Graham Harrison

Extraction of intermediate and low-rank coals with supercritical toluene

Abstract Supercritical gas extractions of 15 UK coal samples of rank CRC 500–900 were carried out in a 500 ml batch autoclave fitted with a condenser and a siphon arrangement. Preliminary experiments showed that extraction yields became constant above 400 °C, so the conditions used for the remaining extractions were 5 min contact time, 425 °C, 50 g of coal, 300 ml of toluene and 50 bar N 2 pressure. Extraction yields were calculated by a mass balance approach. The extracts, the hexane-soluble material and the asphaltenes were analysed for their C, H, N and S contents. Extraction yields showed some dependency on ash contents, volatile matter contents, H:C ratios, sulphur contents, oxygen contents and carbon contents. Often the coals were found to divide into two groups. The oxygen contents of the coals seemed to be the major factor influencing extraction yields. Generally, oxygen-containing fragments were the most difficult to solubilise and sulphur-containing fragments the easiest. The extracts were significantly richer in their hydrogen contents than the starting coals, indicating that lower molar mass compounds were solubilised.

Use of tyre pyrolysis oil for solvent augmentation in two-stage coal liquefaction

A sample of tyre pyrolysis oil (TPO), supplied by Bevan Recycling from their pilot plant, was analysed according to boiling point distribution. G.c.-m.s. analysis of 275°C (TPO+) fractions revealed the presence of a large number of mainly aromatic compounds with a high degree of alkyl substitution and negligible hydrogen donor content. Dissolution experiments using Point of Ayr coal were carried out with hydrogenated anthracene oil containing various amounts of TPO and TPO+ at various temperatures. The results depended little on whether TPO or TPO+ was used, but the extent of dissolution decreased with increasing content of TPO or TPO+. However, the reduction was less than might have been expected according to the reduction in hydrogen donor content and there was evidence that TPO and TPO+ were providing a good hydrogen shuttling capacity. A sample of TPO was prehydrogenated to produce various samples of HTPO. The extent of dissolution with HTPO based on overall hydrogen donor content was higher than that produced by hydrogenated anthracene oil (HAO), probably because of the high degree of alkyl substitution in HTPO compared with HAO.

Fate of hydrogen-donor molecules in two-stage liquefaction using model solvents

Abstract Model solvent mixtures have been prepared by hydrogenating phenanthrene and pyrene in an autoclave. These model solvents were used in coal liquefaction dissolution experiments using Point of Ayr coal under various conditions. Some of the coal liquids were hydrocracked with a CoMo commercial catalyst. The extent of dissolution was compared with the consumption of total hydrogen donor content and the consumption of individual donors; these donor contents were estimated from gas liquid chromatograms of the initial solvents and of the hexane-soluble fraction of the coal liquid. The extent of regeneration of the hydrogen donors after hydrocracking was also determined. From the various results, conclusions have been made concerning the importance of both total and individual hydrogen-donor contents for coal liquefaction processes.

Coal liquefaction with solvent augmentation by heavy oil residues in presence of disposable iron catalyst

Abstract Coal liquefaction experiments were carried out in batch autoclaves with Point of Ayr coal, a process-derived recycle solvent and heavy oil residues (HORs) under a range of conditions. Before the experiments iron sulfide was precipitated on to the coal, mostly at 6 wt% Fe, and the experiments were carried out under a modest hydrogen overpressure. Two HORs were used, namely the highly aliphatic Forties AR and the more aromatic decant oil produced from fluidized catalytic cracking of oil. The influence of amount of HOR added, temperature and time on the percentage dissolution of coal was considered and related to the H-donor contents of the various solvents measured by a chemical test using sulfur as a hydrogen acceptor. It was found that an augmented solvent mixture containing 20 wt% decant oil in process-derived recycle solvent (PDRS) produced the greatest conversion values under the optimum conditions of 400°C for 1 h, with synergistic action in terms of hydrogen transfer. The coal liquid produced from repeat solvent augmentation experiments with decant oil was subjected to hydrocracking with simulated solvent recycle, and the changes in composition of the liquid product were considered, particularly in relation to the fate of the main hydrogen donors present in process-derived recycle solvents. Reasonable conversion to lower-boiling-point material was found, but the H-donor content was not made up to its original value. There was an indication that the PDRS was hydrocracked preferentially relative to the decant oil.

Hydrocracking of a coal extract with various catalysts

Abstract Catalytic hydrogenations using a number of bimetallic and monometallic catalysts were performed in an autoclave fitted with a falling/spinning catalyst basket. The catalysts were used as oxides with and without the addition of carbon disulphide to the autoclave charge. The products were separated by vacuum distillation and the performance of the catalysts was assessed by combining the yields from vacuum distillation with the peak area distribution of the gas chromatographs of the distillation fractions. The presence of carbon disulphide reduced the yield of material boiling below 260 °C and was particularly effective in reducing the yield of material boiling below 175 °C. Bimetallic catalysts which included molybdenum as one component generally performed better than similar bimetallic catalysts which included tungsten as one component and better than monometallic catalysts. Commercial CoMo performed well both with and without added carbon disulphide but commercial NiMo was inferior to most other catalysts when carbon disulphide was not added and to many when carbon disulphide was added. The sulphur content of the liquid products was not significantly affected by the addition of carbon disulphide to the charge.

