Process for the hydroconversion of heavy oil products with recycling

Abstract

A process for the hydroconversion of heavy oil products includes the following steps where heavy oil products and hydrogen are supplied to a slurry hydroconversion section having a molybdenum-based catalyst: separating the reaction effluent into a vapour phase and a slurry phase; and sending the slurry phase to a separation section having the function of separating the Vacuum Gas Oil, Heavy Vacuum Gas Oil, Light Vacuum Gas Oil, and Atmospheric Gas Oil fractions, from a stream of heavy organic products which contains asphaltenes, unconverted feed, catalyst, and solid formed during the hydroconversion reaction. This stream is partly sent to the reaction section and partly forms a purge stream, which is heated and made fluid between 185° C.-220° C., and subjected to a static settling unit up to at least 100° C. From the settling unit two new products, clarified component and cake, are obtained. The clarified component is recycled to the hydroconversion reaction section.

Claims

1. A process for the hydroconversion of heavy oil products which comprises the following steps: Supplying to a slurry-phase hydroconversion section a Molybdenum-containing catalyst precursor, heavy oil products and a hydrogen-containing stream; Conducting a hydroconversion reaction producing a reaction effluent which is subsequently separated at high pressure and high temperature into a vapour phase and a slurry phase; Subsequently sending the separated vapour phase to a gas treatment section with the function of separating a liquid fraction from the hydrogen-containing gas; Subsequently sending the slurry phase to a separation section which has the function of separating the Vacuum Gas Oil (VGO), Heavy Vacuum Gas Oil (HVGO), Light Vacuum Gas Oil (LVGO), Atmospheric Gas Oil (AGO), from a stream of heavy organic products which contains asphaltenes, unconverted feed, catalyst and solid formed during the hydroconversion reaction; Recycling a part of said heavy organic products to the reaction section and forming a purge stream with the remainder; Heating said purge stream at a temperature greater than or equal to 185° C. and not above 220° C. and, subsequently; Subjecting said heated purge to settling by lowering the temperature in a progressive and controlled manner up to the minimum temperature of 100° C., without shaking the purge, so as to form a light phase, called clarified component, and a heavy phase, called cake, as a function of density; Recycling the clarified component to the slurry-phase hydroconversion section.

2. The process for the hydroconversion of heavy oil products according to claim 1, wherein the slurry-phase hydroconversion reactor is a bubble reactor.

3. The process for the hydroconversion of heavy oil products according to claim 1, wherein the reaction takes place in one or more hydroconversion reactors placed in parallel and similarly the effluent separation takes place in one or more high pressure and temperature separators placed in parallel.

4. The process for the hydroconversion of heavy oil products according to claim 1, wherein the vapour treatment section comprises heat exchangers alternated with a washing column (VGO), a high pressure and medium temperature separator, a high pressure and low temperature separator.

5. The process for the hydroconversion of heavy oil products according to claim 1, wherein said liquid separation section comprises a high temperature and low pressure separator which works as an accumulator; a pre-flash column, possibly a stripper to separate the lights, and lastly a vacuum distillation column to recover the VGO fraction, the LVGO fraction, the HVGO fraction, the Wash Oil and the vacuum Residue.

6. The process for the hydroconversion of heavy oil products according to claim 1, wherein the purge is heated at a temperature comprised between 185° C.-220° C.

7. The process for the hydroconversion of heavy oil products according to claim 6, wherein the purge is heated at a temperature comprised between 200° C. and 220° C.

8. The process according to claim 1, wherein the heated purge is cooled at a temperature which varies in the range comprised between 100° C. and 170° C.

9. A method according to claim 8, wherein the purge is cooled at a temperature comprised between 100° C. and 160° C.

10. The process for the hydroconversion of heavy oil products according to claim 1, wherein the weight ratio of recycled clarified component and fresh feed varies in the range from 2% to 13%.

11. The process for the hydroconversion of heavy oil products according to claim 10, wherein the weight ratio of recycled clarified component and fresh feed varies in the range from 3% to 10% by weight.

12. The process for the hydroconversion of heavy oil products according to claim 1, wherein the time required for the formation of a heavy phase or cake varies from 15 minutes to 2 hours.

13. The process for the hydroconversion of heavy oil products according to claim 12, wherein the time required for the formation of a heavy phase or cake varies from 20 minutes to 1 hour.

14. The process for the hydroconversion of heavy oil products according to claim 1, wherein the settling speed is comprised between 85 mm/hour and 300 mm/hour.

