Corrosion Inhibitors For Refining & Petrochemical Processing Equipment

Abstract

A process for the prevention of corrosion in refinery systems by the injection of an imidazoline compound into the overhead vapor line. The imidazoline compound is formed from the reaction of a naphthenic acid and dipropylene triamine.

Description

INTRODUCTION

This invention relates to a process for the prevention of corrosion in refinery systems by injecting an imidazoline compound into the overhead vapor line. More specifically, this invention relates to the addition of an imidazoline compound having corrosion inhibition properties to the refinery system, the imidazoline being capable of preventing corrosion inside the refinery system. The preferred imidazolines are formed by the reaction of dipropylene triamine and naphthenic acid.

The imidazoline surfactant is known to the art as a corrosion inhibitor. The composition and its use as a corrosion inhibitor in motor fuel and on metal surfaces is disclosed in U. S. Pat. No. 2,466,517 and U. S. Pat. No. 3,510,282, the specifications of which are to be incorporated by reference in its entirety. In particular, the imidazoline surfactant formed by the reaction of dipropylene triamine and a naphthenic acid is disclosed as a corrosion inhibitor.

In refinery processing there is usually a significant amount of water present with the crude petroleum. Water is present with the crude petroleum when it is extracted from the ground. In addition, substantial amounts of water are present from condensation resulting from the use of steam in the distilling stage. In refinery processing due to the presence of both water and crude petroleum, it has been found that the water and crude petroleum easily mix, the result being the formation of an emulsion. When such an emulsion is formed it is often quite time consuming and expensive to break the emulsion to rid the system of the water. It, therefore, would be desirable to inject into the system a chemical which would prevent or reduce this emulsion formation.

It has been found that when the imidazoline compound is injected into a refinery system, in addition to its corrosion inhibition properties, it also exhibits the ability to reduce formation of an emulsion of water and crude petroleum.

OBJECTS

It is an object of this invention to provide a process for the prevention of corrosion in refinery systems by injecting into the overhead vapor line an imidazoline compound.

It is an object of this invention to provide an imidazoline compound to prevent emulsion formation between water and the crude petroleum in refinery processing.

It is also an object of this invention to provide an imidazoline compound useful in preventing emulsion formation between water and crude petroleum in refinery processing, said surfactant having corrosion inhibition properties.

It is a further object of this invention to provide an imidazoline compound formed by the reaction of dipropylene triamine and naphthenic acid, said compound preventing emulsion formation of water and crude petroleum in refinery processing.

Further objects will appear hereinafter.

THE INVENTION

This invention relates to a process for the prevention of corrosion in refinery systems comprising the step of injecting into the refinery system a composition consisting of:

A. from 10-40 percent by weight of an organic solvent; and

B. from 60-90 percent by weight of an imidazoline compound having corrosion inhibition properties, said compound formed by the reaction of dipropylene triamine and a naphthenic acid in the ratios of 1:2 to 2:1.

The preferred composition consists of:

A. 20 percent by weight of an organic solvent; and

B. 80 percent by weight of an imidazoline surfactant having corrosion inhibition properties, said surfactant formed by the reaction of dipropylene triamine and a naphthenic acid in the ratio of 1:2.

ORGANIC SOLVENT

The organic solvent of the composition acts merely as a solvent or carrier for the imidazoline surfactant. The organic solvent may be aliphatic or non-aliphatic liquid. Generally, the organic solvent is a hydrocarbon liquid having from 3 to 22 carbon atoms. Typically, high boiling aromatic organics are used in the practice of this invention. For example, kerosene is a preferred organic solvent. Other solvents which may be used are propane, butane, and heptane. The organic solvents used in this invention are not limited to those mentioned above but include a large type and variety of organic solvents in which the imidazoline surfactant is soluble.

IMIDAZOLINE SURFACTANT

The imidazoline surfactant of this invention is formed by the reaction of dipropylene triamine and a naphthenic acid in a ratio of 1:2 to 2:1. The preferred ratio of dipropylene triamine to naphthenic acid is 1:2. It has been found that when ratios of the dipropylene triamine to naphthenic acid outside the above mentioned range are used, an inferior imidazoline surfactant is obtained which is not as efficient in preventing the formation of an emulsion between water and the fuel.

The naphthenic acid used in this invention is defined in U.S. Pat. No. 3,510,282 as being a petroleum refining by-product obtained when the alkali liquor from the caustic treatment of gas oil is acidified with sulfuric acid. This treatment produces a dark brown about 12 on the Gardner color scale (when cut 1 to 9 with mineral spirits) oily liquid which separates to the top of the aqueous liquor. The mixed acids can be divided roughly into three groups having the general formulas: C.sub.n H.sub.2n O.sub.2, C.sub.n H.sub.2n.sub.-2 O.sub.2, and C.sub.n H.sub.2n.sub.-4 O.sub.2. The first group occurs largely in the lower boiling fraction of the mixture. They usually contain 6 or 7 carbon atoms and are colorless.

