CA1291637C - Antioxidant material and its use - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention is directed to antioxidant materials and their use in petroleum and petrochemical processes to reduce and/or control fouling problems. The inventive antioxidant materials are composed of non-hindered or partially hindered phenols in combination with a strongly basic material such as an organo amine.

Description

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ANTIOXIDANT MATERIAL AND ITS USE

BACKGROUND OF THE INVENTION

Fouling can be defined as the accumulation of unwanted matter on heat transfer surfaces. This depos~tion can be very costly in refinery and petrochemical plants since it increases fuel usage, results in interrupted operations and production losses and increases maintenance costs.

Deposits are found in a variety of equipment: preheat exchangers, overhead condensers, furnaces, fractionating towers, reboilers, compressors and reactor beds. These deposits are complex; broadly, they can be characterized as organic and inorganic. They consist of metal oxides and sulfides, soluble organic metals, organic polymers J coke, salt and various other particulate matter. Chemlca1 antifoulants have been developed that effectively combat fouling.

The chemical composition of organic foulants is rarely identified completely. Organic fouling is caused by insoluble polymers which sometimes are degraded to coke. The polymers are usually formed by reactions o~ unsaturated hydrocarbons, although any hydrocarbon can polymerize. Generally, oleflns tend to polymerize more readily than aromatics, which in turn polymerize .~

lZ9~;37 more readily than paraffins. Trace organic materials containing hetero atoms such as nitrogen, oxygen and sulfur also contribute to polymerization.

Polymers are formed by free radical chain reactions.
These reactions, shown below, consist of two phases, an initiation phase and a propagation phase. In reaction 1~ the chain initiation reaction, a free radical represented by R, is formed (the symbol R
can be any hydrocarbon). These free radicals, which have an odd electronJ act as chain carriers. During chain propagation, additional free radicals are formed and the hydrocarbon molecules (R) grow larger and larger (see reaction 4), forming the unwanted polymers which accumulate on heat transfer surfaces.

Chain reactions can be triggered in several ways. In reaction 1, heat starts the chain. Example: when a reactive molecule such as an olefin or a diolefin is heated, a free radical is produced. Another way a chain reaction starts is shown in reaction 3. Here metal ions initiate free radical formation.
Accelerating polymerization by oxygen and metals can be seen by reviewing reactions 2 and 3.

Coke formation is the result of polymerization initially, but as ~he polymer sticks to a heat transfer surface, more and more hydrogen is driven off until the polymer is eventually converted to coke.

1. Chain Initiation R-H ~R- + H+

~291637 2. Chain Propagation a. R- + 2 ~ R-0-0 b. R-0-0 + R' - H -~ R' + R-0-0-H

3. Chain Initiation a. Me++ + RH ~ Me+ + R- + H+
b. Me++ + R-0-0-H -- ~ Me~ + R-0-0- + H+

4. Chain Termination a. R- + R' -- - > R-R' b. R- + R-0-0 -----~ R-0-0-R

In some cases, foul~ng and corrosion may be related problems. In that case, solving the corrosion problem which exists upstream may well eliminate the fouling problem.

In refineries, deposits usually contain both organic and inorganic compounds. This makes the identification of the exact cause of fouling extremely difficult. Even if it were possible to preclsely identify every single deposit constituent, this would not guarantee uncovering the cause of the problem. Assumptions are often erroneously made that if a deposit is predomlnantly a certain compound, that campound is the cause of the foul~ng, In reallty, a mlnor constltuent in the deposit could be actlng as a binder, a catalyst, or in some role that influences actual deposlt formation.

The final form of the deposit as viewed by analytical chemists may not always indicate its origin or cause. Before openings, equiplnent is steamed, waterwashed, or otherwise readied for inspection. During this preparation, fouling matter can be changed both physically and chemically. For example, water-soluble ~29~637 salts can be washed away or certain deposit constituents oxidized to another form.

In petrochemical plants, fouling matter is often organic.
Fouling can be severe when monomers convert to polymers before they leave the plant. This can occur in streams high in ethylene, propylene, butadiene, sytrene and other unsaturates. Probable locations for such reactions include units where the unsaturates are being handled or purified, or in streams which contain these reactive materials only as contaminants.

