CA1055250A - Process for the production of ashless liquid fuels - Google Patents

Abstract

PROCESS FOR THE PRODUCTION OF ASHLESS LIQUID FUELS

ABSTRACT OF THE DISCLOSURE

An ashless liquid fuel of good quality is produced by combining powdery coal with a heavy oil of the petroleum series in an amount of at least 50 parts by weight of heavy oil per 100 parts by weight of the powdery coal, subjecting the mixture to a heat treatment conducted at 400-450°C and thereafter, removing a solid coagualted material formed in the treated product. An especially good result is obtained when a heavy oil of petroleum series having an atomic ratio C/H of at least 0.9 is used.

Description

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BACKGROUD OF THE I~VENTION
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This inventlon relates to a process for the production of ashless liquid fuels which comprises subjecting coal to a solvent treatment, especially to a solvent treatment using a heavy oil of petroleum series as solvent, to convert ashes contained in the coal into a coagulated material in an easily separable size and there-after, removing the coagulated material.
Coal has been used as fuel for a very long period of timc from the beginning of human history. With the increasing output of petroleum in recent years, however, the position of coal as indus-trial and domestic energy source is being replaced by petroleum.
Major reasons therefor are that coal is solid and is inconvenient in storage and transport as compared with liquid petroleum, that coal contains a large amount of ashes and that coal is low in com-bustion efficiency. In order to improve these shortcomings of coal, various attempts have been made to liquify coal. The methods for liquifying coal are roughly classified into a hydrogenation method and a solvation method, the former comprising the treatment of coal at a hi~h temperature with highly pressurized hydrogen for producing chiefly light oils such as gasoline and the latter com-prising the steps of mixing coal with a solvent and subjecting themixture to a heat treatment conducted at 300-400C thereby liqu~fy-ing coal to produce heavy oils chiefly. Illustrative of the solvents used in the latter method are heavy oils of coal series such as creosote oil, anthracene oil and coal tar (U.S. Patents 3,375,188; -3,109,803; and 3,379,638).
On the other hand, much research has been carried out on effective utiliza~ion of heavy oils of petroleum series produccd in a large amount as a by-product with the recent increase in consump-tion of petroleum. One research attempts the utilization of heavy oils às a solvent for liquefaction of coal. As heavy oils of pctro-

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leum series are hardly miscible with those of coal series, however, no success has been reported hitherto in attempts to liquefy coal with a heavy oil or petroleum series as solvent.
U.S. Patent 3,705,092 discloses a method for liquefying coal wherein a solid bituminous coal is dispersed into a heavy oil of petroleum series and the dispersion is treated at a high temperature with high pressure hydroger. The heavy oil of pet-roleum series used in this method merely functions as a dis-persant for the bituminous coal but does not serve as a solvent therefor.
Liquid products obtained by the prior art methods for liquefaction of coal have been regarded improper, like the above-mentioned heavy oils of petroleum series, as fuel. This is as-cribable to the reason that the liquid products are contaminated with ashes contained in the starting coal which forms scales on combustion and eventually lowers the combustion efficiency.
Accordingly, the production of a liquid fuel by liquefaction of coal is a key problem in the fields of the fuel industry.
It is an object of this invention to provide a method for liquefying coal to obtain an ashless liquid product which can be used as fuel.
Summary of the Invention It has now been found that when heav~ oils of the petroleum series are thermally treated at a temperature above 400C., the amount of aromatic components gradually increases and this coagulates to form optically anisotropic spherules.
When coal is allowed to be present during such thermal treat-ment, the coal readily dissolves in the heavy oils by virtue of the aromatic components and the ash contained in the start-ing coal is incorporated in the coagulated material, therebybeing removed with the coagulated material. Thus, according to the process of the present invention, a liquid fuel absolutely or substantially free from ashes can be obtained by combining powdery coal with a heavy oil of the pe~roleum series in an amount of at least 50 parts by weight per 100 parts by weight of the coal, heaving the mixture at 400-450C.
under atmospheric or superatmospheric pressure, whereby an insoIuble coagulate of spherules is formed and thereafter removing the insoluble coagulate of optically anisotropic spheres by separation from the tr~ated product, e.g. by cent-rifugal separation or filtration.
When the viscosity of the product obtained by com-bining coal with a heavy oil of petroleum series and subject-ing the mixture to a heat treatment is so high that it is difficult to effect centrifugal separation and filtration, the product may be diluted with an organic solvent, an oil of coal series or an oil of petroleum series.
_ESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferable examples of coal utilizable for the process of this invention include bituminous coal and brown coal.
Usually, the coal is divided finely and used in the form of powder.
Illustrative of heavy oils of petroleum series utili-zable as solvent in the process of this invention are residual oils obtained by distillation of crude oil under atmc,spheric pressure or in vacuo and tars obtained as by-product in thermal cracking of asphalt or naphtha. Those having an atomic ratio C/H of at least 0.9 are especially preferable. Such heavy oils of petroleum series can easily be prepared, for examp~e, by subjecting a residual oi] obtained by distilling crude oil under atmospheric or subatmospheric pressure to a heat treatment conducted at a temperature of at least 400C., or alternatively ~ _ 4 _ by cutting a low boiling point fraction of a heavy oil such as naphtha tar. The heavy oil of petroleum series is used n an amount of at least 50 parts by weight, preferably at least 100 parts by weight per 100 parts by weight of coal used.

