CA1084686A - Corrosion control method using methoxypropylamine (mopa) in water-free petroleum and petrochemical process units - Google Patents

Abstract

ABSTRACT OF TIE DISCLOSURE

A method of inhibiting corrosion in separation units of water-free petroleum and petrochemical hydrocarbon processing systems which com-prises adding a compound corresponding to Formula I below either alone or in combination with a film-forming amine corrosion inhibitor to the hydro-carbon being processed:

Formula I
R-O(CH2)nNH2, wherein n is 2 or 3 and R is a lower alkyl radical of not more than 4 carbon atoms.

Description

~ 3'16~36 B~CKGROUND O~ THE INVENITO~
~ he present invention is directed to the prevention or control of corrosion in the separation units of water-free petro-leum hydrocarbon processing systems such as re~inery and petro-chemical units. Typical of the refinery systems are catalytic reformers, hydrosulfurization units and debutani~er towers.
Typical petrochemical systems are benzene and styrene units.
In particular, the subject invention entails a method ~or eliminating corrosion which occurs during the distillation process of refining and petrochemical systems utilizing water-free fee~s The most troublesome corrosion sites appear in distillation over-heads and in related down stream processing equipment. The corrosion problem, it is believed, arises due to the presence of -aeidie species in the various process feeds.

Corrosion occurs, for example, on the rnetal surfaces o fractionating towers, trays within these towers, heat exchanyers r receiving tanks, connecting pipes, ete. Serious corrosion appear~
in condensers and in overhead lines leading rom fractionating towers. (The overhead line of concern here is used to connect the distillation tower to the condensers.) The acidic materials pres ent in the separation unit charge, and the overhead product inelude HCl, hydrogen sulfide/ hydrogen c~anide, CO2, etc.
The corrosion problems experienced in the water-free petro-leum and petrochemical system separation units with which the present invention is concerned are similar to the corrosion problems experienced in "wet" crude oil dis-tillation. However, as discussed in more deiail below, we and others skil~ed in the art have ex.perienced deposit forma-tion problerns in the water-~ree sy~-tems wnich are much more severe than those seen in "wet" s~stems.

These deposits si~nificantly reduce separation unit capacity and promote corrosion at the deposi-tion sites.

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6~ ' t may be useful to look at the special need for this co~rosion inhibitor in the catalytic re~ormer. The catalytic re-foxmer handles a liyht hydrocarbon cut which is pr~treated to remove nitrogen and sulfur and to screen particulate matter. This pretreated feed is then brought into contact with a catalyst (generally noble metal and very expensive, i.e. platinum or palladium). The catalyst is usually activated by an excess of organic chloride con~aining-compound such as ethylene dichloride which releases chlorine to the catalyst. The excess bleeds o~f over a period of time: 1000-2000 ppm for 1-2 weeks is not un~
common. This chlorine eats up the overhead section and, therefore, constitutes a significant source of corrosion problems. Since the catalytic reformer is a water-free system, present corrosion inhibitors cannot be used without serious deposition problems.
We have, however, found a composition effective in overcoming this serious chlorine induced corrosion without causiny concommitant deposit formation problems.
When we use the term "water-free," we mean systems whose separation units see about 1% by weight o~ water based on the overhead product. In practice, water-free systems generally con-tain about 1/2-1% by weight of water in the overhead product.
When we use the term "wet," we mean separation unit with overhead product containing greater than 1% by weight of water. Generally, wet systems contain 2-15% by weight of water with an average of 4-5% water.
Numerous corrosion inhibitors useful in wet systems (e.y.
crude oil rPEininy) ha~e been tested in the separation units of the water-free systems described above. Prior to I
I

our discovery of the invention described herein, not one of the wet system inhibitors proved practically useful in water~free systems. Although inef-ficiency or cost-ineffectiveness may be a factor in rejecting some of the wet system inhibitors, the overwhelming reason for the rejection of the ; prior known inhibitors was deposit formation. As noted in the examples be-low, the wet system corrosion inhibitors when utilized in water-free systems form highly objectionable deposits which prevent efficient operation of the separation apparatus and, in many cases, cause plugging of lines, etc.

