Method of controlling process of removing reduced permanganate compounds when using methanol carbonylation technology

FIELD: chemistry.

SUBSTANCE: first version of the method involves the following steps: distillation of a mixture which contains methyl iodide and acetaldehyde in a distillation apparatus in order to obtain an overhead fraction and a residue, measuring density of the said overhead fraction, determination of relative concentration of methyl iodide, acetaldehyde or both in the overhead fraction based on the measured density and regulation of at least one process variable, associated with the said distillation apparatus. As a response reaction to the said measured density or relative concentration calculated from the measured density, the said process variable is selected from heating intensity, column pressure, the composition fed, condensate composition and coefficient of flow reversal.

EFFECT: effective reduction of amount and removal of acetaldehyde and methyl iodide from a carbonylation system.

6 cl, 5 dwg

Description of the prior art

Ablest technology to which the invention relates

The present invention relates to an improved method of removing permanganate, restored compounds and iodide Akilov formed at carbonyliron methanol in the presence of a carbonylation catalysts based on metals of group VIII. More specifically, the present invention relates to an improved method of reducing and/or removing predecessors permanganate, restored compounds and iodide Akilov of interim flows during the formation of acetic acid by using this technology carbonylation.

2. Prior art

Among the currently used methods of obtaining acetic acid, one of the most commercially successful is catalyzed carbonylation of methanol with carbon monoxide, as disclosed in U.S. patent No. 3769329 issued Paulik et al. October 30, 1973, the carbonylation Catalyst contains rhodium, or dissolved or otherwise dispersed in a liquid reaction medium or deposited on an inert solid, together with the halogen-containing promoter and a catalyst, such as described in example methyl iodide. Rhodium can be introduced into the reaction system in any of the numerous who's forms, and the exact nature of the rhodium component in the active catalytic complex is uncertain. Thus, the nature of the halide promoter is not critical. The patentees disclose a very large number of suitable promoters, most of which are organic iodides. The most typical and effective reaction is carried out with continuous bubbling fluidised bed gas of carbon monoxide through the liquid reaction medium in which is dissolved catalyst.

In the prior art improved method for the carbonylation of an alcohol to obtain carboxylic acid having one carbon atom more than the alcohol, in the presence of a rhodium catalyst, are disclosed in U.S. patent No. 5001259 (issued March 19, 1991), 5026908 (issued June 25, 1991) and 5144068 (issued September 1, 1992) and European patent # EP 0161874 B2, published July 1, 1992, As disclosed in the above patents, acetic acid is produced from methanol in a reaction medium containing acetate, methyl halide, especially methyl iodide and rhodium, present with a catalytically effective concentration. These patent owners revealed that the catalytic stability and performance of the carbonylation reactor can be maintained at surprisingly high levels, even at very low is oncentrated water, ie 4 wt.% or less in the reaction medium (despite the common industry practice of maintaining approximately 14 wt.% or 15 wt.% water), maintaining in the reaction medium, along with a catalytically effective amount of rhodium, at least, a limited concentration of water, methyl acetate and methyl iodide, given the concentration of iodide ion in addition to the content of iodide, which is present in the form of methyl iodide or other organic iodide. The iodide ion is present as a simple salt, and lithium iodide is preferred. In the patents found that the concentration of acetate and iodide salts are essential parameters influencing the rate of carbonylation of methanol upon receipt of acetic acid, especially at low concentrations of water in the reactor. Using relatively high concentrations of acetate and iodide salts, received a surprising degree of catalytic stability and performance of the reactor, even when the liquid reaction medium contains water with concentrations reduced to about 0.1 wt.%, so small that it can roughly be defined simply as a "very small concentration" of water. Additionally, the reaction medium improves the stability of the rhodium catalyst, i.e. its resistance to deposition catalysis is the Torah, especially during the stages of extraction of the product in the process. At these stages distillation is aimed at the extraction of acetic acid with the ability to remove ligands of carbon monoxide from the catalyst, which in the environment is supported in the reactor, are ligands having a stabilizing effect on the rhodium. U.S. patent No. 5001259, 5026908 and 5144068 included in this description by reference.

It is established that, although the method of carbonylation with low water content in the production of acetic acid leads to the reduction of such by-products as carbon dioxide, hydrogen and propionic acid, the amount of other impurities usually present in trace quantities, will also increase, and as acetic acid, sometimes worse, when attempts are made to increase the speed of its production by the improvement of catalysts or by modification of reaction conditions.

These trace amounts of impurities affect the quality of acetic acid, especially when recycle impurities in the reaction. Impurities, which reduce the time permanganate acetic acid, include carbonyl compounds, unsaturated carbonyl compounds. As used herein, the term "carbonyl" is intended to denote compounds which contain aldehyde or ketone functional group, such compounds can be saturated or unsaturated. SeeCatalysis of organic reactions(Catalysis of Organic Reactions) 75,369-380 (1998) for further discussion of the role of impurities in the system by reaction of the carbonyl.

