MXPA97009877A - Destruction of formic acid and formaldehyde encorrientes de dese - Google Patents

Abstract

The present invention relates to a method for destroying formaldehyde and formic acid, present in a liquid aqueous stream, converting formaldehyde to formic acid and converting formic acid to carbon dioxide and water, characterized in that it comprises the steps of: a) putting into contact the liquid stream with a supported catalyst of a metal of group VIII, at a temperature in the scale that goes from the ambient temperature until around 90 ° C, and at a pressure in the scale that goes from the atmospheric to around 14.06 kg / cm2; and b) introducing air or molecular oxygen into the liquid stream to obtain and maintain the concentration of dissolved oxygen in the range of about 1-7 ppm in the vicinity of said catalyst, in order to oxidize a desired amount of acid formaldehyde. formic and formic acid to carbon dioxide and ag

Description

DESTRUCTION OF PHYMIC ACID AND FORFIRLDEHYDE IN DISPOSAL CURRENTS BACKGROUND Field of the Invention This invention incorporates the effective treatment of an aqueous stream containing formic acid and / or formaldehyde, regulated by the government. In particular, this invention relates to a process for destroying formic acid and / or formaldehyde in a residual aqueous stream, by oxidation catalyzed by precious metal.

Description of the Related Art It is believed that the invention can generally be put into practice, together with aqueous streams containing thermal acid and / or formaldehyde. Given its potential for broad application, it has been shown that the present invention has particular advantageous application in the treatment of a waste stream containing formic acid and formylidene generated with respect to the manufacture of N- or fonornetylglycine. N-phosphonorner? Igi? C? Na, which is known in the agricultural chemical industry as glyphosate or glypho ate acid, is an extremely effective and important herbicide, important to control the growth of seeds that germinate, seedlings that emerge, woody and herbaceous vegetation in maturation and established, and aquatic plants. Glyphosate and its salts are conveniently applied in an aqueous formulation, such as a broad-spectrum herbicide (ie, effective on a wide variety of plants), for post-emergence. For example, in US Patent No. 4,724,103, to Gentiicore, there is disclosed a process for preparing N-phosphonor-nyliminodiacetic acid (glyphosate intermediate). This process involves sequentially reacting an alkali metal salt of imodiazodic acid with a strong mineral acid, to form a strong mineral acid salt of the iminodiacetic acid and the alkali metal salt of the strong mineral acid, and phosphonomethylarylninodiacetic acid by reaction. n with forrrtaldehyde and phosphorous acid to provide a mixture of N-phosphonoinethyliminodiacetic acid and an alkali metal salt. Also involved in the process is a step by which the desired intermediate product is separated from the other reaction products, leaving a residual solution containing formaldehyde, which is easily treatable according to the process of the present invention, when separated. by distillation the -fo rnaldohi do and the formic acid of the heavy organic waste stream, by means of superior evaporation.

US Pat. No. 3,969,398 to Hershrnan discloses a process for the production of N-phosphonorne iigi icin, by oxidation of N-phosphono etimimodiacetic acid, using a gas containing molecular oxygen, as an oxidant, in the presence of a catalyst that It comprises activated carbon. As a characteristic of the production of glyphosate, such as in this process, a conventional distillation step is frequently provided, by which formic acid and a higher waste stream containing forrnaldehi are formed or, when these undesirable ingredients are separated from the product of N-phosphonornethylglycine desired, for example, by distillation. The liquid waste stream thus formed is a solution that contains significant amounts of formaldehyde and formic acid, which are substances that cause toxicological concern and are suspected to be carcinogenic. Eliminate formaldehyde and formic acid from this stream in high yields, in such a way, it is convenient. The present invention provides a technically simple and direct process, by means of which substantially all the formic acid and fornaldehyde present in an aqueous organic stream and, in particular, the waste streams obtained with respect to the extraction of N-acid are substantially eliminated. phosphonornethylammoniacetic (ie, the intermediate of glyphosate) and N-phosphonornethylglycine or glyphosate acid. This disproportionately high oxidation / conversion of formaldehyde to formic acid and of formic acid, in turn, to carbon dioxide and water, occurs surprisingly rapidly and efficiently, with respect to the process of the present invention.

