Chemistry of inorganic compounds – Halogen or compound thereof – Elemental halogen
Reexamination Certificate
2001-07-20
2004-03-30
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Elemental halogen
C423S507000
Reexamination Certificate
active
06713035
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing chlorine. In particular, the present invention relates to a process for producing chlorine comprising oxidizing hydrogen chloride in a gas containing hydrogen chloride with a gas containing oxygen.
BACKGROUND ART
Chorine is a useful raw material for the production of vinyl chloride, phosgene, etc. and it is well known that chlorine is obtained through the oxidization of hydrogen chloride. For example, a process comprising catalytically oxidizing hydrogen chloride with molecular oxygen in the presence of a catalyst to obtain chlorine is known. With this process, a copper base catalyst, which is called a Deacon catalyst, is known to have a good catalytic activity, and various Deacon catalysts comprising copper chloride, potassium chloride and various kinds of compounds as third components are proposed. Besides the Deacon catalysts, processes using chromium oxide or its compound, or a ruthenium oxide or its compound, as a catalyst are also proposed.
However, since the oxidation reaction of hydrogen chloride is an exothermic reaction with 59 kJ/mol-chlorine, it is important to suppress excessive hot spot in a layer packed with the catalyst from the viewpoint of reducing the thermal degradation of the catalyst and maintaining the stability and easiness of operation. Furthermore, the excessive hot spot may induce a runaway reaction in the worst case, or the high temperature gas corrosion of a reactor material may be caused with hydrogen chloride and/or chlorine. “Catalyst” Vol. 33, No. 1 (1991) describes that, in the reaction of pure hydrogen chloride with pure oxygen in the presence of chromium oxide as a catalyst, it is difficult to remove the hot spot in a fixed bed reaction system, and that it is necessary to use a fluidized bed reactor in a practical apparatus.
DISCLOSURE OF INVENTION
Under such circumstances, one object of the present invention is to provide a process for producing chlorine comprising oxidizing hydrogen chloride in a gas containing hydrogen chloride with a gas containing oxygen in a fixed bed reaction system having a reaction zone comprising a catalyst-packed layer, in which the stable activity of the catalyst is maintained by suppressing the excessive hot spot in the catalyst-packed layer and making effective use of the catalyst-packed layer, and which is very advantageous from the viewpoint of a catalyst cost, an equipment cost, an operation cost, and the stability and easiness of the operation.
According to the present invention, this object can be achieved by a process for producing chlorine comprising the step of oxidizing hydrogen chloride in a gas containing hydrogen chloride with a gas containing oxygen in a fixed bed reaction system having a reaction zone comprising a catalyst-packed layer, wherein a superficial linear velocity of the gas in a column is from 0.70 to 10 m/sec.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
As a gas containing hydrogen chloride to be used in the present invention, any gas containing hydrogen chloride, that is generated through a pyrolysis or combustion reaction of chlorine-containing compounds, a phosgeniting dehydrogen chlorination or chlorination reaction of organic compounds, combustion in an incinerator, etc., may be used.
The concentration of hydrogen chloride in the gas containing hydrogen chloride is usually at least 10% by volume, preferably at least 50% by volume, more preferably at least 80% by volume. When the concentration of hydrogen chloride is less than 10% by volume, the separation of chlorine formed, and/or the recycling in the case of recycling unreacted oxygen may become complicated.
Components other than hydrogen chloride, which are contained in the gas containing hydrogen chloride, include aromatic chlorohydrocarbons (e.g. o-dichlorobenzene, monochlorobenzene, etc.), aromatic hydrocarbons (e.g. toluene, benzene, etc.), aliphatic chlorohydrocarbons (e.g. vinyl chloride, 1,2-dichloroethane, methyl chloride, ethyl chloride, propyl chloride, allyl chloride, etc.), aliphatic hydrocarbons (e.g. methane, acetylene, ethylene, propylene, etc.), and inorganic gasses (e.g. nitrogen, argon, carbon dioxide, carbon monoxide, phosgene, hydrogen, carbonyl sulfide, hydrogen sulfide, etc.).
In the course of the reaction of hydrogen chloride and oxygen, the aromatic chlorohydrocarbons and the aliphatic chlorohydrocarbons are oxidized to generate carbon dioxide, water and chlorine, the aromatic hydrocarbons and the aliphatic hydrocarbons are oxidized to generate carbon dioxide and water, carbon monoxide is oxidized to generate carbon dioxide, and phosgene is oxidized to generate carbon dioxide and chlorine.
As the gas containing oxygen, oxygen or an air is used. Oxygen may be produced by usual industrial methods such as a pressure-swing method of an air, deep-cooling separation of an air, etc.
While the theoretical molar amount of oxygen necessary for oxidizing one mole of hydrogen chloride is 0.25 mole, it is preferable to use oxygen in an amount exceeding the theoretical amount, and more preferably, 0.25 to 2 moles of oxygen is used per one mole of hydrogen chloride. When the amount of oxygen is too low, the conversion of hydrogen chloride may decrease. When the amount of oxygen is too high, it may be difficult to separate formed chlorine from unreacted oxygen.
In the present invention, preferably, the catalyst-packed layer is divided into at least two reaction zones, and the gas containing oxygen is divided into at least two portions and introduced in the respective reaction zones.
One example of a method for introducing the gas containing oxygen with dividing it into portions is a method comprising introducing the whole volume of the gas containing hydrogen chloride and a part of the gas containing oxygen in the first reaction zone, and introducing the reaction mixture from the first reaction zone and the rest of the gas containing oxygen in the second reaction zone. Herein, the first reaction zone means a reaction zone in which the raw material gas is firstly introduced, while the second reaction zone means a reaction zone in which the raw material gas is introduced subsequent to the first reaction zone. The divided amount of the gas containing oxygen, which is introduced in the first reaction zone, is from 5 to 90%, preferably from 10 to 80%, more preferably from 30 to 60% based on the whole volume of the gas containing oxygen. When this divided amount is too low, it may be difficult to control the temperature in the second and subsequent reaction zones.
The catalyst used in the oxidation reaction according to the present invention may be any known catalyst that is used in the production of chlorine through the oxidation of hydrogen chloride. Examples of such a catalyst include catalysts comprising copper chloride, potassium chloride and various compounds as third components, catalysts comprising chromium oxide, catalysts comprising ruthenium oxide, etc. Among them, the catalysts comprising ruthenium oxide are preferable, and those comprising ruthenium oxide and titanium oxide are more preferable. The catalysts comprising ruthenium oxide are disclosed in JP-A-10-182104 and EP 936 184, and the catalyst comprising ruthenium oxide and titanium oxide are disclosed in JP-A-10-194705 and JP-A-10-338502. The amount of ruthenium oxide in the catalyst is preferably from 0.1 to 20% by weight. When the amount of ruthenium oxide is too low, the catalytic activity may be low and thus the conversion of hydrogen chloride may decrease. When the amount of ruthenium oxide is too high, the catalyst may become too expensive.
The shape of the catalyst may be any of conventionally used shapes such as a spherical particle, a cylindrical pellet, an extruded form, a ring form, a honeycomb form, or a granule having a suitable size which is produced by milling of a molded material and sieving thereof. The size of the catalyst is preferably 10 mm or less. When the size of the catalyst exceeds 10 mm, the catalytic activity may deteriorate. Although the lower limit o
Iwanaga Kiyoshi
Suzuta Tetsuya
Yoshii Masayuki
Nguyen Ngoc-Yen
Sumitomo Chemical Company Limited
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