US3261774A - Reducing fouling in refining of petroleum products - Google Patents

Description

United States Patent 3,261,774 REDUCING FOULING [N REFINING 0F PETROLEUM PRODUCTS John D. Newkirk, Westmont, and Richard M. Miller, La Grange, lll., assignors to Nalco Chemical Company, Chicago, 111., a corporation of Delaware N0 Drawing. Filed Sept. 1, 1965, Ser. No. 484,466 5 Claims. (Cl. 208-48) This invention relates to improvements in the processing or refining of hydrocarbons. Specifically, the invention is concerned with chemical additives for normally liquid or gaseous charge stocks used to produce finished hydrocarbon products.

It is common practice to add chemical agents to finished petroleum hydrocarbon products such as gasolines, kerosenes, fuel oils, finished solvents, and the like, to give these products desirable properties and characteristics. Modern processing operations use a large number of hydrocarbon charge stocks which are intermediates in the production of finished products. Until recently little attention was paid to the properties of these charge stocks since they were rapidly processed through processing equipment where they were converted to products having different physical and chemical characteristics from those of the starting material.

With the commercial growth of the petrochemical industry and the ever-increasing need for higher octane gasolines, improved aviation fuels and improved residual fuels, it has become the practice to treat the various refinery charge stocks to extract improved fuel values therefrom or to convert them to valuable petrochemicals. These various processes have tended to increase processing problems which, in the past, were not so critical.

One of the worst problems encountered in the treatment of various hyrocarbon charge stocks is the phenomenon which is now recognized and is descriptively called fouling. This phenomenon manifests itself in the form of deposits which frequently form on the metal surfaces of the processing equipment and tend to materially decrease the efiiciency of the intermediate processing operations. The direct results of fouling appear in the forms of heat transfer loss, increased pressure drops, loss in through-put and,

in some instances, a specific type of corrosion product which is associated with the deposits.

The charge stocks which most commonly cause fouling in the intermediate refinery equipment are naphthas, gas oils, crudes, and petroleum gases. The naphthas or light distillate stocks may be considered as a light oil and usually have a boiling point range of 90-500 F. The gas oils are intermediates between the so-called kerosene fractions and the light lubricating cuts, and generally distill from 520 F. and 750 F. These gas oils are usually used as charges to cracking units where the molecules are broken down into smaller components. The crude oils which most commonly cause the problem of fouling are virgin products charged to the first refining stage operations and contain all of the petroleum fractions normally removed in the refining processes. For the purposes of this invention, crude stocks are intended to cover the so-called residual or pot fractions which remain after the volatile components and solvent extractable components of the crudes have been removed.

Another class of hydrocarbons to which the invention pertains is the petroleum gases or normally gaseous, alkane and alkene hydrocarbons, which usually boil between 250 -F. and 100 F., i.e., methane, ethane, propane, butane, ethylene, propylene, etc. These hydrocarbons may be in the liquefied state or gaseous state during processing thereof in the practice of the invention. For example, these normally gaseous stocks may become lique- 3,261,774 Patented July 19, 1966 ice fied when subjected to super-atmospheric pressures or low temperatures.

The various charge stocks mentioned above are most frequently subjected to one or more of the following general type thermal or catalytic processes to produce fuels: reforming, cracking, alkylation, isomerization, polymerization, desulfurization, hydrogenation, and dehydrogenation. A description of these various processes and their modifications are described in the publication, Petroleum Refiner, September 1962.

Similar problems arise in equipment used in the petrochemical industry wherein the hydrocarbon charge stock is, in many cases, heated at normal or elevated pressure, For example, in the production of acetylene by the BASF process, light naphthas or natural gas is preheated prior to partial combustion thereof with oxygen to form acetylene and other by-products. In other acetylene production processes, hydrocarbons such as naphthas are cracked thermally. In the alkylation of aromatics, benzene or other aromatic hydrocarbon is mixed with an olefin-containing gas, preheated to the alkylation temperature, and reacted in the reactors. Ammonia is produced by processes involving a first stage comprising mixing a compressed hydrocarbon gas, liquid hydrocarbon, or the like, with steam, preheating the mixture and forming in a reactor a gas product composed primarily of carbon monoxide and hydrogen, the latter being reacted with nitrogen at a later processing stage. Benzene and hydrogen are reacted in equipment utilizing heat exchangers to produce cyclohexane. Light alkane hydrocarbons, monoolefins and mixtures thereof are pre-heated before catalytic dehydrogenation into mono-olefins and di-olefins. Ethylene feed is preheated under pressure before reaction with water to produce ethanol. Light and heavy crude oil or crude oil fractions are preheated before thermal cracking thereof into ethylene and propylene and C 'olefins. In the hydrodealkylation of lower alkyl aromatics into simple aromatics and gas, the lower alkyl aromatics are mixed with hydrogen and preheated before the hydrodealkylation reaction.

