The structure and reactivity of brown coal

The structure and reactivity of brown coal 12. Time-sampled autoclave studies: reactor design, operation and characterization

Peter J. Cassidy, W. Roy Jackson, Frank P. Larkins”, Michael 6. Louey, Douglas Rash and Ian 0. Watkins Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia * University of Tasmania, Hobart, Tasmania 7001, Australia (Received 9 June 1987; revised 20 October 7987)

The design and operation of a time-sampled reactor system are described. It can be used to charge reactants rapidly into a preheated stirred-tank autociave and to sample its contents throughout the course of reaction. Results are presented that show representative sampling of the liquid phase is achieved. Gas solubility results are presented showing that gas yield data are also reliable. The hydroliquefaction of Morwell brown coal employing this reactor facility in both the hot-charge and slow heat-modes has been investigated. An insight into the mechanisms in the initial reaction period is provided.

(Keywords: brown coal; reactivity; autoclave studies)

An early study by Neavel’ demonstrated that coal was physically altered after only a few minutes of reaction at temperatures as low as 350°C. Recent work has also shown that coal-related model compounds* and lignin3, believed to be one of the precursors of coal, displayed significant thermal degradation in the 200-300°C temperature range. It is therefore not surprising that interest has increased in the study of primary coal degradation reactions in coal liquefaction, as these reactions may have an important bearing on the ultimate degree of coal conversion. Fundamental coal liquefaction studies have generally been performed using conventional batch autoclaves or continuous reactors. Although these systems provide an adequate description of the conversion process for long residence times, their configurations do not permit the initial reaction period to be monitored with accuracy. Long times spent by the coal under non-isothermal conditions and difficulties in accurately determining hold-up times for studies employing conventional batch autoclaves and continuous reactors respectively are major reasons for uncertainty in attempts to describe the initial reaction period.

Attempts have been made by other workers to overcome the problems associated with conventional reactor types by using reactors into which coal slurry can be charged after the reactor has been heated to reaction temperature 46. In these studies, the entire contents of the autoclave are either rapidly cooled or discharged after reaching the desired residence time. Therefore, only one residence time could be examined for each experiment performed. Consequently, detailed examination of the first few minutes of reaction was tedious and time consuming. Studies employing micro tubing (bomb) arrangements are also limited by the need for a series of experiments at different residence times.

This paper discusses the design, operation and characterization of a reactor facility used as part of a 0016-2361/89/0100324,8%3.00 0 1989 Butterworth & Co. (Publishers) Ltd.

32 FUEL, 1989, Vol 68, January

major investigation into the liquefaction of a wide range of coals being carried out a Monash University in the Department of Chemistry. The facility can be used to rapidly charge reactants into a preheated autoclave and frequently sample both the gas and liquid phases of the reaction mixture during the course of the reaction. A considerable amount of information can therefore be gained from only one experiment, as a complete product distribution profile can be generated over the whole residence time range and, in particular, in the interval where most of the dissolution of the coal takes place. Results of specifically-designed experiments that test whether representative sampling was achieved for both the liquid and gas phases in the autoclave will be presented and some typical results of the hydroliquefaction of Morwell brown coal will be discussed. More detailed coal liquefaction studies are reported in the accompanying paper’.

EXPERIMENTAL

Design basis

The reactor facility was designed along similar lines to that used by Rindt et al.5 at the University of North Dakota Energy Research Centre. A modified, 41, magnetically-stirred batch autoclave (Autoclave Engineers Inc., Erie PA) was used to process 300 g of dry coal during a typical experiment in which up to 75 liquid samples (including flushes which preceded each sample for analysis) and nine gas samples were taken. A hydraulically-operated piston accumulator (ram) was used to charge the reactants into the preheated autoclave in < 15 s. The reactor was also equipped with a 20 1 receiver vessel that quenched the entire autoclave contents upon discharging at the end of the experiment. Operational safety was a major consideration in the reactor design and this aspect was reinforced with an extensive and rigorous reactor maintenance routine.

The structure and reactivity of brown coal. 12: P. J. Cassidy et al.

Figure 1 Schematic of the time-sampled autoclave

Reactor lay-out The reactor facility was housed in a well-vented re-

inforced cell fitted with a light blow-out skylight.