- 4a -~ he process of this invention is preferably carricd out by heating a mixture of coal and a heavy oil of petroleum scrics at a temperature above 400C with stirring under atmospheric or super-atmospheric pressure. When the amount of the heavy oil of petroleum series used in this case becomes less than 50 parts by wei~h~ per 100 parts by weight of coal, stirring of the mixture becomes diffi-cult so that the reaction would hot smoothly be promoted. In the case of atmospheric pressure, a decomposition product will be dis-tilled off by heating. In the case of superatmosphcric pressure,such decomposition product will not be distilled out of the system, but the viscosity of the thermally treated product will be reduced.
The temperature adopted for the heat treatment is so high that it is sufficient enough for thermally cracking heavy oils of petroleum series, forming aromatic hydrocarbon by a thermal polymeri-zation reaction and forming an aggregate of this compound. ~ ranqe of such temperature is from 400C to 450C. If the temperature is lower than 400C, dissolution of coal will become insufficient so that the yield of the desired liquid fuel will be decreased. On the other hand, if the temperature is higher than 450C, carbonization will rapidly proceed so that a homogeneous pitch-like material will ~ot be obtained.
By the heat treatment conducted at a temperature within the above-mentioned range, coal is softened and at the same time de-stroyed in its structure to disperse into the heavy oil. In this case, ashes contained in the coal and metals contained in the heavy oil function as nuclei for forming the aggregate. The size of the aggregate depends on the conditions for the heat treatment. When the conditions are severe, the aggregate grows in size. Ilowever, the size becomes an almost definite value of about 5~ m by the in-fluence of ashes contained in the coal. Considering the level of separation techniques at the present time, a size of at least ~bou~lJum will suffice for separation. ~ conventional means such elS cen-trifugal separation or filtration is applied to separation of theaggregate. If desired, the viscosity of the thermally treated ~ro-duct may be reduced bv adding thereto an organic solvent such as quinoline, pyridine or nitrobenzene which is a good solvent for bi-tuminous n:aterials; an oil of petroleum scries such as an oil aboul)d-ing in aromatic hydrocarbons; or an oil of coal series such as an-thracene oil, creosote oil or pitch oil, for the purpose of facili-tating separation of the aggregate. Alternatively, the viscosity of the thermally treated product may be reduced by heating. ~t least 90~ of ashes contained in the starting coal can be removed by this separation treatment. If necessary, an organic solvent is re-covered from the thermally treated product from which thc a~re~at~
has been removed. An oil of petroleum or coal series is then added to the product thus treated, so as to furnish the resulting fuel with suitable physical properties. In the case of using an oil of petro-leum or:coal series for separating the aggregate from ~he thcrmally treated product, care is also taken so to obtain a product poss~ss-ing physical properties suitable as fuel. A liquid fuel absolutely or substantially free of ashes is thus produced from coal.
The process of this invention requires neither troublesome operation nor difficult conditions and is carried out satisfactorily with a simple apparatus. Moreover, the process of this invention is characterized in that ashes contained in coal can easily be ~e-parated.
This invention will now be illustrated in more detail by way of examples which are not intended to limit the scope of the invention.
Example 1 To 100 g of Miike coal (ash content: 6.2 wt. OD) were added 200 g of a residual oil obtained by distilling Kafji crude oil under vacuum. The mixture was then subjected to a heat treatment eonducted at 430C for 60 minutes under atmospheric pressure. 1'he resultant thermally treated product was 56.3 wt. ~ of the startin~
material, with the balance being a small amount of gas fractions and a thermally cracked oil composed chiefly of light oil frac~ions.
To the thermally treated produc~ was added cIuinolinc in an amourlt of three times as much as the product, and then the product was dissolved and dispersed into quinoline. A quinoline-insoluble fraction was removed by the aid of a centrifugal separator and a quinoline-soluble fraction was collected as a residual pitch-like substance after recovery of quinoline by distillation under reduced pressure. To the pitch-like substance was added 50 wt. ~ of the thermally cracked oil obtained by the aforementioned heat treatment, and the mixture was mixed under heating. A heavy oil substance thus obtained was found to correspond to Heavy Oil B defined by JIS
K2205. Tab~e 1 shows the vields of the thermally treated product and the fractions separated by quinoline as well as a result of measurements made for ashes according to JIS X2272.
Table 1 I ~ ... _._ - Yiel d (wt. %) l l Based on the Based on the IAshes IR~te of starting ma- thermally I idistri-terial treated pro- I (wt.~)¦bution duct I !of aslles Thermally treated product 56.3 100 3.23 100 Quinoline-insoluble frac-11 8 21 o 14.70 95.6 tion of the product . .

