JP2001207178A - Method for reducing the content of sulfur compounds and polycyclic aromatic hydrocarbons in distillate fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low-sulfur distillate fuel having a low polycyclic aromatic hydrocarbon content and thereby improve specific gravity and cetane number characteristics, by using a hydrogenation reactor and an after-treatment reaction To avoid phase separation and hydrogenation with the vessel. The problem is solved by cooling the effluent leaving the hydrogenation reactor and passing the cooled product through a small aftertreatment reactor containing a suitable catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to distillate fuel improvement. In particular, the invention relates to a method for reducing the concentration of sulfur and polycyclic aromatic compounds in the fuel.

[0002]

BACKGROUND OF THE INVENTION Many countries have strict regulations on the sulfur content of diesel fuel in their manufacturing processes. Current legislation specifies, for example, the highest sulfur content in diesel fuel in the European Union from 50 wppm from 2005 and 15 wp in California from 2004
pm. Current regulations for low sulfur diesel fuels often also include limits on maximum polycyclic aromatic hydrocarbon content, maximum density (or specific gravity) and minimum cetane number. It is anticipated that regulations on all three properties will be tightened in the near future to meet the demand for reducing emissions from diesel engines.

[0003] Sulfur can be removed by hydrogenation.
Diesel fuel is passed over a suitable catalyst under pressurized hydrogen and elevated temperatures. Typical conditions are hydrogen pressure of 15-70 bar; average reactor temperature of 300-400 ° C .;
Liquid space velocity (LHS) at 0 m ³ (oil) / m ³ (catalyst) / hour
V). The exact conditions will depend on the type of feed, the degree of desulfurization required, and the desired run length. The reactor temperature (at start-up) with fresh catalyst is generally at the lower end of the above range, and when the catalyst is deactivated, the reactor temperature is increased to offset the loss of catalyst activity. Operation generally ends when a temperature set for the reactor is reached, determined by the metal material of the reactor.
The lower the starting temperature, the higher the final temperature of the operation, and the longer the run length of the catalyst at a constant catalyst deactivation rate. Run length is a very important point for refinery. Shorter run lengths result in higher costs due to faster catalyst replacement rates and relatively long downtime for catalyst replacement (ie, flow down time) resulting in reduced revenue due to reduced diesel fuel production. Means that

[0004] Hydrogenation units are generally based on the required charge of feed and the defined reactor (catalyst) capacity based on the L
It is designed to set HSV. Low sulfur products are LH
It can be obtained by lowering the SV (eg by adding catalyst capacity). Starting with a feedstock containing 1% sulfur as an example, producing a diesel fuel with a sulfur content of 500 wppm to produce a diesel fuel with a sulfur content of 50 wppm at the same reactor temperature and hydrogen pressure Generally 3-4 than when
Twice as many catalysts are required. In some cases, LHSV
The start-up temperature may be increased to obtain a lower sulfur content product without changing In the above example, the start-up temperature would generally need to be increased by 35-45 ° C. to reduce the sulfur content from 500 wppm to 50 wppm. Firstly, the additional reactor volume entails a substantial investment and, secondly, the run length is significantly reduced. In many cases, equipment designed to meet more stringent sulfur regulations will use both possibilities. For example, increase the catalyst volume by a factor of 2-3 (LHSV decreases by a factor of 2-3) and raise the starting temperature by 10-20 ° C.
Will increase. By doing so, the same run length will be achieved. This is because the rate of deactivation is slower at lower LHSVs and this offsets a smaller temperature span between start-up and end of run.

[0005] Run length is further limited when diesel regulations require reducing polycyclic aromatic hydrocarbon content besides reducing sulfur. Polycyclic aromatic hydrocarbons (PAHs) are defined as fused polycyclic aromatic compounds having two or more aromatic rings. The concentration of PAH can be measured by the standard analysis method IP391-95. PAH compounds react readily under hydrogenation conditions. The tricyclic aromatic compound is hydrogenated to a bicyclic aromatic compound, and the bicyclic aromatic compound is hydrogenated to a monocyclic aromatic hydrocarbon. Monocyclic aromatic compounds react slowly under common hydrogenation conditions to produce naphthenes. This reaction is reversible and at high reaction temperatures and low hydrogen pressures the conversion of PAH compounds is thermodynamically limited by equilibrium. As a result, the conversion of PAH compounds in the hydrogenation unit producing low sulfur diesel fuel increases only when the reaction temperature increases, and decreases when the temperature is further increased to suppress equilibrium at high temperatures. This can have a negative effect on run length as detailed in the examples below:
Designed to produce a diesel fuel with a starting temperature of 0 ° C. and a content of 50 wppm. This reactor has 400
It is designed to be operable up to the catalyst average temperature of ℃ (50
Run length is 2 years (based on temperature span of ° C). The PAH content of the feed is 10% by weight and the product produced at start-up contains 2% by weight of PAH. Assume that the new regulations for diesel fuel regulate PAH content by up to 3% by weight. This assumption is achievable at start-up, but the conditions used in the equipment exceed this 3% limit at temperatures above 365 ° C.
This reduces the temperature between the start of operation and the end of operation by one.
Means to reduce to 5 ° C., reducing run length to about 1/3. This is clearly unacceptable and requires a significant investment in extra reactor volumes or construction of new equipment under high hydrogen pressure to maintain run length.

