Residuum Processing

Abstract

A residual petroleum fraction or similar hydrocarbon oil boiling in excess of about 700.degree. F. is contacted in liquid phase with a finely divided, noncaking coal in a contacting zone at a temperature in the range between about 700.degree. F. and about 900.degree. F., cracked products derived from the oil and hydrocarbons from the coal are recovered overhead from the contacting zone and fractionated to produce a heavy recycle stream and lighter products, and a solid char is recovered as a bottoms product from the contacting zone. The contacting of the oil with coal in a fluidized bed at relatively low oil-to-coal ratios results in the production of a low sulfur solid fuel having a Btu content in the range of from about 12,000 to about 18,000 Btu/lb.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to the upgrading of residual petroleum fractions and similar heavy oils and is particularly concerned with a process for converting a residual fraction or similar oil into lighter products by contacting the oil with coal at elevated temperature and pressure.

2. Description of the Prior Art

Conventional low cost processes for the conversion of residual petroleum fractions and similar heavy hydrocarbon oils into lower boiling naphthas and gas oils, such as delayed coking and thermal cracking, generally require a high level of heat input and often result in the production of relatively large quantities of low value coke and gas. These disadvantages can be overcome in most cases by resorting to more complex processes such as fluid coking or fluidized catalytic cracking, but these normally entail much higher initial investments and in some cases may therefore not be economically feasible.

A number of methods for converting residual fractions and other oils into lighter products have been suggested in the prior art, including methods involving the concurrent processing of coal and oil. Early proposals along these lines included the thermal cracking of crude oil containing colloidally dispersed coal, gilsonite or similar material in a still to permit the recovery of liquid and gaseous hydrocarbons from the oil and solid material, the mixing of powdered coal with hot oil to form a heavy plastic mixture which is then baked or carbonized to produce a solid fuel and oil vapors suitable for cracking and further processing, the passing of cracked oil vapors through a bed of hot coal particles to dissolve and distill the more volatile constituents from the coal and produce coke, the coking of coal in the presence of a low boiling fuel oil or similar petroleum fraction, and the replacement of water in the pores of brown coal or a similar material with oil which is subsequently cracked within the pores of the solid particles. More recently, processes for the treatment of coal and related materials with relatively low boiling, highly aromatic oils to extract liquid constituents from the coal have been developed. None of these methods, however, has provided a highly effective, low-cost process for the upgrading of residual petroleum fractions and similar high boiling oils into more valuable lower boiling products.

SUMMARY OF THE INVENTION

This invention provides an improved process for the conversion of high boiling residual petroleum fractions and similar oils into lower boiling hydrocarbons which alleviates many of the difficulties encountered heretofore and has pronounced advantages over methods proposed in the past. In accordance with the invention, it has now been found that residual petroleum fractions and other hydrocarbon oils composed primarily of constituents boiling in excess of about 700.degree. F. can be converted into lower boiling hydrocarbons by contacting the oil in liquid phase with a noncaking coal at a temperature in the range between about 700.degree. F. and about 900.degree. F., recovering an oil containing cracked products overhead from the contacting zone, fractionating this oil to produce a heavy recycle fraction and lighter products, and recovering solid char as a bottoms product from the contacting zone. The process may be carried out in either a fixed or moving bed vessel at a space velocity between about 0.1 and about 3.0 pounds of oil per hour per pound of coal. In general, the use of relatively high oil-to-coal ratios and low temperatures tends to promote the production of high yields of liquid products in the gas oil boiling range; whereas lower oil-to-coal ratios and higher temperatures result in formation of more light ends and char product. Contacting of the oil and coal in a moving bed at oil-to-coal ratios less than about 10:1 permits the recovery of a relatively low sulfur char which normally has a Btu content between about 12,000 and about 18,000 Btu/lb. and is useful as a high quality solid fuel.

