JP4785250B2 - Production of low sulfur / low aromatic distillate - Google Patents

Description

[0001]
Disclosure background
Field of the Invention The present invention relates to a process for hydrotreating a hydrogenated liquid distillate stream to produce a stream with significantly less sulfur as well as aromatics. The hydrogenated distillate stream is further hydrogenated in an equal flow reaction zone, where the reaction product is sent to a separation drum where the vapor product is collected overhead and the liquid product is combined with a hydroprocessing gas stream. Sent to counter-flowing aromatic saturation.
[0002]
Background of the invention Due to environmental and regulatory initiatives, increasingly lower levels are required for both sulfur and aromatics in distillate fuel oils. For example, the proposed sulfur level for distillate fuels launched in the European Union is less than 50 wppm in 2005. There are also regulations that require lower levels of total aromatics in hydrocarbons, more specifically polycyclic aromatics found in distillate fuel oils and heavy hydrocarbon products. In addition, U.I. S. For all road diesels, CARB reference diesels, and Swedish Class I diesels, the maximum permissible aromatic levels are 35, 10 and 5 vol%, respectively. In addition, for CARB and Swedish Class I diesel fuel oils, polycyclic aromatics of less than 1.4 and 0.02 vol%, respectively, are permitted.
[0003]
Much research is currently underway on hydroprocessing due to the stronger demand to remove heteroatoms, most notably sulfur, from transportation and heating fuel oil streams. Hydrodesulfurization in the case of hydrogenation or sulfur removal is well known and usually requires treating a petroleum stream with hydrogen under hydrogenation conditions in the presence of a supported catalyst. The catalyst typically comprises a Group VI metal supported on a refractory support along with one or more Group VIII metal promoters. Hydrocatalysts are particularly suitable for hydrodesulfurization and hydrodenitrogenation, where generally molybdenum or tungsten on alumina is supported with a metal such as cobalt, nickel, iron, or combinations thereof. Touched and included. Cobalt-assisted alumina-supported molybdenum and nickel-supported alumina-supported molybdenum catalysts are most widely used when the limiting specification is hydrodesulfurization, while nickel-supported alumina-supported molybdenum catalysts are Most widely used for hydrodenitrogenation and partial aromatic saturation.
[0004]
Much work has been done to develop more active catalysts and improved reactor designs to meet the demand for more effective hydroprocessing processes. Various improved instrument configurations have been proposed. One of these forms is a counter-current design, in which the feedstock flows down through a continuous catalyst bed in counter-current with a rising process gas (typically a hydrogen-containing process gas). The catalyst bed downstream of the feed stream will contain a high performance or otherwise more sulfur sensitive catalyst. This is because the process gas that flows up carries away heteroatom components such as H ₂ S and NH _{3 that} are detrimental to sulfur and nitrogen sensitive catalysts. Although these countercurrent reactors have commercial potential, they are nevertheless prone to flooding. That is, the processing gas and the gas product that flow up impede the flow of the raw material that flows down. These flooding trends increase with increasing process gas velocity.
[0005]
Other process configurations include using multiple reaction stages in either a single reactor or separate reactors. Catalysts that are more sulfur sensitive will be used in the downstream stage as the level of heteroatom components is progressively lower. European Patent Application No. 93200165.4 teaches a two-stage hydrogenation process carried out in a single reactor. However, there is no suggestion of a unique stripping arrangement for the liquid reaction stream from each reaction stage.
[0006]
Two types of process schemes are generally employed to achieve substantial hydrodesulfurization (HDS) / aromatic saturation (ASAT) of distillate fuel oil. Both are operated under relatively high pressure. One is a one-stage process operated at a pressure of over 800 psig using a Ni / Mo or Ni / W sulfide catalyst. It is sought to achieve high saturation pressure levels above 2,000 psig. The other is a two-stage process. In this case, the feed is first treated under moderate pressure on a Co / Mo, Ni / Mo or Ni / W sulfide catalyst to reduce the heteroatom level, while little aromatic saturation is observed. After the first stage, the product is stripped to remove H ₂ S, NH ₃ and light hydrocarbons. The first stage product is then reacted under high pressure over a Group VIII metal hydrogenation catalyst to achieve aromatic saturation. The two stage process is typically operated between 600 and 1,500 psig.