Even though some petrochem~cal fouling problems seem similar, subtle differences in feedstock, processing schemes, equipment and contaminants can lead to variations in fouling severity. For example, ethylene plant depropanizer reboilers experience fouling that appears to be primarily polybutadiene in nature. The severity of thls problem varies significantly from plant to plant, however. Average reboiler run length may vary frcm one to two weeks up to four to six months (without chemical treatment).

Although it is usually ~mpractical to ident~fy the fouling problem by analytlcal techniques alone, this information, alony with knowledge of the process, processing condit~ons and the factors that contribute to fouling, are all essential to understanding the problem.

There are many ways, mechanical as well as chemical, to reduce fouling. Chemical additives offer an effective means;
however, processing changes, mechanical modifications equipment and other methods available to the plant should not be overlooked.

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Antifoulan~s are formulated from several materials: some prevent foulan~s from forming, others prevent foulants from depositing on heat transfer equipment. Materials that prevent deposit formation include antioxidants, metal coordinators and corrosion inhibitors. Compounds that prevent deposition are surfactants which act as detergents or dispersants. Different combinations of these properties are blended to provide maximum results for different applications. These "polyfunctional"
antifoulants are generally more versatile and effective since they are designed to combat various types of fouling that can be present in any given system.

Research indicates that even very small amounts of oxygen can cause or accelerate polymerization. Accordingly, antioxidant-type antifoulants have been developed to prevent oxygen from initiating polymerization. Antioxldants act as chain-stoppers by forminy inert molecules with the oxidized free radical hydrocarbons, in accordance with the following reaction:

Chaln Termination ROO Antioxidant - ~ ROOH ~ Antioxidant (H) Surface mod~f1ers or detergents change metal surface characteristics to prevent foulants from depositing. Dispersants or stabilizers prevent insoluble polymers, coke and other particulate matter from agglomerating into large particles which can settle out of the process stream and adhere to metal surfaces of process equipment. They also modify the part~cle surface so that polymerizatlon cannot readily take place.

Antifoulants are designed to prevent equipment surfaces from fouling. They are not designed for clean up. Therefore, an 129~63 antifoulant should be started immediately after equipment is cleaned. It is usually good to pretreat the system at double the recommended dosage for two or three weeks to reduce the initial high rate of fouling immediately after startup.

The increased profit possible with antifoulants varies from application to application. It can include an increase in production, fuel savings, maintenance savings and other savings from greater operating efficiency.

There are many areas in the hydrocarbon processing ~ndustry where antifoulants have been used successfully; the main treatment areas are discussed below.
.

In a refinery, the crude unit has been the focus of attention, especially because of the recen~ tremendous increases in fuel cost. Antifoulants have been successfully applied at the exchangers; downstream and upstream of the desalter, on the product side of the preheat train, on both sides of the desalter makeup water exchanger, and at the sour water stripper.

Hydrodesulfurization units of all types experience preheat fouliny problems. Among those that have been successfully treated are reformer pretreaters processing both straight run and coker naphtha, desulfurizers processing catalytically cracked and coker gas 0;1SJ and distillate hydrotreaters. In one case, fouling of a Unif~ner stripper column was solved by applying a corrosion ~nhibitor upstream of the problem source.

Unsaturated and saturated gas plants [refinery vapor recovery units) experience fouling in the various fractionation columns, rebo~lers and compressors. In some cases~ a corrosion ~291637 control program along with the antifoulant program gave the best results. In other cases, antifoulants alone were enough to solve the problem.

Cat cracker preheat exchanger fouling, both at the vacuum column and at the cat cracker itself, has also been corrected by the use of antifoulants.

In petrochemical plants, the two most prevalent areas for fouling problems are ethylene and styrene plants. In an ethylene plant, the furnace gas compressors, the various fractionating columns and reboilers are subject to fouling. Polyfunctional antifoulants, for the most part, have provided good results in these areas. Fouling can also be a problem at the butadiene extraction area. Both antioxidants and polyfunctional antifoulants have been used with good results.

In the different design butadiene plants, absorption oil 16 fouling and distillation column and reboiler fouling have been corrected with various types of antifoulants.

