Selective Extractiion Of Coal Based Liquid Products Based On The Theory Of Solubility Parameter

Low temperature coal tar is a mixture with complicated composition. It contains thousands kinds of compounds, the boiling points of which have a span of hundreds degrees, and their chemical properties are also with tremendous differences. Thus, the efficient utilization of coal tar always requires a proper pre-separation process, e.g. the preparation of liquid fuel from low-temperature coal tar. Different components in coal tar(i.e. aromatics and non-aromatics) demand different optimized conditions in the catalytic hydrogenation and/or cracking process, while other components(e.g. phenols and heterocyclic compounds) could harm catalytic processing and affect the utilization of refined oil. However, phenols and heterocyclic compounds are high value-added materials in the chemical industry. Besides, aromatic hydrocarbons with 2 or 3 rings are with good hydrogenation activity and relatively high solubility in organic solvent, and thus are suitable feedstock for producing liquid fuel; whill aromatic hydrocarbons with 4 or more than 4 rings are high value-added chemicals.In coal direct liquefaction process, a black solid residual(ca. 30 wt.% in the raw coal) would be produced. The residual contents Unreacted coal, heavy product of the liquefaction process, inorganic mineral and iron-based catalyst. It could be a kind of suitable feedstock to prepare high value-added carbon material with a effective pretreatment of de-ashing.Coal tar is a typical coal-based liquid product, and coal direct liquefaction residual is a relevant solid product of coal-based liquid. To selectively separate major components in low temperature coal tar and effectively collect organic composition from coal direct liquefaction residue, a study on supercritical fuild extraction and traditional extraction of the low temperature coal tar and coal direct liquefaction residue was conducted basing on the theory of solubility parameter. Hansen solubility parameter is a theory forcusing on solution, and is widely used on solvent selection and condition optimation for an extraction process. It would bring benefits on the enhancement of selectivity for extraction process of coal based liquids, but only few work has been done on this issue because of the lack of basic parameters of components in coal based liquid(e.g. polycyclic aromatic hydrocarbons) and the possible inapplicability of the existing dissolving model(e.g. Hansen solubility sphere) in complex miscibility system.According to the discussion above, this study contains 4 major parts: estimating Hansen solubility parameter of PAHs components by turbidimetric titration, a 3-step separation process of low temperature coal tar enhanced by a dissolving model basing on the theory of Hansen solubility sphere, supercritical fluid extraction of a distillate of low temperature coal tar(>300oC) using n-pentane as solvent, and supercritical organic solvents extraction of coal direct liquefaction residue.In the study of estimating Hansen solubility parameter of PAHs components by turbidimetric titration, Hansen solubility parameters of naphthalene, acenaphthene, anthracene, phenanthrene, pyrene, and fluoranthene, which were little studied by former literature, were evaluated by a new approach which is formed by turbidimetric titration and a calculating program based on the method of exhaustion; the relationship between solubility and solubility parameter distance(Ra) was investigated and thus a modified ellipsoidal model for solvent selection was established; extended Hansen approach was applied to verification of the new approach and evaluation of the solubility for the six PAHs components in different solvents. The results show that the new method can clearly identify the differences on Hansen solubility parameters caused by various benzene ring combination between some isomers(e.g. anthracene and phenanthrene). The modified ellipsoidal model is applicable to a general estimation of dissolving properties between solute and solvent. Among the six PAHs compounds, high relativity between their Hansen solubility parameters and solubility data has been found, indicating a satisfactory reliability of the new approach. Extended Hansen approach is appropriate for solubility estimation of the six PAHs with accep Tab. deviations. What‘s more, the relationship between Hansen solubility sphere and the extended Hansen approach has been revealed by regression analysis.In the study of building selective extraction model for coal tar compounds by the theory of Hansen solubility parameter, the selectivity of organic solvent extraction for separating non-aromatic hydrocarbons, aromatic hydrocarbons and polar components in low-temperature coal tar was enhanced by applying the Hansen Solubility Parameters theory. Naphthalene, toluene and n-octadecane were used as model compounds, and the modified dissolving model in terms of the