US3645886A - Reducing fouling deposits in process equipment - Google Patents

Abstract

TO REDUCE OR PREVENT THE FOULING OF PROCESS EQUIPMENT IN PETROLEUM OR CHEMICAL INDUSTRIES WHEREIN AN ORGANIC FEEDSTOCK IS SUBJECTED TO HEAT EXCHANGE AT A TEMPERATURE OF FROM ABOUT 200* TO ABOUT 1300*F., GHERE IS ADDED TO THAT ORGANIC FEEDSTOCK A VERY LOW CONCENTRATION, OF THE ORDER OF ABOUT 0.5 TO 200 PARTS PER MILLION, A MIXTURE OF ABOUT 75 TO 99 ST. PERCENT OF A FATTY ACID ESTER OF AN ALKANOLAMINE AND FROM ABOUT 1 TO 25 WT. PERCENT OF A PHOSPHOROUS ACID OR A MONO, DI, OR TRI-ORGANIC PHOSPHITE ESTER HAVING THE FORMULA:

R-O-P(-O-R'')-O-R"

WHEREIN R, R'' AND R" ARE HYDROGEN OR A HYDROCARBON RADICAL, INCLUDING ALKYL, ARYL, ARALKYL, ALKARYL, CYCLOALKYL, OR ALKENYL, OR A SIMPLE HALOGENATED DERIVATIVE OF SUCH HYDROCARBON RADICAL.

Description

United States Patent Ofice 3,645,886 REDUCING FOULING DEPOSITS IN PROCESS EQUIPMENT Bruce G. Gillespie, Cranford, and Jack E. Ryer, East Brunswick, N.J., assignors to Esso Research and Engineering Company No Drawing. Continuation-impart of application Ser. No. 778,751, Nov. 25, 1968, now Patent No. 3,558,470, which is a continuation-in-part of application Ser. No. 694,039, Dec. 28, 1967. This application May 15, 1970, Ser. No. 37,846

Int. Cl. Cg 9/16; C101 1/26; C23f 14/00 US. Cl. 208-48 AA 9 Claims ABSTRACT OF THE DISCLOSURE To reduce or prevent the fouling of process equipment in petroleum or chemical industries wherein an organic feedstock is subjected to heat exchange at a temperature of from about 200 to about 1300 F., there is added to that organic feedstock a very low concentration, of the order of about 0.5 to 200 parts per million, a mixture of about 75 to 99 wt. percent of a fatty acid ester of an alkanolamine and from about 1 to 25 wt. percent of a phosphorous acid or a mono, di, or tri-organic phosphite ester having the formula:

wherein R, R and R" are hydrogen or a hydrocarbon radical, including alkyl, aryl, aralkyl, alkaryl, cycloalkyl, or alkenyl, or a simple halogenated derivative of such hydrocarbon radical.

This application is a continuation-in-part of copending application Ser. No. 778,751, filed Nov. 25, 1968 (now US. Pat. 3,558,470), which in turn is a continuation-inpart of application Ser. No. 694,039, filed Dec. 28, 1967, and now abandoned.

This invention concerns a method for reducing or preventing the fouling of process equipment in chemical industries. It is particularly applicable to process equipment involving heat transfer at high temperatures. Preferably, the improved method comprises adding to the feedstock of a processing unit handling a hydrocarbon fraction or other organic chemical stream being heated, a very low concentration of a mixture of a fatty acid ester of an alkanolamine and a phosphite ester or a phosphorous acid.

In industrial processes that involve the heating of a feedstock to a high temperature, particularly in the petroleum industry, severe fouling of the equipment is often encountered. This is particularly so in the distillation of crude oils, in naphtha desulfurization processes, in gas oil cracking units, and in visbreaking operatings involving heavy petroleum fractions. Thus, fouling problems may occur when feedstocks are heated to any temperature Within the range of from about 220 F. up to cracking temperatures, and particularly at temperatures of 200 to 1300 F. The fouling problem is a serious one because, among other things, it causes heat transfer losses, increased pressure drops, and loss in throughput. The types of mechanical equipment that are most frequently affected by fouling include furnaces, pipes, heat exchangers, reboilers and condensers.