Laboratory work has shown that the simultaneous treatment of noncaking coal and high boiling oils in accordance with the invention has a synergistic effect on product yields. The coal apparently acts as a catalyst to promote cracking of the oil and thus provides higher distillate product yields than might otherwise be obtained; while at the same time the heavy oil apparently tends to solubilize the coal and permit the recovery of coal-derived liquids. Significantly more naphtha and gas-oil are produced than are normally obtained in delayed coking and similar operations. These high yields, coupled with the relatively low heat input level required and the relatively simple, inexpensive equipment employed in carrying out the process, permit the conversion of residual petroleum fractions and similar oils at a cost considerably lower than that of conventional fluid coking, delayed coking and related operations and thus make the process of the invention widely applicable.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 in the drawing is a schematic diagram illustrating the conversion of a residual petroleum fraction or similar oil into lighter products by contacting the oil with a sub-bituminous coal in a fixed bed; and

FIG. 2 depicts a process which is similar to that of FIG. 1 but is carried out in a fluidized bed.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The high-boiling oil employed as a feed material in the process depicted in FIG. 1 of the drawing may be a distillate or residual petroleum fraction, a shale oil, or a similar hydrocarbon oil composed primarily of constituents boiling in excess of about 700.degree. F. Suitable oils include atmospheric and vacuum residuums obtained by the distillation of crude oils, bottoms fractions from catalytic cracking units and other refinery operations, asphalts, raw creosote oils, high-boiling crude oils, heavy shale oils, high-boiling oils derived from tar sands, and the like. Such oils will normally contain constituents boiling above 700.degree. F. in concentrations of about 90 weight percent or higher and will have API gravities of about 25.degree. or lower, carbon contents of about 80 percent of higher, and Conradson carbon values of about 1 percent or more. The use of high-boiling residual petroleum fractions having initial boiling points above about 700.degree. F. is generally preferred for purposes of the invention.

In the particular embodiment of the invention shown in FIG. 1, a high boiling residual petroleum fraction or similar heavy oil is introduced into the system from a pipe still or similar unit at a temperature of about 700.degree. F. and passed through line 10 into the lower end of fractionating tower 11. Here the oil is heated and the lighter fractions are flashed off. Lighter constituents boiling below about 450.degree. F. are taken off overhead from the fractionator through line 12, cooled in condenser 13, and passed to flash drum 14. Noncondensable gases are taken off overhead through line 15 and distillate in the naphtha boiling range is withdrawn through line 16. The gas and naphtha streams may be passed to downstream processing units for further treatment and subsequent utilization. The heavier condensate separated from the overhead stream is recycled to the upper end of the fractionating tower as reflux through line 17. A heavier gas oil fraction boiling in the range between about 450.degree. and about 700.degree. F. is withdrawn from the fractionating tower through line 18 and passed to downstream units for further processing.

The bottoms products from fractionator 11 are withdrawn through line 19 and passed to furnace 20 where the heavy oil is heated to the required conversion temperature between about 700.degree. F. and about 900.degree. F., preferably to a temperature between 750.degree. F. and 850.degree. F. The heated oil withdrawn from the furnace through line 21 is then passed into one of two or more parallel fixed bed reaction vessels 22 and 23. These vessels are fitted with inlet lines 24 and 25 containing valves 26 and 27 so that the heated oil can be directed into either vessel. One of the vessels is normally used for contacting the heated oil with coal while the other is being cleaned and readied for reuse. The reaction vessels are provided with overhead outlet lines 28 and 29 containing valves 30 and 31. These valves and those in the inlet lines can be operated manually or fitted with electrical or hydraulic controls and programmed to operate in a predetermined sequence. As indicated earlier, more than two reaction vessels may be employed if desired.

