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Method for preventing fouling and corrosion caused by ammonium chloride & ammonium sulphate

Prevention fouling and corrosion caused by ammonium chloride and ammonium sulphates particularly formed or present in crude oil refinery processes
  • Ammonium chloride and ammonium sulphates are corrosive, as gas, as solid, or in solution.
  • Ammonium chloride is acidic, complexes metal ions, and contains the corrosive chloride ion.
  • Ammonium sulphate is acidic and complexes metal ions.

Corrosion protection is one of the major concerns in refinery operations where ammonium chloride and ammonium sulphates are generated through the process itself or being imported from other units with the feedstock. Several forms of corrosion are observed.

  • The extent of corrosion largely depends on, for example the ammonium chloride concentration, the pH, and the temperature.
  • Equipment made from iron, aluminium, lead, stainless steels, or non ferrous metals is especially prone to stress corrosion cracking.
  • Solid ammonium chloride has a specific gravity d of 1,530. Its average specific heat c p between 298 and 372K is 1,63 kJ/kg.
  • Ammonium chloride has two modifications. The transformation between the two is reversible at 184.5°C: a-NH4Cl (cubic, CsCl type) ¢> ß-NH4Cl (cubic, NaCl type) ¢> AH= +4.3 kJ/mole.
    The a modification is the one stable at room temperature.
  • Ammonium sulphates cannot be melted at atmospheric pressure without decomposition, releasing ammonia and leaving bisulphate. However, the ammonia vapour pressure of pure, anhydrous ammonium sulphates are effectively zero up to 80°C. Above 300°C, decomposition gives N2, SO2 and H20 in addition to ammonia.
  • The salts do not form hydrates. The solubility of ammonium sulphates is reduced considerably by addition of ammonia: At 10°C, from 73 g ammonium sulphate in 100 g of water, nearly linearly, to 18 g salt in 100 g of 24. 5% aqueous ammonia.
  • The fouling and corrosion phenomena in the crude oil refinery processes, such as hydro-treating, hydro- cracking, catalytic reforming, catalytic cracking, but not limiting to these processes, is a great concern of the operator. A typical conversion refinery is spending a lot of money for maintenance, renewal of equipment, while the downtime of the unit is accounting for a substantial loss in production and profits.
  • Equipment being exposed to ammonium chloride fouling has to be thoroughly washed with an alkaline solution, to avoid stress-corrosion cracking. Ammonium bisulphate is depositing at higher temperatures as compared to ammonium chloride, and therefore, more difficult to remove by washing with water.
  • Typical areas for fouling and corrosion are, for example but not limiting, feed-effluent exchangers from reactors and distillation columns, recycle gas compressors transporting hydrogen containing ammonium chloride to the reactor feedstock, stabiliser, reboiler and overhead section.
  • The invention aims to provide a method for preventing fouling and corrosion caused by ammonium chloride and ammonium sulphates.
  • According to the invention this aim is reached by injecting as an additive a choline or a derivative thereof, more specifically a derivative with one of the following general formulas: (CH3) 3 N+-CH2CH2-0-, (CH3) 3 N+-CH2CH2-OH-0-H, and (CH3) 3 N+-CH2CH2-OH-0-R, wherein R = alkyl with C1-C20.
    Choline, known as choline base, is a liquid strong organic base: trimethyl (2-hydroxyethyl) ammoniumhydroxide having the general formula [(CH3) 3 N+-CH2CH2-OH]-OH. It is usually not encountered as a free base, but as a salt or derivative such as choline hydroxyde, choline chloride, choline hydrogen tartrate, tricholine citrate which are commercially available and are used in medical / applications and as nutrients.
  • By injection, the additive to the process flow, the ammonium chloride and ammonium sulphates are converted into non-corrosive and non-depositing components which are surprisingly liquid and neutral, freeing the various processes from fouling and corrosion created by ammonium chloride and ammonium sulphates.
  • It is known to add amines for corrosion inhibition, but these amines form a salt which remains sticky (form a paste) or solid, and when dissolved in water show an acidic pH value (< 7,0).
  • The chloride salt formed with the additive is a volatile chloride which can be removed from the process stream by stripping or gas recycling.
  • In a particular unit called catalytic reformer, the volatile formed component can be recycled through the hydrogen recycle gas stream to the reactor, thereby reducing the amount of organic chloride used for activation of the reformer catalyst. Up to 40 % savings in organic chloride product has been demonstrated in a pilot plant.
  • The quantity of additive injected, is preferably situated between 1 ppm and 5000 ppm, dosed on the amount of chlorides or sulphates present.
