AU603299B2 - Coal liquefaction process - Google Patents

Description

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7 P/00/011 99 Form PATENTS ACT 1952-1973 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Class: Int. CI: Application Number: Lodged: i a Complete Specification-Lodged: Accepted: Published: Priority: Q 9 Related Art: TO BE COMPLETED BY APPLICANT SName of Applicant: KOBA STEEL LTD., of 3-18 Wakinohama-cho 1-chome, Chuo-ku, Kobe 651, SJAPAN, MITSUBISHI KASEI INDUSTRIES LTD., of 5-2 Marunouchi 2-chome, Chiyoda-ku, Tokyo, 100 JAPAN, IDEMITSU KOSAN LTD., of 1-1 Marunouchi 3-chome, Chiyoda-ku, Tokyo, 100, S JAPAN., ASIA OIL LIMITED., 1-1, Shibaura 1-chome, Minato-ku, Tokyo 105, JAPAN and Address of Applicant: NIPPON BROWN COAL LIQUEFACTION CO., LTD., of 8-2, Marunouchi 1-chome, Chiyoda-ku, Tokyo 100,. JAPAN.

I t Actual Inventor: Osamu OKUMA, Shuichiro SUDA, Tatsuo HIRANO, Shigeo TACHIBANA, Kaora MASUDA, Shinichi NAGAE and Noriyuki OKUYAMA Address for Service: Care of: LAWRIE James M. Register No. 113 RYDER Jeffrey A. Register No. 199 HOULIHAN Michael J. Register No. 227 Patent Attorneys 72 Willsmere Road, Kew, 3101, Victoria, Australia.

Complete Specification for the invention entitled: COAL LIQUEFACTION PROCESS The following statement is a full description of this invention, including the best method of performing It known to me:- 'Note: The description is to be typed in dobble spacing, pica type face, in an area not exceediig 250 mm In depth and 160 mm In width, on tough white paper of good quality and it is to be inserted Inside this form.

11710/76-L C( J lni ('Cin'fmlc.ihh( Goernnment Printc.rCjnhtrrj 1A-

SPECIFICATION

COAL LIQUEFACTION PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a coal liquefaction process, and more particularly, it is concerned with a process for producing oil fractions such as naphtha by hydrogenating pulverized coal (such as brown coal), said process being characterized by that the residues left after hydrogenation and distillation are effectively utio. lized.

00 4 2. Description of the Prior Art: S0 a 15 Typical among the conventional coal liquefaction proo a cesses is the extraction-hydrogenation process. This process includes the steps of subjecting a mixture of coal, catalyst, and solvent to hydrogenation, separating the resulting liquid by distillation into naphtha, middle I 20 oil, and distillation residue (composed of insoluble ash Land heavy oil), and subjecting the residue to the deashing treatment or deashing-de-preasphalting treatment, thereby yielding heavy oil fractions, and optionally further performing the secondary hydrogenation and distillation for the heavy oil fractions, thereby yielding naphtha.

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i 2 The above-mentioned deashing treatment is accomplished by the solvent deashing process. As shown in Fig.

2, this process includes the steps of adding a solvent to the distillation residue, dissolving and extracting the heavy oils from the distillation residue, precipitating insoluble matters (such as ash) in the settler thereby separating the mixture into a slurry containing concentrated ashes (referred to as "ash concentrated slurry" hereinafter) and a supernatant liquid almost free of ash, which is a solution of heavy oils and preasphaltenes, discharging the separated supernatant liquid from oaoo' the top of the settler and discharging the ash concentrated slurry from the bottom of the settler o Optionally, the supernatant liquid subsequently undergoes o 0 15 solvent removal, secondary hydrogenation, and distillao tion. (The conventional process including the abovementioned deashing treatment will be referred to as "conventional process hereinafter.) Incidentally, the ash concentrated slurry undergoes the steps of solvent 0 C' separation and recovery. The solvent separation and recovery from the ash concentrated slurry and the supernatant liquid are accomplished by the evaporation and vaporization of the solvent.

4: 3 The solvent to be added to the distillation residue in the above-mentioned deashing treatment should preferably be a low-boiling solvent, which permits the easy aggregation of ash particles and hence permits the easy sedimentation of ash, thereby increasing the deashing ratio. (This solvent will be referred to as "deashing solvent" hereinafter.) For this reason, a relatively low-boiling solvent is recommended for the increased deashing ratio. For example, Australian Patent No.k52-i discloses a process for deashing treatment which employs a deashing solvent having a boiling point lower than 154'C.

o Incidentally, the deashing ratio is defined by A/B x 100%, o where A represents the amount of ash in the ash concen- °trated slurry, and B represents the amount of ash in the 0 0 15 distillation residue.

00 The above-mentioned deashing-de-preasphalting treatment for the distillation residue is accomplished by a0, adding a solvent to the distillation residue, thereby dissolving the heavy oils in the distillation residue, pre- -20 cipitating insoluble matters (such as ash) and preasphaltenes, and separating the mixture into a slurry containing o" coicentrated insolubles and preasphaltenes and a solution of heavy oils. Optionally, the solution subsequently undergoes solvent separation, secondary hydrogenation, and distillation. (The conventional process including the J- A> 0 -4above-mentioned deashing-de-preasphalting treatment will be referred to as "conventional process hereinafter.) Incidentally, the slurry undergoes the steps of solvent separation and recovery.

