TW201610141A - A process for hydrotreatment of a gas stream and a reactor system for carrying out the process - Google Patents

Abstract

A process for hydrotreatment of a gas stream to lower the total content of sulfur compounds to 10-20 ppm by weight (ppmw) or even below 10 ppmw is performed in a reactor system consisting of three fixed-bed reactors: A pre-hydrogenating reactor R1 for pre-treating diolefins, a hydrogenating reactor R2 and a post-treating reactor R3 used for reacting traces of carbonyl sulfide. The pre-hydrogen-ating reactor R1 can be omitted if the content of diolefins in the feed gas is sufficiently low. All reactors contain catalysts which after activation comprise mixed sulfides of Co or Ni and Mo or W supported on [gamma]-alumina (Al2O3) as high-surface-area carrier.

Description

Process for hydrotreating gas stream and reactor system for carrying out the process

This invention relates to a process for the hydrotreating of a gas stream such as a coker gas, a gasifier outlet gas or a gas produced in a distiller. The invention further relates to a reactor system for carrying out the process. The reactor system is a single pass or recycle reactor system comprising three fixed bed reactors wherein the gas composition is as follows: up to 20% H ₂ S

Up to 35% of total olefins

Up to 10% diolefin

Up to 12% CO+CO ₂ +COS

Up to 20% H ₂

Up to 2% organic sulfur compounds

And the rest is saturated light hydrocarbons

The gas is treated by the process of the invention in order to reduce the total content of sulfur compounds to a maximum of 10-20 ppm by weight, preferably less than 10 ppm by weight.

In the refining industry, sulfur removal or recycling is a very important issue that often does not receive the attention it deserves. Sulfur is one of the major pollutants in petroleum fractions, and regulations are not only The allowable sulfur content of the finished product is defined and the atmospheric emissions of the refinery are limited. Therefore, sulfur removal and recovery is a critical process for refinery and gas plant operations. In most locations, sulfur is hydrotreated and thus converted to hydrogen sulfide, which can be scrubbed from various streams or streams. The hydrogen sulfide collected from the hydrotreater and/or the gas plant can then be treated, for example, by the Claus process.

Various gas treatment methods for sulfur removal are described in the prior art. For example, US 8,080,089 B1 describes a method and apparatus for efficient gas treatment wherein the SO _X compound is removed such that the concentration of SO _X remaining in the gas is between 0 and 10 ppmv. Furthermore, US 7,374,742 discloses a method for removing sulfur species from a gas stream without the use of a sulfur species removal process such as amine scrubbing. The sulfur species are removed by subjecting the gas stream directly to a sulfur recovery process, such as the Claus process at high pressure and moderate temperatures, wherein the sulfur recovery process comprises a catalyst that does not contain activated carbon.

WO 2009/026090 A1 discloses a process for the removal of sulfur from a fuel gas stream additionally containing diolefins and oxygen and organic sulfur compounds. In this process, a fuel gas stream is treated in a pretreatment reactor to reduce the amount of any diolefins and oxygen contained therein, followed by hydrodesulfurization in a hydrotreating reactor wherein the organosulfur compound is converted to hydrogen sulfide. Hydrogen sulfide is removed from the hydrotreating gas stream by an absorption treatment such as amine treatment to produce a treated fuel gas stream having a reduced concentration of hydrogen sulfide and an overall low sulfur content. It is pointed out in this description that a treated fuel gas stream having a hydrogen sulfide concentration of less than 40 ppmv and more particularly less than 10 ppmv will be particularly desirable. However, this document does not contain examples or materials showing that such low concentrations are actually obtained.

The same is true of WO 2008/148077 A1, which discloses a method for self-contained A method of removing sulfur from a fuel gas stream having carbon dioxide and light diolefins. The process comprises a hydrotreating step followed by a reduction or hydrolysis step.

