Method to Valorize Middle Distillate Streams from Crude Oils

The present disclosure relates to methods of evaluating middle distillate samples.

In a refinery, crude oil is typically fractionated into one or more fractions such as light gases, light naphtha streams, heavy naphtha streams, middle distillates, vacuum gas oil, and vacuum residue fraction. The middle distillates from the crude oil distillation include fractions such as gas oils and can be blended into diesel fuels, jet fuels and/or furnace oils, directly or following hydrotreating to obtain ultra-low sulfur diesel. Several properties of gas oil and diesel streams can be evaluated, including API gravity, sulfur, nitrogen, carbon and hydrogen contents, and cetane number. For diesel engines, the fuel must have characteristics that favor auto-ignition. The ignition delay period can be evaluated by the fuel characterization factor called cetane number (CN). The behavior of a diesel fuel is measured by comparing its performance with two pure hydrocarbons: the first is n-cetane or n-hexadecane (n-CH) which has a cetane number 100, and the second is α-methylnaphthalene which has a cetane number of 0. As an example, a diesel fuel has a cetane number of 60 if it behaves like a binary mixture of 60 vol % n-cetane or n-hexadecane and 40 vol % α-methylnaphthalene. Sometimes in practice, heptamethylnonane (HMN) is used instead of α-methylnaphthalene. HMN is a branched isomer of n-cetane and has a cetane number of 15. Therefore, in practice the cetane number can be defined as:

The cetane number of a diesel fuel can be measured in a laboratory by various test methods, for example, the ASTM D613 test method. The shorter the ignition delay period a diesel fuel has, the higher its cetane value is. Higher cetane number fuels reduce combustion noise and permit improved control of combustion resulting in increased engine efficiency and power output. Higher cetane number fuels help with easier starting and faster warm-up in cold weather and can also help reduce air pollution.

It is very difficult to evaluate the diesel streams based on their hydrocarbon distributions. Rather, all the diesel fractions must be brought to a commercial product stream for evaluation purposes. In regard to the above background information, the present disclosure is directed to provide a technical solution for effective methods and systems for evaluating middle distillates.

In certain embodiments, a method for evaluating a middle distillate sample is provided. The method comprises analyzing the middle distillate sample to determine a sample sulfur concentration. The middle distillate sample can optionally be analyzed to also determine a sample cetane number. A target sulfur concentration of a target product stream from a reactor under design for hydrodesulfurization of a feedstock consisting of the middle distillate sample is provided. The reactor under design can include a defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. A sulfur conversion to achieve the target sulfur concentration of the target product stream is calculated as a function of the sample sulfur concentration and the target sulfur concentration. This can be done by dividing the difference in sulfur concentration of the middle distillate sample and the target product stream by the sulfur concentration of the middle distillate sample. A sample requisite hydrogen partial pressure in the reactor under design is determined as a function of the sulfur conversion, wherein the sample requisite hydrogen partial pressure is determined experimentally or by simulation. A severity index is calculated as a function of the sample requisite hydrogen partial pressure. This can be done by dividing the requisite hydrogen partial pressure by a reference hydrogen partial pressure, wherein the reference hydrogen partial pressure is a required hydrogen partial pressure for hydrodesulfurization of a feedstock consisting of a reference middle distillate to achieve approximately the target sulfur concentration with approximately the defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio.

In some embodiments, the sample requisite hydrogen partial pressure is determined by simulation. In these embodiments, the process includes the step of analyzing the middle distillate sample to determine a sample cetane number.

In some embodiments, the process also includes providing a computer comprising a processor coupled to a non-volatile memory, wherein the non-volatile memory stores calculation modules and data. Data including the sample sulfur concentration and optionally the sample cetane number is entered into the computer.