In the meantime, the "conventional process has the following disadvantages when it employs a deashing solvent having a boiling point lower than 154°C as disclosed in the above-mentioned Australian Patent. Having a low extracting power, the low-boiling solvent permits the comparatively heavy substances in the heavy oil fraction to remain undissolved and to exist on the surface of ash particles. Such undissolved residual matters are in the 0 D soft molten state and are sticky at the deashing treatment temperature. (They are referred to as "molten sticky sub- 15 stance" hereinafter.) Therefore, ash particles aggregate 0and precipitate by this molten sticky substance. As the result, the ash concentrated slurry accumulates in the 04r bottom of the settler, and the ash-containing undissolved matter grows further into a mass or an extremely viscous W, 20 layer. They clog the outlet of the settler or the piping connected thereto when the concentrated ash slurry is dis- Irj charged from the settler, making it difficult or impossible to discharge the ash concentrated slurry (referred to as "slurry discharge")

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PTN A. In other words, the deashing treatment which, employs a deashing solvent having a boiling point lower than 154°C can achieve a high deashing ratio but has a drawback of making it difficult to perform slurry discharge in a stable manner. However, this does not hold true for aromatic solvents such as toluene having a boiling point lower than 154"C. When used as the deashing solvent, they permit the slurry discharge to be performed in a comparatively stable manner because they have a high extracting power.

A disadvantage of the process which employs a lowboiling aromatic solvent as the deashing solvent is that it is necessary to supply the deashing solvent separately "o from the outside of the process system because it forms in o0 15 a limited amount within the coal liquefaction process.

(This process will be referred to as "process (ai) hereinafter.) This disadvantage makes the coal liquefaction C; 4 process complex and uneconomical, and hence it presents a serious problem.

20 Another disadvantage of "process which employs a low-boiling aromatic solvent as the deashing solvent is 41 that the solvent cannot treat satisfactorily the heavy 4 a oils in the distillation residue which vary in properties -[4 6 from time to time, because it decreases in deashing ratio and/or extracting power depending on the properties of the heavy oils.

"Conventional process has a disadvantage arising from the solvent separation and recovery from the ash concentrated slurry obtained in the solvent deashing treatment. If the residue in the slurry is ash alone, which is not sticky, the solvent recovery is easy. In actual, however, the ash concentrated slurry obtained in the solvent deashing treatment contains a solution of heavy oils in addition to ash, so that the slurry can be handled 0 0 0 in a stable manner. Usually, the ash content is less than 0 a' 8 50 wt%, or 20-30 wt% in many cases. Therefore, the ratio 03 o o of dissolved heavy oils to ash is in the range of 0.5 to 1 by weight. The heavy oil separates out, remaining 00 (O o 0 together with ash, when the ash concentrated slurry is heated for solvent separation and recovery by evaporation .0 and vaporization. The heavy oil which has separated out is in the soft molten state at the temperature at which 0 at a 20 the solvent is evaporated and vaporized. It combines ash particles to one another, forming a large amount of sticky O'I o substance having poor fluidity. This sticky substance sticks to the vessel for heating the ash concentrated slurry for evaporation and vaporization and also to the piping for solvent separation and recovery. In addition, -7 this sticky substance becomes such a hard solid when cooled that it cannot be removed easily. This hinders the normal operation of the coal liquefaction plant.

"Conventional process also has another disadvantage in the case where it includes the secondary hydrogenation step. The secondary hydrogenation is performed after the solution of heavy oils and preasphaltenes has been freed of solvent. The raw material for the secondary hydrogenation contains a large amount of preasphaltenes which poison the catalyst, with considerable deactivation.

In other words, "conventional process has a disadvantage of catalyst poisoning in the secondary hydrogenation.

On the other hand, "conventional process is free 00 0 from the problem of catalyst poisoning in the secondary o° '15 hydrogenation, unlike "conventional process because 0 0 0 i, the secondary hydrogenation is performed after the solution of heavy oils has been separated from the slurry of Olt, concentrated insoluble matters and preasphaltenes and the o solution has been freed of solvent. Nevertheless, it has a disadvantage that the slurry of concentrated insoluble $oil matters and preasphaltenes is discharged from the coal liquefaction system. The preasphaltenes in the slurry could become oils upon hydrogenation. This leads to a low oil recovery ratio.

rl I 8 "Conventional process has another disadvantage attributable to the deashing-deasphalting treatment which concentrates insoluble matters and preasphaltenes. The deashing-deasphalting treatment, which is performed at a high temperature, causes preasphaltenes to separate out in the soft molten state to form an extremely viscous substance upon combination with insoluble matters such as ash. This viscous substance solidifies upon cooling, clogging the bottom and discharging pipe of the settler used for the deashing-deasphalting treatment. This prevents the normal operation of the coal liquefaction unit.

SUMMARY OF THE INVENTION ooo000 The present invention was completed to eliminate the above-mentioned disadvantages. It is an object of the present invention to provide a coal liquefaction process o which is capable of providing all the deashing solvent from the coal liquefaction system, maintaining a high level of deashing ratio at all times, permitting the slurry to be discharged in a stable manner, and hence performing coal liquefaction at a high deashing ratio and increasing the productivity of coal-derived oils, without making the coal liquefaction process complex and uneconomical and causing troubles in slurry discharging.

-9- The process of the present invention is intended to recover solvents from the slurry resulting from the deashing treatment by solvent extraction, while preventing the sticky substance from occurring and sticking to the vessel and piping, thereby to carry out the normal operation of the coal liquefaction unit with an increased productivity.