Chlor~nated hydrocarbon plants, such as VCM, EDC and perchloroethane and trlchloroethane have all experienced various types of fouling problems. The metal-coordinating/antioxidant-type antifoulants give excellent service in these areas. The present invention ~s directed to antioxidant compositions and their use in controlling fouling in petroleum and petrochemical processing systems as above exemplified.

1~9~6~7 DESCRIPTION OF THE INVENTION

The present invention relates to the formulation of specific phenolic antioxidants in a non-aqueous medium which incorporates a sufficient amount of an oil soluble base such that the antioxidant material l~ould experience a basic environment (pH~
10.5) and would at the same time become soluble in a hydrocarbon medium. The specific phenolic antioxidants encompassed by the invention include any unhindered or partially hindered phenol.
Unhindered phenols with strong electron donating groups such as an alkyl or alkoxy group (OX) where the alkyl (X) contains from 1 to 10 carbon atoms, amine group (-NH2) or an alkyl substituted amine, in the para position.

The phenols utilizable are those that have the structural formula OH

R1 ~ R

wherein R and Rl are hydrogen and a carbon gr~uping (1 to 8 carbon atoms), with the proviso that not more than one of R and Rl be a secondary or tertiary carbon grouping, and R2 is alkylJ alkoxy or an amine grouplng.

Specific examples of the phenols include, but are not limited to, p-cresol, p-methoxyphenol, p amino-phenol, p (p-methoxy benzylideneamino) phenol, and 2-tert-butyl-4-methoxyphenol (butylated hydroxy anisole).

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The oil soluble strong bases which are used in conjunction with the phenol may be exemplified by monoethanolamine, N(2-aminoethyl) piperazine, cyclohexylamine, and 1,3-cyclohexane bis (methylamine). However, any amine which has the NR5R6R7 where R5, R6 and R7 are hydrogen, alkyl, aryl, or subs~ituted alkyl or aryl or in any combination thereof. The amine functions, it is D believed, in a dual capacity. It generally is included in su&h 5 amount that the pH of the composition increases to a pH of-~3-or above, thereby solubilizing the phenol in any hydrocarbon solvent which might be used to enhance the solubility of the phenol in the petroleum or petrochemical being processed. It has also been unexpectedly determined that the presence of the amine,~in small percentages by weight (active) of the phenol to amine of 98:2 to 2:98 and preferrably 40 to 60 enhances the antioxidant capabilities of the phenol. The test data recorded hereinafter will in fact illustrate this conclusively.

The treatment range for the composition, i.e., amine/phenol, clearly is dependent upon the severity of the fouling problem due to free radical polymerization encountered as well as the activity and constituency of the combinat~on util~zed. For this reason, the success of the treatment is totally dependent upon the use of a sufficlent amount for the purpose of whatever the composition of choice is. Broadly speaking, the treatment recommendation could be in the range of 0.1 to 2000 parts per million of petroleum or petrochemical being processed with perhaps 10 to 200 ppm being applicable in most cases.

Specific Embodiments ,. ~ The ASTM test method D-525 ~*~e4y-~neortor~e~

~2gl6~7 e$~r~Y~ was carried out under accelerated conditions (high 2 content) that would normally not be experienced in an actual field environment. Nevertheless, when examining potential antioxidant candidates, the test provides reliable data on the effectiveness of a given antioxidant material to inhibit the polymerization of certain petroleum feedstocks.

The method (ASTM D-525) covers the determination of the stability of gasoline under accelerated oxidation conditions.

According to the procedure the sample is ox~dized in a bomb initially filled with oxygen. The pressure ~s read at stated intervals or recorded continuously until the break point is reached. The time required for the sample to reach this point is the observed induction period at the temperature of the test, from which the induction period at lOO~C may be calculated.

The induction period may be used as an indication of the tendency of ~otor gasoline to form gum in storage. In accordance with the test, an increase in induction time indicates that the candidate antioxidant material is performing its Function. Further difunctional aspects and the actual procedure can be determined from an actual reYiew of the test procedures described in ASTM D-525.