The foregoing examples of petrochemical processes are illustrative but not exhaustive of processes in which the invention may be used to advantage in reducing deposit formation on heat exchange surfaces by hydrocarbons employed therein. Other petrochemical processes to which the invention applies may be found in the Petrochemical Handbook issues of the Hydrocarbon Processing and Petroleum Refiner, the latest issue of which appears at pages 129 ft. of vol. 42, No. 1, November 1963 (Gulf Publishing Co.).

The deposits previously mentioned most frequently occur on heat exchange surfaces at elevated temperatures which range between F. and 2000 F. and more often between 200 F. and 2000 F. The types of mechanical equipment most commonly affected are furnaces, heat exchangers, reboilers, condensers, compressors and auxiliary equipment. Catalyst beds may also become severely fouled by these deposits. In the mechanical types of equipment, the charge stock is usually caused to flow through various types of heat processing equipment such as pipes, heat exchangers, furnaces, etc. which, for purposes of simplification, are referred to herein as conductors.

The deposits forming on the heat exchange surfaces such as metal surfaces are varied in composition and may be either organic, inorganic, or mixed organic and inorganic. The organic deposits are primarily polymerization products and are usually black, gummy masses which may be converted to coke-like masses at elevated temperatures. The inorganic portions of the deposits will frequently contain such components as silica, iron oxide, sulfur trioxide, iron sulfide, calcium oxide, magnesium oxide, inorganic chloride salts, sodium oxide, alumina, sodium sulfate, copper oxides, and copper salts. The source of the inorganic components of the deposits is difficult to locate in any one given operation, but frequently they may be ascribed as coming from such sources as ash components of the crude oils, corrosion products from the metal surfaces which the charge stocks contact, and contaminants resulting from the contact with the various metallic catalytic reagents used to process the stock.

The problems described above are distinguishable from the prior art phenomena of corrosion and sludge formation which frequently occur in finished products. The problem of sludge or deposit formation in finished products is not related to that of fouling since deposits of the former type may be readily solubilized using such organic solvents as benzene, acetone, and the like. The deposits which are referred to herein as fouling are not readily solubilized by common organic solvents. The inorganic deposits which occur as fouling products are frequently much more complex in their make-up than the conventional corrosion products; hence they are readily distinguishable on this basis.

When the fouling phenomenon first became apparent, it was believed it could be corrected by using known antioxidants or stabilizing chemicals to mitigate the problem. The experience with these additives soon developed the fact that conventional petroleum additives were relatively ineffective.

It would be a valuable contribution to the art if the problems described above could be overcome by using economical chemical additives at relatively low dosages. This invention presents such a solution to the problem.

The invention in its simplest form comprises a petroleum refining process for the production of liquid and gaseous hydrocarbons or hydrocarbon processing processes for production of petrochemical products and hydrocarbon products wherein a hydrocarbon charge stock contacts a heat exchange surface such as a metal conductor under conditions of temperature and pressure which cause the formation of deposits on the surfaces of the heat exchanger. To prevent the formation of these deposits or fouling, the process if performed in the presence of a chemical additive which is admixed with the charge stock. The chemicals capable of preventing the fouling are specific N-alkyl amidophosphoric acids listed below.

( o o 0 0 11 u O N RrRz (i) (I) and mixtures thereof where R R R R R and R are radicals selected from the group consisting of hydrogen, alkyl, alkenyl, alkaryl, aryl, cycloaliphatic, cycloheteryl, and the foregoing radicals having substituents thereon, with the proviso that in at least one occurrence one of the foregoing radicals contains at least eight carbon atoms.

