MXPA99005131A - Procedure for the regeneration of liquid vinyl acetate cr - Google Patents

Abstract

Process for the regeneration of crude liquid vinyl acetate containing acetic acid and water, as well as ethyl acetate and possibly other smaller amounts of other impurities, by distillation, which is characterized in that it is fed to the distillation column, above the place of addition of the crude liquid vinyl acetate, from 0.1 to 5% by weight of water, in relation to the incorporated liquid liquid vinyl acetate, and from 0.1 to 60% by weight of acetic acid, in relation to the crude liquid vinyl acetate incorporated

Description

PROCEDURE FOR THE REGENERATION OF CRUDE LIQUID VINYL ACETATE DESCRIPTIVE MEMORY The present invention relates to a process for the regeneration of crude liquid vinyl acetate, which contains acetic acid and water, as well as ethyl acetate and, if necessary, further impurities. In the process for the production of vinyl acetate, a crude crude liquid vinyl acetate containing essentially still acetic acid and water, as well as ethyl acetate and possibly still other impurities, is often obtained. A product of such a nature can be obtained, for example in the production of vinyl acetate by the transformation of ethylene and acetic acid and oxygen in the gas phase, at elevated temperature and at normal or high pressure, in the presence of a catalyst, while the gases leaving the reactor are cooled and / or washed with acetic acid. Such a production of vinyl acetate is generally carried out with acetic acid supernatant, in which the untransformed acetic acid is fed back into the cycle in the production of vinyl acetate. DE-AS 1 768 412 discloses a regeneration of crude liquid vinyl acetate, practicable from such a production process, which still contains acetic acid and water, as well as ethyl acetate and possibly further impurities. In this process, the crude vinyl acetate is azeotropically distilled, the main mass of water is extracted together with vinyl acetate above the head, by replenishing the vinyl acetate obtainable by condensation and phase separation of the overhead product, and both vinyl acetate is fed back, that an acetic acid is obtained as a residual product, which contains approximately 0.5 to 6% by weight of water. Eventually, a side derivative can be extracted! liquid of this distillation, in which there is concentrated ethyl acetate. The vinyl acetate. obtainable after condensation and phase separation of the gaseous overhead product, it contains about 100 to 500 pprn by weight of ethyl acetate. DE-PS 1 282 014 and DE-PS 1 668 063 describe another known process for the regeneration of crude vinyl acetate. In this case, the water is distilled as an azeotropic mixture and the boiling by-products inferior to the vinyl acetate overhead in a first distillation column and the virtually anhydrous deposit is distilled in a second distillation column, whereby the extracts vinyl acetate at the head of the second distillation column, at least most of the boiling byproducts superior to vinyl acetate of one or more concentration zones between the head and the deposit and the acetic acid below the cloud more lower concentration or as deposit, and eventually the residue of the by-products. The vinyl acetate which originates in the first column after condensation and phase separation is in general fed back to the first column and vinyl acetate is extracted only from the head of the second column. According to the teaching of DE-PS-1 668 063, the same amount of water can be extracted at the head of the second column, raising the pressure in the first distillation column from the normal pressure to 1 atm effective, to approximately half in the amount of reflux. Details of the water content of the gaseous overhead product are not given; the content of the ethyl acetate in the separated vinyl acetate is about 1000 ppm. DE-OS 2 943 985 discloses a process for the separation of water from mixtures with vinyl acetate and acetic acid, in which a concentrate obtained by cooling the gas mixture leaving the zone is mentioned. reaction, which contains the main mass of acetic acid, vinyl acetate and water, of a solution obtained by absorption with acetic acid, which contains the remaining non-concentrated vinyl acetate and water, on different plates of rectification column to a distillation column. The overhead product can then contain about 3 to 5% by weight of water. It is not manifested in this DE-OS if the crude vinyl acetate contained in the vinyl acetate can be regenerated and what ethyl acetate contents are then present in the separated vinyl acetate. Finally, DE-AS 1 618 240 discloses a separation of acetate from vinyol acetate, in which an extractive distillation with water is carried out as a entraining agent. With a water weight ratio the crude organic feed, consisting of 99.8% by weight of vinyl acetate and 0.2% by weight of ethyl acetate, of 0.19: 1 and in a reflux ratio of about 3: 1 , a purified vinyl acetate derivative is extracted above the head, which contains less than 500 ppm by weight of ethyl acetate, in relation to the vinyl acetate. However, the incorporated vinyl acetate does not contain in this case any insignificant amount of water and / or acetic acid. In addition, by the patent of E.U.A. No. 3,404,177 is a process for the separation of vinyl acetate, water, acetic acid and optionally acetaldehyde from gaseous reactive mixtures. Such