Process for separation of solids from liquid hydrocarbons

Abstract

 A process for the separation of sonds from nquid hydrocarbons in which liquid hydrocarbons compnsmg oils, asphaltenes and pre-asphaitenes containing insoluble solids are contacted with a volatile solvent compatible with the liquid hydrocarbons for solubilizing said oils, aspnaltenes and pre-asphaltenes. The liquid hydrocarbons containing solids are contacted with the volauie solvent in stages to form a carrier solution which preferably is displaced by the volatile solvent, preferably by a countercurrent or crosscurrent contacting mode. to produce a slurry of insoluble solids with volatile solvent substantially free of the said liquid hydrocarbons to permit a separation and removal of said insoluble solids by gravity settling, preferably under centrifugal forces, sucn that a minimum of interstitial liquid containing a minor amount of the liquid hydrocarbons is discharged with the insoluble solids. The interstitial liquid, composed largely of the volatile solvent, is substantially recovered from the solids by evaporation.
The liquid hydrocarbons, including substantially all the asphaltenes and pre-asphaltenes, are thus effectively separated from the solids and can be in turn separated from the volatile solvent for conventional processing. High losses of the asphaltenes and pre-asphaltenes mherent in known processes, particularly for low rank coals such as lignite coals, are avoided.

Description

[0001] This invention relates to the processing of liquid hydrocarbons and, more particularly, relates to the removal of insoluble material from liquid hydrocarbons.

[0002] Liquid hydrocarbons can include, for example, products derived from liquefaction of a mixture of coal derived liquids or non coal derived liquids plus coal, with or without a catalyst; or products derived from hydroprocessing of a mixture of coal or non coal derived liquids, with or without a catalyst; or combinations thereof.

[0003] Although the following description of tne process of the invention will proceed with reference to the processing of products of liquefaction of carbonaceous material, it will be understood that this description is exemplary only of the process of the invention applied to the separation of solids from the above liquid'hydrocarbons.

[0004] Liquid hydrocarbons can be classified into the basic components of oils, asphaltenes and pre-asphaltenes. Insoluble solids may comprise one or more of mineral matter, ash, spent catalyst and unreacted or undissolved carbonaceous residue. The oils are soluble in hexane, the asphaltenes are insoluble in hexane and soluble in toluene and the pre-asphaltenes are insoluble in toluene and soluble in tetrahydrofuran.

[0005] Reactor products from liquefaction of carbonaceous material, which is well known in the art for conversion of solid carbonaceous material such as anthracite, bituminous and sub-bituminous coal, lignite and peat, and other carbonaceous material to liquid products are usually in the form of a slurry which contains oils, asphaltenes, pre-asphaltenes and insoluble solids.

[0006] Removal of insoluble solids from the products of coal liquefaction is desirable to permit optimum recovery and processing of liquid hydrocarbons. The presence of insoluble solids leads to difficulties in the subsequent downstream refining and upgrading of liquid hydrocarbons. Separation of insoluble solids from the coal extract liquids is difficult to effect due to the wide particle size range of the discrete insoluble solids, the relatively high viscosity of the liquid phase even at high temperatures, the small differences between the density of the liquid phase and the density of the solids, and the inherent characteristics of the constituents of the coal liquefaction products.

[0007] The separation of discrete mineral matter such as insoluble solids from the coal extract liquids remains a continuing problem. Filtration provides for a high liquid yield by means of washing with a light oil and subsequent recovery of the light oil by drying of the filter cake and separation from the filtrate. A dried filter cake contains typically by weight 5 to 10% liquid product. That is, the cake consists of 90 to 95% solids and 5 to 10% of the desired liquid product on a dried solids cake basis. Filtration, although it provides a good liquid yield, still has as drawbacks: slow filtration rates, cost of pre-coat materials, and handling of the filter cake. Centrifuges do not achieve as sharp a separation of the solids as by filtration. Also, mechanical problems arise in the continuous removal of solids due to their abrasive and adhesive properties. A centrifuged 'solids cake' typically still contains 50 to 55% of liquid product on a total cake weight basis. Hydroclones achieve an even less sharp separation and are at best used for pre-thickening purposes in combination with other unit operations. Solvent extraction and leaching have been used for removal of only part of the solids. Coarser-and heavier particles need to be removed by other means. Magnetic separation processes can only also remove part of the solids. Tne organic compounds of coal are diamagnetic while the ash, i.e. inorganic mineral matter compounds, are paramagnetic which makes it possible to separate these by magnetic means. However, the unconverted coal cannot be separated. Shou J.K.P. and Collins D.J. describe these problems in: "A Review of Solid-Liquid Separation Technology in Coal Liquefaction Processes", Proceedings of the 28th Can. Chem. Eng. Conf., Publ. by Can. Soc. for Chem. Eng., Ottawa, Canada, 1978.