The process according to the invention is a process for the hydrotreating of a gas stream to reduce the total content of sulfur compounds to 10-20 ppm (ppmw) or even less than 10 ppmw by weight. The method comprises the steps of: - mixing a feed gas with hydrogen to form a process gas, - introducing the process gas stream into a prehydrogenation reactor as appropriate, in which the gas is contained The process gas stream is contacted with a hydrogenation catalyst under conditions in which any diolefin is substantially converted to a monoolefin, and the prehydrogenated gas stream having a low content of diolefin is introduced into the hydrogenation reactor, In the reactor, the pre-hydrogenated gas stream is contacted with a hydrogenation catalyst to react a sulfur-containing compound with a monoolefin, cooling the process gas from the hydrogenation reactor, mixing it with high-pressure steam, and cooling the resulting gas. Mixture, - feeding the gas mixture into a post-treatment reactor containing an alumina catalyst to react with any traces of carbonyl sulfide (COS), and - subjecting the hydroprocessed gas to a chemisorption treatment for removal Hydrogen sulfide.

The reactor system according to the present invention, also referred to as a gas hydrotreater, comprises a catalyst technology having the ability to substantially reduce the sulfur content of a mercaptan-rich refinery gas.

When a gas such as a coker gas is treated by the method according to the invention, it has been surprisingly found that after the final chemisorption step (typically based on amine) for removing residual H ₂ S, the content of sulfur-containing compounds can It is reduced to a maximum of 10-20 ppm by weight and even less than 10 ppm.

The reaction occurring in the reactor system according to the present invention is all gas phase reactions except for various hydrocarbons in an environment containing H ₂ , CO, CO ₂ and H ₂ S.

The reactor system according to the invention is a reactor system comprising three continuous fixed bed reactors, more particularly a single pass reactor system or a recycle reactor system, wherein - the first reactor (R1) is used for pretreatment a prehydrogenation reactor for diolefins, which may be used as appropriate, - the second reactor (R2) is a hydrogenation reactor, which is a main reactor for reacting a sulfur-containing compound with a monoolefin, and - a third reaction The vessel (R3) is a post-treatment reactor for reacting trace amounts of carbonyl sulfide (COS) present in the outlet stream from (R2). The composition of the reactor system is shown in the figures.

The first reactor R1 needs to avoid colloidal formation of diolefins in the later stages of the process. In the second reactor R2, all sulfur-containing compounds are reacted with the olefin, but some traces of mercaptans and COS may still be present. These traces of compound are treated in a third reactor R3.

If the amount of diolefin in the feed gas exceeds 1000 ppmw, the first reactor R1 is optional. In the event that the amount is below 1000 ppmw, R1 may be omitted and the feed gas stream is then directed directly to the inlet of the second reactor R2 via feed/effluent heat exchanger E2.

The main challenge is to treat the mercaptans while simultaneously handling the diene, H ₂ S and COS contents. Therefore, the exotherm in the first reactor R1 must be carefully controlled, which typically has to manipulate the conversion of diolefins to monoolefins. Since it is possible to control the processes such that only the diene reaction actually occurs, the system arrangement can be designed to have only a simple low cost flame heater.

As mentioned, all the gas phase reactors such as reaction, and competing exothermic reaction to a saturated mono-olefins and to H ₂ S + alkane thiols. There is an ideal temperature window of about 130 ° C to 210 ° C, and the reaction can be controlled during this temperature window with suitable equipment arrangements and catalyst systems. Thus, the ideal temperature window in the first reactor R1 can actually contribute to an economically very advantageous system arrangement for processing the coker gas.

The basic core concept of the present invention is to make hydrodesulfurization of a gas stream such as a coker gas stream more efficient. The first reactor R1 ("hydrotreater" or pre-hydrogenator) is located upstream of the amine scrubbing unit and substantially reduces the sulfur content of the gas prior to entering the main unit R2. As mentioned previously, the first reactor R1 needs to avoid colloidal formation of diolefins in the later stages of the process. However, it was confirmed to be necessary only when the content of the diene in the feed gas stream exceeded 1000 ppmw. The main unit R2 is a hydrogenation reactor, and the reactor R3 is a COS post-treatment hydrolysis reactor.

