Effect of pre-swelling of coal at mild temperatures on its hydro-liquefaction properties

The effects of pre-swelling treatment of Shenhua coal at mild temperatures (less than 160 °C) on its hydro-liquefaction properties were determined in this paper. It was found that with the increase of pre-swelling temperature in tetralin (THN) up to 120 °C, the liquefaction conversions of swollen coals increased. However, when N-methyl-2-pyrrolidinone (NMP) was used as swelling solvent, the liquefaction conversion decreased with the increase of pre-swelling temperature. The liquefied product distributions were very much dependent on the pre-swelling pretreatment conditions, and the mechanism was discussed. Based on the results obtained, a new swelling-liquefaction combining technology (SLCT) was advanced, in which the liquefaction conversion and oil + gas yield were enhanced.     

Examination of the role of CS2 in the CS2/NMP mixed solvents to coal extraction

The roles of CS₂ in the CS₂/NMP mixed solvent to coal extraction and solubilization were investigated in this study. There was little effect of removing of CS₂ from the solutions on the solubilities of UF coal extract and pyridine insoluble (PI) of the extract in the NMP/CS₂ mixed solvent, suggesting that NMP has high enough solubilities to the UF coal extract and PI. Six Argonne different rank coals were extracted with the CS₂/NMP mixed solvent and NMP, respectively. It was found that the extraction yield difference between NMP and CS₂/NMP mixed solvent for UF coal is largely deviated from the curve obtained for the other 5 coals, suggesting that the pre-swelling of CS₂ in the mixed solvent may be one of important roles for high extraction yield of UF coal in the CS₂/NMP mixed solvent. FTIR indicated that there was a strong interaction between CS₂ and NMP in the CS₂/NMP mixed solvent of 1 : 1 volume ratio, which made the strong absorbance at 2156 cm^− 1 in the FTIR spectra, and this interaction may disrupt the dipole based association of NMP thus making the CS₂/NMP mixed solvent lower viscosity, to penetrate more quickly into the network structure of coal, resulting in the larger solvent partner (NMP) to enter and break the stronger coal–coal interactions.     

Study on the hydrothermal treatment of Shenhua coal

In this paper, the hydrothermal treatment of Shenhua coal was carried out under 0.1 MPa (initial pressure) nitrogen and different temperature. Effects of hydrothermal treatment on the structure and the hydro-liquefaction activity of Shenhua coal were investigated by the ultimate and proximate analyses, the FTIR measurements and TG analyses of hydrothermally treated coals, and the characterizations of extraction and swelling properties, and the batch hydro-liquefaction of treated coal were also carried out. The results indicate that hydrothermal treatment above 200 °C can increase the hydrogen content of treated coal and decrease the yield of volatiles and the content of ash, especially a large amount of CO and CH₄ are found in gas products obtained by the hydrothermal treatment above 250 °C. Hydrothermal treatment disrupts the weak covalent bond such as ether, ester and side-chain substituent by hydrolysis and pyrolysis, and changes the distribution of H-bond in coal. The swelling ratio and the Soxhlet extraction yield of treated coal decrease with the increase of hydrothermal treatment temperature. The conversion of liquefaction and the yield of CS₂/NMP mixed solvent extraction at ambient temperature are enhanced by hydrothermal treatment at 300 °C. Therefore hydrogen donation reactions and the rupture of non-covalent bond and weak covalent bonds present in the process of hydrothermal treatment resulting in the changes of structure and reactivity of Shenhua coal. The results show that the hydro-liquefaction activity of Shenhua coal can be improved by hydrothermal pretreatment between 250 °C and 300 °C.     