The present invention is directed to the reduction and/or removal of permanganate, restored compounds (PRC's), as, for example, acetaldehyde, acetone, methyl ethyl ketone, Butyraldehyde, CROTONALDEHYDE, 2-tilkroliarord and 2-ethylbutyraldehyde and the like, and products of aldol condensation. The present invention also leads to reduction of propionic acid.

Carbonyl impurities described above, such as acetaldehyde, may interact with iodine catalytic promoters with the formation of poly-carbon iodide Akilov, for example, ethyl iodide, butyl iodide, iodine hexyl and the like. It is desirable to remove iodine alkali from the reaction product, because even small amounts of these impurities in the product acetic acid tend to poisoning of the catalyst used in the production of vinyl acetate - product, most often derived from acetic acid. The present invention thus also aimed at removing iodide Akilov, in particular iodine compounds Akilov_2-12. Accordingly, because a lot of p is imesa is formed with acetaldehyde, the first task is to remove or reduce the content of acetaldehyde and alkyl iodide in the proposed technology.

Conventional methods for removing impurities include processing of the product acetic acid oxidants, ozone, water, methanol, activated carbon, amines and the like, while such processing may be combined with the distillation of acetic acid or not. The most typical treatment includes a series of distillations of the final product. It is also known, for example, from U.S. patent No. 5783731, removing carbonyl impurities from organic streams by processing organic threads amine compound, as hydroxylamine, which interacts with the carbonyl compounds with the formation of Asimov, followed by distillation to separate the purified organic product from the reaction products of education Asimov. However, additional processing of the final product increases the cost of the technological process, and distillation of the treated product acetic acid can result in the formation of additional impurities.

Although you may receive acetic acid of relatively high purity, the product acetic acid, obtained by carbonyliron with low content of water and the above-described processing to clean it often is stetsa to some extent imperfect with respect to time permanganate due to the presence of a small fraction of residual impurities. Because sufficient time permanganate is an important industrial criterion acid product must meet in order to be suitable for many applications, the presence of impurities, which reduce the time permanganate, is undesirable. In addition, it is not economically or commercially viable removal of minor amounts of such impurities from acetic acid by distillation, since some of the impurities have a boiling point close to the boiling point of the commodity acetic acid.

Thus, it becomes important to define cost-effective ways to remove impurities somewhere in another place in the process of carbonylation without contamination of the final product or increase unnecessary costs. In U.S. patent No. 5756836 included in this description by reference, disclosed a method of obtaining acetic acid with a high purity by the regulation of the concentration of acetaldehyde reaction solution below 1500 ppm. Stated that, by maintaining the concentration of acetaldehyde below the specified threshold, it is possible to suppress formation of impurities so that you only need one distilling the crude product acetic acid to obtain high-purity acetic acid.

In European patent number EP 0487284 B1, published on 12 April the 1995, reveals that the carbonyl impurities which are present in the product acetic acid, are concentrated in the upper pursuit of columns of light fractions. Accordingly, the upper wrap columns of light fractions treated with amine compound (such as hydroxylamine), which interacts with carbonyl compounds, forming derivative Akimov, which can be separated from the remaining top product distillation, resulting in a product of acetic acid with improved time permanganate.

In the application for the grant of the European patent # EP 0687662 A2 and U.S. patent No. 5625095 describes how to obtain acetic acid of high purity in which the concentration of acetaldehyde 400 ppm or less support in the reactor, using one - or multistage distillation for removal of acetaldehyde. The streams proposed for processing for the removal of acetaldehyde include a light phase containing primarily water, acetic acid and methyl acetate; heavy phase containing primarily methyl iodide, methyl acetate and acetic acid; flow of the upper ring-containing, primarily, methyl iodide and methyl acetate; or a recycle stream that is formed by combining light and heavy phases. In the above links did not report any of these threads has the highest end is Tracia acetaldehyde.

In the patent EP 0687662 A2 and U.S. patent No. 5625095 also reveals the management conditions of the reaction to control the formation of acetaldehyde in the reactor. Although it is stated that the formation of such by-products as CROTONALDEHYDE, 2-tilkroliarord and iodide Akilov decreased in the control for the formation of acetaldehyde, also indicated that the management conditions of the reaction increases the formation of propionic acid is an undesirable by-product.

Recently, it was disclosed in a public U.S. patent No. 6143930 and 6339171 that may significantly reduce the undesirable impurities in the product acetic acid multistage cleaning the top of a shoulder strap of the column of light fractions. In these patents disclose a method of cleaning in which the upper shoulder strap light fractions distil twice, in each case removing acetaldehyde top of a shoulder strap and returning the residue enriched in iodine stands in the reactor. The acetaldehyde-rich distillate is extracted with water to remove most of acetaldehyde to reset, leaving a much lower concentration of acetaldehyde in the raffinate, which recycle to the reactor. U.S. patent No. 6143930 and 6339171 included in this description by reference in full.

