DE4323682A1 - Process for the preparation of dimethyl carbonate - Google Patents

Abstract

Dimethyl carbonate (DMC) is prepared by continuous gas-phase reaction of carbon monoxide and methyl nitrite on a heterogeneous catalyst. The reaction product is subjected to a multi-stage work-up which contains the following steps: 1. In a scrubber/condenser, the reaction product is separated into gaseous and liquid fractions; the gaseous fractions are fed back for new formation of methyl nitrite and the liquid fractions are subjected to a 2-stage distillation. 2. In the first distillation stage carried out at 5-15 bar, DMC is obtained as the bottom effluent. The top product is fed to the second distillation stage. 3. In the second distillation stage carried out at 0.2-1.5 bar, methanol is obtained as the bottom effluent, which can be subjected to the new formation of methyl nitrite. The top product of the second distillation stage is again subjected to the first distillation stage.

Description

Subject of the invention

The invention relates to a new process for the continuous production of dimethyl carbonate, since characterized in that carbon monoxide and methyl nitrite in the gas phase of a hetero genes catalyst to react with each other and the dimethyl carbonate formed in one after switched process step isolated. The method according to the invention is particularly suitable for technology production of dimethyl carbonate.

Dimethyl carbonate is an important raw material for the production of aromatic polycarbonates. It takes place further use as a starting material for the synthesis of aliphatic and aromatic mono- and di Isocyanates, as a methylating agent, as a substitute for the toxic phosgene in the manufacture of pharmaceuticals and agrochemical products, as a solvent, octane number improver for petrol and as an intermediate product in the manufacture of synthetic lubricants.

State of the art

The reaction between carbon monoxide and methyl nitrite, which underlies the formation of dimethyl carbonate lies, can be described by reaction equation (1)

For this purpose, methyl nitrite itself can be carried out in a manner known per se in an advanced reaction according to one of the Reaction equations (2) - (5) are generated.

4 NO + O₂ + 4 CH₃OH → 4 CH₃ONO + 2 H₂O (2)

NO + NO₂ + 2 CH₃OH → 2 CH₃ONO + H₂O (3)

N₂O₄ + CH₃OH → CH₃ONO + HNO₃ (4)

2 NaNO₂ + H₂SO₄ + 2 CH₃OH → 2 CH₃ONO + Na₂SO₄ + 2 H₂O

The production of dimethyl carbonate by the reaction of carbon monoxide and methyl nitrite in the gas phase in the presence of a heterogeneous catalyst, which is preferably a support-fixed platinum tall catalyst, has been described in various ways, for example in the following scientific Chen publications, published documents and patent specifications:

JP 60 181 051 (28.02.1984 JP / 14.09.1985) Found: Y. Okumura TOA NENRYO
X.-Z. Jiang et al .; Cuihua Xuebao 10 (1), 75-78 (March 1989)
EP 425 197 (24.10.1989, 31.07.1989 JP / 02.05.1991) Det .: K. Nishihira et al. UBE
X.-Z. Jiang; Platinum Metals Rev. 34 (4), 178-180 (1990)
EP 464 460 (30.06.1990 DE / 08.01.1992) Det .: A. Klausener et al. BAYER
EP 503 091 (09/28/90, 09/28/90 JP / 09/16/92) Det .: T. Matuzaki et al. UBE
EP 501 507 (01.03.91, 24.01.92 JP / 02.09.92) Det .: K. Nishihira et al. UBE
EP 503 618 (03/15/91, 03/26/91 JP / 09/16/92) Det .: T. Matuzaki et al. UBE
EP 523 508 (16.07.91 DE, 21.03.93) Det .: H. Landscheidt et al. BAYER
EP 523 728 (19.07.91 JP, 20.01.93) Erf .: K. Nishihira et al. UBE
EP 538 676 (21.10.91 DE, 28.04.93) Det .: H. Landscheidt et al. BAYER

Except for the European patent application EP 523 728 mentioned, none of the publications listed teaches one Path that would be suitable for the continuous technical production of dimethyl carbonate. So be generally obtained as reaction products mixtures in which in addition to the desired target compound Dimethyl carbonate other substances are present, such as dimethyl oxalate, which in the course of a Reaction equation (6) occurring side reaction arises, methyl formate, formaldehyde dime thylacetal, water and especially methanol. For many of the possible uses of the dimethylcar Such mixtures are completely unsuitable for bonats.

A continuous process control to be aimed at from an industrial point of view must fundamentally correspond to the principle shown in FIG. 1 and thus to a cyclic process. It must be designed in such a way that the nitrogen oxides produced in the course of reaction equation (1) and the formation of dimethyl carbonate, as well as all other gaseous and condensed products, by-products and auxiliaries, are either usable as far as possible or do not negatively affect the economy or the technical safety of the overall process impairing, complete or largely returned to the process, or, insofar as these components adversely affect the economy or the technical safety of the overall process, be removed completely or to the extent necessary for the undisturbed continuous operation of the overall process.

In EP 523 728 a process is described, the principle of which is shown in FIG. 2 and that the continuous production of dimethyl carbonate by reaction of methyl nitrite with carbon monoxide in the gas phase on a heterogeneous catalyst, which is preferably a support-fixed platinum metal contact acts, as well as the subsequent isolation of the resulting as a mixture with methanol, dimethyl oxalate and other impurities dimethyl carbonate in the course of an extractive distillation, wherein the extractant used is dimethyl oxalate. EP 523 728 also includes the recycling of the nitrogen oxides released in the course of the reaction of methyl nitrite with carbon monoxide together with the unreacted gaseous reaction partners and the additional gas required for inerting, preferably nitrogen, in a process step preceding the actual production process of the dimethyl carbonate, the reaction equation ( 2 ) corresponds and in which the methyl nitrite required for the reaction is regenerated by feeding in methanol and oxygen and with the greatest possible removal of the water liberated in the process. Thus, it is, based on the gaseous components involved, namely with regard to the inert gases and auxiliaries, the unreacted gaseous reactants such as the unreacted methyl nitrite and carbon monoxide and the nitrogen oxides involved in a cycle.

