Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
1998-06-22
2002-04-02
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S552000, C423S554000, C423S555000, C423S481000, C423S483000, C071S063000
Reexamination Certificate
active
06365122
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the reaction of metal chlorides with sulfur dioxide and/or sulfur trioxide gas in a truly fluidized state, with the production of a solid having a composition composed of the metal and one or more constituents of the sulfur dioxide or trioxide and a gaseous acid. More particularly, the invention relates to the production of potassium sulfate fertilizer and hydrochloric acid using sulfur dioxide or sulfur trioxide gas and potassium chloride in an energy efficient and non aqueous medium using counter current flow and true fluidized bed technology. The unique aspects of this process is that it permits the reaction to take place at a very rapid rate (minutes versus days) at moderately elevated temperatures while retaining essentially the same crystal size and screen analysis as the original potassium chloride. The counter current aspects of the invention permit the production of high purity potassium sulfate and a hydrochloric acid gas essentially free of sulfur dioxide.
BACKGROUND OF THE INVENTION
Potassium is one of three essential elements (N.P.K.) in the life cycle of all plants. Fertilizers therefore generally contain all three in one form or another. Potassium, however is generally present as a chloride since it is the most readily available, least expensive potassium compound. For many crops (e.g., citrus, tobacco) a fertilizer containing small amounts of chlorides is toxic. Thus, there is created a sizable demand for manufactured potassium sulfate as a non chloride source of potassium. However, it must be produced at a relatively low cost to compete with existing processes such as that produced from natural deposits and brines. Potassium sulfate is not known to occur in nature except as a double salt “K
2
SO
4
2MgSO
4
”, (langbeinite), which is mined and sold as such. While the magnesium is a desirable micronutrient, the proportion present in the langbeinite 15.25% reduces its desirability as a substitute for potassium chloride.
In addition langbeinite generally occurs with interstitial sodium chloride “NaCl” and requires careful washing and size control to produce a product of ninety five percent langbeinite. Pure potassium sulfate can be produced from langbeinite by reaction with potassium chloride:
K
2
SO
4
2MgSO
4
+4KCl→3K
2
SO
4
+2MgCl
2
However, the process requires dissolution of the solid followed by evaporation and crystallization to recover potassium sulfate. Control of the process is difficult and the product produced is borderline in purity and particle size.
Hargreaves, et. al taught in U.S. Pat. No. 149,859, Apr. 24, 1874, that sodium and potassium chloride could be converted to the sulfate salts and hydrochloric acid by contacting the chloride salts with sulfuric acid made by a process similar to the old chamber process involving oxidation of sulfurous acid with air and water vapor by increasing the rate of conversion of sulfurous acid to sulfuric acid by the addition of niter or nitric acid. The conversion of the chlorides was accomplished in a rather crude vessel by forcing or inducting the sulfuric acid vapor through a fixed bed of the alkali salts until conversion was complete. Heat was added to the air, sulfurous acid and water before, during, and after mixing to elevate (superheat) the gases and acid vapors. Many processes utilizing this fundamental reaction have been proposed. A number of these use the term “fluidized bed” to describe spouting beds similar to those produced in “Wurster” type apparatus, or to describe a “dense phase gas agitated bed in a state of substantial fluidity” or to describe “an allutriated zone”, or to describe gas conveyed or entrained solids. While these may fall under the generic term “fluidized” they are not true or conventional fluidized beds. “In a true fluidized bed particles are kept in a randomly moving, fluidized condition by a stream of pressurized gas. This is usually accomplished by placing the particles on a perforated support usually a metal plate or screen. A pressurized gas is forced through the perforations in the plate and causes the particles to fluidize. True fluidization is characterized by the particles moving in a random turbulent fashion similar to a gently boiling liquid”. (See Darrah et. al. U.S. Pat. No. 5,399,186 Mar. 21 1995 column 4, line 44). In Nguyen U.S. Pat. No. 4,495,163 Jan. 22, 1985 column 3, line 34, the author found it necessary to define fluidized beds generically as follows to distinguish his process. “The term fluidized bed as used herein is intended to include conventional fluid beds, fast moving fluid transport systems wherein the pellets are carried in the gas stream separated and returned to a point of introduction, spouting beds, etc”. It is important to emphasize this distinction since true or conventional fluidization causes the solids to flow and act like liquids. True fluidization as used in the instant invention is that which meets the definition outlined in the Darrah patent, which permits the use of counter current gas and solid flows, which results in the production of high purity potassium sulfate and hydrochloric acid, retention of crystal integrity, rapid conversion rates, simplicity of the apparatus, very efficient energy conservation and the elimination of environmentally controlled emissions, and excludes sporting beds, dense phase gas agitated beds, allutriated zones or fast moving transport systems since using such means other than that described as conventional or true fluidization will not accomplish the results described.
DESCRIPTION OF THE RELATED ART
The Potash Company of America used the Hargreaves process to produce potassium sulfate from potassium chloride utilizing sulfur dioxide in a small plant at Dumas, Tex., now shut down as commercially unprofitable. This process required the compaction of approximately 1 ounce of pulverized 100 mesh potassium chloride into oval shaped briquettes approximately 2 inches long by ¾ inches thick, which are dried in a gas fired rotary dryer, screened, and stored prior to loading into a conversion chamber. The plant contained 8 conversion chambers which were brick lined pits 16 feet square and 14 feet deep to a floor of cast iron grates on which approximately 50 tons of briquettes were distributed. The chambers were covered by a 1 piece insulated steel cover. Seven of the chambers were maintained in operation while one was being unloaded and reloaded with new briquettes.
Heavy 24 inch piping connected the chambers in series so that the sulfur dioxides gas produced by burning sulfur in the presence of air and water vapor entered the bottom of each chamber and left at the top at a diagonally opposite corner. The chamber in operation the longest (the first chamber) received the strongest gas, while the newly charged chamber received the weakest sulfur dioxide gas. The first chamber in the series was unloaded and reloaded each day so that 7 chambers were in operation at any one time. The second chamber then became the first in the series, the new chamber the last with the intermediate chambers moving up in place in the series. The process had to be shut down each day to connect the newly charged chamber and remove the oldest chamber for unloading. Piping had to be rerouted to accommodate this charging and unloading process. Briquettes unloaded from the chamber were crushed and screened, providing a significant amount of fines. Considerable energy was also used to dry the compacted briquettes, which were formed from wetted potassium chloride. Hydrochloric acid, produced by the reaction, was sold as a commercial grade.
Aside from the inefficiency associated with daily shut down and start up of the process, it is also obvious from the description of this process that it was very labor intensive and inefficient in this respect. The integrity of the initial potassium chloride crystals was also lost because of the mechanical grinding prior to briquette compaction and following conversion which resulted in uncontrolled production of fines. In addit
Cochran Keith D.
Holt Timothy G.
Rigby William J.
Emrich & -Dithmar
Nave Eileen E.
Rigby William J.
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