The deposits that are encountered as a result of the fouling phenomenon may consist of sticky, tarry, polymeric, or carbonaceous material. In some instances the fouling deposits will be associated with inorganic ma- 3,045,886 Patented Feb. 29, 1972 terials such as sand, scale, or salts which are cemented or otherwise caused to adhere to the surface of the equipment by this type of sticky, tarry, or carbonaceous fouling material. The sand may be present because of the lack of proper filtering of the crude oil that is being fed to the unit, while the scale may occur from deterioration of the metal in the equipment. Salts occur in the crude oil stream as a result of incomplete desalting of the crude or because the crude has not been subjected to any desalting treatment. Ordinarily, a crude is not desalted if the amount of salt does not exceed about 20 pounds per 1000 barrels of oil.

The fouling problems that are solved by the present invention are not confined solely to those wherein inorganic salts or sand or scale are also present, but include any of the fouling phenomena encountered in high temperature processing. Such fouling is believed to involve polymerization, or a combination of polymerization and oxidation or oxidative polymerization which in some respects is similar to that which causes gum to form in gasoline. The high temperatures that are attained in a heat transfer operation such as in the distillation of a crude oil or in process heating equipment feeding a catalytic reforming operation or a visbreaking operation, for example, can cause oxygen to react with the hydrocarbons in the feed to form a polymeric material which can deposit on the surfaces of the heat transfer equipment. If this polymerization can be prevented, fouling will likewise be prevented, since the binder for the inorganic deposits will thereby be eliminated. While fouling sometimes can be controlled by excluding oxygen from the feedstock, often this is not economically feasible. For example, the ordinary floating roof tank in which feedstocks are frequently stored will not completely prevent contact with oxygen of the air. Furthermore, many feedstocks contain oxygen when they are received at the refinery or at a unit in the refinery. When oxygen contamination thus cannot be prevented, use of an antifoulant is one solution to the problem.

DESCRIPTION OF THE PRIOR ART Various antifoulants have been suggested in the prior art. For example, US. Pat. 3,235,484, and its Reissue 26,330, teach the use of acylated amines, e.g. imides, prepared from polyamines and aliphatic substituted succinic acids or their anhydrides as antifoulants for hydrocarbon feedstocks that are subjected to high temperatures. Also, US. Pat. 3,364,130 teaches the use of amide condensation products of monocarboxylic acids and polyamine. Application Ser. No. 778,751, of which the present application is a continuation-in-part, discloses and claims the use as an antifoulant of a mixture of a phosphorus acid or of a mono-, dior tri-organo phosphite ester and an amide or imide condensation product of the types described in the aforementioned patents.

DESCRIPTION OF THE INVENTION In accordance with the present invention it has been found that an antifoulant that is superior to prior art antifoulants comprises a mixture of an alkanolamine ester of a saturated or unsaturated fatty acid and a phosphorus acid or a phosphite ester. The phosphorous acid or the phosphite makes up from 1 to 25 wt. percent, or more usually 1 to 20 wt. percent, of the mixture, and the alkanolamine ester makes up from to 99%, or more usually to 99 wt. percent, of the mixture.

The alkanolamine ester is the reaction product of an alkanolamine wherein the alkanol group has from 2 to 5 carbon atoms and from 1 to 3 alkanol groups, with' a saturated or unsaturated fatty acid having from about 12 to 24 carbon atoms. A particularly effective alkanolamine ester comprises an ethanolamine ester, particularly the ester of diethanolamine or triethanolamine with oleic acid or with a mixture of fatty acids containing oleic acid. Other suitable fatty acids include lauric, myristic, linoleic, arachidic, palmitic, stearic, hypogaeic, eicosinic, elaidic, eleostearic, and punicic. Particularly suitable is a mixture of fatty acids from tall oil.

Suitable alkanolamines, include ethanolamine, isobutanolamine, pentanolamine, diethanolamine, 2 amino-2- methylpropanol 1, methyl diethanolamine, 2-amino-2- methylbutanol l, triethanolamine, butyl ethanolamine, monoisopropanolarnine, diethyl ethanolamine, diisopropanolamine, triisopropanolamine, dimethyl isopropanolamine, and dibutyl isopropanolamine. A particularly useful mixture of alkanolamines comprises the still bottoms from the distillation of triethanolamine. These bottoms are predominantly triethanolamine along with various amounts of higher boiling compounds. See, for example, Kirk- Othmer Encyclopedia of Chemical Technology (Second Edition), vol. 1, page 814. Usually in preparing the esters, more than stoichiometric proportions of alkanolamine to fatty acid will be used.