BRIEF DESCRIPTION OF LP INVENTION In accordance with the practice of the present invention, an aqueous waste stream containing unreacted formic acid and / or formaldehyde is treated by oxidation catalysed by means of a supported metal precious catalyst. In a particular embodiment, formaldehyde and formic acid are generated, each of which is present in a representative aqueous waste stream, in respective amounts of about 6,000 pprn and 4,000 pprn, from the manufacture of N-phosphonornethylglycine, by the reaction of N-rosphonomethyl-1,3-diacetic acid, water and oxygen. In accordance with the invention described herein, each of these materials is substantially removed and reduced to a commercially acceptable and safe level of 200 ppm or less, in which case the stream becomes suitable for recirculation. The novel and useful method of the present invention is capable of being put into practice either in an intermittent format or as a continuous process. Traditionally, although various supported metal catalysts can be used, in the practice of the present invention, and particularly those supported catalysts containing any of the metals selected from group VIII, contained in the Periodic Table of the Elements, a heterogeneous catalyst of Pt on carbon is the preferred catalyst for practicing the process of the present invention. The adherence to certain variables of the process according to the invention, including the temperature, the pressure and the level of air or oxygen dissolved in the solution to be treated, is also important to obtain the maximum advantage of the invention. When compared with the alternative undesired formaldehyde and / or formic acid b otavation, it is believed that several significant advantages have an effect on the process of the present invention. In particular, the catalytic oxidation of these undesirable substances is considered less intense, in terms of capital, traditionally, avoids the generation of biological sludge and, very importantly, when treating the upper streams of the evaporator according to the present invention, it can be generated an aqueous stream substantially free of undesirable substances, which is suitable for circulating it through the original procedure.

DETAILED DESCRIPTION OF LR INVENTION As indicated above, the present invention can be practiced in conjunction with the removal of formaldehyde and formic acid, in general, from aqueous organic streams. However, because these undesirable compounds are produced in relation to the manufacture of N-phosphonomethylene, and because it has been found that the present invention is particularly useful for treating waste streams produced in connection therewith, it will be reference to an embodiment of the invention in which formaldehyde and formic acid are destroyed in the effluent of the production of N-phosphonomethylglycine. Rsi then, in this context the following description will be given, which will fully describe the invention and will set out in detail its mode of operation. Significant amounts of formic acid and formaldehyde are generated as waste products, for example, in the manufacture of N-phosphonornethylglycine. The destruction of formic acid and / or formaldehyde in waste streams is required to reduce emissions of these potentially toxic materials regulated by government authorities.