While the above methods have been successfully removed in the carbonyl impurities from the system carbonylation and mainly in the control of causing the difficulty levels of acetaldehyde and time permanganate in the final product acetic acid, further improvements can still be made. Accordingly, there remains a need for alternative solutions for this problem with the aim of improving productivity and cost effectiveness for removing acetaldehyde. The present invention provides one such alternative solution.

The invention

In one aspect, the present invention, a method of separating acetaldehyde from methyl iodide using distillation. The method includes the stage of distillatory mixtures containing methyl iodide and acetaldehyde in the distillation apparatus to obtain the upper shoulder straps and sediment; measuring the density of the upper ring; and control at least one variable process associated with the specified distillation apparatus in response to the measured density or calculated from it the relative concentration where variable process selected from the intensity of heat, pressure column, the feed composition, the composition of phlegmy and turnover of the stream.

In another aspect, the present invention developed a way of separating ACET is legido from methyl iodide. The method includes the stage of distillatory mixtures containing methyl iodide and acetaldehyde in the distillation apparatus to obtain the upper shoulder straps and sediment; the extraction of the upper shoulder strap with water to obtain an aqueous extract and a raffinate; density measurement, at least one of the following: top of shoulder strap, extract and raffinate; and control at least one variable process associated with the distillation apparatus or stage of extraction in response to the measured density or calculated from it relative concentration. Variable process selected from the group consisting of heating intensity of the column, the pressure of the column, the composition of the feedstock, the composition of phlegmy and coefficient of circulation flow in the distillation apparatus, and the speed of the water in the extractor.

In another aspect, the present invention provides a method for obtaining acetic acid. The method includes the following stages: the interaction of methanol with carbon monoxide in a reaction medium containing water and methyl iodide in the presence of a catalyst; the reaction medium in the vapor phase containing acetic acid, methyl iodide, acetaldehyde and water, and in the liquid phase; distilling the vapor phase to obtain pure product acetic sour is s and first upper shoulder strap, containing methyl iodide and acetaldehyde; condensation of the first upper shoulder strap and extraction with water to obtain an aqueous extract and a raffinate containing methyl iodide; the density measurement, at least one of the following: top of shoulder strap, extract and raffinate; and regulating at least one regulatory process parameter associated with distillation or extraction of the second upper shoulder strap, on the basis of the measured density or relative concentration of acetaldehyde or methyl iodide, calculated on the basis of these data.

Brief description of drawings

Figure 1 illustrates the method of the prior art, which is disclosed in U.S. patent No. 6339171 to remove carbonyl impurities from the intermediate stream in the course of the carbonylation process upon receipt of acetic acid via carbonylation reaction.

In figures 2-4 are illustrated preferred embodiments of the present invention, in which the densitometer is placed in the stream having the same composition as that of the upper shoulder strap from the second distillation columns.

Figure 5 illustrates the correlation between the measured flux density of the upper ring 54 and the corresponding concentrations of acetaldehyde and methyl iodide in the same thread.

Although the invention d is putting forth various modifications and alternative forms, specific embodiments of shown as an example in the drawings and will be described in detail in this publication. However, it should be understood that the invention is not implied by the existence of restrictions associated with a particular open forms. Rather, it is understood that the invention covers all modifications, equivalents and alternatives included in the scope of the invention, which is defined in the attached claims.

Description of illustrative options

Illustrative variants of the present invention is described below. In the interest of clarity, not all features of actual implementation described in this description. Of course, it will be clear that the development of any such actual variant requires numerous specific to the implementation of solutions to achieve the specific goals of the developer, such as the constraints associated with the system and related commercial interests, which will vary from one option to another. In addition, it will be clear that such attempts developments can be difficult and time-consuming, but, nevertheless, can be a common practice for specialists in this field of technology that take advantage of this discovery.

The cleaning method in the present invention are useful in L. the BOM method, using carbonylation of methanol with the formation of acetic acid in the presence of a metal catalyst of group VIII, such as rhodium and iodide promoter. In particular, a useful method is the rhodium-catalyzed carbonylation of methanol at low water content with the formation of acetic acid, as shown for example in U.S. patent No. 5001259. It is usually assumed that the rhodium component of the catalyst system is present in the form coordination compounds of rhodium and halogen component, providing at least one of the ligands for such coordination compounds. In addition to the coordination of rhodium and halogen, also believe that carbon monoxide is coordinated with rhodium. The rhodium component of the catalyst system can be provided by introducing into the reaction zone of rhodium in the form of metallic rhodium, of rhodium salts such as oxides, acetates, iodides, etc. or other coordination compounds of rhodium, etc.

Halogen-promoting component catalytic system consists of halide compounds, including organic halide. Thus, the alkyl-, aryl - substituted alkyl - or aryl-halides can be used. Preferably the halide promoter is present in the form of alkyl-halide, in which alkilirovanny radical corresponds alkilirovan the resultant radical introduce alcohol, which carbonyliron. Thus, when carbonyliron methanol with the formation of acetic acid halide promoter is methyl halide, and preferably iodide stands.

