EP3230411B1

EP3230411B1 - A method for diesel production

Info

Publication number: EP3230411B1
Application number: EP14835732.0A
Authority: EP
Inventors: Delalettin NASUHBEYOGLU; Ersen ERTAS; Yesim KÖPRÜLÜ
Original assignee: Turkiye Petrol Rafinerileri AS Tupras
Current assignee: Turkiye Petrol Rafinerileri AS Tupras
Priority date: 2014-12-11
Filing date: 2014-12-11
Publication date: 2023-01-11
Anticipated expiration: 2034-12-11
Also published as: WO2016093777A1; EP3230411A1

Description

Technical Field of the Invention

The present invention relates to a method for production of diesel from a hydrocarbon mixture having an initial T95 distillation temperature within the range between 375ºC and 395ºC.

Background of the Invention

Due to environmental considerations and new regulations recently entered into force, fuel specifications are rendered tighter. In order to meet required specifications, petroleum refineries must accordingly adjust their production schemes and operations.
According to new regulations, the sulfur and nitrogen in content of diesel fuels shall be removed, and for instance, ultra-low sulfur diesel (ULSD) must meet the requirement of having less than 10 wppm sulfur content. To this end, more severe and deep hydrodesulfurization processes are to be applied, thereby reducing the diesel production due to cracking to lighter products like naphtha and LPG.
Additionally, the 95% distillation temperature of diesel (ASTM D86) is required to be less than 360°C and reduction in the 95% distillation temperature (T95) of diesel represents the decrease in the volume of diesel produced.
Considering the stringent product specifications and constantly increasing global demand for middle distillate products (diesel and jet fuel) for the last decades, there is a continuous need for improved methods of producing more diesel fuel from hydrocarbon feedstocks.
To meet the new specifications, middle distillate hydrocarbon streams from crude distillation units must be treated in hydrodesulfurization units. The feedstock is processed with a suitable desulfurization catalyst under a temperature ranging between 350°C and 450°C and a hydrogen partial pressure ranging between 60 bars and 80 bars. The requirement that the T95 of diesel is to be maximum 360°C (ASTM D86) determines a maximum boiling range for the feedstock. A limited extent of T95 reduction can be achieved in hydrodesulfurization processes, which is generally around 5 to 10°C. Accordingly, maximum T95 of the feedstock is limited to the range between 360°C and 365°C.
In deep hydrodesulfurization units which comprise one or more catalytic reactors, diesel boiling range hydrocarbon mixtures are processed with suitable desulfurization catalyst(s) under temperatures ranging between 350°C and 450°C and with hydrogen partial pressures within the range of 60 bars to 80 bars. With the help of the hydrodesulfurization reactions, sulfur content of said hydrocarbon mixtures is reduced to a maximum value lower than 10 wppm. In some deep hydrodesulfurization units, dewaxing catalysts are employed prior to reactor outlets, to improve cold filter plugging properties especially in winter seasons. Similar with that by hydrodesulfurization units mentioned above, only a limited T95 reduction can be achieved at deep hydrodesulfurization units. The requirement for compliance with ASTM D86 which indicates a maximum T95 of 360°C, determines the maximum boiling range of respective feedstock, i.e. the 95% distillation temperature of feedstock is to be less than 365°C which is already very close to the diesel boiling range.
Such hydrodesulfurization processes are in conventional use and they are very well known by refining industry. At these processes, feedstocks involving heavier hydrocarbons are to be converted into lighter products like diesel using further conversion units, e.g. hydrocracking reactors. The amount of middle distillate produced from a crude distillation unit can generally be considered to be insufficient for supplying the demand for diesel and jet fuel. Therefore conversion processes like hydrocracking are employed in petroleum refineries.
To satisfy the above mentioned demand using hydrocracking reactors, heavy feedstocks such as vacuum gas oils are processed with suitable hydrocracking catalysts under elevated temperatures ranging between 400°C and 500°C and pressures ranging between 160 bars and 200 bars in presence of hydrogen. The operating conditions and choice of hydrocracking catalysts in a hydrocracking reactor affect respective product yields. Partial or full conversion hydrocracking is used to produce diesel with lower yield of unconverted oil that is fed to other units such as fluid catalytic cracking (FCC) units. Additionally, the conversion level might be reduced in the hydrocracking and unconverted oil with improved quality can be utilized in lube production. Such hydrocracking processes are conventionally in use and very well known by the refining industry. US 2014/332443 A1 and US 2014/124407 A1 disclose methods for producing diesel range products through hydrocracking of hydrocarbon feedstocks.
Mild hydrocracking is also used in petroleum refineries in order to improve the properties of unconverted oil that is fed to other downstream units while partially converting heavy feedstocks such as vacuum gas into lighter products like diesel. Mild hydrocracker units are operated under less severe conditions, i.e. lower temperatures and pressures with respect to abovementioned hydrocracking processes. Accordingly, conversion levels achieved with mild hydrocracker units are relatively low compared to conventional hydrocracking processes.
At a typical petroleum refinery, a typical diesel boiling range feedstock hydrodesulfurization unit having a 100 tonnes of feed capacity outputs 95 tonnes of diesel product in average throughout the catalyst cycle length with a density of 839 kg/m³ (which corresponds to about 113.2 m³ diesel production per day), and 5 tonnes of lighter hydrocarbon mixture with a lower T95 distillation temperature with regard to diesel. Additionally, heavier hydrocarbon fractions with higher T95 distillation temperatures in comparison with diesel boiling range fraction have lower economical value with regard to diesel.