Molecular dynamic simulation of coal-solvent interactions in Permian-aged South African coals

Molecular dynamic simulations were used to examine the initial stages of solvent-coal interactions during solvent swelling. Large-scale (> 10,000 atoms) vitrinite-rich Waterberg and inertinite-rich Highveld coal models used in this study were previously constructed. Isothermal-isobaric molecular dynamics simulated the experimental conditions used for the solvent swelling of these coals. Partially solvent swollen structures were constructed by the addition of solvent molecules to the original coal molecules using an amorphous building approach. The various solvated coal models were simulated using pyridine, N-methylpyrrolidone (NMP) and CS₂/NMP solvents. The changes in bonding and nonbonding energies due to solvent swelling were determined by comparing original coal models to corresponding swollen models. Simulation studies showed that coal-coal nonbonding interactions changed due to disruption of the van der Waals interaction energies. The distributions of hydrogen bonds were calculated and provided a method to evaluate solvent-coal hydrogen interactions. It was found that hydroxyl groups associated with the bituminous coal structure are the dominating hydrogen bond donor in solvent interaction. Therefore, the contributions of nonbonding interactions in coal play an important role during coal-solvent swelling. Molecular modeling and simulation is a useful tool to probe these changes in energies and nonbonding interactions in coal with various solvents.     

微波溶胀对五彩湾煤直接液化影响的研究

采用NMP/CS(2体积比1︰1)混合溶剂,在微波辐射下对五彩湾煤进行溶胀处理,并将原煤和微波溶胀煤样进行对比表征和加氢液化实验,考察了液化反应温度、反应气氛、溶胀剂对液化效果的影响。结果表明:微波溶胀后,煤样孔隙结构显著增加,结构发生变化。在液化条件是温度450℃、氢初压6.0 MPa、溶煤比1.75︰1和反应时间60 min,油产率和转化率分别是原煤55.02%和76.76%,微波溶胀煤74.03%和84.78%。     

The effect of extraction condition on ‘HyperCoal’ production (1)—under room-temperature filtration

In order to produce ashless coal (HyperCoal) in a high yield, extractions with several organic solvents—tetralin, 1-methylnaphthalene, dimethylnaphthalene and light cycle oil (LCO) at 200–380 °C were conducted for various ranks of coals, and subsequent solid/solution separation was done at room temperature. LCO was found to be a useful, cost-effective solvent, since it gave similar extraction yields to three other reagent solvents. The extraction yield for Illinois No. 6 coal gradually increased over 200 °C, and a significant increase in extraction yield was observed from 350 to 360 °C. We succeeded in producing ashless coal with less than 0.1% in ash content for seven of nine coals used in this study.     

Solvent swelling behavior of Permian-aged South African vitrinite-rich and inertinite-rich coals

Two South African coals similar in rank and age, but different in maceral composition, were studied using solvent swelling. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were evaluated for swelling extent and swelling rate using N-methylpyrrolidone (NMP) and CS₂/NMP. A stop-motion videography method was developed to study individual particle swelling behavior. This method allowed observation of overshoot and climbing-type swelling, as well as swelling kinetics. Single-particle swelling experiments showed that both coals exhibited overshoot-type and climbing-type swelling. The inertinite-rich coal swelled much faster (in both solvents) than the vitrinite-rich coal. The swelling in CS₂/NMP was faster for both coals. Kinetic parameters showed that solvent swelling was governed by relaxation (super-Case II relaxation) of the coal structure. X-ray computed tomography was conducted over a 50 h swelling period in NMP for single particles of each coal. Anisotropic swelling was observed in all the particles (swelling greater perpendicular to the bedding plane than parallel to it). The subtle changes in molecular structure, fine structural and physical differences resulted in significant differences in solvent swelling behavior.     

Fractionation of coal by use of high temperature solvent extraction technique and characterization of the fractions

The authors have recently presented a new coal fractionation method that can separate a bituminous coal into several fractions, just like petroleum distillation, without decomposing coal. In this paper this method was applied to two bituminous coals and a brown coal. Sequential solvent extraction at different temperatures lower than 350 °C successfully separated the two bituminous coals into several fractions having different molecular mass compounds. Since all the extracted fractions are almost free from mineral matter, and some fractions were found to be fusible like a synthesized pitch when heated, the possibility of producing high performance carbon materials from the coal fractions was investigated. On the other hand, fractions obtained from the brown coal by the sequential solvent extraction were very close in both chemical composition and molecular mass, although the sequential extraction could greatly suppress the decomposition of the brown coal below 350 °C. The difference in the extraction behavior between the bituminous coals and the brown coal were attributed to the difference in their chemical structure.     