The primary technical novelty of this process is to modify the pre-processor catalyst to selectively treat the diolefin rather than the monoolefin to provide the proper temperature in the main reactor R2 in a cost effective manner.

The coker gas that can be treated in accordance with the present invention is typically a coker sour gas from a coker sponge absorber. In a hydrotreater device, a non-H ₂ S-type sulfur compound is converted to H ₂ S. Typically, this coker sour gas has the composition indicated in Table 1 below:

In addition, the coker sour gas can contain traces ( 0.01 mol% of carbonyl sulfide, 1,3-butadiene, HCN/RCN, benzene, toluene, xylene and ammonia.

The catalysts present in the three reactors of the system according to the invention are those typically employed in hydrodesulfurization (HDS) processes. The HDS catalyst typically contains Co or Ni and a mixed sulfide of Mo or W supported on a high surface area support such as gamma-alumina (Al ₂ O ₃ ) after activation. The main reason it is widely used for its high resistance to H arising during the hydrotreating reaction of ₂ S. Industrial applications of Co-Mo sulfide catalysts have been reported 70 years ago and are still the most common catalysts for HDS reactions.

The processing method according to the present invention will hereinafter be described in more detail with reference to the accompanying drawings.

As mentioned above, the hydrotreater device consists of three reactors: a prehydrogenator R1, a hydrogenation reactor R2 and a COS hydrolysis reactor R3.

The feed gas (f) is mixed with hydrogen (h). The resulting process gas is then preheated in the first feed/effluent heat exchanger E1 and passed through the prehydrogenator R1, as appropriate, but not necessarily (depending on the amount of diolefin in the feed gas). It is then further preheated in the second feed/effluent heat exchanger E2, then into the hydrogenation reactor R2, if necessary after entering the hydrogenation reactor R2 by starting the heater (sh). If the level of diolefin in the feed gas is sufficiently low, the feed gas/hydrogen mixture is fed directly to the inlet of hydrogenation reactor R2 via second feed/effluent heat exchanger E2.

The process gas from hydrogenation reactor R2 is cooled in a second feed/effluent heat exchanger E2. The bypass on the hot side of the second feed/effluent heat exchanger is used to control the outlet temperature of R2.

The cooled process gas from the second feed/effluent heat exchanger is mixed with high pressure steam (hps) and subsequently further cooled in process gas boiler B, and subsequently passed to COS hydrolysis reactor R3, which is used to A post-treatment reactor from the trace COS reaction present in the outlet stream of R2.

The process gas from R3 is recycled to the inlet of R1 (shown as a dashed arrow in the figure) or cooled in the first feed/effluent heat exchanger E1, heating the gas to a diolefin prehydrogenator R1. The gas is further cooled in the water cooler W, in which the steam is condensed. The process condensate (c) is separated from the hydrotreated gas in a process condensate separator V.

The hydrotreated gas is passed from process condensate separator V to amine treatment unit A to remove H ₂ S. The stream (1) containing very little amine is passed through the amine treatment unit and exits the apparatus in the form of an amine-rich stream (r). The product (p) contains 10-20 ppm by weight, preferably less than 10 ppm by weight of sulfur.

The system may also include a salt water flush NH ₄ Cl (formed by reaction between ₃ HCl and NH) to prevent the obstruction member (not shown).

Prehydrogenation reaction and catalyst

The coker sour gas feed contains more than 1000 ppmw of diolefin. The diolefin in the coker sour gas feed has a high tendency to form a gum due to polymerization or carbon formation at the normal operating temperature of the hydrogenation reactor R2. To prevent such problems, the diene in the coker acid gas feed is converted in a prehydrogenation reactor R1 containing a hydrogenation catalyst, such as the applicant's nickel-molybdenum hydrogenation catalyst TK-437.

TK-437 catalyzes the following reaction: R ₁ =R ₂ -R ₃ =R ₄ +H ₂ →R ₁ =R ₂ -R ₃ HR ₄ H

R ₁ =R ₂ -R ₃ =R ₄ +2H ₂ → HR ₁ -HR ₂ -R ₃ HR ₄ H

R ₁ =R ₂ +H ₂ → HR ₁ -HR ₂

Wherein R is a hydrocarbon group.