A disadvantage of the method described in EP 523 728 are the following points, which are its industrial character Question economic and ecological applicability:

For the production, isolation and purification of the dimethyl carbonate, large amounts of auxiliaries must be used Circle. For example, if you put the details of Example 1 of the mentioned patent application the following quantities per kg DMC result in a circle:

4.8 kg of methanol
6.0 kg of dimethyl oxalate
2.8 kg methyl nitrite
1.6 kg carbon monoxide
1.2 kg of nitrogen monoxide
7.8 kg nitrogen

In particular, due to the large excess of methanol, which is fed into the methyl nitrite reactor 3 of FIG. 4 and which is approximately 500% of the stoichiometrically required amount, a very considerable amount of distillation is required, which leads to high energy costs if one wants to recover the unreacted portion of methanol from the bottom drain of the reactor.

Since the recycling of these auxiliaries or secondary components (water, nitric acid, formic acid methyl ester, formaldehyde dimethyl acetal), especially with regard to methanol and dimethyl oxalate, a distillative Ab Separation of the desired reaction product requires dimethyl carbonate, this process is extreme energy-intensive and therefore unat. not only from an economic but also from an ecological point of view tractive.

Basically, oxalic acid dimethyl ester forms by reaction with traces of water, which derives from the manufacture of the methyl nitrite in the methyl nitrite reactor 3 of FIG. 2 and which, because of the separation which is never completely successful there, is typically contained in reactant gas mixtures and thus also in product gas mixtures of dimethyl carbonate production. according to the reaction equations (8) and (9) Ox as half-acid ester or oxalic acid. Due to their acidity in the extraction column 2 and in particular due to the higher temperature in the methanol column 4 of FIG. 2, these can convert the methanol present there to dimethyl ether according to reaction equation (10). This process is autocatalytic, since with each reaction event a further equivalent of water is released, which in turn can react again with dimethyl oxalate.

In addition, the half ester of oxalic acid formed according to reaction equation (8) can form Decarboxylate methyl formate according to reaction equation (11).

H₃COOC-COOH → HCOOCH₃ + CO₂ (11)

In addition, technically available carbon monoxide contains small amounts even after extensive cleaning under the conditions of dimethyl carbonate production of inert gaseous impurities as in for example hydrogen, methane and carbon dioxide.

The inevitable accumulation of volatile secondary components in the recycle gas, it may now are those that are formed in the course of undesirable side reactions, or those that as Contamination in the raw materials used requires the removal of one corresponding proportion of the circulating gas. This is basically in the procedure  Description of the mentioned patent application EP 523 728 mentioned, but are about the scope and treatment No details given regarding the amount of gas discharged. In any case, it is expected that both eco nomie as well as ecology of the procedure are thereby affected.

In addition to these considerations, the description of the method is in the following places, for example inconsistent or incorrect:

Thus, in column 11, lines 40-42 of patent application EP 523 728, a tube collar consisting of 6 tubes delreaktor, the pipes of which each have a diameter of 26.1 mm and a length of 500 mm, described. Such a reactor has a maximum volume of 1.6 l. After line 43 of the patent application However, EP 523 728, this reactor is filled with 1.73 l of catalyst.

According to column 12, line 15 of the patent application EP 523 728, the dimethyl carbonate extracti on column (cf. number 2 in FIG. 2, corresponding to number 2 in FIG. 1 of patent application EP 523 728) 2.8 kg / h removed from an absorption solution and the distillation column (cf. number 4 in FIG. 2, corresponding to number 4 in Fig. 1 of patent application EP 523 728). After column 12, lines 51-52 of the patent application In EP 523 728, however, this is 3.5 kg / h.

According to column 13, lines 2-4 of patent application EP 523 728, the bottom of the first distilla is removed tion column (methanol distillation I, see number 4 in Fig. 2, corresponding to number 4 in Fig. 1 of the patent application EP 523 728) a mixture consisting of 14.3% dimethyl carbonate and 87.5% dimethyl oxalate. However, this is not mathematically possible.

According to column 13, line 21 of patent application EP 523 728, the bottom of the second distillation column (Dimethyl carbonate distillation, see number 5 in Fig. 2, corresponding to number 5 in Fig. 1 of the patent application EP 523 728) removed 4.69 kg / h of dimethyl oxalate. However, this amount is at least 0.6 kg larger than it according to the information in column 12, lines 51 and 55 of patent application EP 523 728 can be.

The methanol portion of the gas that runs the methyl nitrite synthesis reactor (number 3 in FIG. 2, corresponding to number 3 in Fig. 1 of patent application EP 523 728) and that after admixing carbon monoxide in the Dimethyl carbonate synthesis reactor is fed (number 1 in Fig. 2, corresponding to number 1 in Fig. 1 of Pa tentanmeldung EP 523 728), is at given pressure and predetermined proportions of the rest in Ge gaseous components present through the outlet temperature of the at the head of the Me thylitrite synthesis reactor located capacitor. It is not a freely selectable size, son This corresponds to the partial pressure which arises under these conditions and is 1 for example of said patent application EP 523 728 between 5.5 and 5.8 vol .-%. Are mentioned in Example 1 Column 11, lines 51-52 of said patent application, however, 1.8% by volume.

Finally, the information for the amount formed or discharged corresponds to that in the production of Methyl nitrite accumulating water (0.07 / kg / h) not the amount, based on that in Example 1 of the above-mentioned EP 523 728 reaction yields of dimethyl carbonate and dimethyl oxalate would be expected, namely 0.14 kg / h.

It was therefore the task of finding a process which was based on a lower raw material and energy wall, by a lower accumulation of by-products as well as by a more effective and as simple as possible Isolation and purification of the desired dimethyl carbonate is characterized by the state of the art Technology is described. This object is achieved by the method according to the invention.  

Description of the invention General

For the production of dimethyl carbonate by reaction carried out according to reaction equation (1) of carbon monoxide with methyl nitrite on heterogeneous platinum metal support contacts in the gas phase are in various catalysts or catalyst types are described in the literature.