[0007]
In light of the above, there is a need for an improved desulfurization / aromatic saturation process in order to meet the increasingly stringent environmental regulations for processing feed streams.
[0008]
SUMMARY OF THE INVENTION The present invention provides a two-stage process for hydrotreating a hydrogenated distillate feedstock. The process includes
(A) The raw material is reacted in a first reaction stage in the presence of a hydrogen-containing process gas cascaded or partially cascaded from the second stage, wherein the first reaction stage is hydrodesulfurized. Including one or more reaction zones operated at conditions, each reaction zone comprising a hydrogenation catalyst bed;
(B) sending the resulting reactant to a separation zone where a gas phase stream and a liquid phase stream are produced;
(C) collecting the vapor stream in overhead;
(D) sending the liquid phase stream to a second reaction stage in the presence of a hydrogen-containing process gas, the reaction stage including one or more reaction zones operated at aromatic saturation conditions, and each reaction zone Including a saturated aromatic catalyst bed, wherein the hydrogen-containing process gas is routed through the reaction stage countercurrently to the liquid phase stream;
Is included.
[0009]
In a preferred embodiment of the present invention, the liquid phase stream is stripped of dissolved gas in contact with the vapor before being sent through the second reaction stage.
[0010]
DETAILED DESCRIPTION OF THE INVENTION A feedstock suitable for being processed according to the present invention is a petroleum based feedstock having a boiling point above the distillate range and is pre-hydrogenated to sulfur. And nitrogen levels are reduced. Typical sulfur levels in these hydrogenated distillates are in the range of less than about 3,000 wppm, more preferably to less than about 1,000 wppm, most preferably to less than about 500 wppm, ideally Up to about 350 wppm. Non-limiting examples of these feedstocks include diesel fuel oil, jet fuel oil, heating oil, and lubricating oil. These feedstocks typically have a boiling range of about 150 to about 600 ° C, preferably about 175 to about 400 ° C. It is highly desirable for refiners to improve the quality of these types of feedstock by removing as much sulfur as possible, as well as aromatic saturation.
[0011]
The process of the present invention will be better understood by describing the preferred embodiment shown in FIG. 1 herein. The present invention presents an advance over the prior art by simply using a once-through hydroprocessing gas. For discussion purposes, the first reaction stage R1 is a hydrogenation stage to further reduce sulfur and nitrogen levels, and the second reaction stage R2 is an aromatic saturation stage. The hydrogen reacts with impurities to convert them to H ₂ S, NH ₃ , and water vapor, which are removed as part of the vapor effluent. And hydrogen also saturates olefins and aromatics. Various reactor interiors, valves, pumps, thermocouples, heat transfer devices, etc. are not shown for simplicity. FIG. 1 shows a reaction vessel R1 including reaction zones 10a and 10b, although only one or more reaction zones can be used. Each is composed of a hydrogenation catalyst bed. The catalyst is preferably in the reactor as a fixed bed, although other types of catalyst arrangements such as slurry or ebullated bed can be used. Downstream of each reaction zone is a non-reaction zone 12a and 12b. The non-reacting zone is typically free of catalyst. That is, it will be the hollow part of the tank with respect to the catalyst. Although not shown, a liquid distribution means will also be provided upstream of each reaction stage. The type of liquid dispensing means is believed not to limit the practice of the present invention. However, the tray arrangement is preferably a sieve tray, a bubble cap tray, or a tray having spray nozzles, chimneys, tubes, etc., and a vapor-liquid mixing device (not shown) is used for quenching fluid (not shown) for controlling the temperature ( (Liquid or vapor) would be used in the non-reacting zone 12a.