Objects of the Invention

Primary object of the present invention is to eliminate the above-mentioned shortcomings in the prior art.
A further object of the present invention is to provide a method to increase the volumetric production capacity for diesel boiling range hydrocarbons in refineries.
A further object of the present invention is to provide a method to increase the mass production capacity of diesel boiling range hydrocarbons in refineries.
A further object of the present invention is to provide a method which increases the added value production.at petroleum refineries.
A further object of the present invention is to provide a method which reduces the T95 distillation point of a feedstock by converting heavier hydrocarbon fractions into diesel boiling range hydrocarbons under less severe conditions in comparison with conventional hydrocracking processes for hydrocracking of such heavier hydrocarbon fractions.

Brief Description of the Invention

The present invention proposes a method for production of diesel according to claim 1.

Detailed Description of the Invention

Although several processes, respective operating conditions and catalysts are employed in refining industry as explained above, there remains still unfulfilled demand for new production methods which provide high yield, lower cost and improved product properties. Constructing new production units can be a long and costly process. However, using innovative solutions to optimize existing assets is an economically attractive alternative.
The present invention proposes a method for production of diesel from a hydrocarbon mixture having an initial T95 distillation temperature within the range between 360°C and 420°C,

using a continuous reactor system which comprises the following features:
the reactor system temperature is within the range of 350°C and 450°C,
the hydrogen partial pressure within the reactor system is within the range of 60 bar and 80 bar,
the reactor system comprises a hydrodesulfurization zone comprising hydrodesulfurization catalyst,
the reactor system further comprises a hydrocracking zone comprising a hydrocracking catalyst;
wherein said method comprises the following sequential steps:
1. a) preparation of a hydrocarbon mixture by admixing a diesel range stream having a T95 distillation temperature of maximum 360°C with a heavy stream having a T95 distillation temperature higher than 360°C, the weight ratio of diesel range stream to the heavy stream being within the range between 10:0.5 and 10:1.5, and the initial T95 distillation temperature of the hydrocarbon mixture is within the range between 375°C and 395°C;
2. b) feeding the hydrocarbon mixture into the reactor system,
3. c) forwarding the hydrocarbon mixture such that the hydrocarbon mixture flows through the hydrodesulfurization zone,
4. d) forwarding the hydrocarbon mixture such that said hydrocarbon mixture flows through a hydrocracking zone.

