PROGRESSIVE HYDROTREATMENT OF HOKKAIDO COALS (JAPAN)

ABSTRACT

Hokkaido coals were subjected to benzene extraction and non-catalytic hydrotreatment, alternatively, under progressive increase of temperature from 200 to 400 °C. For Taiheiyo coal the aliphatic materials in the hydrogen-rich part of the coal were converted to benzene soluble products at lower temperatures. With the increasing reaction temperature, aromaticity of the benzene solubles increased gradually. On the other hand, for Ohyubari coal, the structure of the benzene solubles were essentially the same for products obtained under all temperatures. Also, in the case of Taiheiyo coal (C : 76.9 %) the plastic state was not observed up to 400 °C, but for Ohyubari coal (C : 85.6 %) the onset of the plastic state was evident. It was assumed that there was an intimate relationship between the occurrence of plastic state and the structural uniformity of coal.     

THERMAL REACTIVITIES OF SOME TURKISH LIGNITES

A DTA study has been made to investigate the thermal reactivities of five Turkish lignites (Elbistan, Ilgin, Karliova, Xangal, Yatagan) in an air atmosphere. The coal samples exhibited thermal reactivity at temperatures starting from 20 °C and continuing up to 671 °C. Endothermic peaks were observed at the lower end of the temperature range, the highest endothermic peak temperature being 146°C for Elbistan lignite. Exothermic peaks appeared at around 260, 360 and 600 °C. These temperatures are considered to signify the release and combustion of single benzene ring structures and combustion of condensed aromatic rings respectively. Corresponding stages are observed in the TGA traces. After correcting for differences in methodology, the overall heat effects measured by DTA are within greater than 90% of the calorific values of the coal samples determined by bomb calorimetry.     

ELEMENTAL COMPOSITION OF ASPHALTENES FROM COAL LIQUEFACTION

The elemental composition (C, H, N, S, O) of asphaltenes isolated from coal liquefaction experiments carried out at different temperatures and tetralin/coal ratios has been determined. The liquefaction experiments were conducted in a 250 ml autoclave, with 10 g of a Spanish subbituminous A coal, for 1 hour, and at 17 ± 1 MPa operating pressure and 400 rpm stirring speed. The liquefaction products were fractionated into oils, asphaltenes and preasphaltenes using pentane, toluene and THF as extractive solvents. The % S and % O are lower in asphaltenes than in coal, while the % C and % N are higher and % H depends on the temperature and tetralin/coal ratio used. On the other hand asphaltenes % C decreases, and % H and % O increase as the tetralin/coal ratio is raised at every temperature except 475 °C, while % S and % N do not have a clear variation.     

LIQUEFACTION OF BEYPAZARI LIGNITE USING NiCl2-KCl-LiCl CATALYSTS. 1. DIFFERENCE IN SOLID AND MOLTEN SALT CATALYSIS

Liquefaction of Beypazan lignite in tetralin using NiCl₂-KCl-LiCl (14:36:50 molar percentages) as catalyst was investigated. Effects of the catalyst/lignite ratio and temperature were determined in experiments done at 275°C, 300°C and 360°C. Liquid products were separated into oils, asphaltenes and asphaltols by a solvent extraction method. Yield of liquefaction increased with temperature in all experiments, the highest yield was observed in experiments performed at the eutectic temperature of the catalyst mixture. The highest yields of oils were 20% and 30% with a catalyst/coal ratio of 0.5 at 275°C and 300°C, respectively. The activity of the catalyst increased in experiments in which the catalyst was molten. The yield of asphaltenes were not affected with increases in the catalyst/coal ratio in the experiments done at 275°C or 300°C in which the catalyst mixtures were in solid state. Asphaltene yields decreased from 25% to less than 5% with increasing values of catalyst/coal ratio and the asphaltol yields remained constant at 10% between catalyst/coal ratios of 0.25 and 1.00 and suddenly increased to 30% and 40% for catalyst/coal ratios of 1.50 and 2.00, respectively, at 360°C. The molecular weights of the oils decreased from 340 to a minimum value of 245 as the catalyst/coal ratio was increased from 0 to 1.00 in experiments done at 360°C where the catalyst was molten. As the catalyst/coal ratio was further increased from 1.00 to 2.00 the molecular weight increased to 310.It seemed that the N1Cl₂-KCl-LiCl catalyst mixture in all catalyst/coal ratios was more efficient in molten phase than it was used as a solid mixture.     