[0008] Distillation or evaporation is a possible means of separation. Very sharp separation can be achieved but liquid carry-over must be minimized. The bottoms of such units typically comprise 55% liquid product and 45% solids, resulting in substantial liquid losses. Coking is another process which provides a sharp separation. However, a considerable amount of liquid product is lost due to gasification of the light oil fraction and due to coking of the heavier liquid hydrocarbon products.

[0009] Anti-solvent deashing is a process whereby the solids are co-precipitated with some of the asphaltene and pre-asphaltene portion of the liquid liquefaction product due to the solution equilibrium imbalance brought about by the addition of an anti-solvent. The precipitated solids phase typically comprises 55 to 6G% liquid product. Examples of such processes are described in U.S. Patents nos 3,790,407; 3,852,182; 3,856,675 and 4,180,456. U.S. Patent 3,790,467 is typical in disclosing the use of an anti-solvent to precipitate from solution "quasi-solid" materials to cause an increase in size of smaller solids for enhanced separation using size as a separation parameter. Valuaole liquefaction product thus is lost or tied up with the solids fraction.

[0010] Critical solvent processes affect separation by the greatly enhanced dissolving power of the solvent in the range of pressure and temperature near the critical values for the solvent. Two processes that apply this property are described in U.S. Pat. Nos. 3,607,716 and 3,607,717. By proper choice of solvent, pressure and temperature, such a process can effectively produce separate process streams enriched in solids, asphaltenes, pre-asphaltenes, and oils. After recovery of the critical solvent by evaporation, the solids phase typically still comprise 35 to 40% of the liquid product.

[0011] The asphaltenes and pre-asphaltenes are considered to be non-distillable in that they "crack" into gaseous and liquid hydrocarbons and coke upon heating, with a poor liquid recovery. If the asphaltenes and pre-asphaltenes are separated with the insoluble solids from the oil by distillation, anti-solvent deashing or critical solvent deashing, subsequent recovery of the asphaltenes and pre-asphaltenes as liquid product becomes as best marginal. For low rank coals, these processes provide a low liquid yield.

[0012] According to the process of the present invention, mixtures of liquid hydrocarbons and insoluble solids are contacted with a volatile solvent compatible with the oils, asphaltenes and pre-asphaltenes for solubilizing said oils, asphaltenes and pre-asphaltenes as opposed to the above prior art processes in which the solvent functions as anti-solvent or a critical solvent. The said liquid hydrocarbons and solids are contacted with the volatile solvent in stages to form a carrier solution. The carrier solution is displaced by the volatile solvent, preferably by a countercurrent or crosscurrent contacting mode, to produce a slurry of insoluble solids with volatile solvent substantially free of the said liquid hydrocarbons to permit a separation and removal of said insoluble solids by gravity settling, preferably under centrifugal forces, such that a minimum of interstitial liquid containing a minor amount of the liquid hydrocarbons is discharged with the insoluble solids. The interstitial liquid, composed largely of the volatile solvent, is substantially recovered from the solids by evaporation.

[0013] The liquid hydrocarbons, including substantially all the asphaltenes and pre-asphaltenes, are thus effectively separated from the solids and can be in turn separated from the volatile solvent for conventional processing. High losses of the asphaltenes and pre-asphaltenes inherent in known processes, particularly for low rank coals such as lignite coals, are avoided.