15. The process for the hydroconversion of heavy oil products according to claim 1, wherein the catalyst precursor is a solution of Mo-octoate (2-ethyl hexanoate) in 2-ethylexanoic acid, containing 15.5% by weight of Mo.

16. The process for the hydroconversion of heavy oil products according to claim 1, wherein the hydroconversion reactors and the high pressure and temperature separators operate in a temperature range comprised between 420° C. and 440° C., at a pressure comprised between 155 atm and 160 atm.

17. The process according to claim 1, wherein the controlled temperature lowering takes place: by using an adequately sized and thermostated tank, or by mixing a hot stream to be decanted with a cold stream, considering the appropriate thermal balance of the process to calculate the flow rates thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further purposes and advantages of the present disclosure will become more apparent from the following description and the appended figures, which are provided purely by way of a non-limiting example, which represent preferred embodiments of the disclosure.

(2) FIG. 1 illustrates a preferred embodiment of the process according to the present disclosure, in which the fresh feed (1) is supplied together with the catalyst precursors (2) in a hydroconversion reactor (A). The reaction effluent is supplied to a high pressure and temperature separator (B) which forms a gaseous stream (5) and a slurry (7). The gas (5) is supplied to the treatment section (C) where a gaseous stream containing hydrogen (4) is separated from naphtha, atmospheric gas oil (AGO) and Vacuum Gas Oil (VGO) indicated with 6.

(3) The slurry (7) is supplied to a vacuum separation section (D) to separate Vacuum Gas Oil (VGO) from a heavy product which partly recycles to the reactor (12) and partly forms a purge stream (9). The purge is subjected to settling (E) where a cake (10) is separated from a clarified component (11) which is recycled to the reactor (A).

(4) FIG. 1 also indicates a saturation gas (13) cut from the gaseous recycling which is supplied onto the bottom of the high pressure and temperature separator (B).

(5) FIG. 2 is substantially identical to FIG. 1 and does not provide for the saturation gas.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) The process for the hydroconversion of heavy oil products is now described in detail, also with reference to FIG. 1, which integrates a hydroconversion section with a purge treatment section through separation by static decantation obtaining a recycle stream.

(7) Precursors of a catalyst based on Molybdenum (2), heavy oil products (the feed, 1) and a hydrogen-containing stream (3,4) are supplied to a slurry-phase hydroconversion reactor (A) in which they are converted, producing a reaction effluent which is subsequently separated in a high pressure and high temperature separator (B) into a vapour phase (5) and a slurry phase (7).

(8) Preferably, the slurry-phase hydroconversion reactor is a bubble column. One or more hydroconversion reactors placed in parallel can be used; similarly, one or more high pressure and high temperature separators placed in parallel can be used.

(9) Preferably a part of the hydrogen-containing recycle gas (13) is supplied to the high pressure and high temperature separator.

(10) The separated vapour phase is subsequently supplied to a gas treatment section which has the function of separating a liquid fraction from the hydrogen-containing gas.

(11) The vapour treatment section operates at gradually decreasing pressure and temperature.

(12) Said section can comprise heat exchangers alternated with a washing column which uses VGO as a solvent, a high pressure and medium temperature separator, a high pressure and low temperature separator.

(13) From the vapour treatment section, naphtha, atmospheric gas oil (AGO), vacuum gas oil (VGO) and gaseous stream rich in hydrogen are recovered, which contains hydrocarbon gases having from 1 to 4 carbon atoms, and which is recycled to the hydroconversion section (4), except for a gaseous sample that can be supplied into the high pressure and high temperature separator (B).

(14) The slurry phase (7) is subsequently sent to a liquids separation section (D) which has the function of separating the Vacuum Gas Oil (VGO, 8) from a stream of heavy products which contain unconverted feed, metal sulphides, catalyst and solid formed during the hydroconversion reaction. Said liquids separation section can preferably comprise a series of decreasing pressure and temperature devices. In a first passage the slurry is supplied to a high temperature and low pressure separator which works as an accumulator; in a second passage the separated vapour phase is supplied into a pre-flash column, eventually the bottom stream is supplied to a stripper to separate the lights, and finally in a third passage the enriched stream exiting the stripper is supplied to a vacuum distillation column; alternatively, the stripper is not present and the bottom stream is supplied to a vacuum distillation column. From the vacuum column the Vacuum Gas Oil (VGO) fraction, the Light Vacuum Gas Oil (LVGO) fraction, the Heavy Vacuum Gas Oil (HVGO) fraction, the Wash Oil and the vacuum Residue are recovered. The Vacuum residue exits from the bottom of the vacuum column and is rich in asphaltenes, solids, metals and catalysts and forms a stream of heavy products.