SUPERCRITICAL EXTRACTION AND DESULPHURIZATION OF BEYPAZARI LIGNITE BY ETHYL ALCOHOL/NaOH TREATMENT 2. KINETICS

The reaction of Beypazari lignite with ethyl alcohol/NaOH was carried out using a microreactor of 15 ml capacity. The microreactors were developed to examine the reaction kinetics of coal extraction and desulphurization under supercritical conditions. The experimental temperature in the microreactor was adjusted to 245°C, 275°C and 295°C. The duration of the experiments was changed between 0 to 90 minutes.

The solubilization of Beypazari lignite increased sharply from 15% to 50% within 30 minutes after the temperature reached to 245°C and gradually decreased from 50% to 48% in 90 minutes. The total sulphur (pyritic and organic) content of the acid washed lignite decreased from 3.78% to 2.50% in the first 10 minutes and insignificant changes were observed at longer durations. The percentage of the pyritic sulphur remained constant at about 0.25% throughout the experiments. As the temperature was increased from 245°C to 295°C the time for steady state decreased from 32 minutes to 21 minutes. Solubilities obtained in the steady state for experiments at 245°C, 275°C and 295°C were 50%, 52% and 60%, respectively. The order of the reaction changed between 0.85-0.89 for experiments run at 245°C, 275°C and 295°C. The activation energy of the solubilization reaction for the interaction of Beypazari lignite with ethyl alcohol/NaOH system was calculated as 28.8 kcal/mole. As the reaction time is increased from 18 minutes up to 90 minutes the infrared spectra became more complex and both the number of the peaks due to sulphur groups and the intensity of these peaks increased. When the temperature was increased from 245°C to 295°C the average molecular weight of the liquid products increased from 465 to 550.     

PRODUCTS FROM FLASH PYROLYSIS OF A TURKISH LIGNITE IN A FREE-FALL REACTOR UNDER VACUUM

Flash pyrolysis of a Turkish lignite under vacuum in a free-fall reactor was examined at a temperature range of 400 - 800 °C. Gaseous products were analysed with an on-line GC equipped with a manuel injection valve. Solvent fractionation was applied to the liquid product to separate preasphaltenes, asphaltenes and oils fractions. Two particle distributions of the lignite were used: -0.315+0.2 mm and -0.1 mm. The liquid yield increased with temperature up to 650 °C and, thereafter decreased for the larger particles. The maximum liquid yield, excluding pyroltic water, was found to be 8 % wt (dal) at 650 °C. In the case of the smaller particles the liquid yield increased steadily with temperature and the yield of liquid, excluding pyrolytic water, was 5.9 % wt (da) at 850 °C. The gaseous product yield also increased with temperature for both size fractions, and CO and CO₂ in the gaseous products were present in large amounts.     

PYROLYSIS OF SUNNYSIDE (UTAH) TAR SAND: CHARACTERIZATION OF VOLATILE COMPOUND EVOLUTION

Sunnyside (Utah) tar sand was subjected to programmed temperature pyrolysis and the volatile products were detected by tandem on-line mass spectrometry (MS/MS) in real time analyses. A heating rate of 4°C/min from room temperature to 900°C was employed.

Evolution of hydrogen, light hydrocarbons, nitrogen-, sulfur-, and oxygen-containing compounds was monitored by MS or MS/MS detection. Evolution of volatile organic compounds occurred in two regimes: 1) low temperature (maximum evolution at 150 to 175°C), corresponding to entrained organics, and 2) high temperature (maximum evolution at 440 to 460°C), corresponding to cracking of large organic components. Alkanes and alkenes of two carbons and higher had temperatures of maximum evolution at approximately 440°C, and methane at approximately 474°C. Aromatic hydrocarbons had temperatures of maximum evolution slightly higher, at approximately 450° C. Some nitrogen-, sulfur-, and oxygen-'ccntaining compounds were also detected in the volatile products.

Comparing the Sunnyside pyrolysis to the pyrolysis of other domestic tar sands indicated the following for hydrocarbon evolution: 1) the evolution of entrained organics relative to the total evolution was much less for Sunnyside tar sand, 2) the temperatures of maximum evolution of hydrocarbons due t o cracking reactions were slightly lower, and 3) the temperatures of maximum evolution for benzene and toluene are slightly higher than observed for other tar sands.

