MXPA06011299A - Catalytic removal of dissolved oxygen from organic liquids - Google Patents

Abstract

A process is disclosed for removing dissolved oxygen from organic liquids using a solid catalyst. The dissolved oxygen is converted into water by the action of a reducing agent.

Description

CATALYTIC REMOVAL OF DISSOLVED OXYGEN OF ORGANIC LIQUIDS FIELD OF THE INVENTION The present invention relates to a method for removing dissolved oxygen from organic liquids by the use of a solid catalyst. By doing this dissolved oxygen is converted to water by the action of the reducing agent. BACKGROUND OF THE INVENTION The presence of dissolved oxygen in organic liquids that are used in chemical processes in extremely large quantities of several metric tons per hour can cause corrosion of undesirable equipment parts or secondary reactions with other materials of the charge. Due to high yields, the amounts of oxygen in the ppm range are sufficient for this to occur. In most chemical processes there are high temperatures and pressures, which facilitate the occurrence of unwanted reactions between dissolved oxygen and other materials in the load. The removal of dissolved oxygen from water is already known (K. Matt, Chemie-Technik, 20 (10), 44-45, 1991 / A.

Brehm, U. Antons, Reduction of Oxygen Dissolved in Water by Means of a Fluidized Bed Reactor, Chemie Ingenieur Techik 70 (1 + 2), 176-181, 1998). This action is mainly used REF.:175782 to avoid corrosion of pipes and appliances in water circuits. In WO 01/85622 a catalytic method is described for the removal of oxygen from seawater which was subsequently used in underground petroleum deposits. As a matter of principle it is necessary to differentiate physical and chemical methods in the removal of oxygen. Physical methods include thermal degassing, separation, gas removal by evacuation or combinations of these methods. Physical methods are naturally characterized by high investment costs and considerable energy consumption for high yields. And yet the remaining oxygen concentrations are still very high. For these reasons chemical methods are also used for the removal of oxygen from water. For example, after the addition of hydrazine the oxygen reacts completely to produce water and nitrogen. However, hydrazine is poisonous, highly hazardous to water, corrosive and may be involved in unwanted side reactions with other materials. Additionally, chemical methods are known that resort to the use of sodium sulfite or amines. For the chemical removal of oxygen from water it is also possible to use catalytic methods that use different catalysts in the presence of reducing agents such as hydrogen (J.-S. Moon,.-K. Park, S.-W.Yun, G. Seo , A study on the Application of a New Dissolved Oxygen Removal System Using Activated Carbon Fiber Cartridge Catalyst, Official Proceedings - International Water Conference 61, 186-204, 2000). The state of the art for the removal of oxygen from organic liquids has not been described. If it is desired to remove dissolved oxygen from an organic liquid it is necessary to make sure in advance that a chemical reaction with the organic liquid will not take place leading to the formation of unwanted side products as a result of the catalyst or the reducing agent. This could interfere dramatically with the entire course of production. On the other hand, the organic liquid to be treated must not deactivate the catalyst that is used, which may cause, for example, the formation of sediment. In addition, if the solubility of oxygen is higher in organic liquids than in water and consequently the amount to be removed is also significantly higher. For example, oxygen dissolves approximately 10 times better in methanol than in water (J. Tokunaga, Solubilities of Oxygen Nitrogen and Carbon Dioxide in Aqueous Alcohol Solutions, J. Chem. Eng. Data 20, 1, 41-46, 1975, and K.

Fischer, M. Wilkens, J. Chem. Thermodynamics, 33, 1285-1308, 2001). As a result it is necessary to use very active catalysts thatIn addition, in the preferred embodiment, they convert oxygen into, for example, water at room temperature without the application of heat. To aggravate matters, in the removal of oxygen from organic liquids there is also the fact that these are not present as a pure substance in chemical processes, but that most of the time they contain a small amount of other organic substances and / or inorganic which are also not inert. In the known purification methods according to the state of the art, water on the other hand is mainly used in separate heating and cooling circuits without contact with other means. When mixtures of several different substances are present in the chemical plants, the removal of dissolved oxygen from the organic liquids may be especially necessary if the mixtures can cause undesired side reactions with oxygen. For example, oxygen dissolved in an organic liquid can, upon contact with sulfur-containing compounds at higher temperatures, cause oxidation of these compounds to cause the formation of elemental sulfur. This can have fatal consequences if the elemental sulfur is deposited as a solid and clogs the parts of the equipment. Through the removal of dissolved oxygen a greater availability of the facilities is obtained, which is of enormous economic interest. In addition, the safety of the plant is also improved because the operation with hazardous material is not a factor that interferes with the operation of the plant. In addition, the introduction of dissolved oxygen into the installations can lead to the formation of explosive mixtures with organic compounds in the event that the oxygen introduced, for example by degassing, is enriched in parts of the installation and comes into contact with organic compounds. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide a method for the catalytic removal of dissolved oxygen from organic liquids in a manner that avoids unwanted secondary reactions and dangerous plant conditions related to safety. DETAILED DESCRIPTION OF THE INVENTION In order to remove dissolved oxygen in the most economical way possible, the method should preferably operate at room temperature without thermal treatment.