For example, according to the scientific publication Cuihua Xuebao 10 (1), pp. 75-78 (March 1989), as Catalysts, for example palladium (II) halides, preferably palladium (II) chloride and in particular on Activated carbon carriers fixed palladium (II) chloride, which with iron, lithium and / or copper compounds is doped or modified, using high selectivities and space-time yields on the desired Obtained dimethyl carbonate. Similar catalyst systems are described in patent applications EP 425 197, EP 464 460, EP 503 091, EP 503 618 and EP 523 728. Catalysts of this type generally deliver the desired dimethyl carbonate in a not completely satisfactory selectivity. As a by-product the undesired dimethyl oxalate is formed according to reaction equation (6). On the one hand, this is to be considered striving for the highest possible utilization of the raw materials used and on the other hand requires one additional separation effort in the course of the isolation and cleaning of the desired dimethyl carbonate. Wei Furthermore, many catalysts of the type mentioned are subject to discharge in the course of longer operating times on halide, especially on chloride ions, generally in the form of hydrogen halide, especially chlorine formation of hydrogen. This may be due to a decrease in the selectivity for the dimethyl carbonate Formation and a decrease in the activity of the catalyst, but this is reduced by the addition Quantities e.g. B. of hydrogen halide, especially of hydrogen chloride to the reactant gas mixture, as in about of said patent application EP 425 197 is described, can be avoided. By introducing the mentioned small amounts of hydrogen halide, especially hydrogen chloride, there are increased requirements to the materials from which the parts of the system touched are to be manufactured. The Formation of characteristic by-products such as methyl chloride, which according to the reaction equation (12) by the reaction of hydrogen chloride which takes place parallel to the conditioning of the catalyst Small amounts of methanol are always present in the reactant gas mixture. Under that face points, it can be advantageous to use catalysts that have no or only a reasonably low level of deactivation due to the aforementioned discharge of halide ions, especially chloride ions if such contacts, as for example in the patent applications EP 503 091, EP 503 618 and EP 523 728 are described, a rather unfavorable selectivity, due to the formation of oxalic acid dime thylester, show.

CH₃OH + HCl → CH₃Cl + H₂O (12)

In order to prevent the accumulation of by-products within a technical cycle, Proportion of the circulating gas and the condensed reaction products to be determined, insofar as it is it is not dimethyl carbonate itself, continuously or discontinuously, preferably continuously be removed.

Detailed description of the method according to the invention

The method according to the invention is shown schematically in FIG. 3. It essentially includes the reaction of methyl nitrite with carbon monoxide over a catalyst containing palladium in the gas phase within a suitable reactor in the presence of an inert gas. The gaseous reaction products are separated into gaseous and liquid phases in a scrubber / condenser. The gaseous fraction, which contains, inter alia, the nitrogen monoxide formed during the reaction of the methyl nitrite, is reacted with oxygen and methanol in a suitable manner in a further reactor in order to regenerate it. The resulting water is passed on to waste water treatment, while the regenerated methyl nitrite is returned to the production of dimethyl carbonate. The liquid reaction products obtained in the scrubber / condenser are fed to a pressure distillation in which dimethyl carbonate and high boilers are removed as bottom product from overhead product containing methanol and dimethyl carbonate. Finally, the desired reaction product dimethyl carbonate is isolated in high purity in a final distillation step, while valuable materials such as methanol are largely returned to the process and waste materials such as waste water, waste air and high boilers are removed.

The extraordinarily high effectiveness of the interconnection of the apparatuses according to the invention, which is explained in detail in the following text is surprising and is not in the literature previously described. On the contrary, more complex or side reactions became significant operations more susceptible to interference, such as those proposed above and described in EP 523 728, are proposed. The outstanding and particularly energetic point of view is particularly surprising advantageous and thus resource-saving adjustment of the pressure distillation in the Overall process concept, if not as isolated, as described in the literature cited Process step optimized, but, as it corresponds to the inventive method, in combination with Recycling steps for recyclables such as in particular the methanol to be recycled is used.

Description of the individual devices and their functions

The formation of dimethyl carbonate takes place within apparatus 1 (dimethyl carbonate synthesis, cf. FIG. 3) in accordance with reaction equation (1). For this purpose, the circulating gas stream (d) originating from apparatus 3 (methyl nitrite synthesis) and containing the regenerated methyl nitrite (d) after passing through a heat exchanger which allows the setting of a defined temperature, as stream (d1) with carbon monoxide (a) and optionally (not ) contain batchwise or continuously in Fig. 3, treated with an additional gaseous excipients such as small amounts of halogen or hydrogen halide and directed as a feed gas stream (d2) in said apparatus. 1 The heat of reaction released in the course of the formation of dimethyl carbonate must be removed in whole or in part.

In the said apparatus 1 , it is therefore, for example, a tube bundle reactor which is cooled for example with hot water.

Preferably, said apparatus 1 is an apparatus divided into two reaction zones, within which the first reaction zone is configured as a tube bundle reactor, which is cooled, for example, with hot water, and the second as a downstream adiabatically operated reactor. In another preferred variant, the apparatus 1 is designed as a flat bed reactor which can be operated adiabatically with intermediate cooling or isothermally. In a third variant, the apparatus 1 mentioned is an adiabatic reactor operated with intermediate cooling.

Within apparatus 2 (dimethyl carbonate scrubber / condenser, see FIG. 3), the product gases (e) flowing out of the dimethyl carbonate synthesis are converted into condensable and non-condensable reaction products (f) and under specified conditions (pressure, temperature, gas velocity, etc.) (h) separated. In addition, the apparatus mentioned is optionally fed with a partial stream (b2) of the fresh methanol which has been introduced into the overall process and which is fed into its upper region. The stream (f) obtained at the top of the apparatus 2 , after branching off the portion (f2) intended for the discharge, is passed on as a circulating stream (f1) to a heat exchanger which sets the desired inlet temperature for the further reaction within the apparatus 3 (methyl nitrite Synthesis) allowed. The stream (f3) heated in this way passes the compressor and is combined as stream (f4) with the nitrogen (s) and, as shown in FIG. 3, nitrogen (s) and fresh nitrogen oxide (in FIG. 3, nitrogen monoxide) (r), which is preferably and as shown in FIG. 3 Stream (s1) combines before it flows into the production of methyl nitrite as feed gas stream (f5).

The discharged portion of the circulating gas (f2) can optionally be treated downstream operations, such as those in DOS 3 834 065 (10/06/1988 / Union Carbide) be described. Such post-treatment can serve the goal Valuable materials remaining in the discharged portion (f2) of the circulating gas stream, such as, for example recover unreacted methyl nitrite, nitrogen monoxide or gaseous dimethyl carbonate and in attributed the process of dimethyl carbonate production. In this way, the levy will also be toxic gaseous substances, such as methyl nitrite or nitrogen monoxide, avoided to the environment.  