reactive mixtures contain in addition to ethylene, oxygen and CO2. Ethyl acetate is not mentioned and its separation in this writing; neither effects that are accompanied by a water supply or azeotropic formation. Finally, EP-B-0 072 484 mentions a process for the regeneration of crude liquid vinyl acetate containing acetic acid and water, as well as ethyl acetate and possibly other small amounts of impurities, by distillation, whereby obtained as a top product a mixture containing essentially vinyl acetate and water and as a deposit product essentially acetic acid and a side derivative is extracted, in which there is concentrated ethyl acetate, and with which the overhead product is condensed and after phase separation, part of the vinyl acetate phase is fed back as reflux to the distillation, which is characterized in that liquid vinyl acetate is fed to the distillation, below the addition site of the crude liquid vinyl acetate, from 0.1 to 5% by weight of water, in relation to the incorporated liquid liquid vinyl acetate. The known process leads to sufficient dehydration in the distillation and to a decrease in the ethyl acetate content in the vinyol acetate obtained as a top product. It is known from DE-OS-2 132 299 that mixtures containing liquid vinyl acetate and ethyl acetate can be subjected to an extractive distillation with acetic acid as the entraining agent. The above procedure leads to a decrease in the content of ethyl acetate in the vinyl acetate extracted in the column head to about 200 ppm by weight. According to the teachings of DE-OS-2 132 299, however, 60 g of acetic acid must be fed per 100 g of incorporated liquid liquid vinyl acetate. Surprisingly, it was discovered that the ethyl acetate content in the gases leaving the overhead distillation can be decreased and that the side derivative leaving the distillation can be raised, and that the extraction of vinyl acetate on this side derivative, when fed, to the distillation column above the place of addition of the crude liquid vinyl acetate, from 0.1 to 5% by weight of water, in relation to the incorporated crude liquid vinyl acetate, and from 0.1 to 60% by weight of acetic acid, in relation to the incorporated liquid liquid vinyl acetate. The object of the present invention relates in accordance with the foregoing to a process for the regeneration of crude liquid vinyl acetate containing acetic acid and water, as well as ethyl acetate and optionally other smaller amounts of other impurities, by means of distillation, whereby a mixture containing essentially vinyl acetate and water is obtained as a overhead product and with the residual product essentially acetic acid and a side derivative is extracted, in which there is concentrated ethyl acetate, and with which condensed in the overhead product and fed back after the phase separation a part of the vinyl acetate phase as reflux to the distillation column, characterized in that it is fed to the distillation column above the addition site of the acetate of raw liquid vinyl, from 0.1 to 5% by weight of water, in relation to the incorporated liquid liquid vinyl acetate, and from 0.1 to 60% by weight of acetic acid, in relation to crude liquid vinyl acetate incorporated. To be used in the process according to the invention, for example, crude liquid vinyl acetate containing approximately 12 to 30% vinyl acetate, approximately 3 to 10% by weight of water, approximately 0.01 to 0.2, is suitable. % by weight of ethyl acetate and, as complementary to 100% by weight, acetic acid. Other impurities, for example and acetates, polymers, acetamide and / or methyl acetate, may also be present, likewise small amounts, for example in each case in amounts of 0.5% by weight. Such impurities may have formed in the production of vinyl acetate or have already been introduced with the products incorporated in the production of vinyl acetate. A suitable liquid or crude vinyl acetate can be obtained in a different manner for its incorporation into the process according to the invention. For example, ethylene, oxygen or gases containing oxygen and acetic acid can be converted in a known manner in the gas phase, at elevated temperature and normal or high pressure, to noble metals and / or their compounds containing catalysts, and to cooling and / or washing the gases coming from this transformation, for example with acetic acid or washing liquid containing acetic acid, and incorporating the crude liquid vinyl acetate thus obtained to the process according to the invention. In Figure 1 a schematic representation of the regeneration of crude liquid vinyl acetate is reproduced. The crude liquid vinyl acetate is fed by incorporating (derivative 1) to a distillation column 10. Suitable distillation columns are for example those containing 50 to 1 10, preferably 55 to 105 rectification column plates and they operate at normal pressure or slightly elevated pressure, for example at 0.1 and up to 0.5 MPa absolute, preferably however at normal temperature. The addition of the crude liquid vinyol acetate can take place, for example, at the location in the intermediate region of the column 10, preferably between the middle and the lower third of the column 10. The column 10 is operated in such a way that a gaseous mixture containing essentially vinyl acetate and water and as a residual product (derivative 7) essentially acetic acid is obtained as the overhead product (derivative 2). In addition, a