The fixed beds in reaction vessels 22 and 23 are charged with a sub-bituminous or lower rank noncaking coal which has previously been crushed and screened into the desired particle size. In general, suitable coals include sub-bituminous coals, brown coals, lignites, and similar materials having oxygen contents of about 15 percent or higher and hydrogen contents of about 2 percent of lower. The coal size employed will depend upon the particular method used to support the coal within the reaction vessels. It is generally preferred to employ relatively coarse particles between about 1/4 inch and 1 inch in size in order to reduce the pressure drop through the bed and minimize plugging but other particles may also be used, particularly if the bed is supported on suitable grids or other devices designed to control distribution of the upflowing oil and promote effective contact between the coal and oil. As pointed out above, one of the reaction vessels is employed for contacting oil with coal while the other vessel is being cleaned and recharged with fresh coal. While oil is being introduced into vessel 22 through line 24 containing valve 26, for example, valve 27 in line 25 is closed. The heated oil from furnace 20, at a temperature between about 700.degree. F. and about 900.degree. F. and a pressure within the range between about 10 pounds per square inch gauge and about 100 pounds per square inch gauge, is passed upwardly through the bed of sub-bituminous coal, lignite, brown coal or the like in vessel 22 at a space velocity within the range between about 0.1 to about 3.0 pounds of oil per hour pound of coal. In general, space velocities between about 0.5 and about 1.5 pounds of oil per hour per pound of coal are preferred. The upflowing oil is catalytically cracked in the pressure of the coal to form lower boiling products. Some extraction of liquids from the coal by the oil apparently also takes place. The cracked products are withdrawn overhead from vessel 22 through line 28 containing valve 30 and passed through line 32 through the lower end of fractionation tower 11. Valve 31 in line 29 is closed to prevent the flow of products into vessel 23 during this period. The cracked products fed to the fractionation tower supply heat to the heavy oil introduced through line 10 and are ultimately recovered from the fractionating tower through lines 12 and 18. Any high-boiling constituents present in the stream introduced through line 32 are mixed with the heavy oil feed and recycled through line 19 to the contacting zone.

While vessel 22 is thus being used for the contacting of heavy oil with the coal, vessel 23 is being cleaned and recharged with fresh coal. Steam, water or other suitable cooling medium can be introduced into vessel 23 to recover heat from the char produced by the reactions taking place between the oil and coal and facilitate removal of the char. Mechanical means for dislodging the char can also be employed if necessary. The char product is recovered through line 33 containing valve 34 and may be employed as a fuel, fed to a gasifier, or used for other purposes. The bed in vessel 23 is then recharged with fresh sub-bituminous coal, lignite, brown coal or the like. When the conversion rate in the vessel 22 falls below the desired level, valves 27 and 31 are opened to permit the circulation of heated oil through vessel 23 and valves 26 and 30 are closed to permit the cleaning and charging of vessel 22. The two vessels are thus cycled to permit semicontinuous operation.

FIG. 2 in the drawing illustrates an alternate embodiment of the process in which a moving bed of coal is employed as a catalyst in lieu of the fixed bed described above. In this embodiment, finely divided sub-bituminous or lower rank coal is introduced continuously through line 50 into hopper 51 from storage or a suitable preparation plant. The coal employed will normally have a particle size less than about 8 mesh, preferably less than about 20 mesh, on the Tyler Screen Scale. The finely divided coal is discharged from the hopper through screw conveyor or a similar device 52 into reaction vessel 53. Here the coal particles form a downwardly moving bed supported by upflowing oil introduced into the lower end of the reaction vessel through line 54. Hot char particles are withdrawn near the lower end of the reaction vessel through line 55 and are passed to a heat recovery unit not shown in the drawing before being utilized as fuel or employed for other purposes. The fluidized bed in vessel 53 is maintained at a temperature within the range between about 700.degree. and about 900.degree. F. and at a pressure between about 10 and about 100 psig. The space velocity is preferably controlled between about 0.5 and about 1.5 pounds of oil per hour per pound of coal to permit the recovery of a low sulfur, high Btu solid fuel through line 55. Higher space velocities which will result in the production of a lower quality solids product and increased yields of liquid products may be employed if desired.