  • The additive is preferably injected as a solution containing 1% weight to 65 % weight additive in a solvent, for example an alcohol, preferably an aliphatic alcohol having up to 8 C atoms, an ether, an aromatic or water. The concentration of the choline base of choline derivative in the solution may for example vary from 1 % to 65 % in weight. A stabiliser may be added such as for example an unsubstituted hydroxylamine salt.
  • The additive is usually fed upstream the formation or deposition of ammonium chloride and ammonium sulphates to prevent formation of ammonium chloride and ammonium sulphates or to convert ammonium chloride and ammonium sulphates to other components.
    The additive may also be fed downstream the formation or deposition of ammonium chloride and ammonium sulphates to convert ammonium chloride and ammonium sulphates to other components, but it is not limiting its feeding point to a particular place in the process.
  • The following example explains the invention: A pilot catalytic reformer with continuous regeneration catalyst, shown in the enclosed figure, is used to test the performance of the additive at various levels of ammonia and chloride. As shown in the figure, this reformer comprises mainly a reactor 1, an airfin cooler 2, a separator 3 and a stabiliser 4 mounted in series.
  • The feedstock is fed to the reactor 1 over a feed- effluent exchanger 5 and a catalytic reformer furnace 6.
  • The feedstock consists of a typical heavy full range naphta with varying levels of ammonia and with an end boiling point of 192°C. The hydrogen to hydrocarbon molar ratio is 4,0 operating at an outlet temperature of 510 °C and the pressure in the reactor 1 is 9,8 bar. The catalyst used is R 22 from UOP and is continuously recycled as shown by reference numeral 7. The organic chloride catalyst activator is fed at a rate of 2 ppm.
  • The conditions in the reactor 1 were governed to maintain a reformate RON (Research Octane Number) of 98.
  • The gases from the separator 3 are compressed in compressor 8 and reintroduced in the feed stock. The liquid from the separator 4 is fed to the reformate stabiliser 4. The gases are cooled in airfin cooler 9 followed by a water cooler 10 and then collected in an overhead accumulator 11. The remaining gases are evacuated via the off-gas 12, while the liquid is returned as a reflux to the upper part of the stabiliser 4. The reformate is evacuated from the bottom of the stabiliser 4 and part of it is recycled over a stabiliser reboiler furnace 13.
  • Blank test : Reactor Stabiliser Recycle Stabiliser Stabilised Product Feedstock Outlet feed gas off-gas reformate Analysis in ppm Reformate Ppm Ppm Ppm ppm ppm NH3 1, 5 HCl 0, 5 NH4Cl - 2,5 1,3 0,3 < 0,1 < 0, 1 Roc1 2* *Organic chloride fed to reactor Stabiliser Hydrogen Stabiliser Stabiliser Analysis/overhead recycle overhead overhead Observation water airfin cooler airfin cooler accumulator cooler Corrosion 0, 559 1, 143 1, 727 0, 940 mmpy rate mmpy mmpy mmpy (3 7 mpy) (22 mpy) (45 mpy) (68 mpy) Salt Yes Yes Yes No deposition PH saturated 2,7 2,3 1,7 3,5 water Test data : A solution of 44 wt. % of trimethyl (2- hydroxyethyl) ammonium hydroxide or choline in methanol to which 1% hydroxylamine acetate was added as stabiliser, was fed to the reformate leaving the reactor 1 prior to the feed-effluent exchanger 5 at a dosage rate of 4,5 ppm per ppm chloride based on mass flow-rate, as indicated by the arrow 14 in the figure.
  • The corrosion due to ammonium chloride can be reduced to levels below 1,270 mmpy (millimeter per year = 5 mpy or mills per year) and fouling created by ammonium chloride can be eliminated completely.
  • Also the amount of RC1 (organic chloride) fed to the reactor could be reduced by 40 % as demonstrated through the analyses of CH3Cl in the recycle gas stream. Reactor Stabiliser Recycle Stabiliser Stabilised Product Feedstock Outlet feed gas off-gas reformate Analysis in ppm Reformate Ppm Ppm Ppm Ppm ppm NH3 1, 5 HCl 0, 5 NH4Cl - 2,5 < 0,1 < 0,1 < 0,1 < 0, 1 CH3Cl - - < 0,1 1,1 < 0,1 < 0, 1 Roc1 2* *Organic chloride fed to reactor Hydrogen Stabiliser Stabiliser Stabiliser Analysis/ recycle airfin overhead airfin overhead overhead Observation cooler Cooler water cooler accumulator Corrosion 0,076 mmpy 0,058 mmpy 0,102 mmpy 0,038 mmpy rate (3 mpy) (2 mpy) (4 mpy) (1, 5 mpy) Salt No No No No deposition PH saturated 6,3 7,6 7,0 7,1 water The additive can be applied under a wide range of temperatures and pressures, usually between 0,02 bara and 200 bara and-10 °C and + 250 °C.
  • In other embodiments, the additive was a derivative of choline with the general formula (CH3) 3N-CH2CH2-O, (CH3) 3 N+-CH2CH2-OH-O@H, or (CH3) 3 N+-CH2CH2-OH-O-R, wherein R = an alkyl with C1-C2o. such as a choline hydrogen tartrate, choline dihydrogen citrate, tricholine citrate or choline gluconate.
  • Dosages are usually determined through the analysed or calculated concentration of ammonia and hydrochloric acid, or by dew point calculations of the sublimation of ammonium chloride or ammonium sulphates. The dosage could be as low as 1 mg/1 up to 5000 mg/1.
From-  http://www.wipo.int/