The phosphite ester or phosphorus acid additive em ployed in association with the alkanolamine ester will be either a mono-, a di-, or a tri-ester, or mixtures of two or more of these three types of esters, or a phosphorus acid, or a mixture of phosphorus acid and one or more phosphite esters. The organic substituent employed in the ester formation, and which is generally obtained from the respective monohydric alcohol or phenol in a conventional manner, is a hydrocarbyl or halogenated hydrocarbyl radical. The phosphorus acid or phosphite can be represented by the formula:

wherein R, R and R" are hydrogen or a hydrocarbyl radical selected from the group consisting of alkyl, haloalkyl, aryl, haloaryl, alkaryl, haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl, aralkyl and haloaralkyl.

The total number of carbon atoms for each of R, R' and R" ranges between about 1 and about 50 with the preferred range being between about 8 and about 20 carbon atoms per hydrocarbyl radical. Typical examples of the phosphite esters and phosphorus acid are the following specific phosphite compounds (the specific listing of the monoester is intended to include the like listing of the corresponding diand tri-ester as well; thus, for example, methyl phosphite is intended to include dimethyl phosphite and trimethyl phosphite, but in instances where R, R' and R" are not the same, the diand tri-esters are set forth in full). The examples include: phosphorus acid; methyl phosphite; ethyl phosphite; n-propyl phosphite; isopropyl phosphite; butyl phosphite; pentyl phosphite; hexyl phosphite; cyclohexyl phosphite; heptyl phosphite; nonyl phosphite; decyl phosphite; lauryl phosphite; cetyl phosphite; octadecyl phosphite; heptadecyl phosphite; phenyl phosphite; alpha or beta naphthyl phosphite; benzyl phosphite; tolyl phosphite; methyl, phenyl phosphite; dimethyl, phenyl phosphite; arnyl, phenyl phosphite; bis(diamyl phenyl) phosphite; diamyl, phenyl phosphite; nonylphenyl phosphite; nonyl, phenyl phosphite; 4-amylpheny1 phosphite; 4-amylphenyl, diethyl phosphite; dioctadecyl di-phenyl phosphite; octadecyl di-phenyl phosphite; isobutyl phenyl phosphite; nonyltolyl phosphite; nonyl, ditolyl phosphite; polyisobutenyl diphenyl phosphite; dipolyisobutenyl phosphite; di-polyisobutenylphenyl phosphite; polyisobutenylphenyl phosphite; bromoethyl phosphite; chlorobutyl phosphite; chlorooctyl phosphite; fluorophenyl phosphite; chlorobenzyl phosphite; chlorotolyl phosphite; bromopolyisobutenyl, diphenyl phosphite; di- (chloropolyisobutenyl) ethyl phosphite; di-polyisobutenyl, chlorobenzyl phosphite; di-polyisobutenyl, chloropolyisobutenyl phosphite. Particularly useful are the diesters and triesters of C to C monoalkyl and dialkyl phenols, e.g.

of diamyl phenol, hexyl phenol, isooctyl phenyl, nonyl phenol, dodecyl phenol, and hexadecyl phenol. Nonyl phenol made commercially by alkylation of phenol with tripropylene usually is a mixture of a major proportion of monononyl phenol with a minor proportion of dinonyl phenol.

Many of the above esters, particularly those containing the smaller number of carbon atoms per molecule, are readily available commercially and their methods of preparation are conventional. Some of the esters, particularly those having the longer alkyl chains or hydrocarbon radicals or halogenated hydrocarbon radicals of the higher number of carbon atoms per radical, although presently not available commercially, are readily prepared by reaction one, two, or three moles of the corresponding a1- cohol or phenol with each mole of phosphorus trihalide such as phosphorus trichloride or phosphorus tribromide. This is a conventional reaction and while there are other ways, also conventional, of producing these various phosphite esters, the present invention is not concerned with the particular method by which the phosphite esters are produced. In those cases where monoor di-esters are formed, it is sometimes desirable, following the esterification reaction, to treat the reacted mixture with water, dilute aqueous caustic, or dilute aqueous mineral acid in order to hydrolyze off the residual chlorine or bromine atoms present by reason of the particular trivalent phosphorus compound employed as an original reactant. The hydrolysis of a phosphorus trihalide yields phosphorous acid also.

The invention is particularly applicable to the treatment of any normally liquid hydrocarbon feed stream and especially to the treatment of liquid petroleum fractions ranging through light distillate stocks, e.g., naphthas, kcrosenes and the like, middle distillate stocks such as gas oils, lubricating oil fractions, cycle stocks from cracking operation, virgin crude oils, topped crude oils, etc., as well as individual hydrocarbon streams, as for example ethyl benzene or dicyclopentadiene.