Reactor description A simplified schematic of the reactor facility is given in

Figure 1.

Reactant charge facility. Liquid and solid reactants were charged into the preheated autoclave using a hydraulically-operated ram employing a maximum delivery pressure of 60 MPa. A second, smaller ram which contained a small amount of reactant solvent was linked in parallel and was sequenced into action when the piston of the main ram had reached the end of its travel (i.e. delivered all of its contents). This operation effectively cleared the lines downstream of any particulate matter so that the valves could seal.

Autoclaue. A 4 1, magnetically-stirred autoclave (Autoclave Engineers Inc.) was supplied fitted with a flush valve located at the base of the autoclave. Some modifications were made to improve mixing of the autoclave contents. These modifications included increasing the number of baffles from two to four; locating a two-bladed, pitched impeller high on the stirrer stem to increase mixing of the gas phase; increasing the diameter of the original impeller from 5 cm to 6.5 cm (half of the internal diameter of the autoclave) by enlarging the size of the paddles; removing the bottom skirt of the original impeller to increase mixing of the region immediately below the impeller; fitting an insert in the flush valve to reduce the amount of dead volume in the assembly.

The stirrer was operated at 900 rpm in all experiments. Heating of the autoclave was by means of two electrical heaters encased in a common jacket. Internal temperatures were measured by a thermocouple inserted through the head of the autoclave.

Liquid sampling system. Samples of the autoclave liquid phase were taken via a series of valves located at the base of the autoclave. This was achieved by allowing an aliquot of the reaction mixture to fill a liquid sample loop. The sample loop was then isolated from the autocalve and vented into an open Pyrex test tube. A liquid sample collector which held all of the test tubes ensured that no

two samples were vented into the same test tube. The sampling sequence took no longer than 10 s to perform. All the sample lines and the valve bodies were thermally insulated to prevent blockages occurring during the sampling process.

Gas sampling system. Samples of the gas phase were taken through the cap of the autoclave via a series of valves similar in configuration to that used for liquid samples. Each of the samples was stored in an individual reservoir ready to be analysed at a later time by gas chromatography.

Larger gas phase samples could also be taken through the cap of the autoclave via a different series of valves. These samples permitted the vaporized solvent component of the gas phase to be monitored with time.

Product quench system. The entire contents of the autoclave were discharged at the end of reaction and the non-permanent gaseous products were collected in a series of quench vessels consisting of a 20 1, and a 500 ml steel container linked by a cooling coil kept at -78°C. Both quench vessels were precooled with dry-ice. A bahle arrangement in the 20 1 container ensured that most of the condensable products were effectively knocked-out. The permanent gaseous products were not collected during the autoclave discharge procedure.

klues. All of the valves used on the reactor facility were supplied by Autoclave Engineers Inc. and were air operated, high temperature, high pressure types (30VM series valves). Valves that were adjacent to heated apparatus were equipped with a high temperature extended stuffing box option. Valves that were immediately adjacent to the autoclave and were operated at some stage during the reaction were linked in series with a second, back-up valve which was actuated in unison. The valves were controlled at the operator’s console located in the main laboratory area.

Operational safety. All electrical wiring in the reactor cell was of the flame-proof type. Solenoid valve actuators were located outside the cell and were independently wired. Over-temperature and over-pressure alarms were featured on the operator’s console. An emergency shut- down system that rapidly depressurizes the autoclave and aborts the experiment was incorporated as a one button execution on the operator’s console.

EXPERIMENTAL

Experimental conditions The procedure for reactions which were performed

using the hot-charge facility on the reactor unit was as follows :

The time sample autoclave (TSA) was pressurized with reactant gas (3 MPa) and internal standard gas (helium, 0.5 MPa) at room temperature and then heated to reaction temperature (425°C) at 3°C min- ‘. Upon reaching reaction temperature, approximately two-thirds of the reaction solvent (12OOg homogenized solvent) was charged via the hydraulic ram and the TSA allowed to recover to reaction temperature.

