A RECYCLING HYDROGEN-DONATING SOLVENT FOR DIRECT COAL LIQUEFACTION AND PREPARATION METHOD THEREFOR AND USE THEREOF

Abstract

The invention provides a recycling hydrogen-donating solvent for direct coal liquefaction and a preparation method therefor and use thereof, the recycling hydrogen-donating solvent provided by the preparation method of the invention can be used for obtaining the recycling hydrogen-donating solvent with good hydrogen-donating capacity through a relatively simple process flow. The preparation method comprises the following steps: 1) carrying out first fractionation on a direct coal liquefaction oil to obtain liquefied medium oil and liquefied heavy oil; 2) feeding the liquefied heavy oil into a first hydrogenation reactor and carrying out a first-stage hydrogenation reaction; 3) feeding the liquefied medium oil and the liquefied heavy oil subjected to the first-stage hydrogenation reaction in the step 2) into a second hydrogenation reactor, and carrying out a second-stage hydrogenation reaction to obtain hydrogenated product oil; 4) performing second fractionation on the hydrogenated product oil to obtain medium-temperature solvent oil and high-temperature solvent oil; and 5) mixing the medium-temperature solvent oil and the high-temperature solvent oil to prepare the recycling hydrogen-donating solvent.

Claims

1. A method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction, wherein it comprises the following steps: 1) carrying out first fractionation on a direct coal liquefaction oil to obtain a liquefied medium oil and a liquefied heavy oil, wherein the liquefied medium oil is a distillate oil of 220-320 C., and the liquefied heavy oil is a distillate oil of more than 320 C.; 2) feeding the liquefied heavy oil into a first hydrogenation reactor and carrying out a first-stage hydrogenation reaction; 3) feeding the liquefied medium oil and the liquefied heavy oil subjected to the first-stage hydrogenation reaction in step 2) into a second hydrogenation reactor and carrying out a second-stage hydrogenation reaction to obtain a hydrogenated product oil; 4) performing second fractionation on the hydrogenated product oil to obtain a medium-temperature solvent oil and a high-temperature solvent oil, wherein the medium temperature solvent oil is a distillate oil of 220-350 C., and the high temperature solvent oil is a distillate oil of more than 350 C.; and 5) mixing the medium-temperature solvent oil and the high-temperature solvent oil to prepare the recycling hydrogen-donating solvent.

2. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 1, wherein in step 2), the first hydrogenation reactor is a suspended bed hydrogenation reactor; and in step 3), the second hydrogenation reactor is a fixed bed hydrogenation reactor.

3. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 2, wherein in step 2), the first-stage hydrogenation reaction is carried out under conditions of: a reaction temperature I of 350-400 C., a volume space velocity I of 0.5-3 h.sup.1, a hydrogen to oil volume ratio I of 400-2000:1 (Nm.sup.3/m.sup.3); in step 3), the second-stage hydrogenation reaction is carried out under conditions of: a reaction temperature II of 320-380 C., a volume space velocity II of 0.5-3 h.sup.1, a hydrogen to oil volume ratio II of 400-1600:1 (Nm.sup.3/m.sup.3); and the reaction temperature I is higher than the reaction temperature II, the volume space velocity I is not lower than the volume space velocity II, and the hydrogen to oil volume ratio I is not lower than the hydrogen to oil volume ratio II.

4. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 3, wherein in step 2), the first-stage hydrogenation reaction is carried out under conditions of: a reaction temperature I of 360-390 C., a volume space velocity I of 0.8-2.5 h.sup.1, a hydrogen to oil volume ratio I of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure I of 13-19 MPa; in step 3), the second-stage hydrogenation reaction is carried out under conditions of: a reaction temperature II of 340-370 C., a volume space velocity II of 0.8-2 h.sup.1, a hydrogen to oil volume ratio II of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure II of 13-19 MPa; and the reaction temperature I is higher than the reaction temperature II, the volume space velocity I is higher than the volume space velocity II, and the hydrogen to oil volume ratio I is higher than the hydrogen to oil volume ratio II.

5. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 1, wherein the first-stage hydrogenation reaction is carried out in the presence of a first hydrogenation catalyst, and the second-stage hydrogenation reaction is carried out in the presence of a second hydrogenation catalyst; the first hydrogenation catalyst comprises a first support and a first active component; the second hydrogenation catalyst comprises a second support and a second active component; the first active component and the second active component are each independently one or more selected from oxides of Group VIB metal elements and oxides of Group VIII metal elements.

6. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 5, wherein in the first hydrogenation catalyst, the first support is contained in a content of 60-90 wt %, and the first active component is contained in a content of 10-40 wt %; and in the second hydrogenation catalyst, the second support is contained in a content of 60-90 wt %, and the second active component is contained in a content of 10-40 wt %.

7. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 6, wherein the first active component and the second active component are each independently a combination of oxide(s) of Group VIB metal element(s) and oxide(s) of Group VIII metal element(s).

8. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 1, wherein in step 5), a mass ratio of the medium-temperature solvent oil to the high-temperature solvent oil is 4:1 to 1:3.

9. A recycling hydrogen-donating solvent, wherein the recycling hydrogen-donating solvent is prepared by the method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 1.