Used liquid reaction medium may include any solvent compatible with the catalyst system, and may include pure alcohol or alcohol mixture of the raw materials and/or the desired carboxylic acid and/or esters of these two compounds. The preferred solvent and liquid reaction medium in the way carbonylation with low water content contains the product of the carboxylic acid. Thus, when carbonyliron methanol with the formation of acetic acid is the preferred solvent is acetic acid.

Water present in the reaction medium, but with concentrations significantly lower than those previously assumed in practice to achieve a significant rate of reaction. Previously believed that in the rhodium-catalyzed carbonylation reactions of the type described in the present invention the addition of water has a beneficial effect on the reaction rate (U.S. patent No. 3769329). Thus, most industrial implementations were carried out at concentrations in water of at least about 14 wt.%. Accordingly, quite unexpectedly, that karasti reaction, essentially equal to and greater than the rate of reaction obtained with such high levels of water can be achieved with a concentration of water of less than 14 wt.% and to as low as about 0.1 wt.%.

In accordance with the method carbonyl most effective for the production of acetic acid according to the present invention, the desired reaction rate even at low concentrations of water are added to the reaction medium of acetate and an additional iodide ion, which complements the iodide present as a catalytic promoter, for example methyl iodide or other organic iodide. Additional iodide promoter is an iodide salt, preferably lithium iodide. It is established that at low concentrations in water methyl acetate and lithium iodide act as promoters speed, only when each of these components is present in relatively high concentrations, and that the promotion becomes higher when there are simultaneously both (U.S. patent No. 5001259). Suppose that the concentration of lithium iodide used in the reaction environment preferred reaction system carbonylation is very significant compared to the low concentration in the prior art, having the General case with the use of halide salts in the reaction systems of this type. The absolute concentration of iodide ion is not a limitation on the usefulness of the present invention.

The carbonylation reaction of methanol to form acetic acid can be carried out by the interaction of matalana, which is in the liquid phase, with gaseous carbon monoxide, barotrauma through the liquid acetic acid, solvent reaction medium containing a rhodium catalyst, methyl iodide as promoter, methyl acetate, and additional soluble iodide salt in the conditions of temperature and pressure suitable for the formation of the product of the carbonylation. Usually consider what is important is the concentration of iodide ion in the catalytic system, and not the cation associated with the iodide, and that when selected molar concentration of iodide nature of the cation is not as significant compared to the effect of the concentration of iodide. Any iodide salt of a metal iodide or any salt of any organic cation, or Quaternary cation such as a Quaternary amine or phosphine or inorganic cation, may be used provided that the salt is sufficiently soluble in the reaction medium to provide the desired level of iodide. When iodide is added as a metal salt, it is preferable that it is a salt of iodide represented the indicator group, consisting of metals of group IA and group IIA of the periodic table, as described in the Handbook "Handbook of Chemistry and Physics" published by CRC Press, Cleveland, Ohio, 1975-76 (56th edition). Particularly suitable are the iodides of alkali metals, and lithium iodide is preferred. In the method of carbonylation with low water content, the most suitable in the present invention, the added iodide supplements organic iodide promoter present in the solution of the catalyst in an amount of from about 2 to about 20 wt.%, the acetate is present from about 0.5 to about 30 wt.%, and lithium iodide is present from about 5 to about 20 wt.%. The rhodium catalyst is from about 200 to about 2000 parts per million by weight (ppm).

The typical reaction temperature of the carbonylation of approximately from 150 to 250°C with a temperature range from about 180 to 220°C, which is the preferred area. The partial pressure of carbon monoxide in the reactor can vary widely, but typically is from about 2 to about 30 atmospheres and preferably from about 3 to about 10 atmospheres. Due to the partial pressure of the by-products of the reaction and the vapor pressure are liquids, the total pressure in the reactor will be in the range from about 15 to about 40 atmospheres.

Typical reaction of the system, and then the extraction system acetic acid, used for iodide-promoted rhodium-catalyzed carbonylation of methanol with the formation of acetic acid is shown in figure 1 and includes the carbonylation reactor, the flash evaporator and the column of the low-boiling fractions methyliodide and acetic acid 14, which has a lateral diversion of the flow of acetic acid 17, which is sent for further purification. In figure 1 does not show the reactor and the flash evaporator.

Considered standard equipment currently well known in the field of engineering carbonylation. The carbonylation reactor 10 is usually or tank with agitator or is a bubble column, in which the dosage of interacting liquids or slurries are maintained automatically at a constant level. Inside the specified reactor continuously introduce fresh methanol, carbon monoxide, a sufficient quantity of water required to maintain at least a limited concentration of water in the reaction medium, recirculating catalytic solution from the bottom of the flash evaporator recirculating phase methyl iodide and methyl acetate and recirculating the aqueous phase of acetic acid from the top of the shoulder strap receiving compartment of the decanter low-boiling fractions of methyl iodide and acetic acid or the separation column 14. Distill the operating system used in order to provide a means to recover crude acetic acid and recycling the catalyst solution, methyl iodide and methyl acetate in the reactor. In a preferred method, the carbon monoxide is continuously introduced into the carbonylation reactor is slightly below the location of the mixer used for mixing the component. Gaseous raw material is completely dispersed through the reaction liquid using these tools mixing. Gaseous purge stream produced from the reactor to prevent the accumulation of gaseous by-products and to support the set of partial pressure of carbon monoxide at a given total reactor pressure. The temperature of the reactor control and supply of carbon monoxide carried out at a rate sufficient to maintain the desired total pressure in the reactor.

