Process for reducing the acidity of hydrocarbon mixtures

Abstract

Process for reducing acidity in hydrocarbon mixtures, through thermal treatment of hydrocarbon streams, such as petroleum products, fractions and its derivatives, in the presence of a spent hydrorefinery catalyst, in other words, that has already been used in the Hydrotreatment units (HDT) of a refinery.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon, claims the benefit of, priority of, and incorporates by reference, the contents of Brazilian Patent Application No. PI 0403556-9 filed Aug. 26, 2004.

SCOPE OF THE INVENTION

The scope of the invention for the present application is found among processes to reduce the acidity of hydrocarbon mixtures. Preferably, within the processes that involve treatment of hydrocarbon mixtures such as, for example, petroleum products, their fractions and derivatives, in the presence of compounds capable of reducing the acid concentration in said mixtures.

DESCRIPTION OF THE STATE OF THE ART

Newly discovered oil reservoirs possess characteristics that are quite peculiar. The predominance of heavy fractions with high content of contaminants and acidity has been a challenge for petroleum processing companies, in the sense of being able to rapidly adapt processing units to the new qualities of petroleum streams. The adequacy of industrial units as well as pipes and metal equipment is dependent on the distribution of naphthenic acids in petroleum fractions. This distribution is subject to change such as the processing of petroleum streams coming from the new wells.

The high acid content not only affects the processing of petroleum products and their fractions but also influences the marketing of crude oil. Currently, it is known that the market devalues the price of raw materials in an amount ranging between US$ 0.50 and US$ 0.70 per barrel per unit with a total acid number (TAN) of over 0.5 mg KOH/g of oil.

Furthermore, with the increase in the production of heavier oils, it makes it that much more problematic to separate water/oil emulsions. The polar character of carboxyls present favors the formation of emulsions that reduce the efficiency of the desalting stage of petroleum. Therefore, reducing acidity is a critical stage not only in terms of costs, but also in the refining process.

Some patents protect processes for reducing the acidity of petroleum and derivatives. One of the first approaches would be to use oil mixtures with different levels of acidity.

The application of corrosion inhibitors is another solution used to work around the problem of acidity. In this vein, the North American patent U.S. Pat. No. 5,182,013 contends that organic polysulphides are inhibitors effective against corrosion caused by naphthenic acids in refinery distilling units.

North American patent U.S. Pat. No. 4,647,366 recommends adding an alkynediol and a polyalkylene polyamine as inhibitors to naphthenic corrosion.

Acidity may be reduced even by treating oil with alkaline solutions of sodium hydroxide or potassium hydroxide, as discussed in North American patent U.S. Pat. No. 4,199,440. However, this approach demands the use of very concentrated alkaline solutions. In this case, the formation of emulsions that cause separation difficulties is a critical point. Therefore this solution would be applicable only for low basic concentrations.

Treatment with a calcium sulphonate or naphthenate based alkaline detergent is recommended in North American patent U.S. Pat. No. 6,054,042 to work around the problem of emulsions. The oil is treated at temperatures between 100° C. and 170° C. with stoichiometric proportions of calcium for acid functionality in the oil of close to 0.025:1 up to 10:1 moles, or 0.25:10:1, or other proportions.

The North American patent U.S. Pat. No. 6,258,258 recommends the use of polymeric amines, such as polyvinyl pyridine, with the purpose of reducing acid content of petroleum.

Patent U.S. Pat. No. 4,300,995 recommends treatment of carbon and liquids obtained from carbon, coming from vacuum gas oil and petroleum sediment that introduce acidic functionalities, with alkaline solutions of quaternary ammonium hydroxides in alcohol or water, such as hydroxide of tetramethylammonium.

International patent WO01/79386 uses an alkaline solution with group IA, IIA metal and ammonium hydroxides and the application of a transfer agent such as, for example, non-alkaline quaternary salts and polyethers. North American patent U.S. Pat. No. 6,190,541 already uses bases and/or phosphates with an alcohol.

In North American patent U.S. Pat. No. 6,086,751, naphthenic acidity is reduced through the application of a thermal treatment. The oil is initially submitted to a heating process in a reactor with a short dwell time to remove water and then is submitted to temperatures of between 340° C. and 420° C., with a pressure lower than 100 psig and reaction times of up to 2 hours.