(15) A part of the heavy products is recycled to the reaction section (12), while the remainder forms a purge stream (9).

(16) The purge is then heated at a temperature greater than or equal to 185° C. and not above 220° C., preferably between 200 and 220° C.

(17) Subsequently the purge is subjected to settling by lowering the temperature in a progressive and controlled manner up to the minimum temperature of 100° C., preferably comprised between 100° C. and 170° C., more preferably comprised between 100° C. and 160° C. The lowering of the temperature in a controlled manner can take place in different ways: by using an adequately sized and thermostated tank, for example a hot-oil thermostat, or by mixing the warm stream to be decanted, for example the heated purge, with a cold stream, for example the clarified component which can be at a temperature that varies from 200° C. to 80° C., considering the appropriate thermal balance of the system to calculate the flow rates thereof.

(18) The lowering of the temperature is of a value that varies from 3° C. per minute to 10° C. per minute, preferably from 5° C. per minute to 10° C. per minute, more preferably 10° C. per minute.

(19) During the static settling, the temperature must be such as to make the asphaltenes insoluble and at the same time make the clarified component movable allowing for its extraction.

(20) In the temperature range comprised between 100° C. and 160° C. the separation of the dense phase is optimal.

(21) During the settling phase the purge is not shaken. The settling forms a light phase, called clarified component, and a heavy phase, called cake, as a function of density.

(22) The clarified component is recycled to the slurry-phase hydroconversion section.

(23) The weight ratio between the clarified component and the fresh feed can vary in the range from 2% to 13%, preferably from 3% to 10% by weight.

(24) The time required for the formation of a heavy phase or cake can vary from preferably 15 minutes to 2 hours, more preferably it varies between 20 minutes and 1 hour. The settling rate is preferably comprised between 85 mm/hour and 300 mm/hour.

(25) The cake produced is “glassy” at room temperature with a softening point that can vary from 80° C. to 100° C. and penetration 2 dmm.

(26) The consistency of the cake is due to the presence of solids (THFi) in greater concentration than the other streams and the presence of asphaltenic compounds.

(27) The catalyst is generated “in situ” by an oil soluble Mo-containing precursor, supplied to the hydroconversion liquid-phase reactor directly with the feed. The normally used precursor is a solution of Mo-octoate (2-ethylhexanoate) in 2-ethylhexanoic acid, containing 15.5% by weight of Mo.

(28) The catalyst precursor is liquid and reacts with the sulphide coming from the feed and the hydrogen present in the reactor forming MoS.sub.2 (solid molybdenite finely dispersed in the liquid phase) in lamellas.

(29) The hydroconversion reactors can operate in a temperature range comprised between 420° C. to 440° C., at a pressure comprised between 155 atm and 160 atm. The high pressure and high temperature separators operate under the same operating conditions as the hydroconversion reactors, except for the load losses and the heat losses along the line that connects the reactors to the separators.

(30) Some application examples of the present disclosure are now described which have a purely descriptive and non-limiting purpose and which represent preferred embodiments.

EXAMPLES

(31) The following examples are the result of process calculations, wherein the hydroconversion process envisages the presence of a settler. The hydroconversion process is sized so as to provide the results of example 1. In all cases wherein the settler is present, the process conversion increases, as the flow rate to be sent to the battery limits decreases.

Comparative Example 1

(32) 160.2 t/h of vacuum column residue and 6.4 t/h of make-up hydrogen (which takes into account not only the effective consumption of hydrogen but also the losses in the various points of the plant) are supplied to a hydroconversion reactor at a temperature of 426.8° C. and at pressure of 160 bara; the catalyst used is molybdenum octoate, containing 15.5% of molybdenum; the catalyst flow rate was 190.4 kg/h.

(33) The process does not envisage the settling of the purge, which is therefore sent to the battery limits. Since there is no settling process, neither clarified component nor cake are produced. Therefore, the recycling of clarified component is not envisaged.

(34) The total conversion is calculated according to Equation 1:
Total conversion(% weight)=(100−% purge weight).
The results are reported in Table 1.