The second group, usually the largest, contains acids of 8 to 12 carbon atoms having the structure: ##SPC1##

The third group contains the heaviest molecules which are polycyclic and have from 12 to 23 carbon atoms. All fractions from a carefully distilled naphthenic acid (24) contain some color which, so far, has proved impossible to remove. Tarry residues account for the dark color of the crude, but these are largely removed by distillation. Since naphthenic acids are saturated and primarily cyclic, their soaps have much greater stability than those of other common liquid acids. The crude acid as delivered has a density of 8.04 to 8.44 pounds per gallon and a viscosity of 1.25 poises at 77.degree. F. The acid values range from 160 to 270, but naphthenic acid used for soap manufacture usually has an acid value between 220 and 230. pH of the water extract is about 5.5 and the iodine value between 8 and 11. Unsaponoifiables are held below 12 percent. The initial boiling points vary widely from shipment to shipment. Individual batches have boiled below 200.degree. F. and up to almost 400.degree. F. at 3.5 inches of mercury.

A typical formula in connection with some of the commercially available naphthenic acids is the following: ##SPC2##

These particular acids are available in at least three different grades; Grade 1 having an average molecular weight of 290-300. Generally speaking, there is present about 6 percent of non-saponifiables and this type is perhaps characteristic of the most common commercially available naphthenic acid.

Grade 2 has a somewhat higher molecular weight, for instance 320-330 and contains about 8 percent of non-saponifiable matter. Grade 3, which finds considerable utility, has a molecular weight range of 410-420 and contains about 10 percent nonsaponifiable matter.

Any naphthenic acid may be used but preference is to use the commercial grades above described, or in some instances, mixtures of two different grades so as to give, for example, an average molecular weight of 360 to 370 in some instance, and in others, a molecular weight of about 310, or thereabouts.

In examining the formula immediately preceding, with the formula preceding the above formula, and ignoring difference in the cyclic structure of the naphthenic acids, it is apparent that in at least some naphthenic acids which are available commercially the cyclic structure is part of the beta carbon atom. On the other hand, as far as is known, and referring to the formula ##SPC3##

there are available naphthenic acids in which apparently x in the formula represents a small whole number, for instance, 3 or 4 or the like.

In practicing the present invention preference is given to the higher molecular weight naphthenic acids, for example those having an average molecular weight of at least about 2,000 such as about 250 to 500, or greater, for example from about 290 to 420 but preferably from about 325-375.

Since commercial grades of naphthenic acids are employed, these contain many individual species over a molecular weight range.

The most preferred naphthenic acid those known as "Sunaptic" acids which are high-molecular-weight naphthenic acids prepared by the caustic extraction of selected base stocks. They range in acid number from 120 to 180, in molecular weight from 300 to 415, and are available in three grades, A, B, and C.

Specifications and typical analyses for the three Sunaptic acids are given in the table below. They are mono-carboxylic acids and, having no olefinic unsaturation, are highly resistant to oxidative rancidity. They have low pour points and contain relatively low amounts of unsaponifiable matter. Sunaptic acids are soluble in most hydrocarbons. ##SPC4##

THE DIPROPYLENE TRIAMINE

The amine that reacts with the naphthenic acid to form the imidazoline surfactant of this invention is dipropylene triamine. One molecule of dipropylene triamine reacts with two molecules of naphthenic acid to form two isomers: ##SPC5##

One molecule of dipropylene triamine reacts with one molecule of naphthenic acid to form two isomers: ##SPC6##

Thus, there are four possible imidazoline surfactant isomers which may be formed from the reaction of dipropylene triamine and naphthenic acid.

APPLICATION

As mentioned above, water is usually present in the refinery system. Water is present with the crude petroleum when extracted from the ground and, in addition, substantial amounts of water are present from condensation resulting from the use of steam in the distilling stage. In order to prevent the formation of an emulsion between the water and the crude petroleum, the imidazoline surfactant is injected into the refinery system. The imidazoline surfactant is generally diluted by an organic solvent. The preferred concentration of the imidazoline surfactant is 20 percent by weight.

The diluted imidazoline surfactant can be injected at numerous stages of the refinery system. The preferred points of injection are at the overhead vapor line and at the reflux line. Generally, the composition is injected as a spray. The imidazoline surfactant will distribute throughout the system preventing formation of an emulsion as well as preventing corrosion on the metal surfaces inside the refinery unit. Generally from 2-5ppm of the composition is injected.

To further illustrate the invention, the following examples are presented:

EXAMPLE 1

At a petroleum refinery in Southern California, an imidazoline surfactant dissolved in kerosene was injected into the overhead vapor line as a fine spray. The composition consisted of 80 percent kerosene and 20 percent imidazoline surfactant.