[0014] In its broad aspect, the process of the present invention for separating insoluble solids from liquid hydrocarbons containing oils, asphaltenes and pre-asphaltenes comprises the steps of: contacting the liquid hydrocarbons with a volatile solvent compatible with the oils, asphaltenes and pre-asphaltenes to solubilize the said oils, asphaltenes and pre-asphaltenes to form a carrier solution; separating insoluble solids from the carrier solution by gravity separation and displacing said carrier solution from the solids by volatile solvent whereby said insoluble solids are discharged with interstitial volatile solvent; recovering said volatile solvent from the residual solids; and recovering oils, asphaltenes and pre-asphaltenes substantially free of insoluble solids.

[0015] Gravity separation is applied, preferably by centrifugal forces which accelerate the rate of separation, utilizing the density differences between the insoluble solids and liquid phase. The volatile solvent is contacted with the liquid hydrocarbons in an amount in the range of about 10 to about 250% by weight of the liquid hydrocarbons preferably in countercurrent or crosscurrent stages applying centrifugal forces to each stage whereby the final insoluble solids residue is compacted with a minimum of interstitial liquid, said final interstitial liquid comprised largely of the volatile solvent for ease of recovery.

[0016] Coal liquefaction products are particularly suited for the application of the process of the invention with the use of a coal extract volatile solvent, said volatile solvent normally being recovered for recycle. The coal liquefaction products are processed for the asphaltene, pre-asphaltene and oils recovery and recycle of the volatile solvent.

[0017] The accompanying drawing is a simplified schematic flow diagram of the process of the invention applied to the processing of coal liquefaction products, it being understood that the scope of the invention is not to be limited thereby.

[0018] Referring now to the drawing, reactor products from coal liquefaction are mixed with a compatible volatile coal extract solvent introduced by line 52 either in pre-mixer l0 or directly in separator 14. Contact of the reactor products with tne solvent is accomplished, preferably in a series of multiple-stage countercurrent or crosscurrent mixers with the application of gravity separation such as by the use of centrifuges at each stage, such that the solids residue in the final mixing and separating stage is contacted with fresh volatile solvent for discharge of compacted solids residue therefrom containing interstitially volatile solvent essentially free of coal liquefaction products. The use of pre-mixer 10 assists in the solubilizing of the asphaltenes and pre-asphaltenes by the volatile solvent. The multiple-stage contacting can be effected in a single device having multiple internal stages.

[0019] The volatile coal extract solvent is recovered from subsequent processing to be described and is compatible with the oils, asphaltenes and preasphaltenes. The volatile solvent is prepared from a coal derived oil fraction having at least 80% by volume distillation temperature between about 205° and 535°C for compatibility with the coal liquefaction products. A typical volatile solvent, shown in Table 1, comprises by volume about 98.3% distillation temperature between about 205° to 515°C.

[0020] The volatile coal extract solvent is contacted and mixed with the reactor products in an amount by weight in the range of about 10 to about 250%, preferably about 20 to about 100%, of the coal liquefaction slurry product. The quantity employed will vary according to the particular volatile solvent used and the characteristics of the reactor products which are determined by the coal starting material and the manner of liquefaction. Separator 14 is maintained at a temperature in the range of about 50° to 350⁰C under a pressure within the range of sub-atmospheric pressure to about 3.5 MPa.

[0021] Separation 14 is effected by gravity separation, in a conventional gravity settling vessel or in a centrifuge with the application of multiplied settling forces, for separation primarily according to differences in densities between the homogeneous carrier solution comprised of solvent and liquefaction products and the insoluble solids. The carrier solution is recovered as an overflow substantially free of solids and the solids recovered as an underflow, the amount of underflow preferably being kept to a minimum such as by the use of centrifugal forces to compact the solids and to minimize the volume of interstitial carrier solution at each stage and to minimize the amount of volatile solvent escaping witn the solids at the last stage.

[0022] The underflow containing solids with interstitial carrier solution, mainly volatile solvent, is withdrawn through line 16 and fed to recovery unit 18, which may constitute part of separator 14 or consist of a separate vessel in which the volatile solvent is evaporated at a temperature within the solvent boiling range. The evaporated solvent and any contained liquefaction product are fed by lines 22, 25 to series condensers 24, 26 with condensed product recycled to separator 40, to be described, by lines 28, 30, or discharged by line 32 as product.