The apparatus 2 mentioned is, for example, a tube bundle heat exchanger which can be constructed in a standing or lying construction, a plate heat exchanger, a spiral current heat exchanger, a spray condenser, a scrubber provided with a top condenser, a finned tube heat exchanger or a combination of the condensers mentioned - or heat exchangers and laundry types, for example around an injection condenser with downstream fins tubular heat exchanger.

In a preferred embodiment, said apparatus 2 is used as a spray condenser, ie as a special variant of a direct-contact heat exchanger, with spray cans arranged one behind the other, which are fed with cold condensate via a circuit and in this way enable the realization of two or more theoretical separation stages, executed.

In a further preferred embodiment, the apparatus 2 mentioned is a scrubber provided with a top condenser, within which a number of more than three theoretical plates are implemented.

The apparatus 2 mentioned is particularly preferably operated, for example as a washer, in a manner in which the temperature corresponding to the boiling point of the dimethyl carbonate under the given reaction pressure is set in the bottom region (for example about 128 ° C. at 3 bar), in order to do this Place methanol present in the raw product mixture mainly as part of the top stream (f) in gaseous form and essentially as an azeotrope with dimethyl carbonate from virtually pure liquid dimethyl carbonate as the main constituent of the bottom stream (h).

Within the apparatus 3 (methyl nitrite synthesis, cf. FIG. 3), the formation or regression of the methyl nitrite takes place in accordance with, for example, one of the reaction equations (2), (3) or (4). For this purpose, the nitrogen oxides acting as methyl nitrite equivalents or precursors are mixed with oxygen (c) and methanol (fresh methanol and methanol backflows from methanol separation in apparatus 7 and from wastewater distillation in apparatus 6 ) (b3, b4, 1, m1, m3) reacted. The resulting water and any by-products formed, such as nitric acid, are removed at the bottom of the apparatus (g), the product gas mixture (d) containing methyl nitrite is discharged after passing through a condenser (not shown in FIG. 3) at the top of the apparatus and for the Formation of dimethyl carbonate provided. The methanol introduced into the apparatus 3 thus serves on the one hand as a reactant in the formation of methyl nitrite according to one of the reaction equations (2), (3) or (4), and on the other hand, in particular in the form of the partial streams applied to the upper part of the apparatus ( b3, 1, m1) and the return line dripping back from the top condenser, as washing liquid for removing the water formed. The nitrogen oxides used for the reaction are essentially nitrogen monoxide, which is released in the course of the formation of dimethyl carbonate according to reaction equation (1) and, in a mixture with other gaseous components such as the inert gas and possibly incompletely converted gaseous reactants such as carbon monoxide or Methyl nitrite itself, in the sense of a cyclic process (see also FIG. 1) is returned according to reaction equation (2) (f- <f1- <f3- <f4). Fundamentally possible losses of methyl nitrite itself or of methyl nitrite equivalents or precursors, namely nitrogen monoxide, nitrogen dioxide, nitrous oxide or dinitrogen tetroxide, can occur due to undesired side reactions or also discharges (f2). The undesired side reactions mentioned can be, for example, the minor process of nitric acid formation according to reaction equation (4) or the possible formation of nitrogen or dinitrogen monoxide from nitrogen monoxide, as is the case according to reaction equations (13) and ( 14) can be formulated.

2 NO + 2 CO → N₂ + 2 CO₂ (13)

2 NO + 2 CO → N₂O + CO₂ (14)

Losses of the type mentioned can be compensated for, for example, by the fact that the total process lacks methyl nitrite itself or corresponding amounts of methyl nitrite equivalents or precursors, namely, nitrogen monoxide, nitrogen dioxide, bistractant trioxide, dinitrogen tetroxide or mixtures of individual components, batchwise or continuously, preferably continuously be added. In Fig. (3) ge this happens, for example, by the joint supply of the inert gas nitrogen and nitrogen monoxide (s1), but the method according to the invention is not restricted to this embodiment.

In general, from an ecological point of view, it is not acceptable to release nitric acid-containing waste water, even if it is only a small amount, without releasing aftertreatment. For this reason, the method according to the invention includes a preferably continuously operated neutralization step, in which a suitable base is used to trap any nitric acid formed. In Fig. 3, for example sodium hydroxide solution is used, but there are also other bases such as potash lye, lime milk or aqueous solutions of sodium carbonate and sodium bicarbonate in question. After admixing the base in question, for example sodium hydroxide solution (q) to the bottom stream (g) of apparatus 3 , a neutralized stream (g1) essentially containing water and methanol is thus obtained, which stream is passed on to apparatus 6 (wastewater distillation).

The apparatus 3 mentioned is, for example, a column-type scrubber which is provided with internals for improving the heat and mass exchange, as are usually used in thermal separation tasks. Examples of such internals are packing elements, trays such as bubble trays, sieve trays or valve trays, ordered packings or spray nozzles.

If necessary, the lower area of the apparatus is equipped with a sump evaporator, with the help of which a defined bottom temperature in through the phase equilibria of the substances present in the bottom certain certain limits can be set.

Basically suitable and usable for the mixing of the liquid and gaseous components or streams (b4, c, f5, m3) to be fed in at the lower end of the apparatus 3 mentioned are static mixers, jet mixers, rotating mixers, single and dual-substance nozzles, fluidized bed mixers, as they are, for example sold by Sulzer, mixing chambers, such as those sold by Pfaudler, in line full-turbulence tubes, HI mixers, such as those sold by Toray, Komax mixing elements, spiral mixers, Kennix mixers, with packing , such as Raschig rings, filled pipes and combinations of such elements. Oxygen (c) is preferably fed into the lower part of apparatus 3 . A partial stream (b3) of the fresh methanol and the methanol return streams (1) and (m1) are introduced in liquid form into the upper part of the reactor. Another part of the methanol (b4) and the methanol backflow (m3) are fed into the lower part of the apparatus 3 separately or together with the total stream (f5) formed from the recycle gas and the freshly fed nitrogen oxide and inert gas streams. In Fig. 3 only one of the possible variants according to the invention is shown, in which the supply of oxygen (c), the methanol partial stream (b4) and the combined stream of recycle gas to be recycled, newly fed inert gas and freshly fed nitrogen oxide (f5) in separate Form is made. However, the method according to the invention is in no way limited to this embodiment. Especially when using special feed units such as in particular two-substance nozzles and / or static mixers as well as combinations of such elements, it is advantageous to combine the flows (f5) and / or (b4) and / or (m3) and the oxygen flow (c) together in the lower ones Introduce part of the apparatus 3 .