Liquid product is removed from the carbonylation reactor at a rate sufficient to maintain the rector constant level, and is sent to the flash evaporator. In the flash evaporator catalytic solution extract as the main thread (mainly acetic acid containing rhodium catalyst and an iodide salt along with small amounts of methyl acetate, methyl iodide and water), while the gas flow of the upper ring-flash-COI is ritala contains mostly the product of acetic acid along with iodine stands, the acetate and water. Dissolved gases leaving the reactor and entering the flash evaporator, contain part of the carbon monoxide along with such gaseous byproducts, such as methane, hydrogen and carbon dioxide, and they come out from the flash evaporator as part of the flow of the upper shoulder strap. Thread the top of the shoulder strap guide in the column of the low-boiling fractions or the separation column 14 as stream 26.

Was disclosed in U.S. patent No. 6143930 and 6339171 that a higher concentration, about 3 times PVA and, in particular, acetaldehyde, is contained in the light phase than in the flow of heavy phase leaving the column 14. Thus, in accordance with the present invention, the stream 28 containing PVA,sent to the upper ring-receiving compartment of the decanter 16, where the phase boiling fractions, stream 30, is sent to distillation column 18.

The present invention in a broad sense be seen as a way to remove the PVA primarily aldehydes and iodide Akilov, from the flow of the vapor phase acetic acid. The flow of the vapor phase distil and extracted to remove the PVA. A typical method of removing aldehydes and iodide Akilov and lower levels of propionic acid from the flow of the first vapor phase acetic acid includes the following stages:

a) condensation of flow of the first vapor phase acetic acid in the PE the first capacitor and two-phase separation with the formation of the product of the first heavy liquid phase and the product of the first light liquid phase;

b) distillatory product first light liquid phase in the first column distillation with the formation of flow of the second product vapor phase acetic acid, which is enriched with aldehydes and iodine alkilani relative to the flow of the first vapor phase acetic acid;

c) condensing flow of the second vapor phase in the second capacitor with the formation of the product of the second liquid phase;

(d) distillatory product of the second liquid phase in the second distillation column to reduce and/or remove impurities iodine alkyl, aldehyde and propionic acid in the flow of the first vapor phase acetic acid stream upper ring of the aldehyde and alkyl iodide; and

e) measuring the flux density of the upper shoulder strap, optional counting on the basis of the relative concentrations of acetaldehyde and methyl iodide, and control the operation of the second distillation columns based measured density or calculated on the basis of concentrations.

Variant implementation of the prior art as disclosed in U.S. patent No. 6339171 shown in figure 1. According to figure 1, the flow of the first vapor phase acetic acid (28) contains methyl iodide, methyl acetate, acetaldehyde and other carbonyl components. The specified stream is then condensed and separated (in the tank 16)separating the product of the heavy phase containing the th greater part of the catalytic component, which recycle to the reactor (not shown in figure 1)and light phase (30)containing acetaldehyde, water, and acetic acid.

Any phase of the upper ring of the low-boiling fractions may then be distilled to remove PVA and, above all, acetaldehyde flow components, although it is preferable to remove the PVA of the light phase (30), because it is established that the concentration of acetaldehyde in the light phase several times. In the embodiment shown and described herein, the distillation is performed in two stages; but it should be understood that distillation can be performed in a single column with the same success. Light phase (30) is sent to the column 18, which is used for formation of the second vapor phase (36), enriched with aldehydes and iodine alkilani compared with stream 28. Par 36 condense (tank 20) with the formation of the product of the second liquid phase. The second liquid phase (40)containing acetaldehyde, methyl iodide, methanol and methyl acetate, sent to the second distillation column (22), in which acetaldehyde is separated from the other components. In the above method was found to decrease and/or remove at least 50% of impurities alkyl iodide identified in the stream of acetic acid. It was also shown that acetaldehyde and its derivatives reduced and/or removed as a result of, what about the least 50%, most often more than 60%. As a result, it is possible to maintain the concentration of propionic acid in acetic acid below about 400 ppm by weight, preferably below about 250 parts per million.

From the upper part of the column of the low-boiling fractions or the separation column 14 pairs removed by means of a thread 28, condensed and sent to the tank 16. Vapors are cooled to a temperature sufficient to condense and separate capable of condensation of methyl iodide, methyl acetate, acetaldehyde and other carbonyl component and water into two phases. Part of the flow 28 includes such is not capable of condensing gases, such as carbon dioxide, hydrogen, etc. and they can be removed, as shown in figure 1, the thread 29. Also leaving the upper shoulder of the receiving compartment of the decanter 16 is a heavy phase stream 28, but on the figure 1 is not shown. Usually found on heavy phase for recycle to the reactor, but part of the flow, usually a small number, for example 25 %by volume, preferably less than about 20 % by volume of the heavy phase may also be directed to implement the technology carbonyl processing, and the remainder recycled to the reactor or reactor system. A specified part of the flow of heavy phase can be processed separately, or be combined with a light phase (stream 30)for further distillation and extraction of carbonyl impurities.

