PROCESS FOR CONTROLLING CORROSION IN PETROLEUM REFINING UNITS

Abstract

A process for controlling corrosion and fouling in petroleum refining units. The corrosion controlling agent comprises an amine and an alcohol. The process comprises the step of adding the amine and the alcohol to the overhead system of the petroleum refining unit, either separately or in combination.

Claims

1. A process for controlling corrosion in an overhead system of a refining unit comprising water condensate and petroleum products comprising the step of adding to the system an amine and an alcohol.

2. The process of claim 1 wherein the amine is an alkylamine, an alkanolamine, or mixtures thereof.

3. The process of claim 1 wherein the amine is dimethylethanolamine (DMEA), dimethylisopropanolamine (DMIPA), ethylenediamine (EDA), methoxypropylamine (MOPA), monoethanolamine (MEA), dimethylaminopropylamine (DMAPA), morpholine, trimethylamine (TMA), picoline, pyridine, or mixtures thereof.

4. The process of claim 1 wherein the alcohol is a polyol, polyether diol, polyether triol, or mixtures thereof.

5. The process of claim 1 wherein the alcohol is a polyol based on ethylene glycol reacted with ethylene oxide, a polyol based on ethylene glycol reacted with propylene oxide, or a polyol based on ethylene glycol reacted with ethylene oxide and propylene oxide, or mixtures thereof.

6. The process of claim 1 wherein the alcohol is a polyol based on glycerol reacted with ethylene oxide, a polyol based on glycerol reacted propylene oxide, a polyol based on glycerol reacted butylene oxide, a polyol based on glycerol reacted ethylene oxide and/or propylene oxide and/or butylene oxide, or mixtures thereof.

7. The process of claim 1 wherein the alcohol is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, or mixtures thereof.

8. The process of claim 1 wherein the alcohol is diethylene glycol, ethylene glycol, glycerol, or mixtures thereof.

9. The process of claim 1 wherein the amine and the alcohol are added to the system separately.

10. The process of claim 1 wherein the amine and the alcohol are added to the system together.

11. The process of claim 1 wherein the amount of the amine and the alcohol independently range from 1 to 10,000 ppm based on the petroleum products.

12. The process of claim 1 further comprising the step of adding the amine and the alcohol to the system at a rate sufficient to maintain the pH of water condensate in the system at a pH of equal to or greater than 4.0.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a plot of the solubility of monoethanolamine hydrochloride and ethylenediamine hydrochloride in diethylene glycol at different temperatures.

[0018] FIG. 2 is a plot of the viscosities of room temperature saturated solutions of monoethanolamine hydrochloride and ethylenediamine hydrochloride in diethylene glycol at different temperatures.

[0019] FIG. 3 is a plot of the viscosity of room temperature saturated solutions of monoethanolamine hydrochloride and ethylenediamine hydrochloride in glycerine at different temperatures.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Methods and compositions are disclosed for neutralizing acid environments and controlling corrosion in distillation overhead systems of petroleum product processing facilities, including, but not limited to distillation columns, vacuum distillation columns, preflash towers, and the like. The neutralizer composition comprises an amine compound and an alcohol.

[0021] For decades, refiners have struggled with providing adequate neutralization in overhead systems without forming corrosive salts. Ammonia and several amines have been tried to control corrosion with random successes and failures. The neutralizer compositions of the invention will allow reduction of fouling tendency of the corrosive salts without changing the neutralization power of ammonia and amines.

[0022] The water vapor/condensate coming out of the overhead of the crude distillation unit (CDU) in the refinery is very acidic primarily due to the presence of acidic components, such as hydrochloric acid (HCl), which is formed when the crude oil passes through a heating furnace (composed of metal chlorides such as MgCl.sub.2, CaCl.sub.2, etc.) prior to entering the CDU. Water vapor and HCl rise to the top of the distillation tower along with the light components of the crude oil such as liquefied petroleum gas and naphtha. This stream passes through an overhead line and then enters a condenser, after which the water stream will be separated from naphtha and off-gas and sent to a water treatment unit. The acidic HCl stream (often having a pH less than 2) is highly corrosive and needs to be neutralized (preferably to a pH of 4 or greater, more preferably 5 or greater). The neutralizing composition is added to the overhead system, traditionally, neutralizers are injected into the overhead system between the CDU and the condenser.

[0023] In one embodiment of the present invention, the neutralizing composition may be added to the overhead system upstream of the aqueous dew point. This addition point is usually the overhead line off of the distillation column or the vapor line off of a dry first condensing stage accumulator.

[0024] It will be appreciated that it is not necessary for corrosion in distillation overheads or other equipment to completely cease for the method of this invention to be considered successful. Indeed, the inventive method should be considered operative if corrosion is inhibited to a measurable extent. In the context of this invention, the term controlling corrosion is defined to include any cessation, prevention, abatement, reduction, suppression, lowering, controlling or decreasing of corrosion, rusting, oxidative decay, etc. Similarly, the term neutralize refers to such corrosion inhibition by reducing the acidity of the chemicals or components in the system such as by raising pH, but does not require adjusting pH to be 7, but rather raising of pH and moving from acidity to basicity to some measurable extent. Furthermore, the nature of the metal surfaces protected in the methods of this invention is not critical. The metals in which the system operates may include, but are not necessarily limited to iron alloys, copper alloys, nickel alloys, titanium alloys, and these metals in unalloyed form as well, etc.

[0025] The first component of the neutralizing composition is an amine compound, preferably one or more alkylamine or alkanolamine, preferably dimethylethanolamine (DMEA), dimethylisopropanolamine (DMIPA), ethylenediamine (EDA), methoxypropylamine (MOPA), monoethanolamine (MEA), dimethylaminopropylamine (DMAPA), morpholine, and trimethylamine (TMA). The one or more alkylamine or alkanolamine is added in an amount of from 1 ppm to 10,000 ppm based on the petroleum products.

[0026] Preferably the amine compound is added in an amount of equal to or greater than 1 ppm, preferably equal to or greater than 1 ppm, more preferably equal to or greater than 10 ppm, and more preferably equal to or greater than 100 ppm based on the petroleum products. Preferably the amine compound is added in an amount of equal to or less than 5,000 ppm, preferably equal to or less than 1,000 ppm, and more preferably equal to or less than 500 ppm based on the petroleum products.

[0027] The second component of the neutralizing composition is an alcohol. Any suitable alcohol may be used. Preferably, the alcohol is a polyol, polyether diol, polyether triol, or mixtures thereof. In one embodiment, the alcohol s a polyol based on ethylene glycol reacted with ethylene oxide, a polyol based on ethylene glycol reacted with propylene oxide, a polyol based on ethylene glycol reacted with butylene oxide or a polyol based on ethylene glycol reacted with ethylene oxide and/or propylene oxide and/or butylene oxide, or mixtures thereof. In another embodiment, the alcohol is s a polyol based on glycerol reacted with ethylene oxide, a polyol based on glycerol reacted propylene oxide, a polyol based on glycerol reacted ethylene oxide and propylene oxide, or mixtures thereof. In yet another embodiment, the alcohol is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, or mixtures thereof. The one or more alcohol is added in an amount of from 1 ppm to 10,000 ppm based on the petroleum products.

[0028] Preferably alcohol is added in an amount of equal to or greater than 1 ppm, preferably equal to or greater than 1 ppm, more preferably equal to or greater than 10, and more preferably equal to or greater than 100 ppm based on the petroleum products. Preferably the alcohol is added in an amount of equal to or less than 5,000 ppm, preferably equal to or less than 1,000 ppm, and more preferably equal to or less than 500 ppm based on the petroleum products.

[0029] It will be appreciated that it is difficult to predict what the optimum dosage rate would be in advance for any particular system. The dosage will depend upon a variety of complex, interrelated factors including, but not necessarily limited to, the exact nature of the stream being fractionated, the temperature and pressure of the distillation conditions, the particular amine blends used, etc. In one non-limiting embodiment of the invention, the dosage rate will be determined on a case-by-case basis depending upon the acid content of the system. It may be desirable to use computer modeling to determine the optimum rate. Nevertheless, to provide some understanding of expected or possible dosage rates, the amount of the amine compound and alcohol may independently range from 1 to 10,000 ppm, based on the petroleum products. In another non-limiting embodiment, the amount of the amine compound and alcohol may independently range from 1 to 500 ppm.

[0030] The desired pH range for all points in the system is from 4 to 8.5, and in another non-limiting embodiment may be from 5 to 7. Alternatively, to give another idea of expected dosage rates, the neutralizing composition may be added to the system at a rate sufficient to maintain the pH of water condensate in the system at a pH of equal to or greater than 4.0. In another non-limiting embodiment, the neutralizing composition may be added to the system at a rate sufficient to maintain the pH of equal to or greater than 5.0.

EXAMPLES

[0031] The solubility of the monoethanolamine hydrochloride (MEA.HCl) and or ethylenediamine hydrochloride (EDA.2HCl) in diethylene glycol or glycerol is determined as follows: to 10 g of diethylene glycol or glycerol is added an excess amount of the salt and the reaction mixture is stirred rigorously for at least 1 h at the desired temperature. The stirring is then stopped and the reaction mixture is allowed to settle. The solubility of the salt in ethylene glycol or glycerol is calculated from the chloride concentration measured by Ion Chromatography. The viscosity of the saturated solution is measured on a Stabinger Viscometer.

Example 1

[0032] The solubility of MEA.HCl and EDA.2HCl in diethylene glycol at different temperatures is shown in FIG. 1 and the viscosity of the room temperature saturated solution of MEA.HCl and EDA.2HCl at different temperatures is shown FIG. 2.

Example 2

[0033] At 25 C., the solubility of MEA.HCl and EDA.2HCl in glycerol is determined to be 44.5 wt % and 12.8 wt %, respectively. The viscosity of the room temperature saturated solution of MEA.HCl in glycerine and EDA.2HCl in glycerine at different temperatures is shown in FIG. 3.