[0023] The solids, substantially free of solvent, are withdrawn from unit 18 as dried, friable, non-sticking solids which may be crushed and conveyed by line 20 to a gasifier or burner. Separation of oil, asphaltenes and pre-asphaltenes in separator 14 from the solids is substantially complete due to the effective separation of the liquefaction products solubilized in the carrier solution and displaced by the volatile solvent, substantially eliminating loss of coal liquefaction product with solids in line 20.

[0024] The overflow of carrier solution from separator 14 is fed through line 36 to separator 40 and mixed with a coal derived light oil which is incompatible with the asphaltene and pre-asphaltene materials. The carrier solution and said light oil, such as light naphtha, are processed in separator 40 at a temperature in the range of about 50° to about 150°C at a pressure of from atmospheric pressure to about 3.5 MPa, the light oil being introduced in an amount by weight in the range of about 30% to about 100% of the carrier solution. The addition of the incompatible light oil precipitates a substantial part of the asphaltenes and pre-asphaltenes in the form of an immiscible liquid and/or solid phase having a greater density than the density of the carrier solution from which they are precipitated.

[0025] The immiscible phases can be separated from each other by gravity settling, preferably under centrifugal forces, to produce a non-viscous liquid overflow and a sticky semi-solid underflow comprised mainly of asphaltenes and pre-asphaltenes. The underflow is withdrawn by line 42 and is: returned to the liquefaction reactor, not shown, for furtner conversion into lighter oils; discharged for use as a solids product with a low ash content; or upgraded such as by hydrocracKing into distillable oils.

[0026] The liquid overflow from separator 40 is fed by line 44 to recovery unit 46 for stripping and recovery of the light oil fraction by flash evaporation and fractionation, or by distillation, for recycle by line 54 to separator 40. The bottoms are withdrawn by line 48 and discharged as product through line 50 or recycled by line 52 to separator 14 or pre-mix vessel 10. The bottoms of vessel 46 may be passed through a hydroprocessor 49 to convert remaining asphaltene and pre-asphaltene fractions to distillates and to increase the hydrogen concentration, i.e. to regenerate the volatile solvent. Replacement of light oil taken from tne system by removal of the two product streams 42, 50 can be made up by coal extract oil from coal liquefaction through line 38.

[0027] The overflow of carrier solution from separator 14 may be directly fed to alternative processing unit 58 instead of to separator 40. The unit depicted by numeral 58 may be a hydrocracker from which the liquids are subsequently separated in a distillation column into products, recycle oil for the slurrying of coal, and recycle volatile coal extract solvent compatible with the asphaltenes and pre-asphaltenes; a distillation column for separation of overflow by boiling range; or a solvent deasphalting process such as a propane deasphalting process or Duosol process in which the asphaltenes and pre-asphaltenes are separated from the solvent.

[0028] The process of the invention was carried out for the processing of reactor product resulting from the direct liquefaction of lignite in separator 14 and recovery unit 18. Separator 14 was a batch centrifuge operated at 1500 G's at atmospheric pressure with carrier solution maintained at 150⁰C. The reactor liquid product consisted of 86.49 mass units of liquid hydrocarbons and 13.51 mass units of unreacted coal and ash. Contacting was carried out in a three-stage crosscurrent mode using a total of 205.34 mass units of volatile coal extract solvent. The last underflow was fed to a vacuum flask for evaporation of the volatile solvent from the residual solids. Table 2 indicates the distribution of components in the feed to the separator, combined separator overflow and final underflow and recovery unit overflow and bottoms. For a feed to the separator of 86.49 mass units of reactor liquid product, 1.84 units of reactor liquid product were lost with the insoluble solids in the recovery unit bottoms, resulting in a recovery of 97.9% of the reactor liquid product.