side derivative (derivative 6) is extracted, in which there is concentrated ethyl acetate. Preferably, the column 10 is operated in such a way that a water content of 0.5 to 6% by weight and a vinyl acetate content of 1 to 30 ppm by weight are adjusted in the acetic acid extracted in the tank (derivative 7). and the side derivative (derivative 6) extracted below the inflow of the incorporation mixture contains for example up to 15% by weight of ethyl acetate together with fluctuating amounts of vinyl acetate, acetic acid and water. This side derivative 6 can be extracted in liquid or gas form; it is preferably extracted in liquid form. The overhead product (derivative 2) is condensed and divided into a phase separator 1 1 in a saturated vinyl acetate phase of water and a lower saturated water phase of vinyl acetate, which is discharged as derivative 5. A phase separator of the usual construction type, for example a decanter can be used. After separation of the resulting phases, part of the saturated vinyl acetate phase of water is refilled as reflux to the distillation column 10. The portion of vinyl acetate saturated with water that is fed back can be regulated otherwise it is possible to adjust the desired water content in the tank of column 10, for example in the range of 0.5 to 6% by weight. For this, a reflux ratio (in relation to the vinyl acetate returned to the extracted one) in the range from 1: 1 to 8: 1 is generally advantageous. The saturated vinyl acetate is separated from unreturned water (derivative 4) and can still be further purified, if required. The residual product resulting from the distillation (derivative 7), which generally contains more than 90% by weight of acetic acid, can be returned to the process for the production of vinyol acetate, possibly after the removal of impurities, for example polymers. Water (derivative 8) is fed above the addition site of the crude liquid vinyl acetate. The source from which the water is fed through the derivative 8 is not critical. The added water may also contain up to 5% by weight of organic ingredients, relative to the total amount of the derivative 8. Such organic ingredients are for example vinyl acetate or ethyl acetate. The amounts of water, which are fed in this manner, are relatively small, generally from 0.1 to 5% by weight, preferably from 0.1 to 2% by weight, relative to the incorporated liquid crude vinyl acetate. The procedure described up to now, including the subsequent purification to be carried out optionally of the separated vinyl acetate and the resulting acetic acid in the tank, is known, for example, from DE-AS 1 768 412 and EP-B-0- 072 484. The measure to be taken in accordance with the present invention in the regeneration of crude liquid vinyl acetate consists then in introducing water (derivative 8), above the addition site of the crude liquid vinyl acetate, in an amount that is not greater than the amount that is required to reach a maximum water content of the gases leaving the distillation column 10 in the head (derivative 2) and in introducing, above the place of admission of the liquid vinyl acetate and crude, acetic acid (derivative 9) in an amount not greater than the amount required to reach the maximum content of acetic acid in the gases leaving the distillation column 10 in the head (derivative 2). The source from which acetic acid is fed through the derivative 9 is not critical. The acetic acid content of the derivative 9 is generally more than 80% by weight and preferably more than 90% by weight. Other ingredients of the derivative 9 are water and optionally small amounts of organic compounds, such as for example ethyl acetate. Small amounts of water, in general from 0.1 to 5 and preferably from 0.1 to 2% by weight, in relation to the incorporated liquid crude vinyl acetate, and acetic acid, in general from 0.1 to 60, preferably from 0.1 to 30 and especially preferred from 0.1 to 10% by weight, in relation to the incorporated crude liquid vinyl acetate, which is fed in this manner, allow the water content in the gases leaving the distillation in the head to be lowered (derivative 2). ) and thus result in sufficient dehydration in the distillation and cause a decrease in the vinyl acetate content of the separated vinyl acetate above the head of the distillation column 10. This operation also causes the content of vinyl acetate in the side derivative (derivative 6) extracted from below the addition site of the crude liquid vinyl acetate to be reduced. In this way more vinyl acetate is obtained above the head of the distillation column 10. Another advantage of the process according to the invention is that the content of ethyl acetate in the side derivative (derivative 6) is increased and thus vinyl acetate is obtained above the top of the column 10 in greater purity. The addition of water causes the water content to rise in the gas leaving the distillation of the head (derivative 2), which results in sufficient dehydration in the distillation. Water can be incorporated in this way up to such an amount until the water content of the gases leaving the distillation column 10 in the head (derivative 2) is at most 7.3% by weight. It is known that the azeotropic mixture of vinyl acetate and water can exhibit a maximum content of 7.3% by weight of water (see Advances in Chemistry, Series 1 16, Azeotropic Data III, American Chemical Society, Washington D.C., 1973). However, this value