10. A method for direct coal liquefaction, wherein the recycling hydrogen-donating solvent used in the direct coal liquefaction method is the recycling hydrogen-donating solvent of claim 9.

11. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 3, wherein in step 2), the first-stage hydrogenation reaction is carried out under a reaction pressure I of 12-20 MPa; and/or in step 3), the second-stage hydrogenation reaction is carried out under a reaction pressure II of 12-20 MPa; and/or the volume space velocity I is higher than the volume space velocity II, and the hydrogen to oil volume ratio I is higher than the hydrogen to oil volume ratio II.

12. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 5, wherein the Group VIB metal elements are selected from Mo and/or W, and the Group VIII metal elements are selected from Co and/or Ni; and/or the first support and the second support are each independently one or more selected from alumina, Y-type molecular sieve and molecular sieve.

13. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 7, wherein in the first hydrogenation catalyst, the oxide(s) of Group VIB metal element(s) are contained in a content of 10-35 wt %, and the oxide(s) of Group VIII metal element(s) are contained in a content of 4-10 wt %; and/or in the second hydrogenation catalyst, the oxide(s) of Group VIB metal element(s) are contained in a content of 10-30 wt %, and the oxide(s) of Group VIII metal element(s) are contained in a content of 1-6 wt %.

14. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 8, wherein in step 5), a mass ratio of the medium-temperature solvent oil to the high-temperature solvent oil is 1:1 to 3.5:1.

15. The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction of claim 8, wherein in step 5), a mass ratio of the medium-temperature solvent oil to the high-temperature solvent oil is 2.5:1 to 3.5:1.

Description

DESCRIPTION OF DRAWINGS

[0038] FIG. 1 shows a schematic diagram of the preparation process flow of a recycling hydrogen-donating solvent according to an embodiment.

DETAILED DESCRIPTION

[0039] To facilitate the understanding of the present invention, the present invention will be further explained below in conjunction with embodiments. It should be understood that the following embodiments are provided only for a better understanding of the present invention and are not meant that the present invention is limited thereto.

[0040] Unless otherwise defined, all technical and scientific terms used herein shall have the same meanings as those commonly understood by those skilled in the technical field to which the present invention belongs. The term and/or as used herein includes any and all combinations of one or more relevant listed items. The terms first, second, and third, etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0041] Where specific experimental steps or conditions are not specified in the embodiments, they can be carried out according to the operations or conditions of the corresponding conventional experimental steps in the technical field. The reagents or instruments used of which the manufacturers are not indicated are conventional products that are commercially available.

[0042] One aspect of the present invention provides a method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction, comprising the following steps: [0043] 1) carrying out first fractionation on a direct coal liquefaction oil to obtain a liquefied medium oil and a liquefied heavy oil, wherein the liquefied medium oil is a distillate oil of 220-320 C., and the liquefied heavy oil is a distillate oil of more than 320 C.; [0044] 2) feeding the liquefied heavy oil into a first hydrogenation reactor and carrying out a first-stage hydrogenation reaction; [0045] 3) feeding the liquefied medium oil and the liquefied heavy oil subjected to the first-stage hydrogenation reaction in step 2) into a second hydrogenation reactor and carrying out a second-stage hydrogenation reaction to obtain a hydrogenated product oil; [0046] 4) performing second fractionation on the hydrogenated product oil to obtain a medium-temperature solvent oil and a high-temperature solvent oil, wherein the medium temperature solvent oil is a distillate oil of 220-350 C., and the high temperature solvent oil is a distillate oil of more than 350 C.; and [0047] 5) mixing the medium-temperature solvent oil and the high-temperature solvent oil to prepare the recycling hydrogen-donating solvent.

[0048] The method for preparing a recycling hydrogen-donating solvent for direct coal liquefaction provided by the present invention involves first performing a first-stage hydrogenation reaction on the liquefied heavy oil of more than 320 C. obtained by fractionation of the direct coal liquefaction oil, and then subjecting the same to a second-stage hydrogenation reaction together with the liquefied medium oil of 220-320 C., which can effectively solve the problem of underhydrogenation or overhydrogenation in the prior art. The medium temperature solvent oil of 220-350 C. and the high temperature solvent oil of more than 350 C. obtained by fractionation of the hydrogenated product oil obtained by using the above hydrogenation process are blended to give the recycling hydrogen-donating solvent. When the recycling hydrogen-donating solvent is used in the direct coal liquefaction process, it not only has high hydrogen-donating capacity, but also has a wide distillation range, which can effectively swell coal powder and reduce the viscosity of coal slurry, and is conducive to improving the effect of direct coal liquefaction.

[0049] The recycling hydrogen-donating solvent provided by the preparation method according to the present invention has a higher content of bicyclic and tricyclic hydrogenated aromatic hydrocarbons, and the resulting recycling hydrogen-donating solvent has a better hydrogen-donating capacity. In some embodiments, in the recycling hydrogen-donating solvent according to the present invention, the content of the bicyclic hydrogenated aromatic hydrocarbons is 10-40 wt %, and the content of the tricyclic hydrogenated aromatic hydrocarbons is 5-20 wt %.