At present, these compounds are typically separated from the process streams either by evaporation or by ion exchange, and then are destroyed in biological treatment facilities, using biological treatments, for example, by microorganisms. A waste stream containing undesirably high levels of formaldehyde and formic acid, which the practice of the present invention converts to environmentally acceptable products, is generated by the implementation of the processes described in U.S. Patent Nos. 4,724,103 and 3,969,398. In the first procedure, disodium imododiacetate (DSIDR) and phosphorus tpchloride (PCI3) are heated together in water, at an elevated temperature, to produce a slurry or slurry of hydrochloride of indole diacetic acid, sodium chloride and phosphorous acid. Subsequently, CH2O (as forrnaline) is added slowly. The resulting reaction mixture is cooled, then an aqueous solution of sodium hydroxide is added in an amount sufficient to minimize the solubility of the N-phosphonomethyl-rhamodiacetic acid, which precipitates from the solution. The mixture is filtered or centrifuged and the resulting solid material is recovered. The resulting liquid, derived from the isolation of N-phosphonornethylnitoliacet-1 to acid, is a waste stream containing, among other factors, formaldehyde and formic acid, potentially toxic, selected organic phosphonic acids, sodium chloride and phosphorus mineral acids, selected . When undesirable forrnaldehyde and formic acid are separated by distillation from this highly organic com pound, such as by distillation, to form a second residual stream, the practice of the present invention converts the second stream containing formaldehyde and formic acid to a Predominant mixture of carbon dioxide, environmentally benign, and water. Thus, the current becomes more suitable to discard it or, when a higher current is treated, to recirculate it again through the procedure in question. In accordance with the process of the present invention, the formaldehyde and / or the formic acid is catalytically oxidized and, thus, is removed from the aqueous waste streams containing those undesirable compounds. The catalytic oxidation carried out according to the process of the invention comprises the treatment of an aqueous stream containing fornaldehyde and / or formic acid with a supported metallic catalyst, in the presence of dissolved oxygen or oxygen-containing air. The preferred catalyst support material is carbon and the metal to be charged to the catalyst is selected from group VIII metals. Finally, the basic chemistry involved in the procedure is the following: lethal catalyst on carbon 1. CH20 + 1/2 02) HCOOH lethal catalyst on carbon 2. HCOOH + 1/2 02 >; C02 + H2 0 Reaction 1 shows that, when oxidized according to the present invention, the formaldehyde is converted to formic acid; and reaction 2 shows that the formic acid, in turn, is converted to carbon dioxide and water, environmentally benign. In a broad sense, the reactions shown above can be implemented according to the invention in any conventional reactor, at room temperature and at atmospheric pressure. Additionally, provided that an adequate level of oxygen or air containing oxygen is dissolved in the stream being treated, any of the Group VIII metals may be employed in the practice of the invention. However, in order to obtain the maximum advantage of the invention, and to make it particularly useful in a commercial context, it is required that certain procedural limitations, in accordance with the invention, be followed. In this regard, although any conventional reactor system can be used for the practice of the invention, one which is suitable for operating under pressure, and which has a good type of agitation is preferred. These aspects of the suitable reactor will allow the invention to be put into practice more efficiently because the agitation and pressure facilitate the dissolution of oxygen or oxygen-containing ae in the waste stream, which concentration affects the catalytic activity, such as was mentioned previously. In a similar way, the selection of the particular metal of group VIII and the amount of its charge in the carbon support or substratum will also affect the speed of the oxidation reaction and, thus, the commercial advantage obtained by putting in practice the invention. The inventor has discovered that, of the metals of group VIII, palladium (Pd), rhodium (Rh) and, in particular, platinum (Pt) function in a very convenient manner in conjunction with the invention. For this reason platinum is the preferred metal filler for the catalyst and, therefore, reference is made to it in the data included in this description. The catalyst can contain platinum on the scale of 0. 1% by weight to 10% by weight, approximately, as long as the total proportion of platinum with respect to the working reactor volume, is on the scale of around 0.00015 a 1 to 0.00040 to 1. Those skilled in the art will recognize that while the other metals of group VIII can be used in this invention, they will lead to lower reaction rates, unless they are employed in greater amounts. Those skilled in the art will appreciate that the comparatively high loads of the selected metal in the catalyst are likely to result in improved grouting and improved reaction speed and, therefore, may be preferred over smaller loads. . However, the cost of the catalyst is often a factor influencing its selection and, when, as in this case, the preferred metal charge consists of a precious and expensive metal, such as platinum, there is an obvious advantage in identifying the charges of the catalyst for use in the present invention, then, based on the teachings given herein, those skilled in the art will be able to determine said optimum catalyst. A selection must be made between the practical reaction rates and the cost of the catalyst. As indicated above, a reactor suitable for use in conjunction with the present invention should have a good agitation aspect. Agitation is an instrument that aids in the dissolution of oxygen, which is critical to the satisfactory practice of the invention. For example, it has been found that, when the concentration of loose oxygen is too low, an incomplete reaction occurs. Surprisingly, and by the cont.rapo, too high a concentration of dissolved oxygen is also detrimental to the process of the invention. Stated more specifically, it has been found that the optimum concentration of dissolved oxygen is on the approximate scale of 1-7 ppm. When operating the process of the invention having a dissolved oxygen concentration outside those limits, in the case of the continuous mode, the oxidation reaction is not completed and in the charging mode a longer time is required to complete the reaction. Thus, it is clear that, in order to guarantee that concentration of dissolved oxygen, according to the method of the invention, the interaction between the flow rate of oxygen and / or the oxygen-containing air and the agitation must be considered. An analysis of a typical waste stream, such as that obtained from the manufacture of N-phosphonomethylglycine, before the treatment according to one embodiment of the present invention, is as follows: Component% by weight 10 Water 99.1 Formic acid 0.4 Fopnaldehyde 0.6 EXAMPLES 1-3 15 The procedure described above, under a variety of reaction conditions, was carried out with various waste streams which had been obtained from the production of N-phosphonornetylglycine, generally in accordance with the process of the patent. No. 3,969,398. Each waste stream contained relative formaldehyde and acidic acid concentrations of approximately 6,000 ppm / 0.b% by weight and approximately 5,000 ppm / 0.4% by weight, respectively. The temperature of the The current, while in the reactor, varied from about 5p ° C to about (90 ° C.) The formaldehyde and the physical acid concentrations in the streams were recorded before and after each treatment. The test represents that they have been tabulated below.All the tests were carried out in a continuous way for up to 30 hours.The catalyst used in these tests was 1,659 g of Degasa F199XKYA / U, which has an analysis of 4.49% by weight of Pt, equivalent to 32 mg of Pt. The volume of the reactor was 120 g and the reactor pressure of 7.03 g / cm2. The reactor temperature was maintained at 90 ° C and the liquid feed rate was 6.0 g / mmuto. The oxygen feed rate was 100 cc / rpm and the speed of the agitator was 1,000 rprn. The data was collected every hour to ensure that sustained state conditions were maintained during the tests. An online FTIR was used to measure the concentrations of formaldehyde and formic acid during the course of each operation. Those skilled in the art can appreciate that this process can be carried out on a larger scale easily, for commercial use, without losing its advantages or its efficiency.