In a preferred embodiment, the mixing of the liquid and gaseous components or streams (b4, c, f5, m3) to be fed in at the lower end of the above-mentioned apparatus 3 takes place by means of an effective static mixer, such as that from the company Sulzer (SMX or SMV type) is distributed. The use of such units is described, for example, by MH Pahl et al., Ing. Tech. 51 (5), pp. 307 ff. (1979) or J. Kobatek et al., Chem Eng. Process 25, pp. 59 ff. (1989).

In a further preferred embodiment, one-component or two-component nozzles or combinations of static mixers and one- or two-component nozzles are used to mix the liquid and gaseous components or streams (b4, c, f5, m3) to be fed in at the lower end of said apparatus 3 .

Apparatus 4 (pressure distillation, see FIG. 3) is a distillation column operated under a bottom pressure of approx. 5-15 bar, preferably 7-12 bar. It serves to split the stream (h) into an azeotrope-like mixture consisting of methanol and dimethyl carbonate, which is removed from the top of the apparatus (k) and a bottom product (i) which still contains high boilers, in particular dimethyl oxalate, after passing through one Heat exchanger, which allows the setting of a certain temperature, is passed as stream (i1) to the apparatus 5 (dimethyl carbonate distillation). The exact composition of the top product mentioned depends, among other things, on the absolute pressure at which the distillation was carried out (cf. DOS 2 607 003 (05/21/1975 / ENICHEM) and JP 02-212 456 (02/13/1989 / DAICEL) .

For the apparatus mentioned, distillation columns are generally suitable, which are usually used for the thermal separation of mixtures under pressure can be used, which have an output and a Have amplifier part and, according to the separation problem, the required number of theoretical Have separation stages. Examples are tray columns, packed columns and columns that Contained packs as internals. Packing columns and columns, which contain ordered packs as internals.

Apparatus 5 (dimethyl carbonate distillation, see FIG. 3) is a distillation column which is charged with the bottom product (i1) of apparatus 4 (pressure distillation) and which separates the desired reaction product dimethyl carbonate (o) in the form specified of the bottom product (j) essentially consisting of dimethyl oxalate and other possible high boilers.

For the apparatus 5 mentioned , distillation columns are generally suitable, which are usually used for the thermal separation of mixtures, which have a stripping section and an amplifier section and which, in accordance with the separation problem, have the required number of theoretical plates. For example, tray columns, packed columns and columns which contain ordered packings as internals may be mentioned. Packaged columns and columns which contain ordered packings as internals may be mentioned as preferred.

Apparatus 6 (wastewater distillation, cf. FIG. 3) is a distillation column which is charged with the neutralized bottom outlet (g1) from apparatus 3 (methyl nitrite synthesis). The task of this column is to separate and recycle the methanol contained in said stream (g1) in the form of the top stream (m), that in the form of the partial streams (m1) and (m3) into the apparatus 3 (methyl nitrite synthesis) and as a partial stream (m2), combined with the top stream (s) of the apparatus 7 (methanol removal) to the stream (n1), is returned to the apparatus 4 (pressure distillation). The actual waste water from the overall process (p) is obtained at the bottom of the apparatus 6 .

For the apparatus 6 mentioned , distillation columns are generally suitable, which are usually used for the thermal separation of mixtures, which have a stripping section and an amplifier section and which, in accordance with the separation problem, have the required number of theoretical plates. For example, tray columns, packed columns and columns which contain ordered packings as internals may be mentioned. Packaged columns and columns which contain ordered packings as internals may be mentioned as preferred.

Apparatus 7 (methanol separation, cf. FIG. 3) is a distillation column operated under normal pressure or under reduced pressure. It serves to split up the stream (k) obtained as the top product of the distillation column 4 into an azeotrope consisting of methanol and dimethyl carbonate, which is taken from the top of the apparatus (n) and together with part of the methanol obtained from the distillation column 6 (waste water column) Backflow (m2) is fed back into distillation column 4 (n1), and a bottom drain (I) consisting essentially of methanol, which is returned to the upper part of the methyl nitrite reactor (apparatus 3 ).

For the apparatus 7 mentioned , distillation columns are generally suitable which are usually used for the thermal separation of mixtures under reduced pressure, which have a stripping section and an amplifier section and which, in accordance with the separation problem, have the required number of theoretical plates. For example, tray columns, packed columns and columns which contain ordered packings as internals may be mentioned. Packaged columns and columns which contain ordered packings as internals may be mentioned as preferred.

Characterization of the material flows and reaction conditions

The material flows described in FIG. 3 and the associated pressure and temperature conditions, as are realized when the method according to the invention is carried out, are specified below.

The gas stream (d2) introduced into apparatus 1 in continuous operation generally has a temperature of 35-120 ° C., preferably 50-110 ° C. and a pressure of 1-5 bar, preferably 2-4 bar. It is generally composed of 4-16 mol% carbon monoxide, 0-5 mol% carbon dioxide, 5-25 mol% methyl nitrite, 40-80 mol% nitrogen, 1-10 mol% methanol, 0-5 mol % Dimethyl carbonate, 0-5 mol% nitrogen monoxide, 0-1 mol% water and less than 5 mol% of various, mostly volatile secondary components, preferably made of 8-14 mol% carbon monoxide, 0.5-3 mol% % Carbon dioxide, 10-20 mol% methyl nitrite, 50-75 mol% nitrogen, 1.5-8 mol% methanol, 0-2 mol% dimethyl carbonate, 0.1-5 mol% nitrogen monoxide, 0-0 , 5 mol% water and less than 4 mol% mostly volatile secondary components.

