Chemistry of inorganic compounds – Halogen or compound thereof – Hydrogen halide
Reexamination Certificate
1996-01-24
2001-09-18
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Hydrogen halide
C423S481000
Reexamination Certificate
active
06290927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The production of hydrochloric acid by destruction of chlorinated hydrocarbons yields a product that is coloured yellow, caused by, among other things, the presence of iron, free bromine and free chlorine. Such an acid has small industrial application and is of low value. To increase the value it is therefore necessary to remove this colour from the acid in a simple and cheap way.
2. Description of the Prior Art
In earlier known methods to remove these types of compounds from hydrochloric acid. U.S. Pat. No. 4,349,525 describes a method for purification of hydrochloric acid that is produced by a reaction between alkali chloride and sulfuric acid. It was found that the colour was caused by Br
2
and that simultaneous removal of SO
2
also resulted in a decrease in the colour level. According to this patent, the acid is purified by stripping with inert gas and oxygen. A colourless acid was obtained. However, this is an expensive process as a stripping tower and the supply of a sufficient amount of inert gas/oxygen is needed.
European patent application No. 0 506 050 discloses a method for the removal of fluorine, bromine, iodine and their hydrogen compounds, from hydrochloric acid. This is carried out by a first removal of HF and fluorides by the addition of a stoichlometric excess of a chlorine salt that can be dissolved, which leads to precipitation of their fluoride compounds. Thereafter the acid is distilled. To remove Br
2
, I, bromides and iodides, chlorine is added in such amounts that elementary bromine or iodine is formed and thereafter is removed by stripping with water vapor. This is a very comprehensive and expensive process step.
SUMMARY OF THE INVENTION
The object of the invention is to find a method that removes colouring matter efficiently, is cheap, easy to handle and is safe for inner and outer environment and that will not result in unwanted reaction products in the treated acid.
These and other objects of the invention are obtained by the method and use as described below. The invention is further defined and characterized by the accompanying patent claims.
Thus, the present invention is directed to a method of removing iron and halogens from hydrochloric acid, which comprises removing iron from the hydrochloric acid, and thereafter adding a nitrogen containing reducing agent to the hydrochloric acid.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention concerns a method for the removal of colouring material as iron and halogens from hydrochloric acid. Among the halogens it is especially chlorine and bromine that contribute to the colour. Iron is first removed from the hydrochloric acid, preferably by filtration and ion exchange, and thereafter a nitrogen containing reduction agent is added to the acid. It is preferred to use compounds comprising hydroxyl amine, preferably hydroxylamine hydrochloride (hydroxyl ammonium chloride). The reducing agent is preferably supplied in a stoichiometric excess.
Iron is first removed from the acid, for example by filtration and ion exchange. An analysis of the produced hydrochloric acid showed that the main source for the yellow colour after the removal of iron, was halogens free chlorine and bromine. It was found that it was possible to reduce the surplus of free chlorine and bromine by adding a reducing agent.
The following properties must be fulfilled if a reducing agent shall be acceptable:
1. High efficiency. The compound ought to react as efficiently as possible with chlorine and bromine.
2. Low price.
3. Easy to handle. The compound should be pumpable or easily made pumpable (soluble in water).
4. No unnecessary danger to safety, work environment and outer environment.
5. No unwanted reaction products in the hydrochloric acid.
These demands resulted in a search for possible candidates among simple compounds with low molecular weight. They could not comprise poisonous elements. Several nitrogen containing reduction agents were considered. Among actual compounds the following can be mentioned: organic amines, hydrazine and compounds containing hydroxyl amine (hydroxyl ammonium). The most active compounds were hydrazine and hydroxylamine. Hydrazine will be active, but is environmental alarming. It was found that hydroxylamine satisfies all these demands. Hydroxylamine in the form of hydroxylamine hydrochloride was found to be a useful product and is used in the examples.
Hydroxylamine in hydrochloric acid will occur in the form of the hydroxylammonium ion H
3
NOH
+
. The most probable reactions between the free halogens and hydroxylamine are the following, where reaction 1 is dominant:
1. 2H
3
NOH
+
+Cl
2
=N
2
+2Cl
−
+4H
+
+2H
2
O
2. 2H
3
NOH
+
+2Cl
2
=2HNO+4Cl
−
+6H
+
=N
2
O+4Cl
−
+6H
+
+H
2
O
A surplus of hydroxylamine will probably disproportion to N
2
O and NH
4
+
after the reaction:
4H
3
NOH
+
=2NH
4
+
+N
2
O+3H
2
O+2H
+
The components resulting in colour will thus be reduced to chloride and bromide, which are colourless. Reduction experiments were carried out to find if the reagent removes the colour of the acid and to which extent. It was also necessary to examine how large the amount of reagent consumed was.
The colour numbers of the hydrochloric acids were determined with LOVIBOND 2000 Tintometer (comparator). The colouring extent is given in Hazen.
REFERENCES:
patent: 1770010 (1930-06-01), Payman et al.
patent: 2787523 (1957-04-01), Wilson
patent: 2787525 (1957-04-01), De Witt
patent: 3855400 (1974-12-01), Paolieri et al.
patent: 4349525 (1982-09-01), Yamashita et al.
patent: 2-233503 (1990-09-01), None
patent: WO95/17344 (1995-06-01), None
Translation of JP 2-233,503 (Sep. 1990).*
Aldrich catalogue, 1990 (no month), p. 713.
Nguyen Ngoc-Yen
Norsk Hydro A/S
Wenderoth , Lind & Ponack, L.L.P.
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