Light phase (stream 30) is sent to distillation column 18. Part of the stream 30 is directed back into the column of the low-boiling fractions 14, as the flow phlegmy 34. The remainder of the stream 30 is fed to the column 18 as stream 32, approximately in the middle of the column. Column 18 is used for the concentration of aldehyde flow component 32 in the flow of the upper ring 36 with the separation of water and acetic acid from the lighter component. Thread 32 distil in the first distillation column 18, which preferably contains about 40 plates, and the temperature is changed from approximately 283°F (139,4°C) at the bottom to about 191°F (88,3°C) in the upper part of the column. Extending from the lower portion 18 is a flow 38, containing about 70% water and 30% acetic acid. Stream 38 is treated, usually cooled in the heat exchanger recycle to the upper ring of the decanter columns of the low-boiling fractions 16 through the threads 46, 48 and, ultimately, into the reactor or reaction system. It is established that the recycled portion of the stream 38, indicated as stream 46, returning through the decanter 16, increases the efficiency of the proposed invention method and allows more acetaldehyde to be in the light phase stream 32. For a thread 36 was installed approximately a seven-fold increase in the concentration of aldehyde when the thread 38 recycled through the decanter 1 in a similar way. Leaving the top of column 18 is stream 36 containing PVA and, in particular, acetaldehyde, methyl iodide, methyl acetate and methanol and iodine alkali. Stream 36 is then directed to drive the top of the shoulder strap 20, after it is cooled to condense any capable of condensing gases present.

Facing the top ring drive 20 is stream 40 containing acetaldehyde, methyl iodide, methyl acetate and methanol. Part of the flow 40 return in column 18, as the flow phlegmy 42. The remainder of the stream 40 is fed to the second distillation column 22 near the bottom of the column. Column 22 is used to separate the greater part of the acetaldehyde from methyl iodide, methyl acetate and methanol in stream 40. In one embodiment, column 22 contains about 100 plates and operates in the temperature range from about 224°F (106,6°C) at the bottom to about 175°F (79,4°C) in the upper part of the column. In an additional preferred embodiment, the column 22 contains structured nozzles instead of plates. The preferred nozzle is structured cap with interfacial surface approximately 65 ft²/ft³preferably made of metal alloy, such 2205 or other supplementary material, provided it is compatible with compositions treated is in the column. During testing it was observed that uniform loading of the column, which is required for good separation was better structured nozzles than with plates. An alternative may be used a ceramic nozzle. The remainder of the column 22, the thread 44, out of the lower part of the column, and it recyclery to implement technology carbonylation. It will be obvious to the ordinary skilled professionals that separation made in the distillation columns 18 and 22 could also be performed using a single distillation column.

Acetaldehyde the nails are polymerized in the presence of iodide, bromide with formation of metaldehyde and paraldehyde is recommended. In General, these polymers have low molecular weight, less than about 200. For paraldehyde is recommended was established relative solubility in the reaction liquid, and, above all, in acetic acid. Metaldehyde, after his deposition, is a similar gravel, granular polymer, which has no solubility in the reaction liquid is greater than about 3 wt.% in concentration.

However, as disclosed in U.S. patent No. 6339171 is established that during the reaction and during heating of the column 22 are formed of high molecular weight polymers of acetaldehyde. I believe that these high molecular weight polymers (with molekulyarnoi weight of more than about 1000) are formed during the processing of the light phase, and they are viscous and thixotropic. Because the system uses the heat treatment, the polymer had a tendency to hardening and sticking on the walls of the column, where their removal was difficult. After polymerization, they are only slightly soluble in organic or aqueous solvents, and they can be removed only by mechanical means. Thus, preferably in the column 22 is needed inhibitor to reduce the formation of these impurities, i.e. metaldehyde and paraldehyde is recommended high molecular weight polymers of acetaldehyde (AcH). Inhibitors usually contain alkanols C_l-10, preferably methanol, water, acetic acid and the like used individually or in combination with each other or with one or more other inhibitors. Stream 46, which is part of the remainder of the column 18, and a part of the flow from the stream 38 contains water and acetic acid and, therefore, can be used as the inhibitor. As shown in figure 1, the thread 46 is split with the formation of the threads 48 and 50. Stream 50 is added to the column 22 to inhibit the formation of impurities metaldehyde and paraldehyde is recommended and high molecular weight polymers. As the remainder of the second column 22 recycle to the reactor, any added inhibitors must be compatible with the chemical reactions occurring. Installed, Thu is a small amount of water, methanol, acetic acid, or a combination, do not interfere with the chemical reactions occurring and virtually eliminate the formation of polymers of acetaldehyde. Stream 50 is also preferably used as the inhibitor, since this material does not alter the water balance in the reactor. Although the water in particular, it is not preferable as an inhibitor, other important advantages are obtained by adding water to the column 22.