In certain embodiments, a method for evaluating a middle distillate sample is provided. The method comprises analyzing the middle distillate sample to determine a sample cetane number. The middle distillate sample can optionally be analyzed to also determine a sample sulfur concentration. A target cetane number of a target product stream from a reactor under design for hydrotreatment of a feedstock consisting of the middle distillate sample is provided. The reactor under design can include a defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. A cetane number improvement to achieve the target cetane number of the target product stream is calculated as a function of the sample cetane number and the target cetane number. This can be done by taking the cetane number of the target product stream and subtracting the cetane number of the middle distillate sample. A sample requisite hydrogen partial pressure in the reactor under design is determined as a function of the cetane number improvement, wherein the sample requisite hydrogen partial pressure is determined experimentally or by simulation. A severity index is calculated as a function of the sample requisite hydrogen partial pressure. This can be done by dividing the requisite hydrogen partial pressure by a reference hydrogen partial pressure, wherein the reference hydrogen partial pressure is a required hydrogen partial pressure for hydrotreatment of a feedstock consisting of a reference middle distillate to achieve approximately the target cetane number with approximately the defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio.

In some embodiments, the sample requisite hydrogen partial pressure is determined by simulation. In these embodiments, the process includes analyzing the middle distillate sample to determine a sample sulfur concentration.

In some embodiments, the process also includes providing a computer comprising a processor coupled to a non-volatile memory, wherein the non-volatile memory stores calculation modules and data. Data including the sample cetane number and optionally the sample sulfur concentration is entered into the computer.

In certain embodiments, a method for evaluating a middle distillate sample is provided. The method comprises analyzing the middle distillate sample to determine a sample sulfur concentration and a sample cetane number. A target sulfur concentration and target cetane number of a target product stream from a reactor under design for hydrodesulfurization and hydrotreatment of a feedstock consisting of the middle distillate sample is provided. The reactor under design can include a defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. A sulfur conversion to achieve the target sulfur concentration of the target product stream is calculated as a function of the sample sulfur concentration and the target sulfur concentration. This can be done by dividing the difference in sulfur concentration of the middle distillate sample and the target product stream by the sulfur concentration of the middle distillate sample. A cetane number improvement to achieve the target cetane number of the target product stream is calculated as a function of the sample cetane number and the target cetane number. This can be done by taking the cetane number of the target product stream and subtracting the cetane number of the middle distillate sample. A sample requisite hydrogen partial pressure in the reactor under design is determined as a function of the sulfur conversion and cetane number improvement, wherein the sample requisite hydrogen partial pressure is determined experimentally or by simulation. A severity index is calculated as a function of the sample requisite hydrogen partial pressure. This can be done by dividing the requisite hydrogen partial pressure by a reference hydrogen partial pressure, wherein the reference hydrogen partial pressure is a required hydrogen partial pressure for hydrodesulfurization of a feedstock consisting of a reference middle distillate to achieve approximately the target sulfur concentration and target cetane number with approximately the defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio.

In some embodiments, the sample requisite hydrogen partial pressure is determined by simulation.

In some embodiments, the process also includes providing a computer comprising a processor coupled to a non-volatile memory, wherein the non-volatile memory stores calculation modules and data. Data including the sample cetane number and the sample sulfur concentration is entered into the computer.

In some embodiments the hydrotreating process is hydrogenation, hydrocracking, or both.

In some embodiments, the sulfur conversion is calculated by the following equation (as a fraction conversion, where a weight percent conversion is calculated by multiplying the below quotient by 100):

In some embodiments, the cetane number improvement (point value improvement) is calculated by the following equation:

In some embodiments, the severity index of the middle distillate sample is calculated with the following equation:

In some embodiments, the process also includes calculating a relative cost to process the feedstock consisting of the middle distillate sample by the following equation:

where C1 is the cost to process the reference feedstock, C2 is the projected cost to process the feedstock consisting of the middle distillate sample, and n is a number in the range of about 0.6-0.8.