The liquid and gaseous products produced by the catalytic cracking of the feed oil in the presence of the coal, together with uncoverted heavier hydrocarbons, are taken off overhead from vessel 53 through line 56 and introduced into the lower end of fractionating tower 57. Here the lighter constituents are taken off overhead through line 58, cooled in heat exchanger 59, and passed to flash drum 60. Gaseous constituents are recovered by means of line 61, intermediate products boiling up to about 450.degree. F. are recovered as naphtha through line 62, and the heavier condensate is recycled as reflux through line 63. Liquids in the gas oil range boiling up to about 700.degree. F. are withdrawn as a side stream through line 64. The bottom products from the cracked fluids introduced through line 56 and the heavy constituents from a heavy oil feed introduced into the system through line 65 from a pipe still or similar source are withdrawn from the fractionating tower through line 66, heated to a temperature within the range between about 700.degree. and about 900.degree. F. in furnace 67 and introduced into the catalytic cracking zone in vessel 53 through line 54. The process of the invention can thus be carried out in either fixed bed or fluidized bed operations.

The nature and objects of the invention are further illustrated by the results of laboratory and pilot plant tests carried out in accordance with the invention.

In the first of a series of such tests, approximately equal parts by weight of Wyodak coal and a heavy asphaltic residual petroleum fraction were heated to a temperature of 750.degree. F. in a bench size reaction vessel operating at essentially atmospheric pressure. The reactor was vented to the atmosphere through a condenser to permit the collection of distillation products and through a dry test meter to permit determination of the quantity of gas produced. The reactor was held at the 700.degree. F. reaction temperature for a period of one hour. At the end of that time, the heat was turned off and oil was drained from the bottom of the reaction vessel. The quantities of gas and light ends, distillate, char, and drain oil were measured. A blank run was then made using only the asphaltic oil so that any thermal cracking or distillation of front ends of the oil could be detected. A Fischer Assay of the coal with a terminal temperature of 750.degree. F. was also carried out to determine the yield due to pyrolysis of the coal in the absence of the asphaltic oil. The results obtained in these tests are set forth in Table I below:

TABLE I __________________________________________________________________________ Reaction of Asphaltic Oil With Sub-Bituminous Coal __________________________________________________________________________ Wt., Est'd. from Est'd Net from Coal, Dry Water Free* Product Gms. Asph. Blank, gms. Gms. % Fischer Assay, % __________________________________________________________________________ Gas & Lt. Ends 90 50 40 7.4 5.0 Distillate 309 216 93 17.3 8.3 Char 504 -- 504 93.7 86.7 Drain Oil 478 577 (99) (18.4) -- __________________________________________________________________________ *Fischer Assay with terminal temperature of 750.degree. F.

It will be noted from the above table that the yields of gas and light ends and of distillate obtained by heating the heavy oil in the presence of the sub-bituminous coal were substantially higher than those obtained by heating the oil alone and that the yield of drain oil was considerably less than that obtained when the oil alone was heated. This indicates that the coal apparently had a catalytic effect on the cracking of the heavy oil and resulted in the conversion of a substantial part of the drain oil into gas, light ends and distillate. The Fischer Assay results can be considered a minimum yield available from pyrolysis of the coal in the absence of oil. The estimated net yields from the coal, obtained by subtracting the asphalt blank yields from the actual yields obtained, were significantly higher than the Fischer Assay values. Although some of this difference may have been due to a solvent effect of the asphalt oil upon the coal, the test results indicate that the coal acted as a catalyst to promote cracking and upgrading of the heavy oil.

Tests similar to those described above were carried out with a heavy West Texas vacuum residuum and Wyodak coal at a temperature of 800.degree. F. Again equal parts of the coal and heavy oil by weight were used. A blank test of the residuum without any coal and a Fischer Assay of the coal were run. The results of this second series of tests are set forth in Table II below:

TABLE II __________________________________________________________________________ Upgrading of West Texas Vacuum Residuum With Wyadak Coal __________________________________________________________________________ Wt., Est'd from Est'd Net from Coal, Dry Water Free* Product Gms. Resid. Blank, Gms. Gms. % Fischer Assay, % __________________________________________________________________________ Gas & Lt. Ends 215 64 151 26.7 7.3 Distillate 633 340 293 51.9 10.2 Char 568 -- 568 100.5 82.5 Drain Oil 9 456 (477) (79.1) -- __________________________________________________________________________ *Fischer Assay at 800.degree. F. terminal temperature.