[0050] The preparation method according to the present invention has a simple process flow, is easy to implement in industry, and can effectively reduce the complexity of the processing process while improving the hydrogen-donating capacity of the recycling hydrogen-donating solvent. Specifically, in a preferred embodiment, in step 2), the first hydrogenation reaction is preferably carried out in a suspended bed hydrogenation reactor, and in step 3), the second hydrogenation reaction is preferably carried out in a fixed bed hydrogenation reactor.

[0051] Compared with directly introducing the liquefied heavy oil into a fixed bed hydrogenation reactor for hydrogenation reaction, by first introducing the liquefied heavy oil into a suspended bed hydrogenation reactor for the first-stage of hydrogenation reaction, it can effectively prevent impurities contained in the liquefied heavy oil from contaminating the fixed bed reactor and the catalyst, thereby effectively avoiding the adverse effects on hydrogenation efficiency and the stability of the process operation. Moreover, the liquefied heavy oil is first subjected to the first-stage hydrogenation in the suspended bed reactor, followed by the second-stage hydrogenation in the fixed bed reactor in sequence, which has a relatively longer reaction residence time compared with single stage hydrogenation, which can effectively prevent underhydrogenation of the liquefied heavy oil. At the same time, the liquefied heavy oil is first subjected to the first-stage hydrogenation in the suspended bed reactor, and then subjected to the second-stage hydrogenation together with the liquefied medium oil in the fixed bed reactor, which is not easy to cause overhydrogenation of the liquefied medium oil and underhydrogenation of the liquefied heavy oil. Furthermore, the recycling hydrogen-donating solvent according to the present invention can not only effectively improve the hydrogen-donating capacity of the recycling hydrogen-donating solvent, but also does not require more severe hydrogenation conditions and increased complexity of the hydrogenation process flow due to the improvement of the hydrogen-donating capacity. By first subjecting the liquefied heavy oil to the first-stage hydrogenation in the suspended bed reactor, and then continuously subjecting the same to the second-stage hydrogenation together with the liquefied medium oil in the fixed bed reactor, the advantage of treating inferior raw materials by the suspended bed hydrogenation is retained, meanwhile, the coupling with the fixed bed reactor can improve the hydrogenation efficiency, which is conducive to increasing the service life of the catalyst in the fixed bed reactor, reducing the risk of catalyst blockage by impurities in the liquefied heavy oil, catalyst deactivation, and blockage of the fixed bed reactor by impurities, etc., and improving the stability of the process operation and reducing the operation pressure difference of the plant.

[0052] By adopting the preparation method according to the present invention, the liquefied heavy oil is first subjected to the first-stage hydrogenation, and then to the second-stage hydrogenation together with the liquefied medium oil, wherein different hydrogenation conditions can be flexibly used in the first-stage and second-stag hydrogenations, which is conducive to reducing the energy consumption and hydrogen consumption required in the processing process of the recycling hydrogen-donating solvent.

[0053] In a preferred embodiment, in step 2), the first-stage hydrogenation reaction is carried out under conditions of: a reaction temperature I of 350-400 C., a volume space velocity I of 0.5-3 h.sup.1, a hydrogen to oil volume ratio I of 400-2000:1 (Nm.sup.3/m.sup.3), and preferably, a reaction pressure I of 12-20 MPa; in step 3), the second-stage hydrogenation reaction is carried out under conditions of: a reaction temperature II of 320-380 C., a volume space velocity II of 0.5-3 h.sup.1, a hydrogen to oil volume ratio II of 400-1600:1 (Nm.sup.3/m.sup.3), and preferably, a reaction pressure II of 12-20 MPa; moreover, the reaction temperature I is higher than the reaction temperature II, the volume space velocity I is not lower than the volume space velocity II, and the hydrogen to oil volume ratio I is not lower than the hydrogen to oil volume ratio II; preferably, the volume space velocity I is higher than the volume space velocity II, and the hydrogen to oil volume ratio I is higher than the hydrogen to oil volume ratio II. In the preparation method according to the present invention, the first and second hydrogenation reactions are carried out under the above mentioned conditions, and relatively more severe hydrogenation conditions are used in the first hydrogenation reaction compared with the second hydrogenation reaction, and relatively milder hydrogenation conditions are used in the second hydrogenation reaction, which can increase the content of the hydrogenated aromatic hydrocarbons in the recycling hydrogen-donating solvent to a greater extent, and is conducive to avoiding overhydrogenation and underhydrogenation, and further improving the hydrogen-donating capacity of the recycling hydrogen-donating solvent.

[0054] In some preferred embodiments, in step 2), the first-stage hydrogenation reaction is carried out under conditions of: a reaction temperature I of 360-390 C., a volume space velocity I of 0.8-2.5 h.sup.1, a hydrogen to oil volume ratio I of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure I of 13-19 MPa; in step 3), the second-stage hydrogenation reaction is carried out under conditions of: a reaction temperature II of 340-370 C., a volume space velocity II of 0.8-2 h.sup.1, a hydrogen to oil volume ratio II of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure II of 13-19 MPa; moreover, the reaction temperature I is higher than the reaction temperature II, the volume space velocity I is higher than the volume space velocity II, and the hydrogen to oil volume ratio I is higher than the hydrogen to oil volume ratio II. When the above preferred hydrogenation conditions are adopted, it is conducive to further improving the hydrogen-donating capacity of the recycling hydrogen-donating solvent and obtaining a recycling hydrogen-donating solvent with excellent hydrogen-donating capacity.