In some embodiments, the process also includes calculating a plurality of severity indices corresponding to a plurality of middle distillate samples to produce a database of severity indices. In these embodiments, the severity index of each of the middle distillate samples in the plurality of middle distillate samples is calculated as a function of the sample requisite hydrogen partial pressure. This can be done by dividing a requisite hydrogen partial pressure by a reference hydrogen partial pressure, wherein the reference hydrogen partial pressure is a required hydrogen partial pressure for hydrodesulfurization, hydrotreatment or both hydrodesulfurization and hydrotreatment of a feedstock consisting of a reference middle distillate to achieve approximately the target sulfur concentration, target cetane number or both the target sulfur concentration and cetane number with approximately the defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. In these embodiments, the requisite hydrogen partial pressure of each of the middle distillate samples in the plurality of middle distillate samples is determined as a function of a sulfur conversion, a cetane number improvement or both a sulfur conversion and a cetane conversion. The sample requisite hydrogen partial pressure can be determined experimentally or by simulation.

In some embodiments, a ranking value for the middle distillate sample is assigned by comparing the severity index value for the middle distillate sample and the database of severity indices.

In some embodiments, the middle distillate sample has a sulfur content in the range of about 100-50,000 ppmw sulfur.

In some embodiments, the target sulfur content of the target product stream is in the range of about 10-1,000 ppmw.

In some embodiments, the middle distillate feedstock has a boiling range in the range of about 150° C. to 400° C.

In some embodiments, a crude oil is fractionated into one or more streams, wherein the middle distillate sample is one of the streams. In some embodiments, the one or more streams further includes one or more of light gases, a light naphtha stream, a heavy naphtha stream, a vacuum gas oil, and a vacuum residue fraction. In some embodiments, the fractionation is by atmospheric distillation, vacuum distillation, or both.

In some embodiments, the plurality of middle distillate samples is obtained from fractionating a plurality of crude oils. In some embodiments, the plurality of crude oils is from one or more sources of crude oil.

Any combinations of the various embodiments and implementations disclosed herein can be used. These and other aspects and features can be appreciated from the following description of certain embodiments and the accompanying drawings and claims.

The present disclosure provides a system and method that can compare plural middle distillate streams to determine rank valuation to give the refiner a basis for determining which stream may be processed first. Also, present disclosure provides a system and method for evaluation of middle distillate streams derived from crude oils from various sources to establish an objective basis for comparison. Systems and methods herein evaluate a middle distillate sample by determining the hydrogen partial pressure requirements in a reactor under design for processing a feedstock consisting of the middle distillate sample to achieve a target sulfur concentration and/or cetane number in a target product stream.

In certain embodiments, the term “middle distillate” is used with reference to one or more fractions containing hydrocarbons having a nominal boiling range of about 160-400, 160-380, 160-370, 160-360, 160-340, 170-400, 170-380, 170-370, 170-360, 170-340, 180-400, 180-380, 180-370, 180-360, 180-340, 190-400, 190-380, 190-370, 190-360, 190-340, 193-400, 193-380, 193-370, 193-360, or 193-340° C. In certain embodiments, the term “straight run middle distillate” is used with reference to one or more straight run fractions from the atmospheric distillation unit. In embodiments in which other terminology is used herein, the middle distillate fraction can also include all or a portion of atmospheric gas oil range hydrocarbons, all or a portion of kerosene, all or a portion of medium atmospheric gas oil range hydrocarbons, and/or all or a portion of heavy kerosene range hydrocarbons. The term “atmospheric gas oil” and its acronym “AGO” as used herein refer to hydrocarbons having a nominal boiling range of about 250-400, 250-380, 250-370, 250-360, 250-340, 250-320, 260-400, 260-380, 260-370, 260-360, 260-340, 260-320, 270-400, 270-380, 270-370, 270-360, 270-340 or 270-320° C. The term “kerosene” as used herein refers to hydrocarbons having a nominal boiling range of about 160-280, 160-270, 160-260, 170-280, 170-270, 170-260, 180-280, 180-270, 180-260, 190-280, 190-270, 190-260, 193-280, 193-270 or 193-260° C. The term “heavy kerosene” as used herein refers to hydrocarbons having a nominal boiling range of about 225-280, 225-270, 225-260, 230-280, 230-270, 230-260, 235-280, 235-270, 235-260 or 250-280° C. In additional embodiments, term “middle distillate” is used to refer to fractions from one or more integrated operations boiling in this range.

shows a process flowchart of a method of one or more embodiments. A middle distillate sample is analyzed in step. In some embodiments, the sample is analyzed according to any known test methods to determine the sulfur content of the sample and/or the cetane number of the sample.