Example 1

(35) 160.2 t/h of vacuum residue are supplied to a hydroconversion reactor at a temperature of 426.8° C. and at pressure of 160 bara. The catalyst is always the same as in the comparative example 1 and its flow rate is 190.4 kg/h; also the hydrogen has the same flow rate as the comparative example 1 (6.4 t/h).

(36) In this case the separation process via static settling is applied to the purge stream. Therefore, the purge stream is totally sent to the settler which acts in such a manner that a clarified component stream and a cake stream are obtained. In this case the clarified component recycle is not considered, that is both the cake stream and the clarified component are sent to the battery limits. The settling process considers a yield of the cake from 35% to 40% and a yield of the clarified component from 60% to 65%.

(37) The total conversion is calculated according to Equation 2:
Total conversion(% weight)=(100−(% clarified component weight+% Cake weight)),

(38) both of them being considered as being sent to the battery limits.

(39) In this case the yields of the products in cuts (calculated as kg/h of each cut exiting from the plant divided by the fresh feed flow rate plus the catalyst flow rate) and the process conversion do not change with respect to the comparative example 1 being only a phase separation of the purge stream. The results are reported in Table 1.

Example 2

(40) Example 1 is repeated also adding the recycle of the clarified component.

(41) The clarified component stream is recycled at the inlet of the hydroconversion reactor, maintaining unchanged the operating temperature of 426.8° C. in addition to the sizing of the entire hydroconversion system. The reactor pressure is always 160 bara, the flow rate of the catalyst (the same as the comparative example 1, molybdenum octoate) is 197.6 kg/h and the hydrogen flow rate is 6.4 t/h.

(42) The clarified component stream reacts by increasing the yields of the products with a boiling point lower than 500° C. In addition to the operating temperature, the THFi variable is set in the purge stream, which ensures that the amount of purge to be treated to the settling unit raises, increasing the yield in Cake. In this example only the cake is exited at the battery limits being the clarified component completely recycled to the hydroconversion unit.

(43) The conversion of example 2, applying Equation 2, being inserted the static settling unit increases to 97.2%.

(44) The results are reported in Table 1.

(45) TABLE-US-00001 TABLE 1 comparison of different examples at constant process temperature and THFi in the purge, varies the capacity of the plant. Comparative Example Example 1 Example 2 Inserted no yes yes static settler Clarified no no yes component recycle T reaction, 426.8 426.8 426.8 ° C. Fresh feed, 160.2 160.2 148.6 t/h Solid, weight 8 8 8 Yields, % wt Consumption −2.4 −2.4 −2.6 H.sub.2 H.sub.2S 4.2 4.2 4.2 NH.sub.3 0.2 0.2 0.2 C1 1.8 1.8 2.0 C2 1.7 1.7 1.8 C3 1.8 1.8 2.0 C4 2.9 2.9 3.0 C5-170 9.4 9.4 9.9 170-350 30.1 30.1 31.1 350-450 29.8 29.8 31.3 450-500 10.6 10.6 11.0 500+ 3.3 3.3 3.3 Purge 6.8 0.0 0.0 Clarified 0.0 4.3 0.0 component Cake 0.0 2.5 2.8 Conversion, 93.2 93.2 97.2 % wt

(46) The hydrogen consumption is calculated as the ratio between the difference of the hydrogen kg/h in the products minus the hydrogen kg/h in the reactants divided by the sum of the flow rates of fresh feed and catalyst. The product yields in the cuts are calculated as kg/h of each cut exiting from the plant divided by the flow rate of fresh feed plus the flow rate of catalyst. The sum of the yields equals 100 plus the hydrogen consumption.

Example 3

(47) Starting from Example 2, the temperature of the hydroconversion reactor is varied from 426.8° C. to 428.6° C. The reactor pressure is always 160 bara. The purge stream exiting from the hydroconversion section is sent to the settling unit, there is a production of clarified component which is recycled to the hydroconversion section and cake which is sent to the battery limits.

(48) Table 2 shows Example 2 and compares it with Example 3 in which it is shown that by recycling the clarified component to the hydroconversion reactor the process conversion can be maintained by increasing the temperature from 426.8° C. to 428.6° C. restoring the capacity of the plant at that present in the comparative example 1 without having to re-size the entire plant. The hydrogen flow rate of this new case is 6.9 t/h, while the catalyst flow rate is 218.3 kg/h.