One common corrosion inhibitor -ammonia- it has been found, causes lesser deposit problems. However, this material produces severe corrosion through its hydrochloride salt.
A specific corrosion inhibitor utilized in crude oil (wet system) - distillation is morpholine. This compound is used either alone or in combi-nation with film-forming inhibitors as disclosed and claimed in United States Patent 3,4~7,~91. Another commercial product used in these crude oil systems is hexamethylene diamine. l~e have found that neither of these compounds is effective in water-free refining or petrochemical systems. While it has been found that over long periods of time in wet systems, hydrochloride salts of these amines tend to form deposits in the wet system distillation columns, column pump-arounds, overhead lines and overhead heat exchangers, in dry sys-tems, the deposits formed over even relatively short periods of times are in-tolerable.
Thus, the discovery of a corrosion inhibitor which performs in water-free separation units without significant and troublesome deposit for-mation would constitute an important contribution to the art.

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The present invention seeks to provide a method of inhibiting corrosion in water-free petroleum refining and petrochemical system separa-tion units.
The present invention further seeks to provide a corrosion inhi-bitor which does not tend to form significant deposits when utilized for practical periods of time, and which is compatible with film-forming inhibi-tors.
The invention comprises the discovery that the addition of a small ~; amount of a composition corresponding to Formula I below:
Formula I

( 2)n 2 ; wherein n is 2 or 3 and R is a lower alkyl radical of not more than 4 carbon atoms to the distilland of a water-free petroleum or petrochemical hydro-.
carbon processing system separation unit will control or eliminate corrosion -that ordinarily occurs at or beyond the point of initial condensation of vapors within the distilling unit. This composition, if employed per the teaching of the present invention, will have no a~verse effect on copper alloys and the like.

Illustrative of compounds falling within composition 1 are methoxy-propylamine ~MOPA), ethoxypropylamine~ methoxyethylamine and the like. The : most preferred compound is MOPA. To simplify further discussions herein of the invention, it will be illustrated hy using MOPA although it is understood that the other compounds fallin~ within Formula I are also operative.

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iO846~36 A very important aspec-t of the present invention is the discovery tha-t MOPA will control or prevent corrosion without forrn-ing significant or troublesome deposits over either short or prolonged periods of time. In contrast to MOPA, o-ther presently known corrosion inhibitors tested in water-free systems cause significant deposit formation. MOPA is thus far superior to the known corrosion inhibitors.
The explanation for this outstanding characteristic o~ ~OPA
may lie in the apparent ability of MOPA to form liquid hydrochloricle salts under dry conditions at ambient temperature. Although the salts may separate from the hydrocarbon stream, they do no. form significant solid deposits.
- MOPA ~an be added to the separation unit at any convenient point after the hydrocarbon leaves the reactor portion of ~he sys-tem for treatment in the separation uni-t. A convenient point o~
addition would be just before the hydrocarbon passes through the distillation column. The inhibitor can also be pumped directly into the gaseous overhead line. The particular point at which MOPA
is added will depend largely on the desicJn o~ the particular equip-ment and the point where greatest corrosion problems are manifested.
The dosage level of MOPA will depend on system parameteLs as well as the nature of the hydrocarbon. Corrosion inhibiting amounts will have to be determined on a case by case basis. Gener-ally, the dosages will lie in the range of 5-500 ppm. Since tne corrosion is caused by the acid content of the hydrocarbon, a useful dosage approach may be to adjust the pH of the first condensate. I
this case, the pH should be adjusted to above pH 4.0 and preferably above pH 5Ø Unlike systems utilizing ammonia as a corrosion inhi bitor, it is not essential that the pH be maintained belot~ ~ given ;
point--upper limits depend largely upon econom:ic considerations.
As noted earlier, MOPA may readily be usecl to control corro sion in conjunction with filrn-form:incJ corrosion inhibitors. Such filrrl-forminy inhibitors operate most economially at a pl~ above ~.5.