[0012]
The raw material stream is supplied to the reaction vessel R <b> 1 through the line 10 together with the hydrogen-containing processing gas through the line 12. A hydrogen-containing process gas is cascaded from reaction stage R2. Also, a make-up hydrogen-containing process gas will be added via line 14. The introduction ratio of the processing gas is preferably 3 times or less, more preferably less than about 2 times, and most preferably less than about 1.5 times the chemical hydrogen consumption in both stages of the reaction. The feed stream and the hydrogen-containing process gas are sent in equal flow through one or more reaction zones of the reaction vessel R1. Reactor R1 represents the first reaction stage, where the feed stream is further hydrogenated to remove substantially all heteroatoms from the feed stream. The first reaction stage contains Co—Mo or Ni—Mo supported on a refractory supported catalyst, and the downstream reaction stage contains Ni—Mo supported on a refractory supported catalyst.
[0013]
The term “hydrogenation” as used herein refers to a process in which a hydrogen-containing process gas is used in the presence of a suitable catalyst. In so doing, the catalyst is primarily active in removing heteroatoms such as sulfur and nitrogen and in hydrogenating some aromatics. Suitable hydrogenation catalysts for use in the present invention are any conventional hydrogenation catalyst, including at least one Group VIII metal (preferably Fe, Co and Ni, more preferably Co and / or). Ni, most preferably Co), and at least one Group VI metal (preferably Mo and W, more preferably Mo) on a high surface area support material (preferably alumina). . Other suitable hydrogenation catalyst supports include zeolites, amorphous silica-alumina, and titania-alumina. A noble metal catalyst will also preferably be used when the noble metal is selected from Pd and Pt. It is within the scope of the present invention to use more than one type of hydrogenation catalyst in the same reactor. The VIII foot metal is typically present in an amount in the range of about 2-20 wt%, preferably about 4-12%. The Group VI metal will typically be present in an amount ranging from about 5 to 50 wt%, preferably from about 10 to 40 wt%, more preferably from about 20 to 30 wt%. All metal wt% is "to support". “To carrier” means that% is based on the weight of the carrier. For example, if the support weighs 100 g, 20 wt% Group VIII metal will mean that 20 g of the Group VIII metal is on the support. Typical hydrogenation temperatures range from about 100 ° C. to about 400 ° C. with a pressure of about 50 psig to about 3,000 psig, preferably about 50 psig to about 2,500 psig.
[0014]
The combined liquid and gas phase product streams exit reaction vessel R1 via line 16 and enter separation zone S. Thus, the liquid phase product stream is separated from the gas phase product stream. The liquid phase product stream will typically have a boiling component in the range of about 150 ° C. to about 650 ° C., but will not have a higher boiling range than the feed stream. The gas phase product stream is collected overhead via line 20.
[0015]
The liquid reaction product from the separation zone S is sent to the reaction vessel R2 via the line 20, and is sent downward through the reaction zones 22a and 22b of the reaction stage R2. Prior to being sent down through reaction stage R2, the liquid reaction product stream will first be contacted in the stripping zone to remove the associated vapor component from the liquid stream. For example, as the liquid product stream flows through the stripping zone, it causes the hydroprocessing gas to flow under conditions effective to transfer at least a portion of the source impurities in the vapor into the liquid. Contacted by. Contact means include any known vapor-liquid contact means. That is, Raschig rings, beryl saddles, wire meshes, ribbons, open honeycombs, and gas-liquid contact trays such as bubble cap trays and other devices.
