feasible feedstock for pulverized coal gasifier, because the temperature of iron crystallization is below the tapping temperature of 1350 °C and the viscosity is less than 25 Pa·s.

Theoretical Study on the Mechanism of Hydrogen Donation and Transfer for Hydrogen-Donor Solvents during Direct Coal Liquefaction

As a country that is poor in petroleum yet rich in coal, it is significant for China to develop direct coal liquefaction (DCL) technology to relieve the pressure from petroleum shortages to guarantee national energy security. To improve the efficiency of the direct coal liquefaction process, scientists and researchers have made great contributions to studying and developing highly efficient hydrogen donor (H-donor) solvents. Nevertheless, the details of hydrogen donation and the transfer pathways of H-donor solvents are still unclear. The present work examined hydrogen donation and transfer pathways using a model H-donor solvent, tetralin, by density functional theory (DFT) calculation. The reaction condition and state of the solvent (gas or liquid) were considered, and the specific elementary reaction routes for hydrogen donation and transfer were calculated. In the DCL process, the dominant hydrogen donation mechanism was the concerted mechanism. The sequence of tetralin donating hydrogen atoms was α-H (C1–H) &gt; δ-H (C4–H) &gt; β-H (C2–H) &gt; γ-H (C3–H). Compared to methyl, it was relatively hard for benzyl to obtain the first hydrogen atom from tetralin, while it was relatively easy to obtain the second and third hydrogen atoms from tetralin. Comparatively, it was easier for coal radicals to capture hydrogen atoms from the H-donor solvent than to obtain hydrogen atoms from hydrogen gas.

Effects of temperature and solvents on structure variation of Yunnan lignite in preheating stage of direct liquefaction

Preheating stage is of significance for direct coal liquefaction process, especially for the low-rank coals, with high reactivity and suitable for direct coal liquefaction. Properties of solvents used in preheating stage could greatly affect structure of coal and conversion of its oxygen-containing functional groups. In this work, the preheating process of one Chinese Yunnan lignite (YN lignite) was conducted in tetralin (THN) and 1-methylnaphthalene (1-MN) to figure out the interactions between YN lignite and nonpolar aromatic solvents. In-situ diffuse reflectance infrared Fourier transformation (DRIFT) technique coupled with curve-fitting analysis and ion-exchange titration analysis and solid-state 13C NMR were used to investigate the structural changes of YN lignite when preheated in different solvents at different temperatures. Additionally, swelling ratio determination and density function theory (DFT) calculation were employed to evaluate the strength of interactions existing between YN lignite and THN or 1-MN. The results show that, the decrease of oxygen-containing functional groups and increase of aromaticity occur when YN lignite are preheated in THN and 1-MN, and these changes are intensified with temperature rising. Moreover, THN and 1-MN have different effects on variation of YN lignite, especially for phenolic hydroxyl groups, which are more likely to be decomposed in THN, while carboxyl groups break down more easily in 1-MN at 200–300 °C. DFT calculation and swelling ratio results show that stronger noncovalent interactions (OHπ hydrogen bonds in particular) between THN and YN lignite result in weaker OH bond in phenolic hydroxyl groups and subsequently decomposition of more phenolic hydroxyl groups compared to 1-MN.