ADDITIVES FOR REDUCING COKING OF FURNACE TUBES

Abstract

Fouling of hot furnace surfaces in selected refinery processes can be stopped or at least mitigated using an antifouling agent. The antifouling agents include sulfurized oil and may include other components selected from the group consisting of magnesium and aluminum overbases, a-olefin copolymers, and combinations thereof. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b)

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application Ser. No.: 61/235957, filed Aug. 21, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to additives useful for reducing fouling in furnaces. The present invention particularly relates to sulfur based additives useful for reducing fouling in furnaces.

2. Background of the Art

Petrochemical plants, which include both Chemical Production Installations as well as Oil Refineries, are known to employ two basic types of furnaces. The first of these is a steam cracker furnace. Steam crackers are used in applications including the production of ethylene. The second of these is a “steam reformer” furnace, which can be used to make hydrogen. Both types of furnaces include a number of tubes, generally arranged vertically, that form a continuous flow path, or coil, through the furnace. The flow path or coil includes an inlet and an outlet. In both types of furnaces, a mixture of a hydrocarbon feedstock and steam are fed into the inlet and passed through the tubes. The tubes are exposed to extreme heat generated by burners within the furnace. As the feedstock/steam mixture is passed through the tubes at high temperatures the mixture is gradually broken down such that the resulting product exiting the outlet is ethylene in the case of a steam cracker furnace and hydrogen in the case of a steam reformer furnace.

Other types of furnaces may also be used, but the one element that they have in common is the passing of a feed material through a flow path that is subject to heat from a burner or other heat source. The deposit of any insulating material on the heat exchange surfaces of the flow path can be undesirable in that it can result in increased energy costs as temperatures are increased to overcome the effect of the insulating deposits and increase operational costs when the furnaces are shut down for periodic cleaning of the heat exchanging surfaces. It would therefore be desirable in the art of manufacturing products using processes which include subjecting hydrocarbon streams to heat to avoid or mitigate the formation of fouling deposits on heat exchanging surfaces.

SUMMARY OF THE INVENTION

In one aspect the invention is a process for reducing furnace fouling comprising treating a furnace feed stream with an antifouling agent wherein the antifouling agent comprises sulfurized oil.

In another aspect, the invention is an additive useful for reducing furnace fouling comprising sulfurized oil.

In still another aspect the invention is an admixture of a furnace feed material and an additive useful for reducing furnace fouling comprising sulfurized oil. Exemplary of such an admixture is a hydrocarbon feed stream for a coking or visbreaking process and a sulfurized oil antifouling additive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment, the present invention is an antifouling agent comprising sulfurized oil. The sulfurized oil useful with the process of the disclosure may, in one embodiment, include sulfurized polyolefins. The sulfurized oil, for example a sulfurized triisobutylene, may be prepared by a process including the steps of (a) mixing a mole ratio of triisobutylene to sulfur of between about 1:2.5 and 1:5 at between 50 and 100° F.; (b) continuously blowing the resultant mixture with an inert gas under continuous pressure and under elevated temperatures until the free sulfur weight in the said resultant reaction mixture is less than 0.3 weight percent; (c) stripping the blown mixture with inert gas at an elevated temperature at sub-atmospheric pressure; and (d) filtering the stripped product.

Other polyolefins may also be used. Differing ratios of reactants and process conditions may be used to prepare the sulfurized oil. Any method known to those of ordinary skill in the art to prepare such materials may be used.

Other forms of sulfurized oil useful with the disclosure include, but are not limited to: sulfurized lard, sulfurized fish oil, sulfurized whale oil, sulfurized soybean oil, sulfurized pinene oil, sulfurized sperm oil, sulfurized fatty acid, 1,3,4-thiadiazol derivatives, thiuram disulfide, dithiocarbamate ester, and the like. Compounds having the general formula:

R—S_X—R

Wherein: X is 1 or 2, each R is independently an alkyl group, a cyclic alkyl group, an olefin, or a polyolefin group, may be used as the sulfurized oil useful with the disclosure.

In some embodiments of the invention, antifouling agents of the application include magnesium and aluminum overbases. These overbases and dispersions are soluble in hydrocarbons, even though it is generally harder to get these additives dispersed in hydrocarbon as contrasted with aqueous systems. In some embodiments, the metal overbases contains at least about 1 wt % magnesium or aluminum. In an alternative embodiment, the additive contains about 5 wt % metal, in another non-limiting embodiment, the amount of metal or alkali earth metal is at least about 17 wt %, and in a different alternate embodiment, at least about 40 wt %.

