GB2153841A - Reduction of heat exchanger fouling - Google Patents

Abstract

The fouling produced in a heat exchanger when a hydrocarbon stream, which is to be heated or cooled therein, is passed through the heat exchanger is reduced by incorporating in the hydrocarbon a small amount of the order of from 1 to 500 parts per million of an antifouling additive which is an alkylamino alkylphenol of the general formula: <IMAGE> or a mixture of such additives, wherein R and R1 are independently alkyl groups of 1 to 20 carbon atoms; R2 is hydrogen, or an alkyl group of 1 to 20 carbon atoms or an alkylphenolic methyl group; R3 is hydrogen, or an alkyl group of 1 to 6 carbon atoms; and n is 1 to 10.

Description

SPECIFICATION Reduction of heat exchanger fouling This invention relates to heat exchangers, particularly heat exchangers used in the processing of crude oil. More particularly, the invention relates to the use of an additive for reducing heat exchanger fouling.

In the processing of petroleum, numerous heat exchangers are utilized to heat or cool process streams. Since refineries typically process very large quantities of petroleum ranging from 25,000 to 200,000 or more barrels per day, the heat exchangers in the refinery represent a very large capital investment. After a period of operation, deposits build up on the heat exchanger tubes greatly reducing heat exchanger efficiency and greatly increasing the energy consumed. Eventually, the heat exchanger must be taken out of operation and the tubes cleaned or replaced. Increasing heat exchanger efficiency and reducing the amount and rate offouling can provide tremendous energy savings in refineries and other facilities that use heat exchangers.

Numerous heat exchangerantifoulant additives are well known in the art, for example, U.S. Patent Nos. 3,437,583 and 3,442,791 which disclose as antifoulants for petroleum hydrocarbon streams the combination of a metal deactivator and a condensate product of an alkylphenol, polyamine, and formaldehyde. Similarly, U.S. Patent No.3,132,085 discloses the use ofthe condensation product of ammonium hydroxide, formaldehyde and an alkylphenol as a heat exchanger antifoulant.

According to the present invention there is provided a methodofreducing heatexchangerfouling caused when a liquid hydrocarbon stream is passed through a heat exchanger, generally at a temperature in the range from 0 to 1 500F (-17.8 to 81 5.6 Ci wherein an effective amount, generally from 1 to 500 parts per million, of an antifoulant additive is incorporated in said hydrocarbon stream, said additive comprising at least one aikylamino alkylphenol of the formula:

wherein: Rand R1 are independently alkyl groups of 1 to 20 carbon atoms; R2 is hydrogen, oran alkyl group of 1 to 20 carbon atoms or an alkylphenolic methyl group; R3 is hydrogen, oran alkyl group of 1 to 6 carbon atoms; and n is 1 to 10.

The heat exchangers utilized in the present invention are of any type where deposits accumuiate on a heattransfer surface. The most common type of heat exchanger used is commonly known as a shell and tube heat exchanger.

The hydrocarbon stream passing through the heat exchanger is preferably a crude oil stream. Particularly preferred are petroleum stocks that contain reactive hydrocarbons such as olefins, sulfur, and nitrogen compounds. However, any hydrocarbon stream which leads to fouling of the heat exchanger can be utilized in the present invention, particularly various fractions ofthe crude oil. Generally, the streams passing through the heat exchanger will be heated or cooled attemperatures ranging from 0 to 1500"F (-17.8 to 81 5.60C), preferably 50" to 800"F (10 to 426.7 C).

The Alkylamino Alkylphenols The alkylamino alkylphenol additives useful as antifoulants in the present invention have the general structure:

wherein: Rand R, are independently alkyl groups of 1 to 20 carbon atoms; R2 is hydrogen, or an alkyl group of 1 to 20 carbon atoms or an alkylphenolic methyl group; R3 is hydrogen, or an alkyl group of 1 to 6 carbon atoms; and n is 1 to 10. Representative alkyl groups include methyl, ethyl, dodecyl, octadecyl and octyl. These alkyl groups may be linear or branched.

Preferably, R is a branched alkyl group of 9to 15 carbon atoms which may be obtained by oligomerizing propylene, while R1 is preferably a low molecular weight alkyl group such as methyl and R2 is either hydrogen or another alkylphenolic methyl group. R3 is preferably either hydrogen or a low molecular weight alkyl group, and more preferably R3 is H.

Preferably n is 1 to 4. Mixtures of the above types of compounds are contemplated and are particularly preferred.

Preparation of the Alkylamino Alkylphenols The additives are obtained by the condensation reaction of an alkylphenol, an aidehyde and an amine.

This reaction is well known in the art as the Mannich condensation reaction. Depending on the reactants, the ratio thereof, and reaction conditions, one or more ofthe above-described alkylamino alkylphenols is obtained.