The results of the testing were as follows:

~16~37 Active Induction Conc. Solvent Time Sample Additive (ppm) System (min.) WITHOUT AMINE
1 pyro1ysis None - N.A. 10 gasoline 2 " P-[p-methoxy-benzylidine amino] phenol 200 DMF or HAN 55 3 " p-methoxy phenol 200 HAN 55 4 " butylated hydroxy anisole 200 HAN 105 " p-cresol 200 " 10 WITH AMINE 300 ppm N-(2-Amino-ethyl) Piperazine (AEP) 2 " p-[p-methoxy-benzy1idine amino] phenol 200 - 160 3 " p-methoxy phenol 200 - lOS
4 " butylated 200 - 160 hydroxy anisole " p-cresol 200 - 20 6 " AEP 300 -- 10 1~9~637 While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims (20)

1. A method of controlling fouling on heat transfer surfaces in a petroleum or petrochemical processing system which comprises adding to the petroleum or petrochemical being processed a sufficient amount for the purpose of an antioxidant composition comprising (a) an unhindered or partially hindered phenol which possesses the following formula:

wherein R and R1 are selected from the group consisting of hydrogen and carbon groupings, with the proviso that not more than one of the R and R1 be a secondary or tertiary grouping and R2 is alkyl, alkoxy or an amine group; (b) at least one oil soluble strongly basic alkyl substituted amine compound; and (c) having a pH of at least 10.5.

2. A method according to Claim 1 wherein the composition is added to said system in an amount of from 0.1 to 2000 ppm of the petroleum or petrochemical being processed.

3. A method according to Claim 2 wherein the phenol is selected from the group consisting of butylated hydroxy anisole, p-cresol, p-methoxyphenol, and [p(p-methoxy benzylideneamino)phenol].

4. A method according to Claim 3 wherein the amine is monoethanolamine, cyclohexylamine, N(2-aminoethyl) piperazine and 1,3 cyclohexane bis (methylamine).

5. A method according to Claim 4 wherein the composition is in an organic solvent.

6. A method according to Claim 5 wherein the phenol and the amine are present in a percentage weight ratio of 2 to 98 to 98 to 2.

7. A method according to Claim 6 wherein the composition comprises 60% amine and 40% phenol.

8. A method according to Claim 7 wherein the composition is further contained in an organic solvent.

9. A method according to Claim 8 wherein the solvent is a heavy aromatic naphtha, dimethylformamide or mixtures thereof.

10. A composition for use as an antioxidant for controlling fouling on heat transfer surfaces in petroleum or petrochemical processing system comprising (a) an unhindered or partially hindered phenol possessing the formula wherein R and R1 are selected from the group consisting of hydrogen and a carbon containing group, with the proviso that not more than one of R or R1 be a secondary or tertiary carbon grouping and R2 is alkyl, alkoxy or an amino group;

(b) at least one strongly basic oil soluble alkyl substituted amine compound; and (c) having a pH of at least 10.5.

11. A composition according to Claim 10 wherein the composition is contained in an organic medium.

12. A composition according to Claim 11 wherein the amine is in sufficient amount to assure the solubility of said phenol in said medium.

13. A composition according to Claim 10 or 12 where the amine and phenol are present in said composition in a percentage by weight phenol to amine of 98:2 to 2:98.

14. A composition according to Claim 13 wherein the percentage by weight of phenol and amine is 40% and 60%, respectively.

15. A composition according to Claim 10 wherein said phenol is selected from the group consisting of butylated hydroxy anisole, p-cresol, p-methoxyphenol, and [p(p-methoxy benzylideneamino)phenol].

16. A composition according to Claim 15 wherein the amine is monoethanolamine, cyclohexylamine, N(2-aminoethyl) piperazine and 1,3 cyclohexane bis (methylamine).

17. A composition according to Claim 16 wherein the amine and phenol are present in said composition in a percentage by weight ratio of 98:2 to 2:98.

18. A composition according to Claim 17 which is contained in an organic solvent for such.

19. A composition according to Claim 18 wherein said solvent is a heavy aromatic naphtha, dimethyl formamide or mixtures thereof.

20. A composition according to claim 18 wherein the amine and phenol are present in percentage by weight of about 60% and about 40%, respectively.