In one non-limiting embodiment, the metal overbase is made by heating a tall oil with magnesium hydroxide. In another embodiment the overbases are made using aluminum oxide. In still another embodiment, dispersions are made using magnesium oxide or aluminum oxide. Dispersions and overbases made using other metals would be prepared similarly. In one non-limiting embodiment the target particle size of these dispersions and overbases is about 10 microns or less, alternatively about 1 micron or less. It will be appreciated that all of the particles in the additive are not of the target size, but that a “bell-shaped” distribution is obtained so that the average particle size distribution is 10 μ or less, or alternatively 1 μ, or less.

The metal dispersions or complexes useful in some embodiments of the invention may be prepared in any manner known to the prior art for preparing overbased salts, provided that the overbase complex resulting there from is in the form of finely divided, and in one non-limiting embodiment, submicron particles which form a stable dispersion in the hydrocarbon feed stream. Thus, one non-restrictive method for preparing the additives of the present invention is to form a mixture of a base of the desired metal, e.g., Mg(OH)₂, with a complexing agent, e.g. a fatty acid such as a tall oil fatty acid, which is present in a quantity much less than that required to stoichiometrically react with the hydroxide, and a non-volatile diluent. The mixture is heated to a temperature of about 250-350° C., whereby there is afforded the overbase complex or dispersion of the metal oxide and the metal salt of the fatty acid. The above described method of preparing the overbase complexes of the present invention is particularly set forth in U.S. Pat. No. 4,163,728 which is incorporated herein by reference in its entirety, wherein for example, a mixture of Mg(OH)₂ and a carboxylic acid complexing agent is heated at a temperature of about 280-330° C. in a suitable non-volatile diluent.

Complexing agents which may be used include, but are not necessarily limited to, carboxylic acids, phenols, organic phosphorus acids and organic sulfur acids. Included are those acids which are presently used in preparing overbased materials (e.g. those described in U.S. Pat. Nos. 3,312,618; 2,695,910; and 2,616,904, ALL fully incorporated herein by reference) and constitute an art-recognized class of acids. The carboxylic acids, phenols, organic phosphorus acids and organic sulfur acids which are oil-soluble per se, particularly the oil-soluble sulfonic acids, are especially useful. Oil-soluble derivatives of these organic acidic substances, such as their metal salts, ammonium salts, and esters (particularly esters with lower aliphatic alcohols having up to six carbon atoms, such as the lower alkanols), can be utilized in lieu of or in combination with the free acids. When reference is made to the acid, its equivalent derivatives are implicitly included unless it is clear that only the acid is intended. Suitable carboxylic acid complexing agents which may be used herein include aliphatic, cycloaliphatic, and aromatic mono- and polybasic carboxylic acids such as the naphthenic acids, alkyl- or alkenyl-substituted cyclopentanoic acids, alkyl- or alkenyl-substituted cyclohexanoic acids and alkyl- or alkenyl-substituted aromatic carboxylic acids. The aliphatic acids generally are long chain acids and contain at least eight carbon atoms and in one non-limiting embodiment at least twelve carbon atoms. The cycloaliphatic and aliphatic carboxylic acids can be saturated or unsaturated.

The metal additives acceptable for the method of the disclosure may also include true overbase compounds where a carbonation procedure has been done. Typically, the carbonation involves the addition of CO₂, as is well known in the art.

The antifouling agents of the method of the disclosure may include a magnesium overbase. In some embodiments, the magnesium overbase is a magnesium carbonate overbase and in other embodiments it is a magnesium sulfonate overbase. In still other embodiments, it may be a mixture of both magnesium sulfonate and magnesium carbonate. Similarly, aluminum sulfonates and carbonates may be used.