can not be obtained entirely in the practical realization of the method according to the invention. The water contents obtainable in the practical embodiment of the process according to the invention in gases leaving the distillation column 10 in the head (derivative 2) amount to approximately 6.8% by weight. Preferably, just as much water is added in a manner according to the invention that in the water content derivative 2 it amounts to 6.7 to 6.9% by weight. The addition of acetic acid causes a separation of ethyl acetate from vinyol acetate and water. This is indeed known from the prior art (DE-OS-2 132 299), but 60 g of acetic acid must be introduced per 100 grams of crude liquid vinyl acetate incorporated. The amounts of water and acetic acid to be introduced according to the invention are relatively small. They generally amount from 0.1 to 5% by weight of water, in relation to the incorporated liquid crude vinyl acetate, and in general from 0.1 to 60% by weight of acetic acid, in relation to the incorporated liquid liquid vinyl acetate. Preferably, the water content is from 0.1 to 10% by weight, based on the incorporated liquid crude vinyl acetate. The amount of acetic acid is preferably from 0.1 to 30% by weight and more preferably from 0.1 to 10% by weight, based on the incorporated liquid crude vinyl acetate. It can be determined, possibly by simple tests, what amounts of water and what amounts of acetic acid are necessary in the particular case, to achieve the highest possible water content and at the same time the lowest possible ethyl acetate content in the case the gases that leave the distillation of the head (derivative 2), as well as the highest possible content of ethyl acetate in the side derivative that leaves the distillation (derivative 6). These amounts depend for example on the amounts of water, acetic acid and vinyl acetate in the incorporated liquid liquid vinyl acetate. The amounts of acetic acid and water to be added according to the invention can be introduced, in liquid form or as steam to the distillation column 10. The addition of acetic acid and water takes place above the place of addition of crude liquid vinyl acetate. If acetic acid and water are fed below the inflow of the crude liquid vinyl acetate, then no satisfactory dehydration and no satisfactory decrease in the ethyl acetate content of the vinyl acetate separated from the overhead product of the distillation is observed in the distillation. . For the process according to the invention, it is therefore essential to carry out the introduction according to the invention of acetic acid and water above the addition of the crude liquid vinyl acetate, generally from 2 to 50 column plates of rectification, preferably from 10 to 35 plates of rectification column above the addition site of the crude liquid vinyl acetate. The acetic acid and the water can be introduced on the same rectification column plate, but both materials can be introduced on different rectification column plates. It can be determined, possibly by simple tests, that there are places of addition for the small amounts of acetic acid and water above the place of addition of the liquid liquid viniio acetate that are necessary in the particular case, to achieve the highest possible water content and, at the same time, the lowest possible ethyl acetate content in the gases leaving the distillation in the head (derivative 2), as well as at the same time an ethyl acetate content high possible in the lateral derivative that leaves the distillation (derivative 6). The process according to the invention has the following advantages: The separation between vinyl acetate and ethyl acetate is improved. This means that a vinyl acetate centered on the overhead product of the distillation (derivative 4), which contains up to about 40% less ethyl acetate than hitherto, can be obtained in the unaltered reflux of vinyl acetate. If the content of ethyl acetate in the vinyl acetate separated from the overhead product of the distillation is found in the order of magnitudes as hitherto, the process according to the invention then allows the carrying out of the distillation in a small flow of vinyl acetate and / or the incorporation of a liquid crude vinyl acetate with a higher content of ethyl acetate and / or the use of a shorter distillation column. - The amount of vinyl acetate is reduced by the lateral extraction of ethyl acetate (derivative 6). That means that up to 60% less vinyl acetate is expelled through lateral extraction in the same amount of ethyl acetate in this side extraction !. In this way, the loss of vinyl acetate is considerably reduced. It is particularly advantageous that the achievable improvements according to the invention are achieved without raising the cost for the distillation, for example in relation to the number of rectification column plates, the reflux amounts and the energy requirement. It is surprising that these two effects can be achieved, namely the decrease in the ethyl acetate content in the vinyl acetate resulting from the overhead product of the distillation (derivative 4) and the decrease in the vinyl acetate content in the ethyl acetate. ethyl outwardly expelled through the lateral extraction (derivative 6), by a simple action, namely the addition of water and acetic acid according to the invention. The following examples should explain the process according to the invention, but without limiting it.