The invention can be applied to any of a number of treating steps, including treating a crude petroleum feedstock entering a crude distillation unit, the reduced crude feedstock entering a visbreaking unit, the light naphtha stock entering a pre-treating zone prior to a catalytic reforming zone, the naphtha or heavier feedstock entering the feed heat exchanger to a desulfurizing unit, and the gas oil feed entering the preheater of a catalytic cracking unit. Other processes to which the method is applicable include thermal hydrodealkylation of aromatics, dehydrogenation of ethyl benzene, high temperature steam cracking or petroleum hydrocarbons, and depolymerization of dicyclopentadiene. While the antifoulant could be fed directly to the unit in which fouling occurs, it is preferred to add it to the feedstock just ahead of the zone in which the problem arises.

Only relatively small amounts of the alkanolamine ester containing the added phosphite ester or phosphorous acid are required in order to produce outstanding results in the reduction of fouling deposits. In general, the combined amount of the dual additive will range from about 0.5 to about 200 parts per million (ppm) by weight based on the total feedstock. While amounts greater than 200 ppm. can be employed, usually this is not eco nomically justified because the possible increased antifouling effect is not sufficiently great to warrant the use of large amounts of the additive. Generally, in the treatment of the various petroleum feedstocks, the amount of the dual antifoulant will be from about 0.5 to 60 parts per million by weight. Some hydrocarbon streams, e.g. dicyclopentadiene, may require as much as ppm. of antifoulant. The use of the antifoulant does not interfere in any way with the process to which the feed stream is being subjected.

In some instances reduction of fouling is further improved by employing in conjunction with the antifoulant additives certain antioxidants, including phenyl alphanaphthyl amine, and amino alkyl phenols, which are the condensation products of C to C aldehydes, C to C alkylene diamines and alkyl phenols of C to C alkyl groups. These antioxidant materials may comprise from 5 to 50% by weight of the antifoulant package.

Admixtures of the alkanolamine esters and the phosphite esters and/or phosphorous acid will normally be used as such. The invention also encompasses the reaction products of such alkanol-amine esters with the phosphite material (which includes phosphorous acid).

The following examples, which include a preferred embodiment, are intended to illustrate this invention. However, it is not intended that the invention be limited to these examples.

Example 1 Triethanolamine still bottoms, weighing 9.4 pounds per gallon, which contains triethanol amine along with various amounts of higher boiling compounds, is charged to an esterification kettle that is provided with an agitator, with means for heating the kettle, and with means for collecting and condensing volatile products of the reaction. Then a mixture of fatty acids from tall oil is added to the kettle in an amount approximating 1.5 moles of fatty acids per mole of alkanol amines. A representative example of tall oil fatty acids comprises 8% conjugated linoleic acid, 36% nonconjugated linoleic acid, 50% oleic acid, and 6% stearic acid, all percentages by weight.

After the tall oil fatty acids and the triethanol amine still bottoms are placed in the kettle there is added eight volume percent of xylene based on the total mixturer Then the kettle agitator is started and heating of the kettle is begun, the reaction temperature being that which will cause refluxing of the xylene. Water of reaction is collected in a trap as an azeotrope with xylene. The azeotrope is sent to a separator from which the xylene is continuously returned to the reaction mixture. Esterification is complete when no more water is collected over head in the azeotrope, or when the temperature of the liquid in the esterification kettle reaches about 380-390 F. When it is determined that the reaction has been completed, the liquid reaction mixture is cooled and then about 20 vol. percent of xylene and 30 vol. percent of heavy aromatic naphtha, both percentages being based on the volume of reaction mixture, are added as solvents. Thereafter, 8 vol. percent, based on the mixture, of tris- (nonylphenyl)phosphite is added to the mixture. The resulting product is an antifoulant prepared in accordance with this invention. The antifoulant has the following approximate overall composition in percentage by volume:

Percent Triethanolamine ester 62.2

Xylene 14.0 Heavy aromatic naphtha 18.8 Tris-(nonylphenyl)phosphite 5.0

The tris(nonylphenyl)phosphite was obtained by the reaction of three moles of commercial nonyl phenol with one mole of PCl Example 2 The antifoulant of Example 1 was compared with other prior art materials marketed as antifoulants with respect to the effectiveness of these materials to reduce fouling in the 5-hour Erdco CRC Fuel Coker Test described in the article of A. W. Frazier et al., published in the Oil and Gas Journal, May 3, 1965, vol. 63, No. 18, page 117. In one set of tests, the feedstock that was used was a heavy gas oil from a visbreaking operation, having a boiling range of about 450 to 750 F. In a second set of tests the feedstock was a vacuum residuum. In a third set of tests the feedstock was a conventional feed entering a catalytic reformer. This feed had an initial boiling point of 160 F. and a final boiling point of 325 F. In the first set of tests the amount of anti- 6 foulant that was used was 40 parts by weight per million of feedstock; in a second set of tests the amount was 50 parts per million; and in the third set of tests, the amount of antifoulant was 25 parts per million of feedstock. Comparative tests were also run with each feedstock containing no added antifoulant.

