Pyrolysis studies of organic oxygenates. 2. Benzyl phenyl ether pyrolysis under batch autoclave conditions

Benzyl phenyl ether (BPE) is a reactive organic oxygenate which contains the ether functionality believed to be present in subbituminous and bituminous coals. With an $\text{H}\text{C}$ of 0.92 it has a $\text{hydrogen}\text{carbon}$ ratio similar to that found in bituminous coals. Benzyl phenyl ether reacts readily at 375 °C either in the presence or absence of added donor hydrogen sources. The major products are toluene and phenol. Other, heavier products are also produced in significant quantities. In general, as available donor hydrogen is reduced, the products tend to have higher molecular weights. Conventional pyrolysis products become lighter (more desirable) materials when the pyrolysis is carried out in the presence of added hydrogen.     

Alcohols as H-donor media in coal conversion. 1. Base-promoted H-donation to coal by isopropyl alcohol

Isopropyl alcohol can act as a hydrogen donor to coal, as can tetralin. In contrast to tetralin, however, the transfer of hydrogen by the alcohol can be promoted by the presence of either potassium isopropoxide or KOH. Acetone is formed from the alcohol in quantities that accord with the amounts of hydrogen transferred to the coal. In runs at 335 °C for 90 min, coal was converted with isopropyl alcohol in the presence of either the alkoxide or KOH to a fully pyridine-soluble product with $\text{H}\text{C}$ ratios from 0.88 to 1.13, in contrast to coal (0.79). The organic sulphur content of the coal was reduced from 2.1% to 1%. Model-compound studies with anthracene and diphenyl ether showed that the anthracene was reduced in the system to 9,10-dihydroanthracene, but the ether was recovered unchanged. The coal products from the alcohol/base treatment are very rich in aliphatic hydrogen and have number-average molecular weights in the 450–500 range. The scheme suggested to explain the conversion at 335 °C includes initial hydrogenation of anthracene-like structures in the coal, followed by thermolysis of the dihydro-intermediate.     

Coal solvolysis in a series of model compound systems

A series of 23 model donor solvents was used to rank their efficacy for the dissolution of Western Kentucky No. $\text{9}\text{14}$ coal. The transfer of hydrogen from the solvent to the coal fragments, as measured by coal conversion, was examined at three levels of available hydrogen. The hydrogen donors are ranked according to their ability to convert coal to THF-solubles. Aromatic analogs of the model donors showed little ability to convert coal to THF-solubles. Factors which influence hydrogen donation include the presence of heteroatoms or substituents both internal and external to the aromatic or hydroaromatic rings, the degree of hydrogenation, the aromaticity or non-aromaticity of the hydroaromatics, and the presence of five-membered rings. A relation between heats of formation and hydrogen donor ability is shown for hydroaromatics within two ring or three ring homologous series. A model hydrogen acceptor, benzophenone, is also used to rank model donors. No correlation exists in the ranking of hydrogen donors by the model acceptor used in this work and in other experimental studies and that obtained by conversion of Western Kentucky coal at typical liquefaction conditions.     

Statistical aspects for the production of novolacs

Statistical parameters for the phenol (P)-formaldehyde (F) condensation under acid conditions are derived in the frame of Flory-Stockmayer's theory. Phenol is assigned an average functionality f = 2.31 as proposed by Drumm and Le Blanc (1972). Results show that a molar ratio $\text{(}\text{F}\text{P}\text{) = 0.881}$ leads to gelation at full formaldehyde conversion. Free phenol and number and weight average molecular weights are calculated, showing a significant dependence on the final formaldehyde conversion and the selected molar ratio (F/P). A good agreement between theoretical predictions and experimental results is obtained.     

Conversion of solvent-refined coal to liquid products in the presence of Lewis acids

The formation of liquid products from a solvent-refined coal (SRC) was studied using Lewis acid catalysts in the presence of either benzene or cyclohexane as an extracting solvent. The soluble products were characterized by elemental analysis, ¹H-n.m.r., and, in some experiments, by gel permeation chromatography. Only ZnCl₂ and SnCl₂, the weakest Lewis acids examined, enhanced the dissolution of SRC over that observed in the absence of a catalyst. Increases in solubility were accompanied by increases in $\text{H}\text{C}$ and aliphatic character and by decreases in average molecular weight. These changes are ascribed to the ability of ZnCl₂ and SnCl₂ to promote depolymerization and hydrogenation of the SRC. Alkylation with isopropanol was also found to enhance the solubility of SRC in benzene and cyclohexane.     