The just recited compounds may be formed via a number of known synthetic routes. However, the preferred mode of preparation involves sequential reaction of phosphorous pentoxide, and a primary or secondary amine followed by reaction with an alcohol. From this synthesis a mixture of products listed above as A, D and E, are produced. To realize compositions B, C and F, partial or complete neutralization of compounds A and D is effected, yielding the claimed salts of amidophosphates. The last substance, compound G, is best formed by reaction of phosphorous pentoxide and a primaryor secondary amine in a specific ratio of 1:6 of phosphorous to amine.

A wide variety of reactants may be employed to realize specific compounds falling within the described classes of amido phosphoric acid compositions. As mentioned above, phosphorous pentoxide is a preferred phosphorouscontaining reactant. However, a variety of other phosphorous-containing acidic compounds may also be chosen. For example, phosphoric acid, phosphorous oxychloride, phosphorous anhydride, etc., may be equally employed.

The amine reactant may be either a primary or secondary amine, having at least one available reactive hydrogen to form the corresponding amido group. It has been determined that in at least one instance the primary or secondary amine should contain a radical of the type listed above having at least eight carbon atoms. Materials of this type have superior corrosion inhibiting properties when added to normally liquid hydrocarbon stocks being processed or stored. Illustrative amines which may be employed in producing the compositions of the invention are listed below. These materials may be used via a first reaction with a phosphorous-containing acid followed by reaction of the product with an alcohol to produce compositions A, D and E, from which the corresponding salts may be easily synthesized by neutralization, or they may be reacted solely with a phosphorouscontaining acid to produce composition G.

Table I A particularly preferred class of amine reactants are highly alkyl substituted imidazolines. Preferred imidazolines are defined by one of the following formulas:

6 More specifically, the'tertiary-alkyl primary amine constitutes a compound wherein R and R are lower alkyl groups, us-ually methyl groups, and R constitutes a long Formula I chain alkyl radical composed of 8 to 19 carbons. Ter- Y 5 tiary-alkyl primary amines which have been found to be I eminently suitable for the instant invention are Primene 8l-R and Primene JM-T. Primene 81-R is re- R-c ported by its manufacturer to be composed of principally tertiary-alkyl primary'amines having 11-14 carbons and l I 10 has a molecular weight principally in the range of 171- H 213, a specific gravity at 25 C. of 0.813, a refractive Formula 11 index of 1.423 at 25 c., and a neutralization equivalent of 191. Primene JM-T is reported by the manufac- N turer to be composed of tertiary-alkyl primary amines 15 having 18-22 carbons with a molecular weight principally in the range of 269-325, a specific gravity at C. of

f 1.456, and a neutralization equivalent of 315. (R1NH) H The primary constituent of Primene Sl-R is re Formula III Ported to be:

Y 20 CH3 CH3 CH3 HaC( JCH2 ?CH2( ]NH2 I OH: CHs CH3 The primary constituent of Primene JM-T is re- 5 ported to be essentially the same structure as Primene I H 81-R, but with 22 carbons. where is an aliphatic group of carbon atoms in The alcoholic reactant may likewise be chosen from a chain length, Y and Z are selected from the group con- Wlde vanety of alcohols but Pnmary and Sisting of hydrogen and lower aliphatic hydrocarbon alcohols are greatly preferred. These alcohols have radigroups of not more than 6 carbon atoms in chain length, cals corresponding to the types enumerated in the claimed R is an alkylene radical of 1-6 carbon atoms, R is a composltlonsradical selected from the group consisting of R and hydro- Example of alcohohc reactants are normal stralght gen, and n is an integer of 1-50. Imidazolines of the cham alcohols such as ethyl H'PTOPYL n'butYL type shown in Formulas I, II, and III are conveniently n'hePtyL Q u prepared by reacting a monocarboxylic acid such as a nyl (lauryl), ntetradecyl (myristyl), n-hexadecyl saturated or unsaturated fatty acid with an alkylene poly- (cetyl)! and f (stealfyl); branched F mine or hydroxyalkyl alkylene diamine in accordance l alcohols Such as 1 s u yl, ls amyl, 2,2,4-tr1methyl-1- with well-known methods. The product imidazolines may hexanol and be further reacted via oxyalkylation to produce other Octanol; and Secondary alcohols Such as lsopropyl, useful derivatives. The methods of preparing imidazo- 40 butylg 'P L 2'octanol, 'P and lines of this type are given in the article, Chemistry 2,4-d1methyl-3-pentanol. Examples of alicyclic alcohols of the 2-I mid azolines and l-mi-dazolidines, by R. J. Ferm are Cyclopfintanol, cy lohexanol, cycloheptanol, and menand J. L. Riebsomer, Chemical Reviews, 0L 54, No 4, thol. Examples of alcohols of the class having ethylenic August 1954. Particularly useful imidazolines for use uPsatu'rated are allyli Crotyl, oleyl (cis'9'octadecen'l'one in the practice of the invention are those described in cltroneuol, and g Acetylenic unsaturation is illustrated by propargyl alcohol. Araliphatic alcohols are illustrated by benzyl, 2- phenylethanol, hydrocinnamyl, and alpha-methyl-benzyl alcohols. Cinnamyl alcohol is an example of an alcohol containing both aromatic and ethylenic unsaturation.