TABLE 1 Formal Duration dehi or Formal dehide, of the o-effluent, for concentration concentration final concentration in ppm. (my minutes) average. 1 . 1728 32 0 2. 1205 41 18 3. 821 51 0 The average concentration of formaldehyde in the effluent, as indicated in Table 1 above, was calculated by averaging all the formaldehyde concentration data compiled during the entire test operation. Based on the experimentation, it was observed that the concentrations of formic acid in the effluent were lower than the concentrations of formaldehyde. Thus, the concentrations of formic acid were not routinely analyzed. The above information is illustrative of the efficient manner in which the present invention can be operated continuously. However, the process of the invention can also be advantageously carried out under intermittent conditions. For example, in an autoclave reactor having a volume of t, r-ab of 120 nl, a suspension of 0.4% by weight of a catalyst of 5% by weight of Pt on carbon oxide 5,800 pprn of forrnaldeh do and 3,800 pprn of thermal acid in a solution, at oliegomenos levels, in the term of 35 minutes or less. The temperatures during the reactions varied from about 55 ° C to 90 ° C, and the pressure was 7.03 or 10.54 kg / cm * rnanomet rich. Oxygen flow regimes were 25 or 100 oc / minute. Surprisingly, the maximum regime differences were observed in relation to changes in oxygen flow rate, rather than changes in temperature or pressure. The in situ chemical conversion of formaldehyde to formic acid and formic acid, in turn, to carbon dioxide and water, as provided by the practice of the present invention, has proven to be a highly effective alternative in cost of disposal by biological treatment of formaldehyde and / or formic acid from residual aqueous streams. Due to the catalytic nature of the reaction, it has been demonstrated that a continuous mode procedure which requires a relatively short residence time of around 20 minutes is technically feasible for the substantial destruction of all formaldehyde and formic acid. , to form carbon dioxide and water, environmentally benign, in a suitable aqueous solution to recirculate it. The environmental compatibility of the product, which is the result of the practice of the present invention, in such a manner, has been demonstrated. Although the illustrative embodiments of the invention have been described in detail, it will be understood that various other modifications will be apparent to those skilled in the art, and that they can be easily made by them, without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited by the examples and description that have been given in the foregoing; but rather, that the claims be considered as covering all aspects of patentable novelty that reside in the present invention, including all aspects that could be treated as equivalents thereof by those skilled in the art to which the invention pertains.

Claims (14)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for destroying formic acid and formic acid, present in a liquid aqueous stream, converting formaldehyde to formic acid and converting formic acid to carbon dioxide and water; characterized in that method comprises the steps of: (a) contacting the liquid stream with a supported catalyst of a metal of group VIII, at a temperature in the scale ranging from room temperature to about 90 ° C, and a pressure in the scale that goes from atmospheric to around 14.06 kg / cm *; and (b) introducing air or molecular oxygen into the liquid stream to obtain and maintain the dissolved oxygen concentration in the range of about 1-7 ppm in the vicinity of said catalyst, in order to oxidize a desired amount of formaldehyde to acid. Formic and formic acid to carbon dioxide and water.

2. The method according to claim 1, further characterized in that the group VIII metal is selected from the group consisting of platinum, palladium and rhodium.

3. The method according to claim 1, further characterized in that the catalyst is heterogeneous platinum, loaded on a powder carbon support.