The method according to the present invention preferably further comprises a step of forwarding the hydrocarbon mixture from the reactor system into a fractionator, subsequent to the above step 'd)', such that diesel boiling range hydrocarbons are separated from lighter hydrocarbons such as naphtha and LPG.
Preferably, the initial T95 distillation temperature of the hydrocarbon mixture is within the range between 380°C and 390°C. Thus, an optimum heavy fraction ratio in the hydrocarbon mixture can be supplied by obtaining suitable conversion of large molecules into molecules having boiling points within the diesel-range.
Preferably, the space velocity of the hydrocarbon mixture within the reactor system is within the range of 0.5 h^-1 and 3 h^-1, and more preferably within the range of 1 h^-1 and 2 h^-1. Thus, an optimum residence time can be obtained for suitable conversion of large molecules into molecules having boiling points within the diesel-range.
Preferably, gas to oil ratio is within the range of 300 Nm³/m³ and 1000 Nm³/m³, and more preferably within the range of 600 Nm³/m³ and 850 Nm³/m³. This provides an optimum density within the reactor system for obtaining diesel boiling range hydrocarbons with desired reaction rates throughout the reactor system.
The reactor system having hydrodesulfurization zone and the hydrocracking zone could be a single reactor or a series of several reactors.
Preferably, the reactor system further comprises a quench zone between the hydrodesulfurization zone and the hydrocracking zone; for cooling the hydrocarbon mixture with a hydrogen-rich gas stream. Preferably, hydrodesulfurization zone and/or hydrocracker zone comprises one or more inter-quench zones, for prevention of superheating of hydrocarbons flowing through the reactor system; since there might be more than one catalytic bed in each catalytic zone.
With the method according to the present invention, reduction of %95 distillation temperature of a hydrocarbon feedstock is reduced under less severe conditions with regard to those by conventional hydrocracking processes.
The present invention enables low cost production of ultra-low sulfur diesel within required specifications by hydrodesulfurization of diesel boiling range hydrocarbon feed and more importantly T95 reduction of hydrocarbon feeds having a boiling range higher than that of diesel, by performing a less severe hydrocracking than those which are performed in conventional processes.
According to the present invention, hydrodesulfurization and/or dewaxing catalysts in subsequent bed(s) of an existing hydrodesulfurization unit or in an already existing reactor of an existing hydrodesulfurization unit can be replaced with hydrocracking catalyst which operates in line with hydrodesulfurization zone, i.e. under less severe conditions compared to conventional hydrocracking process. Using such revised catalyst configuration, heavier hydrocarbon feeds with a boiling range higher than that of diesel can be co-processed along with a stream of diesel boiling range hydrocarbons in same process unit. Thus with the process according to the present invention, T95 limitation of a maximum value of 365°C of the hydrocarbon mixtures used as diesel production reactor feed in the prior art is rised up to 400°C, and preferably up to 385ºC. The hydrocarbon mixture used as reactor feed in the method according to the present invention is prepared by admixtion of a heavy stream (i.e. a hydrocarbon mixture having a higher T95 distillation temperature compared to that of a diesel range stream which has a T95 distillation temperature of maximum 360°C in accordance with ASTM D86) with a diesel range stream. Said heavy stream is preferably selected from the list consisting of a heavy fraction of atmospheric gas oil (AGO), light vacuum gas oil (LVGO), a light fraction of the heavy vacuum gas oil (HVGO), visbreaker gas oil (VBGO) and FCC light cycle oil (LCO) and a mixture thereof.
The hydrodesulfurization zone employed in the method according to the present invention preferably involves conventional catalysts in appropriate amounts, activity, etc. which can be decided/chosen/calculated by a skilled person in the art, to achieve deep hydrodesulphurization for complying with relevant legislations such that reducing the sulfur content of the hydrocarbon mixture to a value less than 10 wppm. The hydrodesulphurization catalyst can be selected from the list consisting of NiMo on alumina, CoMo on alumina, and a mixture thereof. Preferably the catalyst is NiMo on alumina due to its high hydrogenation and hydrodenitrogenation activity.
The hydrocracking zone employed in the method according to the present invention preferably involves conventional catalysts in appropriate amounts, activity, etc. which can be decided/chosen/calculated by a skilled person in the art, to obtain both hydrocracking and hydrogenation. Cracking occurs by an acidic site which is e.g. a silica-alumina based zeolitic structure; and hydrogenation occurs by a metal site which is e.g. Ni, W, Co etc. Thus, the hydrocracking catalyst according to the present invention preferably comprises a silica or alumina-based catalyst having metallic sites selected from the list consisting of Nickel, Wolfram, Cobalt and a mixture thereof. The hydrocracker catalyst plays an important role on the yields obtained using the method according to the present invention. The activity of the hydrocracking catalyst shall be compatible with hydrodesulfurization catalyst so that the cracking level to lighter products such as naphtha and LPG is controlled, thereby maintaining higher concentrations of desired diesel boiling range substances in the product stream.
At a refinery with a constant capacity of diesel boiling range fraction production to be fed into a desulfurization unit, an already-set-up diesel desulfurization unit can be utilized to perform the method according to the present invention. Since the diesel boiling range fraction production capacity is almost constant depending on the crude oil processing capacity, the entire diesel boiling range fraction is to be processed run down in order to avoid extra storage costs. The method can be easily applied if the capacity of the desulfurization unit is not fully utilized. But if the unit is at its design capacity, the method can be also applied by operating the desulfurization unit at higher capacity than its design capacity without exceeding the hydraulic and safety limits. By admixing a suitable amount of heavier fraction into the diesel boiling range fraction such that the capacity of the hydrodesulfurization unit can still be utilized without surpassing its maximum capacity limits (i.e. hydraulic and safety limits) calculated at initial design thereof, i.e. up to around 110% of the normal capacity of a hydrodesulphurization unit. Hence, an increase in T95 distillation temperature of a hydrocarbon mixture can be achieved to perform the method according to the present invention, along with increasing unit feed rate into an existing hydrodesulfurization unit in a refinery. The main advantage obtained in this case is conversion of a heavy fraction of low economical value hydrocarbons with regard to a diesel boiling range fraction into higher economical value diesel boiling range products. Thus, heavier fractions are partly included into diesel boiling range fractions and a more economical use of heavier fractions is achieved. The heavier fraction having lower economical value with regard to diesel is directed to increase the overall diesel production in a refinery, and a greater added value is provided in such refinery.
According to the invention, the weight ratio of heavy stream in the feedstock to the diesel range stream in the feedstock is within the range between 0.5:10 and 1.5:10; and preferably within the range between 0.5:10 and 1:10. This provides prevention of heavier hydrocarbons in the product and further costs arising due to separation requirement of heavier hydrocarbons and diesel boiling range hydrocarbons is avoided by setting upper limits to heavy stream content in the feedstock (i.e. the hydrocarbon mixture). Additionally, in case of violating the upper limits to heavy stream, the operating temperature of the reactor system is to be increased in order to produce diesel without heavy hydrocarbons, thereby the cracking level of lighter products increases. This results in reducing diesel production.
The reactor system to be employed for the method according to the present invention can be arranged by including hydrocracking catalyst into latter stage(s) of a multistage hydrodesulfurization reactor system which can comprise reactor plurality of reactors, or prior to the product outlet of a hydrodesulfurization reactor. In the latter case, ' a single-volume hydrodesulfurization reactor comprises hydrodesulfurization catalysts and successive hydrocracking catalysts with regard to the flow direction of the hydrocarbon mixture in process. In both cases, the reactor system comprises a hydrodesulfurization zone and a successive hydrocracking zone.