The antifouling agents useful with the disclosure may also include a dispersant. Suitable dispersants include, but are not necessarily limited to, copolymers of carboxylic anhydride and alpha-olefins, particularly alpha-olefins having from 2 to 70 carbon atoms. Suitable carboxylic anhydrides include aliphatic, cyclic and aromatic anhydrides, and may include, but are not necessarily limited to maleic anhydride, succinic anhydride, glutaric anhydride, tetrapropylene succinic anhydride, phthalic anhydride, trimellitic anhydride (oil soluble, non-basic), and mixtures thereof. Typical copolymers include reaction products between these anhydrides and alpha-olefins to produce oil-soluble products. Suitable alpha olefins include, but are not necessarily limited to ethylene, propylene, butylenes (such as n-butylene and isobutylene), C₂-C₇₀ alpha olefins, polyisobutylene, and mixtures thereof.

A typical copolymer is a reaction product between maleic anhydride and an alpha-olefin to produce an oil soluble dispersant. A useful copolymer reaction product is formed by a 1:1 stoichiometric addition of maleic anhydride and polyisobutylene. The resulting product has a molecular weight range from about 5,000 to 10,000, in another non-limiting embodiment.

The antifoulants agents of the method of the disclosure may include a sulfurized oil, magnesium overbase and a cc-olefin copolymer. The ratio of the sulfurized oil to the other components may range from about 10:1 to 1:10. In some embodiments, the range may be from about 3:1 to 1:3. In other embodiment, the ratio may be about 1:1.

In some embodiments, it may be desirable to use a solvent. The solvent may be any that is compatible with the antifouling agent components. For example, in one embodiment, the solvent is an aromatic solvent. Any solvent known to those of ordinary skill in the art to be useful for preparing compositions including the antifouling agent components may be used.

The antifouling agents of the disclosure may be used in processes wherein hydrocarbons are contacted with extreme heat to reduce or mitigate fouling. For example, the antifouling agents are particularly useful in furnace feed streams in coking and visbreaking applications. In one embodiment of a visbreaking process, the process takes place in a facility having: (1) a train of exchangers into which the process feed enters for initial pre-heating, (2) followed by a furnace in which thermal cracking takes place, (3) then a fractionating column, from the base of which flows the residue (tar), which passes through (4) the exchangers, transferring part of its heat to the charge. In some applications there is also a “soaker” between the furnace and the fractionating column which increases the time at which the process feed is held at high temperature. The operating conditions of a plant of this kind include a furnace temperature of from about 420 to about 500° C. (in the presence or in the absence of “soaker”, respectively) and a pressure of between 3 and 20 bar. Typically, the process feed is a primary distillation residue or of a vacuum residue. A visbreaking process is typically managed with the aim of obtaining maximum transformation of hydrocarbons into medium and light distillates.

Coking, a term associated with the refining of the heavy bottoms of petroleum, is a process in which the heavy residual bottoms of crude oil are thermally converted to lower-boiling petroleum products and by-product petroleum coke. Delayed coking involves the rapid heating of reduced crude in a furnace and then confinement in a coke drum under proper conditions of temperature and pressure until the unvaporized portion of the furnace effluent is converted to vapor and coke. In either process the feed is typically a very heavy hydrocarbon, often a residue from another process within a refinery.

The anti-fouling agent of the invention may be used with other refinery process as well. For example, the method of the invention may be used with vacuum distillation tower furnaces. The process of the invention may be used in any circumstance where a hydrocarbon feed is being fed through a furnace at temperatures that would induce fouling of the heat exchanging surfaces of the furnace. For the purposes of the invention, these temperatures are those from about 260° C. to about 870° C. Further, also for the purposes of the invention, the term “furnace feed stream” means not just feeds going into a furnace, but rather any circumstances wherein a hydrocarbon is brought into contact with a surface, especially the surface of a heat exchanger, at a temperature of from 260° C. to about 870° C.

The antifouling agents of the invention may be used in any amount that is effective to stop or mitigate fouling. The amount that is necessary will be, to some extent, dependent upon the properties of the hydrocarbon feed in which it will be used. In most cases, the hydrocarbon feed will be a very heavy hydrocarbon feed with a significant tendency to produce fouling. The amount of antifouling agent useful with method of the invention will range, as a weight percent of the hydrocarbon feed (furnace feed stream), of from about 50 ppm to about 10,000 ppm. In one embodiment, the range is from about 100 ppm to about 600 ppm. In another embodiment, the range is from about 250 ppm to about 500 ppm.