[0029] 

Claims

1. A process for separating insoluble solids from liguig. hydrocarbons containing oils, asphaltenes, pre-asphaltenes comprising the steps of:

contacting the liquid hydrocarbon with a volatile solvent compatible with the oils, asphaltenes and pre-asphaltenes to solubilize the said oils, asphaltenes 2nd pre-asphaltenes to form a carrier solution;

separating insoluble solids from the carrier solution by gravity separation and displacing said carrier solution from the solids by volatile solvent whereby said insoluble solids are discharged with interstitial volatile solvent;

recovering said volatile solvent from the insoluble solids; and

recovering oils, asphaltenes and pre-asphaltenes substantially free of insoluble solids.

2. A process as claimed in Claim 1 in which volatile solvent is recovered from said oils, asphaltenes and pre-asphaltenes.

3. A process as claimed in Claim 2 in which the said liquid hydrocarbons are products of coal liquefaction and said volatile solvent is a coal extract.

4. A process as claimed in Claim 1, 2 or 3 applying said gravity separation in a centrifuge whereby said insoluole solids are compacted to minimize the volume of interstitial carrier solution or volatile solvent.

5. A process as claimed in Claim 1, 2 or 3 in which said volatile solvent is added in an amount by weight in tne range of about 10 to 250% of the liquid hydrocarbons.

6. A process as claimed in Claim 1, 2 or 3 in which the liquid hydrocarbons are contacted with the volatile solvent in a pre-mixer prior to the gravity separation for a time sufficient to effect substantial solubilization of the liquid hydrocarbons.

7. A process as claimed in Claim 1, 2 or 3 in which the liquid hydrocarbons are contacted with the volatile solvent in a single stage or a multi-stage crosscurrent or countercurrent system.

8. A process as claimed in Claim 1, 2 or 3 in which the gravity separation is effected under centrifugal forces sequentially with addition and mixing of the volatile solvent with the liquid hydrocarbons, said volatile solvent being added in an amount by weight in the range of 10 to 250% by weight of the liquid hydrocarbons crosscurrent or countercurrent to the flow of liquid hydrocarbons whereby the insoluble solids in a final mixing and separating stage is contacted with fresh volatile solvent for discharge of compacted insoluble solids containing interstitially volatile solvent essentially free of said liquid hydrocarbon.

9. A process as claimed in Claim 1, 2 or 3 in which the gravity separation is conducted at a temperature in the range of about 50⁰ to 350⁰C at a pressure in the range of sub-atmospheric pressure to about 3.5 MPa.

10. A process as claimed in Claim 1, 2 or 3 in which at least 80% by volume of the volatile solvent has a distillation temperature in the range of 2050 to 535°C.

11. A.process as claimed in any of Claims 1 to 10 in which the substantially solids-free carrier solution recovered from the gravity separation is fed to one of a hydrocracker from which the liquids are separated in a distillation column into products, recycle oil for slurrying.of coal and recycle solvent compatible with the asphaltenes and pre-asphaltenes; a distillation column for separation of said overflow by boiling range; or a solvent deasphalting process in which the asphaltenes and pre-asphaltenes are separated from the solvent.

12. A process as claimed in Claim 1, 2 or 3 in which the substantially solids-free carrier solution recovered from the gravity separation is contacted with a light oil incompatible with the asphaltenes and pre-asphaltenes in an amount sufficient to precipitate a portion of the said asphaltenes and pre-asphaltenes, separating the said precipitated asphaltenes and pre-asphaltenes from the liquid phase, and recovering the light oil for recycle to the substantially solids-free carrier solution.

13. A process as claimed in any of the preceding claims in which the recovered asphaltenes and pre-asphaltenes substantially free of insoluble solids are converted by hydrocracking to distillates.

14. A process as claimed in any of the preceding claims in which the said liquid hydrocarbons are at least one of products derived from liquefaction of a mixture of coal derived liquid plus coal, products derived from hydroprocessing of a mixture of coal or non coal derived liquids, said products with a catalyst, and combinations thereof.

15. A process as claimed in Claim 1, 2 or 3 in which part of the carrier solution from which the light oil and most of the asphaltenes and pre-asphaltenes have been separated is fed to a hydroprocessor to regenerate the volatile solvent.

Drawing