JP4904258B2 - Process for producing dialkyl carbonate - Google Patents

Description

The present invention relates to a process for producing a dialkyl carbonate (particularly a C ₁ -C ₃ dialkyl carbonate) in which the reaction and the separation of the reactant and the carbonate ester product are performed simultaneously. More specifically, the present invention relates to a method of reacting an alcohol with urea and / or alkyl carbamate in the presence of a complex compound catalyst. More particularly, the present invention relates to a method of removing feed stream impurities to obtain stable catalyst performance, improved reaction rates, and smooth downstream operation of the apparatus.

  Dialkyl carbonate is an important industrial compound, the most important of which is dimethyl carbonate (DMC). Dimethyl carbonate is used as a methylating agent or carbonylating agent and as a raw material for producing polycarbonate. Dimethyl carbonate can also be used as a solvent instead of a halogenated solvent such as chlorobenzene. Although the current price of dimethyl carbonate and diethyl carbonate is prohibitively high as a fuel additive, both can be used as oxygen additives in reformed gasoline and octane components. Dimethyl carbonate has a much higher oxygen content (53%) than MTBE (methyl tert-butyl ether) and TAME (tert-amyl methyl ether) and therefore requires very little to achieve the same effect. Dimethyl carbonate has a RON of 130 and is less volatile than MTBE and TAME. Dimethyl carbonate has a pleasant aroma and, unlike ether, is more easily biodegradable.

  In traditional industrial processes, dimethyl carbonate was produced from methanol and phosgene. Due to the intense toxicity and high cost of phosgene, various investigations have been made to develop better methods that are not based on phosgene.

  In one new industrial process, dimethyl carbonate is produced from methanol, carbon monoxide, molecular oxygen, and cuprous chloride via oxidative carbonylation in a two-stage slurry process. Such a method is disclosed in EP0460735A4. The major disadvantages of this method are the slow production rate, the high cost of separating the product and reactants, the formation of by-products, stringent recycling requirements, and corrosion-resistant reactors and processes. Is that the line is needed.

  Other new methods are disclosed in EP0742198A2 and EP0505374B1, and according to these patent documents, dimethyl carbonate is produced by forming methylnitrile instead of the above cupric methoxychloride. By-products are nitrogen oxides, carbon dioxide, methyl formate, and the like. The dimethyl carbonate in the product stream from the reactor is separated by solvent extraction distillation using dimethyl oxalate as a solvent so as to break the azeotrope. Although this chemistry seems simple but also improves production rates, many materials must be separated, materials must be balanced in the various flow sections of the process, process control The process is extremely complex due to the complexity of the process and the handling of methyl nitriles (hazardous chemicals).

  In other industrial processes, dimethyl carbonate is produced from methanol and carbon dioxide in a two-stage process. In the first stage, cyclic carbonates are produced by reacting epoxides with carbon dioxide (disclosed in US Pat. Nos. 4,786,741; 4,851,555; and 4,400,559). In the second stage, dimethyl carbonate is produced together with glycol by an exchange reaction between cyclic carbonate and methanol. For example, “Dimethyl Carbonate Production for Fuel Additives” by Y. Okada et al., “ACS, Div. Fuel Chem., Preprint, 41 (3), 868, 1996” and by John F. Knifton et al. ““ Ethylene Glycol-Dimethyl Carbonate Cogeneration ”, Journal of Molecular Chemistry, vol. 67, pp389-399, 1991”. Although this method has several advantages, the reaction rate of epoxide and carbon dioxide is slow, and the reaction requires high pressure. Furthermore, the exchange reaction between cyclic carbonate and methanol is limited by equilibrium, and methanol and dimethyl carbonate form an azeotrope, which makes separation difficult.

  As is well known, dialkyl carbonates can be used to form primary aliphatic alcohols (e.g. methanol) and urea in the presence of various heterogeneous catalysts and homogeneous catalysts (e.g. dibutyltin dimethoxide and tetraphenyltin). It can be produced by reacting (1). See, for example, “Synthesis of Carbonates and Polycarbonates by Reaction of Urea with Hydroxy Compounds”, C1 Mol. Chem., Vol. 1, pp95-108, 1984, by P. Ball et al. Ammonia is a by-product that can be recycled to urea as shown in the reaction sequence below (2).

  Carbamates are produced at lower temperatures and then dialkyl carbonates are produced at higher temperatures, with ammonia being generated in both steps.