The coal slurry mixture (600g homogenized solvent + 300g coal dried at 70°C under vacuum) was then

FUEL, 1989, Vol 68, January 33


Table 1 Chemical analysis of Morwell coal bulk sample”

Moisture (%ar) 10.8 Ash (%db) 3.6 Minerals and inorganics (%db) 2.2

Proximate and ultimate-%dmif

Volatile matter 48.6 Carbon 70.4 Hydrogen 4.9 Nitrogen 0.52 Sulphur (organic) 0.26 Oxygen (by difference) 24.0

Heating value-MJ/kg

Gross dmif 26.88

Coal minerals and inorganics-_%db

SiO, 0.65 A&G, 0.07 R,G 0.011 TiO, 0.008 FeS, Ca 0.76

FeNp 0.26 Mg 0.30

Na 0.08 Cl 0.05 ST 0.25 Fer 0.26

calculated ash (%db) = 3.4

’ Analysis performed by The State Electricity Commission of Victoria Research and Development Department; Laboratory report no. CSj79/85. ar, as received; db, dry basis; dmif, dry mineral, inorganic free; ST, total sulphur; Fq, total iron; F%p, non-pyritic iron

introduced into the hydraulic ram and charged into the TSA. The coal charge was complete when the secondary ram containing a small amount of solvent had finished delivering its charge. Zero time was taken when the piston of the major ram had reached the end of its travel.

The reactant levels used for hydrogenation experiments are summarized as follows: 300g 70°C vacuum dry Mot-well brown coal (-60 British Standard mesh); 900 g tetralin and 900 g decalin or 1800 g total solvent; 3 MPa initial reducing gas pressure; 0.5 MPa initial helium gas pressure; 425°C reaction temperature; 1 h total reaction time; coal slurry composition 1:2 dry coal :solvent weight ratio.

A total solvent charge of 1800g was necessary for maintaining effective stirring of the autoclave contents. Decalin (a relatively poor hydrogen donating solvent) was used as a diluent in reactions to keep the desired coal: tetralin ratio while maintaining effective stirring.

The coal came from Drum 287/8 of the Coal Corporation of Victoria 100 tonne Mot-well (Latrobe Valley) bulk sample from No. 5 Open Out. The coal was freshly won from the lower levels of Mot-well Open Out during October 1982. The chemical characteristics of the coal are given in Table 1.

Experiments using coal product simulants to establish whether representative sampling of the liquid phase was achieved employed 140g dry charcoal (-60 British Standard mesh) and 140g n-octacosane (n-C,,) instead of 300 g dry coal. In some experiments designed to study the effect of temperature on gas solubility, the octacosane was replaced by a similar amount of silicone oil (Dow Coming 550 Fluid). The results for these experiments, however, will not be presented here, although the trends were similar to the experiments using octacosane.

SAMPLING PROCEDURE

Liquid products

A high frequency of liquid sampling (1 sample every


15 s) was used during the first 1.5 min after injection of the coal slurry. Sample intervals after the initial 1.5 min period were varied according to the expected reaction rate of the coal and sequence typically used included up to 35 samples for analysis taken during the course of reaction. Each liquid sample was preceded by a flush cycle to clear the lines and valves of material from the previous sample to avoid cross-contamination. The liquid sample loop used throughout this study delivered a total sample weight of approximately 2.3-3.5 g. Therefore, during the reaction, less than 5 wt y0 of the contents of the autoclave were sampled.

Gaseous products

The gas sampling system allowed the gas sample loop, sampling lines and storage reservoir to be evacuated prior to sampling to avoid cross-contamination. Up to nine gas samples were taken during the reaction and the sampling frequency was highest in the first few minutes after charging the coal.

LIQUID PRODUCT ANALYSIS PROCEDURE

Time-sample products

Liquid products were separated into three fractions according to their solubility in various solvents. The fractions that were generated are listed below together with their solubility characteristics. 1. Insolubles-insoluble in excess methylene chloride. 2. Asphaltene-insoluble in excess light petroleum (Shell

X4), soluble in methylene chloride in the presence of coal derived product and the reaction solvent.

3. Oil-soluble in excess Shell X4 in the presence of reaction solvent. Shell X4 comprised mainly C6 hydrocarbons.

The oil fraction was determined by difference by quantitating the portion attributed to reaction solvent (tetralin, decalin and naphthalene) by gas chroma-

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E) Carbon dioxide A Hydrogen X Helium

Figure 2 Effect of temperature on gas solubility (normalized with respect to initial pressure)-liquid phase results


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Figure 3 Effect of temperature on gas solubihty-gas phase results

tography (i.e. wt % daf oil = [ 100 - [insolubles + net gas + asphaltene + solvent]]).