EXAMPLES A schematic description of the examples given below should be seen in the figure.

EXAMPLE 1 (EXAMPLE OF COMPARISON) In the distillation column 10 with 98 rectification column plates, 62 t of a mixture of incorporation of the following compound on the 48th rectification column plate through the foot of the column (derivative 1) was delivered hourly. Vinyl acetate 25.00% by weight Ethyl acetate 0.07% by weight Water 7.00% by weight Acetic acid 67.50% by weight Other 0.43% by weight The incorporation mixture contained methyl acetate, acetaldehyde and other impurities, for example diacetates and polymers, in each case in amounts of less than 1000 ppm by weight. The overhead product was condensed (derivative 2), cooled to 26 ° C and a phase separator 11 was conducted.

From the vinyl acetate phase, 33.5 t / h were pumped as reflux on the top of the distillation column (derivative 3) in such a way that the remainder was extracted (derivative 4). The composition of the separated vinyl acetate (derivative 4) was as follows: Ethyl acetate 270 ppm by weight Water 1.20% by weight Vinyl acetate complementary to 100% by weight An aqueous phase (derivative 8) was pumped with an amount 0.7 th over the 69 ° rectification column plate through the foot of the column. The composition of the aqueous phase (derivative 8) was as follows: Water 98.0% by weight Vinyl acetate 2.0% by weight The amount of water extracted from the phase separator 1 1 (derivative 5) was 2.2 t / h. The composition of this water phase was as follows: Water 98.0% by weight Vinyl acetate 2.0% by weight From the 17th rectification column plate, a liquid side derivative (derivative 6) was extracted above the base of column 10 in an amount of 3.6 t / h with the composition: Vinyl acetate 2.0% by weight Ethyl acetate 1.0% by weight Water 10.0% by weight Acetic acid 87.0% by weight It was pumped on the 1st plate of the rectification column, above the column foot, a liquid derivative consisting essentially of acetic acid (derivative 9), in an amount of 3.5 t / h. The composition of this acetic acid derivative was as follows: Water 10.1% by weight Acetic acid 89.9% by weight EXAMPLE 2 The distillation column 10 described in Example 1 was treated under the same conditions as Example 1. Contrary to Example 1, the acetic acid derivative (derivative 9) was conducted with an amount of 3.5 t / h over 69 °. Rectification column plate through column foot. The composition of the separated vinyl acetate (derivative 4) was as follows: Ethyl acetate 200 ppm by weight Water 1.20% by weight Vinyl acetate complementary to 100% by weight Of the 17 ° rectifier column plate was extracted above of the foot of the column 10 a liquid side derivative (derivative 6) in an amount of 3.6 t / h with the composition: Vinyl acetate 1.00% by weight Ethyl acetate 1.00% by weight Water 10.00% by weight Acetic acid 88.00% by weight As is evident from example 2, the addition of water and acetic acid according to the invention leads to a decrease in the content of the ethyl acetate in the vinyl acetate resulting from the overhead product of the distillation (derivative 4) and a decrease in the vinyl acetate content of the ethyl acetate expelled outwards by the operated extraction (derivative 6).