In general, the noncondensible gases, H₂, CO, and CO₂, exhibited evolution associated with hydrocarbon cracking reactions, and high temperature evolution associated with mineral decomposition, the water-gas shift reaction, and gasification reactions. Pyrolysis yields were dominated by the evolution of carbon oxides and water. The CO₂ primarily appeared t o cane from the decomposition of carbonate minerals. Compared t o other domestic tar sands, the gas evolution reflected more mineral decomposition character for Sunnyside tar sand.     

DIRECT HYDROGENATION OF A SPANISH LOW RANK COAL. THE EFFECT OF PROCESS VARIABLES

The effect of operating conditions on the liquefaction behaviour of a Spanish lignite was studied using a 250 ml stirred autoclave, and the following operating conditions (except otherwise specified): 400 °C, 1 hour, 3.5 MPa initial (cold) H₂ pressure, 400 rpm and 40 g/10 g tetralin/coal charge. The liquefaction products were fractionated into oils, asphaltenes, preasphaltenes and solid residue using pentane, toluene and THF as extractive solvents

The influence of temperature was explored in the 300-475 °C range, observing little further improvement in liquefaction yields over 400 °C, and retrogressive reactions over 450 °C. The effect of time was studied from 0 to 180 minutes and was concluded that 1 hour is an appropriate period for liquefying a black lignite, since there is little further conversion for longer times. The influence of pressure and gas type was studied using 0, 3.5 and 7.0 MPa initial (cold) pressure of H₂ and of N₂, and the effect of stirring using 0 and 400 rpm. Little influence of these variables was observed, which is attributed to the strong H-donor solvent, high solvent/coal ratio and long reaction time used.     

COMPARATIVE REACTION STUDY OF METHYLCYCLOHEXANE AND 3-METHYLHEXANE IN H2 AND N2 ON Pt/Al2O3 CATALYST

The reaction of methylcyclohexane and 3-methylhexane were studied in a pulse microcatalytic reactor using H₂ and N₂ carriers on Pt/Al₂O₃ catalyst at temperatures from 350 to 500°C, contact times (W/F) of 1.25 × 10^-3-3.75 × 10^-3 g min/ml and a total pressure of 4.0 kg/cm². In N₂, there was complete conversion of methylcyclohexane to methane, benzene and toluene while similar products were produced for 3-methylhexane, albeit with diminished conversion level. In H₂, methane was produced from 3-methylhexane conversion while aromatization without demethylation was obtained in addition to some cracking for methylcyclohexane at the low temperature range (350-400°C); a higher temperature range (460-500°C) resulted in complete fragmentation for methylcyclohexane. In H₂-N₂ mixtures, the presence of N₂ of not less than 50% in the carrier gas stream yielded an aromatic catalyst at conditions where only cracking activity was previously evident. The differences in product distribution and/or product types for the two reactants in H₂ and N₂ suggest a different reaction mechanism for both reactants.     

SOLID STATE 13C NMR STUDY OF THERMALLY UPGRADED LOW RANK COALS

The results of solid-state ¹³C NMR study aimed at evaluating the chemical changes and extent of upgrading achieved in the thermal treatment of two western Canadian low rank coals are discussed. The coals were thermally treated at varying temperatures (200 - 500°C) using different process media (nitrogen, steam and products of combustion)

Apparent aromaticity of the two coals was increased after the thermal treatment and increased with treatment temperature. Significant chemical changes, such as loss of the protonated aromatic carbons, quaternary carbons in alkylated rings and aliphatic ethers, were observed at 400°C and above. Condensation and polymerization of the chemical components were also evident. The effect of process medium was found to depend on the coal feed and the treatment temperature.     