In the experiment where n-octocosane was used to simulate the oil in preliminary testing experiments for the TSA, the oil was determined directly by gas chromatography.

End-of-run discharged products

The procedure for the work-up of the products discharged from the autoclave at the end of the experiment differred slightly from that used for the time- samples due to the large quantities of materials used. The products were recovered from the quench vessel using acetone and weighed after solvent removal by vacuum rotary evaporator. The insolubles were filtered from the neat liquid products and extracted with methylene chloride. The extractable products were combined with the neat liquid products and a known aliquot was taken and added dropwise to a stirred container of Shell X4 to precipitate the asphaltene fraction. The coal-derived oil was isolated upon removing the Shell X4 vacuum rotary evaporator after which the liquefaction solvents (tetralin, decalin and naphthalene) were removed by vacuum distillation (9O”C, 30 mmHg) in a conventional distillation apparatus.

The percentages of the liquid product components were therefore directly determined since all of the coal-derived fractions, with the exception of product gas and water, were weighed.

GAS ANALYSIS PROCEDURE

The analysis of each of the product gas samples was performed concurrently on three dedicated gas chromatographs where up to 10 gases could be detected (I&, He, C&, CO, CH,, GH,, C,H,, W-L Cd-b, i- Cd-b n-Cd-ho).

The number of moles of each of the product gas components was calculated using the following

relationship.

Z” = (X/X,)Z*

where

X = moles of helium charged into the autoclave; XT = mole% helium in sample; Z, = mol% of gas component in sample; Z, = moles of gas component, n=CO,, CO, H,, C,-

C, hydrocarbon gases.

GAS SOLUBILITY DETERMINATION PROCEDURE

Determining the extent of solubilization for each of the product gas components in the solvent system commonly used in TSA reactions was achieved by the following procedure.

A gas mixture that simulated the approximate composition and quantity of product gas found in conventional reactions using Morwell brown coal was introduced into the evacuated TSA. The composition of the gas mixture was as follows: mol % He 14.6, CO1 2 1.7, CO 0.8; CH, 1.5, H, 61.4. Initial pressure=3.43 MPa.

The autoclave was then charged with a total of 1400 g of degassed solvent (700 g tetralin, 700 g decalin) via the hydraulic ram. The stirrer was then turned on and the autoclave was slowly heated (3°C min-‘) stepwise to predetermined temperature settings.

Upon reaching each isotherm, the autoclave contents were allowed to equilibrate for approximately 10min. The stirrer was then turned off and after 1 min, a gas sample was taken and a corresponding liquid sample was taken via a dip-tube through the cap of the autoclave. These liquid samples were collected in preweighed 70ml batch autoclaves.

The product gas dissolved in the liquid phase samples was then analysed by gas chromatography to determine its composition and its volume was measured by a wet gas meter. The product gas composition was determined in the manner described above.

The 70 ml autoclaves were then weighed and the mass of solvent collected by the sampling procedure was then calculated by difference. The amount of each of the product gas components dissolved in the solvent was then calculated from the volume, composition and solvent recovery data.

The gas composition results of the corresponding gas phase samples were used to complement and verify the trends observed from the liquid samples.

PROCEDURE FOR DETERMINING THE AMOUNT OF OIL IN THE GAS PHASE

The apparatus used to determine the amount of oil simulant in the gas phase at 425°C employed a 35 ml, and a 70ml batch autoclave connected in series by three valves. The larger of the two autoclaves was charged with tetralin (15 g), decalin (15 g), charcoal (3 g), and oil simulant (3 g) in relative proportions used in TSA experiments (with respect to reactor volume). The smaller autoclave was used as the sampling vessel and its volume was smaller to reduce the amount of rapid solvent vaporization while sampling. Both autoclaves were heated to 425°C. The autoclaves were held at this



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OO In 5 10 1 15 * 20 8 2s 11 30 3s 8 40 * 45 11 50 55 8 60 1

Residence time (min.)