[0055] In the present invention, the I and II in reaction temperature I, reaction temperature II, volume space velocity I, volume space velocity II, hydrogen to oil volume ratio I, hydrogen to oil volume ratio II, etc., are only for convenience in distinguishing and describing the respective reaction conditions for the first-stage and second-stage hydrogenation reactions.

[0056] In the preparation method according to the present invention, the corresponding catalysts commonly used in the direct coal liquefaction oil hydrogenation process in the art can be used for the first-stage and second-stage hydrogenation reactions. In some embodiments, the first-stage hydrogenation reaction is carried out in the presence of a first hydrogenation catalyst, and the second-stage hydrogenation reaction is carried out in the presence of a second hydrogenation catalyst; the first hydrogenation catalyst comprises a first support and a first active component; the second hydrogenation catalyst comprises a second support and a second active component; and the first active component and the second active component are each independently one or more selected from oxides of Group VIB metal elements and oxides of Group VIII metal elements. Preferably, the first support and the second support are each independently one or more selected from alumina, Y-type molecular sieve and molecular sieve.

[0057] Preferably, the Group VIB metal elements are selected from Mo and/or W; and the Group VIII metal elements are selected from Co and/or Ni. Further preferably, the Group VIB metal elements in the first hydrogenation catalyst are selected from Mo and W; and preferably, the first active component in the first hydrogenation catalyst is an oxide of Ni, Mo, and W. Further preferably, the second active component in the second hydrogenation catalyst is an oxide of Ni and Mo, or an oxide of Ni, Mo and W, which is embodied as NiMo binary or NiMoW ternary active metal.

[0058] In some embodiments, in the first hydrogenation catalyst, the content of the first support is 60-90 wt %, and the content of the first active component is 10-40 wt %; and in the second hydrogenation catalyst, the content of the second support is 60-90 wt %, and the content of the second active component is 10-40 wt %. In some preferred embodiments, the first active component and the second active component are each independently a combination of oxide(s) of the Group VIB metal element(s) and oxide(s) of Group VIII metal element(s); preferably, in the first hydrogenation catalyst, the content of oxide(s) of the Group VIB metal element(s) is 10-35 wt %, and the content of oxide(s) of the Group VIII metal element(s) is 4-10 wt %; and preferably, in the second hydrogenation catalyst, the content of oxide(s) of the Group VIB metal element(s) is 10-30 wt %, and the content of oxide(s) of the Group VIII metal element(s) is 1-6 wt %. The use of the first and second hydrogenation catalysts with the above compositions is conducive to improving the catalytic activity of the first-stage and second-stage hydrogenation reactions.

[0059] In some embodiments, the first hydrogenation catalyst has a specific surface area of 200 m.sup.2/g or more, a pore volume of 0.3 ml/g or more, and a pore diameter of 6 nm or more; and preferably, the first hydrogenation catalyst has a specific surface area of 200-300 m.sup.2/g, a pore volume of 0.35-0.5 ml/g, and a pore diameter of 7 nm or more. In some embodiments, the second hydrogenation catalyst has a specific surface area of 150 m.sup.2/g or more, a pore volume of 0.24 ml/g or more, and a pore diameter of 4 nm or more; and preferably, the second hydrogenation catalyst has a specific surface area of 180-260 m.sup.2/g, a pore volume of 0.25-0.45 ml/g, and a pore diameter of 5 nm or more.

[0060] The first and second hydrogenation catalysts with the above compositions and characteristics can be the corresponding catalysts that are commercially available in the art, or the corresponding catalysts that can be prepared using the catalyst preparation technologies disclosed in the prior art. Specifically, in some embodiments, the first hydrogenation catalyst is, for example, but not limited to, the FFT-2 catalyst, etc., from Dalian Research Institute of Chemical Industry, and the second hydrogenation catalyst is, for example, but not limited to, the Type HTS-358 catalyst supplied by AXENS Institute in France.

[0061] In some embodiments, the active components in the first and second hydrogenation catalysts catalyze the first-stage and second-stage hydrogenation reactions in a vulcanized state, respectively. Specifically, for example, after charging the corresponding hydrogenation catalyst in the hydrogenation reactor, the catalyst is vulcanized using a vulcanizing agent, such as carbon disulfide or dimethyl disulfide, etc. The vulcanization of the hydrogenation catalyst is a conventional technology in the art and will not be described in detail here.

[0062] In a preferred embodiment, in step 5), the mass ratio of the medium-temperature solvent oil to the high-temperature solvent oil is 4:1 to 1:3, preferably 1:1 to 3.5:1, and further preferably 2.5:1 to 3.5:1. The medium-temperature solvent oil and high-temperature solvent oil obtained in the present invention are blended according to the preferred ratio as the recycling hydrogen-donating solvent, which has excellent hydrogen-donating capability when applied to the direct coal liquefaction process, and can improve the conversion rate of coal and oil yield in the direct coal liquefaction process, and reduce the asphalt yield and gas yield at the same time.