Leaving the top of column 22 is containing PVA stream 52. Stream 52 is sent to the condenser and then to the upper ring of the receiver 24. After condensation of any unable to condensation of substances released from the receiver 24; condensed matter leave the receiver 24 in the form of a stream 54. Stream 56, the portion of the stream from the stream 54, is used as the phlegm to the column 22. Exiting the bottom of column 22 is stream 44 containing methyl iodide, methanol, methyl acetate, methanol and water. This stream is combined with a stream 66, which will be described below, and sent to the reactor.

For the mechanism of extraction is important that the flow of the upper ring of the column 22 is still cold, usually at a temperature of about 13°C. This stream may be received or stored at about 13°C conventional methods known to skilled professionals in the art, or any device that would normally be accepted in this paragraph is the itsindustry.

After exiting the receiver 24 stream 58 is preferably directed through the condenser/cooler (now stream 62) and then the extractor 27 removal and recycling of small amounts of methyl iodide from the aqueous stream PVA. In the extractor 27 PVA and iodine alkali extracted with water, preferably water from the underlying stream, so as to maintain water balance within the reaction system. As a result of such extraction of methyl iodide is separated from the aqueous PVA and phase of the alkyl iodide. In the preferred embodiment, using a mixer-settler with the ratio of water to raw about 2.

The flow of aqueous extract of 64 leaves the extractor from its upper part. This PVA-enriched and, in particular, acetaldehyde-enriched aqueous phase is sent for recycling. Also coming out of the extractor 22 is refined stream 66 containing methyl iodide, which is typically recycled to the reaction system and, ultimately, into the reactor.

Currently, the authors of this application have found that it is advantageous to analyze the composition of the condensed upper ring 54 of the second column 22 and using data analysis to support the process of distillation control system with feedback. Despite the fact that it is extremely desirable disposed in the floor with the help of acetic acid such amount of acetaldehyde and other PVA as possible, it is important to do this without compromising cost-effectiveness. The main aspect of the method described herein, is that because methyl iodide is extremely expensive substance, which is also very expensive to reset as a result of expenditures made during processing, in particular it is desirable to carry out improvements to the method that will be able to remove acetaldehyde, preventing the formation of iodine Akilov PVS, but at the same time save methyl iodide, to the extent possible. It will be clear that the difficult problem of the connection of these technical requirements at the same time is not obvious, because methyl iodide and acetaldehyde have similar boiling point, which makes it difficult to achieve optimal separation. For each ordinary skilled in the art should be understood, the method of distillation for the separation of methyl iodide from acetaldehyde is extremely sensitive to relatively small variations in temperature, rate of circulation of the thread, etc. Therefore, it is desirable to have the most accurate information about the process related to the quality of the separation of methyl iodide/acetaldehyde.

The authors of this application have found that the above SP is own distillation can be controlled with greater accuracy by measuring the relative concentrations of methyl iodide and acetaldehyde in the condensed distillate in stream 54, 56, 58 or 62. Surprisingly, this can be achieved simply by measuring the density of the distillate. In contrast to acetaldehyde, which has a density of about 0,78 g/cm³at room temperature (like many common organic compounds), methyl iodide has a density of about 2.3 g/cm³almost three times greater. This difference in density is large enough, so that the relative concentration of methyl iodide and acetaldehyde in a mixture of two compounds can be calculated directly from the density values. Density can be measured under normal process conditions, or after cooling the sample to room temperature. It is preferable to measure the density at actual conditions to eliminate unnecessary time delay in the control circuit, which must be the result of time pre-cooling.

Density can be measured in any of the threads 54, 56, 58 or 62 (all of them contain the same composition), using a conventional interactive densitometer, indicated as 70 in figures 2-4. For example, the authors conducted a series of experiments to identify the correlation of the measured flux density of the upper ring 54 with the measured concentrations of methyl iodide (MeI), acetaldehyde (AcH) and dimethyl ether (DME). Were obtained the following data:

Figure 5 shows a correlation of the concentrations of methyl iodide and acetaldehyde with current density measurements. Similar linear trends were observed for the concentrations of bromide and iodide concentration of acetaldehyde, while showing that under typical process conditions, the two concentrations can be calculated from one density measurement.

These density measurements, or calculated on the basis of their relative concentrations, can be used as the basis for managing the process of distillation in the column 22 to optimize the separation of methyl iodide and acetaldehyde. Optimization can be achieved, for example, by increasing or decreasing the density of the heat flow in the distillation column in response to changes in the ratio of methyl iodide to acetaldehyde. Alternatively, the speed phlegmy within the column can be adjusted (for example, by varying the separation between the threads 58 and 56) in response to the concentration ratio. As another alternative, the concentration of phlegmy columns can be adjusted in response to measured concentrations of acetaldehyde and yo the East methyl, by increasing or decreasing the flow rate for stream 50. This can be achieved, for example, by regulating the distribution part of the thread 46 between threads 48 and 50. Pressure in the column can also be controlled in response to the calculated concentration.