Oxidative Dehydrogenation of Methanol on Chromium Oxide/Montmorillonite K10 Catalysts

Methanol conversion was carried out on a mesoporous material—chromia/montmorillonite K10 (MK10)—in a pulse microcatalytic system. Methanol was converted to formaldehyde and ethylene by two different mechanisms. Methanol dehydrogenation increases by increasing reaction temperature (300-400°C) and as chromia loading decrease. On the other hand, the dehydration of methanol occurs at a higher temperature (400-500°C) and as chromia loading increase, 3-18% Cr. Redox and exposed nonredox Cr³⁺ are responsible for formaldehyde formation. There is a relationship between increased C₂H₄ production and the increase of Cr⁶⁺ phase according to the acidity of chromia catalysts 34 and 76 μL tert-Butylamine/g catalyst for 3% Cr and 18% Cr, respectively. Formaldehyde formation is diffusionally controlled at high temperatures (400-500°C) and kinetically controlled at a lower reaction temperature (300-400°C), while methanol dehydration to ethylene is surface reaction controlled at 400-500°C.     

VARIATION IN THE CHEMICAL NATURE OF ASPHALTENES WITH THE PROCESS, THE COAL AND THE REACTION CONDITIONS

Average structure data for twelve asphaltenes are reported, based on ¹³C- and H- n.m.r. spectroscopy combined with elemental, molecular weight and functional group analyses. The asphaltenes were from supercritical gas extraction, flash pyrolysis and hydrogenation of a brown and a bituminous coal. The effect of the reaction temperature and, for hydrogenation, the catalyst and solvent on the nature of the asphaltene produced was studied. The asphaltene obtained from supercritical gas extraction of the brown coal at 350°C was the least aromatic (f_a = 0.44) with the highest H/C atomic ratio (1.16) and probably consists mainly of single ring aromatlcs with about half of the aromatic sites substituted. A significant proportion of the carbon in this asphaltene is in long alkyl chains and the hydroxyl content is high. Whereas, the asphaltenes produced by hydrogenatlon of the bituminous coal at 450°C were far more aromatic with more highly condensed but less substituted aromatic ring systems and few, if any, long alkyl chains, together with a lower hydroxyl content. The asphaltenes obtained from the brown coal are less aromatic with less condensed aromatic ring systems but a higher degree of aromatic substitution than those produced from the bituminous coal under the same conditions. The asphaltenes formed at 450°C had lower H/C atomic ratios, molecular weights and degree of aromatic substitution, but higher aromaticities Ohan those produced at 35O°C or 400°C under like processing conditions. The asphaltene produced in the presence of both stannous chloride catalyst and tetralin was less aromatic than when either of these species was absent.     

COMPARISON OF COAL LIQUEFACTION IN BATCH AND CONTINUOUS REACTORS

Liquefaction of Akabira coal with a sufficient amount of tetralin was conducted in a 27 cm³ batch reactor and two types of continuous reactors - a 5000 cm³stirred tank reactor and a 800 cm³ tube reactor. These reactors were mainly operated at 673°K and 5.4 MPa. The batch reactor was heated at different rates from 4°K/nrin to 150°K/min to examine the effects of the heating rate on the conversion of coal to benzene solubles. Conversions in the continuous reactors were measured together with the residence time distributions of coal particles.

In the batch reactor, change of the conversion with time differed appreciably depending on the heating rate even when other operating variables were the same. With increasing heating rate the conversion during heating period decreased while the apparent reaction rate constants increased. Using the kinetic data together with the observed residence time distribution of the coal particles, the conversion in the continuous reactor was predicted. From a comparison between the predicted and the observed conversions, it is concluded that conversions in a continuous reactor can be predicted on the basis of kinetic data obtained in a batch reactor with the same heating rate.     

CHARACTERIZATION OF ASPHALTENE PARTICLES BY LIGHT SCATTERING AND ELECTROPHORESIS

The solubility of asphaltenes in heptane/toluene mixtures was studied at several temperatures. A significant increment in asphaltene solubility was observed when the temperature increases from 0°C to 20°C and a moderate increase when the temperature rose from 20°C to 50°C. These results indicate that asphaltenes behave as a higher consulate temperature system, similar to nonpolar waxes. Examined by photon correlation spectroscopy, diameters from the particles formed a range between 125 and 400 nm, depending on the amount of non-solvent (n-heptane) used for the precipitation process and the initial concentration of asphaltenes. The particles presented a small positive surface potential that was not altered by the addition of resins.     

