Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Reexamination Certificate
1999-10-14
2001-03-13
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C205S510000, C205S516000, C205S536000
Reexamination Certificate
active
06200455
ABSTRACT:
BACKGROUND
The present invention relates to the manufacture of alkali metal hydroxides, commonly known as caustic. Alkali metal hydroxides are typically from the group which includes sodium, lithium, cesium, potassium and rubidium. Caustic is made using different types of electrolytic cells, including membrane and diaphragm-type cells and then further treating the caustic to concentrate the solution. The present invention is directed to the method of further treating sodium hydroxide caustic which was created using a diaphragm electrolytic chlorine cell, but it is contemplated that this method of manufacture can be utilized in other alkali metal hydroxide processes to reduce the plating of metal on production equipment.
A need has long existed in the caustic industry for a technique to remove metals, such as nickel and/or iron from build up on the insides of manufacturing vessels and piping which occurs during the caustic manufacturing process without adding additional chemicals to the process. A need has existed for an environmentally friendly method to reduce metal plating buildup which lowers the cost to manufacture caustic, lowers the turn around time for the manufacturing facilities and can be usable in any alkali metal hydroxide manufacturing process.
Alkali metal hydroxide solutions have been prepared by the electrolysis of alkali metal salt solutions in electrolytic cells. Diaphragm cells are known for producing alkali metal hydroxide solutions electrolytically. In this type of cell, a porous cathode with an overlying porous diaphragm is used to separate or to serve as a barrier between the catholyte and anolyte compartments of the cell. After separation of the components, the caustic solution is then further treated to increase the concentration of caustic in the solution. An objectionable feature of known methods for handling this process to increase caustic concentration is that the process can require the addition of sodium borohydride to the caustic solution to minimize the reaction of hot caustic with the first device for driving off water, which is commonly known as the “first effect evaporator”. The first effect evaporator is usually nickel or coated nickel and the caustic reacts with the nickel causing the build up of hydrated nickel oxide on the interiors of the remaining processing equipment. The use of the sodium borohydride has produced a significant build up of nickel oxides as well as free nickel in the manufacturing process on the vessels, pipes and valves used in the process. The build up on the processing equipment results in increased maintenance and decreased operating efficiency. This invention overcomes this buildup.
The present invention is directed at a method for reducing the amount of free nickel and nickel oxides, free iron and ferrous oxides in the chlor-alkali systems, particularly for the diaphragm types of cells without the need for additional chemicals, additional sodium borohydride, or other contaminants.
In order to overcome the disadvantages of the prior art the present invention proposes the use of magnets in situ in the manufacturing process to overcome these problems with the nickel and the iron.
SUMMARY OF THE INVENTION
The present invention relates to an alkali metal hydroxide manufacturing process and a unique method to reduce the amount of metal build up on the interiors of reaction vessels and piping. The method involves using at least two magnets to remove various metals, including free nickel oxides and nickel particulate and iron oxides, ferrous oxides and in the aqueous alkali metal hydroxide manufacturing process. As the metals disengage from the deposit sites of the manufacturing process, the magnets collect the metals without the need to stop the manufacturing process to clean the manufacturing equipment, vessels and piping.
The method involves passing a cell liquor containing about 10-13 wt % caustic through a first magnet at a flow rate of about 600-900 gallons per minute removing a significant amount of metal, such as nickel and iron forming a first fluid, then evaporating a significant amount of water out of that first fluid and raising the temperature of that first fluid to above 225 F. Typically sodium borohydride is then added to the solution and it is heated again above 330 F. After this step this resulting more concentrated caustic solution is cooled to a temperature of between about 75 and 100 F forming a cooled solution. The cooled solution is passed through a second magnet and additional metal, such as additional nickel and additional iron is magnetically removed forming a second cooled solution. This solution is then filtered and then passed through an optional third magnet to remove additional remaining metals forming a more highly concentrated caustic solution with a low presence of metals.
Two additional magnets can be used in this novel process to reduce metal cladding during production.
It is an object of this invention to provide a method, which enables caustic to be manufactured in a more environmentally friendly manner with shorter maintenance turn around times, and less maintenance than was required in commercially known processes.
It is an object of this invention to provide a method by which caustic can be manufactured less expensively than known techniques by reducing the amount of metal cladding occurring during the manufacturing process on the equipment.
These and other objects and advantages of the invention disclosed herein will become apparent to those skilled in the art from a reading of the following specification and the appended claims and by reference to the attached Figures.
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Eriez Manufacturing Co., Ferrous Traps (SB-420P), 1998, 8 pages, no month available.
OxyTech Systems, Inc. (Tilak Bommaraju & Paul Orosz), Caustic Evaporator Coorosion: Causes and Remedy, Mar. 1992, 15 pages.
Hegeman John William
Pickle Todd Richard
Sulik Gary Lee
Buskop Wendy K.
Buskop Law Group PC
Phasge Arun S,.
Pioneer (East) Inc.
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