The alkylated phenols useful in making the alkylamino alkylphenols used in this invention are ofthe formula:

wherein R may be a straight or branched chain alkyl group having from 1 to 100 carbon atoms and preferablyfrom 10 to 30 carbon atoms. The R groups oralkyl groups may be present on any or all ofthe sites around the phenolic ring, i.e., ortho, meta or para. Preferably, the R groups will be predominantly meta or para. That is, less than 40 percent ofthe R groups will be in the ortho position and preferably less than 15 percent of the R groups will be in the ortho position. A particularly preferred alkylated phenol is dodecylphenol.

Examples of suitable alkyls inciude octyl, decyl, dodecyl, ethylhexyl and triacontyl; radicals derived from petroleum hydrocarbons such as white oil,wax and olefin polymers (e.g., polypropylene and polybutylene). While one specific structure is indicated by the above formula, it should be recognized that mixtures of alkylated phenols can be successfully employed.

Aldehydes having the following formula are suitable for use in the condensation reaction:

wherein R3 is selected from hydrogen and alkyl radicals containing from 1 to 6 carbon atoms.

Examples of suitable aldehydes include formaldehy de, acetaldehyde, propanaldehyde, butyraldehyde, hexaldehyde and heptaldehyde. The most preferred aldehyde reactant is formaldehyde, which may be used in its monomericorpolymericform, such as paraformaldehyde.

The amines suitable for use in the condensation reaction contain one amino group and at least one active hydrogen atom. Suitable amines include primary amines and secondary amines. Examples include the primary alkyl amines such as methyl amine, ethyl amine, n-propyl amine, isopropyl amine, n-butyl amine, isobutyl amine, 2-ethylhexyl amine, dodecyl amine and stearyl amine. Also, dialkyl amines may be used, such as dimethyl amine, diethyl amine, methylethyl amine and methylbutyl amine. A preferred amine is methyl amine.

The condensation reaction will occurbysimply warming the reactant mixture to a temperature sufficientto effectthe reaction. The reaction will proceed attemperatures ranging from about 50"C to 200"C. A more preferred temperature range is from 75"C to 175"C. The time required to complete the reaction depends upon the reactants employed and the reaction temperature used. Under most conditions, reaction is complete in about 1 to 8 hours.

The amountofalkylated phenol, formaldehyde and amine presentwithin the reaction medium generally ranges from 0.5 to 5 molar parts of primary amine and from 0.75 to 4 molar parts of formaldehyde per molar partofalkylated phenol. Preferably, the molar ratio of the phenol to the amine to formaldehyde varies from 1:1-4:2-3.5 and more preferably is from 1:1-1.5:2-3.

Also, preferably, the reactants are chosen such that the total number of carbon atoms in the reaction product is less than 46 and more preferably less than 36.

To substantially reduce heat exchanger fouling, an effective amount, generally from 1 to 500 parts per million, preferably5to 99 permillion, and most preferably 10 to 49 parts per million of the above described alkylamino alklphenol is added to the stream passingthroughthe heatexchanger. One surprising feature of the present invention resides in the finding that such small quantities of the abovedescribed additive are effective in reducing heat exchanger fouling.

Example 1-Preparation of theAlkylaminoAlkylphe nols This example is presented to illustrate preparation of one ofthe additives of the present invention.

Into a stainless steel vessel equipped with a vacuum distillation system is placed 60.4 parts of polypropylene phenol wherein the polypropylene has from 12 to 15 carbon atoms. The polypropylene phenol normally has approximately 5 percent of dialkylphenols. The vessel is evacuated to 250 mm mercury absolute pressure and thevacuum released with nitrogen. The vessel is again evacuated to 250 mm mercury absolute pressure and the vacuum again released with nitrogen. The vessel is then opened to the atmosphere while the nitrogen purge is maintained in the vapor space. Thereafter, 16.3 parts of isobutyl alcohol are charged to the vessel with agitation followed by 14.6 parts of paraformaldehyde. The vessel is closed and 7.25 parts of liquid monomethylamine are charged to the vessel over a period ofthree hours with constant agitation.The temperature ofthe vessel is maintained between 120"F (48.9"C) and 150 F (65.6 C) during the addition of the monomethylamine. The mole ratio of alkylphenol to monomethylamine to formaldehyde is approximately 1:1.05:2, respectively.

The reactor charge is mixed for 15 minutes after addition ofthe amine has been completed and is then vented. The temperature is raised to 1 900F (87.8"C), the vessel closed and the temperature raised to 275"F (135"C). The reaction is carried outforfive hours at a pressure of about 20 psig (2.4 kg/cm2).The intermediate condensation productformed is then cooled in the vessel to about 180"F (82.2"C) and a quantity of mid-continent 100 neutral oil equal to 39.7 percent by weight of the previously charged constituents is added, i.e. 39.7 parts ofthe oil is added to the 100 parts already in the reactor. A quantity of water equal to 19.5 percent by weight ofthe original 100 parts charged is charged to the vessel and the system mixed for 15 minutes at a temperature of 1700 to 180'C (76.7 to 82.2'C).