The results obtained with the heavy West Texas vacuum residuum were even more striking than those obtained with the heavy asphaltic oil. It will be noted that the yields of gas and light ends and of distillate were again much higher than those obtained from the run in which no coal was present. At the end of the 1-hour reaction period, only 9 grams of the oil remained in the system. This is about the holdup of oil in the pipe nipple connecting the drain valve to the bottom of the reaction vessel. On comparing the estimated net yields from coal with the minimum pyrolysis yields by the Fischer Assay tests, it can be seen that sharply enhanced residuum conversion must have contributed strongly to the yields of gas, light ends and distillate. It is thus evident that the sub-bituminous coal has a pronounced catalytic effect on the cracking of the heavy oil and that this effect can be employed to permit the upgrading of the residuum into more valuable lighter products.

Following the tests described above, additional tests in which a heavy West Texas residual petroleum fraction was contacted with a fixed bed of Wyodak coal were carried out. In these tests, wet coal was charged to a fixed bed reactor provided with an oil inlet at its lower end and a product outlet at the upper end. Nitrogen was passed through the reactor as it was brought up to temperature to sweep out moisture and any coal pyrolysis liquids formed. After the desired temperature had been reached, the heavy residual oil was passed over the coal and the products formed were accumulated. Runs were carried out at temperatures of 750.degree. F.., 800.degree. F. and 850.degree. F. and space velocities of from 0.3 to 1.2 pounds of oil per pound of coal per hour. The reactor was operated at a pressure of 25 pounds per square inch gauge. The results of these tests are shown in Table III below:

TABLE III __________________________________________________________________________ Continuous Flow of West Texas Resid Over a Packed Bed of Wyodak Coal Average of 12-Hour Runs __________________________________________________________________________ Pressure, psig 25 25 25 25 25 Temperature, .degree.F. 750 750 800 800 850 Approximate Space Velocity.sup.a 0.3 1.0 0.3 1.2 1.0 Product Distribution Based on Oil Charged, Wt. % Oil Recovered 100.4 98.6 52.0 77.3 -- Gas + Light Ends 0.6 0.2 19.1 12.6 -- Net Char Made.sup.b 1.3 3.1 27.2 9.5 -- Total 102.3 101.9 98.3 99.4 --.sup.c __________________________________________________________________________ .sup.a Wt. resid feed/wt. wet coal charged/hour. .sup.b Net of total char made and Fischer Assay char on coal charged. .sup.c Run terminated under noncontrolled conditions because of reactor plug.

The data in the above table show that relatively little gas, light ends and char were formed at 750.degree. F. As the temperature was increased, the cracking became more severe and hence the oil yield was reduced and more gas, light ends were formed. It should be noted that the split between oil recovered and gas and light ends in the above table was not precise because of inadequate light liquid recovery equipment when operating the unit at essentially atmospheric pressure and that the run carried out at 850.degree. F. was terminated early because of rapid coke buildup and plugging.

Following the runs described above, the oil recovered from the run carried out at 800.degree. F. and a space velocity of 1.2 was fractionated and the ultimate product distribution in a full scale unit where the bottoms product would be recycled was estimated on the basis on the oncethrough product distribution. The selectivity, based on the 950.degree. F.+ constituents in the feedstock, was also determined for the estimated ultimate product distribution. The yields that would be obtained from this feedstock in a 950.degree. F. fluid coking reaction were predicted on the basis of the feed characteristics and established fluid coking correlations. The results of these are shown in Table IV below:

TABLE IV __________________________________________________________________________ Product Distribution and Selectivity __________________________________________________________________________ For 800.degree. F., 1.2 Space Velocity Product Dis- Selectivity 950.degree. F. Fluid tribution Based on Oil Estimated of 950.degree. F. + Coking Charged, Wt. % Once-Through Ultimate Conversion Prediction __________________________________________________________________________ Gas + Light Ends 12.6 18.0 22.7 8.5 C.sub.4 /430.degree. F. 8.5 12.1 15.2 14.8 430/950.degree. F. 45.7 56.1 44.1 60.7 950.degree. F.+ 23.7 0 -- 0 Char 9.5 13.8 18.0 16.0 100.0 100.0 100.0 100.0 __________________________________________________________________________

The results set forth above show that the Wyodak coal has a surprisingly pronounced effect on the cracking of the heavy residual petroleum fraction and that the ultimate results are comparable to those obtained at 950.degree. F. in a fluid coking unit. Since fluid coking requires a heavy investment in complex equipment and is expensive to operate because of the higher temperature level and the complexity of the equipment, the economics of the process of the invention appear favorable.