[0063] In a preferred embodiment, in the preparation method according to the present invention, in step 2), the first-stage hydrogenation reaction is carried out under conditions of: a reaction temperature I of 360-390 C., a volume space velocity I of 0.8-2.5 h.sup.1, a hydrogen to oil volume ratio I of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure I of 13-19 MPa; in step 3), the second-stage hydrogenation reaction is carried out under conditions of: a reaction temperature II of 340-370 C., a volume space velocity II of 0.8-2 h.sup.1, a hydrogen to oil volume ratio II of 500-1200:1 (Nm.sup.3/m.sup.3), and a reaction pressure II of 13-19 MPa; moreover, the reaction temperature I is higher than the reaction temperature II, the volume space velocity I is higher than the volume space velocity II, and the hydrogen to oil volume ratio I is higher than the hydrogen to oil volume ratio II. Meanwhile, in step 5), the mass ratio of the medium-temperature solvent oil to the high-temperature solvent oil is 1:1 to 3.5:1, more preferably 2.5:1 to 3.5:1. When this preferred embodiment is adopted, not only the hydrogen consumption during the hydrogenation process is reduced, but also more excellent hydrogen-donating capability of the resulting recycling hydrogen-donating solvent can be achieved, which can further significantly improve the conversion rate of coal and oil yield.

[0064] In some embodiments, in step 1) of the preparation method according to the present invention, the first fractionation is carried out in a distillation column or a rectification column. The first fractionation is preferably carried out under conditions of: an operation pressure of 0.1-0.8 MPa, an operation temperature at the bottom of 300-380 C., and an operation temperature at the top of 80-200 C. Liquefied light oil (distillate oil of less than 200 C.), liquefied medium oil, and liquefied heavy oil are obtained from the direct coal liquefaction oil by the first fractionation. Among them, the liquefied light oil can be sent to the downstream hydrogenation and upgrading units for the production of naphtha and diesel products, while the liquefied medium oil and the liquefied heavy oil are sent to the subsequent steps 2) and 3).

[0065] In some embodiments, in step 4) of the preparation method according to the present invention, the second fractionation is carried out in a rectification column. The second fractionation is preferably carried out under conditions of: an operation pressure of 0.1-0.8 MPa for the rectification column, an operation temperature at the bottom of 300-380 C., and an operation temperature at the top of 120-220 C. The hydrogenated light oil (distillate oil with a distillation range of less than 220 C.), the medium-temperature solvent oil, and the high-temperature solvent oil are obtained upon the second fractionation, wherein the medium-temperature solvent oil and the high-temperature solvent oil are used to prepare the recycling hydrogen-donating solvent of the present invention.

[0066] By using the preparation method according to the present invention to prepare the recycling hydrogen-donating solvent, 1) as many hydrogenated aromatic hydrocarbons as possible can be obtained, which has good hydrogen-donating capacity; moreover, the recycling hydrogen-donating solvent has a wide distillation range and good swelling capacity for coal powder. When it is applied in the direct coal liquefaction process, it is conducive to obtaining coal slurry with lower viscosity, which is convenient for transportation. 2) The process flow for preparing the recycling hydrogen-donating solvent is simple, and can be easily implemented in industrial plants. 3) In the preparation method according to the present invention, the liquefied heavy oil is first subjected to a first-stage hydrogenation reaction, and then subjected to a second-stage hydrogenation reaction together with the liquefied medium oil, the liquefied heavy oil undergoes two stages of hydrogenation, and different degree of severe hydrogenation conditions can be flexibly adopted for the hydrogenation of the liquefied heavy oil and the liquefied medium oil during the hydrogenation process, which is conducive to maximizing the content of hydrogenated aromatic hydrocarbons in the obtained recycling solvent, avoiding overhydrogenation and underhydrogenation; Moreover, compared with the existing hydrogenation processes for direct coal liquefaction oil, the preparation method according to the present invention can effectively reduce the hydrogenation severity and the hydrogen consumption, having good economical efficiency and operational stability. 4) In the process of preparing recycling hydrogen-donating solvent, the liquefied light oil is cut out of the direct coal liquefaction oil. This part of oil has a low hydrogenation severity and can be sent to the subsequent product processing units, thereby improving the processing efficiency of the recycling hydrogen-donating solvent; the hydrogenated light oil of less than 220 C. is cut out of the obtained hydrogenated product oil to avoid the negative effects such as reduced reactor utilization efficiency due to the gasification of this part of oil during the liquefaction process.

[0067] The present invention also provides a recycling hydrogen-donating solvent, which is prepared using the preparation method described above.

[0068] The present invention also provides a method for direct coal liquefaction, wherein the above recycling hydrogen-donating solvent is used in the direct coal liquefaction method.