LESEND Q cha-coal A Octacomne(direct nasnrement>

Fire 4 Yields of insolubles and oil obtained by direct measurement from the experiment using coal product simulants

temperature for 30 min before the valve system was opened. The system was allowed to equilibrate for 5 s before shutting the valves and quenching the autoclaves. The contents of each autoclave were analysed in the conventional manner.

RESULTS AND DISCUSSION

Reactor performance The thermal recovery of the TSA was an important

aspect of the hot-charging technique as it was desirable to keep the nonisothermal period to a minimum. The temperature profile of a typical experiment first showed a temperature drop due to the initial solvent-only charge. The purpose of this charge was two-fold. The autoclave required at least 600 g of solvent at 425°C to saturate the vapour phase so that the solvent of the coal slurry would not flash on charging. Secondly, this minimized the amount of material that had to be heated when the coal was injected and hence reduced the temperature drop and the thermal recovery time to reaction temperature.

A second temperature drop was observed due to injection of the coal slurry. The thermal recovery profile showed that the lowest temperature experienced by the coal was never less than 350°C unlike the solvent-only charge which dropped below 300°C. Recovery to 400°C was achieved in <2 min. The relatively slower response for the autoclave to reach the set temperature (425°C) after 2 min was caused mainly by the temperature controller which limited the heating rate to minimize the temperature over-shoot.

Gas solubility results Selective dissolution of product gas components in the

vehicle solvent would result in unreliable gas yield data being obtained. There are several reports in the literature which showed that temperature significantly affected the solubility of COz, CO, CH, and H, and that the relative

solubilities of these various permanent gases differed in coal related liquids and tetralin-containing mixtures depending on the temperatures used*-lO.

To determine whether there was any difference in the solubility of H,, CO,, CO, CH, and, in particular, He (internal standard) in the solvent system generally used, the TSA was charged with tetralin, decalin and a gas mixture approximating the final product gas composition in reactions employing Morwell brown coal (refer experimental section for gas mix composition). The autoclave was then heated and both liquid and gas samples were taken during heating to 425°C.

The results of the gas solubility experiment (normalized with respect to pressure) are shown in Figure 2. The solubility of CO, in the solvent was found to pass through a minimum between ambient and 425°C. The behaviour of the solubility of H, and He was similar but the minimum value was less marked. It is important to note that there was no significant difference in the solubilities of the major gas components in the solvent system at the temperature normally used (425°C). It is also interesting to note that the solubility of the gases rose substantially at temperatures above 350°C.

Results for the composition of the gas taken via the normal gas sampling system (Figure 3) showed that the proportion of CO, relative to He in the gas phase,

(nCO+He,) X (nHei”itiaJnCO2initial)

where n= number of moles; T= temperature when sampling occurred, was lower during the heating period which confirmed the solubility data. Results for the proportion of the hydrogen in the gas phase relative to helium (refer Figure 3) indicated that the molar ratio, Hz/He, remained constant over the total temperature range and was only marginally affected by the introduction of the solvent at ambient temperature which again confirmed the solubility data.

The above results demonstrate that the gas yield data obtained in TSA experiments at reaction temperature are reliable and that there is minimal selective gas dissolution in the solvent.

DETERMINATION OF THE RELIABILITY OF THE LIQUID SAMPLING SYSTEM

Results of experiments using coal product simulants It was imperative to demonstrate that the liquid

sampling procedure provided aliquots that were representative of the bulk liquid mixture in the autoclave. Verification was performed by hot charging the TSA in the conventional manner with a mixture of thermally stable constituents and comparing the composition of samples taken out via the established liquid sampling system with that of the known bulk ‘reaction’ mixture. Charcoal and octacosane were the materials chosen to simulate the residue and oil derived from the coal during liquefaction respectively. It was decided to use an oil simulant that could bequantitated directly rather than by difference as was the case with reactions using coal (refer to experimental section for work-up procedure). The long, straight-chain hydrocarbon, octacosane, was chosen as the oil simulant for this experiment since its boiling point (432°C) was above the reaction temperature being used. The thermal stabilities of the coal simulants were checked by heating them independently to 425°C for



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LEGEND Q CH2C12 ~nsolubles m ospholtme x 011 + tots1 g-we*

Fire 5 Product yields from the hot-charge reaction of untreated Monvell brown coal (Note: values in circles refer to yields of products discharged at the end of the experiment)

1 h in 70 ml batch autocalves and by heating them together in the presence of tetralin and decalin. In all instances the starting materials were quantitatively recovered. In the experiment where octacosane was heated alone, no significant increase in reactor pressure was observed indicating that little octacosane had vaporized.