[0016]
New hydrogen-containing process gas is introduced into reaction stage R2 via line 24 and sent in an upward direction countercurrent to the liquid reaction product stream. By introducing a clean process gas (a gas substantially free of H ₂ S and NH ₃ ) into the reaction stage R 2, the reaction stage R 2 has an effect of suppressing the activity of the catalyst affected by H ₂ S and NH _3. Is reduced, and the H ₂ partial pressure is increased, but the operation is more efficient. This type of two-stage operation is particularly attractive for the very high removal of sulfur and nitrogen or when more sensitive catalysts (eg hydrocracking, aromatic saturation, etc.) are used in the second reactor. Is. Another advantage of the present invention is that the process gas fraction is relatively low compared to many conventional processes. The use of a relatively low processing gas ratio is mainly due to the use of a distillate feedstock that has been previously hydrogenated. Additional efficiencies are obtained by not requiring process gas recirculation.
[0017]
The liquid / vapor separation means (S) will be a simple flush or will include adding stripping steam or gas to improve the removal of H ₂ S and NH ₃ . The liquid stream and process gas are sent counter-current to each other and through one or more catalyst beds, or reaction zones 22a and 22b. The resulting liquid product stream exits reaction stage R2 via line 26, and the hydrogen-containing vapor product stream exits reaction stage R2 and is cascaded to reaction stage R1. Further, the reaction stage R2 includes non-reaction zones 23a and 23b following each reaction zone. The catalyst in this second reaction stage is an aromatic saturated catalyst.
[0018]
The drawing also shows several options. For example, lines 30 and 32 will carry kerosene that will be used as a quench fluid. Unsaturated feedstock will also be introduced into the first reaction stage via line 28. The degree of unsaturation will be up to about 50 wt%.
[0019]
The reaction stage used in the practice of the present invention is operated at a temperature and pressure appropriate for the desired reaction. For example, typical hydroprocessing temperatures will range from about 40 ° C. to about 450 ° C. at a pressure of about 50 psig to about 3,000 psig, preferably 50 to 2,500 psig.
[0020]
For purposes of hydroprocessing, and in the context of the present invention, the terms “hydrogen” and “hydrogen-containing process gas” are synonymous and will be either pure hydrogen or a hydrogen-containing process gas. A hydrogen-containing process gas is at least a sufficient amount of hydrogen for the intended reaction and in addition to this any other gas (eg nitrogen) that will not inhibit or adversely affect either the reaction or the product. , And light hydrocarbons such as methane). Impurities such as H ₂ S and NH ₃ are undesirable, but if present in significant amounts, they will normally be removed from the process gas before being fed into the reactor. The process gas stream introduced into the reaction stage will preferably contain at least about 50 vol%, more preferably at least about 75 vol% hydrogen, and most preferably at least 95 vol%. In an operation where unreacted hydrogen in any particular stage steam effluent is used for any stage hydroprocessing, there is sufficient hydrogen in the new process gas introduced into that stage, The thing must contain enough hydrogen for the next stage. In practicing the invention, it is preferred that all or a portion of the hydrogen required for the first stage hydrogen treatment is contained in the second stage steam effluent fed into the first stage. The first stage vapor effluent will be cold condensed and hydrogenated, relatively clean heavy (eg C ₄ -C ₅₊ ) hydrocarbons will be recovered.
[0021]
Non-limiting examples of aromatic hydrogenation catalysts include nickel, cobalt-molybdenum, nickel-molybdenum, and nickel-tungsten. A noble metal-containing catalyst may also be used. Non-limiting examples of noble metal catalysts include those based on platinum and / or palladium. It is preferably supported on a suitable support material, typically refractory oxide materials such as alumina, silica, alumina-silica, kieselguhr, diatomaceous earth, magnesia, and zirconia. A zeolite carrier may also be used. These catalysts are typically susceptible to inhibition or poisoning by sulfur and nitrogen. The aromatic saturation stage preferably has a temperature of about 40 ° C. to about 400 ° C., more preferably about 200 ° C. to about 350 ° C., a pressure of about 100 psig to about 3,000 psig, preferably about 200 psig to about 1,200 psig, and It is operated at a liquid space velocity (LHSV) of about 0.3 V / V / Hr to about 10 V / V / Hr, preferably about 1 to 5 V / V / Hr.
