Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-01-23
2002-04-16
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S840000
Reexamination Certificate
active
06372947
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for producing a solution of a metal alcoholate and to a process for removing alkali metal residues from a vessel used in the manufacture, storage and shipping of alkali metals.
BACKGROUND OF THE INVENTION
The alkali metals are very reactive metals and are not found in elemental form in nature. Electrolytic reduction is typically used to produce these metals. Sodium is by far the most commercially important of the alkali metals, and therefore the technology description is focussed on sodium. For many decades, the generally used process for making sodium has been the Downs electrolytic process. This process uses a molten salt electrolyte consisting of a mixture of NaCl, CaCl
2
, and BaCl
2
, and is operated at a high temperature of about 600° C.
Sodium metal electrolytically produced by this process contains small amounts of calcium metal co-deposited at the cathode because the decomposition potentials of the two metals are very close to one another. Elaborate and costly cooling, precipitation and/or filtration procedures are necessary to remove most of the calcium from sodium before the sodium is ready for shipment to customers. Typically the calcium so removed is in the form of a sodium/calcium filter-cake mixture, which is then purified by a high temperature recovery process.
In spite of these calcium removal steps, a small amount of calcium remains dissolved in the liquid sodium metal when it is transferred to a tank car or other vessel. Upon gradual cooling, more calcium eventually precipitates from the liquid sodium and settles to the bottom of the tank car as sludge containing a mixture of calcium, sodium and other impurities. After a number of tank car shipments, the sludge build-up becomes substantial and the sludge needs to be removed from the bottom of the tank car. Currently this is done by a cumbersome and fundamentally hazardous operation involving manual labor, jackhammers and the like to physically dig out the sludge. This labor-intensive operation is inherently hazardous because the sodium metal has a very low auto-ignition temperature in air of only about 120° C., and even at ambient temperatures can fire in the presence of water and air. This means that the manual removal of the accumulated sludge requires elaborate safety precautions, making this operation tedious, costly, and generally undesirable. The tank car sludge so removed is typically recycled back to the high temperature recovery process.
Purified alkali metal such as purified sodium is in the manufacture of alkali alcoholate such as, for example, sodium methylate. Sodium methylate is used widely as a reagent and catalyst for various chemical reactions. It is generally used as a solution in methanol for easy handling. Sodium methylate can be produced by batch reaction of sodium metal with methanol such as, for example, by adding bars, pieces, or molten sodium to an oxygen-reduced or removed, such as nitrogen-flushed, vessel operating at atmospheric pressure and containing an excess of methanol. It is based on the reaction 2Na+2CH
3
OH→2NaOCH
3
+H
2
. This reaction is highly exothermic, and reaction heat is typically removed by boiling off and refluxing methanol. The reaction is carefully controlled to avoid the entry of air into the vessel during the feeding of the sodium to avoid creating an explosive mixture. In large-scale production, by-product hydrogen and small amounts of nitrogen and methanol are usually vented to a flare for environmental emissions control.
Numerous efforts have been made to develop alternate processes to reduce the costs and hazards inherent in the above procedure. For example, East German Pat. No. 118,068 discloses a process for the continuous manufacture of sodium methylate using a sodium dispersion in an inert solvent to react with methanol. U.S. Pat. No. 4,596,895 discloses the reaction of methanol with a sodium amalgam manufactured by the once-important amalgam process as a means to produce sodium methylate. U.S. Statutory Invention Registration No. H1697 discloses a continuous process to make sodium methylate by feeding molten sodium and methanol to a stirred reactor under controlled conditions. These processes require the use of commercially pure sodium or sodium-mercury amalgam.
U.S. Pat. No. 4,857,665 discloses a process for converting the sodium contained in the residue accumulating in the filtration of liquid crude sodium from a fusion electrolysis process, and containing sodium, calcium, and their oxidation products, into a sodium alcoholate with a low content of sodium oxide, sodium hydroxide and sodium carbonate. This is done by heating the residue under intense mixing to temperatures in the range from 300° C. to 600° C. for 2 to 6 hours, adding the heat-treated residue to an alcohol, and separating the undesirable impurities by filtration. This process is costly to operate, and is not suitable for the removal of sodium sludge from tank cars and/or concomitant production of sodium methylate.
Therefore, there is a need to develop a process that can be used to produce an alkali metal alcoholate and can be safely and economically used for removing the sludge. The advantages of the invention include safer than the known process because it eliminates manual labor and personnel exposure for the clean-out operation; substituting the known “digging out” methods with a chemical dissolution process; producing a sodium methylate solution sodium/calcium sludge as a useful product; and cost-effective manner because no additional reactors, or agitators are required.
SUMMARY OF THE INVENTION
A process comprises contacting a mixture, which comprises an alkali metal and an alkaline earth metal, with an alcohol under a condition sufficient to produce an alkali metal alcoholate and alkaline earth metal alcoholate and, optionally, separating and recovering the alkali metal alcoholate.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention can be carried out in any suitable vessel, container, or reactor, known to one skilled in the art. The terms “vessel”, “container”, and “reactor” are interchangeable in this application and can refer to the tank car, storage tank, or other vessels used in the manufacture process of an alkali metal as discussed in the BACKGROUND OF THE INVENTION section. A suitable vessel is preferably equipped with a reflux condenser or other means of heat removal known to one skilled in the art to effect the production of an alkali metal alcoholate. The vessel can also be equipped with a piping system for the introduction of alcohol and an inert gas, and a venting system for the removal of the hydrogen produced. For example, a suitable vessel can be a sodium tank car or sodium storage tank equipped with heat removal equipment such as a reflux condenser.
The mixture can comprise an alkali metal and an alkaline earth metal, preferably about 65 to about 99 weight % alkali metal such as sodium and about 1 to about 35 weight % alkaline earth metal such as calcium. Preferably the mixture is a mixture of sodium and calcium obtained from the sludge deposited from molten sodium shipment or storage, or obtained during a sodium purification process (sodium/calcium filter cake), or a combination of these. Other impurities can also be present.
The preferred alcohol used to produce the alkali metal alcoholate is a substantially or essentially anhydrous liquid under ambient conditions. It can contain from 1 to about 10, preferably 1 to 4, carbon atoms. The presently preferred alcohol is methanol, ethanol, or combinations thereof. The most preferred alcohol is methanol.
Generally, it is preferred that a vessel containing the mixture is substantially or essentially free of oxygen. Oxygen can be substantially or essentially removed by flushing the vessel with an inert gas. The flushing can be done before, contemporaneously with, or after an alkali metal and an alkaline earth metal are introduced to the vessel. Examples of inert gases include nitrogen, argon, helium, or combinations of two or mo
Ely Wayne B.
Renner Carl Andrew
Barts Samuel
E. I. du Pont de Nemours and Company
Price Elvis O.
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