In still further tests of the process, runs were carried out with heavy shale oils, fluid catalytic cracking bottoms, and creosote oils. These tests were carried out at temperature of 800 and 850.degree. F. in a fixed bed reactor containing Wyodak sub-bituminous coal at substantially atmospheric pressure. The results of these later tests are shown in Tables V, Vi and VII below:

TABLE V __________________________________________________________________________ Catalytic Cracking of Shale Oil Over Wyodak Coal __________________________________________________________________________ Distillations Feed 800.degree. F. Product 850.degree. F. Product __________________________________________________________________________ Wt.% at 430.degree. F. 0.0 8.52 7.51 950.degree. F. 72.0 96.0 89.0 Recoveries, Wt. % 800.degree. F. Run 850.degree. F. Run Measured Normalized Measured Normalized __________________________________________________________________________ Oil 94.7 93.48 92.3 90.49 Gas 0.1 0.10 3.0 2.94 Char 6.5 6.42 6.7 6.57 101.3 100.00 102.0 100.00 Yields, Wt. % 800.degree. F. Run 850.degree. F. Run Gross Net Ult. Gross Net Ult. __________________________________________________________________________ Gas (Incl. C.sub.5 + in Gas) 0.10 0.12 2.94 4.56 C.sub.5 -430.degree. F (Not Incl. C.sub.5 + in Gas) 7.96 9.19 6.80 10.55 430-950.degree. F. 81.78 9.78 83.28 73.74 1.74 74.70 950.degree. F.+ Liquid 3.74 -24.26 0.00 9.95 -18.05 0.00 Char 6.42 7.41 6.57 10.19 100.00 100.00 100.00 100.00 __________________________________________________________________________

TABLE VI __________________________________________________________________________ Catalytic Cracking of Fluid Catalytic Cracking Bottoms Over Wyodak __________________________________________________________________________ Coal Distillations Feed 800.degree. F. Product 850.degree. F. Product __________________________________________________________________________ Wt.% at 430.degree.F. 0.0 0.0 0.0 950.degree.F. 80.5 88.0 99.2 Recoveries, Wt. % 800.degree. F. Run 850.degree. F. Run Measured Normalized Measured Normalized __________________________________________________________________________ Oil 98.8 97.05 80.0 86.68 Gas 0.6 0.59 1.0 1.08 Char 2.4 2.36 11.3 12.24 101.8 100.00 92.3 100.00 Yields, Wt. % 800.degree. F. Run 850.degree. F. Run Gross Net Ult. Gross Net Ult. __________________________________________________________________________ Gas (Incl. C.sub.5 + in Gas) 0.59 1.47 1.08 1.12 C.sub.5 -430.degree.F. (Not Incl. C.sub.5 + in Gas) 0.00 0.00 0.00 0.00 430-950.degree. F. 85.40 4.90 92.67 85.99 5.49 86.19 950.degree. F.+ Liquid 11.65 -7.85 0.00 0.69 -18.81 0.00 Char 2.36 5.86 12.24 12.69 100.00 100.00 100.00 100.00 __________________________________________________________________________