Conversion of bituminous coal in COH2O systems: 2. pH Dependence

Under $\text{CO}\text{H}{}_2\text{O}$ systems at initial pH values s> 12.6, an Illinois No. 6 coal, PSOC-26, was converted to a fully pyridine-soluble product, with benzene and hexane solubilities of 50% and 18%, respectively. The product gases were H₂ and CO₂. However, the expected $\text{H}{}_2\text{CO}{}_2$ ratio of 1.0 based on the water gas shift reaction was not observed, but the deficit in hydrogen was found in the increased hydrogen content of the coal product. 95% coal carbon recovery and good hydrogen balances were obtained, and the coal products were found to be very similar to those from conventional tetralin systems. The results suggest an efficient base-catalysed process, and that $\text{CO}\text{H}{}_2\text{O}$ systems are useful for coal studies.     

Coal-derived asphaltenes: effect of phenol content and molecular weight on viscosity of solutions

Phenol contents and molecular weights of coal-derived asphaltenes are shown to affect the viscosity of their solutions. Phenol contents were determined by non-aqueous titrimetry. Intermolecular aggregation probably involving hydrogen bonding is a prime factor in the increase in viscosity found with increased asphaltene concentration in a reference solvent system composed of an $\text{88}\text{12}$ ($\text{wt}\text{wt}$) mixture of 1-methylnaphthalene and o-cresol. Aggregation effects are greater for those asphaltenes with relatively higher phenol contents. Asphaltenes were separated into fractions of different polarity by adsorption chromatography. The more polar subfraction was found to increase viscosity in the reference solvent to a greater extent than the less polar subfraction. The logarithmic viscosity numbers of solutions of the asphaltenes and their subfractions are correlated by a linear combination of molecular weights and phenol contents. It is concluded that an effective means of reducing the viscosity of coal-derived liquids would be to reduce the phenol content of the asphaltene fraction.     

Liquefaction of coal and related materials

Bituminous coal, lignite, peat and more recent biogenic materials were reacted as water slurries at 380 °C for short periods with hydrogen, directly and from the water-gas shift reaction, without organic solvents or catalysts. Conversion increases with $\text{H}\text{C}$ and $\text{O}\text{C}$ ratio of the input material and reaches 90%. For benzene-soluble products $\text{O}\text{C}$ is always lower and $\text{H}\text{C}$ usually higher than for the original material.     

Catalytic liquefaction of coal with supercritical water/CO/solvent media

This paper describes studies of the catalytic activity of cobalt molybdenum sulphide, cobalt molybdenum oxide, iron sulphate, iron acetate dibasic and H₂S during the reaction between supercritical CO and water, and during liquefaction of coal using supercritical CO-water-solvent mixtures. The kinetics of the water gas shift reaction was studied first and was found to be first order in all the catalysts studied. The activity of the catalysts decreased in the following order: cobalt molybdenum sulphide > cobalt molybdenum oxide > iron salts. The presence of toluene, tetralin, and THQ decreased the CO conversion on the cobalt catalysts but increased CO conversion in the presence of iron salts catalysts. Moderate coal conversion of toluene soluble products (25%–35%) were obtained in the presence of supercritical water and water/CO mixtures. Addition of organic solvents to a supercritical water/CO medium increased conversion of toluene soluble products to 70–80% for THQ, to 50–60% for tetralin, and to 35–40% for toluene. Addition of H₂S to the solvent/water/CO medium increased conversion to toluene soluble products even further. In the presence of H₂S/solvent/water/CO, the presence of catalysts had only a minor effect on coal conversion and were not required to achieve high coal conversions. The optimum operating conditions for an Illinois No. 6 coal were obtained using a H₂S/THQ/CO/water medium at 3600 psi, and 400 °C. Higher conversions were attained with a subbituminous Wyodak coal. These studies clearly demonstrate that high conversions to soluble products can be attained using a supercritical water/Co/solvent medium.     

Flash pyrolysis of coals: behaviour of three coals in a 20 kg h−1 fluidized-bed pyrolyser

Flash pyrolysis of Loy Yang brown coal, and Liddell and Millmerran bituminous coals has been studied using a fluidized-bed reactor with a nominal throughput of 20 kg h^?1. The apparatus and its performance are described. The yields of tar and hydrocarbon gases are reported for each coal in relation to pyrolysis temperature, as also are analytical data on the pyrolysis products. The peak tar yields for the dry, ash-free Loy Yang and Millmerran coals were respectively 23% wt/wt (at ≈ 580 °C) and 35% wt/wt (at $\text{\$}\text{?}$600 °C). The tar yield from Liddell coal was 31% wt/wt at ≈ 580 °C. Hydro-carbon gases were produced in notable quantities during flash pyrolysis; e.g. Millmerran coal at 810 °C gave 6% wt/wt (daf) methane, 0.9% wt/wt ethane, 6% wt/wt ethylene, and 2.5% wt/wt propylene. The atomic $\text{H}\text{C}$ ratios and the absolute levels of hydrogen in product tars and chars decreased steadily with increasing pyrolysis temperature.     