One excellent source of alcohol which may be used is that class of compounds known as oxo alcohols. These are normally a mixture of various intermediate molecular weight alcohols ranging from 4 to about 16 carbon atoms. Their preparation and description is described in the book Higher Oxo Alcohols by L. F. Hatch, Enjay Company, Inc., 1957, which disclosure is hereby incorporated by reference. The general range of both alcohols and ester by-products typifying an oxo alcohol still bottom of the type which may be used in the invention, is as follows.

1-(2-hydroxyethyl)-2-undecyl imidazoline 1-(2-hydroxyethyl) -2-tridecyl imidazoline 1-(2-hydroxyethyl)-2-pentadecyl imidazoline 1-(2-hydroxyethyl)-2-heptadecyl imidazoline 1-(Z-aminoethyl)-2-heptadecyl imidazoline 1-[ (2-aminoethyl)-aminoethyl-1]-2-undecyl imidazoline 1-[(Z-aminoethyl)-aminoethyl-1]-2-tridecyl imidazoline Ingredient: P nt 1 h 1 Mixed 1soand n-octyl alcohol 2-20 The fatty aci s are most general y reacted wit a po y- Mixed and nmonyl ale 0h 01 540 alkylene polyamine such as diethylene triamine, triethylene tetramine, tetr-aethylene pentamine, or mixtures thereof, or a polyamine alcohol such as aminoethyl ethanolamine. The amine reactant may likewise be substituted with lower alkyl groups.

Mixed isoand n-decyl and higher alcohols 25-90 Esters 20-80 A typical 0x0 alcohol still bottom which finds excellent use in preparing the N-alkyl amidophosphoric acid com- A particularly preferred class of amine reactants are tertiary-alkyl primary amines. The tertiary-alkyl primary 7 amines have the formula:

R5 R7(|3NH2 1'1.

pounds of the invention has the following composition.

Ingredient: Weight percent C alcohols 5 C alcohols 10 C and higher alcohols 35 Esters 45 Soaps 5 As mentioned above, compositions represented by Formulae A, D and E are conveniently formed by reaction of a phosphorous-containing acid and an amine followed by further reaction with an alcohol of the type described above. The compounds represented by Formula G are formed by reacting varying amounts of amine and phosphorous-containing acid alone. Depending upon the number of excess moles of amine employed per mole of phosphorous compound determines the degree to which a phosphorous compound such as phosphorous pentoxide is amidified. A 6:1 ratio of amine to phosphorous compound yields a fully amidified compound .and one also 'fully neutralized, that is one containing 3 amide groups and 3 salt groups. By varying the ratio one can form partially or completely neutralized compounds.

To achieve compounds represented by Formulae B, C and F, one merely has to neutralize compositions A and D by adding an amine. The neutralizing amine may be chosen from any of those already discussed or others such as those listed below in Table II.

Table II where R is an alkylene radical selected from among -CH CH CH CH CH and H CHa( J OHa and x is an integer of 1-5 S-benzimidazole Z-hydroxyethyl imidazole Z-methyl imidazole Pyrazine Pyridine Piperidine Z-cyanomethyl-Z-imidazoline Cyclohexyl amine The following examples illustrate typical modes of preparation of illustrative antifoulants of the invention.