Additionally dissolved oxygen should be removed almost completely from the organic liquid.

This problem is solved by the following procedure: in a first step the reducing agent, preferably hydrogen. It is introduced into the organic liquid. The form and type of introduction of the reducing agent is not decisive for the effectiveness of the method as long as a sufficient exchange of material between the organic liquid and the reducing agent is ensured. The introduction of the reducing agent can be carried out in different ways such as, for example, by means of a static mixer, a bubble column, a falling film absorber, an agglomerated material or filled column, or a radiator. The amount of the reaction media must be measured so that it is at least sufficient to reduce the oxygen that is present. If a greater amount of gaseous reducing agent is used than it dissolves in the liquid, then, in a preferred embodiment, the excess portion should be removed prior to contacting the saturated organic liquid of reducing agent with the catalyst. This can be done, for example, by simple gas-liquid separation. In this mode, a part of the dissolved oxygen is removed along with the excess reducing agent. Subsequently they are brought into contact with a suitable catalyst, the organic liquid of the reducing agent it contains. This is especially carried out in known reactors with a catalyst in solid form, preferably in reactors of the fixed fact on which the catalyst is loaded. In another embodiment of the invention it is also possible for the reducing agent to be contacted directly with the organic liquid and with the catalyst in the reactor without previously entering the organic liquid. This reduces the equipment expense of the method. In a preferred embodiment of the method, no additional heating is provided in any of the steps. The method is preferably operated continuously at room temperature. The method can be operated at reduced pressure, atmospheric pressure or excess pressure. Preferably pressures are applied from atmospheric pressure to 100 bar. However, the necessarily very active hydrogenation catalyst must have a completely inert behavior with respect to the organic liquid. On the other hand, the organic liquid must not deactivate the catalyst. It is found that commercially available noble metals and transition metal catalysts, preferably supported noble metal catalysts, are particularly suitable, with Pd-containing catalysts being especially preferred with aluminum oxide supports, activated carbon, silica or resins. The grain size of the catalysts used is preferably between 0.2 mm and 10 cm. The catalyst can also be present in the form of a coating on the wall, in components or supports. If the introduction of the reducing agent or the mixture of the reducing agent with the organic liquid and the conversion of the dissolved oxygen are carried out in an apparatus, it is also useful to use a static mixer which is coated with Pd-containing catalyst. Suitable organic compounds are known solvents or their mixtures which, if unsaturated, are not hydrogenated under the test conditions. Particularly suitable are branched or unbranched aliphatic alcohols having 1 to 12 C atoms, cyclic or non-cyclic aliphatics, ethers comprising alkyl groups with 1 to 5 C atoms as well as aromatic hydrocarbons with or without substitutes. Typical organic liquids are, for example, methanol, ethanol, isopropanol, acetone, cyclohexanol, cyclohexenes, ethyl acetate, dimethylformamide, benzene, toluene or xylene. However, the term organic compound is not limited to organic solvents. The method according to the invention has proven to be particularly advantageous when dissolved oxygen is essentially removed from liquid organic compounds and these are subsequently contacted with organic compounds containing sulfur or liquids containing them or gas mixtures. In these cases the elemental sulfur is no longer deposited, in particular if H2S is fed. It is demonstrated that organic liquids treated at room temperature according to this catalytic method can be released almost completely from dissolved oxygen (<; 100 ppb, in particular 80 ppb to 0 ppb). The Pd-containing catalysts that are preferably used are sufficiently active to remove dissolved oxygen in organic compounds at room temperature. Even the impurities of the organic compounds do not impede the effectiveness of the method. On the one hand it was possible to verify the removal of oxygen by online measurements of the oxygen stream after the use of the catalyst (Clark Cell principle). On the other hand, for the objective evidence of dissolved oxygen in the organic liquid treated according to this method it is possible to add other chemical products (related to the process as in chemical facilities) such as, for example, hydrogen sulfide. If oxidation occurs with oxygen to elemental sulfur, it can then be checked by HPLC analysis of the organic liquid with respect to elemental sulfur. Examples: Comparative Example: 4 1 / h of methanol was metered continuously into a glass flask by a pump. A stream of nitrogen at 3.0 1 / hr is also fed to the vessel through a frit (porous glass). The mixture was then passed through a 200 ml column loaded with glass spheres. After this the gas was separated by phase separation in another flask. The whole apparatus was operated at room temperature and atmospheric pressure. Using an oxygen measurement probe, it was determined that the dissolved oxygen content was 35 ppm at the outlet of the column. The oxygen concentration in the methanol used was 70 ppm. Example 1: 4 1 / h of methanol was metered continuously into a glass flask by a pump. A stream of nitrogen at 1.0 l / h through a frit is also fed to the vessel. The mixture was then passed through a 200 ml column loaded with glass spheres. After this the gas was separated by phase separation in another flask. Then the methanol containing hydrogen was pumped at 4 1 / hr to a fixed reactor filled with 70 g of catalyst (0.5% by weight of Pd on? -Al2 03). Using an oxygen measurement probe, it was determined that the dissolved oxygen content was 80 ppb at the reactor outlet. However, the oxygen concentration in the methanol used was 70 ppm. 7 g of hydrogen sulphide was passed through 200 ml of dissolved oxygen free methanol, so that it was not possible to detect elemental sulfur (<1 ppm) by HPLC analysis. Through the use of untreated methanol, in contrast, more than 40 ppm of elemental sulfur were formed. Example 2: Example 1 was repeated with a stream of 5 1 / h of methanol containing small amounts of impurities (amines and sulfur compounds), and 69.5 g of a catalyst containing Pd (Lewatit 3433, from Co. Bayer AG) supported on an ion exchange resin. The oxygen content dissolved in 0 ppb at the outlet of the reactor was determined by means of an oxygen measurement probe. Example 3: Example 2 was repeated with a modified installation. Thus, for the entry of hydrogen a falling film absorber was used, where the methanol containing small amounts of impurities flows from the top to the bottom in the form of a thin film along the inner wall of a pipe in an atmosphere of hydrogen. A hydrogen outlet was additionally dispensed with. Using an oxygen measurement probe it was determined that the content of dissolved oxygen in 0.5 ppb at the exit of the reactor. Example 4: Example 1 was repeated with a flow of 5 1 / h of cyclohexane. An oxygen measuring probe determined that the content of dissolved oxygen at the outlet of the reactor was 55 ppb. Example 5: Example 1 was repeated with a flow of 5 1 / h of toluene. An oxygen measuring probe determined that the content of dissolved oxygen at the outlet of the reactor was 20 ppb. Example 6: Example 1 was repeated with a current of 3 1 / h of acrolein. An oxygen measuring probe was used to determine that the content of dissolved oxygen at the outlet of the reactor was 100 ppb.