The mixture that was charged into the TSA contained equal quantities of dry charcoal (140g) and octacosane (140 g) along with 900 g of tetralin and 900 g of decalin thereby providing a 1: l(50 y0 : 50 %) product composition distribution (excluding solvent). Hence, an oil and insolubles yield of 50 %wt input was anticipated. Octacosane was introduced into the TSA before heating to reaction temperature since it was a solid at room temperature and its physical characteristics made it difficult to inject using the hydraulic ram. The results displaying the effect of time on the sample composition at 425°C are shown in Figure 4. The results showed that the experimentally derived product yields were far from the theoretically expected values based on the input mixture composition. Approximately 40 wt y0 of the input oil was consistently not sampled which subsequently raised the yield of insolubles (charcoal) by 20 wt % input. These results were verified by a repeat experiment.

Analysis of the material discharged at the end of the experiment displayed a product composition (insolubles yield 49 wt %, oil simulant yield 5 1 wt %) similar to that of the input mixture. It is important to recognize, however, that although the product yields were not in agreement with the expected values, because the octacosane was solubilized in both the gas and liquid phase tetralin- decalin solvent as discussed below, reproducible liquid sampling was achieved within 15-30 s after injection.

The effect of varying operating parameters including stirrer speed, reactor operating pressure, flush valve

opening time and impeller design was also investigated, but it was found that the existing conditions were optimal.

Results of gas phase sampling experiments

Although it has already been mentioned that octacosane only exerted a low partial pressure when heated to 425°C alone, it was possible that in the presence of tetralin or decalin, the oil simulant was dissolved in the solvent and was therefore distributed over the total autoclave volume instead of being found only in the liquid phase. A significant amount of the solvent in TSA experiments would have been in the gas phase since decalin was supercritical at 425°C and a considerable part of the tetralin would have been in the gas phase. Therefore, a sample of the gas phase would have contained oil simulant in approximately the same weight ratio with respect to solvent as the input mixture. It would be expected then that since the charcoal charged would have only been dispersed in the liquid phase this would have explained the high yields of charcoal observed in samples taken at 425°C.

To determine whether octacosane was carried-over into the gas phase in the presence of solvent, a gas phase sampling experiment was performed using two coupled autoclaves. A description of the experimental procedure and apparatus are given earlier. The reaction mixture used in this experiment had the same composition and the same quantities per unit volume of the autoclave as that reported for the TSA experiment.

The results (refer Table 2) showed that sampling if the gas phase was successfully achieved as indicated by only trace amounts of charcoal in the sample. The value found for the weight ratio, octacosane/solvent, for the gas phase was in good agreement, within experimental uncertainty, with the ratio of the input mixture which indicated that the oil simulant was distributed over the total reactor volume at 425°C. These results explain the trends observed in the above-mentioned TSA experiment in which liquid samples displayed apparent high yields of insolubles.

Based upon the above calibration experiments, the following conclusions may be drawn concerning the operation of the TSA reactor facility. The reaction mixture in the TSA equilibrated within 15-30 s after hot- charging and reproducible liquid sampling was then achieved. The mixture comprising the liquid phase in the TSA becomes homogeneous within this time also. (In the presence of solvent, the oil simulant, octacosane, was distributed over the entire autoclave volume at 425°C.

Table 2 Results of gas phase sampling experiments

Input charge

Wt. charcoal fg) 3.00 Wt. octacosane fg) 3.00 Wt. tetralin fg) 15.00 Wt. decalin (9) 15.cO

Wt % octacosane/solvent = 10 %

Gas phase sample composition

Total wt. gas phase sample fg) 5.2 Wt. octacosane (9) 0.581 Wt. total solvent (g) 4.630 Wt. charcoal (g) 0.005

Wt % octacosane/solvent = 13 %



However, it was anticipated that the oil derived from coal would display this behaviour to some degree. Results of the TSA experiments using coal will show that the amount of oil distributed in the gas phase was small.) These findings imply that representative sampling of the liquid phase was achieved rapidly after hot-charging.