The mixer is then shut off andthe system allowed to settle for about one hour. The water layer is then drawn off until an emulsion cuff appears. The system is then ailowed to settleforabout one-half hour and thewaterlayerisagain drawn off until a heavy cuff appeared. The above-described washing procedure is repeated using 16.5 pa rts of water. The product is the Mannich condensation reaction product of polypropylene phenol, paraformaldehyde and monomethylamine in an oil diluent.

Example 2- Anti fouling Tests Amixtureofalkylaminoalkylphenolsprepared from the condensation of dodecylphenol, parafor maldehydeand monomethylaminesimilartothat illustrated in Example 1 was tested for its antifouling characteristics using a standard ALCOR TestApparatus and various test stocks. This test involves feeding a test stock material at a fixed rate and for a fixed period oftime and at constant inlet temperature into a tube containing a stainless steel electricaliy heated rod while supplying enough heat to the rod to maintain the outlettemperature ofthe test stock constant.As fouling deposits form on the rod, the temperature ofthe rod must be increased to maintain a constant outlet temperature of the test stock. The initial rod temperature and final rod temperature are measured along with the initial and final weight of the rod. The increase in rod temperature and the amount of deposits on the rod are indicative of the degree and rate of fouling.

Eachtest runwasforthree hours and either no additive was used or 50 parts per million of additive was added to the test stock. The inlet temperature of the test stock was maintained at 70 F (21.1 C) and the outlettemperaturewas maintained at either 5000F (260"C) or 600"F (315.6"C) as indicated. The results are shown below in Table I.

TABLE I Test Stock Outlet Test Temper- AT, Deposit do. Test Stock and Additive nature, F('c) F Wt, mg Jet Feed to Hydrofiner 1 No Additive 600 (315.6) -2 2.8 2 Alkylamino allcylphenol 600 (315.6) -2 0.5 Naphta Feed to Hydrotreater 3 No Additive 600 (315.6) 4 15.3 4 Alkylarino alkylphenol 600 (315.6) 16 0.5 Jet Feed to Nydrofiner - 5 No Additive 600 (315.6) 3 3.0 6 50 ppm Pyrole 600 (315.6) 37 5.1 7 50 ppm Pyrole and 50 ppm alkylamino alicylphenol 600 (315.6) 3 1.5 Western Wyoming Crude 8 No Additive 500 (260) 11 6.0 9 Alkylamino alkylphenol 500 (260) 10 0

Claims (13)

1. A method of reducing the fouling of a heat exchanger caused when a liquid hydrocarbon stream is passed therethrough, which comprises incorporating in the liquid hydrocarbon stream an effective amount of an antifouling additive comprising at least one alkylamino alkylphenol of the formula:

wherein: Rand R1 are independentlyalkyl groups of 1 to 20 carbon atoms: R2 is hydrogen, or an alkyl group of 1 to 20 carbon atoms or an alkylphenolic methyl group; R3 is hydrogen, oran alkyl group of 1 to 6 carbon atoms; and n is 1 to 10.

2. A method according to Claim 1, wherein said stream is composed of crude oil or a fraction thereof.

3. A method according to Claim 1 or 2, wherein in said formula R is a branched alkyl group of 9to 15 carbon atoms.

4. A method according to Claim 1,2 or3,wherein in said formula R1 is methyl.

5. A method according to Claim 1,2 or 3, wherein in said formula R2 is hydrogen oran alkylphenolic methyl group and R3 is hydrogen.

6. A method according to Claim 1,2,3 or 4, wherein R3 is hydrogen and n is 1 to 4.

7. A method according to any preceding claim, wherein from 1 to 500 parts per million of said additive are added to said stream.

8. A method according to Claim 7, wherein from 5 to 99 parts per million of the additive are added.

9. A method according to any preceding claim, wherein said hydrocarbon stream is passed through said heat exchanger at a temperature in the range from 0 to 1 5000F (-17.8 to 81 5.6'C).

10. A method according to Claim 9, wherein the hydrocarbon stream is at a temperature in the range from 50 to 800"F (10 to 426.7 C).

11. A method according to any preceding claim, wherein said alkylamino alkylphenol is made from the condensation of dodecylphenol, paraformaldehyde and methylamine.

12. A method according to any preceding claim, wherein said heat exchanger is a shell and tube heat exchanger.

13. A method in accordance with Claim 1 for reducing heat exchanger fouling, substantially as described in the foregoing Example 2.