CA2065905A1 - Crude oil antifoulant - Google Patents

Abstract

ABSTRACT

This invention relates to methods for inhibiting fouling of heat exchanger surfaces in crude oil processing systems. The methods comprise adding an effective amount of an aminoalkyl piperazine compound to the crude oil being processed. Preferably, the aminoalkyl piperazine compound is l-(2-aminoethyl) piperazine.

Description

2~65~

CRUDE OIL ANTIFOULANT

FIELD OF THE INVENTION

The present invention relates to methods for inhibiting the fouling of heat exchangers during the refining of crude oils.
The methods are particularly useful at inhibiting fouling of heat exchangers processing high carbonyl containing crude oils.

BACKGROUND OF THE INVENTION

Fouling can be defined as the accumulation of unwanted matter on heat transfer surfaces. This deposition can be very costly in refinery and petrochemical plants since it increases fuel usage, results in interrupted operations and production losses and increases maintenance costs.

Deposits are found in a variety of equipment: preheat exchangers, overhead condensers, furnaces, heat exchangers, fractionating towers, reboilers, compressors and reactor beds.

, . .

, .

These deposits are complex but they can be broadly characterized as organic and inorganic. They consist of metal oxides and sulfides, soluble organic metals, organic polymerst coke, salt and various other particulate matter. Chemical antifoulants have been developed that effectively combat fouling.

The chemical composition of organic foulants is rarely identified completely. Organic fouling is caused by insoluble polymers which sometimes are degraded to coke. The polymers are usually formed by reactions of unsaturated hydrocarbons, although any hydrocarbon can polymeri~e. Generally, olefins tend to polymerize more readily than aromatics, which in turn polymeri~e more readily than paraffins. Trace organic materials containing hetero atoms such as nitrogen, oxygen and sulfur also contribute to polymerization, often through a condensation mechanism.

In refineries, deposits usually contain both organic and inorganic compounds. This makes the identification of the exact cause of fouling extremely d;fficult. Even if it were possible to precisely identify every single deposit constituent, this would not guarantee uncovering the cause of the problem. Assumptions are often erroneously made that if a deposit is predominantly a certain compound, then that compound is the cause of the fouling. In reality, oftentimes a minor constituent in the deposit could be acting as a binder, a catalyst, or in some other role that influences actual deposit formation.

.

The final form oF the deposit as viewed by analytical chemists may not always indicate its origin or cause. Before openings, equipment is steamed, waterwashed, or otherwise readied for inspection. During this preparation, fouling matter can be changed both physically and chemically. For example, water-soluble salts can be washed away or certain deposit constituents oxidized to another form.

In petrochemical plants, fouling matter is often organic in nature. Fouling can be severe when monomers convert to polymers before they leave the plant. This is most likely to happen in streams high in ethylene, propylene, butadiene, styrene and other unsaturates. Probable locatinns for such reactions include units where the unsaturates are being handled or purified, or in streams which contain these reactive materials only as contaminants.

Even through some petrochemical fouling problems seem similar, subtle differences in feedstock, processing schemes, processing equipment and type of contaminants can lead to variations in fouling severity. For example, ethylene plant depropanizer reboilers experience fouling that appears to be primarily polybutadiene in nature. The severity of the problem varies significantly from plant to plant, however. ~he average reboiler run length may vary from one to two weeks up to four to six months (without chemical treatment~.

:

:
.

~ 3 Although it is usually impractical to iden~ify the fouling problem by analytical techniques alone, this information combined with knowledye of the process, processing conditions and the factors known to contribute to fouling, are all essential to understanding the problem.

There are many ways to reduce fouling both mechanically and chemically. Chemical additives often offer an effective anti-fouling means; however, processing changes, mechanical modifications equipment and other methods available to the plant should not be overlooked.

Antifoulant chemicals are formulated from several materials: some prevent foulants from forming, others prevent foulants from depositing on heat transfer equipment. Materials that prevent deposit formation include antioxidants, metal coordinators and corrosion inhibitors. Compounds ~hat prevent deposition are surfactants which act as detergents or dispersants.
Different combinations of these properties are blended together to maximize results for each different application. These "poly functional" antifoulants are generally more versatile and effective since they can be designed to combat various types of fouling that can be present in any given system.