Claims (10)

NOVELTY OF THE INVENTION CLAIMS

1. - Process for the regeneration of crude liquid vinyl acetate which contains acetic acid and water, as well as ethyl acetate and possibly other smaller amounts of other impurities, by distillation, with which a mixture containing a mixture is obtained as a overhead product. essentially vinyl acetate and water and as residual product essentially acetic acid that a side derivative is extracted, in which there is concentrated ethyl acetate, and whereby the overhead product is condensed and after phase separation a part is fed back of the vinyl acetate phase as reflux to the distillation column, further characterized in that 0.1 to 5% by weight of water is fed to the distillation column above the addition site of the crude liquid vinyl acetate. in relation to the incorporated liquid liquid vinyl acetate, and from 0.1 to 60% by weight of acetic acid, in relation to the liquid raw vinyl acetate inco rporado. 2. Method according to claim 1, further characterized in that a crude liquid vinyl acetate containing from 12 to 30% by weight of vinyl acetate, from 3 to 10% by weight of water, is regenerated from 0.01 to 0.

2. % by weight of ethyl acetate and the complementary to 100% by weight of acetic acid.

3. - Process according to claims 1 and 2, further characterized in that the crude liquid vinyl acetate additionally contains diacetates, polymers, acetaldehyde and / or methyl acetate, in each case in amounts less than 0.5% by weight.

4. Method according to claims 1 to 3, further characterized in that so much water is fed that the water content is in the gases left in the distillation column in the head, in the range of 6.7 to 7.3% in weigh.

5. Method according to claims 1 to 4, further characterized in that water is fed in liquid form.

6. Method according to claims 1 to 4, further characterized in that water is fed in the form of steam.

7. Process according to claims 1 to 6, further characterized in that water is fed to 2 and up to 50 rectification column plates above the addition site of the crude liquid vinyl acetate.

8. Method according to claims 1 to 7, further characterized in that water is fed to 10 and up to 35 rectification column plates above the addition site of the crude liquid vinyl acetate.

9. Process according to claims 1 to 8, further characterized in that 0.1 to 30% by weight of acetic acid is fed to the distillation column, above the addition point of the crude liquid vinyl acetate, in relation to with the liquid liquid vinyl acetate incorporated.

10. - Process according to claims 1 to 9, further characterized in that 0.1 to 10% by weight of acetic acid is fed to the distillation column, above the admission point of the crude liquid vinyl acetate, in relation to the Crude liquid vinyl acetate incorporated. 1. Method according to claims 1 to 10, further characterized in that acetic acid is fed in liquid form. 12. Method according to claims 1 to 10, further characterized in that acetic acid is fed in vapor form. 13. Method according to claims 1 to 12, further characterized in that water is fed to 2 and up to 50 rectification column plates above the addition site of the crude liquid vinyl acetate. 14. Method according to claims 1 to 13, further characterized in that acetic acid is fed to 10 and up to 35 rectification column plates above the addition site of the crude liquid vinyl acetate. 15. Method according to claims 1 to 14, further characterized in that acetic acid and water are fed over the equivalent of the 2 to 50 rectification column plates above the addition site of the crude liquid vinyl acetate. 16. Method according to claims 1 to 15, further characterized in that acetic acid and water are fed over the equivalent of the 10 to 35 rectification column plates above the addition site of the crude liquid vinyl acetate.