RECOVERY OF ASPHALTENES FROM TAR SAND BY SUPERCRITICAL FLUID EXTRACTION

Many non-oil producing countries are enriched with other sources of energy, for example tar sand, oil shale, coal, biomass, and uranium, that are not fully utilized. Supercritical fluid extraction (SFE) of tar sand was carried out in a batch autoclave at different temperatures. Extracts recovered from SFE were fractionated into oils, asphaltenes, preasphaltenes and gases by solvent extraction. The highest yield) of SFE (24.3 wt % dry basis) from tar sand was obtained with n-pentane/benzene (1/1, v/v') mixture at 655 K. Comparison of the amount of n-alkanes (C1-C4) evolved at 585 K and 685 K shows that the amount of methane is significantly increased at 685 K whereas the amount of C4 alkane is reduced. At 685 K, hydrogen and methane represent 45·1 vol % of the gases evolved from the SFE. The yields of C1-C3 alkane hydrocarbons were higher for supercritical fluid extracts at 685 K as compared to those obtained at 585 K. The quantity of olefines (C₂H₄ + C₃H₆) was found between 5·1 and 10·1 vol %.     

Characterization of Thermally Degraded Asphaltene Fractions Using Gel Permeation Chromatography

Petroleum asphaltene goes through three stages of mass reduction under thermogravimetric analysis from 25°C to 1,000°C at a heating rate of 1°C/min. The products from thermal degradation of asphaltene at three different temperature intervals are collected. Two residual fractions left in the sample cup are also obtained at two specific temperatures. The collected fractions and the residual fractions are characterized using gel permeation chromatography. The fraction collected between 25°C and 350°C demonstrates similar molecular weight distribution to that collected between 350°C and 450°C, with both fractions showing a typical molecular weight distribution for polymeric material. The fraction collected between 450°C and 650°C illustrates three different molecular weight distributions. The chromatogram of the residual fraction obtained at 350°C resembles that of the undegraded asphaltene. The residual fraction obtained at 450°C also demonstrates three different molecular weight distributions. The experimental data indicate that the mass reduction of asphaltene heated from 25°C to 350°C is mainly due to the evaporation of low boiling point and/or low molecular weight substances in asphaltene. Thermal decomposition and coke production occur significantly in the 350°C-450°C temperature interval. Thermal degradation continues to finish until 650°C.     

Rheology of Middle Distillate. I. Role of Composition

The rheological behavior of middle distillate (250-375°C) fraction, obtained from the waxy Bombay-High Off-shore crude oil, and its five narrow sub-fractions of 25°C interval each, i.e., Fr 1 (250-275°C), Fr 2 (275-300°C), Fr 3 (300-325°C), Fr 4 (325-350°C), and Fr 5 (350-375°C), have been studied below their ASTM pour point temperatures. The rheograms (the shear stress vs. rate of shear) of the fraction and sub-fractions, at various temperatures below their pour points, are recorded on a Haake RV-12 Co-axial Rota Viscometer fitted with a NV sensor and a temperature programmer (PG-20) and attached with a programmed heating/cooling system. From these rheograms the flow parameters like plastic viscosity, apparent viscosity, and yield stress are obtained and their variations with temperature and shear rate have been studied in terms of compositions of the fraction/sub-fractions. These results might be useful in devising methodology for overcoming the wax separation phenomenon from middle distillates at low temperatures.     

Variation in Composition of Subfractions of Petroleum Asphaltenes

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

Thermal Hydrocracking Kinetics of Chinese Gudao Vacuum Residue

The thermal hydrocracking kinetics of Chinese Gudao vacuum residue was studied in a batch autoclave reactor. The temperature ranged in 390-435°C and the initial hydrogen pressure was 7.0 MPa at 20°C. Ammonium phosphomolybdate (APM) in its dispersed phase was the catalyst. The reaction products, gas, naphtha, atmospheric gas oil (AGO), vacuum gas oil (VGO) and coke, were separated during and after experiments, and their yields vs. reaction time were obtained, for four reaction temperatures: 390, 405, 420, and 435°C. The activation energy was calculated from a traditional kinetic model to be 218.6 kJ/mol. A new kinetic model was proposed in this work that allows for the calculation of activation energy with a minimum number of three tests, each at a different temperature. This is comparable to the traditional model which requires a minimum of 12 tests; a minimum of four tests for one temperature and a minimum of three temperatures. The activation energy calculated from the new model with four tests is 229.6 kJ/mol, only 5% greater than that obtained from the traditional model. The reaction rate constants obtained from this model are also consistent with those from the traditional model.