[0069] The direct coal liquefaction oil produced by a megaton of direct coal liquefaction plant was used as the feedstock oil in the following examples, and the properties of the direct coal liquefaction feedstock oil used are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Properties of Direct Coal Liquefaction Feedstock Oil Density at 20 C., g/cm.sup.3 0.9641 Aromatic carbon ratio 0.51 S, mg/L 27.10 N, mg/L 527.26 D-1160 Distillation curve (LV %) C. 5% 164 10% 216 30% 266 50% 295 70% 337 90% 388 98% 470 Hydrocarbon composition, 4.9 wt % alkanes Total naphthenes 6.8 Monocyclic aromatic hydrocarbons 41.6 Bicyclic aromatic hydrocarbons 30.0 Tricyclic aromatic hydrocarbons 8.8 Tetracyclic aromatic hydrocarbons 2.0 Total aromatic hydrocarbons 82.4 Colloid 2.4 Ash, wt % 0.01%

Evaluation of Liquefaction Performance of Recycling Hydrogen-Donating Solvent:

[0070] The recycling hydrogen-donating solvents obtained in the following examples and comparative examples were subjected to a direct coal liquefaction experiment in a high-pressure reactor using the same coal sample to evaluate the liquefaction performance of the recycling hydrogen-donating solvents. The liquefaction conditions included: a reaction temperature of 455 C., an initial hydrogen pressure of 10 MPa, a constant temperature reaction time of 1 h, a catalyst of Fe.sub.2O.sub.3 (with an addition amount of 1 wt % of dry coal), and a co-catalyst of sulfur (with an atomic ratio of S to Fe in the catalyst being 2:1), and the mass ratio of coal sample to recycling hydrogen-donating solvent of 45:55. Unless otherwise specified, the direct coal liquefaction experiment mentioned above was conducted in accordance with the High-Pressure Reactor Test Method for Coal Liquefaction Reactivity (GB/T33690-2017).

Example 1

[0071] The schematic diagram of the process flow of Example 1 is shown in FIG. 1. The direct coal liquefaction oil was used to prepare a recycling hydrogen-donating solvent according to the following steps: [0072] 1) The direct coal liquefaction oil was subjected to the first fractionation in a rectification column 1, wherein the operation temperature at the bottom of the rectification column 1 was 360 C., the operation temperature at the top was 160 C., and the operation pressure was 0.2 MPa, and a liquefied light oil of less than 200 C., a liquefied medium oil of 220-320 C., and a liquefied heavy oil of more than 320 C. were obtained by the first fractionation. [0073] 2) The liquefied heavy oil obtained in step 1) was fed into a suspended bed hydrogenation reactor 2 for the first-stage hydrogenation reaction, wherein the catalyst used was NiMo hydrogenation refining catalyst (i.e. commercially available FFT-2 catalyst supplied by Sinopec Dalian Chemical Research Institute); and the process conditions for the first-stage hydrogenation reaction included: a reaction temperature of 380 C., a reaction pressure of 15 MPa, a volume space velocity of 2 h.sup.1, and a hydrogen to oil volume ratio of 1000:1 (Nm.sup.3/m.sup.3). [0074] 3) The hydrogenated product obtained in step 2) and the liquefied medium oil obtained in step 1) were mixed and fed into a fixed bed hydrogenation reactor 3, wherein the catalyst used was NiMo hydrogenation refining catalyst (i.e. Type HTS-358 catalyst supplied by AXENS, France); and the process conditions for the second-stage hydrogenation reaction included: a reaction temperature of 360 C., a reaction pressure of 15 MPa, a volume space velocity of 1.5 h.sup.1, and a hydrogen to oil volume ratio of 800:1 (Nm.sup.3/m.sup.3).

[0075] Before carrying out the first-stage and second-stage hydrogenation reactions mentioned above, the catalyst in the above step 2) and the catalyst in the above step 3) were prevulcanized by heating the virgin kerosene (containing 2 wt % of dimethyl disulfide) to 360 C. at a heating rate between 10 C./min and 15 C./min in a hydrogen atmosphere, and then maintaining the temperature for 12 hours until the vulcanization was completed. [0076] 4) The hydrogenated product oil obtained in step 3) was subjected to a second fractionation in a rectification column 4 under the following process conditions: an operation pressure of the rectification column of 0.2 MPa, an operation temperature at the bottom of 310 C., and an operation temperature at the top of 180 C.; and the hydrogenated light oil with a distillation range of less than 220 C., a medium temperature solvent oil of 220-350 C., and a high-temperature solvent oil of more than 350 C. were obtained. [0077] 5) The high-temperature solvent oil and the medium-temperature solvent oil obtained in step 4) were formulated into a recycling hydrogen-donating solvent in a mass ratio of 1:3.

Example 2

[0078] This Example was carried out with reference to Example 1, except that the high-temperature solvent oil and the medium-temperature solvent oil were formulated into a recycling hydrogen-donating solvent in a mass ratio of 3:1 in step 5).

Example 3

[0079] This Example was carried out with reference to Example 1, except that the high-temperature solvent oil and the medium-temperature solvent oil were formulated into a recycling hydrogen-donating solvent in a mass ratio of 1:1 in step 5).

Example 4

[0080] This Example was carried out with reference to Example 1, except that the high-temperature solvent oil and the medium-temperature solvent oil were formulated into a recycling hydrogen-donating solvent in a mass ratio of 1:4 in step 5).