EXAMPLE 1:

The example aims only better understanding of the method according to the present invention. The exemplary numerical values are not provided for limiting the scope of the present invention.
Basis: a hydrodesulfurization reactor having a normal capacity designed in accordance with diesel boiling range fraction capacity of 100 tonnes per day, and an operational period of 1 day.
8 to 10 tonnes of heavier fraction is admixed with 100 tonnes of diesel boiling range fraction such that 108 to 110 tonnes of combined hydrocarbon mixture (hydrocarbon mixture to be processed according to the present invention) having an initial T95 distillation temperature within the range of 360°C to 385°C. As the outcome of the method according to the present invention, about 96.8 tonnes of diesel and 13.2 tonnes of lighter hydrocarbon mixture are obtained. Both diesel and said lighter hydrocarbon mixture (i.e. hydrocarbon mixture having a T95 distillation temperature lower than accepted minimum of diesel) represent higher economical value than heavier hydrocarbon fractions having a T95 distillation point higher than 360°C. Thus, 10 tonnes of heavier hydrocarbon fractions are directed to diesel production, and the diesel production is increased by about 1.9 percent with regard to that of a typical hydrodesulfurization process (i.e. 95 tonnes) mentioned in the prior art.
The diesel obtained with the method according to the present invention has a density of 828 kg/m³. This corresponds to about 116.9 m³ diesel production per day, which is about 3.3% volumetric increase in diesel production with regard to a conventional process.