8 EXAMPLE I To a clean, dry nitrogen-blanketed -gallon stainless steel reactor provided with an efiicient stirrer and a watercooled steam-heated jacket is charged 130.5 lbs. of kerosene and 60.0 lbs. of phosphorous pentoxide. These materials are stirred together rapidly to form a slurry wherein the phosphorous pentoxide is suspended as fine particles. To this dispersion is added slowly 40.2 lbs. of Primene 81-R. During the slow addition the rate is maintained such that a temperature of 100 C. is not exceeded. The above reaction mix is then stirred for 1.0-1.25 hours at 100 C., maintaining a nitrogen atmosphere throughout the process and preferentially at pressures slightly higher than atmospheric. After the above time period the reaction mix is cooled to 40 C. and 137.5 lbs. of isooctanol is added slowly, maintaining the temperature during this addition at from 40 C. to 50 C. with cooling as needed. After the isooctanol addition, the mixture is heated to 100 C. for 2.0-2.5 hours and after this period of time the solution was clear.

The compounds formed corresponded to Formulae A, D and E, wherein the R radical is hydrogen, the R radical is and R is an isooctyl radical. These products were formed in approximately equal ratios as indicated by potentiometric titration and could be separated by conventional means such as solvent extraction and the like. The useful materials could be employed in mixture form since they were all effective in varying degrees as corrosion inhibitors. The actual ratio of P O :amine:alcohol reactants in this case was 1:1:5.

EXAMPLE II A mixture of products, corresponding to Formulae B and D above was synthesized by partial neutralization of the mixture of N-alkyl amidophosphoric acids of Example I. In this instance a Primene Sl-R amine was the neutralizing agent.

EXAMPLE III In this example the fully neutralized salts of the mixture of N-alkyl amidophosphoric acid products of Example I was obtained. Primene 81-R Was again the neutralizing reagent and compounds corresponding to Formulae E and F were synthesized.

EXAMPLE IV In this example the same reactants of Example I were employed with exception that the ratio of P O zaminezalcohol was 1:2:4. The same mixture of substances were obtained as described in Example I with the exception that the two materials varied in proportion to one another.

EXAMPLE V In this experiment the reactants of Example I was employed but in a 1:1:5.5 ratio. The products were then fully neutralized with Primene 81-R amine.

EXAMPLE VI In this example a synthesis was efiected involving only P 0 and amine, and specifically Prirnene 81-R. In this instance, the compound corresponding to Formula G Was made, wherein R R R R and R are radicals derived from the amine reactant. The molar ratio of amine to P 0 was 6: 1.

EXAMPLE VII In this example the technique of Example I was followed With the exception that .an imidazoline was employed instead of the Primene 8lR amine material.

The particular imidazoline employed was prepared by reaction of aminoethyl ethanolamine and mixed heptadecenyl and heptadecadienyl fatty acids. The molar ratio of the three reactants was again 1:1:5 and the final product was 50% active in kerosene.

EXAMPLE VIII The procedure of Example I was again exactly followed but in this instance the final product was 50% active in kerosene.

. EXAMPLE IX In still another experiment the product of Example I was synthesized but at a 80% active form in kerosene.

A variety of other substances falling within the scope of the invention but involving use of different amines, alcohols, phosphorous containing acids and neutralizing amines other than the above illustrative reactants were made with equal simplicity and ease of reaction. The above specific examples are merely typical preparations and it is understood, of course, that a great number of varying reagents may be employed of the types outlined above to produce useful compositions.

It has been determined that preferred N-alkyl amidophosphoric acid compounds of the invention and mixtures thereof have acid numbers which range from about 220 to about 280. Such products particularly exhibited excellent antifoulant activity in liquid hydrocarbons.

The mechanisms of fouling of heat exchange surfaces must be evaluated in the light of the feed stock. In the distillation range of approximately ZOO-400 F., a variety of compounds derived from crude oil distillation can exist. The addition of cracked stocks to straight run naphtha stream and the oxidation of these naphthas in storage add other hydrocarbon and nonhydrocarbon compounds. For the purpose of discussing fouling mechanisms, these compounds will be considered individually according to classification.

Parafiinic compounds may be straight chain or branched hydrocarbons. Generally, they are relatively stable to oxidation at elevated temperatures. It has been reported that oxygenated products are produced in the vapor phase reaction of paraffins with oxygen at 570 to 750 F. For example, n-heptane reacts with oxygen at 590 F. to produce ethylene and a peroxide. Acids, aldehydes, alcohols, and esters are formed in the oxidation of parafiins through the formation of intermediate hydroperoxides and dihydroperoxides. Other investigators have shown that these hydroperoxides are able to condense and form polymeric materials and water. Evaluations have shown that straight run naphthas containing no measurable olefin-s, hydrogen sulfide, mercaptans, or dissolved oxygen do not form more than trace amounts of deposit in the heat exchangers unless the bulk oil temperature exceeds approximately 750 F. At this temperature and above, thermal cracking of the parafiin occurs, producing compound which can react to form polymeric deposits. As will be discussed later, metallic catalysts may participate in the reaction.