In addition, the process of the present invention is intended to improve the recovery ratio of oils by the conversion of preasphaltenes into oils without causing the catalyst poisoning by preasphaltenes in the secondary hydrogenation, thereby to improve the productivity of coal-derived oils.

o ;10 Accordingly, the present invention provides a coal liquefaction process 0* of the type including the steps of hydrogenating a mixture of feed coal, catalyst, and solvent, distilling the hydrogenated product, thereby separating it into naphtha (N 1 middle oil, and distillation residue, treating the distillation residue with a deashing solvent (DS) for the solvent extraction of ash, thereby separating the distillation residue into a solution of heavy oil and a slurry containing insoluble matters such as ash, separating said solution of heavy oil into a solvent and a heavy oil and optionally further subjecting said heavy oil (H) to a second hydrogenation, distilling the hydrogenated product into naphtha (N 2 and middle oil, wherein the improvement comprises producing from said naphtha (N 1 and/or N 2 the deashing solvent (DS) having an average boiling point of 155- 220 C, containing less than 5 wt% of oxygen, and containing aromatic carbon whose ratio to the total carbon is adjusted to 0.2-0.6.

In a preferred aspect of the present invention the process includes the second hydrogenation step.

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4' The process further preferably comprises adjusting the slurry separated by solvent extraction such that the solution of heavy oil in the slurry contains oils and insoluble matters (such as ash) in a ratio smaller than 0.3 by weight.

In another preferred aspect the process comprises adding the deashing solvent to the slurry separated in the deashing treatment by solvent extraction, thereby performing additional deashing treatment by solvent extraction at least once, and separating it into a slurry containing insoluble matters (such as ash) and a heavy oil fraction.

The process may also preferably comprise adjusting the slurry separated in the final deashing treatment by solvent extraction such that the ratio of the heavy oil dissolved in the slurry to the insoluble matters (such as ash) in smaller than 0.3 by weight.

Another preferred embodiment of the present invention comprises subjecting to deasphalting treatment the solution of heavy oil separated in the deashing treatment by solvent extraction, thereby separating it into a slurry of concentrated preasphaltenes and a solution of heavy oil, subjecting the solution of heavy oil to the secondary hydrogenation, separating the hydrogenated product into naphtha and middle oil by distillation, and simultaneously using the slurry S of concentrated preasphaltenes as a feedstock for the primary hydrogenation.

In the final aspect of the invention, the process may preferably comprise adjusting the solution of heavy oil separated in the de-preasphalting treatment such that the content of preasphaltenes in the solution is less than wt% of the heavy oil fraction.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relationship between the boiling point '4.

P .1 f 4 -11 C) of the deashing solvent and the content of ash in the heavy oil fraction recovered from the supernatant liquid, in Example 3.

Fig. 2 is a simplified flowchart of the deashing treatment.

Fig. 3 is a simplified flowchart of the deashing treatment in Example 2.

Fig. 4 is a graph showing the relationship between the weight ratio (A) (on the abscissa) and the amount of deposit substance resulting from the steam distillation of the slurry (on the ordinate).

Fig. 5 is a flowchart of the coal liquefaction process in Example 8.

i. and/or N 2 the deashing solvent (DS) having an average boiling point of 155- 220"C, containing less than 5 wt% of oxygen, and containing carbon whose ratio to the total carbon is adjusted to 0.2-0.6.

DETAILED DESCRIPTION OF THE INVENTION The coal liquefaction process pertaining to the present invention comprises producing from the naphtha obtained by distillation after hydrogenation a solvent having an average boiling point of 155-220'C, containing less than 5 wt% of oxygen, and containing the aromatic carbon whose ratio to the total carbon is adjusted to 0.2-0.6, and using the solvent as the deashing solvent.

This deashing solvent can be obtained in large amounts by distillation from the coal-derived oils resulting from hydrogenation, because it has an intermediate ratio of aromatic carbon to total carbon (referred to as "aromaticity index" hereinafter) or a comparatively low o 0 aromaticity index, unlike the low-boiling, high-aromatic 15 solvent used in the "conventional process In other words, all the deashing solvent required can be obtained from the coal liquefaction system, and it is not necessary to supply it from the outside of the system. Not only does the deashing solvent have a low aromaticity index but it also has a high average boiling point. If the deashing solvent has a low aromaticity index alone, it does not perform slurry discharge in a stable manner because it contains more saturated hydrocarbons which lower the It

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P. Off The following statement Is a full description of this invention, Including the best method of performing It known to 'Note: The description is to be typed in double spacing, Pica type face. In an area not exceedliig 250 mm In depth and 160 mm In width, on tough white paper of good quality and it is to be Insetted Inside this form.

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extracting power. The high average boiling point contributes to the greatly increased extracting power of the solvent as mentioned later and hence to the stable slurry discharging.

In addition, the deashing solvent has a higher boiling point than the low-boiling, high-aromatic solvent used in "conventional process therefore, it has a higher extracting power and dissolves comparatively heavy col-positions in heavy oils, leaving no sticky substance.

