Process for reducing the total acid number in refinery feedstocks

Abstract

A process is described for reducing the total acid number of a refinery feedstock. A refinery feedstock containing naphthenic acids is contacted with an effective amount of solid catalyst that has been pretreated with an aqueous caustic base, for a period of time sufficient to neutralize at least a portion of the naphthenic acids in the feedstock. Thereafter, the aqueous phase is separated from the neutralized refinery feedstock.

Claims

1. A process for reducing the total acid number of a refinery feedstock containing naphthenic acids, the process comprising contacting the refinery feedstock containing naphthenic acids with an effective amount of solid catalyst that has been pretreated with a caustic base for a period of time sufficient and at a temperature of at least 200 C to neutralize at least a portion of the naphthenic acids in the refinery feedstock to produce a treated product having reduced total acid number.

2. The process of claim 1, which further includes adding an emulsion breaking additive to the treated mixture to minimize emulsion formation.

3. The process of claim 2, wherein the emulsion breaking additive is triethanolamine, ethoxylated phenol resins, zinc chloride, or polymerized trithionylamine.

4. The process of claim 1, wherein the solid catalyst is a single or a group of catalysts which exhibit basic properties.

5. The process of claim 1, wherein the solid catalyst comprises at least one metal oxide including one or more materials selected from the group consisting of zinc oxide, aluminum oxide, zinc aluminates, and layered double hydroxides including magnesium/aluminum.

6. The process of claim 1, wherein the refinery feedstock contains carboxylic acids.

7. The process of claim 1, wherein the caustic base is sodium hydroxide or potassium hydroxide.

8. The process of claim 1, wherein the refinery feedstock is supplied with a liquid hourly space velocity in the range of from 0.1 to 10 h.sup.1.

9. The process of claim 1, wherein the refinery feedstock is supplied with a liquid hourly space velocity in the range of from 0.5 to 4 h.sup.4.

10. The process of claim 1, wherein the refinery feedstock is supplied with a liquid hourly space velocity in the range of from 1 to 2 h.sup.4.

11. The process of claim 1, wherein the neutralization reaction is conducted at a temperature in the range of from 200 to 600 C.

12. The process of claim 1, wherein neutralization reaction is conducted at a temperature in the range of from 300 to 400 C.

13. The process of claim 1, wherein neutralization reaction is conducted at a temperature in the range of from 300 to 350 C.

14. The process of claim 1, wherein neutralization reaction is conducted at a pressure in the range of from 1 to 20 Kg/cm.sup.2.

15. The process of claim 1, wherein neutralization reaction is conducted at a pressure in the range of from 1 to 10 Kg/cm.sup.2.

16. The process of claim 14, wherein the pressure is maintained by refinery feedstock pressure alone, without any supply of added overhead or blanketing gas.

17. The process of claim 1, wherein the pretreatment of the solid catalyst is carried out in situ in a neutralization vessel used for contacting the refinery feedstock by, before contacting the refinery feedstock, loading the solid catalyst in the neutralization vessel, passing the caustic base at a temperature and for a period of time effective for pretreatment, and then contacting the refinery feedstock with the solid catalyst that has been pretreated to neutralize naphthenic acids in the refinery feedstock.

18. The process of claim 1, wherein the pretreatment of the solid catalyst is carried out ex situ in a by contacting the solid catalyst in a separate vessel with the caustic base at a temperature and for a period of time effective for pretreatment, and loading the solid catalyst that has been pretreated into a separate vessel for contacting the refinery feedstock with the solid catalyst that has been pretreated to neutralize naphthenic acids in the refinery feedstock.

19. The process of claim 18, wherein the separate vessel for pretreatment of the solid catalyst is a batch vessel or a continuous tubular vessel.

20. The process of claim 1, wherein the solid catalyst comprises zinc oxide.

21. The process of claim 1, wherein the solid catalyst comprises aluminum oxide.

22. The process of claim 1, wherein the solid catalyst comprises zinc aluminates.

23. The process of claim 1, wherein the solid catalyst comprises layered double hydroxides including magnesium/aluminum.

24. The process of claim 1, wherein the solid catalyst comprises at least one metal oxide including one or more materials selected from the group consisting of zinc oxide, zinc aluminates, and layered double hydroxides including magnesium/aluminum.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The foregoing summary as well as the following detailed description will be best understood when read in conjunction with the attached drawing. It should be understood, however, that the invention is not limited to the precise arrangements and apparatus shown.

(2) FIG. 1 is a process flow diagram of a system for reducing the TAN of a refinery feedstock.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring to FIG. 1, a system 10 for reducing the TAN of a refinery feedstock is schematically illustrated. Details such as pumps, instrumentations, heat exchangers, boilers, compressors, and similar hardware have been omitted as being non-essential to understand the techniques involved in this invention. System 10 includes a neutralization vessel 4 and a separator drum 6. Neutralization vessel 4 includes an inlet 3 for receiving a hydrocarbon feedstock via conduit 1 and an aqueous caustic base via conduit 2, and an outlet 5 for discharging a treated mixture. Separator drum 6 includes an inlet 11 for receiving the treated mixture, an outlet 7 for discharging a neutralized hydrocarbon feedstock, an outlet 8 for discharging an aqueous phase, and an outlet 9 for discharging light gases. In certain embodiments, emulsion breaking additives can be incorporated in separator drum 6, e.g., via conduit 12 (shown in dashed lines).