Monoand bicycloparaffin have been reported in the gasoline fraction of crude oil. The monocyoloparaffins consist mostly of cyclopent-anes and hexanes with minute amounts of cycloheptane. The bicycloparaffins may consist of methyl-(2.2.1) bicyclohept-ane, bis-bicyclo-(3.3.0) octane, Tetralin and Decalin. Little is known of the thermal stability of the first two of these compounds, but their decomposition would probably be similar to that of the normal paraffirrs. Tetralin and Decalin enter into dehydrogenation reactions at elevated temperatures. If benzene is the final product, a more thermally stable compound is produced with the balance consisting of unsaturates.

With refiners reaching deeper into the crude barrel to produce more gasoline, it is not surprising that the products of thermal and catalytic cracking of heavier fractions currently contribute up to twenty-five percent of the feed to hydrodesulfurizers and reformers. The primary useful product of cracking processes is a naphtha high in olefin content plus sulfur, nitrogen, and oxygen compounds. The conjugated olefin content may be as high as five percent. In many cases, gum formers in coker distillates have been found to be these conjugated olefins.

That olefins are capable of intrareacting to produce polymeric compounds, is well known. They are also able to react, via metal catalysts, with oxygen, oxygen-organosulfur compounds, and oxygen-organo-nitrogen compounds.

The oxygen-olefin reaction, in the presence of metal catalyst, has been reported by several investigators. The primary reaction product is a peroxide. It has been proposed that the metal at an oxidation state of plus two, is capable of extracting hydrogen from an olefin, producing a free radical. This free radical reacts with an oxygen molecule to produce a peroxide. The peroxide free radical reaction products may rearrange, losing water, to form a variety of aldehydes, ketones, acids and esters. Some of these, in turn, are able to react with other components in the feed stock, producing polymeric substances. These reactions will be considered in greater detail below.

Laboratory evaluations have shown that naphthas containing cracked stocks, or the cracked stocks by themselves, have markedly higher fouling rates and give greater tube deposit ratings than straight run stocks. Evaluations of naphthas from field units have shown that oxygen exists even in nitrogen-blanketed naphtha feed stocks. This effect of dissolved oxygen is used in laboratory fouling evaluations to increase the fouling rate, and thus shorten the length of each test, via pre and continued saturation of the feeds with air.

The sulfur content of straight run naphthas may range from 0.010.l7 percent. In the cracked naphthas it may be as high as 0.5 percent. The sulfur compounds in these naphthas consist of thiols (mercaptans), heterocy'clics, sulfides, and polysulfides and thioethers.

It has been reported that mercaptans are capable of interreacting to form olefins and hydrogen sulfide. The mechanism involves the decomposition of the mercaptan to a free radical. This radical then undergoes an intramolecular splitting which results in the olefin and hydrogen sulfide. The reactions at 750 F., produced considerable olefin and hydrogen sulfide. At lower temperatures, this reaction was not pronounced.

Sulfur compounds are also capable of reacting with olefins producing polymeric compounds. Authors have reported the reaction of olefin-s with mercaptans in the presence of oxygen to produce a substituted 2-hydr0xyethyl sulfoxide.

A wide variety of nitrogen compounds have been found in crude oil. Straight run naphthas obtained from high nitrogen crudes may contain some of the lower molecular weight cyclic or heterocyclic nitrogen compounds. Another source of nitrogen compounds in reforming feed stocks is cracked naphtha. Cracked naphthas containing high nitrogen contents are usually highly colored and exhibit high fouling rates both in the field and in laboratory evaluations.

Refinery naphtha streams usually contain trace amounts of dissolved or suspended metal salts, primarily as a result of corrosion reactions. Evaluations indicate that not only copper, but others such as iron, nickel, and chromium may augment deposit formation.

Thus far only possible chemical reactions in the formation of exchanger deposits have been considered. These reactions are most probably affected by temperature, pressure, mass flow rate, residence time, and the physical condition of the reactor, in this case the exchanger tube.

