MXPA98010163A - Recovery of molibd epoxidation catalyst - Google Patents

Abstract

An aqueous stream of epoxidation process containing molybdenum and sodium values is treated for the removal of organics through incineration and an aqueous solution containing molybdenum and sodium is recovered, cooled, acidified and contacted with activated carbon and a reduced aqueous stream in molybdenum is recovered, furthermore the reduction of molybdenum can be achieved through the treatment with a basic ion exchange resin.

Description

RECOVERY OF MOLYBDENUM EPOXIDATION CATALYST BACKGROUND OF THE INVENTION Field of the Invention The production of oxirane compounds such as propylene oxide through the catalytic reaction of an olefin with an organic hydroperoxide is a process of great commercial importance. Generally, a homogeneous molybdenum catalyst is employed. The oxirane process for the co-production of ethylene oxide and styrene monomer is illustrative of this technology.

The process of this invention relates to the recovery of molybdenum epoxidation catalyst values from process streams in said epoxidation process technology.

Description of the Related Art An extremely useful process for the coproduction of propylene oxide and styrene monomer involves the oxidation of molecular oxygen from ethylbenzene to form ethyl hydroperoxide of I-benzene, the catalytic reaction of the hydroperoxide with propylene to form propylene oxide and 1-phenyl-ethanol, and dehydration of 1-phenyl ethanol to the styrene monomer. The basic patent that describes this process is the patent of E.U.A. 3,351,635.

During the practice of the process, the epoxidation reaction mixture usually after removal of the unreacted propylene through distillation, is treated with aqueous caustic soda in an amount in excess of that necessary both to react with molybdenum values contained to form sodium molybdate to react with organic impurities such as acids and phenols, which are also contained in the epoxidate. See patents of E.U.A. 4,405,572, 5,210,354, 5,276,235 and 5,171,868, for example. A problem that has existed in said prior practices has been the formation of relatively large amounts of an aqueous process stream containing molybdenum, sodium and organics, and the disposal of said aqueous process streams. The presence of molybdenum is particularly problematic since this material must be removed before discharge to meet environmental restrictions. The patent of E.U.A. 5,439,657 and EP-A-0757046 relate to said molybdenum-containing streams and to the separation of molybdenum therefrom. EP-A-0 518,499 discloses a process wherein an epoxidation reaction product formed by the reaction catalyzed with propylene molybdenum with tertiary butyl hydroperoxide to provide propylene oxide and tertiary butyl alcohol is removed through distillation. The dissolved molybdenum content of the heavy distillation fraction is adjusted from about 300 to 500 ppm of dissolved molybdenum, if necessary, by treatment with a precipitating agent and contacting a solid adsorbent consisting essentially of a silicate. of amorphous magnesium with a high surface area, porous, synthetic. Despite substantial previous work, there is still an aspect to improve the treatment of process streams, and especially in the removal of molybdenum, in terms of enormously severe environmental considerations. According to the present invention, a process is provided to reduce the level of molybdenum in an epoxidation process stream containing molybdenum and sodium, obtained through the epoxidation of propylene to propylene oxide through the reaction with hydroperoxide organic using a molybdenum epoxidation catalyst characterized in that it comprises acidifying the process stream, contacting the acidified stream with solid activated carbon and recovering an aqueous stream with a low molybdenum content. In one embodiment, the aqueous epoxidation process stream containing molybdenum and sodium as well as organic values is treated through incineration, first to separate the organics prior to the carbon bed treatment. During the incineration process, the particulate ash composed of molybdenum and sodium values, passes down through the incinerator with the incinerator gases. The gases containing ash are extinguished by mixing with water to form the downward blowing stream of the incinerator. The downward blowing is an aqueous solution of the molybdenum value, as well as sodium molybdate, a sodium value, as well as sodium carbonates, of the epoxidation process stream. The down-blown solution can not be directly discharged due to environmental hazards associated with the molybdenum heavy metal contained therein. According to this embodiment of the present invention, the downwardly flowing aqueous stream substantially free of organic, preferably after being cooled, is acidified, as with H2SO4, so that the carbonates are converted to C02, which can be easily removed. Then, the essentially carbonate free stream is contacted with a solid activated carbon adsorbent to separate the molybdenum values contained therein. The resultant aqueous solution greatly reduced in contained molybdenum, can then be conveniently discarded or, if the maximum molybdenum specifications are very severe, the aqueous effluent of the carbon treatment is further treated by contacting a basic ion exchange resin to effect the removal of substantially complete molybdenum. Instead of incineration, other known methods such as wet air oxidation or biotreatment can be used to remove the organic materials before the carbon treatment. In such cases, acidification is not necessary as described above to separate CO2. However, incineration represents the preferred method for separating organic materials. The invention will now be described in greater detail with reference to a preferred embodiment and with the aid of the accompanying drawing, which schematically illustrates the practice of the invention. In accordance with the preferred practice of the present invention, an aqueous epoxidation stream containing molybdenum catalyst values, sodium values from the caustic soda treatment and organic materials, is incinerated according to known procedures. An essentially complete combustion of the organic materials is achieved. The values of molybdenum and sodium, mainly as sodium molybdate and sodium carbonate, are recovered as a descending blowing stream from an aqueous incinerator. The downward blowing stream containing molybdenum and sodium is cooled and then acidified to a pH of 5 or less through the addition of sulfuric acid or HCl, and with appropriate agitation the carbonates are converted to CO2, which is vaporized and separated . Sodium is converted to the sodium salt of the added acid. Temperatures of 10 ° C to 50 ° C can be used to obtain CO2 removal, while minimizing corrosion and special construction materials.