The temperature at which PAH equilibrium is met depends on many factors, including hydrogen pressure, feed PAH content and composition, LHSV and product requirements. Increasing the pressure or reducing the LHSV in this way makes it possible to extend the run length, but both of these measures require significant investment.

Wakee et al. (European Patent Application Publication (A)
1) No. 699,733) describes sulfur in distillate petroleum
Compounds and aromatic compounds,
Converted to hydrogen sulfide, which is toxic to stream catalysts
Of hydrogenation by a method using a hydrogenation apparatus
I have. The effluent is sent to a separator to remove gaseous phase and water
Element is added to the separated effluent. Separation and hydrogenation
Is a liquid hydrocarbon / H _TwoThe gas mixture is subjected to a second post-treatment
Repeat at least once before introducing into the reactor. Second anti
The reactor is a precious metal that is effective in reducing the concentration of aromatic compounds.
Contains metal catalyst. This means that the two reactors
Alternatively, at least two separators and at least two degrees
It means that hydrogenation is necessary.

[0008]

The general object of the present invention is to produce low sulfur distillate fuels with low polycyclic aromatic hydrocarbon content and thereby improve specific gravity and cetane number characteristics. , Avoid phase separation and hydrogenation between the hydrogenation reactor and the aftertreatment reactor.

[0009]

SUMMARY OF THE INVENTION The present invention is a process for obtaining a low PAH content distillate stream with little additional investment in reactor volume and without reducing run-range. The essence of the process according to the invention consists in cooling the effluent leaving the hydrogenation reactor and passing the cooled product through a small aftertreatment reactor containing a suitable catalyst. The PAH content of the product present in the hydrogenation reactor is reduced in the aftertreatment reactor due to the relatively low temperatures favoring equilibrium conditions. As a result, the final operating temperature in the main reactor of the hydrogenation is not limited by the PAH content of the product exiting the main reactor, and for a given run length, a small total reactor volume (hydrogen (Reactor + post-treatment reactor). In another embodiment of the process, instead of using a work-up reactor, the final catalyst bed of the hydrogenation main reactor is operated at a relatively low temperature. This method can be used to lower the specific gravity and increase the cetane number of diesel fuel. P
The specific gravity of the AH compound is generally higher than the corresponding monocyclic aromatic compound, and the lower the PAH content of the product, the lower the specific gravity of the product. Similarly, the cetane number and cetane index of PAH compounds are lower than the corresponding monocyclic aromatic compounds,
Decreasing the H content increases the cetane number and cetane index.

The petroleum distillate used in the present invention is from 120 to
Boiling in the range of 450 ° C, PA in the range of 5 to 50% by weight
H content. Examples of distillate include straight distillate from atmospheric crude distillation, light distillate from vacuum crude distillation, distillate obtained by fractionation of product from liquid catalytic reformer, and cooking. There are distillates obtained from the fractionation of oil from the included thermal reforming process, and mixtures thereof. The process is particularly suitable for mixtures of distillates containing pyrolyzed oil and catalytic reforming distillates. This is because these oils generally have a high PAH content.

The layout of the method will be specifically described with reference to FIG. The feed is mixed with hydrogen, heated in a furnace (1) and passed through a hydrogenation reactor (2). The conditions used in the hydrogenation reactor are the same as those usually used for deep desulphurisation of distillates. Typical hydrogen pressure = 15-70 bar; typical reactor average temperature = 30
0 to 400 ° C .; general LHSV = 0.5 to 3.0 m ³
(Oil) / m ³ (catalyst) / hour and a general ratio of hydrogen gas to oil = 100 to 1000 Nm ³ / m ³ . The distillate from the hydrotreater is cooled before passing through the work-up reactor (4) by heat exchange with the feed to the hydrotreater or by other means (3). The temperatures used in the work-up reactor are generally in the range from 250 to 350 ° C. and are generally at least 50 ° C. lower than the outlet temperature of the hydrotreater. LHSV There is generally about 2 to 20 m ³ (oil) / m ³ (catalyst) / range when and total pressure at the post-processing reactor is on the same level as that in the hydrogenation reactor.