It has been found that increased temperature, and residence time generally increase the fouling rate. Flow rates are dependent upon pressure and the volatility of the feed stock. When a feed stock is vaporized, the heat fiux is higher, to obtain a specific temperature, than when no vaporization occurs. Thus, the skin temperature of the exchanger tube is higher, so that increased cracking and coking occurs. However, the increased velocity of the naphtha as a gas tends to sweep the surface, removing a portion of the coke, sometimes giving the appearance of a lower fouling rate. In this area, the type of coke formed may not lend itself to this sweeping and velocity will have little effect.

To summarize briefly, reactive olefins in the feed stock are probably capable of forming free radicals via trace metal catalysts, which then react with oxygen to produce peroxides. These peroxides probably react with themselves, sulfur and/o-r nitrogen compounds producing polymeric substances. These polymeric substances are thermoplastic and may stick to the hot metal surfaces of the exchanger tube and to corrosion products present in the feed stock. Subsequent reactions take place at the exchanger surface which transform the gum deposit to coke dispersed with corrosion product.

This invention is a departure from the dispersant theory for reducing fouling of hot, heat exchange surfaces. It has been discovered that fouling of hot surfaces of heat exchange tubes, catalyst beds and the like in direct contact with liquids or vapors of gas oils, lower alk-anes, lower alkenes, aromatics, naphthas and crude oils in hydrocarbon processing operations can, in many cases, be considerably improved at materially lower dosages than the commercially-used dispersant antifouling by dispersing or dissolving in a refinery petroleum stock of the aforesaid character an antifoulant of the type described in a small, but sufficient amount. It is believed that rather than by dispersant action or by inhibition of polymerization reactions, the antifoulants of the invention act by adsorption phenomenon or reaction on heat exchange surfaces.

The antifoulants of the invention are added to and dispersed in the stock of the aforesaid character prior to contact of the stock with the hot, heat exchange surface whereby fouling is reduced. The stock-contacting surface of the heat exchanger is hotter in a flow type heat exchanger than the temperature of the stock, the former temperature being in the order of 200-2000 F.

The antifoulants of the invention are used at dosage ranges from as little as one part per million to dosages ranging as high as 1000-2000 parts per million or in some instances as high as 5000 p.p.m. The optimum treatment level which will work is dependent upon the type of charge stock, the type of operation to which the stock is subjected, and the temperature to which the particular hydrocarbon is heated. As a general rule, the dosage range will be between 1 part per million and 1000 parts per million and preferably 5-500 parts per million.

One of the most interesting features of the invention is that the additive remains preferentially with the liquid phase of the charge stock during the various refining stages. Thus, for instance, if a gas oil is subjected to a catalytic process, the additive does not carry over to any appreciable extent into the finished product, but will remain behind with the residual and non-converted components of the liquid or be catalytically destroyed.

The additives may be added to the charge stock at any point in the process to be protected and will carry along with the production until such a point in the refining operation where the production is converted into a different chemical component or species.

Thus, where a crude stock is passed through heat exchangers to a thermal distillation unit to remove the lighter fractions, the additive may be added just prior to the heat exchanger section of the operation and will afford protection to both the exchanger surface and other surfaces of the distillation or fractionation unit.

By indicating that the surfaces of the various units are protected, it is meant that the charge stock has been rendered nonfouling as to the heat exchange surfaces such as metal surfaces; hence, deposit build-up does not occur. The process may, therefore, be considered as preventive rather than corrective in its operation. In some cases, the additives will remove existing fouling, but in most instances, the function of the additives is to prevent fouling rather than remove existing deposits.

The invention and its advantages will be further appreciated from the following specific examples thereof.

The laboratory unit employed to evaluate antifouling properties of various compositions consisted of a feed tank, a nitrogen pressurizing system, a valve and rotameter to control the bleed-off of nitrogen from the waste tank, valves to control the flow of feed stock from the fuel tank to the heater section and the waste tank, and a heater section which consists of an annnular heat exchanger through which the feed stock flows and is heated to field process temperatures. Flow from the feed tank to the waste tank by way of the heat exchanger is accomplished by maintaining the pressure in the waste tank lower than that of the feed tank.

A feed stock entering at the bottom of the exchanger system is at room temperature and the desired pressure. As the feed travels up the exchanger, it is heated to temperatures ranging from F. to in excess of 1000 F. and as high as 2000 F. During this rapid change in heat content, the feed degrades, forming particles which tend to adhere to the exchanger surface.