EFFECT OF RESIDENCE TIME ON THE HYDROLIQUEFACTION OF UNTREATED MORWELL BROWN COAL

Presentation of results The results for the analysis of liquid samples from

reactions employing coal were expressed on an approximate daf coal basis by allowing for the weight of gas produced. However, it was not possible to measure the water and light oil (b.p. ~220°C) produced during these experiments and so these products were proportioned between the insolubles, asphaltene and oil. The problem of carry over of light coal-derived oil into the gas phase by the solvent was considered to be low as it was found that the composition of the whole liquid product discharged at the end of the experiment was generally in good agreement with the last time sample taken via the flush valve. Where significant discrepancies occurred (e.g. in the run shown in Figure 5), the value of oil determined in the total liquid discharge was always lower than that of the last time sample.

Hot-charge hydrogenation of Morwell coal The results of the hydrogenation of Mot-well coal,

charged into the preheated autoclave of the TSA unit using the hot-charge facility, are displayed in Figure 5. The insolubles were found to return an initial yield of approximately 70 wt % daf coal in the first few minutes of reaction. After an initial large scatter of values in the first two minutes after injection, successive data points showed good agreement with each other. The oil in turn displayed yields in the range 20-25 wt % daf coal over this interval and the gas yield rose sharply to approximately 6 wt % daf coal. The production of asphaltene was negligible, displaying a yield of only l-2 % after 5 min of reaction. These findings provide strong evidence to show that part of the brown coal structure breaks down readily to produce predominantely oil under the influence of thermal shock and that any entrained material (guest) in the more rigid coal lattice structure (host) was rapidly released in accord with the structural model for brown coal developed by Redlich et al.“.

In the interval, 5 min<t<30 min, the oil yield rose markedly to approximately 40 wt y0 daf coal. The asphaltene yield also increased slightly to 6 wt % daf coal while the insolubles yield decreased by 30% to 40wt y0 daf coal. During this period, the guest material was further degraded and the breakdown of the polycyclic macromolecular host network occurred. The production of gas was almost complete within 10 min of injecting the coal, though the maximum yield (13 wt y0 daf coal) was not reached until 20 min had elapsed. Most of the product gas was CO, (10.5 wt % daf coal) while the remainder was mainly CO and CH,.

The hot-charge experiments of Strachan et a1.6 at 380°C showed a similar high release of gas in the early stages of reaction but oil yields were much lower at this low temperature (7.6 wt % daf coal) after 4 min. The coal was a Loy-Yang (Victoria) medium light lithotype for


which chemical characteristics were not given. It is possible that the coal contains significantly less guest material than the Morwell coal used in this study or that the guest component is not released quickly at 380°C.

High yields of liquid products after short reaction times were reported by the Grand Forks Energy group for a reaction of a lignite in a mixture of anthracene oil and tetralin using their hot-charge, time-sampled autoclave systenP.

The samples taken from 30 min to the final sample after 60 min showed that the rate of conversion was considerably lower in this period, the insolubles yield falling by only 15 % giving a final product distribution of approximately 20 wt % daf coal insolubles, 55 wt % daf coal oil, 8 wt % daf coal asphaltene and 13 wt % daf coal gas. In addition to further degradation of coal during this period, the interconversion of products will undoubtedly occur”.

The amount of naphthalene present in the solvent was only approximately 2 wt % initial tetralin after the first minute of reaction which demonstrates that the production of the rapidly formed oil predominantly from the guest component of the coal required negligible hydrogen from the solvent, However, the level of naphthalene rose over the whole reaction period and the greatest rise observed in the interval where most conversion activity was observed (O-20 min). It was considered that this interval principally corresponded to the degradation of the host component of the coal. Hydrogen consumption from the gas was also negligible in the first minute of reaction (0.08 wt% daf coal) but increased to 0.3 1 wt % daf coal after 10 min and finally reached 0.65 wt % dafcoal by the end of the reaction. The total hydrogen consumed in the reaction after 60 min was 2.6 wt % daf coal. Since no catalyst was added to this

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Figure 6 Product yields from the slow heat-up reaction of untreated Morweil brown coal. (Note: values in circles refer to the yields of products discharged at the end of the experiment)


system, minimal rehydrogenation of the naphthalene to tetralin was expectedi2.