Example 5

[0081] This Example was carried out with reference to Example 1, except that the high-temperature solvent oil and the medium-temperature solvent oil were formulated into a recycling hydrogen-donating solvent in a mass ratio of 4:1 in step 5).

[0082] From Examples 1 to 5, it can be seen that in Examples 1 to 4, the mass ratio of high-temperature solvent oil to medium-temperature solvent oil was controlled between 3:1 and 1:4, resulting in a relatively high hydrogen-donating index for the recycling hydrogen-donating solvent, as well as a relatively higher conversion rate of coal and oil yield in the direct coal liquefaction experiment. By controlling the mass ratio of high-temperature solvent oil to medium-temperature solvent oil between 1:1 and 1:3.5, it is possible to achieve relatively high hydrogen-donating index, conversion rate of coal and oil yield without the need to add excess medium-temperature solvent; and in Example 1, by controlling the mass ratio of high-temperature solvent oil to medium-temperature solvent oil between 1:2.5 and 1:3.5, it is possible to simultaneously achieve more excellent hydrogen-donating capacity, and conversion rate of coal and oil yield.

Example 6

[0083] This Example was carried out with reference to Example 1, except that [0084] in step 2), the process conditions for the first-stage hydrogenation reaction included: a reaction temperature of 400 C., a reaction pressure of 20 MPa, a volume space velocity of 0.5 h.sup.1, and a hydrogen to oil volume ratio of 2000:1 (Nm.sup.3/m.sup.3); and [0085] in step 3), the process conditions for the second-stage hydrogenation reaction included: a reaction temperature of 380 C., a reaction pressure of 20 MPa, a volume space velocity of 0.5 h.sup.1, and a hydrogen to oil volume ratio of 1600:1 (Nm.sup.3/m.sup.3).

Example 7

[0086] This Example was carried out with reference to Example 1, except that [0087] in step 2), the process conditions for the first-stage hydrogenation reaction included: a reaction temperature of 350 C., a reaction pressure of 12 MPa, a volume space velocity of 3 h.sup.1, and a hydrogen to oil volume ratio of 400:1 (Nm.sup.3/m.sup.3); and [0088] in step 3), the process conditions for the second-stage hydrogenation reaction included: a reaction temperature of 320 C., a reaction pressure of 12 MPa, a volume space velocity of 3 h.sup.1, and a hydrogen to oil volume ratio of 400:1 (Nm.sup.3/m.sup.3).

[0089] From the comparison of Examples 1, 6, and 7, it can be seen that when Example 1 adopted more preferred conditions for the first-stage and second-stage hydrogenation reactions, not only relatively low hydrogen consumption in the hydrogenation reaction is achieved, but also the recycling hydrogen-donating solvent had higher hydrogen-donating index than that in Examples 6 and 7 formulated by using the obtained high-temperature solvent oil and medium-temperature solvent oil in the same mass ratio, thus achieving higher conversion of coal rate and oil yield in the direct coal liquefaction experiments.

Comparative Example 1

[0090] Compared with Example 1, the difference lied in that the step 1) was omitted. Specifically, the direct coal liquefaction oil was directly sent to step 2) for the first-stage hydrogenation reaction, and then the hydrogenated product was sent to step 3) for the second-stage hydrogenation reaction, then the hydrogenated product obtained in step 3) was sent to step 4) for the second fractionation, and the high-temperature solvent oil and medium-temperature solvent oil obtained in step 4) were formulated in a mass ratio of 1:3 to form the recycling hydrogen-donating solvent. Those not specified in this Comparative example 1 were carried out with reference to Example 1.

[0091] When compared with Example 1, it can be seen that the hydrogen consumption of hydrogenation reaction in Comparative example 1 was significantly increased. Although the high-temperature solvent oil and the medium-temperature solvent oil obtained in Comparative example 1 were formulated into the recycling hydrogen-donating solvent in same mass ratio as in Example 1, the hydrogen-donating index of the recycling hydrogen-donating solvent in Comparative Example 1 was significantly reduced, and the conversion rate of coal and oil yield in the direct coal liquefaction experiments were significantly reduced.

Comparative Example 2

[0092] Compared with Example 1, the difference lied in that step 2) was omitted, and the liquefied heavy oil and liquefied medium oil obtained in step 1) were mixed and subjected to hydrogenation reaction according to step 3). Other operations were the same as in Example 1.

[0093] Although the high-temperature solvent oil and the medium-temperature solvent oil obtained in the hydrogenation process of Comparative example 2 were formulated into the recycling hydrogen-donating solvent in the same mass ratio as in Example 1, the hydrogen-donating index of which was significantly reduced, and the conversion rate of coal and oil yield in the direct coal liquefaction experiments were significantly reduced.

Comparative Example 3

[0094] Compared with Example 1, the difference lied in that the liquefied heavy oil and liquefied medium oil obtained in step 1) were mixed and subjected to hydrogenation reaction in a suspended bed hydrogenation reactor according to step 2) and the hydrogenation reaction in a fixed bed hydrogenation reactor in step 3) was not carried out. The obtained hydrogenated product oil was subjected to a second fractionation according to step 4) of Example 1, and formulated into a recycling hydrogen-donating solvent according to step 5) of Example 1. The direct coal liquefaction experiment was then carried out with reference to Example 1.

