Chemistry of inorganic compounds – Halogen or compound thereof – Hydrogen halide
Reexamination Certificate
2001-02-16
2004-01-13
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Hydrogen halide
C423S488000, C423S551000, C423S552000
Reexamination Certificate
active
06676917
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for the production of sulfates and hydrochloric acid and, more particularly, to a process for the production of hydrochloric acid and neutralized sulfates without the need of any diluting step.
DESCRIPTION OF THE RELATED ART
Hydrochloric acid is broadly used in domestic operations, as well as in industry in which it has very important applications, such as a pickling agent in the iron and steel industry, as a well re-activator in the petroleum industry and generally as a descaling agent.
More than 3.5 tons of HCl are produced and consumed annually just in the U.S.A.
The most commonly used process for the production of hydrochloric acid in industry employs as raw materials elemental residual hydrogen and elemental chlorine generated by the caustic soda plants produced by the sodium chloride electrolysis process. Notwithstanding its high production cost, however, it is the best use for the residual hydrogen.
The first antecedent of an industrial process for the production of hydrochloric acid dates from the 18th century and is denominated the “LEBLANC” process, which reacts concentrated sulfuric acid and crystalline sodium chloride on a dry basis in order to produce hydrochloric acid and sodium sulfate.
Hydrochloric acid has been well know since the era of the alchemist as the “salt spirit”, according to works and studies attributed to Basilius Valentinus in the 15th century, when hydrochloric acid was produced by reacting sulfuric acid with sodium chloride on a dry basis.
In such processes, the chemical reaction is the following:
The low efficiency of the furnaces used for the production of hydrochloric acid via the dry basis process, the high pollution levels produced, its high energy consumption and the low quality of the products obtained with said furnaces led to research on a process which can be carried out under more moderate conditions. As a result of these investigations, it was found that by reacting sulfuric acid with sodium chloride on a wet basis, it was possible to produce hydrochloric acid at temperatures below 300° F., but instead of producing a neutralized sodium sulfate, acid sodium sulfate and hydrochloric acid were obtained in accordance with the following reaction:
The majority of the processes that operate on a wet basis, separate the hydrochloric acid from the acid sulfates produced by distillation at temperatures between 65° C. and 150° C., even if the hydrochloric acid can be separated from the sulfates by solvent extraction.
Also, the processes which operate on a wet basis use excess sulfuric acid in order to complete the reaction at a 100% and to ease the complete separation of the hydrochloric acid by distillation.
The acid sodium sulfate is a very corrosive product and for all practical purposes it does not have any commercial value. Accordingly, the processes which operate on a wet basis and which have as raw materials sulfuric acid and ammonium or alkaline metal chlorides, require additional steps in order to transform the acid sulfates into neutralized sulfates.
U.S. Pat. No. 4,054,543 of Sardisco, discloses a process for the production of potassium sulfate and hydrochloric acid on a wet basis using as raw materials sulfuric acid and potassium chloride.
U.S. Pat. No. 4,588,573 of Worthington et al., discloses a process for the production of hydrochloric acid and potassium sulfate using as raw materials sulfuric acid and potassium chloride. In the process of U.S. Pat. No. 4,588,573, once it has generated the acid potassium sulfate and separated the hydrochloric acid by distillation, the mass is cooled in order to crystallize the acid potassium sulfate and to separate it from the liquor by centrifugation and distillation, said liquor being recycled to the reactor.
The acid potassium sulfate crystals separated by centrifugation are transferred for a partial dissolution to an agitated tank called converter, in which a partial conversion of the acid sulfate to a neutralized sulfate is carried out, using the liquor of a second crystallization as dissolution agent.
Subsequently, the already converted crystals are separated from the liquor and are fed to an evaporator in order to reduce the water content in the system, thus making it possible for the process to work adequately.
The converted and separated crystals in the last step are transferred to a second agitated tank, denominated a converter, in which said crystals are dissolved with water at carefully controlled volumes.
With a final mass cooling step a second crystallization is obtained, thus yielding neutralized potassium sulfate crystals.
Furthermore, Worthington discloses a system phase diagram (sulfuric acid-potassium sulfate-water) in which three well defined zones are shown. In the A zone, only neutralized potassium sulfate is crystallized; in the B zone a mix of acid potassium sulfate and neutralized potassium sulfate is crystallized, and in the C zone, characterized by its low water content and its high sulfuric acid content, acid sodium sulfate with sulfuric acid is crystallized.
In accordance with Worthington's phase diagram, it is possible to move the system from the B zone to the A zone only by a simple dilution operation, since the dilution operation lowers the sulfuric acid concentration and thus it is possible to crystallize neutralized sodium sulfate by a cooling operation.
The first crystallization step of acid potassium sulfate is very important and necessary to Worthington's process in order to carry on the subsequent steps, since the acid potassium sulfate crystals separated by centrifugation remain without any water content and without excess of sulfuric acid.
The acid potassium sulfate crystals may be represented in a re-arranged molecular system suggested by Worthington, as a mix of 64% of neutralized potassium sulfate and 36% of sulfuric acid, said resulting mixture remaining clearly located in the B zone of the phase diagram.
When the referenced mixture is diluted until its water content is about 50%, the mass changes from the B zone to the A zone, in which neutralized potassium sulfate is crystallized by cooling.
The referenced molecular re-arrangement can be represented by the next equation in which the molecular weights have been included in order to quantify the contents of the mixture:
Both processes disclosed in the U.S. Pat. No. 4,054,543 and in the U.S. Pat. No. 4,588,573 employ the same raw materials, and almost the same reaction temperatures and sulfuric acid excesses.
The first difference between the two above-referenced processes is related to the hydrochloric acid distillation system. The Sardisco process, in comparison with the Worthington process, evaporates a larger water volume contained in the reacting mass until a magma is formed inside the reactor containing mixed crystals of acid potassium sulfate crystals and neutralized potassium sulfate in a liquor. Once the hydrochloric acid is separated in the evaporation step, and without separating the crystals, water is again added to the reactor until the mass is changed from the B zone to the A zone of the phase diagram, thus converting the original magma with mixed crystals to a magma containing only neutralized potassium sulfate crystals which are separated by centrifugation or filtration for subsequent drying and commercialization.
Worthington's process consumes less energy than the process of Sardisco because it has to evaporate less water. However, the Worthington process requires larger and more complex equipment compared with Sardisco's process and, thus, for Worthington's process, the fixed investment is higher for the same production capacity than that of Sardisco's process.
In view of the above-referenced disadvantages, the instant process for the production of hydrochloric acid and neutralized sulfates has been developed having a low energy consumption and a low fixed investment.
The process comprises the steps of: a) reacting sulfuric acid with an alkaline metal chloride in order to obtain a liquor
Abelman ,Frayne & Schwab
Nguyen Ngoc-Yen
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