In each case, a five-gallon sample of the untreated or treated feedstock was used. When additive concentrates were used they were diluted with an equal volume of kerosene before addition to the feedstocks. Upon running the feedstocks through the apparatus shown in FIG. 1 of the article referred to, under the test conditions set forth in that article, and after measuring the pressure drops across the porous filter, the pressure drop was plotted against the length of the test, in minutes, and the linear slope Was determined. By linear slope is meant the slope calculated as if the approximately semilogarithmic plot of Frazier et al. were linear, i.e. a 45 line will have a slope of unity. The lower the slope, the less fouling occurred; the higher the slope, the more fouling occurred. Also, in some of the runs appearing in the following Table I, the pressure drop in inches of mercury ("HgAP) across the filter is given. A high fouling feed quickly reaches a 25-inch pressure differential while a low fouling feed more slowly reaches this same pressure differential.

TABLE I.FUEL COKER TEST RESULTS Coker test data Linear Hg AP at Min. to 25 Additive slope 250 min, Hg AP 30 p.m. in heavy gas oil:

None .65 Amino ester alone a 0. 40 Polyamine amide 0. 50 Example 1 product- 0.00

50 p.p.m. in vacuum residuum:

None Polyamine amide b Amide plus phosphite Amide plus amino phenol 4 Example 1 product 25 ppm. in cat. reformer tee Amide plus phosphite Example 1 product It is to be noted from the data in Table I that the additive mixture of the present invention was superior to all of the other prior art antifoulants when used in each of the feedstocks that were tested.

It is to be understood that the specific embodiments herein presented are by way of example and that the scope of the invention is not to be limited thereto. The scope of the invention is defined by the appended claims.

What is claimed is:

1. A method for treating an organic feedstock that is fed to a heat exchange step wherein it is subjected to a temperature in the range of about 200 F. to about 1300 F. which comprises adding to said feedstock from about 0.5 to about 200 parts per million, based on the weight of the feedstock, of a mixture of from about 75 to 99 wt. percent of a C to C fatty acid ester of an alkanolamine and from about 1 to about 25 wt. percent of a phosphite compound having the formula:

wherein R, R, and R" are hydrogen or a hydrocarbon radical selected from the group consisting of alkyl, halo- 7 alkyl, aryl, haloaryl, alkaryl, haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl, aralkyl, and haloaralkyl, whereby fouling of heat exchange equipment as the result of oxidation or polymerization of feed stock constituents is reduced.

2. A method as defined by claim 1 wherein the amount of said mixture is between about 0.5 and 60 parts by weight per million of said feedstock.

3. Method as defined by claim 1 wherein said organic feedstock comprises a normally liquid petroleum hydrocarbon fraction.

4. Method as defined by claim 1 wherein said fatty acid ester comprises ethanolamine esters of oleic acid or of mixed fatty acids including oleic acid.

5. Method as defined by claim 1 wherein said fatty acid ester comprises the tall oil fatty acid esters of triethanol amine.

6. Method as defined by claim 1 wherein said fatty acid ester comprises the tall oil fatty acid esters of triethanol amine still bottoms.

7. Method as defined by claim 1 wherein said phosphite is an ester of a C to C alkyl phenol.

8. Method as defined by claim 1 wherein said phosphite comprises tris(nonylphenyl)phosphite.

9. An organic feedstock normally tending to form fouling deposits in heat exchange equipment when subjected to a temperature exceeding about 200 E, which has been treated to reduce said fouling tendency by incorpowherein R, R, and R" are hydrogen or a hydrocarbon radical selected from the group consisting of alkyl, haloalkyl, aryl, haloaryl, alkaryl, haloalkaryl, cycloalkyl, halocyclo alkyl, alkenyl, haloalkenyl, ar-alkyl, and haloaralkyl.

References Cited UNITED STATES PATENTS 2,889,389 11/1959 Fierce et a1. 208348 3,218,137 11/1965 Belo et a1. 4466 3,364,130 1/1968 Barnum 20848 AA DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKO-NS, Assistant Examiner US. Cl. X.R.