The gas stream (s) leaving the apparatus 1 in continuous operation generally has a temperature of 80-150 ° C., preferably 100-130 ° C. and a pressure of 1-5 bar, preferably 2-4 bar. It is generally composed of 0-13 mol% carbon monoxide, 0-5 mol% carbon dioxide, 0-20 mol% methyl nitrite, 40-80 mol% nitrogen, 1-10 mol% methanol, 1-10 mol -% Dimethyl carbonate, 3-15 mol% nitrogen monoxide, 0-0.5 mol% water and less than 5 mol% of various, mostly volatile secondary components, preferably from 1-12 mol% carbon monoxide, 0.5-3 Mol% carbon dioxide, 5-15 mol% methyl nitrite, 50-75 mol% nitrogen, 1.5-8 mol% methanol, 2-8 mol% dimethyl carbonate, 5-14 mol% nitrogen monoxide, 0-0 , 5 mol% water and less than 4 mol% mostly volatile secondary components.

The gas stream (f) leaving the apparatus 2 in continuous operation generally has a temperature of 0-40 ° C., preferably 5-35 ° C. and a pressure of 1-5 bar, preferably 2-4 bar. It is generally composed of 0-13 mol% carbon monoxide, 0-5 mol% carbon dioxide, 0-20 mol% methyl nitrite, 40-80 mol% nitrogen, 0-10 mol% methanol, 0-3 mol -% Dimethyl carbonate, 3-15 mol% nitrogen monoxide, 0-0.5 mol% water and less than 5 mol% of various, mostly volatile secondary components, preferably from 1-12 mol% carbon monoxide, 0.5-3 Mol% carbon dioxide, 5-15 mol% methyl nitrite, 50-75 mol% nitrogen, 1-8 mol% methanol, 0-2 mol% dimethyl carbonate, 5-14 mol% nitrogen monoxide, 0-0.5 Mol% water and less than 4 mol% mostly volatile secondary components.

The amount of the portion of the circulating gas discharged as gas stream (f2) in continuous operation is generally 0-5% by weight, preferably 0.1-4% by weight, based on the top stream (f) of the apparatus 2 .

The main stream (f1) remaining after discharge of the gas stream (f2) becomes after passing one Heat exchanger and a compressor, if necessary (cf. 3) with previous addition fresh nitrogen oxide and / or inert gas, into the apparatus3rd fed.

The feed rate of the gaseous nitrogen oxide, which is generally brought in at ambient temperature as stream (r), into the apparatus 3 (cf. FIG. 3) in continuous operation is 0-1 mol%, preferably 0-0.3 mol%, based on the Gas flow (f4). Instead of nitrogen monoxide, equivalent amounts of nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, methyl nitrite or any mixtures of these substances can in principle also be added.

The feed rate of the gaseous nitrogen, which is generally produced as stream (s) at ambient temperature, into the apparatus 3 (cf. FIG. 3) in continuous operation is 0-1 mol%, preferably 0-0.3 mol%, based on the Gas flow (f4).

The temperature of the gas stream (f5) is generally 5-60 ° C., preferably in the case of continuous operation 20-40 ° C, at a pressure of 1-5 bar, preferably 2-4 bar.

In continuous operation, the amount of methanol fed in via feed line (b4) is advantageously so chosen so that the molar ratio between this methanol and the gas stream fed in (f5) nitrogen monoxide contained 0.1-5, preferably 0.1-2. The temperature of the feed methanol is generally 10-80 ° C, preferably 20-60 ° C.  

The amount of methanol fed in via feed line (b3) in continuous operation is advantageously so chosen so that the molar ratio between this methanol and the gas stream fed in (f5) nitrogen monoxide contained 0.1-5, preferably 0.2-4. The temperature of the feed methanol is generally 10-40 ° C, preferably 10-35 ° C.

In continuous operation, the amount of the generally at ambient temperature via supply line (c) induced oxygen advantageously chosen so that the molar ratio between oxygen and the nitrogen monoxide contained in the supplied gas stream (f5) is 0.125-0.25, preferably 0.15-0.245.

The internal pressure of the apparatus 3 mentioned is generally 1-5 bar, preferably 2-4 bar, its internal temperature is variable within wide limits. The temperature profile over the entire length of the apparatus is a function of the quantity, inlet temperature and physical state of the individual feeds, total pressure, conversion of the reactants introduced, reflux of the top condenser and energy supply at the bottom of the apparatus.

The apparatus 6 (wastewater distillation) is generally operated at a pressure of 0.5-2 bar, preferably 0.5-1.5 bar. The condensed top product (m) is obtained in continuous operation at a temperature of 15-50 ° C., preferably 15-35 ° C., and has a composition of 60-95 mol% of methanol, 1-35 mol% of dimethyl carbonate and 0 -7 mole% water, preferably 70-88 mole% methanol, 2-30 mole% dimethyl carbonate and 0-5 mole% water.

The amount of the methanol / dimethyl carbonate mixture recycled as a partial stream (m2) can, depending on Content of dimethyl carbonate, adjusted so that they 0-90%, preferably 0-30% of the total current (m) includes.

 The amount of the methanol / dimethyl carbonate mixture recycled as partial stream (m1) can, depending on Dimethyl carbonate content, adjusted to be between 0 and 100% of the total current (m) includes. The same applies to the amount of methanol returned as a partial flow (m3).

The carbon monoxide generally fed in at ambient temperature as stream (a) becomes used in chemically pure form, however, depending on the type of production, foreign gases such as small ones Contain quantities of hydrogen (<0.1 mol%) or methane (<0.1 mol%). It is fed in continuous operation in such a way that the molar ratio between metered carbon monoxide and produced dimethyl carbonate is 1-1.2 and a constant concentration of carbon monoxide in the Gas flow (d2) is present.

The dimethyl carbonate distilled in apparatus 5 has a purity of 99.0-99.9%, depending on the reflux / withdrawal ratio.

example Catalyst production

0.835 g of PdCl₂ are dissolved in 4 ml of water with the addition of 2 g of sodium chloride. Be at room temperature 25 ml of a 25% ammonia solution are added with stirring.

100 ml of activated carbon Norit ROX 0.8 are soaked in this solution and then in a stream of nitrogen dried.

Manufacture of dimethyl carbonate

In a tube bundle reactor made of the active ingredient 1.4571 and consisting of 4 reaction tubes of approx. 900 mm length (dimension of the tubes: 25.0 × 800 mm, wall thickness 2.0 mm) becomes 960 ml of the catalyst introduced, the catalyst level is about 700 mm.