If the operating temperature is low enough, the last reaction is unlikely to occur.

For any given feedstock, a certain flow of hydrogen is required to carry out the hydrogenation reaction. Sufficient hydrogen must be added all the time to minimize the risk of polymerization or carbon formation.

The TK-437 catalyst is pre-vulcanized and does not require vulcanization prior to operation.

Another suitable catalyst is Applicant's molybdenum-based catalyst TK-719, which is particularly suitable for use in olefin-containing feeds where active classification is required to prevent gel formation.

Hydrogenation reaction and catalyst

The hydrogenation reactor R2 is loaded with a nickel-molybdenum hydrogenation catalyst, preferably by the applicant TK-261 catalyst, which was placed in a single bed in the reactor.

TK-261 catalyzes the following reactions: RSH+H ₂ → RH+H ₂ S

R ₁ SSR ₂ +3H ₂ → R ₁ H+R ₂ H+2H ₂ S

R ₁ SR ₂ +2H ₂ → R ₁ H+R ₂ H+H ₂ S

(CH) ₄ S+4H ₂ → C ₄ H ₁₀ +H ₂ S

COS+H ₂ → CO+H ₂ S

CO ₂ +H ₂ S → COS+H ₂ O

R ₁ =R ₂ +H ₂ → HR ₁ -R ₂ H

The conversion of olefins to saturated hydrocarbons is a strongly exothermic reaction. Depending on the amount of olefin in the feed, the temperature will rise substantially between 50 ° C and 90 ° C.

A minimum of 10% excess hydrogen must be present at the outlet of the hydrogenation reactor R2 to prevent carbon formation or olefin polymerization. If the hydrogen flow is insufficient, this also causes poor conversion of the organic sulfur compound and an increase in leakage of the organic sulfur through the unit.

The gas leaving the hydrogenation reactor can contain up to 150 ppm of olefins. This remaining amount of olefin can be recombined with H ₂ S present in the gas at a concentration of about 14%. The general reaction scheme is: C _n H _2n +H ₂ S C _n H _2n+1 SH (n=1-4)

C _n H _2n +H ₂ S 2C _n H _2n+1 SH (n=3, 4)

C _n H _2n +H ₂ S (CH ₃ ) ₃ CSH

The maximum activity of the hydrogenation catalyst depends on the hydrogen concentration and temperature at the inlet of the reactor. The recommended reactor outlet temperature is 400 °C. At temperatures above 400 ° C, it will be reminded The coke is formed on the surface of the agent to reduce the activity of the catalyst.

There are two places that are critical: pipes and heat exchangers that carry gas from the outlet of the hydrogenation reactor (R2) to the inlet of the COS hydrolysis reactor (R3); and the CKA catalyst in R3, which provides Increase the large contact surface area of the recombination reaction.

The gas leaving the hydrogenation reactor R2 will be at equilibrium or very close to equilibrium at 400 ° C for olefin hydrogenation, organic sulfur hydrogenation, COS hydrolysis and water-gas conversion. The balance between the first two will imply that the recombination reaction is also in equilibrium, and the balance between the latter two will imply that COS hydrogenolysis is in equilibrium.

The catalyst was heated with a single pass of natural gas and hydrogen during start-up. In the case of hydrogen-free hydrocarbons, the catalyst must not be operated above 300 ° C because carbon deposition would otherwise occur and thereby block the catalyst surface. Therefore, hydrogenation will be insufficient.

The TK-261 catalyst can be obtained in pre-vulcanized form or as an oxidized product. The pre-vulcanized catalyst does not require vulcanization prior to the ingress operation. The oxidized catalyst must be vulcanized on site to obtain its activity.

Operation of the non-sulfided catalyst will increase the risk of hydrocracking, resulting in severe temperature fluctuations. Olefin has a significant tendency to affect the formation of carbon on non-sulfided catalysts. Affinity for carbon formation is higher at low hydrogen partial pressures and high temperatures. Affinity for carbon formation also depends on the type of olefin.