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Since MOPA is particularly effective in increasing the p~l of the initial condensate, the amount of film former that is required is thus substantially lessened.
Among the film-forming corrosion inhibitors which can be used in conjunction with MOPA to provide an overall system of protection are com-pounds formed by reacting certain aliphatic monoamines with polymerized fatty acids under salt-forming conditions.
The aliphatic monoamines used in preparing film-forming inhibitors are those amines having the general structural formula:

10R~ - N - R

where R9 is an aliphatic hydrocarbon radical of 8 to 22 carbon atoms in chain ; length and both R2 and R3 are selected from the group consisting of hydrogen and an aliphatic hydrocarbon radical of 1 to 22 carbon atoms in chain length.
The above structural formula includes both primary and secondary aliphatic monoamines as well as the tertiary aliphatic monoamines. Illustra-tive compounds coming within the above general formula include such primary ~ -amines as n-dodecyl amine, n-tetradecyl amine, n-hexadecylamine, lauryl amine, myristyl amine, palmityl amine, stearyl amine, and oleyl amine. Other com-mercially available primary amines include coconut oil amine, tallow amine, hydrogenated tallow amine and cottonseed oil amine. Useful secondary amines are dilauryl amine, dimyristyl amine, dipalmityl amines, distearyl amine, dicoconut amine and dihydrogenated tallow amine. In the case of many of the above amines, it will be noted that the source of alkyl substituent on the organic nitrogen is derived from a mixed vegetable oil or amimal fat, For purposes of convenience, these compounds have been named from the derivative alkyl-containing components. This system of nomenclature, particularly in the case ' ~

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of alkyl substituents derived from naturally occurring products such as fats, oils and the like, is used for purposes of simplification. It is be-lieved that those familiar with the art will readily understand that the alkyl substituent varies in the case of a coconut substituent with the alkyl groups containing from S to 18 carbon atoms in chain length. Similarly, in the case of hydrogenated tallow, the alkyl substituent will vary from about 12 to 20 carbon atoms in chain length.
In addition to using primary or secondary amines as exemplified above, tertiary amines such as octyl dimethyl amine, octadecyl dimethyl aminej octadecyl methyl benzyl amine, hexyldiethylamine, trilaurylamine, tricoconut amine, tricaprylyl amine, and similar type compounds also may be used.
Preferred aliphatic primary monoamines are amines having the general structural formula:

wherein R is an aliphatic hydrocarbon radical of from 8 to 22 carbon atoms in chain length. A preferred material of this type is the commercial product ;~
"Armeen SD"* sold by the Armour Industrial Chemical Company which is known generically to the art as Soya amine. As applied to the above formula the R group is a mixed aliphatic radical which has the following components:
Percent Ilexadecyl 10 :
Octadecyl 10 Octadecenyl 35 Octadecadienyl 45 : Out of the group of tertiary amines listed above, one of the most effective is dimethyl hydrogenated tallow amine. This preferred species may *Trade Mark ;

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be considered as an ammonium molecule which h~s had its three hydrogen atoms - -replaced by three alkyl groups. Two of these alkyl groups are methyl and the third is a mixed alkyl substituent derived from hydrogenated tallow.
A representative analysis of the mixed radicals of the hydroge-nated tallow group is as follows:
Percent Myristic 2 Palmitic 29 Stearic 68 Oleic One of the preferred commercial sources of this tertiary amine is "ArmeenM2HT"* sold by Armour Industrial Chemical Company.
The polymerized fatty acids are well known and have been described in numerous publications. Excellent descriptions of these materials may be found in Industrial and Engineering Chemistry, 32, page 802 et seq. (1940), and in the text "Fatty Acids" by Klare S. Markley, published by Interscience Publishers, Inc., New York City, 1947, pages 328 to 330. A specific example of such a polymer which has been found to be particularly useful is one which is prepared as a by-product of the caustic fusion of castor oil in the manu-facture of sebacic acid. This material is composed primarily of dicarboxylicacids derived by bimolecular addition in an olefinic polymerization where linkage occurs through the opening of at least two unsaturated bonds. Typi-cal properties of a material so obtained are as follows:
Acid value 150 Saponification value 172 ~nsaponifiable matter, percent 3.7 Iodine No. 36 Moisture content, percent 0.86 *Trade Mark ~':