The acidified downward blowing solution after the removal of C02, or the stream containing equivalent aqueous acid molybdenum, when using organic material removal procedures, is then brought into contact with solid activated carbon so that the greater prevalence of Molybdenum values in the aqueous stream is adsorbed on the carbon and in this way effectively removed from the aqueous stream. One or more carbon beds are employed, which can be discarded or regenerated through an aqueous caustic soda wash when the molybdenum removal capacity has been reduced to a certain level. The above process is effective to reduce the level of molybdenum contained in the aqueous process stream of more than 1000 ppm by weight to about 50 ppm or less. When lower levels of molybdenum are required in plant flow streams, in particularly preferred practice, the aqueous stream after the carbon treatment is further contacted with a basic ion exchange resin or chelator to obtain essentially complete molybdenum separation; that is, to produce an aqueous stream having less than about 10 ppm molybdenum. Activated carbons or useful vegetable carbons include those obtained from lignite, gas black, coconut, bagasse, wood, sawdust, peat, pulp milling waste, blood, bone, etc. Specific activated carbons include granulated carbons from Calgon Corporation such as Calgon F-400, F-200 or granulated activated reactive AW, NORIT carbons such as NORIT C, Cenco activated carbons products from Central Scientific Company, Nuchar activated carbons, West products Virginia Pulp and Paper Company, and products from Darco Division, ICI AMERICAS, Inc. Rohm and Haas Ambersorb carbonaceous adsorbents such as X-340 and the like, can be employed as activated Amberlite from Rohm and Haas. Illustrative commercially available carbons include granular carbon of the CAL type (Calgon Corporation) and granulated activated carbon NORIT ROW 0.8 (NORIT Corporation). Ion exchange resins that can be employed in the practice of the invention are basic anion exchange resins, which are well known articles of commerce. Both strong base resins and weak base resins can be used. The strong base resins can be produced through the reaction between a copolymer of chloromethylated DVB styrene and a tertiary amine such as trimethylamine, which results in a resin with quaternary ammonium groups. The major types of weak base anion exchanges are styrene-DVB copolymer amine derivatives, epichlorohydrin-amine condensation products, and amine derivatives of phenol-formaldehyde products, and may contain primary, secondary or tertiary amine groups , or mixtures of some or all of these groups. The weak base styrene-DVB resins can be made, for example, through the amination of the almost identical chloromethylated copolymer as the weak base styrene-DVB resins can be made, except that primary or secondary amines are generally used instead of a tertiary amine. The U.S. Patents, which describe the preparation of basic anion resins useful in the present invention, include: 4,025,467, 3,791,996, 3,817,878, 3,346,516, 4,082,701, 3,843,566, 3,813,353, 3,812,061, 3,882,053, 3,793,273, 3,296,233, 3,108,922, 3,005,786, 3,637,535 and 4,052,343. For a further description of the above-described preferred practice of the invention, reference is made to the accompanying drawing, Figure 1. Referring to Figure 1, a downward blowing of aqueous incinerator is introduced into cooling zone 1 through the line 2. In zone 1, the temperature of the aqueous stream is reduced by approximately 90 ° C through conventional thermal exchange processes at 40 ° C or less. The cooled stream passes through line 3 to zone 4, where it is acidified from a pH of about 9.5 to a low pH, ie 5 or less, preferably 1-3, through the addition of sulfuric acid via line 5. Other acids such as hydrochloric acid can be used. Through this acidification, carbonate values in the aqueous stream are converted to carbon dioxide, which is normally gaseous and which is removed as steam through line 6. A separation gas such as nitrogen can be introduced. (not shown) in zone 4 to assist in the removal of CO2. The substantially carbon-free solution is passed through line 7 from zone 4 to make contact with the solid activated carbon beds in zones 8 and 9. Although the carbon contact is shown as occurring in the two zones, it will be understood that a greater or lesser number of contact zones can be conveniently employed. As a result of the treatment described above, the contained molybdenum content can be reduced from 1000 ppm to 50 ppm or less in the stream leaving the carbon treatment zone 9. It should be noted that the previous acidification to bring the bed into contact Carbon is essential. When the aqueous stream has not been acidified, the contact of the carbon bed is not effective for the removal of molybdenum. As indicated, the carbon bed contact is effective to remove the large preponderance of molybdenum values, for example, to 50 ppm molybdenum or less. However, in certain more severe areas, reduction requirements in molybdenum content of 10 ppm or less are requested. When even lower molybdenum contents are important, in an especially preferred practice of the invention, after acidification and carbon bed treatment as described above, the aqueous stream passes from zone 9 through line 10 to the contact zone 11, wherein the aqueous stream is contacted with a basic ion exchange resin, which effectively removes the additional molybdenum, so that the aqueous stream leaving the zone 11 through the line 12 it has a molybdenum content of less than 10 ppm, preferably less than 5 ppm. Conveniently, as shown, the pH of the treated aqueous stream is adjusted to 6-8 in zone 13 through the addition of caustic soda via line 14 before total discharge through line 15. In a practice especially preferred, a plurality of beds of both carbon and ion exchange resin is employed. The ion exchange resin beds are conveniently regenerated through an aqueous caustic wash in an especially preferred practice, the molybdenum-containing wash liquid removed from the resin bed is sent back to zone 4 with the molybdenum finally being removed through the adsorption of activated carbon. As illustrated, during the regeneration cycle, the aqueous caustic soda introduced into zone 11 through line 16 and the aqueous regeneration stream containing the molybdenum removed passes through line 17 from zone 11 back to the zone 4 Carbon beds, which have missed the ability to effectively adsorb molybdenum values, are water washed and discarded through drying and used as land or fuel filler.