After vulcanization, the catalyst is pyrophoric and should therefore not be exposed to air at temperatures in excess of 70 °C.

COS hydrolysis reaction and catalyst

The COS hydrolysis reactor R3 is loaded with an activated alumina catalyst, preferably the present application The CKA-3 catalyst was requested and placed in a single bed in the reactor. The CKA catalyst is selectively active against the COS hydrolysis reaction.

COS+H ₂ O CO ₂ +H ₂ S

The CKA catalyst does not require any activation and activation. It is heated in natural gas to a temperature that exceeds the dew point of the process gas by at least 50 °C.

During operation, the gas must be maintained above the dew point by about 50 ° C or above to prevent condensation in the pores of the catalyst. The condensation can destroy the catalyst.

The COS leaking from the COS hydrolysis reactor is determined by equilibrium, and high vapor content and low temperature are beneficial for low COS leakage.

High pressure steam is added to the process gas stream entering the COS hydrolysis reactor to reduce COS leakage from the reactor. Steam loss will cause the COS to break through the reactor. The high CO ₂ content in the feed gas will also cause higher COS leakage due to the movement of the equilibrium reaction.

The invention is further illustrated by the following examples. However, the invention is not limited in any way to these embodiments.

Example 1

Acid semi-coke gas treatment

The acidic semi-coercifier gas from the distillation gas plant has the total composition as indicated in Table 2 below:

The above gas is mixed with hydrogen. The resulting process gas was then preheated to 175 °C in a first feed/effluent heat exchanger. The preheated gas is passed through a prehydrogenator and subsequently further preheated in a second feed/effluent heat exchanger, which is then passed to a hydrogenation reactor at about 290 °C to 400 °C.

The process gas from the hydrogenation reactor is cooled in a second feed/effluent heat exchanger. The bypass on the hot side of the second feed/effluent heat exchanger was used to control the outlet temperature of the hydrogenation reactor to 400 °C.

The process gas from the hydrogenation reactor is mixed with high pressure steam and then further cooled in a process gas boiler prior to delivery to the COS hydrolysis reactor.

Cooling from the COS hydrolysis reactor in the first feed/effluent heat exchanger The process gas is heated to enter the diolefin prehydrogenator. The gas is further cooled in a water cooler where the steam condenses. The process condensate and the hydrotreated gas are separated in a process condensate separator.

Through the gas hydrotreated condensate from the separator during transfer to the processing device to remove the amine H ₂ S. The stream containing very little amine is passed through the amine processing equipment and exits the apparatus in the form of an amine-rich stream. The treated product contained less than 10 ppm sulfur by weight.

Example 2

Coker sour gas treatment

The coker gas having the composition as indicated in Table 1 was subjected to the same treatment as in Example 1. In this case, the final treated product also contains less than 10 ppm sulfur by weight.

Example 3

Gas analysis after equipment startup

This example shows the results of the analysis of the gas samples obtained after the device was started. Get samples at the following locations:

Sample 1 (S1): gas inlet (f)

Sample 2 (S2): Exit of R1

Sample 3 (S3): Exit of R2

The last sample, sample 4 (S4), was taken from the product stream (p).

The results are given in the form of molar ppm compounds as shown in Table 3 below. Compounds below 0.4 mol ppm (for sulfur dioxide, dimethyl sulfide, thiophene, isobutyl mercaptan, dimethyl disulfide, 2-ethylthiophene, 2,5-dimethylthiophene, ethyl methyl Knots of disulfide, tetrahydrothiophene, 2-methylthiophene, 3-methylthiophene, 2-methyltetrahydrothiophene and diethyl disulfide It is not shown in the table.

Regarding the gas, the molar ppm is equal to ppmv.