TABLE VII __________________________________________________________________________ Catalytic Cracking of Creosote Oil Over Wyodak Coal __________________________________________________________________________ Distillations Feed 800.degree. F. Product 850.degree. F. Product* __________________________________________________________________________ Wt.% at 430.degree. F. 8.0 5.94 9.8 950.degree. F. 93.7 96.3 100.0 Recoveries, Wt. % 800.degree. F. Run (107C) 850.degree. F. Run (130C) Measured Normalized Measured Normalized __________________________________________________________________________ Oil 97.6 94.76 94.5 95.36 Gas 0.4 0.39 0.1 0.10 Char 5.0 4.85 4.5 4.54 103.0 100.00 99.1 100.00 Yields, Wt. % 800.degree. F. Run 850.degree. F. Run* Gross Net Ult. Gross Net Ult. __________________________________________________________________________ Gas (Incl. C.sub.5 + in Gas) 0.39 0.88 0.10 0.10 C.sub.5 -430.degree. F. (Not Incl. C.sub.5 + in Gas) 5.63 -2.37 2.65 9.35 1.35 9.35 430-950.degree. F. 85.62 -0.08 85.52 86.01 0.31 86.01 950.degree. F.+ Liquid 3.51 -2.79 0.00 0.00 -6.30 0.00 Char 4.85 10.95 4.54 4.54 100.00 100.00 100.00 100.00 __________________________________________________________________________ * Distillation had poor material balance.

Again the data show that the sub-bituminous coal behaved as a catalyst to promote cracking of the heavy oils into lower boiling, more valuable products. The data obtained with shale oil are particularly significant because such oils contain high concentrations of nitrogen compounds and other materials which rapidly poison conventional catalytic cracking catalysts and are therefore difficult and expensive to upgrade.

In view of the foregoing it should be apparent that the process of the invention has pronounced advantages over conventional residuum conversion processes. These advantages include a heat load which is significantly lower than that required in conventional residuum conversion processes, the use of equipment which is much simpler and less expensive than that required for fluidized coking and the like, yields which are significantly better in terms of naphtha and gas oil than those obtained in typical delayed coking operations, and the ability to produce a high quality, low sulfur, solid fuel by carrying out the process in a moving bed at relatively low residuum-to-coal ratios. As a result of these and other advantages, the process permits the conversion of residual fractions at a cost considerably below that of fluid coking while achieving product yields which are comparable to fluid coking and significantly better than those obtained by delayed coking.

Claims

We claim:

1. A process for the production of low boiling liquid hydrocarbons from coal and a high boiling hydrocarbon oil composed primarily of constituents boiling in excess of about 700.degree. F. which comprises contacting said oil in a contacting zone with a finely divided sub-bituminous or lower rank coal at a temperature in the range between about 700.degree. F. and about 900.degree. F., a pressure in the range between about 10 and about 100 pounds per square inch gauge, and a space velocity between about 0.1 and about 3.0 pounds of oil per hour per pound of coal; withdrawing liquid products overhead from said contacting zone; fractionating said liquid products to obtain a high boiling liquid fraction boiling in excess of about 700.degree. F. and a lighter fraction; recycling said high boiling fraction to said contacting zone; and withdrawing char from said contacting zone.

2. A process as defined by claim 1 wherein said high boiling hydrocarbon oil is a residual petroleum fraction having an initial boiling point in excess of about 700.degree. F.

3. A process as defined by claim 1 wherein said oil is contacted with said coal in a fixed bed.

4. A process as defined by claim 1 wherein said oil is contacted with said coal in a moving bed with an oil-to-coal ratio less than about 10 to 1.

5. A process as defined by claim 1 wherein said oil contains constituents boiling above 700.degree. F. in a concentration greater than about 90 weight percent and has an API gravity of about 25.degree. or lower, a carbon content of about 80 percent or higher, and a Conradson carbon value of about 1 percent or more.

6. A process as defined by claim 1 wherein said coal has an oxygen content of about 15 percent or higher and a hydrogen content of about 2 percent or lower.

7. A process as defined by claim 1 wherein said oil is a shale oil.

8. A process as defined by claim 1 wherein said oil is a creosote oil.

9. A process as defined by claim 1 wherein said oil is a bottoms fraction from a catalytic cracking unit.

10. A process as defined by claim 1 wherein said oil is contacted with said coal at a temperature between about 750.degree. F. and about 850.degree. F. and at a space velocity between about 0.5 and about 1.5 pounds of oil per pound of coal.