Condensation inhibitors include materials that interfere ~ith acidtbase reactions, and others that react with hetero atom compounds such as carbonyls and pyrroles. These inhibitors : , 2~

prevent growth of the hydrocarbon molecules and thus help to inhibit fouling.

Research indicates that even very small amounts of oxygen can cause or accelerate polymerization. Accordingly, antioxidant type antifoulants have been developed to prevent oxygen initiated foul;ng. Antio~idants act as chain~stoppers by forming inert molecules with the oxidized free radical hydrocarbons, in accordance with the following reaction:

Chain Termination ROO Antioxidant _ ROOH + Antioxidant (H) Surface modifiers or detergents change metal surface characteristics to prevent foulants from depositing. Dispersants or stabili2ers prevent insoluble polymers, coke and other particu-late matter from agglomerating into large particles which can settle out of the process stream and adhere to the metal surfaces of process equipment. They also modify the particle surface so that polymerizat10n cannot readily take place.

Antifoulants are designed to prevent equipment surfaces from fouling. They are not designed to clean up existing foulants.
Therefore, an antifoulant should be started immediately after equipment is cleaned. It is usually advantageous to pretreat the system at double the recommended dosage for two or three weeks to reduce the initial high rate of fouling immediately after startup.

; ~ ~
.
.
~ ~ , 2 ~

The increased pro~it possible wi~h the use of antifoulants varies from application to application. It can include an increase in production, fuel savings, maintenance savings and other savings from greater operating efficiency.

There are many areas in the hydrocarbon processing industry where antifoulants have been used extensively; the main areas of treatment are discussed below.

In a refinery, the crude unit has been the focus of attention because of increased fuel costs. Antifoulants have been successfully applied at the exchangers; downstream and upstream of the desalter, on the produçt side of the preheat train, on both sides of the desalter makeup water exchanger and at the sour water stripper.

Hydrodesulfurization units of all types experience preheat fouling problems. Among those that have been successfully treated are reformer pretreaters processing both straight run and coker naphtha, desulfurizers processing catalytically cracked and coker gas oil, and distillate hydro-treaters. In one case, fouling of a Unifiner stripper column was solved by applying a corrosion inhibitor upstream of the problem source.

Unsaturated and saturated gas plants (refinery vapor recovery units) experience fouling in the various fractionation columns, reboilers and compressors. In some cases, a corrosion .
.

control program combined with an antifoulant program gave the best results. In other cases, an application of antifoulants alone was enough to solve the problem.

Cat cracker preheat exchanger fouling~ both at the vacuum column and at the cat cracker itself, has also been corrected by the use of antifoulants.

The two most prevalent areas for fouling problems in petrochemical plants are at the ethylene and styrene plants.
In an ethylene plant, the furnace gas compressors, the various fractionating columns and reboilers are subject to fouling.
Polyfunctional antifoulants, for the most part, have provided good results in these areas. Fouling can also be a problem at the butadiene extraction area. Both antioxidants and polyfunctional antifoulants have been used with good results.

In the different design butadiene plants, absorption oil fouling and distillation column and reboiler fouling have been corrected with various types of antifoulants.

Chlorinated hydrocarbon plants, such as V~M, EDC and perchloroethane and tri-chloroethane have all experienced various types of fouling problems. The metal coordinating/antioxidant-type antifoulants give excellent service in these areas.

2~$~

SUMMARY OF THE INVENTION

The present invention pertains to methods for inhibiting fouling in heat exchangers during the processing of crude oils comprising adding to said crude oils an effective amount for the purpose of 1-(2-aminoethyl) piperazine.

The present invention is particularly useful at inhibiting fouling in heat exchangers upstream or downstream of the desalting unit during the processing of crude oils having a high carbonyl content.

DESCRIPTION OF THE RELATED ART

The use of 1-(2-aminoethyl) piperazine is known in the petroleum refining industry. As evidenced ln U.S. Patent No.
4,744,881, Reid, May 1988, 1-(2-am;noethyl) piperazine is used ;n conjunction with a non-h;ndered or partially h;ndered phenol compound to reduce foul;ng problems in hydrocarbons, specifically refined fractions having a brom;ne number greater than 10.

1-(2-am;noethyl) p;peraz;ne can also be used with a phosphite compound to stab;l;ze d;st;llate fuel oil and ;nhibit color degradat;on. U.S. Patent No. 4,867,754, Reid, September 1989, teaches that th;s combination is more effective than either compound used alone, U.S. Patent No. 4,697,290, Reid, March 1987 , ~ i 2 ~

teaches a combination of 1-(2-aminoethyl) piperazine and N,N-diethylhydroxylamine for color stabilized distillate fuel oils.

U.S. Patent No. 4,200,518, Mulvany, April 1980, teaches the use of a polyalkylene amine compound to reduce fouling in hydrocarbon streams passing through a heat exchanger. Numerous amines are disclosed as being effective as antifoulants, however, 1-(2-aminoethyl) piperazine is not taught as an antifoulant. The polyalkylene amine compounds in Mulvany have molecular weights ranging from 200 to 2700 and preferably in the range of 1000 to 1500. The compound of the instant invention has a molecular weight of 12g.

U.S. Patent No. 4,714,793, Van Eijl, December 1987, teaches a process for inhibiting the polymerization of styrene from hydrocarbon streams using an N-aminoalkyl piperazine compound.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods for inhibiting the fouling of heat exchangers located upstream or downstream of the desalting unit in a crude oil having a high carbonyl content processing system comprising adding to said crude oil an effective amount for the purpose of an aminoalkyl piperazine compound.

2~ 9 ~

The preferred aminoalkyl piperazine compound is l-(2-aminoethyl) piperazine. This co~pound is preferred in certain crudes as some crudes will foul the heat exchangers of the crude processing un;t prior to the desalting unit. The specific crude oils that are treated by the methods of the present invention are those that contain a high carbonyl content.

The use of aminoethyl piperazine (AEP) is known in the petroleum refining industry as an antioxidant in hydrocarbon processing. U.S. Patent No. 4,744,881 Reid which is wholly incorporated by reference herein teaches the use of a composition of an unhindered or hindered phenol and a strongly basic amine compound to control fouling in high temperatures hydrocarbon fluids having a bromine number greater than ten. U.S. Patent No.
4,647,290 Reid which is wholly incorporated by reference herein teaches the use of a composition of N-(2-aminoethyl) piperazine and N,N-d;ethylhydroxyl amine to inhibit color deterioration;of distillate fuel oils.

Reid '881 teaches the use of a synergistic composition of a phenol compound and an amine compound to control fouling in hydrocarbon fluids having bromine numbers in excess of lO. These systems contain unsaturated or olefinic components which are induced by oxygen to polymerize or react. The methods of the present lnvention employ an overpressure of nitrogen to the system. The resulting crude stream is relatively oxygen free.
Crudes generally have bromine numbers less than 10.

. .

~5~

Reid '290 ;s directed towards color inhibition in distil-lation fuel oils through the synergistic combination of N-(2-amino-ethyl) piperazine and N,N-diethylhydroxyolamine. Reid '290 teaches in Col. 5, lines 41-45 and Col. 6, lines 1-2 that neither of these two chemical species, when used alone, are effective antioxidants in the hydrocarbon systems taught in Reid '290. This patent is also directed towards finished products that are in transit or storage and their protection from color contamination.
The present invention is directed to crude oils that are under going petroleum re~ining.

The methods are adapted to inhibit formation and deposition of components that polymerize or react due to the high temperatures of the heat exchanger. Temperatures from 100 to ~00F are o~ten reached in these systems. These systems are primarily composed of ferrous metal. Iron, as well as iron alloys such as low and high carbon steel, stainless steel and nickel-chromium-iron alloys are customarily used for the production of hydrocarbon processing equipment such as heat exchangers.

It has been found that fouling on the carbon steel surfaces utilized in conjunction with the test system described herein is inhibited by use of the aminoalkyl piperazine compounds described above. Accordingly, it is to be expected that coking will also be reduced on iron, nickel and chromium based metallurgical surfaces in contact with the crude oil.

~ ~ ~ 3 ~ ~ ~

The aminoalkyl piperazine compounds may be added to the crude oil being processed at any point along the processing system. The aminoalkyl piperazine compound may be added to the crude oil either as a concentration or as a solution using a suitable carrier solvent which is compatible with the piperazine compound and the crude oil. Heavy aromatic naphtha is representative of those solvents. The pre~erred solution is 1-(2-aminoethyl) piperazine dissolved in heavy aromatic naphtha.

The amount of aminoalkyl piperazine added to the crude oil is clearly dependent upon the severity of the fouling problem at the heat exchanger as well as the concentration of the piperazine compound employed. Accordingly, it is desirable to ensure that the aminoalkyl piperazine compound content of the solution is high enough to ensure that an ample quantity of piperazine compound is dispersed in the crude oil. As such, product formulation lends itself to great flexibility Broadly speaking, the dosage recommendations range from about 1 to about 1000 parts piperazine compound per million parts crude oil. More preferably, a range from about 5 to about 200 parts piperazine compound per million parts crude oil.

The antifoulant compound of the invention may include other additives, if desired. For example, other antifoulants may be used in combination with the piperazine compounds of this invention, or corrosion inhibitors, etc., may be combined with the antifoulants of the invention.

2 ~

In order to more clearly illustrate this invention, the data set forth below was developed. The following examples are included as being illustrations of the invention and should not be construed as limiting the scope thereof.

In order to ascertain the antifouling efficacy of the anti-foulant compounds the materials were subjected to a dual fouling apparatus test. In the dual fouling apparatus, process fluid (crude oil) is pumped from a pressure vessel through a heat exchanger containing an electrically heated rod. Then the process fluid is chilled back to room temperature in a water-cooled condenser before being remixed with the fluid in the pressure vessel. The system is pressurized by nitrogen to minimize vaporization of the process fluid.

The Oual Fouling Apparatus (DFA) used to generate the data shown in the following Table contains two heated rod exchangers that are independent. The Hot Liquid Process Simulator (HLPS) fouling apparatus contains a single heat exchanger. In both tests, the rod temperature was controlled while testing. As fouling on the rod occurs, less heat is transferred to the fluid so that thé
process fluid outlet temperature decreases. Antifoulant protection was determined by comparing the summed areas between the heat transfer curves for control and treated runs and the ideal case for each run. In this method, the temperatures of the oil inlet and outlet and rod temperatures at the oil inlet (cold end) and outlet (hot end) are used to calculate U-rig coeFficients of heat .

transfer every ~ minutes during the tests. From these U-rig coefficients, areas under the fouling curves are calculated and subtracted from the non-fouling curve for each run. Comparing the areas of control runs (averaged) and treated runs in the following equation results in a percent protection value for antifoulants.
Area~ntrol) - Area(treatment) * 100 - % protection Area(control) Antifouling protection in various crude oils was determined as shown in the following tables.

The crude oil tested in Tables I and II was an Australian crude oil. It was characterized by having a neutralization number of 0.01 mg KOH/g, a bromine number of 1 mg Br/g, containing 0.~1 wt.
% asphaltenes and having a carhonyl content of 18,000 parts per million.

, .

.

2 ~

These results are reported in Table I.
TABLE I
Betz Fouling Apparatus 500F Rod Temperature 800 psig Nitrogen Overpressure 23 ml/mn Flow Rate Heat Concentration Transfer (ppm Product/ Oil Tem~. Loss Area ppm Active~ Chanqe(uE) (BTU/Hr/F~SF) (BTU/Fl % P
- Blank 62 13.5 41.3 500/2501 3 2.7 7.4 82 500/1252 54 11.7 25.5 38 5ûO/1253 52 10.8 27.û 35 1 = 1-(2-aminoethyl) piperazine in heavy aromatic naphtha 2 = Blend of hindered phenols and cyclohexamine 3 - aminoalkyl alcohol As seen in Table I, a treatment of 1-(2-aminoethyl) piperazine in heavy aromatic naphtha proved efficacious at inhibiting`fouling in crude oil containing high concentrations of carbonyl type oxygenates which are known to take part in condensation polymerization reactions.
This result was unexpected since this material is ineffective in crude oils with low carbonyl contents. Another example ûf a crude oil with high carbonyl content is shown in Table II. This treatment proved more effective than known antifoulant compositions.

~ ~, 2~ 9 TABLE II
ALCOR HLPS Fouling Apparatus 500F Rod Temperature 3 ml/min Flow Rate, 800 psig Nitrogen Overpressure S 5 Hour Run Times Heat Treatment Transfer Concentration Oil Temp. Loss Area (ppm Active) Chanqe(~E) (BTU/Hr/F.SF) (~LF) % P
Avg. Blank -22~/-I 0.9+/-0.2 1.0~/-0.2 nispersant 1 (62.5) 17 0.9 0.9 10 Dispersant 1 (125) 4 0.1 0.2 80 Dispersant 2 (62.5) 15 0.6 1.2 0 Dispersant 2 (125) 7 0.3 2.0 0 Dispersant 1~
1-(2-aminoethyl) 4 0.2 0.2 80 piperazine (62.5/62.5 1-(2-aminoethyl) piperazine (62.5) 7 0.5 0.5 50 Dispersant 1 = cyclic succinimide dispersant Dispersant 2 = long chain phosphorous dispersant The aminoethyl piperazine compounds of the present invention proved unexpectedly effective in the high carbonyl content crude oil. These compounds were also effective with known dispersant compounds.

The results of Table II indicate that the aminoalkyl piperazine compounds of the present invention are effective when used in combination with other dispersant compositions.

.' ' ', .
.
r, ~ ~ :

6~ 3 The crude oil tested in Tables III and IV was desalted crude oil ~rom Texas. This crude possessed a neutralization number of 0.12 mg KO~/g, a bromine number of O mg Br/gl an asphaltene content of 0.32 wt. % and less than 100 parts per million carbonyls.

TABLE IIT
Desalted Crude from Texas Side 2 of Dual Fouling Apparatus 800F Rod Temperature, 900 psig N2 at 23 ml/min flow rate Heat Concentration Transfer (ppm Product/ Oil TemP. Loss Area pPm Active! Chanqe(F) ~BTUlHr/~E) (BTU/F) % p Blank 35 6.0 13.3 --1000~2501 23 4.4 8.7 29 5~/2002 29 5.5 16.6 0 Blank 29 4.9 11.2 --1000/250 and 500/2503 17 1.8 3.1 75 1000/2504 21 3.1 5.1 58 500/125 and 250/1255 21 3.4 7.6 38 1 = Long-chained phosphorous based dispersant and 30% heavy aromatic naphtha 2 = 50% 1-(2-aminoethyl) piperazine and 50% heavy aromatic naphtha 5 3 = Long-chained phosphorous based dispersant and 30% heavy aromatic naphtha with 50% am;noethyl piperazine and 50% heavy aromatic naphtha 4 - same composition as 1 5 = same composition as 3 .

.
. ' ~
.

, ~ ~
:

2$~3~

TABL~ IV
Betz Fouling Apparatus 500F Rod Temperature 800 psig Nitrogen Overpressure 23 ml/mn Flow Rate Heat Concentration Transfer Oil Temo. Loss Area (~e~ Active) ChanqeL~E) (BTU/Hr/F~SF) (BTU/F~ % P
Avg. Blank 32t/-4 5.5+/-0.8 12.3+/-1.5 Avg. Dispersant (250) 22~/-1 3.8+/-0.9 6.9~/-2.5 44 1-~2-aminoethyl) piperazine (250) 29 5.5 16.6 0 Dispersant 2 and 1-(2-aminoethyl~
piperazine (250/250) 17 1.8 3.1 75 Dispersant 2 and 1-(2-aminoethyl) piperazine (125/125) 21 3.4 7.6 38 Dispersant 2 = Long Chain phosphorous dispersant These results show that 1-(2-aminoethyl) piperazine is ineffective in low carbonyl content crude oils. Further, it proved only slightly more effective when used with a known antifoulant dispersant.

.
, .
, , ~

2 ~ 'a While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

- .
:: :
.

Claims (10)

1. A method for inhibiting the fouling of heat exchangers surfaces in a crude oil processing system wherein said crude oil has a high carbonyl content comprising adding to said crude oil an effective amount for the purpose of an aminoalkyl piperazine compound.

2. The method as claimed in claim 1 wherein said aminoalkyl piperazine compound is 1-(2-aminoethyl) piperazine.

3. The method as claimed in claim 1 wherein said aminoalkyl piperazine compound is in an organic solvent.

4. The method as claimed in claim 3 wherein said organic solvent is heavy aromatic naphtha.

5. The method as claimed in claim 1 wherein said aminoalkyl piperazine compound is added in an amount from about 1 part to about 1000 parts per million parts of said crude oil.

6. The method as claimed in claim 1 wherein said heat exchanger surfaces are metal.

7. The method as claimed in claim 6 wherein said metal is an iron alloy.

8. The method as claimed in claim 7 wherein said iron alloy is carbon steel.

9. The method as claimed in claim 1 wherein said aminoalkyl piperazine compound is added along with an additional antifoulant compound.

10. The method as claimed in claim 1 wherein said heat exchanger is a shell and tube heat exchanger.