Chemistry of inorganic compounds – Halogen or compound thereof – Chlorine dioxide
Reexamination Certificate
2000-01-13
2001-09-11
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Chlorine dioxide
C423S479000, C423S480000
Reexamination Certificate
active
06287533
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of industrial chemicals. More specifically, the invention describes a novel process for producing chlorine dioxide through the reduction of ammonium chlorate in an aqueous acidic solution.
BACKGROUND OF THE INVENTION
Until recently, chlorine was used as a bleaching agent in the production of white pulp and paper. However, environmental protection agencies have prohibited the use of chlorine for pulp bleaching since it has been found to produce highly hazardous organochlorine compounds. Chlorine dioxide has replaced chlorine as the primary bleaching agent in the production of white pulp and paper. Chlorine dioxide is also used for water purification. It is now the most important worldwide commodity for these purposes.
Existing technologies for commercial production of chlorine dioxide involves the reduction of sodium chlorate/chloric acid with reducing agents such as hydrogen peroxide and glycerol, glycol (See e.g. U.S. Pat. Nos. 5,093,097; 5,091,166; 5,380,517; 5,486,344; and 5,487,881 and Japanese Pat. No. JP88-8203), methanol (U.S. Pat. Nos. 4,978,517 and 5,174,868) and chloride (U.S. Pat. No. 5,458,858; Canadian Pat. Nos. 461586 and 782574). The disclosures of these listed patents are hereby incorporated by reference. These commercial processes incorporate the following chemical reactions:
6NaClO
3
+ 3H
2
SO
4
+ 3H
2
O
2
→
6ClO
2
+ 6H
2
O + 3Na
2
SO
4
+ 3O
2
6NaClO
3
+ 3H
2
SO
4
+ 2CH
3
OH
→
6ClO
2
+ 5H
2
O + 3Na
2
SO
4
+ O
4
+
2HCOOH
NaClO
3
+ Alcohols + H
2
SO
4
→
ClO
2
+ Na
2
SO
4
+ CO
2
+ H
2
O
6HClO
3
+ 3H
2
O
2
→
6ClO
2
+ 6H
2
O + 3O
2
6NaClO
3
+ 12HCl
→
6ClO
2
+ 3Cl
2
+ 6H
2
O + NaCl
There are many drawbacks involved with the use of these existing technologies. For instance, methanol is a poisonous and volatile chemical. In addition, as shown above, the major oxidized product formed in methanol reduction processes is formic acid, which is also a toxic chemical. Thus, the use of methanol as a reducing agent in the production of chlorine dioxide creates an environmental hazard.
Chloride as a reducing agent is supplied either as hydrogen chloride or as sodium chloride. While chloride is not expensive, its use as a reducing agent in these processes is also disadvantageous since it makes chlorine dioxide with large amounts of chlorine impurity. This is problematic since there has traditionally been no practical means of disposing of chlorine waste material.
The use of methanol as a reducing agent in chlorine dioxide processes also has the disadvantage of producing the inevitable by-product sodium sulfate (Na
2
SO
4
), which is commercially known as salt cake. A part of the salt cake by-product is consumed by pulp mills to make sodium sulfide, a component of black liquor. However, the bulk of the salt cake does not have any use and must simply be disposed of.
Hydrogen peroxide can also be used as an efficient reducing agent in the production of chlorine dioxide. Although expensive, the use of hydrogen peroxide is an attractive alternative since it does not result in the formation of the formic acid and chlorine toxic by-products. However, the use of hydrogen peroxide also results in the production of large amounts of undesirable salt cake as a waste product.
There is therefore a need in the art for an improved method of producing chlorine dioxide.
It is therefore a primary objective of the present invention to provide a method of producing chlorine dioxide which does not form toxic by-products and is environmentally safe.
It is a further objective of the present invention to provide a means of producing chlorine dioxide in higher yield with a faster reaction rate than commercially known processes.
It is yet a further objective of the present invention to provide a means of producing chlorine dioxide which is economical.
It is a further objective of the present invention to provide a means of producing chlorine dioxide without the need for recycling the by-products.
These and other objectives will become apparent from the following description.
SUMMARY OF THE INVENTION
The present invention describes a method of producing chlorine dioxide using a novel chemical reaction. Specifically, the invention involves the chemical reduction of ammonium chlorate in an aqueous acidic solution. The reducing agent may include any one of hydrogen peroxide, sugars, alcohols, aldehydes, ketones, organic acids, sulfur dioxide, ammonium sulfite, ammonium bisulfite, or mixtures thereof. The reduction reaction is performed with or without a catalyst at elevated temperatures.
The yield of chlorine dioxide in this invention is over 110% on the basis of reducing agents than in existing processes, as well as at least a 50% higher rate. Further, the resulting chlorine dioxide is substantially free of chlorine impurity. Using sulfuric acid as the acidifying agent, ammonium sulfate is produced as a by-product which may be used as a fertilizer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As set forth above, the present invention discloses the production of chlorine dioxide through the reduction of ammonium chlorate in an aqueous acidic solution, preferably in the absence of a substantial amount of sodium ions, meaning that there are insignificant amounts of sodium ions to produce salt cake by-product.
Any source of ammonium chlorate is suitable for this invention. The ammonium chlorate is preferably prepared by the double decomposition reaction of ammonium sulfate and barium chlorate, and most preferably as described in U.S. Pat. No. 5,948,380, the disclosure of which is hereby incorporated by reference. The concentration of chlorate ion (ClO
3
−
) in the aqueous acidic solution is preferably maintained at about 0.5M to saturation, and most preferably between about 1.5M to 4.5M.
The source of acidity for this invention may be any strong acid, with sulfuric acid, ammonium bisulfite, chloric acid, perchloric acid, and mixtures thereof being preferred.
There are four preferred categories of aqueous acidic solutions for use in the invention. The first category is aqueous solutions of chloric acid or a mixture of chloric acid and ammonium chlorate with acidity ranging preferably from about 0.2N to 7N, and most preferably from about 1.5N to 5N. The chloric acid feed solution is available from the reaction of sulfuric acid with barium chlorate. The preparation of barium chlorate is described in U.S. Pat. No. 5,948,380.
The second preferred category of aqueous acidic solutions is aqueous solutions of perchloric acid or a mixture of perchloric acid and chloric acid or a mixture of perchloric acid and chloric acid, with acidity ranging preferably between about 0.2N to 1N, and most preferably between about 1.5N to 5N. The perchloric acid for making such mixtures is available commercially.
The third preferred category of aqueous acidic solutions is aqueous solutions of chloric acid and sulfuric acid, with acidity ranging preferably between about 1N to 14N, and most preferably between about 2N to 8N.
The fourth preferred category of aqueous acidic solutions is aqueous solutions of sulfuric acid and ammonium bisulfate and ammonium sulfate, with acidity ranging preferably between about 1N to 14N, and most preferably between about 2N to 8N. The source of aqueous acidity in these solution is sulfuric acid and ammonium bisulfate.
The concentrated aqueous solution of the reducing agent is fed into a reactor so as to maintain a concentration of reducing agent ranging from about 0.00005M to 0.88M in the reaction mixture. The preferred concentration of reducing agent is from about 0.005M to 0.4M, with the most preferred concentration being maintained in a range of from about 0.01M to 0.2M.
The reducing agent used in this invention is not critical, and may include any conventional reducing agents. These may include, but are not limited to hydrogen peroxide, sugars, alcohols, aldehydes, ketones, o
Hoq M. Fazlul
Khan Mohammed N. I.
Bos Steven
Zarley McKee Thomte Voorhees & Sease
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