[0095] Compared with Example 1, the hydrogen consumption of the hydrogenation reaction in the hydrogenation process of Comparative example 3 was slightly increased. Although the obtained high-temperature solvent oil and the medium-temperature solvent oil were formulated into the recycling hydrogen-donating solvent in the same mass ratio as in Example 1, the hydrogen-donating index of the recycling hydrogen-donating solvent in Comparative example 3 was significantly reduced, and the conversion rate of coal and oil yield in the direct coal liquefaction experiments were significantly reduced.

Comparative Example 4

[0096] This Comparative example 4 was carried out with reference to Example 1, except that in step 3), only the liquefied medium oil was sent to the fixed bed hydrogenation reactor; and in step 4), the hydrogenated product obtained in step 2) was mixed with the hydrogenated product obtained in step 3) for the second fractionation.

[0097] Compared with Example 1, although the high-temperature solvent oil and the medium-temperature solvent oil obtained in Comparative example 4 were formulated into the recycling hydrogen-donating solvent in the same mass ratio as in Example 1, the hydrogen-donating index of the recycling hydrogen-donating solvent in Comparative example 4 was significantly reduced, and the conversion rate of coal and oil yield in the direct coal liquefaction experiments were significantly reduced.

TABLE-US-00002 TABLE 2 Results of Examples (Ex.) and Comparative examples (Ex.) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 CEx. 1 CEx. 2 CEx. 3 CEx. 4 Density at 0.9603 0.9936 0.9785 0.9518 1.0023 0.9521 0.9796 0.9524 0.9631 0.9609 0.9688 20 C., g/cm.sup.3 Hydrogen 1.96 1.96 1.96 1.96 1.96 2.35 1.85 2.23 1.85 2.01 1.76 consumption of hydrogenation reaction, wt % Aromatic 0.43 0.48 0.46 0.42 0.49 0.42 0.46 0.46 0.45 0.43 0.46 carbon ratio Hydrogen- 24 20.5 22 24 20 23 22 22 22.5 23.5 22.5 donating index, PDQI Conversion 91.3 89.6 90.5 91.1 89.3 90.6 90.5 89.6 90.1 90.6 90.2 rate of coal, % Oil yield, % 61.4 56.8 59.8 60.9 56.2 60.1 59.2 59.4 59.8 60.3 59.9

[0098] In the above Table 2, the hydrogen-donating index refers to the mass in mg of active hydrogen at the beta-site of cycloalkyl group on the cycloalkyl aromatic hydrocarbons per 1 g of the recycling hydrogen-donating solvent, and high hydrogen-donating index indicates that the solvent has strong hydrogen-donating capacity and good solvent performance.

[0099] In the above Table 2, the density, aromatic carbon ratio, and hydrogen-donating index are the measurement results of the recycling hydrogen-donating solvent, and the hydrogen consumption of the hydrogenation reaction is the hydrogen consumption in the process of preparing the recycling hydrogen-donating solvent by the hydrogenation of the direct coal liquefaction oil; and the conversion rate of coal and oil yield are the experimental results of direct coal liquefaction experiments.

[0100] In the above Table 2, the calculation formula for hydrogen consumption of hydrogenation reaction is: mass of hydrogen consumption/mass of direct coal liquefaction oil100%; [0101] the calculation formula for conversion rate of coal is: mass of reacted coal/mass of feedstock coal100% (on the moisture-free and ash-free basis); and [0102] the calculation formula for oil yield is: mass of product oil/mass of feedstock coal100% (on the moisture-free and ash-free basis).

[0103] From the above experimental results, it can be seen that the preparation method according to the present invention can obtain a recycling hydrogen-donating solvent with good hydrogen-donating capacity, and the preparation process flow is simple.

[0104] In a preferred embodiment, the preferred process conditions are adopted in the preparation method of the present invention for the first-stage and second-stage hydrogenation reactions, not only the preparation method is conducive to reducing the hydrogen consumption of the hydrogenation reaction, but also the resulting recycling hydrogen-donating solvent has better performance and more excellent hydrogen-donating index than that prepared under other process conditions and with the same mass ratio of high-temperature solvent oil and medium-temperature solvent oil. Therefore, a higher conversion rate of coal and oil yield can be achieved.

[0105] In a preferred embodiment, the high-temperature solvent oil and the medium-temperature solvent oil obtained by the preparation method according to the present invention are formulated in a mass ratio of 1:1 to 1:3.5, preferably 1:2.5 to 1:3.5, into a recycling hydrogen-donating solvent, which can result in products with better hydrogen-donating capacity, and is conducive to further improving the conversion rate of coal and oil yield.

[0106] It will be appreciated the above examples are given for clear illustration and do not imply that the present invention is limited thereto. For those ordinarily skilled in the art, different forms of changes or variations can be made based on the above description. All embodiments need not and cannot be exhaustively listed herein. The obvious changes or variations resulting therefrom are still within the scope of protection of the present invention.