It also permits undissolved particles of ash to aggregate in the unbonded state, settling at the bottom of the settler in the form of ash concentrated slurry. The ash particles in the slurry are easily separable because they are in the aggregate state but are not bonded to one another by the sticky substance. This makes the ash concentrated slurry highly flowable. Consequently, the slurry can be discharged in a stable manner from the bottom of the settler without the clogging of the outlet and piping of the settler. If the deashing solvent has a 20 high average boiling point alone, it has a low deashing ratio; however, the deashing solvent in the present invention is free from this shortcoming because it contains a small amount of oxygen as mentioned later. Therefore, the deashing ratio in the present invention is equal to or higher than that in "conventional process 444 4 4 .4 .4 4 4 4 The deashing solvent in the present invention contains a small amount of oxygen and hence performs deashing at a high ratio as explained in the following. Oxygen in the solvent is present in the form of oxygen-containing compounds, and such compounds are mostly phenols such as phenol and cresol. Such oxygen-containing compounds lower the deashing ratio, depending on the amount of oxygencontaining compounds and the amount of oxygen in such compounds. Therefore, the lower tihe oxygen content, the higher the deashing ratio. The low oxygen content alone leads to a low extracting power and difficulty in stable slurry discharging. This shortcoming is avoided in the co« present invention by using the deashing solvent having a higher average boiling point, as mentioned above.

15 The coal liquefaction process pertaining to the 0 t 9o1 present invention is characterized in that the deashing 0o a solvent has a low aromaticity index, contains a small amount of oxygen, and a high average boiling point, as mentioned above. These properties make up for one ano- 1 20 ther's disadvantages and exhibit their advantages synerk gistically. This leads to the advantage of the present invention that all the deashing solvent can be supplied from the coal liquefaction system, the high deashing level It can be maintained at all times, and the slurry discharge 44 -ican be performed in a stable manner. The ability to maintain the high deashing level permits the process to cope with change in the properties of the heavy oils.

According to the present invention, the deashing solvent should have an oxygen content less than 5 wt%.

Otherwise, the deashing solvent cannot maintain a sufficiently high deashing level. The oxygen content should preferably be lower than 2 wt%, at which the deashing solvent provides a higher deashing level than in "conventional process According to the present invention, the deashing solvent should have an average boiling point in the range 1, of 155-220"C. With an average boiling point higher than o 220"C, the deashing solvent does not provide a sufficiently high deashing level on account of the decreased Ssedimentation velocity of ash. Conversely, with an get :Ot average boiling point lower than 155"C, the deashing solvent has a low extracting power and prevents smooth slurry discharge. The average boiling point should pre- 20 ferably be in the range of 160-180°C, at which the deashing ratio is certainly high.

According to the present invention, the deashing solvent should have an aromaticity index in the range of 0 9 A 0.2-0.6. With an aromaticity index greater than 0.6, the deashing solvent is highly aromatic and cannot be obtained

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in large amounts by distillation from the hydrogenation product. Conversely, with an aromaticity index smaller than 0.2, the deashing solvent does not permit the smooth slurry discharging. The aromaticity index should preferably be in the range of 0.3-0.5. The deashing solvent having such an aromaticity index permits the smooth slurry discharging and can be obtained in large quantities by distillation with certainty.

The coal liquefaction process pertaining to the present invention is not limited to the single-stage process; it includes the two-stage process and multiplestage process. The two-stage process will be performed in the following manner. In the first stage, hydrogenation .(or the primary hydrogenation) is performed, and the o, 15 hydrogenation product is separated into naphtha, middle oil, and residue by distillation. The distillation residue undergoes the solvent deashing treatment to yield a solution of heavy oils, which is subsequently freed of solvent to give a heavy oil fraction. In the second S* 20 stage, the heavy oil fraction undergoes hydrogenation (or the secondary hydrogenation), and the hydrogenation product is separated into naphtha and middle oil. The naphtha obtained in the first stage or the second stage t! F r r- P1_ may be used as the solvent for the above-mentioned deashing treatment. In other words, the naphtha as the deashing solvent can be obtained not only in the first stage but also in the second and subsequent stages according to the present invention.

According to the present invention, adjustment should be made so that the ash concentrated slurry obtained in the deashing treatment by solvent extraction contains the solution of heavy oil in which the ratio of heavy oil to ash (referred to as "weight ratio A" hereinafter) is smaller than 0.3 by weight. This is important for the slurry to permit smooth solvent separation and recovery.

oO "Weight ratio A" smaller than 0.3 was established on the o, o basis of the findings obtained by experiments and 15 researches, as explained in the fol.lowing.

'With a smaller "weight ratio the ash concentrated slurry provides a less amount of heavy oil fraction when it is heated for solvent separation and recovery by evapo- °j ration and vaporization. As the result, the ratio (by weight) of heavy oil fraction to ash is small. In this situation, the ash particles mostly remain separate, It although they are partly bound by sticky heavy oil in the soft molten state. Nevertheless, the thus formed aggregates have a small diameter and a very low stickiness, and hence do not stick to the vessel and piping. Even in the eJ -pacase where particles having a large diameter exist and a sticky substance occurs, troubles by aggregation are minimal because there is only a small amount of ash for aggregation.

As the "weight ratio A" is made smaller, the amount of the sticky substance is reduced more and hence the deposit amount is reduced more. When the "weight ratio A" is smaller than 0.3, the deposit of the sticky substance in the vessel and piping is minimal and the normal operation of the coal liquefaction unit is ensured. Incidentally, when the "weight ratio A" is 0.3, the deposit of the sticky substance in the vessel and piping is very little although the occurrence of the sticky substance is Snot completely zero. In this case, it is possible to run o 15 the coal liquefaction unit more stably than in the conven- 0 01. tional case. When the "weight ratio A" is smaller than 8 0.15, the occurrence of the sticky substance is zero and there is no deposit of the sticky substance in the vessel S4and piping. This leads to the extremely stable operation of the coal liquefaction unit.