EXAMPLE 2:

The example aims only better understanding of the method according to the present invention. The exemplary numerical values are not provided for limiting the scope of the present invention.
Basis: a hydrodesulfurization unit having a normal capacity designed in accordance with diesel boiling range fraction capacity of 100 tonnes per day, and an operational period of 1 day.
In a first stream of the diesel production process, 10 tonnes of a 100 tonnes diesel boiling range fraction is directed to an existing medium pressure and relatively old hydrodesulfurization unit which is designed in accordance with conventional design concept. Thus, said 10 tonnes of diesel boiling range hydrocarbons which is preferably light portion of diesel boiling range hydrocarbons is processed in said hydrodesulfurization unit; with smaller setup and operational costs. Thus, 9.5 tonnes of diesel and 0.5 tonnes of lighter hydrocarbons are obtained using this process.
In a second stream of the process, parallel to the above first stream, 10 tonnes of heavier fraction is admixed with the remaining 90 tonnes of the diesel boiling range fraction is such that 100 tonnes of combined hydrocarbon mixture (hydrocarbon mixture to be processed according to the present invention) having an initial T95 distillation temperature within the range of 370°C to 395°C. As the outcome of the method according to the present invention, about 88 tonnes of diesel and 12 tonnes of lighter hydrocarbon mixture are obtained.
Upon combining the above mentioned first and second streams, 88+9.5=97.5 tonnes of diesel and 12+5=17 tonnes of lighter hydrocarbons are obtained. Furthermore, 10 tonnes of heavier hydrocarbon fractions are directed to diesel production, and the diesel production is increased by about 2.6 percent with regard to that of a typical hydrodesulfurization unit (i.e. 95 tonnes) mentioned in the prior art.
If the capacity of the hydrodesulfurization unit is already fully utilized, it does not mean that the process of the invention can not be applied. If said capacity is fully utilized, then lighter feed components of the feedstock can be transferred to a lower pressure hydrodesulfurization units, i.e. conventional hydrodesulfurization units, thus extra capacity can be generated in the hydrodesulfurization zone. Thus, heavy fractions can be processed in the mentioned reactor system, thereby increasing the total hydrodesulfurization capacity and diesel production.
The resulting effluent of the hydrocracking zone which is a product including diesel boiling range hydrocarbons and lighter hydrocarbons like naphtha and LPG is sent to a fractionator to obtain the different ranges of products. In contrast to conventional hydrocracking and mild hydrocracking processes, there is no residual or unconverted heavier components in the product stream such that the T95 distillation temperature of the product stream is within the diesel boiling range. In other words, the conversion of the above mentioned heavy stream is 100% and they are completely converted into diesel boiling range hydrocarbons.
With the method according to the present invention, higher boiling range hydrocarbons having lower economical value in comparison with diesel is directed to diesel production process, thus the added value production of refineries is increased.
With the method according to the present invention, hydrogenation activity of hydrodesulfurization catalysts is relatively increased in comparison with that at conventional deep hydrodesulfurization units. Although processing additional heavy feedstock in the reactor system increases the feed density, the density shift, i.e. the density difference between the feedstock (initial density of the hydrocarbon mixture to be processed by the method according to the present invention) and diesel product density, increases with the help of the higher hydrogenation activity, thereby producing lower density diesel. The volume swell that results from lower diesel density corresponds to a higher volumetric diesel production. In parallel with this fact, evaluating the increase in diesel production only in terms of weight can be misleading, since the diesel is sold in volumetric basis and the diesel production is to be also assessed in terms of volume basis.
The increase in T95 distillation temperature of the combined feedstock (hydrocarbon mixture to be processed with the method according to the present invention) may vary depending on the type and amount of the heavy fraction admixed with the diesel boiling range fraction. The aromatic content of the hydrocarbon mixture and the types of the hydrodesulfurization and hydrocracking catalysts also determine the hydrogenation level which affects the yield distribution and diesel density. Furthermore, heavier fractions (i.e. heavy stream) having higher T95 distillation temperatures compared to diesel are converted to diesel boiling range hydrocarbons under less severe conditions, i.e. under 60 bars to 80 bars and 350°C to 450°C, instead of 160 bars to 200 bar and 400°C to 500°C which conditions are employed for hydrocracking in conventional hydrocracking processes for heavy fractions. The product stream of the reactor system can be further directed to a subsequent dewaxing unit for use in winter seasons.
Thus, the below objects are achieved by the composite structure according to the present invention and the proposed method for obtainment thereof:

The above-mentioned shortcomings in the prior art are eliminated,
A volumetrically higher production capacity of diesel boiling range hydrocarbons is achieved,
The mass production capacity of diesel boiling range hydrocarbons in refineries is increased,
The added value production at petroleum refineries is increased
T95 distillation temperature of a feed stock is reduced by converting heavier hydrocarbon fractions into diesel boiling range hydrocarbons under less severe conditions in comparison with conventional hydrocracking processes for hydrocracking of such heavier hydrocarbon fractions.

Claims

A method for production of diesel from a hydrocarbon mixture having an initial T95 distillation temperature within the range between 360°C and 420°C,
using a continuous reactor system which comprises the following features:
the reactor system temperature is within the range of 350°C and 450°C, the hydrogen partial pressure within the reactor system is within the range of 60 bar and 80 bar,

the reactor system comprises a hydrodesulfurization zone comprising hydrodesulfurization catalyst,

the reactor system further comprises a hydrocracking zone comprising a hydrocracking catalyst,

wherein said method comprises the following sequential steps:
a) preparation of a hydrocarbon mixture by admixing a diesel range stream having a T95 distillation temperature of maximum 360°C with a heavy stream having a T95 distillation temperature higher than 360°C, the weight ratio of diesel range stream to the heavy stream being within the range between 10:0.5 and 10:1.5, and the initial T95 distillation temperature of the hydrocarbon mixture is within the range between 375°C and 395°C;

b) feeding the hydrocarbon mixture into the reactor system,

c) forwarding the hydrocarbon mixture such that the hydrocarbon mixture flows through the hydrodesulfurization zone,

d) forwarding the hydrocarbon mixture such that said hydrocarbon mixture flows through the hydrocracking zone.
A method according to the Claim 1, wherein said method further comprises a step of forwarding the hydrocarbon mixture from the reactor system into a fractionator, subsequent to the step 'd)', such that diesel boiling range hydrocarbons are separated from lighter hydrocarbons.
A method according to the Claim 1, wherein the initial T95 distillation temperature of the hydrocarbon mixture is within the range between 380°C and 390°C.
A method according to the Claim 1, wherein the space velocity of the hydrocarbon mixture within the reactor system is within the range of 0.5 h^-1 and 3 h^-1.
A method according to the Claim 4, wherein the space velocity of the hydrocarbon mixture within the reactor system is within the range of 1 h^-1 and 2 h^-1.
A method according to the Claim 1, wherein the initial gas to oil ratio of the hydrocarbon mixture is within the range of 300 Nm³/m³ and 1000 Nm³/m³.
A method according to the Claim 6, wherein the initial gas to oil ratio of the hydrocarbon mixture is within the range of 600 Nm³/m³ and 850 Nm³/m³.
A method according to the Claim 1, wherein the reactor system further comprises a quench zone between the hydrodesulfurization zone and the hydrocracking zone, and preferably said hydrodesulfurization zone and/or the hydrocracker zone comprises one or more inter-quench zones.
A method according to the Claim 1, wherein said heavy stream is selected from the list consisting of a heavy fraction of atmospheric gas oil (AGO), light vacuum gas oil (LVGO), a light fraction of the heavy vacuum gas oil (HVGO), visbreaker gas oil (VBGO) and FCC light cycle oil (LCO) and a mixture thereof.
A method according to the Claim 1, wherein said hydrodesulphurization catalyst is selected from the list consisting of NiMo on alumina, CoMo on alumina, and a mixture thereof.
A method according to the Claim 1, wherein said hydrocracking catalyst comprises a silica-based or alumina-based catalyst having metallic sites selected from the list consisting of Nickel, Wolfram, Cobalt and a mixture thereof.
A method according to the Claim 1, wherein the weight ratio of heavy stream to the diesel range stream is within the range between 0.8:10 and 1:10.
A method according to the Claim 1 or Claim 2, wherein said method further comprises a dewaxing step, such that the product stream of the reactor system is directed to a subsequent dewaxing unit.