Kinetics of coal liquefaction during heating-up and isothermal stages

Direct liquefaction of Shenhua bituminous coal was carried out in a 500 ml autoclave with iron catalyst and coal liquefaction cycle-oil as solvent at initial hydrogen of 8.0 MPa, residence time of 0–90 min. To investigate the liquefaction kinetics, a model for heating-up and isothermal stages was developed to estimate the rate constants of both stages. In the model, the coal was divided into three parts, easy reactive part, hard reactive part and unreactive part, and four kinetic constants were used to describe the reaction mechanism. The results showed that the model is valid for both heating-up and isothermal stages of liquefaction perfectly. The rate-controlled process for coal liquefaction is the reaction of preasphaltene plus asphaltene (PAA) to oil plus gas (O + G). The upper-limiting conversion of isothermal stage was estimated by the kinetic calculation.     

Microwave-assisted hydroconversions of demineralized coal liquefaction residues from Shenfu and Shengli coals

Microwave-assisted hydroconversions of demineralized coal liquefaction residues (DCLRs) from Shenfu (SF) and Shengli coals were investigated using methanol or ethanol as the solvent for both reaction and extraction. The results show that the solubilities of hydroconverted DCLRs in methanol under 0.7 MPa of initial hydrogen pressure (IHP) follow the order: non-catalytic hydroconversion = activated carbon-catalyzed hydroconversion < Pd/C-catalyzed hydroconversion < Ni-catalyzed hydroconversion; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol increases with raising temperature up to 140 °C and with increase in IHP; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol under 0.7 MPa of IHP at 130 °C is higher than that in ethanol. The molecular compositions of the extractable fractions were analyzed with GC/MS and the structural features of some extractable and inextractable fractions were characterized with FTIR.     

Effects of solvent and iron-compounds on the liquefaction of brown coal

Hydrogen-donor solvents such as hydrophenanthrene are the most effective aromatic solvents for the liquefaction of brown coal. The hydrogen-donating ability of the solvent is more important for brown coals than for bituminous coals, because the thermal decomposition and subsequent recombination of the structure of the brown coals occurs rapidly. Three-ring aromatic hydrocarbons are more effective solvents than two-ring aromatics, and polar compounds are less effective solvents with brown coals than with bituminous coals. The thermal treatment of brown coal, accompanied by carbon dioxide evolution at temperatures > 300°C, in the presence of hydrogen-donating solvent did not affect the subsequent liquefaction reaction. However, thermal treatment in the absence of solvent strongly suppressed the liquefaction reaction, suggesting that the carbonization reaction occurred after the decarboxylation reaction in the absence of hydrogen donor. To study the effect of various iron compounds, brown coal and its THF-soluble fraction were hydrogenated at 450°C in the presence of ferrocene or iron oxide. The conversion of coal and the yield of degradation products are increased by the addition of the iron compounds, particularly ferrocene, and the yield of carbonaceous materials is decreased.     

溶胀对神华煤结构及液化性能的影响

采用甲苯和吡啶对中国神华煤进行直接液化前的溶胀处理,通过对溶胀度及抽提率的测定、IR光谱分析、热重分析以及溶胀煤的直接液化实验,探讨了溶胀预处理对神华煤结构及液化性能的影响.结果表明:经溶胀预处理,煤的溶胀度、抽提率获得了显著提高,煤结构中的弱共价键断裂,进而改善了其液化性能并提高了煤的直接液化转化率和油气产率.     