[0022]
The liquid phase of the reaction vessel used in the present invention will typically consist primarily of high boiling components of the raw material. The gas phase is typically a mixture of hydrogen-containing process gases, heteroatom impurities such as H ₂ S and NH ₃ , and vaporized low-boiling components in the new feed as well as light products of the hydroprocessing reaction. Let's go. If the gas phase effluent requires further hydroprocessing, it will be sent to a gas phase reaction stage containing another hydroprocessing catalyst and subjected to hydroprocessing conditions suitable for further reaction. . Alternatively, hydrocarbons in the gas phase product will be condensed, if desired, by cooling the vapor, and the resulting condensed liquid will be recycled to either reaction stage. It is also within the scope of the present invention that the feedstock that already contains suitably low levels of heteroatoms is fed directly into the reaction stage for aromatic saturation and / or decomposition.
[0023]
The invention will be better understood with reference to the following examples. The examples are for illustrative purposes only and are not to be construed as limiting the invention in any way.
[Brief description of the drawings]
FIG. 1 shows a multi-reactor of the present invention, wherein the liquid phase product is separated from the gas phase product and the liquid phase product stream is further processed in an aromatic saturation stage. is there.

Claims (9)

A method of hydrotreating hydrogenated distillate feedstock in a two-stage process,
(A) a step of reacting the hydrogenated distillate feedstock in the first reaction stage in the presence of a once-through hydrogen-containing process gas cascaded from the second reaction stage [where the first The reaction stage comprises one or more reaction zones operated at hydrodesulfurization conditions, each reaction zone comprising a hydrogenation catalyst bed and containing a once-through hydrogen containing cascade from the second reaction stage. The process gas contains all of the vapor effluent from the second reaction stage. ],
(B) A step of sending the obtained reactant to a separation zone [however, a gas phase stream and a liquid phase stream are produced. ],
(C) collecting the gas phase stream overhead;
(D) introducing a new hydrogen-containing process gas into the second reaction stage; and (e) the liquid phase stream in the presence of the new hydrogen-containing process gas from step (d) above. [Wherein said second reaction stage comprises one or more reaction zones operated at aromatic saturation conditions, each reaction zone comprising an aromatic saturated catalyst bed; And the novel hydrogen-containing process gas is sent through the reaction stage countercurrently to the liquid phase flow. ]
Including, and
The liquid phase stream is stripped by contacting the liquid with a stripping gas before being sent through the second reaction stage to reduce the content of dissolved gas phase products. Feature method.   The method of claim 1, wherein the stripping gas is a gas phase product from the second reaction stage.   3. The method of claim 2, wherein the stripping gas and liquid are contacted in a vapor / liquid contact zone that is vertically disposed above the second reaction zone.   4. A method according to claim 3, wherein the vapor / liquid contact zone is operated in countercurrent and the vapor countercurrents with the falling liquid phase flow.   The gas phase stream from the first reaction stage is cooled, the resulting condensed liquid stream is separated from the remaining non-condensed stream, and a portion of the condensed liquid stream is combined with the liquid feed to the second reaction stage. The method according to claim 1, wherein:   The gas phase stream from the first reaction stage is cooled, the resulting condensed liquid stream is separated from the remaining non-condensed stream, and a portion of the condensed liquid stream is more than one in the first or second reaction stage. The method according to claim 3, wherein the method is used as a quench liquid between the reaction zones.   The method of claim 3, wherein the first reaction stage is positioned vertically above the vapor / liquid contact area.   8. The method of claim 7, wherein a liquid feedstock flows down through the one or more reaction zones countercurrently with the hydrogen-containing process gas.   The method of claim 1, wherein the hydrogen-containing process gas is cascaded from a vapor / liquid contact zone disposed vertically above the second reaction zone.

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