Hydrocracking of Point of Ayr coal liquid with hydrogen and 90% hydrogen/10% carbon monoxide mixture using CoMo and CoW catalysts

Catalytic hydroliquefaction experiments on a Point of Ayr coal liquid were performed in autoclaves fitted with a falling/spinning basket. The bimetallic catalysts CoMo and CoW on an acidic alumina support were used at different contents of Mo and W in oxide and presulphided forms. Some experiments used H2 alone and some used 90 vol%H2/10 vol%CO. The hydroliquefied products were characterized by vacuum distillation and g.l.c. into 13 product groups. The carbon, hydrogen and sulphur contents of the washed catalysts were determined. Generally, conversions to material boiling below 475 °C were < 80%, and conversions to lower boiling point material were influenced by the presence of CO, the composition of the catalyst, the run time and by presulphidation. On many occasions, increased conversion to low boiling point material resulted only from breakdown of the recycle solvent fractions, and not from increased conversion to material boiling below 475 °C. It was apparent that on altering the metal content of catalysts or after presulphiding, the catalysts CoMo behaved differently from CoW.

Hydroliquefaction of coal liquids with hydrogen and hydrogen/carbon monoxide mixture

Abstract Catalytic hydroliquefaction experiments were performed in autoclaves fitted with a falling/spinning basket. Bimetallic catalysts containing either Mo or W were used for hydrocracking experiments on a coal liquid, formed by dissolving coal in hydrogenated anthracene oil, using either hydrogen alone or 95% hydrogen/5% carbon monoxide. The bimetallic catalysts CoMo, NiMo and ZnMo were used in further experiments on a Point of Ayr coal liquid with hydrogen alone and 90% hydrogen/10% carbon monoxide. The hydrocracked liquid products were characterized by vacuum distillation and gas chromatography, which in combination allowed assessment of the yields of various defined product groups. From the yield assessment, product characterization and elemental analysis, the various catalysts and gas systems were evaluated as to their relative effectiveness for the hydrogenation of the coal liquids; this evaluation took into account the mass balance and distribution of the recycle solvent fraction as well as total conversion and conversion to material boiling below 260 and 275 °C.

Extraction of intermediate and low rank coals with HAO

Abstract Thirty-nine UK coals, CRC 500–900, have been extracted in a 30ml ‘bomb-type’ autoclave with hydrogenated anthracene oil at 400 °C for 4 h. Yields of extract, generally better than 80% of the daf coal, show no correlation with volatile matter, carbon contents or H:C ratios of the coals, but do depend upon total sulphur and inertinite contents. The composition of the inertinites is apparently important. Yields are also independent of nitrogen and oxygen contents but heterocyclic compounds containing these elements tend to concentrate in the undissolved material and the pre-asphaltenes. The results of solvent fractionation of the extracts show no correlation with coal rank; on average, 83% of the extracted coal was insoluble in hexane. Proton and 13 C n.m.r. spectrometry of the asphaltenes showed no clear correlation between hydrogen and carbon types and coal rank; on average, the asphaltenes contain mainly three-ring aromatic clusters with a low degree of substitution by alkyl groups.

Hydrogen transfer reactions in solvent augmented coal liquefaction

Samples of Point of Ayr (POA) coal were dissolved in a solvent mixture of either tyre pyrolysis oil (TPO) and hydrogenated anthracene oil (HAO), or hydrogenated tyre pyrolysis oil (HTPO) and HAO. The addition of TPO caused an apparent reduction in percentage dissolution and introduced coking problems even at relatively moderate conditions. Analysis of the coal liquids by isotopic mass balance suggested the values of actual percentage dissolution calculated by ash balance were corrupted by coking of TPO. When a catalyst activated coal, produced by depositing iron sulphide on POA coal, was used with TPO under various hydrogen overpressures, coking was reduced, with dissolution increasing with increasing hydrogen overpressure. Samples of HTPO were produced by hydrogenating TPO in either a spinning/falling basket autoclave or a trickle bed reactor. The HTPO samples produced from the trickle bed reactor generally were not as effective in dissolving POA coal due to overproduction of saturates; however, the HTPO samples from the autoclave contained a higher proportion of > 450°C boiling point material, indicating underhydrogenation of the TPO feed. Addition of HTPO from the autoclave caused coal dissolution to increase with increasing HTPO content and no coking was observed. Measurements of H-donor contents by a chemical test procedure using sulphur as a hydrogen acceptor, suggested that the increase was probably the result of the introduction of compounds more active towards initiating cleavage of bonds between aromatic centres, rather than differences in the total H-donor contents.

Suitability of UK bituminous and Spanish lignitous coals, and their blends for two stage liquefaction

Liquefaction experiments were carried out in spinning/falling basket autoclaves using samples of Kellingly (UK) and Samca (Spain) coals, and a process derived recycle solvent (PDRS). Hydrocracking experiments were carried out in a bomb type autoclave using sulphided NiMo catalyst. For the dissolution experiments with the individual coals, the influence of temperature 380, 400 and 420°C, and time 1 or 2 h was considered. For hydrocracking, preliminary experiments were carried out with a Kellingly coal liquid to establish appropriate reaction conditions for the hydrocracking of Kellingly and Samca coal liquid blends. There was some evidence of synergistic activity for conversion to dichloromethane (DCM) soluble material and antagonistic behaviour for conversion to tetrahydrofuran soluble/DCM insoluble material for dissolution of the coal blends, but hydrocracking of the coal liquid blends resulted in additive behaviour. For each of the coals, the extent of dissolution correlated with the extent of desulphurisation. The sulphur contents of the solid residues from dissolution tended to increase with the temperature of dissolution, but their H:C ratios decreased and their calorific values were independent.