EXAMPLE The following example illustrates the invention with reference to Figure 1. The aqueous descending process stream of the propylene oxide / styrene monomer process after organic incineration is introduced at a rate of 10,896 kg / hour through the process. line 2 to the cooling zone 1. The downward blowing stream is composed by weight of 86% water, 0.2% sodium molybdate, 14% carbonate and sodium bicarbonate, and 0.01% organic materials. In zone 1, the temperature of the aqueous stream is reduced from 90 ° C to 40 ° C. The cooled stream passes through line 3 to the acidification zone 4, where the pH is reduced from 9.5 to 3 through the addition of 1225.8 kg / hr of 94% sulfuric acid. Carbon dioxide, which is generated through the reaction of carbonate salts with sulfuric acid, is removed as steam through line 6 at a rate of 726.4 kg / hr. The acidified aqueous stream is passed through line 7 and makes contact in zones 8 and 9 with the activated carbon beds. The carbon, which is used, is Calgon F-400, F-200 or React AW, or equivalent. The space velocity per liquid hour is 2-10 times the bed volume per hour and the treated aqueous stream removed from the carbon bed treatment through line 10 has a molybdenum content of 30 ppm or less. The aqueous stream passes at a rate of 11413.56 kg / hr through line 10 to zone 11, where it is contacted at 30 ° C with the weakly basic solid ion exchange resin Rohm & Haas 392 S, in order to reduce the molybdenum content to a present. Other similar resins such as Amberlyst A-21, or NTEC Solutions Inc., Advanced Affinity Chromatographic Resins (AAC), can be used. For best results, the resin must be conditioned to the sulfate form. The space velocity per liquid hour is 4 beds of volumes per hour (2-12 are generally preferred) and the aqueous stream leaving the zone 11 through line 12 has a molybdenum content of less than 5 ppm. The treated aqueous stream passes through line 12 to zone 13, where the pH is adjusted to 6-8 through the addition of aqueous caustic soda through line 14. The resulting aqueous stream is conveniently discarded to through line 15 to the plant discharge, being of a quality that satisfies the most severe requirements. After an ion exchange bed has been expelled as its ability to remove molybdenum values, the bed is regenerated through contact with aqueous caustic soda introduced through line 16 with the stream containing molybdenum removed by passing through line 1 7 to zone 4.

Claims (6)

1. - A process to reduce the level of molybdenum in an epoxidation process aqueous stream containing molybdenum and sodium obtained through the epoxidation of propylene to propylene oxide through the reaction with organic hydroperoxide using a molybdenum epoxidation catalyst, characterized in that it comprises acidifying the process stream, contacting the acidified stream with solid activated carbon and recovering a reduced aqueous stream in molybdenum.

2. A process according to claim 1, characterized in that it comprises incinerating an aqueous epoxidation process stream containing molybdenum, sodium and organic materials, separating an aqueous stream containing the molybdenum and sodium values from the incineration, acidifying the separated aqueous stream, separating the CO2 formed during the acidification, contacting the remaining solution with the solid activated carbon and recovering an aqueous stream with a low molybdenum content.

3. A process according to claim 1 or claim 2, wherein said separated aqueous stream is acidified to a pH below 5.

4. A process according to claim 1, claim 2 or claim 3, wherein said separated aqueous stream is acidified with H2SO.

5. - A process according to claim 1, claim 2 or claim 3, wherein said separate stream is acidified with HCl.

6. A process according to any of the preceding claims, wherein the recovered aqueous stream with a reduced content of molybdenum is brought into contact with a basic ion exchange resin and in addition an aqueous stream with a reduced content of molybdenum.