In the North American patent U.S. Pat. No. 5,985,137, the naphthenic acidity and the sulphur content of the oil are reduced through the reaction with alkaline-earth metal oxides, forming neutralized and alkaline-earth metal sulfide compounds. The temperature must be higher than 150° C. to remove the carboxylic acids and higher than 200° C. for the sulphide salts to form. The pressure applied must keep the material from vaporizing. In general, the majority of the methodologies for reducing naphthenic acidity involving thermal treatments with or without the addition of alkaline solutions demand the application of surfactantes to work around the problem of emulsions.

Another approach is the adsorption of the naphthenic acid through adsorbent compounds with catalytic properties, under temperatures between 200° C. and 500° C., followed by the recovery of the related adsorbent agent. North American patent U.S. Pat. No. 5,389,240 describes a process for removing naphthenic acids from petroleum streams like kerosene in the presence of a material related to Hydrotalcite called MOSS (“metal oxide solid solution”) in combination with a sweetening process. In order for the material to be adequate for the objectives of the patent, it must be calcinated at about 400° C. The invention disclosed is applicable to streams with extremely reduced naphthenic acid content, with TAN range of 0.01 mg KOH/g of oil to 0.06 mg KOH/g of oil, and may reach up to 0.8 mg KOH/g of oil.

North American patent U.S. Pat. No. 6,027,636 protects the process of elementary sulphur removal and sulphurous contaminants present in refined petroleum products through contact of the fluid containing mercaptans through an adsorbent selected from one of the following: Baierite, Brucite and derivatives of Hydrotalcite.

The use of a hydrotreatment catalyst for the reduction of naphthenic acidity is mentioned in North American patent U.S. Pat. No. 5,871,636. Said patent refers to the use of a VIB and VIIIB transition metal sulphide catalyst, supported in alumina. For example, a cobalt and molybdenum catalyst (KF-756 created by Akzo-Nobel), supported in a matrix of porous alumina with a surface area within a range of between 100 to 300 m²/g which has been sulphonated prior to use. By using this patent in an absence of hydrogen, a maximum reduction of naphthenic acidity of 53% in crude oil having an initial TAN of 4 mg KOH/g of oil is achieved.

In spite of advances in the state of the art in processes to reduce acidity in hydrocarbon mixtures, it is still necessary to develop a process that is more efficient, with lower cost and that minimizes emulsion formation, in order to facilitate the separation of the products.

SUMMARY OF THE INVENTION

The process of reducing acidity in hydrocarbon mixtures, which is the object of this invention, attempts to eliminate partially or wholly the above mentioned drawbacks, through thermal treatment of hydrocarbon streams, such as petroleum products, fractions and its derivatives, in the presence of a spent hydrorefinery catalyst, in other words, that has already been used in the Hydrotreatment units (HDT) of a refinery.

Before or after desalting, the stream of hydrocarbons to be treated is heated first. After the heating stage, said stream is placed in contact, continually, with a fixed bed of spent catalyst from the HDT, without using hydrogen. The pressure must be such that, after the treatment, the stream should be at the normal pressure of the downstream system (desalting or atmospheric distillation). Finally, the treated stream containing a reduced value of TAN follows the conventional flow of oil refining process and the spent catalytic is discarded by the usual method used in conventional Hydrotreatment units.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

The process to reduce acidity in hydrocarbon mixtures, the object of the present invention, will be better understood through the description given below, with example headings, together with the drawings below, which are an integral part of the present report.

FIG. 1 shows a solution for the treatment of hydrocarbon mixtures after passing through the desalting unit, in accordance with the present invention.

FIG. 2 shows a solution for the treatment of hydrocarbon mixtures before passing through the desalting unit, in accordance with the present invention.

FIG. 3 shows a table of TAN x reaction time that illustrates the reduction of the TAN according to the process of reducing acidity described in this report.

DETAILED DESCRIPTION OF THE INVENTION

The process proposed in this invention is founded in the reaction between organic acids and the surface of the spent catalyst, already used in the HDT units, which in other instances was considered as industrial refuse. In this way, the process proposed offers and alternative application for the spent HDT catalyst, considered today to be refuse of extremely low value, a pollutant and hazardous waste material.

The present invention refers to a process to reduce naphthenic acidity of hydrocarbon mixtures such as, for example, petroleum products, their fractions and derivatives that contain TAN that fall within a range of between 1 and 10 mg KOH/g of oil, preferably with TAN that falls within a range of between 1.5 and 8 mg KOH/g of oil, through a thermal treatment in the presence of a spent catalyst from a Hydrotreatment unit. Spent catalyst is understood to mean the catalyst or mixture of catalysts already used in HDT units in a refinery. The referred treatment promotes a reduction of TAN in the load of up to 98%.