_ 9 The material is, of course, not pure but predominantly contains dicarboxy-late polymers having about 34 to 36 atoms. A suitable commercial source of this dimer acid is llarchem Division of Wallace and Tiernan, Inc., and is known as "Century D-75 Acid.*"
A typical film~forming corrosion inhibitor useful in conjoint activity with MOPA may be prepared by combining l weight part OL "Armeen SD"*
with 2.57 weight parts of a polymerized fatty acid obtained as the residue of a dry distillation of castor oil with sodium hydroxide and reacting the mixture with stirring at a temperature of 60C. for 20 minutes, The final reaction product is then dispersed in equal weight parts of a heavy aromatic solvent.
Another useful film-forming corrosion inhibitor composition is prepared by heating 14 parts of "Armeen M2HT"* to the melting point and add-ing thereto 36 parts of "Century D-75 Acid,"* The mixture was reacted for 10 minutes at 130 - 150F, and the resultant product added to a heavy aromatic solvent in equal proportions by weight of product to solvent.
Distillation range mm, 760 Initial boiling point C. 171 Percent:
20 10 C. 18~

go C. 260 End point C. 278 ~ n reacting the above recited amines with polymerized fatty acids to obtain the film-forming compositions, care should be taken to maintain salt-forming conditions. This is done primarily by using reaction tempera-tures of from 25 to 100C., and by avoiding the presence of materials which cause the splitting ou~ of water. This environment is sometimes referred to as "neutralizing conditions". It is the salt producible from the above listed ;
raactants which is of primary interest in the instant invention. Further care must be *Trade Mark ,B,, `, `,`. .` `~ ,, . .... , . . ~
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1~ L6136 ta~en in conduc-ing the reac-tion to eliminate the possibility of the presence of free amines in the f,inal reaction product. Reac-tion proportions conduc-tive to accomplishing this typically include the above recited use of a weight ratio o~ typical polymer to typical monoamine of 2.57~
Additional film-forming compositions that can be used in conjunction with the subject inhibitor include those disclosed in U.S. Patent 3,003,955.

'EX~MPLES

~xa'mple 1 ' .
The ability of MOPA to prevent initial condensake corrosion :in'water-fxee separation units withouk ~orming significant deposiks was determined as set forth below. Testing was carried out with MOPA along with other neutralizing amines to determine relative ,, , efficacy from the standpoint of preventing corrosion. Also, the ; ability of MOPA to perform without forming deposits under normal conditions of use was investigated.
,A laboratory test unit was constructed to evaluate the invention. The unit consisted oE a two-inch diameter, fifteen-tray ," glass Oldershaw column fitted with a reboiler and overhead syskem similar to crude distillation units. Preheated naphtha was charg~d into the column at Tray S where ik cascaded downward and mixed with hot vapor rising from the reboiler. Usually, small sidecuts were taken ~rom Tray 10. Warm re~lux was pumped from the ove,rhead re-ceiver back to Tray 15 (top tray) to par-tially cool the hot vapors coming up the column and yoing overhead.
~, Either a dipropylene glycol (DPL) and hydrochloric acid compleY. or dr~ HCL gas provided hydrochloric acid vapor for the kest unit. The acid vapor was injected into the top section of khe reboile,r. 50 ppm or less o~ water were present in the unit feed overall (dissolved in the naphtha charged to the unit).