The composition of supply of raw materials in the column can also be adjusted. Discovered that under certain circumstances it is advantageous to separate and to recycle part of the stream 66 in a convoy of supply of raw materials 40 columns 22. Changing the flow rate of this specified stream in response to changes in the measured relative concentrations of methyl iodide and acetaldehyde in turn would change the composition of supply of raw materials in the column.

Control schemes that allow the modification of more than one of the process parameters associated with the distillation column in response to measured changes in the composition of the distillate, are also within the scope of the present invention. For example, can be carried out the management and supply of raw materials, and formulations of phlegmy at the same time, regulation of the heat capacity of the column, taking into account the changing composition of supply of raw materials, or the speed adjustment phlegmy to compensate for changes in its composition. The possibility is about the implementation of many such changes.

In addition to measuring the density of one or more threads mentioned earlier to control distillation column, preferably using a density measurement to monitor or control the operation of the extractor 27. It should be understood that the extractor 27 operates, making it the phase separation between the heavy phase iodine bromide and less dense aqueous phase containing acetaldehyde. Therefore, a significant change in the measured density or flow of an aqueous extract of 64, or enriched with iodine stands refined flow 66 would indicate a weakening phase separation in the extractor, which, in turn, would indicate that methyl iodide is removed from the stream. As explained in this description and in another place, preferably the preservation of methyl iodide and reuse it in the process to the maximum extent practical; in addition, the presence of methyl iodide in the aqueous extract may adversely affect the wastewater treatment process, which extract is usually subjected. Similarly, the flux density measurement 66 allows you to control the residual concentration of acetaldehyde in the flow, allowing corrective action (for example, increase the water flow in the extractor 27) in response to C is iellamo high concentration of acetaldehyde. With further improvement of the invention only the densitometer can be placed to selectively measure the density of any of the numerous threads throughout the process.

Although the invention is described with reference to preferred embodiments of the obvious modifications and changes can be made normal by qualified specialists in this field of technology. In particular, although the present invention mainly above described, utilityowned low-boiling phase column 14, any thread in the way carbonyl having a high concentration of PVA and iodine Akilov, can be processed in accordance with the present invention. Similarly, although the method described above in relation to the removal of acetaldehyde with a specific configuration, minor modifications of the disclosed configuration, as, for example, replacement of distillation columns 18 and 22 on a single column, is also provided. Therefore, the invention includes all such modifications and changes to the full extent as they entered the next volume next formula, invention or its equivalents.

1. A way of separating acetaldehyde from methyl iodide using distillation, comprising the stage of:
distillatory mixtures containing methyl iodide and acetaldehyde, in the apparatus distilleries obtain the upper shoulder straps and sediment;
density measurement the specified upper shoulder straps;
the determination of the relative concentrations of methyl iodide, acetaldehyde or both at the top chase on the basis of the measured density; and
regulation, at least one process variable associated with the specified distillation apparatus, in response to the specified measured density or calculated from it the relative concentration, the variable process selected from the intensity of heat, pressure column, the feed composition, the composition of phlegmy and turnover of the stream.

2. A way of separating acetaldehyde from iodide, bromide, comprising the stage of:
distillatory mixtures containing methyl iodide and acetaldehyde, in the distillation apparatus to obtain the upper shoulder straps and sediment;
extraction of the upper shoulder strap with water to provide an aqueous extract and a raffinate;
density measurement, at least one of the following:
the specified upper shoulder strap, of the extract and the specified raffinate;
the determination of the relative concentrations of methyl iodide, acetaldehyde or both in at least one of the following:
the specified upper pursuit, specified extract and specified raffinate based on the measured density; and
regulation, on ENISA least one process variable associated with the specified distillation apparatus or a specified stage of extraction, in response to the specified measured density or calculated from it the relative concentration, while the specified process variable selected from the group consisting of: heating intensity is specified distillation apparatus, the pressure of the column in the specified apparatus distillation, the composition of raw materials or phlegmy to the specified distillation apparatus, the ratio of circulation flow in the specified distillation apparatus at a feed rate of water at a specified stage of extraction, and combinations thereof.

3. The method according to claim 2, in which the measured density of the upper ring and the intensity of the heat, or the rate of circulation of the flow regulating in response to the specified density or calculated from her concentration.

4. The method according to claim 2, in which the measured density of the upper shoulder strap, and the intensity of the heat regulate in response to the specified density or calculated from her concentration.

5. The method according to claim 2, in which the measured density of the extract, and the feed rate of water at a specified stage of extraction is controlled in response to the specified density or calculated from her concentration.

6. The method according to claim 2, in which the measured density RA is hinata, and the feed rate of water at a specified stage of extraction is controlled in response to the specified density or calculated from her concentration.