The characterization of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions

A CP-MAS ¹³C NMR study of asphaltenes and preasphaltenes obtained under various coal liquefaction conditions is reported. The carbon aromaticity, f_a, of the solid extracts from the reaction products has a close relation with the reaction conditions. By plotting f_a against the atomatic $\text{H}\text{C}$ ratio for these solid products on the characterization chart for model polycyclic aromatic compounds, the molecular structures with relation to the liquefaction pathway from coal to oil can be proposed.     

Superacid coal chemistry: 1. HF:BF3 catalysed depolymerization—ionic hydroliquefaction of coals under mild conditions

HF:BF₃:H₂ catalysed depolymerization and hydroliquefaction of coal was studied. This superacidic system was found to be extremely effective for low temperature liquefaction of coal. Illinois No. 6 coal could be solubilized in pyridine to the extent of > 90% by treating it at ≈ 105 °C for 4 h. Under somewhat more elevated temperature (150–170 °C) cyclohexane extractabilities of up to 22% and distillability of up to 28% is achieved. A hydrogen donor solvent such as isopentane is shown to improve the efficiency of the superacidic catalyst for the conversion of coal to cyclohexane soluble products.     

Characterization of liquid product from the reaction of coal with hydrogen atoms

An oily product formed by the reaction of a domestic subbituminous coal (Taiheiyo coal) with hydrogen atoms at 200 °C, has been characterized. The material is essentially composed of C₅-C₂₂ alkanes and cycloalkanes. The $\text{H}\text{C}$ ratio, specific gravity and refractive index were 1.81, 0.855 and 1.447, respectively. The absence of heteroatoms, alkenes and aromatics in the product is the outstanding feature of the coal liquefaction induced by hydrogen atoms.     

Reaction of coals in hot acidic phenol at constant acid concentration

Previous work showed that the efficient ‘depolymerization’ of bituminous coals in hot phenol containing p-toluenesulphonic acid failed to occur and that the acid was destroyed during the reaction. Four coals varying in rank from lignite to low volatile bituminous were treated with refluxing phenol containing p-toluenesulphonic acid with the acid concentration held constant. The amount of colloidal material, of pyridine-soluble material, of benzene—ethanol solubles, and the number average molecular weight of the pyridine extractables were measured as a function of time. Although the reaction proceeds better with the lower rank coals, a large portion of the products is colloidal material. Treatment of coals with hot acidic phenol does not lead to their complete depolymerization. Treatment of Bruceton coal with refluxing phenol saturated with BF₃ also failed to give complete depolymerization. The formation of colloidal suspensions during investigations employing spectral and other physical measurements may lead to results that are susceptible to misinterpretation.     

Compositions of distillate recycle solvents derived from direct coal liquefaction in the SRC-I process: 1. Hydrocarbons

The qualitative and quantitative compositions of 260–427 °C distillate recycle solvents derived from direct liquefaction of subbituminous Wyodak coal and bituminous Kentucky $\text{9}\text{14}$ coal in the SRC-I process are discussed. A liquid chromatography method which involves a column switching technique was used to provide solubility characteristics and compound-class compositions. The hydrocarbon compounds, which accountfor> 60 wt% of the distillate recycle solvents, were further analysed using a unique combination of high-performance liquid chromatography (h.p.l.c.) and field ionization mass spectrometry (f.i.m.s.). Thirty homologous series were identified. Carbon number and distribution and concentration of the homologous series were determined. The h.p.l.c./f.i.m.s. method unravelled various hydroaromatic types which otherwise would be very difficult or impossible to determine.     

A mechanistic study of hydrogenation of coal. 2.