(49) TABLE-US-00002 TABLE 2 Comparison of different cases with constant plant capacity and THFi in the purge, varying process temperature. Example 2 Example 3 Inserted static yes yes settler Clarified component yes yes recycle T reaction, ° C. 426.8 428.6 Fresh feed, t/h 148.6 160.2 Solid, % wt 8 8 Yields, % wt Consumption H2 −2.6 −2.6 H.sub.2S 4.2 4.2 NH.sub.3 0.2 0.2 C1 2.0 2.0 C2 1.8 1.8 C3 2.0 2.0 C4 3.0 3.0 C5-170 9.9 9.9 170-350 31.1 31.3 350-450 31.3 31.3 450-500 11.0 10.9 500+ 3.3 3.2 Purge EST 0.0 0.0 Clarified component 0.0 0.0 Cake 2.8 2.8 Conversion, % wt 97.2 97.2

Example 4

(50) Example 3 is taken again for this example. The feed to the plant is maintained constant and equal to 160.2 t/h and the THFi concentration in the purge is reduced starting from the conditions of Example 3 (8%), up to a value of 4%. Reducing the amount of THFi present in the purge means, operationally, increasing the amount of purge exiting from the plant, extracting a larger amount from the hydroconversion unit. The reactor pressure is always 160 bara, the reactor temperature is 426.6° C., the catalyst flow rate is 410.1 kg/h, while the hydrogen flow rate is 6.5 t/h.

Example 5

(51) Example 3 is taken again for this example. The feed to the plant is maintained constant and equal to 160.2 t/h and the THFi concentration in the recycle is increased starting from the conditions of Example 3 (8%), up to a value of 12%. Increasing the amount of THFi present in the purge means, operationally, decreasing the amount of purge exiting from the plant, leaving a larger amount of THFi inside the hydroconversion plant. The reactor pressure is always 160 bara, the reactor temperature is 429.8° C., the catalyst flow rate is 150.1 kg/h, while the hydrogen flow rate is 7.1 t/h.

(52) Table 3 shows the examples 3, 4 and 5 where the plant capacity is maintained fixed, the THFi content in the recycle is changed, that is the amount of purge sent to the static settling unit. This implies a change in the amount of recyclable clarified component. Even in these conditions, process conversions are still higher than the comparative example.

(53) TABLE-US-00003 TABLE 3 Comparison of different examples with constant plant capacity, varying process temperature and THFi concentration in the purge. Example 3 Example 4 Example 5 Static settler yes yes yes Clarified yes yes yes component recycle T reaction, ° C. 428.6 426.6 429.8 Fresh feed, t/h 160.2 160.2 160.2 Solid, % wt 8 4 12 Yields, % wt Consumption H.sub.2 −2.6 −2.5 −2.7 H.sub.2S 4.2 4.2 4.3 NH.sub.3 0.2 0.2 0.2 C1 2.0 1.8 2.0 C2 1.8 1.7 1.9 C3 2.0 1.9 2.0 C4 3.0 2.9 3.0 C5-170 9.9 9.6 10.1 170-350 31.3 30.5 31.7 350-450 31.3 30.2 31.9 450-500 10.9 11.1 10.6 500+ 3.2 3.6 2.9 Purge EST 0.0 0 0.0 Clarified 0.0 0 0.0 component Cake 2.8 4.8 2.1 Conversion, % wt 97.2 95.2 97.9

(54) The examples cover therefore different cases, wherein an increase in process conversion from 93% to 98% with respect to the comparative one is demonstrated; by introducing the static settling unit downstream of the hydroconversion process to treat the entire purge stream and by recycling the entire clarified component stream to the hydroconversion reactor in % between 3-10% wt (clarified component/fresh feed, %).

(55) The illustrated examples show the great advantage obtainable with the present disclosure, which is that of reducing the stream to be sent to the battery limits, obtaining a product by static settling of the purge, which is convertible, recycling it to the hydroconversion section. By applying the settling technology to the purge stream of the hydroconversion section, the potential of the plant is not affected by the introduction of the static settler (see comparison between comparative example 1 and example 1). If, on the other hand, it is chosen to recycle the clarified component stream, the conversion also increases as only the Cake is sent to the battery limits, but at the cost of a reduction in potential (see comparison between examples 1 and 2). The potential can be easily recovered by acting on the operating conditions of the reactor, slightly increasing the temperature (comparison of examples 2 and 3). Finally, with the same plant potential, using different THFi concentrations in the recycle, or by varying the amount of purge sent to the settler and therefore the amount of recycled clarified component to the hydroconversion section, conversions are always greater than in the comparative case.