Example 7: Example 1 was repeated with a current of 3 1 / h of acetone. Using an oxygen measuring probe, it was determined that the content of dissolved oxygen at the outlet of the reactor was 50 ppb. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (15)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Method for removing dissolved oxygen from organic liquids through the use of a catalyst and a reducing agent, characterized in that the oxygen is converted into water.
2. 2. Method according to claim 1 for the catalytic removal of dissolved oxygen, characterized in that it comprises the following process steps: a) entry of the reducing agent into the organic liquid, b) if necessary removal of the insoluble excess of reducing agent , c) reaction of the dissolved oxygen with the reducing agent on a catalyst.
3. Method according to claim 1, characterized in that the reducing agent is fed directly onto the catalyst.
4. Method according to claim 2, characterized in that no more reducing agent is added than it dissolves in the organic liquid.
5. Method according to claim 2, characterized in that the reducing agent is absorbed by the organic liquid.
6. Method according to claim 2, characterized in that the excess reducing agent is separated by a gas-liquid phase separation.
7. Method according to claims 1 and 2, characterized in that the conversion of the dissolved oxygen with the reducing agent is carried out in a fixed bed loaded with catalyst.
8. 8. Method according to claims 1 to 7, characterized in that the catalytic removal of the dissolved oxygen is carried out at room temperature.
9. 9. Method of compliance with the claims 1 to 8, characterized in that the method is continuous operation.
10. 10. Method of compliance with the claims 1 to 9, characterized in that the reducing agent is hydrogen.
11. 11. Method of compliance with the claims 1 to 10, characterized in that the catalyst is a noble metal containing solid material.
12. Method according to claims 1 to 11, characterized in that the catalyst is a material containing Pd.
13. 13. Method according to claims 1 to 12, characterized in that the organic liquid is an organic solvent or a mixture of these.
14. 14. Method according to claims 1 to 13, characterized in that the organic compound is methanol.
15. 15. Method of compliance with the claims 1 or 2, characterized in that the organic liquid liberated essentially from dissolved oxygen is brought into contact with inorganic or organic compounds containing sulfur or with mixtures containing them.