The antifouling agents of the invention may be introduced into their target feed material in any way known to be useful to those of ordinary skill in the art of refining crude oil subject to the caveat that the antifouling agents are introduced prior to the feed contacting the surfaces which are to be protected from fouling. For example, in one application of the invention, the antifouling agent is injected into the feed material as they pass through a turbulent section of a coking process. In another application, the antifouling agent is admixed with the feed in holding vessel that is agitated. In still another application, the antifouling agent is admixed with the feed immediately upstream of a furnace by injecting it into a turbulent flow, the turbulent flow being created by static mixers put into place for the purpose of admixing the antifouling agent with a feed material.

The use of the antifouling agents of the disclosure may provide at least two advantages. The less fouling of a furnace, the longer that that furnace may go without service thereby increasing the time between turn-arounds. Further, less fouling may result in more efficient heat transfer resulting in energy savings too.

EXAMPLES

The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

Experimental High Temperature Fouling Test (HTFT) Procedure

Samples of heated coker feed were poured out in pre-weighed 100 mL beakers. The amount of the sample was weighed and recorded. Prior to a HTFT run, the preweighed beaker with coker feed was heated to about 400° F. (204° C.). The base of a Parr pressure vessel was preheated to about 250° F. (121° C.).

The HTFT furnace was heated to the desired temperature, normally 890° F. (477° C.) to 950° F. (510° C.), dependent on the furnace outlet temperature in which the coker feed was processed. When the coker sample, autoclave base, and HTFT furnace had all reached the appropriate test temperature, the sample beaker was placed into the autoclave base and the autoclave top was secured to the base. The closed vessel was then placed into the heated furnace. An automated computer-based test program then recorded the test elapsed time, sample temperature and autoclave pressure every 30 seconds throughout the test run. When the coker feed had reached the desired test temperature, liquid hydrocarbon and vapors were vented from the vessel at predetermined pressure levels until all available liquid/gas hydrocarbons were removed from the coker feed as coking occurs. This process was usually completed in seven to ten minutes after the coker feed test sample reached the set test temperature, i.e. 910° F. (493° C.). Upon cooling, the percent coke solids were recorded.

Coke Stability Index (CSI)

The Coking Stability Index test is used to measure the stability of asphaltenes in furnace feeds via the determination of the onset of asphaltene flocculation point using a solvent titration method. The Coking Stability Index system uses a solids detection system that uses a near infrared (NIR) laser to determine the onset of asphaltene flocculation. Approximately 20 mL of furnace feed mixture is heated. A non-solvent, such as heptane, is then titrated into the solution and the transmittance of the NIR laser monitored. In the initial stages of titration the transmittance of the laser increases due to the decrease in density of the solution resulting from the addition of heptane. When the asphaltenes begin to flocculate, the laser transmittance will decrease. The apex of the curve corresponds to the point of asphaltene precipitation and provides a relative measure of the stability of the feedstock. The higher the CSI, the more stable the coker feed.

EXAMPLES 1 & 2 (& Comparative Example A)

A hydrocarbon sample is tested with the HTFT procedure using sulfurized oil as the sole antifouling agent component at a concentration of 1000 ppm. The percent coke solids are measure and recorded in the Table as Example 1.

A hydrocarbon sample is tested with the HTFT procedure using magnesium sulfonate as the sole antifouling agent component at a concentration of 1000 ppm. The percent coke solids are measure and recorded in the Table as Comparative Example A.

A hydrocarbon sample is tested with the HTFT procedure using magnesium sulfonate (47.6 wt. %), sulfurized polyolefin (30 wt. %) and an organic solvent (22.4 wt%) as the antifouling agent components at a total concentration of 1000 ppm. The percent coke solids are measure and recorded in the Table as Example 2.

EXAMPLES 3 & 4 (& Comparative Example B)

A hydrocarbon sample is tested with the CSI procedure using sulfurized oil as the sole antifouling agent component at a concentration of 1000 ppm. The Coking Stability Index is determined and recorded in the Table as the Example 3.

A hydrocarbon sample is tested with the CSI procedure using magnesium sulfonate as the sole antifouling agent component at a concentration of 1000 ppm. The Coking Stability Index is determined and recorded below as the Comparative Example B.

A hydrocarbon sample is tested with the CSI procedure using magnesium sulfonate (70 wt. percent) and sulfurized oil (30 wt. %) as the antifouling agent components at a total concentration of 1000 ppm. The Coking Stability Index is determined and recorded below as the Example 4.