Hansen solubility sphere was established in order to select the extraction solvent. In practice, the low-temperature coal tar was successfully divided into three parts(i.e., enriching non-aromatic hydrocarbons, aromatic hydrocarbons and polar components) by a three-step extraction-precipitation process at 298 K and 1atm. The optimized extraction solvents for the aromatics extraction and aromatics precipitation processes were, respectively, NMP+ 17 vol. % H2O/DMF+7 vol. % H2 O and NMP+59 vol. % H2O/DMF+50.5 vol. % H2 O, which were similar to estimates made using the ellipsoidal model. The experimental results demonstrated a high correlation with the estimation made by the ellipsoidal model. The mass percentage of non-aromatic hydrocarbons, aromatic hydrocarbons and polar components in their separation products were all ca. 90 wt. %. The mass percentages of the three products in total feedstock were around 12.7%, 46.11% and 36.51%, respectively. The mass loss during the entire separation process was from 4.5% to 6.0%.In the study of supercritical extraction of a distillate of low temperature coal tar(>300oC) using n-pentane as solvent, two empirical formulas and the theory of solubility parameter were used in this study to estimate the tendencies of dissolving capacity and selectivity of major components in the coal tar feed stock, and a successively extraction process was established to achieve selective separation. The experimental results shows that the empirical formulas used to estimate the dissolving capacity(extraction yield, y1) and selectivity(mass percentage of certain component in extraction product, w1) of major components in coal tar feedstock are sound and applicable, because their correlation coefficients are more than 95% and their AARD% is all less than 14%; the optimized successively extraction process can selectively separate polar and non-polar components in the coal tar feedstock, and especially can be applied to enrich certain non-polar components, e.g. 3-ring aromatic hydrocarbons, mass percentage of which are more than 80% in the corresponding extraction product; high temperature(around 600K) was needed to extract polar components effectively, and no significant selectivity was observed for polar components during the extraction process. The theory of Hansen solubility parameter can‘t be used to evaluate the dissolving capacity during the SFE process because of lacking basic data, while an appropriate explanation about the extraction result can be given by a comparison study between the total solubility parameters of supercritical solvent and the solute. The total solubility parameter of supercritical n-pentane increased with the pressure and decrease with the temperature. The difference value between the total solubility parameters of supercritical solvent and the solute(??) can be an effective indicator during the optimization process of extraction solvent. A good extraction yield would achieve when the value of?? is small.In the study of supercritical fluid extraction of coal direct liquefaction residue, the dissolving capacities of multiple supercritical organic solvents(benzene, acetone and isopropanol) was investigated. Empirical formula and the theory of extended Hansen approach was used to estimate the relationship between extraction results and experimental conditions. Detail analysis for ash content, composition and molecular weight distribution of feedstock and extraction product was also conducted. The results show that the extraction yield of experiments using supercritical benzene as solvent is higher than the other solvents; for the supercritical benzene extraction process, the extraction yield increased with the pressure and decreased with the temperature, and it(>57%) is higher than that of hot quinolone extraction under the optimized condition. Hansen solubility parameter and extended Hansen approach is applicable to reveal the tendency of extraction yield under supercritical conditions because a high correlation was found in the regression process. The total solubility parameter of supercritical solvent is much smaller than it under normal conditions, and the larger extraction yield of supercritical benzene can be contributed to its higher value of dispersion parameter(?d). During the extraction process, the ideal solubility of solute is up with the increase of extraction temperature. The relationship between the extraction yield and experimental conditions obtained in this study is sound and accurate with a maximum relative deviation of 10%. There were 14 experiments with absolute error less than 5% in total 15 experiment indicating a good applicability of extended Hansen approach in the supercritical conditions. The analysis of GPC shows a result which has a consistency with the extraction yield, and a comparison study of total ash content between feedstock and extraction product proved the SFE process can remove ash from the coal direct liquefaction residue effectively.