4. The method according to claim 2, further characterized in that the oxidation is carried out at a pressure ranging from atmospheric to about 10.54 kg / cm2, and where the current is heated to a temperature on the scale Approximately 50 ° C to 90 ° C during oxidation.

5. The method according to claim 1, further characterized in that the formaldehyde is converted to formic acid and the formic acid is converted to carbon dioxide and water, at atmospheric pressure and at a temperature in the approximate range of 50 ° C. at 90 ° C.

6. The method according to claim 1, further characterized in that it further comprises stirring the substance to achieve and maintain a level of dissolved oxygen within the range of about 1 pprn to 7 ppm, during oxidation.

7. The method according to claim 1, further characterized in that the metal of group VIII is platinum.

8. The method according to claim 3, further characterized in that the amount of platinum in the catalyst is in the approximate range of 0.1% by weight to 10% by weight.

9. The method according to claim 1, further characterized in that the pressure is atmospheric.

10. The method according to claim 1, further characterized because the temperature is the ambient temperature. Ll.

The method in accordance with the claim 9, further characterized because the temperature is the ambient temperature.

12. In a process for the manufacture of N-phosphonomethylninodiacetic acid, of the type that produces a residual aqueous acid stream containing organic waste consisting of formaldehyde, formic acid and other waste, the improvement characterized by comprising the following steps: (a) ) subjecting the waste to distillation to form a second stream including formaldehyde and formic acid; (b) contacting the second stream with a catalyst comprising a group VIII metal, supported on a catalyst support; and (c) introducing air or molecular oxygen into the second stream to obtain and maintain the dissolved oxygen concentration on the approximate scale of 1-7 pprn in the vicinity of the catalyst, in order to oxidize a desired amount of formaldehyde to formic acid and from formic acid to carbon dioxide and water.

13. The method according to claim 12, further characterized in that the metal is selected from the group consisting of platinum, palladium and rhodium. 14. The method according to claim 12, further characterized in that the metal of the catalyst is platinum, loaded on powdered carbon, in an amount of approximately 0.1% by weight to 10% by weight. 15.- The method according to the claim 12, further characterized in that the oxidation is carried out at a pressure ranging from atmospheric to about 14.06 kg / crn *, and where the second current is heated to a temperature between about 50 ° C and 90 ° C. 16. The method according to claim 12, further characterized in that the formaldehyde is converted to formic acid and the formic acid is converted to carbon dioxide and water at atmospheric pressure and at a temperature within the range of approximately 50 ° C. at 90 ° C. 17. The method according to claim 12, further characterized in that it comprises stirring the second stream to achieve and maintain a dissolved oxygen level within the range of approximately 1 ppm to 7 pprn. 18. The method according to claim 13, further characterized in that the metal in the supported catalyst is platinum; the platinum being supported on powdered carbon. 19. A method for treating an aqueous stream that contains formic acid and formic acid waste, associated with the manufacture of N-phosphonornetiigiicma, characterized in that it comprises the steps of: (a) contacting the stream with a catalyst comprising a group VIII metal, supported on a catalyst support; and (b) introducing air or molecular oxygen into the stream to reach- and maintain a dissolved oxygen concentration on the approximate scale of 1-7 ppm, in the vicinity of the catalyst, in order to oxidize a desired amount of formaldehyde to Formic acid and formic acid to carbon dioxide and water. 20. The method according to claim 19, further characterized in that the metal is selected from the group consisting of platinum, palladium and rhodium. 21. The method of compliance with the claim 19, further characterized in that the metal is platinum, charged on powdered charcoal in an amount of about 0.1% by weight to 10% by weight. 22. The method according to claim 19, further characterized in that the oxidation is carried out under a pressure ranging from atmospheric to about

14. 06 kg / crn *, and where the current is heated to a temperature between 50 ° C and 90 ° C. 23. The method according to claim 19, further characterized in that the formaldehyde is converted to formic acid and the formic acid is converted to carbon dioxide and water, at atmospheric pressure and at a temperature in the approximate range of 50 ° C. at 90 ° C. 24. The method according to claim 19, further characterized in that the oxidation is carried out at a pressure varying from atmospheric to about 14.06 kg / crn *. 25. The method according to claim 19, further characterized in that it comprises additionally stirring the current pair to achieve and maintain a dissolved oxygen level within the scale of about 1 pprn to 7 ppm.