DISCUSSION OF THE EXAMPLES

The examples clearly show that there is a synergistic effect resulting from combining a metal overbase and sulfurized oil.

TABLE
Sample	Mg Sulfo-	Sulfurized	Solvent	% Coke	Coke Stability
ID	nate %	Oil %	%	Solids	Index
Blank				8.2
Example 1		100	—	2.47	—
Comp. A	100		—	2.51	—
Example 2	47.6	30	22.4	2.00	—
Example 3		100	—	—	85
Comp. B	100		—	—	125
Example 4	70	30	—	—	140

Claims

1. A process for reducing furnace fouling comprising treating a furnace feed stream with an antifouling agent wherein the antifouling agent comprises sulfurized oil.

2. The process of claim 1 wherein the sulfurized oil is prepared using a process comprising the steps of:

mixing a mole ratio of a polyolefin to sulfur of between about 1:2.5 and about 1:5 at between about 50 and about 100° F.;

continuously blowing the resultant mixture with an inert gas under continuous pressure and under elevated temperatures until the free sulfur weight in the said resultant reaction mixture is less than about 0.3 weight percent;

stripping the blown mixture with inert gas at an elevated temperature at sub-atmospheric pressure; and

filtering the stripped product.

3. The process of claim 2 wherein the polyolefin is triisobutylene.

4. The process of claim 1 wherein the sulfurized oil is selected from the group consisting of sulfurized lard, sulfurized fish oil, sulfurized whale oil, sulfurized soybean oil, sulfurized pinene oil, sulfurized sperm oil, sulfurized fatty acid, 1,3,4-thiadiazol derivatives, thiuram disulfide, dithiocarbamate ester, and combinations thereof.

5. The process of claim 1 wherein the sulfurized oil has the general formula: wherein: X is 1 or 2, and each R is independently an alkyl group, a cyclic alkyl group, an olefin group, or a polyolefin group.

R—SX—R

6. The process of claim 1 wherein the antifouling agent additionally comprises an overbase selected from the group consisting of magnesium overbases, aluminum overbases, and combinations thereof.

7. The process of claim 6 wherein the magnesium and/or aluminum content of the overbase is at least about 1 weight percent.

8. The process of claim 7 wherein the magnesium and/or aluminum content of the overbase is at least about 5 weight percent.

9. The process of claim 6 wherein the overbase is prepared with a complexing agent selected from the group consisting of carboxylic acids, phenols, organic phosphorus acids, organic sulfur acids, and combinations thereof.

10. The process of claim 1 wherein the antifouling agent additionally comprises a dispersant.

11. The process of claim 10 wherein the dispersant is a copolymer of a carboxylic anhydride and an alpha-olefin.

12. The process of claim 11 wherein the alpha-olefin has from about 2 to about 70 carbon atoms.

13. The process of claim 11 wherein the carboxylic anhydride is selected from the group consisting of: maleic anhydride, succinic anhydride, glutaric anhydride, tetrapropylene succinic anhydride, phthalic anhydride, trimellitic anhydride (oil soluble, non-basic), and mixtures thereof.

14. The process of claim 1 wherein the antifouling agent includes at least one other component selected from the group consisting of a magnesium and/or aluminum overbase, a dispersant, and combinations thereof, and the weight ratio of sulfurized oil to the other component or components is from about 10:1 to about 1:10.

15. The process of claim 14 wherein the weight ratio of sulfurized oil to the other component or components is from about 3:1 to about 1:3.

16. The process of claim 15 wherein the weight ratio of sulfurized oil to the other component or components is about 1:1.

17. The process of claim 1 wherein the furnace feed stream is a partial or full feed stream selected from the group of feed streams consisting of a coking process feed stream, a visbreaking process feed stream, and a vacuum distillation process feed stream.

18. The process of claim 1 wherein the antifouling agent is present in the feed stream at a concentration of from about 50 ppm by weight to about 10,000 ppm by weight.

19. A process for reducing furnace fouling comprising treating a furnace feed stream with an antifouling agent wherein the antifouling agent comprises sulfurized oil and an overbase selected from the group consisting of magnesium overbases, aluminum overbases, and combinations thereof.

20. A composition comprising a hydrocarbon feed stream for a coking or visbreaking process and an additive comprising sulfurized oil.