At 3130 mbar, an average of 4927 g / h of a mixture heated to about 80 ° C. by means of an upstream tube bundle heat exchanger is allowed to flow, which contains 13.2 mol% carbon monoxide, 2.2 mol% carbon dioxide, 15.1 mol% methyl nitrite, 60.0 mol% nitrogen, 5.1 mol% methanol, 0.7 mol% dimethyl carbonate, 3.3 mol% nitrogen monoxide and 0.2 mol% water (see stream (d2) in Fig. 4). In continuous operation, this gas mixture consists of the gas flowing out of the top of the methyl nitrite reactor (see stream (d) in FIG. 4) and about 128 g / h of freshly added carbon monoxide (see stream (a) in FIG. 4) ) together. The cooling (water) applied to the reactor is automatically regulated so that the gas stream leaving the reactor (cf. stream (s) in FIG. 4) has a temperature of approximately 120.degree. This gas flow is introduced laterally into a washer / condenser (dimensions: 600 × 48.3 mm, wall thickness 2.6 mm) filled with glass Raschig rings (4 × 4 mm), in which partial condensation takes place. At the head of this apparatus, a shell and tube condensing tube heat exchanger is attached, which consists of 7 tubes measuring 2000 × 10 mm (wall thickness 1 mm) and is regulated by cooling with cold water (temperature <10 ° C) so that the gas emerging behind this condenser (see current (f) in Fig. 4) has a temperature of about 15 ° C. At a pressure of 3020 mbar, this gas contains on average 10.7 mol% carbon monoxide, 2.4 mol% carbon dioxide, 9.6 mol% methyl nitrile, 63.9 mol% nitrogen, 2.6 mol -% methanol, 0.8 mol% dimethyl carbonate and 10 mol% nitrogen monoxide. The bottom stream (see stream (h) in FIG. 4), on average 527 g / h, runs at a temperature of approx. 47 ° C. and contains 46.3 mol% of methanol, 49.1 mol% of dimethyl carbonate , 2.2 mol% of dimethyl oxalate and 2.2 mol% of water and is passed into the buffer vessel A (see FIG. 4).

Approximately 0.2% by weight of the gas stream obtained at the top of the scrubber / condenser is continuously discharged in order to prevent the accumulation of gaseous by-products within the cycle (see stream (f2) in FIG. 4). The remaining gas is brought to a pressure of approx. 3250 mbar and a temperature of approx. 28 ° C via a heat exchanger and a piston compressor, combined with an average of additional 2.4 g / h nitrogen monoxide and 4.9 g / h nitrogen and with approx. 56 g / h fresh methanol and approx. 71 g / h oxygen are fed into the lower part of the methyl nitrite reactor (cf. apparatus 3 in FIG. 4) in such a way that all reactants are mixed as suddenly and completely as possible, without critical concentration ranges of ignitable components are crossed.

This is done in such a way that the mixing of the circulating gas with the freshly added gases nitrogen monoxide (cf. stream (r) in FIG. 4) and nitrogen (cf. stream (s) in FIG. 4) takes place within a first static mixer element behind it, the methanol is sprayed in via a single-component nozzle and oxygen is fed in immediately after the addition of methanol and before the subsequent static mixer element, in which all the reaction components present are intensively mixed.

In the upper part of the reactor, an average of 226 g / h of fresh methanol (cf. stream (b3) in FIG. 4), 80 g / h of the recycled methanol (cf. stream (m1) in FIG. 4) are turned off is taken from the buffer vessel C (cf. FIG. 4) and 155 g / h of the mixture essentially containing methanol (cf. stream (I) in FIG. 4), which is taken from the buffer vessel E (cf. FIG. 4) is pumped. The methyl nitrite reactor (dimensions: 2200 × 48.3 mm, wall thickness 2.6 mm) is a reaction vessel containing a packing (glass rings measuring 4 × 4 mm) that has an internal free volume of approx. 2.25 l owns.

At the head of this apparatus, a shell and tube condensing tube heat exchanger is installed, which consists of 7 tubes measuring 10 × 1000 mm (wall thickness 1 mm) and whose cooling capacity is regulated by cooling with cold water (temperature <15 ° C) so that this is behind this condenser escaping gas (see stream (d) in Fig. 4) has a temperature of about 28 ° C. It is at an average pressure of approx. 3140 mbar and is continuously returned to the dimethyl carbonate reactor (see above). The liquid bottom stream (see stream (g) in FIG. 4, on average 219 g / h, runs off at a temperature of about 28 ° C., contains 28.9 mol% of methanol, 5.1 mol% of dimethyl carbonate and 55.6 mol% of water and, after neutralization of the small amounts of nitric acid contained therein, is passed into the buffer vessel B (cf. FIG. 4).

The approx. 45 ° C warm mixture in buffer vessel A (see FIG. 4) is fed laterally into a continuously operating pressure column (apparatus 4 in FIG. 4), which has a pressure range from 9085 (bottom) to 9050 mbar (head ) is operated. This pressure column is a distillation column filled with packing elements (glass rings measuring 4 × 4 mm) (dimensions 33.7 × 2500 mm, wall thickness 2.6 mm), in which approx. 15 theoretical plates are implemented and one Return ratio of 1.1: 1 works. The pressure column mentioned is also fed from the buffer vessel F (see FIG. 4) with the backflow (n1) (see FIG. 4) (see below). The lower end of the pressure column mentioned is a column section with jacket heating. At the upper end of the said pressure column there is a horizontal double tube condenser which is operated with cooling water.