The stages of the process include:

• • Heating the hydrocarbon mixture to be treated at temperatures that fall within a range of between 240° C. and 400° C., before or after desalting, with said hydrocarbon mixture presenting high levels of naphthenic acidity.
  • Placing in contact, continually, said hydrocarbon mixture with a fixed bed of spent catalyst coming from a Hydrotreatment unit, at a temperature within the range of 270° C. and 350° C., preferably, at a temperature within the range of 270° C. and 350° C. The pressure must be such that, after the treatment, the hydrocarbon mixture should be at the normal pressure of the downstream system (desalting or atmospheric distillation). The space velocity in the reactor falls in a range of between 0.25 h⁻¹ and 10 h⁻¹, preferably within a range of between 0.5 h⁻¹ and 4 h⁻¹. The catalyst used in this invention is refuse or a mixture of discarded catalysts from Hydrotreatment units, made of transition metals (Co—Mo, Ni—Mo, etc), supported in refracting oxides that may be chosen from any one of the following: alumina, silica, titanium, zirconium and/or mixtures, among others. The spent catalyst may or may not go through an intermediary stripping stage in the presence of an inert gas;
  • Continual withdrawal of the treated hydrocarbon mixture containing a reduced TAN value for later processing in conventional petroleum refinery units; and
  • Disposal of the catalyst at the end of the campaign time, in the usual way used in conventional Hydrotreatment units.

In a typical petroleum refining process, the petroleum, after the thermal exchange with other refinery streams, is sent for desalting and later to a preflash tower to separate the majority of lighter products. The present process to reduce naphthenic acidity of petroleum products and derivatives containing high levels of TAN may be implemented before desalting or after the preflash tower.

The option to implement the oil treatment process after the desalting is shown in FIG. 1. The petroleum stream treatment takes place through the following stages:

• • the liquid effluent (3) from the preflash tower (2) is at a temperature between 260° C. and 280° C. and is transported towards the furnace (4) that raises the temperature of the effluent to a temperature that when it leaves the fixed reactor bed (trickle bed) (6) it will be approximately equal to the normal temperature of a load from the atmospheric distillation tower (8);
  • the effluent (5) from the furnace (4) is then injected into the top of a fixed bed reactor (trickle bed) (6). In this reactor, the stream flows downward and comes into contact with the heated catalyst, where the removal of the naphthenic acids then occurs; and
  • the treated stream (7) is transported to the atmospheric distillation tower (8) that operates in the conventional manner.

The option of processing the petroleum treatment before desalting offers an additional benefit of increasing the probability of breaking down the emulsions, as the hydrocarbon mixtures have their naphthenic acidity reduced. In this case, the non-treated hydrocarbon mixture must be heated additionally with a treated hydrocarbon mixture, so that the non-treated hydrocarbon mixture will rise in temperature and consequently reduce the temperature of the treated hydrocarbon mixture before entering the desalter. To complete heating so that the reactive temperature necessary for treatment is reached, a furnace should be installed before the reactor.

An example of one possible solution is shown in FIG. 2 for the petroleum acidity reduction process. This would be implemented before going to the desalting unit. In this case, said treatment takes place through the following stages:

• • the non-treated petroleum stream (9), coming from the preheating system, enters into a heat exchanger (10), where it is heated, while the treated stream (7) that has left the fixed bed “trickle bed” reactor (6) is cooled until it reaches the operative temperature of the desalter;
  • the non-treated petroleum stream (11), after having recovered the heat released by the cooling of the stream flow from the desalter, still needs to reach the optimal reactive temperature before entering the top of the trickle bed reactor (6). Afterwards, the non-treated heated petroleum stream (11) goes to the furnace (4) which increases the temperature of said non-treated heated petroleum stream (11) to the optimal reactive temperature;
  • after the above stage, the effluent (5) from the furnace (4) then enters into the top of a fixed bed reactor (trickle bed) (6). In this reactor, the stream flows downward and comes into contact with the heated catalyst, where the removal of the naphthenic acids then occurs;
  • the treated stream (7) leaves the fixed bed reactor (trickle bed) (6) at a higher temperature than the desalter. Afterwards, it is necessary to reduce this temperature to the operational temperature of the desalter (1). For this, the treated stream (7) enters into the first heat exchanger (10) where it will be placed in contact with the non treated petroleum stream (9), with the purpose of cooling the treated stream (12) to the temperature of the desalter, and, therefore, acceptable for entry into the desalter.