In Part 1 the authors reported that liquefaction of coal by hydrogenation in the presence or absence of vehicle and with or without catalyst progresses with characteristic variations of the reaction order. In the present paper, the roles of temperature, hydrogen, vehicle and catalyst have been studied using a free-radical scavenger such as p-benzoquinone or iodine. Based on these results, a set of characteristic reactions has been identified from which the following overall rate equation has been derived: $\text{d[P}{}_{\mathrm{m}}\text{]}\text{dt}\text{= β}{}_1\text{[C] + β}{}_2\text{[C]}{}^2\text{+ β}{}_3$ where [P_m] denotes gas, and benzene-soluble products, [C] represents the percentages of organic matter in coal and benzene insoluble intermediates, and β₁, β₂ and β₃ are constants. The rate equation thus explains the experimentally observed variation of the reaction order, which depends on the predominance of a particular group of reactions. It has been postulated that pyrolysis is the main driving force, and that hydrogenation of coal either with gaseous hydrogen or by hydrogen-donating vehicle is basically influenced by reactions involving free radicals.     

13C, 2H, 1H n.m.r. and gpc study of structural evolution of a subbituminous coal during treatment with tetralin at 427 °C

Subbituminous Kaiparowitz coal was treated with 1,1-d₂-tetralin or tetralin in sealed tubes at 427 °C and 500 °C for varying periods of time and rates of temperature rise (15 °C/s, 3 °C/s, and 1 °C/s). The time dependence of yields, average molecular weights, molecular-weight distributions and changes in hydroxyl-group content and elemental composition were determined. Deuterium FT n.m.r. was used to monitor the incorporation of deuterium from 1,1-dideuteriotetralin into aliphatic and aromatic structures in the fractionated products. The exchange of ²H with phenol in the presence of the coal was examined to aid in the interpretation of ²H n.m.r. results. ¹³C and ¹H FT n.m.r. and i.r. spectroscopy were used to monitor the fractionated products over time. The ultimate obtainable yields of THF-soluble product were not significantly altered by the shorter temperature-rise times. The highoxygen-containing subbituminous coal undergoes an extremely rapid loss of about 20% of its oxygen by dehydration, and was found to enhance the rate of reduction of acetophenone and the scrambling of deuterium label in tetralin. The growth of benzylic aliphatic hydrogen at the expense of β (ArCH₂C$\text{H}$₂) hydrogen was rapid in the early stages of reaction. In spite of apparently labile aliphatic structures, the preasphaltenes exhibited products above MW 1200 that were stable for more than 2 h at 500 °C.     

Depolymerization of Turkish lignites. 2. Effect of phenol concentration in a closed system

A lignite (C, 66.9 wt%) was depolymerized, using sulphuric acid as a catalyst, in a closed system in which the phenol/coal ratio was varied from 1.5 to 10. The products were separated by solvent extraction and silica gel chromatography. The i.r. and n.m.r. spectra, and the molecular weight of the products were measured. In the experiments with a phenol/coal ration of 10, complete depolymerization of the coal was seen provided the temperature of depolymerization was at least 210 °C. The products generally contained disubstituted aromatic structures connected by methylene bridges, it was found that as the phenol/coal ratio was increased there was a decrease in the number of methylene bridges connecting the aromatic structures. The molecular weights of the straight-chain pentane and benzene-soluble material were lower than the molecular weights of similar fractions in depolymerization experiments carried out in open systems. A method for the structural analysis of straight-chain pentane and benzene-soluble material based on i.r., ¹H n.m.r. and molecular weight measurements is suggested.     

Effect of devolatilization on nitric oxide formation from coal nitrogen

A simple heuristic model is proposed to explain the effect of devolatilization on both coal nitrogen conversion and NO formation. The model is cast into three temperature regimes, the intermediate regime II being initiated at $\text{T}\text{\$}\text{?}\text{1100}\text{K}$. Regime II represents pyrolysis of repolymerized volatiles and thus accounts for the effects of temperature and temperature history on fuel nitrogen conversion. Based on this interpretation, NO formation results from volatiles combustion at high temperatures and char combustion at low temperatures ($\text{T}\text{\$}\text{?}\text{1100}\text{K}$), in agreement with recent experimental data.     

Non-aqueous enzymatic solubilization of coal-derived materials

The utilization of enzymes in non-aqueous solvents was explored for the conversion of coal-derived materials to oil-soluble derivatives for use as fuels. A novel three-step process was developed:

1. (1) an initial low-severity conversion to a form that is soluble or dispersible in a polar solvent;

2. (2) formation of an alcohol substrate with a high activity for subsequent enzymatic processing;

3. (3) lipase-catalysed transesterification to a product that is soluble in hydrocarbon solvents.

The process was successful for the conversion of a first-stage liquefaction product from Wyodak subbituminous coal to an acylated product, about half of which is soluble in hexane and the remainder in toluene. Coals, humic acids and several other higher-molecular-weight coal liquefaction products, such as Chemcoal, and their derivatives inhibited the lipases, and thus the alcohol intermediates from these precursors were converted in 0–5% yields to acylated products.