In step, one or more properties of a target product stream from a reactor under design for hydrodesulfurization and/or hydrotreatment of a feedstock consisting of the middle distillate sample is provided. The reactor under design can include a defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. In some embodiments, the property of the target product stream is target sulfur concentration, target cetane number, or both. In some embodiments, the hydrotreating reaction is hydrogenation, hydrocracking, or both. In step, a conversion and/or improvement value is calculated.

In some embodiments, the conversion and/or improvement value calculated in stepis the sulfur conversion that is required to achieve the target sulfur concentration of the target product stream. The sulfur conversion is calculated as a function of the sample sulfur concentration and the target sulfur concentration, specifically, by dividing the difference in sulfur concentration of the middle distillate sample and the target product stream by the sulfur concentration of the middle distillate sample. The sulfur conversion can be calculated by the following equation (as a fraction conversion, where a weight percent conversion is calculated by multiplying the below quotient by 100):

In some embodiments, the conversion and/or improvement value calculated in stepis the cetane number improvement that is required to achieve the target cetane number of the target product stream, as a function of the sample cetane number and the target cetane number, by taking the cetane number of the target product stream and subtracting the cetane number of the middle distillate sample. The cetane number improvement (point value improvement) can be calculated by the following equation:

In step, the hydrogen partial pressure that is required for the hydrodesulfurization and/or hydrotreating reaction of the middle distillate sample to achieve the required sulfur concentration and/or cetane number is determined. This determination can be done experimentally or by simulation.

In some embodiments where the determination of the requisite hydrogen partial pressure is done experimentally, in step, the sample is analyzed to determine the sulfur concentration of the sample and optionally the cetane number. In some embodiments where the determination of the requisite hydrogen partial pressure is done experimentally, in step, the sample is analyzed to determine the cetane number of the sample and optionally the sulfur concentration.

In some embodiments where the determination of the requisite hydrogen partial pressure is done by simulation, in step, the sample is analyzed to determine the sulfur content and the cetane number.

In step, a severity index is calculated as a function of the sample requisite hydrogen partial pressure, by dividing the requisite hydrogen partial pressure by a reference hydrogen partial pressure. The reference hydrogen partial pressure is a required hydrogen partial pressure for hydrodesulfurization and/or hydrotreatment of a feedstock containing a reference middle distillate to achieve approximately the target sulfur concentration and/or cetane number with approximately the defined temperature, liquid hourly space velocity, catalyst age and hydrogen to oil ratio. In some embodiments, the severity index can be calculated by the following equation:

In step, the relative cost to process a feedstock containing the middle distillate sample is calculated by the following equation:

where C1 is the cost to process the reference feedstock, C2 is the relative cost to process the middle distillate feedstock, and n is a number in the range of about 0.6-0.8.

is a flowchart showing details about the middle distillates analysis step, as described in. In some embodiments, a feed such as crude oilis separated in unitinto one or more streams including middle distillates stream. Optional streams,,,andcan also be separated from crude oil. Streamcan include light gases like C2-C4 hydrocarbons such as ethane, propane and butanes. Streamis a naphtha stream and streamis a heavy naphtha stream. Streamincludes vacuum gas oil and streamis a vacuum residue fraction. Separation unitcan be any known separation unit and can include an atmospheric distillation unit and a vacuum distillation unit. The feedcan be crude oil, or the feed can be crude oil that has been subjected to hydrotreating (hydrotreated crude oil), solvent deasphalting (deasphalted oil) or coking, such as delayed coking (coker liquid and gas products).

A middle distillate sample obtained from the middle distillates streamis analyzed according to the process herein, represented as step. It is to be appreciated that the middle distillate characteristics are determined by the source and characteristics of the crude oil.