The catalyst used in the hydrogenation reactor is any conventionally known catalyst used for hydrogenation distillate streams. This catalyst is obtained by supporting at least one kind of metal on a porous heat-resistant inorganic oxide carrier. Examples of metals having hydrogenation activity include Group VI-B and / or VIII metals, such as metals from the group consisting of Co, Mo, Ni, W, Fe, Co-Mo, Ni-Mo and Ni. -W
Are preferred. These metals are used as oxides or sulfides. Examples of porous materials suitable as carriers include alumina, silica-alumina, alumina-titania, natural and synthetic molecular sieves and mixtures thereof, with alumina and silica-alumina being particularly advantageous.

The catalyst used in the aftertreatment reactor is any catalyst used for the hydrodistillate stream. Preferred catalysts are Ni-Mo, Co-Mo and Ni-W supported on alumina.

During operation, the catalyst was sulphided.
d) It must be present at the conditions and it is not necessary to remove H ₂ S from the effluent by phase separation between the two reactors.

The active metals on the catalyst are either presulfurized by conventional means before use or are sulfided in situ by sulfur compounds in the effluent introduced into the aftertreatment reactor.

[0016] The hydrogenation reactor zone is comprised of one or more reactors. Each reactor has one or more catalyst beds. The function of the hydrogenation reactor is primarily to reduce product sulfur. The outlet temperature is generally higher than the inlet temperature due to the exothermic nature of the desulfurization reaction. Some reduction in PAH can be achieved in the hydrogenation reactor, especially at start-up conditions.
As the catalytic activity falls off, deactivated by carbonaceous deposits, sintering of the active phase and other mechanisms, the inlet temperature of the hydrogenation reactor is increased, resulting in an increased outlet temperature. This increases the PAH content in the effluent of the hydrogenation reactor at some point due to equilibrium limits. The temperature at which this occurs depends on the amount and type of aromatics in the oil and the hydrogen partial pressure in the unit.

The function of the aftertreatment reactor is primarily to reduce the PAH content. The relatively low temperature in the aftertreatment reactor ensures more favorable conditions for thermodynamic equilibrium between the PAH compound and the monocyclic aromatic compound. Reduction of PAH lowers the specific gravity of the product oil and increases the cetane number. Both of these are desirable.

A slight reduction in the sulfur content is achieved at the conditions in the aftertreatment reactor.

The present invention is illustrated by the following examples of specific embodiments.

[0020]

EXAMPLES Example 1 (Comparative) Feedstock A (Table 1) is hydrogenated in a semi-adiabatic pilot-plant apparatus operating at an outlet temperature of 390 ° C. This temperature is generally considered an end-of-life (EOR) condition. The pressure is 30 bar. Pure hydrogen is used as gas. Feed A is 50% cycle oil and 50%
With straight run gas oil (SRGO).

[0021] The properties of the product are shown in Table 2.

[0022] This product contains 20.6% by weight of PAH.
This is because the feedstock is 50% circulating oil and 50% SRGO
In a device where the hydrogen partial pressure at the inlet is 30 bar (not taking into account the evaporating diesel)
Common for products obtained under OR conditions.

[0023]Example 2 (Example):Low product A from Example 1
Further hydrogenation with various LHSV at warm. Pressure is product A
Is 30 bar, corresponding to the pressure obtained. Product A
Is obtained in the first hydrotreater, the gas phase
Some amount of H_TwoContains S. This H _TwoAmount of S
Is the amount of sulfur in the feed, gas / oil ratio and degree of desulfurization
Is a function of Product A and the gas in equilibrium with it
As occurs in the first hydrogenation (Example 1), H _TwoS (and others
H) present in the gas phase which is not removed in the internal stage
_TwoIn order to simulate the amount of S,
Contains a small amount of yellow component. Ni-Mo supported on alumina
The used catalyst is used in this test. Table 3 shows the results.

[0024] Although there is virtually no further sulfur removal in this low temperature hydrogenation, it is clear that large amounts of PAH can be removed with relatively high LHSV. From the above example, about 3 at the exit
It can be seen that PAH is optimally removed at 00-330 ° C. and 30 bar hydrogen partial pressure (evaporated diesel oil is not taken into account).