Quinoline-soluble frac-i 44 5 79.0 0.18 ~.3 tlon of the product Thermally cracked oil 43.2 ____ 0.00 0 -The results given in Table 1 obviously show that the clu~n-tity of the quinoline-insoluble fraction is extremely small as com-pared with that of the starting coal and that the quinolinc-insolul~le is extremely high in ash eontent. A microscopic observation of the insoluble fraction showed that it was an optically anisotropic sub-stance having an average particle diameter of about 3~ m. From these results, it was judged that the coal was once dissolved in the resi-dual oil obtained by distillation of Kafji crude oil under va-cuum and thereafter, ashes in the coal chiefly functioned as nuclei to fonm fine particles.
Example 2 To Miike coal (ash content: 6.2 wt. ~) was added a tar o~-tained as by-product by thermal cracking of naphtha in an amount oE
four times as much as the coal. The mixture was subjectcd to a heat treatment conducted at 400C for 120 minutes. The yield of thc re-sultant ther~ally treated product was 38.3 wt. ~ of the starting material. The thermally treated product was dissolved in a three-fold amount of anthracene oil and filtered through a glass filter whereby a fraction insoluble in the anthracene oil was 13.~ wt. ~.
The ash contents in these substances were measured according to a method similar to that described in Example 1 to obtain the followin~
results: 41.3 wt. ~ in the thermally treated product, 29.4 wt. O in the fraction insoluble in anthracene oil, and 0.20 wt. % in the frac-tion soluble therein. These results show that ashes in the coal exist in the rate of distribution in an amount of 95.4 wt. ~ in the fraction insoluble in anthracene oil and in an amount of 4.1 wt.
in the fraction soluble therein.
The fraction soluble in anthracene oil was then distilled to remove light oils in the anthracene oil whereupon a heavy oil was obtained which had physical properties corresponding to those of Heavy Oil A defined by JIS K2205. The ash content of the result-ing heavy oil was 0.05 wt. %.
Example 3 A residual oil ~C/H ratio = 0.7) obtained by distillation of Xafji crude oil under reduced pressure was subjected to a heat treatment conducted at 420C for 60 minutes in a stream of ni-trogen under atmospheric pressure. The yields of the products were as follows: a thermally cracked oil 43.6 wt. ~, a pitch 50.3 wt. ~, and a loss by gasification 6.1 %. A quinolinc-insoluble fraction of the pitch was 3.1 wt. ~ and its C/H ratio was 1Ø One part by - weight of Miike coal (average particle size: 0.3 mm; ash content:
7.1 wt. ~) was added to one part of the pitch and the mixture was heated at 250C and blended by agitation. The mixture was then heated up to 400C at a temperature elevation rate of 3C per minute and maintained at this temperature for 60 minutes. The yicld o~ the resulting pitch-like material was 96.3 ~ while that of a crackcd oil was 1.0 ~. A quinoline-insoluble fraction in the pitch-like material was 10.3%. An observation of the pitch-like material by a polar-ization microscope showed that no coal particle existed in the structure of the pitch-like material.
A quinoline-soluble fraction of the pitch-like material was distilled under reduced pressure to remove quinoline and then measured to determine the ash content thereof, whereby it was found that the ash content was 0.05 wt. ~. One part of creosote oil was added to the quinoline-soluble fraction from which quinoline had been'removed and the mixture was fused by heating it at 100C whereby the mixture became a heavy oil-like substance which was fluid at room temperature. A calorific value of this substance was 9,800 cal./g.
Example 4 A residual oil obtained by distillation under rcduced pres-sure of a mixture of various crude oils produced in many places was subjected to a heat treatment conducted at 400C ~or 60 minutes of a cracked oil whereby 51.9% of a pitch and 42.6~/were obtaincd. The pitch containe~
0.6~ of a quinoline-insoluble fraction and had a C/H ratio of 0.9.
One part by weight of ~iike coal was added to 0.5 part by weight o~