Slow heat-up hydrogenation of Momell coal

A reaction to study the effect of slowly heating the coal to reaction temperature was also performed so that the results could be compared with the results obtained by hot-charging. The reaction was carried out by charging all of the reactants at ambient temperature and then slowly heating the mixture at 3°C min-i until 425°C was reached. The reaction was then held at temperature for 1 h. Sampling of the liquid phase was performed throughout the heat-up interval and while at reaction temperature.

The results of this experiment are summarized in Figure 6. Very little reaction was observed below 300°C and this data is not included in the figure. The product composition observed at 350°C was similar to that found in the interval immediately after hot-charging the coal (refer Figure 5). The minimum temperature of the autoclave during hot-charging also happened to be 350°C which suggested that the added time used to heat the coal up to this temperature in this experiment had little effect. Finally, a significant level of conversion was observed in the heating range between 350°C and 425°C which reduced the amount of insolubles from approximately 70% to 5w5 wt % daf coal. Approximately 55 percentage points out of a possible 80 wt % daf coal was already converted to dichloromethane solubles by the time reaction temperature was reached. The product composition obtained after 1 h at 425°C was similar to that found for the equivalent hot-charge reaction.

The entire products of this reaction were successfully discharged from the autoclave at the end of the desired 60 min period at 425°C (within 1 min of the last time- sample being taken). The results of the product composition was insolubles, 17 wt %; asphaltene, 18 wt %; oil, 55 wt %; total gases, 15 wt Y0 daf coal (the yield of gases was obtained by extrapolating the results obtained by the gas time-samples), which compares favourably with the last time-sample taken after 60 min at 425°C (insolubles, 21 wt %; asphaltene, 10 wt %; oil, 50 wt %; total gases, 15 wt % daf coal). The good agreement between the results strongly supports the view that very little coal-derived oil was carried over into the gas phase by the solvent unlike the case of the oil simulant, octacosane. The slightly lower oil yield and higher asphaltene yield for the total discharged products was attributed to differences in the scale, and time taken to work-up the sample which could result in the conversion of oil to asphaltene13.

CONCLUSIONS

This initial study has shown that reliable information about the liquefaction process can be obtained from this reactor system. The findings of experiments employing thermally stable materials to simulate coal derived products have demonstrated that representative sampling of both the gas and liquid phase in the autoclave of the reactor system was successfully performed and that the liquid phase was homogeneous within 15-30 s of the hot- charging process.

The reaction of Morwell brown coal showed that an oil yield of approximately 20 wt % daf coal was achieved

upon hot-charging the coal at 425°C. This rapidly formed oil, considered to originate predominately from the guest component of the coal, required negligible external hydrogen for its formation. Major conversion activity for the coal was observed in the initial 30 min of reaction, where the methylene chloride insolubles yield was reduced to approximately 40 wt y0 daf coal, while most production of gas was limited to the first 10 min. Most of the conversion activity after approx. 5 min was related to the host component of the coal. The results of the slow heat-up reaction correlated well with some aspects of the hot-charge reaction. The composition of samples taken at 350°C were similar to those found immediately after hot- charging. A significant level of conversion occurred during the heating period over the temperature range 350°C to 425°C.

The time-sampled autocalve facility provides a technique with which one can uniquely study the hydroliquefaction process under reaction conditions. In future papers, an insight into the role of catalysts, the nature of reducing gases and solvents, the dependence on the rank of the coal and, kinetic and mechanistic information will be provided.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support of British Petroleum (London) through their Extra-mural Research Awards and for permission to publish the work. The views expressed in this paper are entirely those of the authors. Dr M. Watson,B.P. Sunbury-on-Thames, and Dr D. Royston, Coal Corporation of Victoria, are thanked for their helpful comments regarding the modifications to the autoclave which led to more efficient mixing of the contents. Dr Marc Marshall is thanked for his helpful discussions. Messrs Jack McMichael and John Taylor are thanked for their technical support. I.D.W. wishes to acknowledge the award of a scholarship by the Coal Corporation of Victoria.

REFERENCES

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