Example 3 (Example) The product A from Example 1 is further hydrogenated at a higher pressure than in Example 2. T = 300 ° C., P =
At an inlet hydrogen partial pressure of 45 bar (evaporated diesel oil is not taken into account) and LHSV = 2h ^-1 remove 2.9% by weight of bicyclic aromatics and 1.8% by weight of tricyclic aromatics Compound. The specific gravity (SG 60/60) is 0.8638. It can be seen that a high hydrogen partial pressure increases the saturation of the polycyclic aromatic compound. When the product A and gas in equilibrium therewith are produced in the first hydrogenation (Example 1), the H ₂ S (and other gases) present in the gas phase, which is not removed in the internal stage, To simulate the amount of ₂ S, a small amount of a sulfur component is again mixed into the product A. A catalyst comprising Ni-Mo on alumina is used in this test. There is virtually no further sulfur removal in this low temperature hydrogenation.

Example 4 (Comparative Example): Feed B (Table 1)
= Hydrogenization at 390 ° C. in an isothermal pilot-plant at two different conditions. This temperature is generally at the end of operation (EO
R) is considered a condition. The pressure is 32 bar. Pure hydrogen is used as the process gas. The ratio of hydrogen to oil is 336 NL / L. Feed B is a mixture of 50% light circulating oil (LCO) and 50% straight run gas oil (SRGO). In this test, a supported catalyst in which Co-Mo is supported on alumina is used. The properties of the products of this test are shown in Table 4.

[0027] The two products contain the same amount of polycyclic aromatic compound, despite the completely different residual sulfur content. The reason for this result is that all the aromatic compounds approach the equilibrium of the tricyclic aromatic compound ← → the bicyclic aromatic compound ← → the monocyclic aromatic compound ← → naphthene due to the high reaction temperature, and P
No effect of LHSV on the amount of AH is observed.

Example 5 (Example): Example 4 with product from Example 4
Further hydrogenation at lower temperatures than T = 300 ° C, P
= 30 bar inlet hydrogen partial pressure (evaporated diesel oil not taken into account) and LHSV = 4 h ^-1 with PAH of 4.
0% by weight of bicyclic aromatic compounds and 1.7% by weight of tricyclic aromatic compounds are excluded. The specific gravity (SG 60/60) is 0.8496. In this test, alumina was Ni-M
A supported catalyst supporting o is used. Large amounts of polycyclic aromatics can be removed at lower temperatures (and at the same pressure) because the equilibrium shifts. This low temperature hydrogenation does not substantially remove any further sulfur.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating one embodiment of the method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Furnace 2 ... Hydrogenation reactor 3 ... Heat exchange means 4 ... Post-treatment reactor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomas Tappet 90740, California, USA Seal Beach, Schooner Way, 468

Claims (9)

[Claims] 1. A method for reducing the content of sulfur compounds and polycyclic aromatic hydrocarbons in a hydrocarbon feed having a boiling range of from 120 to 450 ° C., the method comprising the steps of: Contacting over a hydrogenation catalyst, hydrogenating the feed under hydrogenation conditions and obtaining a hydrocarbon effluent containing hydrogen and hydrogen sulfide, cooling the effluent and subjecting the cooled effluent to hydrocarbon feed The process comprising contacting with a hydrogenation catalyst in a post-treatment step under conditions effective to reduce the polycyclic aromatic hydrocarbon content in the product. 2. The method according to claim 1, wherein the conditions of the post-treatment stage are a temperature 50 ° C. to 150 ° C. lower than the outlet temperature of the hydrotreater. 3. The process according to claim 1, wherein the LHSV in the aftertreatment reactor is 2 to 20 times the LHSV in the hydrogenation reactor. 4. The process according to claim 1, wherein the work-up stage is carried out in the last catalyst bed of the hydrogenation reactor. 5. 50% of the hydrocarbon feed at 200 ° C.
The method of claim 1 having a rising point between 50 ° C. 6. The method according to claim 6, wherein the hydrogenation catalyst used in the post-treatment step comprises adding a group VI-B and / or VIII to the porous heat-resistant inorganic oxide.
2. The method according to claim 1, wherein the catalyst is a supported catalyst supporting a group III metal. 7. The method according to claim 6, wherein the metal is nickel and molybdenum, or nickel and tungsten. 8. The method according to claim 7, wherein the porous heat-resistant inorganic oxide is alumina or silica-alumina. 9. The process according to claim 1, wherein the catalyst in the aftertreatment stage is presulfurized and / or in situ.