Direct liquefaction of sawdust under syngas

Liquefaction of sawdust under syngas was performed in an autoclave and the effects of temperature, initial syngas pressure and reaction time on the product distribution of sawdust liquefaction were studied. The results using different solvents and atmospheres were also compared by product distribution and analyses of GC-MS, TG, IR and GPC. It was found that hydrogen donor solvent showed remarkable effect than either non-hydrogen donor solvent or without presence of solvent and its hydrogenation ability was much higher than gaseous hydrogen. Among various atmospheres H₂ displayed higher activity than syngas and both of them were better than Ar and CO, while CO did not give the favorable influence. With increasing temperature and reaction time (10–30 min) the oil yield increases, while less effect with increasing initial syngas pressure. The thermal decomposition of sawdust to form preasphaltene and asphaltene (PA + A) is a fast step, while longer reaction time is necessary for conversion of PA + A to oil as the 2nd step. The results also indicated that syngas can replace hydrogen in sawdust liquefaction.     

Effect of hydrothermal treatment on the extraction of coal in the CS2/NMP mixed solvent

The extraction of four Chinese different rank bituminous coals with the carbon disulfide/N-2-pyrrolidinone (CS₂/NMP) mixed solvent (1:1 by volume) was carried out in room temperature. It was found that one of middle bituminous raw coal of the four coals gave more than 74% (daf) extraction yield, suggesting an associative structural model for the coal. The four coals were hydrothermal treated under different conditions, and it was found that the extraction yields of the treated coals obviously increased. This will have great significance for coal liquefaction. FTIR measurements show the removal of minerals after the hydrothermal treatment of coals suggesting the dissociation of the coal aggregation structure due to ionic interactions and/or hydrogen bonds broken because of the removal of oxygen and hydroxyl oxygen proceeded through ionic pathways, resulting in the extraction yields of the treated coals increase. However, breaking of π-cation interactions by hydrothermal treatment may be one of possible mechanisms for the enhancement of extraction yield of higher rank of treated coal. The mechanism of hydrothermal treatment of coal was discussed in the paper.     

Catalytic effects of ferric chloride and sodium hydroxide on supercritical liquefaction of thistle (Cirsium yildizianum)

Cirsium yildizianum stalks were liquefied in organic solvents under supercritical conditions with and without catalyst in a cylindrical reactor at temperatures of 260, 280 and 300 °C. The effects of liquefaction temperature, catalyst type and solvent on product yields were investigated. The liquid products (bio-oils) were extracted with diethyl ether and benzene using an extraction procedure. The liquid yields in supercritical methanol, ethanol and acetone were found to as 45.66%, 49.34% and 60.05% in the non-catalytical runs at 300 °C, respectively. The highest conversion (liquid + gaseous products) was obtained in acetone with 10% ferric chloride at 300 °C in the catalytic runs. The produced liquids at 300 °C were analyzed and characterized by elemental, GC–MS and FT-IR. 85, 79 and 60 different types of compounds were identified by GC–MS obtained in methanol, ethanol and acetone, respectively. The liquid products were composed of various organics including aromatics, nitrogenated and oxygenated compounds.     

Effect of coal soluble constituents on caking property of coal

Three cokemaking bituminous coals were extracted by the CS₂/NMP mixed solvents with different content of NMP, and the effect of the amount and the component of coal soluble constituents on the caking property of the extracted residues of coals were investigated in this study. The CS₂/NMP mixed solvent (1:1 by volume) was found to give the maximal extraction yields for the three coals, and the fat coal gave the highest extraction yield of 78.6% (daf) corresponding to its highest caking index of 101. It was found that for coking coal, when the extraction yield got to the maximum of 25.3% in the 1:1 by volume of CS₂/NMP mixed solvent, the residue extracted still had caking property with the caking index of 19. This means parts of the caking constituents of coal are un-extractible because of covalent bonding or strong associative cross-links. The soluble components extracted by the CS₂/NMP mixed solvent and their effects on the caking indexes of the residues at a similar extraction yield quite differed depending on the NMP content in the mixed solvent. The coal solubles extracted by the CS₂/NMP mixed solvent with NMP less than 50% contained less light constituents with less of oxygen groups. This may lead to the decrease in the caking indexes for the residues obtained at the similar extraction yields compared to those of the CS₂/NMP mixed solvent with NMP more than 50%.     