A‧‧‧Amine processing equipment

B‧‧‧Process Gas Boiler

c‧‧‧Process condensate

E1‧‧‧First feed/effluent heat exchanger

E2‧‧‧Second feed/effluent heat exchanger

F‧‧‧feed gas

H‧‧‧hydrogen

Hps‧‧‧high pressure steam

L‧‧‧ material flow with very little amine

P‧‧‧product

r‧‧‧Amine-rich material stream

R1‧‧‧Pre-hydrogenator

R2‧‧‧ Hydrogenation reactor

R3‧‧‧COS hydrolysis reactor

Sh‧‧‧Start heater

V‧‧‧Process Condensate Separator

W‧‧‧Water cooler

Claims (14)

A method for hydrotreating a gas stream to reduce the total content of sulfur compounds to 10-20 ppm (ppmw) or even less than 10 ppmw by weight, the method comprising the steps of: mixing the feed gas with hydrogen to form a process a gas, which is introduced into the prehydrogenation reactor as appropriate, in which the process gas stream is subjected to substantially converting any diolefin contained in the gas to a monoolefin. Contacting the hydrogenation catalyst, introducing the pre-hydrogenated gas stream having a low content of diolefin into a hydrogenation reactor, wherein the pre-hydrogenation gas stream is contacted with the hydrogenation catalyst to cause The sulfur-containing compound is reacted with a monoolefin, the process gas from the hydrogenation reactor is cooled, mixed with high-pressure steam, and the resulting gas mixture is cooled, and the gas mixture is fed into a post-treatment reactor containing an alumina catalyst to Any trace of carbonyl sulfide (COS) is reacted and the hydrogenation process gas is subjected to a chemisorption process to remove hydrogen sulfide. The method of claim 1, wherein the feed gas has the following composition: up to 20% H ₂ S up to 35% total olefin up to 10% diolefin up to 12% CO + CO ₂ + COS up to The remainder of the 20% H ₂ up to 2% organosulfur compound consists of saturated light hydrocarbons. The method of claim 1 or 2, wherein the catalysts comprise Co or Ni and a mixed sulfide of Mo or W supported on γ-alumina (Al ₂ O ₃ ) after activation. The method of claim 1 or 2, wherein the process gas is preheated to about 175 ° C prior to entering the prehydrogenation reactor. The method of any one of clauses 1 to 3, wherein the entry temperature into the hydrogenation reactor is from about 290 ° C to 400 ° C. The method of any one of clauses 1 to 4, wherein the process gas from the hydrogenation reactor is cooled to 160 ° C to 220 ° C after mixing with the high pressure steam. The method of any one of clauses 1 to 6, wherein the catalyst in the prehydrogenation reactor is a nickel-molybdenum hydrogenation catalyst TK-437. The method of any one of clauses 1 to 6, wherein the catalyst in the prehydrogenation reactor is a molybdenum oxide catalyst TK-719. The method of any one of clauses 1 to 6, wherein the catalyst in the hydrogenation reactor is a nickel-molybdenum hydrogenation catalyst TK-261. The method of any one of clauses 1 to 6, wherein the catalyst in the aftertreatment reactor is an alumina catalyst CKA-3. A process according to any one of the preceding claims, wherein the exotherm in the first reactor is controlled such that only a diene reaction occurs which manipulates the conversion of the diolefin to the monoolefin. The method of claim 11, comprising an ideal temperature window of about 130 ° C to 210 ° C in the first reactor, wherein the reactions can be controlled. A reactor system for the hydrotreating of a gas stream to reduce the total content of sulfur compounds by a method according to any one of claims 1 to 12, more specifically comprising three fixed bed reactions a single-pass reactor system or a recycle reactor system, wherein the first reactor (R1) is a pre-hydrogenation reactor for pretreating a diolefin, which may optionally be used, the second reactor (R2) being a hydrogenation reactor which is a main reactor for reacting a sulfur-containing compound with a monoolefin, and the third reactor (R3) is for vulcanizing a trace amount of a carbonyl group present in the outlet stream from (R2) A post-treatment reactor for the (COS) reaction. The reactor system of claim 13 further comprising a feed/effluent heat exchanger (E1 and E2), a process gas boiler (B), a water cooler (W), a separator (V), The heater (sh) is activated and the means for flushing off the NH ₄ Cl salt with water to prevent clogging.