The liquid mixture running off at the bottom (cf. stream (i) in FIG. 4) has a temperature of approximately 180 ° C. on average and is transferred to the buffer vessel D (cf. FIG. 4). The condensate obtained at the top (cf. stream (k) in FIG. 4) has a temperature of approx. 125 ° C. and contains on average approx. 86 mol% methanol, approx. 11 mol% dimethyl carbonate, approx. 1-1 , 5 mol% water and low low boilers. It is fed laterally into a continuously operating distillation column operated at atmospheric pressure (cf. apparatus 7 in FIG. 4), in which a separation into a bottom drain, which predominantly contains methanol and water and which is transferred to the buffer vessel E, and into an overhead product , which contains an average of approx. 83 mol% of methanol, approx. 14 mol% of dimethyl carbonate and small amounts of low boilers, and which is passed as a condensate at a temperature of approx. 60 ° C. into the buffer vessel F (cf. FIG. 4) is done. Into this buffer vessel F, the contents of which are magnetically stirred, an average of 28 g / h of the mixture from the buffer vessel C (see FIG. 4), which originates from the wastewater distillation (see apparatus 6 in FIG. 4), headed. On average 615 g / h of the mixture from the buffer vessel F (cf. FIG. 4) are pumped in laterally into the pressure distillation (cf. apparatus 4 in FIG. 4), thus representing the second inflow from which the in this apparatus ongoing distillative separation is fed. This column is a distillation column filled with packing elements (glass rings measuring 4 × 4 mm) (dimensions 42.4 × 3200 mm, wall thickness 2.0 mm), in which approx. 25 theoretical plates are implemented and one Return ratio of 1.7: 1 works. A column section with jacket heating forms the lower end of the column mentioned. At the top of said column there is a horizontal double tube condenser which is operated with cooling water.

The mixture of substances in the buffer vessel D (see Fig. 4) is, after cooling to approx. 95 ° C, by means of an intermediate simple tube bundle heat exchanger, the cooling capacity of which is automatically regulated so that the escaping liquid has the desired temperature, laterally into a normal pressure operated continuously operating column fed (see. Stream (i1) in Fig. 4). This column is a distillation column filled with packing elements (glass rings measuring 4 × 4 mm) (dimensions 33.7 × 2200 mm, wall thickness 2.6 mm), in which approx. 15 theoretical plates are implemented and one Return ratio of 1: 1 works. A column section with jacket heating forms the lower end of the column mentioned. At the top of said column is a horizontal double condenser that is operated with cooling water.

The top product of the distillation (cf. stream (o) in FIG. 6) is an average of 375 g / h of dimethyl carbonate with a purity of <99.7% (GC). In the floor drain there are high boilers, essentially, more than 90%, dimethyl oxalate.

Of the buffer vessel B (see. Fig. 4) located neutralized floor drain of the methyl nitrite reactor (see FIG. Apparatus 3 in Fig. 4) is laterally fed into a operated at normal pressure column (see FIG. Flow (g1) in Fig. 4). This column is a distillation column filled with packing elements (glass rings measuring 4 × 4 mm) (dimensions 33.7 × 3200 mm, wall thickness 2.6 mm), in which approx. 22 theoretical plates are implemented and one Return ratio of 1: 1 works. A column section with jacket heating forms the lower end of the column mentioned. At the top of said column is a horizontal double condenser that is operated with cooling water.

The top product of the distillation (see FIG. Current (m) in Fig. 6) will be on average 139 g / h of a mixture containing an average of 86 mol% methanol 11% dimethyl carbonate and water and in the buffer vessel C (see Fig. . is directed 4). In the floor drain (cf. stream (p) in FIG. 4) there is water and in particular water-soluble salts.

Claims (5)

1. A process for the continuous production of dimethyl carbonate, characterized in that

• (a) Carbon monoxide and methyl nitrite in the gas phase in the presence of a heterogeneous platinum metal-containing catalyst, preferably a palladium-containing supported catalyst, and an inert gas in the temperature range from 35-150 ° C, preferably from 50-130 ° C, and in the pressure range from 1- 5 bar, preferably 2-4 bar,
• (b) the mixture obtained in the course of this reaction is separated into gaseous and liquid reaction products in a suitable apparatus, preferably designed as a scrubber / condenser,
  the gaseous products,
  preferably after a small portion has been discharged to avoid accumulation of gaseous by-products within the cycle,
  where valuable materials contained in this discharged portion can, at least in part, be recycled into the continuous process for the production of dimethyl carbonate by subsequent treatment,
  in a suitable apparatus for the regeneration of the methyl nitrile with methanol, oxygen and freshly added nitrogen oxide or nitrogen oxide equivalents,
  the gas mixture which contains the regenerated methyl nitrite is discharged at the top of this apparatus and in turn is fed to the production of dimethyl carbonate and water and any further liquid by-products or reaction auxiliaries which may be formed are discharged at the bottom of this apparatus and are preferably discharged after a subsequent recovery of the valuable substances contained therein
  and subjecting the liquid products to a distillative separation,
  which is characterized in that the entire liquid product mixture is first subjected to a first distillation which is carried out at a pressure of 5-15 bar, preferably 7-12 bar,
  the top product from this distillation is fed to a further distillation carried out at normal pressure or reduced pressure, preferably at 200-1500 mbar, in which a bottom product is a methanol-rich process which is used in the process for the production of dimethyl carbonate, preferably in the substep for the regeneration of the Methyl nitrite, is recycled, and in which a top product is obtained which, if appropriate together with other refluxes, is in turn returned to the first distillation,
• (c) and pure dimethyl carbonate is obtained by distillation of the mixtures obtained as the bottom outlet of the first distillation carried out under excess pressure.

2. The method according to claim 1, characterized in that one or more as catalysts Carrier substances, preferably on aluminum oxides, activated carbons, metal phosphates, zeolites Aluminum silicates and heteropolyacids, particularly preferably on aluminum oxides and activated carbons applied palladium-containing compounds, which may have further modifiers, Moderators, stabilizers or other additives were used. 3. The method according to any one of claims 1-2, characterized in that carbon dioxide as the inert gas, Nitrogen or argon, preferably nitrogen is used.   4. The method according to any one of claims 1-3, characterized in that the feed of the Recycle gas, oxygen, freshly added inert gas nitrogen oxides or nitrogen oxide equivalents and and at least a portion of the methanol in the to regenerate the methyl nitrite provided apparatus using a static mixer and / or one or more Single-substance or two-substance nozzles, preferably using a combination of one Static mixer and one or more single-substance or two-substance nozzles. 5. The method according to any one of claims 1-4, characterized in that the floor drain for the mixture resulting from the regeneration of the equipment functioning as methyl nitrite, preferably after Neutralization of acidic components contained therein, is sent to a distillation, in the case of aqueous waste as the floor drain and in the case of recyclable materials as the top product, preferably methanol and condensates containing dimethyl carbonate are obtained, which in the overall process, preferably in the reactor to regenerate the methyl nitrite and optionally in the pressure distillation to work up the product-containing floor drain of the Scrubber / condenser.