(4) In the practice of the system described herein, a hydrocarbon feedstock containing naphthenic acids introduced via conduit 1 is mixed with an aqueous caustic base introduced via conduit 2. The mixture is charged to the neutralization vessel 4 via inlet 3. Neutralization vessel 4 contains a single catalyst or a group of catalysts. The mixture is brought into contact with the catalyst and maintained in contact for a sufficient period of time to neutralize naphthenic acid compounds present in the hydrocarbon feedstock. The treated mixture is discharged via outlet 5 and passed to separator drum 6 via inlet 11.

(5) The treated mixture is separated into three portions: a neutralized hydrocarbon feedstock having a reduced TAN by neutralization of naphthenic acids, which is recovered as product via outlet 7; an aqueous phase containing spent caustic base discharged via outlet 8; and light gases including H.sub.2S, NH.sub.3 and light hydrocarbon gases (e.g., having carbon numbers between 1 and 4) discharged via outlet 9.

(6) In an additional embodiment the catalyst material contained in neutralization vessel is pretreated with a caustic base, such as sodium hydroxide or potassium hydroxide. In this embodiment, the caustic base and separator drum are not present.

(7) The pretreatment of catalyst can be in situ (e.g., in a neutralization vessel) or ex situ (e.g., in a continuous tubular vessel or batch equipment). In an exemplary embodiment of in situ catalyst preparation, an alumina base catalyst is loaded into the neutralization vessel, and a 50 weight % caustic base solution is heated to 320 C. and fed through the catalyst bed at a liquid hourly space velocity of 0.3 h.sup.1 for 5 to 10 hours. After catalyst pretreatment, feedstock can be charged for neutralization of naphthenic acids. In an exemplary embodiment of ex situ preparation, an alumina catalyst in pellet form is heated to 320 C. in a batch vessel and then mixed with a 50 weight % caustic base solution for 3 hours. The caustic base solution is drained and the solid catalyst particles are dried and loaded into the neutralization vessel.

(8) The refinery feedstock for use in above-described apparatus and process can be a crude or partially refined or fractions of hydrocarbon product obtained from various sources. The source of the refinery feedstock can be naturally occurring crude oil, synthetic crude oil, bitumen, oil sand, shale oil, coal liquids, or a combination including one of the foregoing sources. For example, the feedstock can be naphtha, gas oil, vacuum gas oil or other refinery intermediate stream such as vacuum gas oil, deasphalted oil and/or demetalized oil obtained from a solvent deasphalting process, light coker or heavy coker gas oil obtained from a coker process, cycle oil obtained from an FCC process, gas oil obtained from a visbreaking process, or any combination of the foregoing products. Nonetheless, one of ordinary skill in the art will appreciate that other hydrocarbon streams can benefit from the practice of the herein described system and method.

(9) The aqueous caustic base can be sodium hydroxide or potassium hydroxide. In certain embodiments, the amount of caustic base supplied through conduit 2 is in the range of from 0.05 to 30 weight % based on the weight of the catalyst.

(10) Neutralization vessel 4 can be a fixed, moving, fluidized, or swing bed system. In certain embodiments a fixed bed reactor is suitable. In general, the operating conditions of the neutralization vessel include a pressure in the range of from 1 to 20 Kg/cm.sup.2, in certain embodiments from 1 to 10 Kg/cm.sup.2; a temperature in the range of from 200 C. to 600 C., in certain embodiments from 300 C. to 400 C., and in further embodiments from 300 C. to 350 C.; and a liquid hourly space velocity of the refinery feedstock in the range of from 0.1 to 10 h.sup.1, in certain embodiments from 0.5 to 4 h.sup.1, and in further embodiments from 1 to 2 h.sup.1. In certain embodiments, pressure within the neutralization vessel can be maintained by the hydrocarbon pressure alone, without any supply of added overhead or blanketing gas.

(11) The neutralization vessel contains catalysts having basic properties. In certain embodiments the catalyst comprises at least one metal oxide selected from the group consisting of zinc oxide, aluminum oxide, zinc aluminates, and layered double hydroxides including magnesium/aluminum. The catalyst is in the form of pellets, spheres, or any other suitable shape. Generally, catalyst particle size and shape are chosen, as is known in the art, in such a manner as to prevent undue pressure drop across the bed, yet permit adequate diffusion of reactants to active sites on the catalyst surface of within the catalyst particle.

(12) In certain embodiments, demulsifier additives can be added to separator drum 6 to efficiently separate oil and water. These emulsion breaking additives may be selected from the group consisting of triethanolamine, ethoxylated phenol resins, zinc chloride and polymerized trithionylamine.

(13) The process described herein can be conducted at various stages in refinery operations or upstream. For instance, the process can be implemented to treat influent feedstock in a refinery or fractions thereof. In alternative embodiments, the process can be implemented upstream of or within a gas oil separation plant, for instance, downstream of desalting stages.

(14) The method and system herein have been described above and in the attached drawing; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.