EXAMPLE 1

In a Parr reactor, a mixture is made consisting of 700 g from a sample of Marlim Leste crude oil (TAN=3.2 mg KOH/g of oil) not yet desalted, and 210 g of the spent catalyst without any additional treatments and coming from an HDT unit. The mixture was warmed until reaching 350° C. and the TAN variation with the time calculated using the ASTM 664 method. The results reached are found in the table in FIG. 3.

According to said table, it is clearly discernable that, using the spent catalyst of HDT/oil ratio of 0.3, after close to 28 minutes, a reduction in TAN of over 84% is obtained as indicated by the arrow (13). Similar results were obtained when dealing with heavier fraction of the stream.

EXAMPLE 2

A hydrocarbon mixture with a TAN of 2.82 mg KOH/g of oil was continuously pumped into a pre-heating system, followed by a pipe reactor with a fixed bed containing a spent HR348 catalyst coming from an HDT unit. The hydrocarbon mixture was processed at 350° C., in the absence of hydrogen and two space velocity conditions were evaluated. After 20 hours, at space velocities of 4 h⁻¹ and 2 h⁻¹, the TAN of the hydrocarbon mixture effluent, calculated by the ASTM 664 method, was reduced by 62.5% and 64.5%, respectively.

The description made here of the process for reducing acidity in hydrocarbon mixture, the object of the present invention, should be considered only as a possibility or possible models, and any particular characteristics introduced herein should be understood only as something that was described to facilitate understanding. In this way, they should not in any way be considered as limitations of the invention, which is limited to the scope of the claims that follow.

Claims

1. Process for the reduction of acidity in hydrocarbon mixture with high total acidity index, through adsorption and the reaction of organic acids on the surface of a catalyst, characterized by the inclusion of the following stages:

heating of the hydrocarbon mixture to be treated;

placing in contact, continually, said hydrocarbon mixture with a fixed bed of spent catalyst coming from a Hydrotreatment unit, at a pressure such that after the treatment, the hydrocarbon mixture will be at the normal pressure of the downstream system;

continual withdrawal of the treated hydrocarbon mixture containing a reduced total acid number (TAN) value of total acidity for later processing in conventional petroleum refinery units; and

disposal of the catalyst at the end of the campaign time, in the usual way used in conventional Hydrotreatment units.

2. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including hydrocarbon mixtures that may be chosen from: petroleum products, their fractions and derivatives.

3. Process to reduce acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including hydrocarbon mixtures that present a total acid number (TAN) that falls within a range of between 1 and 10 mg KOH/g of oil, preferably with a TAN that falls within a range of between 1.5 and 8 mg KOH/g of oil.

4. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including heating of the hydrocarbon mixtures to be treated at temperatures that fluctuate within a range between 240° C. and 400° C., before the desalting stage.

5. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including heating of the hydrocarbon mixtures to be treated at temperatures that fluctuate within a range between 240° C. and 400° C., after the desalting stage.

6. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including contact of the hydrocarbon mixture with a fixed bed of spent catalyst coming from a Hydrotreatment unit at a temperature within the range of 270° C. and 350° C., preferably at a temperature in the range of between 270° C. and 350° C.

7. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as having a space velocity in the reactor falling within a range of between 0.25 h−1 and 10 h−1, preferably within a range of between 0.5 h−1 and 4 h−1.

8. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized by a catalyst used in this invention that is refuse or a mixture of discarded catalysts from Hydrotreatment units, made of transition metals, supported in refracting oxides that may be chosen from any one of the following:

alumina;

silica

titanium;

zirconium; and

mixtures of refracting oxides.

9. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as having an intermediary stripping stage of the spent catalyst coming from a Hydrotreatment unit in the presence of an inert gas.

10. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as being implemented before the desalter.

11. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as being implemented after the preflash tower for removal of the light [products].

12. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized as including a process of additional heating of non-treated hydrocarbon mixtures with a treated hydrocarbon mixture, so as to reduce the temperature of the treated hydrocarbon mixture before they enter the desalter.

13. Process for the reduction of the acidity of hydrocarbon mixtures, in accordance with claim 1, characterized by including a furnace mounted before the reactor so that the reaction temperature necessary for the treatment is attained.