g _ the pitch and the mixture was fused by heating it at 350C, kneaded and then subjected to a heat treatment conductcd at 400C for 60 minutes whereby 81.6~ of a pitch-like material and 10.3" of a cracked oil were obtained. A quinoline-insoluble fraction in the pitch-like material was 15.8~. An observation of the structure of this fraction by a polarization microscope showed that a small amount of fine coal ;particles remained in the fxaction.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of an ashless liquid fuel, characterized by combining powdery coal with a heavy oil or the petroleum series in an amount of at least 50 parts by weight of said heavy oil per 100 parts by weight of said powdery coal, subjecting the mixture to a heat treatment conducted at 400-450°C. for a time sufficient to produce an insoluble coagulate of optically anisotropic spherules, said insoluble coagulate capturing the ash content of the coal, and thereafter removing said insoluble coagulate of optically anisotropic spherules by separation from the treated product.

2. A process according to claim 1 wherein an atomic ratio C/H of said heavy oil of petroleum series is at least 0.9.

3. A process according to claim 1 wherein said treated product is diluted with a diluent selected from an organic solvent, an oil of petroleum series and an oil of coal series, prior to removal of said insoluble coagulate by separation from said treated product.

4. A process according to claim 2 wherein during said heat treatment the heavy oil is thermally cracked, forming an aromatic hydrocarbon by a thermal polymerization reaction and forming an aggregate of this material.

5. A process according to claim 4, wherein ash contained in the starting powdery coal is incorporated in said aggregate, which forms into an insoluble coagulate.

6. A process according to claim 5 wherein the in-soluble coagulate is separated from the remaining liquid by centrifugal separation or filtration.

7. A process according to claim 2, 4 or 5, wherein at least 100 parts by weight of said heavy oil is used per 100 parts by weight of said powdery coal.