-L~E~46E~6 Generally, heated corrosion inhibitor ~las fed into the reflux line to neutralize the acid vapor cominy up the column.
Deposit formation was observed visually and by chloride analysis of the charge and effluent streams. At the end of each run, the column head was removed and wash water was poured into the column.
This wash water was partially refluxed overhead to remove deposits in the overhead line. ~he two samples of wash water resulting from washing the column and overhead were analyzed for chlorides obtai.ned from each source and compared with the amount of chlorides charged to the unit.
In order to provide a satisfactory test in a limited amount of time, the test unit was operated on a continuous basis and the 'amount of hydrochloric acid charged was 50 ppm active basis over~
head product--about 15-20 times the level usually observed in a separation unit. Operating conditions were selected to provide a satisfactory test in a 20-24 hour-period.
To evaluate the invention and compare it against a typical wet system amine, the following compositions were tested:
Composition 1: 40% MOPA in heavy aromatic solvent;
Composition 2: 40~ Morpholine in heavy aromatic solvent;
Composition 3: 40~ 2-methoxyethylamine The results obtained are xepotred in Table I. The key quantitat.~ve data relating to inhibitor effectiveness and depo~it formation re-ported is residual chloride in both the column and the overhead, Analysis of Table I shows superior performance for MOPA and metho~yethylamine~

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Example 2 Tests were run to aetermine the effect o~ reducing the . ¦ amount of water present in the overhead upon deposit formation.
¦ The laboratory test unit described in Example 1 was used in this experiment. The amine corrosion inhibitor used was 40% morpholine and heavy aromatic solvent. The data is reported in Table II.
Examination of quantitave chloride data and the quantita-tive visual inspection results indicates that reducing the amount : of water present in the overhead from about 4% to about 2% greatly increases the amount of deposits remaining in the column and over-head portion of the test unit. Thus, deposit problems in water-free system are much more severe than tho~e in wet ystems.

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for controlling corrosion in water-free petroleum and petrochemical hydrocarbon processing system separation units, in which the material being processed contains less than 1% of water, which comprises adding a corrosion inhibiting amount of a composition having the formula R-O(CH2)nNH2 wherein n is 2 or 3 and R is a lower alkyl radical of not more than 4 carbon atoms to the hydrocarbon being processed in the separation unit.

2. The process of claim 1 wherein the composition is chosen from the group consisting of methoxypropylamine, methoxyethylamine and ethoxypropyl-amine.

3. The process of claim 1 wherein the composition is methoxypropyl-amine.

4. The process of claim 1 wherein the composition is added to the hydrocarbon before said hydrocarbon is passed through the distillation column of the separation unit.

5. The process of claim 1 wherein the composition is added to the overhead line of the separation unit.

6. The process of claim 1 wherein the amount of the composition added to the hydrocarbon is sufficient to raise the pH of the initial conden-sate to above 4Ø

7. A process for controlling corrosion in water-free petroleum and petrochemical hydrocarbon processing system separation units comprising add-ing to the hydrocarbon a corrosion inhibiting amount of a film-forming amine along with a composition having the formula R-O(CH2)nNH2 wherein n is 2 or 3 and R is a lower alkyl radical of not more than 4 carbon atoms in an amount sufficient to raise the pH of the initial condensate to above 4Ø

8. The process of claim 7 wherein the composition is chosen from the group consisting of methoxypropylamine, methoxyethylamine and ethoxy-propylamine.

9. The process of claim 7 wherein the composition is methoxy-propylamine.

10. A process according to claim 7 wherein the film-forming amine is of the formula wherein R4 is an aliphatic hydrocarbon radical of 8 to 22 carbon atoms, and both R2 and R3 are selected from the group consisting of hydrogen, and an aliphatic radical of 1 to 22 carbon atoms.

11. A process according to claim 10 wherein the film-forming amine is of the formula R4NH2.