The imidazoline surfactant was prepared by the reaction of dipropylene triamine and a commerical naphthenic acid in a molar ratio of 1:2. The naphthenic acid used in the Examples is derived from petroleum and is an organic acid containing a substituted naphthenic ring structure. The naphthenic acid has the following properties:

TABLE II

Flash Point, Tag, Open Cup, .degree.F. 150+ Acid Number, Oil-Included 189 Acid Number, Oil-Free 219 Unsaponifiable Content, (% by wt.) 14.1 Color (ASTM) Black Water Content (% by wt.) Trace Viscosity, at 100.degree.F., SSU Viscosity, at 210.degree.F., SSU Specific Gravity at 60.degree.F. 0.983

the reactants were charged to reactor and heated to 170.degree.C. for 30 minutes at which time a vacuum of about 28 inches was applied for an additional 4 hours. The product was cooled and dissolved in the heptane.

The composition was injected in a concentration of 12ppm. Samples of the fuel were removed from the refinery system and the amount of water emulsified was measured by using the test procedure ASTM D 2550. This is a measure of transmittance with the WISM values ranging from 0-100 with the higher WISM value indicating lower amounts of water present. The WISM value obtained was 97.

Typical WISM values obtained using other surfactants are listed in Table III.

TABLE III

SURFACTANT PPM WISM Value Diethylene triamine + Naphthenic Acid 20 70 Diethylene triamine + Oleic Acid 20 75 Dipropylene triamine + Naphthenic Acid 20 93 Dipropylene triamine + Linoleic Acid 20 67

It is observed from the data presented above that the imidazoline surfactant of this invention results in substantial reduction in the amount of water held in emulsion with the crude petroleum.

EXAMPLE II

The corrosion rate of the imidazoline surfactant as prepared in Example I was measured as compared to the corrosion rates of the surfactants listed in Table III. The resulting corrosion rates are tabulated in Table IV.

The corrosion rates were determined by use of the following procedure:

Through the scale neck of a 1000 ml round bottom, three-neck Pyrex flask having a gas dispersion tube inserted through a cork stopper and a coupon holder is inserted 425 cc of depolarized naphtha and 225 cc of refinery stream water.

The refinery stream water is deionized water containing 1000 ppm hydrochloric acid and 500 ppm acetic acid. The pH of the water is adjusted to 7.5 with ammonium hydroxide. The surfactant is also added at this point. The gas tube holder is inserted into the flask neck and the flow of gas started. The gas consists of 93 percent prepurified nitrogen, 5 percent air and 3 percent hydrogen sulfide and is fed at a rate of 40 cc/min./test through calibrated capillary tubings. The cone drive motor is turned on as is the heating mantle. The test is allowed to run for an hour before the coupon is inserted to attain equilibrium. The coupon is positioned such that the gas dispersion tube is on the downstream side of the coupon, the gas makes a complete circuit of the flask before it hits the coupon.

The corrosion coupon is a 0.9525 cm (3/8 inch) .times. 3.81 cm (1-1/2 inches ) .times. 0.317 cm (1/8 inch) S.A.E. 1020 mild steel coupon. A 0.317 cm diameter hold is drilled or punched through one end of the coupon not less than 0.317 cm from the edge. Prior to use, this coupon is sandblasted and weighed. Contact with skin is avoided. The coupon remains in the system overnight at which time it is removed from the flask, cleaned with cleansing powder to remove loose corrosion products, dipped with agitation in an inhibited acid bath for 30 seconds, in a saturated soda ash bath for 20 seconds, washed in tap water to remove remaining salts, dipped with agitation in an acetone bath and spun dry. The coupon is then dried in a 100.degree.C. oven for 30 minutes and reweighed. The corrosion rate is calculated on the basis of weight loss and test duration.

The corrosion rate of the product formed in Example I was 12 mpy at a dosage of 12 ppm and 14 mpy at a dosage of 6 ppm.

TABLE IV

Surfactant No. Dosage (PPM) Corrosion Rate (MPY) 1 12 25 1 6 35 2 12 27 2 6 38 3 12 29 3 6 37 4 12 23 4 6 39

it is observed from the data presented in Table IV that in a refinery system the imidazoline surfactant of this invention results in substantially improved corrosion rates.

Claims

I claim:

1. A process for the prevention of corrosion in refinery systems comprising the step of injecting into the overhead vapor line of the refinery system a composition consisting of:

A. from 10-40 percent by weight of an organic solvent; and

B. from 50-90 percent by weight of an imidazoline compound having corrosion inhibition properties, said compound formed by the reaction of dipropylene triamine and a naphthenic acid in the ratios of 1:2 to 2:1.

2. The process for the prevention of corrosion in refinery systems as in claim 1 wherein the ratio of dipropylene triamine to naphthenic acid is 1:2.

3. A process for the prevention of corrosion in refinery systems in refinery processing comprising the step of injecting into the overhead vapor line of the refinery system a composition consisting of:

A. 20 percent by weight of an organic solvent; and

B. 80 percent by weight of an imidazoline surfactant having corrosion inhibition properties, said surfactant formed by the reaction of dipropylene triamine and a naphthenic acid in the ratio of 1:2.

4. A process for the prevention of corrosion in refinery systems as in claim 1 wherein from 2-5 ppm of the composition is injected into the overhead vapor line.