The determination of fouling rates by drop in heat transfer coefiicients would be very difiicult in units where vaporization occurs. It was decided, therefore, to develop an empirical, semiquantitative rating system for the heat exchange tubes, involving a measurement of the area covered by each type of deposit and a visual estimate of the severity of each deposit.

The deposits formed on the heat exchangers in units herein depend on the nature of the feed stock and the temperature. Both skin temperature and fluid temperature are significant factors. These deposits may range from a yellow-brown gum or light varnish at the cool end of the tube, to heavy coke at the hot end. The type of deposit on each distinguishable area on the tube was rated visually according to the following system.

Variety of deposit: Rating number Clear tube 0 Tube rainbowing or golden yellow 1 Light layer of varnish 2 Medium layer of varnish 3 Heavy layer of varnish, light coke layer 4 Moderate layer of coke 5 Heavy layer of coke 6 Following this visual rating, the rating number assigned to each distinguishable area on the tube is squared and multiplied by the average length of that area. These numbers are added to give a total rating number for each test.

This procedure is illustrated in the following example:

Type of Deposit Light varnish Medium varnish Light coke Heavy coke Rating 2 3 4 6 Inches 4 2 6 1 X X2 X X1 inate air-naphtha contact. With this approach, gum formation in the drum was minimized, and the naphthas evaluated in the laboratory closely approximated those fed to field units.

Antifouling evaluations with various petroleum stocks are set forth in the following tables. The test conditions chosen were typical of those encountered in heat exchangers located just ahead of the furnace in a hydrosulfurizer operation.

Table V [Thermal cracked naptha evaluated in unit at 700 p.s.i.; feed rate-800 ml. per hr.; 740 F.]

Dosage, Tube Percent AdditiveExample p.p.m. Rating Fouling Reduction From the foregoing disclosure it will be readily understoood that numerous modifications and changes will readily be apparent to those skilled in the art after consideration of the specification and the accompanying claims. Such minor modifications or substantial improvements that may occur to one skilled in the art provided with the benefit of our disclosure are included within the scope of our claims.

We claim as our invention:

1. In a process wherein a hydrocarbon stock is passed in direct, heat exchange contact with a heat exchange surface having a surface temperature of about 100 F. to 2000 F. to heat said stock to a processing temperature, the improvement comprising inhibiting the fouling by organic and inorganic deposits from said hydrocarbon stock on said heat exchange surface by incorporating in 14 said hydrocarbon stock an N-alkyl amidophosphoric acid selected from the group consisting of:

and mixtures thereof where R R R R R and R are radicals selected from the group consisting of hydrogen, alkyl, alkenyl, alkaryl, aryl, cycloaliphatic, cycloheteryl, and the foregoing radicals having substituents thereon, with the proviso that in at east one occurrence one of the foregoing radicals contains at least eight carbon atoms.

2. A process as claimed in claim 1 wherein R and 3. The process of claim 1 wherein said hydrocarbon stock is a petroleum charge stock undergoing refining and is selected from the group consisting of naphthas, gas oils, crudes and petroleum gases.

4. The process of claim 1 wherein said hydrocarbon stock is a petroleum charge stock being refined to produoe petro-chemicals.

5. The process as claimed in claim 1 wherein said N-alkyl amidophosphoric acid is added to said hydrocarbon stock in an amount in the range of 1-5000 p.p.m. by weight, based on said hydrocarbon stock.

No references cited.

DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

Claims (1)

1. IN APROCESS WHEREIN A HYDROCARBON STOCK IS PASSED IN DIRECT, HEAT EXCHANGE CONTACT WITH A HEAT EXCHANGE SURFACE HAVING A SURFACE TEMPRATURE OF ABOUT 100*F. TO 2000*F. TO HEAT SAID STOCK TO A PROCESSING TEMPERATURE, THE IMPROVEMENT COMPRISING INHIBITING THE FOULING BY ORGAIC AND INORGANIC DEPOSITS FROM SAID HYDROCARBON STOCK ON SAID HEAT EXCHANGE SURFACE BY INCORPORATING IN SAID HYDROCARBON STOCK AN N-ALKYL AMIDOPHOSPHORIC ACID SELECTED FROM THE GROUP CONSISTING OF: