Surface passivation method for fouling reduction

Abstract

A method of passivating a metal surface of hydrocarbon processing equipment is provided in which a water soluble molybdate compound is introduced into water or steam which is in contact or will come into contact with a metal surface of the hydrocarbon processing equipment to passivate the metal surface to inhibit surface coke formation.

Claims

1. A method of passivating a metal surface of hydrocarbon processing equipment, the method comprising: removing coke from a metal surface of hydrocarbon processing equipment during a decoking process while the hydrocarbon processing equipment is shut down; and introducing a water soluble molybdate compound into water or steam which is in contact or will come into contact with the metal surface of the hydrocarbon processing equipment to passivate the metal surface while the hydrocarbon processing equipment is shut down, wherein the temperature in the hydrocarbon processing equipment ranges from about 15° C. to about 650° C. during passivation.

2. The method of claim 1, wherein the molybdate compound comprises an alkali metal molybdate, an alkaline earth metal molybdate, ammonium molybdate, molybdic acid, or cerous molybdate.

3. The method of claim 2, wherein the alkali metal molybdate comprises sodium molybdate or potassium molybdate.

4. The method of claim 3 wherein the alkali metal molybdate comprises sodium molybdate.

5. The method of claim 2, wherein the alkaline earth metal molybdate comprises magnesium molybdate.

6. The method of claim 1, wherein the molybdate compound is added to the water or steam in a concentration of about 10 to about 25,000 ppm.

7. The method of claim 1, wherein the molybdate compound is introduced during or after an online spalling, mechanical pigging, or steam/air burning process.

8. The method of claim 7, wherein the molybdate compound is introduced during an online spalling process.

9. The method of claim 7, wherein the molybdate compound is introduced during a mechanical pigging process.

10. The method of claim 7, wherein the molybdate compound is introduced during a steam/air burning process.

11. The method of claim 7, wherein the molybdate compound is introduced after an online spalling process.

12. The method of claim 7, wherein the molybdate compound is introduced after a mechanical pigging process.

13. The method of claim 7, wherein the molybdate compound is introduced after a steam/air burning process.

14. The method of claim 1, wherein the hydrocarbon processing equipment is a pass of a furnace, and the molybdate compound is added and the passivation occurs without shutting down other passes of the furnace or the hydrocarbon processing equipment is part of a refinery or petrochemical plant.

15. The method of claim 1, wherein the hydrocarbon processing equipment comprises a thermal conversion unit, a heat exchanger, a visbreaker, a coker, a fired heater, a fractionator, a tube, a pipe, a tank, or a reactor.

16. The method of claim 1, wherein the molybdate compound is introduced into a water tank connected to a feed inlet of the hydrocarbon processing equipment, or the molybdate compound is introduced into a water or steam inlet of the hydrocarbon processing equipment.

17. The method of claim 1, wherein corrosion or fouling of the metal surface is inhibited as compared to the same metal surface under the same conditions without the passivation.

18. The method of claim 1, wherein induction time before coking occurs on the metal surface of the hydrocarbon processing equipment is increased as compared to the same metal surface under the same conditions without the passivation.

19. The method of claim 1, wherein the passivation is about the same or better than the passivation obtained using a phosphate ester for passivation at the same temperature for the same length of time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a bar graph which depicts the effect of surface passivation on coke deposition mass when treated with a phosphoric acid ester/tert-alkylamine, sodium molybdate, or untreated control.

(2) FIG. 2 is a bar graph which depicts the effect of surface passivation on coke deposition mass when treated with a phosphoric acid ester, sodium molybdate, or untreated control.

(3) FIG. 3 shows the sulfur signature on x-ray micrographs of passivated reactor surfaces post pyrolysis when treated with a phosphoric acid ester/tert-alkylamine, sodium molybdate, or untreated control.

(4) Corresponding reference characters indicate corresponding parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The passivation methods described herein apply a robust chemical film or layer to metal process surfaces in fired heaters or other high temperature thermal conversion, distillation refinery, or petrochemical plant equipment. Since the chemical film or layer can be formed under aqueous conditions from relatively low to ambient or even high temperatures, it can be applied at stages during operation (e.g., online spall) that otherwise would not be possible using conventional approaches.

(6) A method of passivating a metal surface of hydrocarbon processing equipment is provided. The method comprises introducing a water soluble molybdate compound into water or steam which is in contact or will come into contact with a metal surface of hydrocarbon processing equipment to passivate the metal surface to inhibit surface coke formation.

(7) As a result of the method, corrosion or fouling of the metal surface can be inhibited as compared to the same metal surface under the same conditions without the passivation.

(8) As a result of the method, induction time before coking occurs on the metal surface of the hydrocarbon processing equipment is increased as compared to the same metal surface under the same conditions without the passivation. For example, the induction period before coking occurs can be two fold that of the same metal surface under the same conditions without the passivation.

(9) The passivation achieved using the method is about the same or better than the passivation obtained using a phosphate ester for passivation at the same temperature for the same length of time. Unlike the phosphate ester passivation chemistry, the molybdate compound does not poison the hydrotreater catalysts, is not corrosive, and does not pose the risk of loss of primary containment.

(10) The molybdate compound reacts with the metal surface of the hydrocarbon processing equipment to coat the metal surface, reducing interactions between the metal surface and hydrocarbon processed in the equipment. Foulants such as coke do not adhere well to the coating, minimizing formation of obstructions or blockages in the processing equipment.

(11) The molybdate compound can comprise an alkali metal molybdate (e.g., sodium molybdate or potassium molybdate), an alkaline earth metal molybdate (e.g., magnesium molybdate), ammonium molybdate, molybdic acid, or cerous molybdate. Preferably, the molybdate compound comprises sodium molybdate.

(12) The molybdate compound can be anhydrous or can be a hydrate form such as sodium molybdate dihydrate (Na.sub.2MoO.sub.4.2H.sub.2O).

(13) The molybdate compound can be added to the water or steam in a concentration of about 10 to about 25,000 ppm, preferably about 100 to about 5,000 ppm, and more preferably from about 500 to about 2,500 ppm.

(14) If the molybdate compound is introduced as part of a composition, the composition is preferably free of any source of phosphorus such as phosphoric acid or phosphates.

(15) The molybdate compound can be introduced during or after an online spalling, mechanical pigging, or steam/air burning process. Preferably, the molybdate compound is introduced during an online spalling such as toward the end of an online spalling process.

(16) The molybdate compound can be added and the passivation can occur without shutting down the hydrocarbon processing equipment.

(17) The hydrocarbon processing equipment can be any equipment used to refine, store, transport, fractionate, or otherwise process a hydrocarbon such as crude oil, natural gas, petroleum, and petroleum fractions including residues.

(18) The hydrocarbon processing equipment can comprise a thermal conversion unit, a heat exchanger, a visbreaker, a coker, a fired heater, a fractionator, a tube, a pipe, a tank, a reactor, or other heat transfer equipment.

(19) The molybdate compound can be introduced into a water tank connected to a feed inlet of the hydrocarbon processing equipment.

(20) The molybdate compound can be introduced directly into a water or steam inlet of the hydrocarbon processing equipment.

(21) The hydrocarbon processing equipment can be part of a refinery or petrochemical plant.

(22) The hydrocarbon processing equipment is not an engine, hydraulic brake, power steering system, or transmission wherein molybdate may be used as a coolant additive in hydraulic fluid.

(23) The temperature in the hydrocarbon processing equipment typically ranges from about 15° C. to about 650° C. during the passivation, preferably from about 100° C. to about 600° C., and more preferably from about 150° C. to about 550° C.

(24) Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

EXAMPLES

(25) The following non-limiting examples are provided to further illustrate the present invention.

(26) Laboratory testing incorporates the use of a pyrolysis apparatus that simulates process conditions and temperatures as described by Russell et al., Energy Fuels, 24:5483-5492 (2010), which is incorporated herein by reference. One of the more unique aspects of the equipment is the ability to accurately measure surface coke formed during the cracking of heavy resid.

(27) In FIG. 1, the first bar on the chart represents a level of surface coke deposited during the pyrolysis of a particular vacuum residue coker feed, a value referred to as the Blank (untreated) experiment.

(28) Next, a conventional passivation procedure was performed in the laboratory by submersing the reactor inserts in hydrotreated mineral oil, and heating to a temperature of 250° C. At this point, the passivation additive was added at a concentration of 1000 ppm, and left to react for one hour. This laboratory methodology simulates the process on a real unit, where the passivator would be applied over a very short time frame (12 to 24 hours) at a high concentration (at least 1000 ppm) in a hydrocarbon medium during the warm up of the furnace to bring it back online. In the laboratory procedure, the reactor insert was ready for pyrolysis once the residual mineral oil was removed. A typical result from a passivated insert is represented by the second bar in the FIG. 1. For this particular resid composition, a phosphoric acid ester/tert-alkyl amine passivation is successful, with an 80% reduction in coke relative to the blank. However, this method of passivator application may not be applicable at an appropriate time, such as during an online spalling event.

(29) The method of the invention was simulated in the laboratory by submerging clean reactor inserts into water, and heating to 95° C., at which point, sodium molybdate, a water soluble molybdate compound, was added at a concentration of 2000 ppm, and left for one hour. Once dried, the insert was pyrolyzed in the presence of the same resid. The result in terms of surface deposit is represented as the last bar in FIG. 1. Significantly, the water soluble molybdate compound performed similarly to the conventional phosphoric acid ester/tert-alkylamine approach, with an 80% reduction in surface deposit.

(30) A further exemplar vacuum residue is shown in FIG. 2, which is the feedstock for a European-based visbreaker. Here, the conventional passivation additive chemistry was a phosphoric acid ester, which as above, may only be applied during heater warm up in a hydrocarbon medium. The performance of the sodium molybdate passivation is displayed as the last bar, and as with the coker feedstock, there is similar surface coke reduction performance as with the phosphoric acid ester.

(31) The comparison in performance for the coker feedstock vacuum residue was investigated further by examining the surface chemical composition of the post pyrolysis inserts from FIG. 1 using x-ray microscopy. The photo-micrographs are displayed in FIG. 3. The green signature color represents the element sulfur, which is a ubiquitous constituent throughout coke deposits. Therefore, the more prominent the green color, the more prominent the coke deposit. For the Blank sample, the outline structure of the woven mesh reactor insert is clearly distinguished by the vivid green signature of sulfur. For the two reactor inserts that were treated with phosphoric acid ester/tert-alkylamine (A) and sodium molybdate (B), respectively, there is almost no sulfur signature, indicating that the amount of coke on the surface was very low, correlating to the dramatic mass loss demonstrated in FIG. 1.

(32) When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

(33) In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

(34) As various changes could be made in the above methods and compositions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.