Effect of Wyodak coal properties on hydroliquefaction reactivity

The effect of Wyodak coal properties on liquefaction reactivity as measured by distillate yield and cyclohexane conversion has been investigated. Spot samples of four Wyodak subbituminous coals from the Anderson and Canyon coal seams in the Powder River Basin of NE Wyoming were liquefied in microautoclave and batch reactor experiments. Runs were made using two different Wyodak coal-derived solvents. Emphasis in this work was directed toward correlation of C₄-700 K distillate yield and cyclohexane conversion as functions of measurable physical, chemical and petrographic properties of the feed coal. Reactivity rankings were found to be the same using either measure of coal reactivity. However, the data indicated that distillate yields were a function of both solvent quality and feed coal properties. For each solvent studied, selected coal properties, including carbon content, total and organic sulphur content, vitrinite content and total reactive maceral (vitrinite plus exinite) content, were found to give statistically significant correlations with distillate production and cyclohexane conversion. Pyritic and sulphate sulphur contents did not appear to enhance liquefaction yield or conversion at the reaction conditions studied. However, any catalytic effects due to pyrite or sulphate sulphur may have been masked by the use of two high quality liquefaction solvents.     

Dependence of microscopic structure and swelling property of DTF chars upon heat-treatment temperature

Eleven types of coals with different swelling property on a rapid pyrolysis were heat-treated below 1500 °C in a drop tube furnace (DTF), and investigated their microscopic structure by XRD measurement and TEM observation. XRD patterns of the samples were used to estimate the average number of stacking aromatic layers in a crystallite (N_ave), the stacking index (SI) and the average interlayer distance (d₀₀₂). Dependence of these parameters upon heat-treatment temperature showed that N_ave for every sample had a maximum around 800 °C. Amount of change in N_ave from room temperature to 800 °C corresponded well to the swelling ratio in the same temperature range, i.e., coal samples with large swelling ratio were likely to have developing stacking structure. Considering that coals generally swell at a plastic stage, the large variation of N_ave in the swollen chars could be related to the increase of mobility of aromatic layers and their local orientation due to the van der Waals effect. TEM observation of swollen chars illustrated that particle walls consisted of isotropic texture, implying that the possible increase of internal pressure when the particle swells had little effect on the development of stacking structure.     

Coal liquefaction by hydrogen produced from methanol: 3. Examination of reaction conditions

Coals were liquefied in a 50 ml autoclave using hydrogen produced from methanol with decomposition and hydrogenation catalysts under various conditions. The conversion increased with increasing reaction temperature and time. This reaction is more suitable for the liquefaction of lower-rank coals. The hydrogen pressure had little effect on the conversion in the range of the ratio of methanol to coal of 2 g/g. The use of a solvent is very effective in increasing the liquefaction, especially at short times.     

Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Reactivities of several coals of different ranks have been examined in degrading extractions with aromatic solvents under apparently non-hydrogenative reaction conditions. Pyrene and A240 pitch liquefied the fusible coals in high yields and the slightly-fusible coals in moderate yields, indicating the importance of fusibility in such liquefaction processes. A240-LS pitch is a powerful solvent for slightly-fusible coals. Considerable amounts of pyridine- or THF-soluble fractions were produced especially with A240-LS pitch. A240 pitch is a better solvent than pyrene for some slightly-fusible coals. However, the extent of depolymerization of liquefied coal, pyridine- or THF-solubility, was definitely inferior. Yields of such fractions are higher for lower-rank coals. The mechanism of coal liquefaction under apparently non-hydrogenative conditions is discussed with emphasis on the stabilization of thermal fragments derived from the coal.