The deashing treatment by solvent extraction which is 848 performed in the process of the present invention includes the following three cases. First, a single step of sepa- 8 rating the distillation residue into the ash concentrated slurry and the supernatant liquid or the solution of heavy i

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oils. (This is referred to as "single deashing treatment with solvent" hereinafter.) Second, dual steps of separating the distillation residue into the ash concentrated slurry and the solution of heavy oils and subsequently adding the solvent to the slurry again, thereby separating it into a slurry of concentrated insoluble matters and a supernatant liquid. The second treatment is necessary because the ash concentrated slurry usually contains a solution of heavy oils. (This is referred to as "dual deashing treatment with solvent" hereinafter.) Third, the multiple steps of repeating the above-mentioned steps., (This is referred to as "multiple deashing treatment with solvent" hereinafter.) VOt o 0 According to the present invention, the deashing 0o o, 15 treatment with solvent is performed at least once and 0 adjustment is made so that the slurry separated in the final deashing treatment with solvent has a "weight ratio A" smaller than 0.3. In other words, any one of the KI above-mentioned deashing methods can be employed in the 20 present invention. Selection of the deashing methods depends on the conditions (the solvent to be used) and the desired value of "weight ratio If the conditions and the value of "weight ratio A" are the same, the "dual ,2 5 deashing treatment with solvent" is economically advantageous over the "single deashing treatment with solvent" I because the former needs much less amounts of solvent than the latter. The "multiple deashing treatment with solvent" is superior to the "dual deashing treatment with solvent"; but the incremental effect becomes smaller as the number of repetition increases.

The separation and recovery of solvent from the ash concentrated slurry can be carried out in different manners. A proper method should be selected according to the kind of the solvent. For solvents having a high boiling point, it is most desirable to use a spray dryer, gas flow dryer, or fluidized bed drier which can be operated at a comparatively high temperature. For solvents o having a low boiling point, it is desirable to use a S vacuum drier. Steam distillation is suitable for the "dual or multiple deashing treatment with solvent" in which the solvent is naphtha or toluene, which has a low 2 boiling point, although it is not used in all cases.

In the case where the heavy oil solution obtained in the deashing treatment of distillation residue by solvent 20 extraction is subjected to the secondary hydrogenation, it Sis desirable to remove (or reduce) preasphaltenes which act as catalytic poisons, prior to the secondary hydrogenation. The removal (or reduction) of preasphaltenes may 0 be accomplished by treating the heavy oil solution with a solvent for de-preasphalting, thereby separating the heavy igw L- 4~4 oil solution into a slurry of concentrated preasphaltenes and a heavy oil solution, which is subsequently subjected to the secondary hydrogenation. Alternatively, it may be accomplished by separating the heavy oil solution into solvent and heavy oil, which is subsequently subjected to the secondary hydrogenation. After this preliminary step, the feedstock for the secondary hydrogenation contains asphaltenes (as catalytic poisons) in an extremely small amount or almost none in the case where the depreasphalting treatment is performed successfully. Therefore, the preliminary step prevents the catalyst f( the secondary hydrogenation from being poisoned or deacti- S, vated. This leads to the stable operation of the second- P4 t ary hydrogenation over a long period of time.

The slurry of concentrated preasphaltenes, which is obtained in the above-mentioned de-preasphalting treat- S ment, may be added to the feedstock for the primary hydrogenation. This does not cause the problem of catalyst m poisoning, because the catalyst for the primary hydrogenao 1' 20 tion is consumed during use in combination with coal powder. Therefore, preasphaltenes undergo the primary hydrogenation without any trouble, forming heavy oil and/or middle oil. This leads to the increased oil recovi V 4 ery ratio.

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In addition, the slurry of concentrated preasphaltenes does not cause the problem of pipe clogging with the sticking substance in the de-preasphalting treatment, because it has been freed of insoluble matters (such as ash) in the deashing treatment which precedes the depreasphalting treatment. Pipe clogging occurs when preasphaltenes in the soft molten state combine with insoluble matters such as ash, as mentioned above.

In the de-preasphalting treatment, preasphaltenes are in the soft molten state, containing solvents at high temperatures, and they become large particles and rapidly settle in the bottom of the settler. They can be easily transferred by pumping on account of their fluidity. They may be dissolved in the solvent for the primary hydrogena- S 15 tion to increase their fluidity. Therefore, they can be o recycled without any problem as the feedstock for the 9 S primary hydrogenation.

The above-mentioned solvent used for the deashing treatment of the distillation residue should preferably be capable of dissolving not only heavy oils but also preasphaltenes in the distillation residue. To meet this requirement, the solvent for deashing treatment should be one which has an average boiling point in the range of 0 2 °0 0 0 155-220'C, preferably 160-180"C. Examples of such solvents include naphtha from the primary hydrogenation and naphtha from the secondary hydrogenation and a mixture thereof. The first one is desirable.

The heavy oil solution obtained after the abovementioned de-preasphalting treatment should preferably contain preasphaltenes in as small an amount as possible so that the catalyst for the secondary hydrogenation is protected from catalytic poisoning and deactivation. The amount of preasphaltenes should preferably be less than wt% of the heavy oil so as to perform the secondary hydrogenation stably over a long period of time without catalytic poisoning and deactivation.

The reduction of preasphaltenes in the above- 0

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o 15 mentioned heavy oil can be accomplished by using a solvent with a low dissolving power for the de-preasphalting o gt" treatment, so that the amount of preasphaltenes separated o in the de-preasphalting treatment is increased. For the reduction of the amount of preasphaltenes below 10 wt%, the solvent for the de-preasphalting treatment should be one which has an average boiling point lower than 150"C.

0 Examples of such solvents include naphtha from the primary hydrogenation and naphtha from the secondary hydrogenation and a mixture thereof.

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The solution for the de-preasphalting treatment may be added to the solution obtained by the deashing treatment directly or after solvent separation form said solution. In the former case, it is desirable to use a solvent for the de-preasphalting treatment which has a lower boiling point than that used in the latter case.

EXAMPLES

The invention will be described in more detail with reference to the following examples.

Example 1 A mixture of pulverized and dehydrated Morewell brown coal, catalyst, and solvent was subjected to the primary hydrogenation, and the hydrogenated product was separated I by distillation into naphtha, middle oil, and distillation 15 residue. The naphtha yielded a large amount of solvent 0 having an average boiling point of 160°C, containing 0.8 wt% of oxygen, and having an aromaticity index of 0.46.

0o This solvent was subsequently used for deashing.

The distillation residue was crushed and then trans- 20 ferred to a settler. To the distillation residue was added the deashing solvent obtained from the above- Smentioned naphth in an amount four times that of the distillation residue. The mixture was stirred at 250°C to effect the dissolution and extraction of heavy oils from 25 the distillation residue. The mixture was allowed to 4 It i :rrl -1 i *li ~ili. i.

stand still for the settling of ash in the settler. Five minutes later, the mixture separated into a slurry and a supernatant liquid. Incidentally, the extraction, settling, and separation were carried out batchwise.

The supernatant liquid was discharged from the upper part of the settler. After solvent separation, the supernatant liquid yielded heavy oil in an amount corresponding to 85% of heavy oil present in the distillation residue.

In other words, the recovery of heavy oil was 85%. This value is higher than that in "conventional process The heavy oil recovered from the supernatant liquid was found to contain 5000 ppm of ash. This translates to a deashing ratio of 96.3%. This value is comparable to PI that in "conventional process with the same treatment.

a0 °0 The ash concentrated slurry was discharged from the o bottom of the settler. The discharging could be performed o° smoothly without the clogging of the outlet and piping of the settler on account of its high fluidity.

o 20 Example 2 The same procedure for coal liquefaction as in Example 1 was repeated, except that the extraction of heavy oil and the settling and separation of ash were carried out continuously using the continuous apparatus 4

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7o- 2 -jo equipped with an extraction vessel and a settler (3) as shown in Fig. 3. The liquid level in the settler (3) was raised at a rate of 13 cm/min.

The recovery of heavy oil from the supernatant liquid was 80%, the content of ash in the heavy oil was 2000 ppm, and the deashing ratio was 98.5%.

The ash concentrated slurry in the lower part of the settler could be discharged smoothly without the clogging of the outlet and piping of the settler on account of its high fluidity.

Example 3 The same procedure for coal liquefaction as in Example 1 was repeated, except that the deashing treatment was performed with deashing solvents having different opa O* 15 average boiling points obtained from the naphtha. The S deashing solvents had average boiling points in the range of 130 to 220"C, oxygen contents less than 5 wt%, and aro- Sa a Smaticity indices in the range of 0.2 to 0.6.

It was found that there is a relationship between the o 20 boiling point of the deashing solvent and the ash content in the supernatant liquid as shown in Fig. 1. It is noted .g from Fig. I that the higher the average boiling point of the deashing solvent, the higher the ash content and the 0o\* lower the deashing ratio.

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\V04 \I 27 With a deashing solvent having a boiling point of 220°C, the ash content is This indicates that deashing solvents having a boiling point higher than 220°C will not provide a sufficiently high deashing ratio. On the other hand, deashing solvents having a boiling point lower than 155°C achieved high deashing ratios, but caused the ash concentrated slurry to form a non-flowing mass of ash in the bottom of the settler. It was impossible to discharge this slurry smoothly from the settler on account of the clogging of the outlet and piping of the settler.

Example 4 A mixture of pulverized and dehydrated Victorian brown coal, catalyst, and solvent was subjected to the primary hydrogenation, and the hydrogenated product was o 15 separated by distillation into naphtha, middle oil, and distillation residue. The distillation residue was sent a to the step of "single deashing treatment with solvent".

SIncidentally, the distillation residue was found to have a boiling point higher than 420"C and to contain 85% of pyridine solubles and 15% of pyridine insolubles (13% of ash).

In the step of "single deashing treatment with solvent", the distillation residue was incorporated with O 25-times as much naphtha (having an average boiling point 25 of 160°C) obtained from the primary hydrogenation. By -2< raising the temperature to 250*C, heavy oils in the distillation residue were dissolved and ash was allowed to settle. Thus the mixture was separated into a slurry and a supernatant liquid. Incidentally, the pyridine solubles in the distillation residue had a solubility of about 96% at 250"C. After separation, the slurry was found to contain 25% of ash and to have the "weight ratio A" of 0.10.

This slurry was subjected to vacuum distillation, and the solvent was separated and recovered easily and the ash was also recovered easily in the form of powder. The loss of the heavy oil (as the active ingredient) was 8% of the distillation residue.

o Example S 15 The same procedure as in Example 4 was repeated, S9 except that the solvent separation and recovery were carried out by using a spray drier instead of vacuum diso tillation. The solvent was separated and recovered easily and the ash was also recovered easily in the form of powder, as in the case of Example 4.

Example 6 The same procedure as in Example 4 was repeated, except that the distillation residue was subjected to al "dual deashing treatment with solvent" in place of "single 25 deashing treatment with solvent" o 6 In the first deashing treatment with solvent, the distillation residue was incorporated with four times as much naphtha (having an average boiling point of 160°C) obtained from the primary hydrogenation. The mixture was heated to 250°C to dissolve the heavy oil contained in the distillation residue. After precipitation of ash, the mixture was separated into a slurry and a supernatant liquid. Incidentally, the pyridine solubles in the distillation residue had a solubility of about 100% at 250°C.

The slurry was found to contain 25% of ash and to have the heavy oil-to-ash ratio of 0.53 by weight.

In the second deashing treatment with solvent, the slurry was incorporated with three times as much toluene.

The mixture was heated to 250°C and the heavy oil solution o' 15 was diluted. The mixture was separated into the heavy oil solution and the slurry After separation, the slurry was found to contain 25% of ash and to have the a 4 *oi' heavy oil-to-ash ratio of 0.11 by weight.

04 f This slurry was subjected to steam distillation for solvent separation and recovery. There was no deposit S in the vessel and piping at all. The heavy oil solution was subjected to solvent separation and recovery, and the toluene used was all recovered.

o 4 D aa

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X The supernatant liquid obtained in the first deashing treatment was subjected to solvent recovery, and the resulting heavy oil was subjected to the secondary hydrogenation and the hydrogenated product was separated into naphtha and middle oil by distillation.

Incidentally, the first deashing treatment was performed with naphtha (having an average boiling point of 160"C) obtained from the primary hydrogenation, as mentioned above. The object of using such naphtha was to dissolve most preasphaltenes in the distillation residue in this solvent for recovery.

In this example, the second deashing treatment was performed with toluene; however, toluene may be replaced by any solvent which has a comparatively high dissolving 15 power, is able to reduce the "weight ratio has a low boiling point, and is capable of separation from the slurry The solvent for the second deashing treatment should preferably be one which has a boiling point lower 4.

than and/or a dissolving power close to that of the solvent for the first deashinr treatment. Examples of such solvents include toluene and naphtha obtained from the primary hydrogenation.

>S The total amount of solvents (toluene and naphtha obtained from the primary hydrogenation) was 5.8 times 0 I or r a I u -1that of the distillation residue. This amount is smaller than that in Example 4. This indicates the economical advantage of the "dual deashing treatment with solvent".

The loss of the heavy oil (as the active ingredient) was 1.2% of the distillation residue. This suggests that the "dual deashing treatment with solvent" is advantageous to the increased recovery of heavy oils.

Example 7 The same procedure for coal liquefaction and solvent recovery as in Example 6 was repeated, except that a change was made in the amount of toluene added for the second deashing treatment with solvent so that the "weight ratio A" of middle oil to ash in the slurry was in the range of 0.01 to 0.53.

4o° '°15 The "weight ratio A" affects the amount of deposit a4 o o o substance that occurs when the slurry is subjected to Sa steam distillation, as shown in Fig. 4. Incidentally, the 0 04 a heavy oil and ash form particles which stick to the 00 4 0 piping, causing trouble, when they become extremely large.

The amount of deposit substance is the total weight of 0 4 particles having a diameter greater than 3.35 mm. The 0 4' percentage of the weight which accounts for in the total weight of the heavy oil and insoluble matters in the 0. a 0 0 0 o a o Su o i- slurry was obtained. It was plotted as the amount of deposit substance on the ordinate in Fig. 4. The "weight ratio A" was plotted on the abscissa in Fig. 4.

It is noted from Fig. 4 that the amount of deposit substance sharply increases when the "weight ratio A" exceeds 0.3. With the "weight ratio A" below 0.3, the amount of deposit substance is small. Especially, with the "weight ratio A" lower than 0.15, there is no deposit substance. It is desirable to keep the "weight ratio A" below 0.15 in order to eliminate the deposit substance completely; however, in practice, values smaller than 0.3 are satisfactory.

Example 8 The coal liquefaction process was carried out accord- 15 ing to the flowchart shown in Fig. 5. A mixture of pulverized and dehydrated Victorian brown coal, catalyst, and S* solvent was subjected to the primary hydrogenation at 0 Sf 0 a' 450"C and 150 atm. The hydrogenated product was separated 0o by distillation into naphtha, middle oil, and distillation residue. The distillation residue was found to have a A 4 boiling point higher than 420'C and to contain 85% of 00 Spyridine solubles and 15% of pyridine insolubles (13% of l ash).

0 0 Ol /o 33 The separated distillation residue was sent to the step for deashing treatment. In the step of deashing treatment, the distillation residue was incorporated with four times as much naphtha (having an average boiling point of 170°C) obtained from the primary hydrogenation.

By raising the temperature to 250"C, heavy oils in the distillation residue were dissolved and ash was allowed to settle. Thus the mixture was separated into a slurry (Sl) containing insoluble matters such as ash and a solution (Al) containing heavy oils and preasphaltenes.

The solution (Al) was freed of solvent to give a heavy oil fraction. The heavy oil fraction was found to contain 30% of preasphaltenes and 5000 ppm of insoluble matters such as ash. This suggests that not only heavy 15 oil but also most preasphaltenes in the distillation Sresidue were dissolved.

After solvent separation, the residue was incorporated with four times as much naphtha (having an average boiling point of 110"C) obtained from the primary hydrogenation. By raising the temperature to 250"C, depreasphalting treatment was carried out to separate the mixture into a slurry (S2) of concentrated preasphaltenes and a solution (A2) of heavy oil. This de-preasphalting treatment was performed smoothly without any trouble such oas 0 66 L i rq F_ -yas pipe clogging. The slurry (S2) was found to contain, in addition to preasphaltenes, asphaltenes, solvent, and a small amount of oil.

The slurry (S2) containing concentrated preasphaltenes was recycled as the feedstock for the primary hydrogenation. This slurry was a viscous liquid having a viscosity of 800 cp at 250°C. Nevertheless, it could be pumped easily. The slurry (S2) was subjected to the primary hydrogenation, and the hydrogenated product was separated by distillation into naphtha and middle oil.

The middle oil was subjected to the secondary hydrogenation to be finally converted into naphtha.

On the other hand, the solution (A2) of heavy oil was freed of solvent by distillation. After solvent separation, the residue was found to contain, in addition to Sheavy oil, less than 500 ppm of ash and 6% of preasphaltenes. The residue was subjected to the secondary hydro- Sgenation, and the hydrogenated product was separated by distillation into naphtha and middle oil. In the secondary hydrogenation, catalyst poisoning and deactivation were extremely slight.

The coal liquefaction process of the present invention has the following effects. It enables one to obtain 25 all the deashing solvent from the coal liquefaction o 9q o a

I

t system. In addition, it keeps the high deashing ratio at all times and permits the smooth slurry discharging.

Therefore, it performs coal liquefaction at a high deashing ratio without making the process complex and uneconomical and also without causing trouble in the slurry discharging. Thus, it will contribute to the improved productivity of coal-derived oils.

The coal liquefaction process of the present invention suppresses the occurrence of deposit substance when solvent is recovered from the slurry obtained by the deashing treatment with solvent. This protects the vessel and piping from clogging with the deposit substance and ensures the normal operation of the coal liquefaction unit. Thus, it will contribute to the improved productivo* 15 ity of coal-derived oils.

0" The coal liquefaction process of the present inven- 4q 0, tion converts preasphaltenes into oil without the poisonoff ing and deactivation of the catalyst in the secondary 0 hydrogenation, thereby increasing the oil recovery ratio.

Thus, it will contribute to the improved productivity of A coal-derived oils.

0 4 o o -0S 1:S '7 pW i

Claims (7)

1. A coal liquefaction process of the type including She steps of hydrogenating a mixture of feed coal, catalyst, and solvent, distilling the hydrogenated product, thereby separating it into naphtha (N 1 middle oil, and distillation residue, treating the distillation residue with a deashing solvent (DS) for the solvent extraction of ash, thereby separating the distillation residue into a solution of heavy oil and a slurry containing insoluble matters such as ash, separating said solution of heavy oil into a solvent and a heavy oil and optionally further subjecting said heavy oil to a second hydrogenation, I I 10' distilling the hydrogenated product into naphtha (N 2 and middle oil, wherein the improvement comprises producing from said naphtha (N 1 and/or N 2 the deashing solvent (DS) having an average boiling point of 155- 220"C, containing less than 5 wt% of oxygen, and containing aromatic carbon whose ratio to the total carbon is adjusted to 0.2-0.6. 15 2. A coal liquefaction process as claimed in Claim 1, wherein the process includes the second hydrogenation step.

3. A coal liquefaction process as claimed in Claim 1, which further comprises adjusting the slurry separated by solvent extraction such that the solution of heavy oil in the slurry contains oils and insoluble matters such as 20 ash in a ratio smaller than 0.3 by weight.

4. A coal liquefaction process as claimed in any one of Claims 1 to 3, which further comprises adding the deashing solvent to the slurry separated in the deashing treatment by solvent extraction, thereby performing additional deashing treatment by solvent extraction at least once, and separating it into a slurry containing insoluble matters such as ash and a heavy oil fraction. i ja Ia a 64 a at' A AL 4- Z- 0F L r F~ 0 Op 0 0 0 600 aO4 0 o 00 o 00 o oo O0 f 090 °o o o!,5 0 0 00 0 o 2o 2 0 0 Q 0 0 0 0 «0 00 0 *B0 00 o -37- A coal liquefaction process as claimed in Claim 4, which further comprises adjusting the slurry separated in the final deashing treatment by solvent extraction such that the ratio of the heavy oil dissolved in the slurry to the insoluble matters such as ash is smaller than 0.3 by weight.

6. A coal liquefaction process as claimed in any one of Claims 1 to 5, which further comprises subjecting to de-preasphalting treatment the solution of heavy oil separated in the deashing treatment by solvent extraction, thereby separating it into a slurry of concentrated preasphaltenes and a solution of heavy oil, subjecting the solution of heavy oil to the secondary hydrogenation, separating the hydrogenated product into naphtha and middle oil by distillation, and simultaneously using the slurry of concentrated preasphaltenes as a feedstock for the primary hydrogenation.

7. A coal liquefaction process as claimed in Claim 6, which further comprises adjusting the solution of heavy oil separated in the de- preasphalting treatment such that the content of preasphaltenes in the heavy oil is less than 10 wt% of the heavy oil fraction.

8. A coal liquefaction process substantially as described hereindescribed with reference to any one of the Examples and/or drawings.

9. Oil fractions whet, produced by the process as claimed in any one of the preceding claims. DATED this 6th day of August 1990. 4'V^ A^) KOBE STEEL LTD., MITSUBISHI KASEI INDUSTRIES LTD., IDEMITSU KOSAN LTD., ASIA OIL LIMITED and NIPPON BROWN COAL LIQUEFACTION CO.,LTD. By their Patent Attorneys: CALLINA LAWRIE L I