As mentioned above, these two reactions are reversible under the reaction conditions. The order of the catalytic activity of the organotin compound is R ₄ Sn <R ₃ SnX << R ₂ SnX ₂ (wherein X = Cl, RO, RCOO, or RCOS). The use of dialkyltin (IV) compounds has been reported to have the highest reaction rate and the least by-product formation. For most catalysts (Lewis acids), higher catalytic activity is obtained when the reaction is carried out in the presence of a suitable promoter (Lewis base). For example, preferred cocatalysts for organotin (IV) catalysts (eg, dibutyltin dimethoxide, dibutyltin oxide, etc.) are triphenylphosphine and 4-dimethylaminopyridine. However, the thermal decomposition of the intermediate alkyl carbamates and ureas to isocyanic acid (HNCO) or isocyanuric acid ((HNO) ₃ ) and to alcohol or ammonia (a byproduct of urea decomposition) also results in dialkyl carbamates. Promoted by organotin compounds such as dibutyltin dimethoxide and dibutyltin oxide used in the synthesis. WO95 / 17369 discloses a process for producing dialkyl carbonate (eg, dimethyl carbonate) from alcohol and urea in two steps using the chemistry and catalyst described in the literature by P. Ball et al. In the first stage, an alcohol and urea are reacted to produce an alkyl carbamate. In the second stage, an alkyl carbamate and an alcohol are further reacted at a higher temperature than in the first stage to produce a dialkyl carbonate. These reactions are performed by using an autoclave reactor. However, when methanol reacts with methyl carbamate or urea, N-alkyl by-products such as methyl N-methyl carbamate (N-MMC) and N-alkyl urea are also produced according to the following reaction.

  In order to suppress the formation of by-products as much as possible, the dialkyl carbonate is present in the reactor in an amount of 1 to 3% by weight, based on the total content of carbamic acid ester and alcohol in the reactor solution.

  In US Pat. No. 6,010,976, dimethyl carbonate (DMC) is synthesized in high yield from urea and methanol in a single step in the presence of a high boiling point ether and a homogeneous tin complex catalyst.

The ether solvent also acts as a complexing agent to form a homogeneous complex catalyst in situ from dibutyltin dimethoxide or dibutyltin oxide.
The separation of materials associated with the DMC process is a critical issue for commercial reasons for DMC commercial production. EP0742198A1 and US Pat. No. 5,214,185 disclose the separation of DMC from a vapor mixture of methanol and DMC by using dimethyl oxalate (DMOX) as the extraction solvent. Since DMOX has a high melting point (54 ° C), the use of DMOX is inconvenient and requires extra costs for separation.

  Both urea and alcohol are highly hygroscopic. Urea contains ammonium carbamate impurities. Thus, water and ammonium carbamate are impurities in the urea and alcohol feeds. Impurities in the urea and alcohol feeds, such as water and ammonium carbamate, can cause catalyst deactivation in the cold spots of the cooling section (condenser) for overhead vapor streams from the reactor. It has been found that it causes clogging of the line. Water causes deactivation of catalysts containing alkoxy groups. For example, the methoxy group on the organotin complex compound molecule is highly reactive to water molecules, resulting in hydrolysis of the bond between the tin atom and the oxygen atom of the methoxy group. Ammonium carbamate clogs the cooling system (condenser) of the product vapor stream from the dialkyl reactor because of the problem that the back pressure must be controlled in the dialkyl carbonate production reactor and the deposition of ammonium carbamate. Cause the problem of waking up.

Simply put, the present invention
(a) supplying a stream containing urea, alcohol, water, and ammonium carbamate to the first reaction zone;
(b) in the first reaction zone,
(i) reacting water with urea to produce ammonium carbamate; and
(ii) decomposing ammonium carbamate from the reaction of ammonium carbamate in the feed with water and urea into ammonia and carbon dioxide;
Performing simultaneously;
(c) removing ammonia, carbon dioxide and the alcohol from the first reaction zone as a first overhead;
(d) removing urea and the alcohol from the first reaction zone;
(e) supplying the urea and the alcohol to a second reaction zone;
(f) reacting the alcohol with urea in the presence of a homogeneous catalyst containing an organotin complex compound of a dialkylmethoxide in a high boiling point solvent to produce a dialkyl carbonate; and
(g) removing the dialkyl carbonate and the alcohol from the second reaction zone;
Is an improved process for the production of dialkyl carbonates.

Dialkyl carbonate, an alcohol (preferably C ₁ -C ₃ alcohol), urea or alkyl carbamate or with both these, complexes (preferably dibutyltin the high boiling electron donor compounds and organotin compounds which act as solvents (Dialkoxide complex compound) and a reaction in the presence of an oxygen-containing high-boiling organic solvent, wherein the reaction is carried out in a reboiler of a still or simultaneously with dialkyl carbonate distillation. It is preferably carried out in a reactor equipped with a stirrer. The urea and alcohol feeds are purified by removing water, ammonium carbamate, N-alkylated by-products, and very little alkyl carbamate.

  Water is removed by reacting water and urea in a prereactor having a preliminary reaction zone. Ammonium carbamate is removed by decomposition into ammonia and carbon dioxide in a pre-reactor. Urea is further selectively converted to alkyl carbamates partially in the pre-reactor, resulting in faster reaction rates in the primary reactor and the main reaction from the dialkyl carbonate recovery unit or recovery tower. Alcohol recycle to the reactor is reduced and the concentration of dialkyl carbonate in the overhead stream from the main reactor is higher. The higher the concentration of dialkyl carbonate in the overhead stream from the main reactor, the lower the cost for separating the dialkyl carbonate.

  Water impurities in the urea feed and alcohol feed are removed by decomposing ammonium carbamate by decomposing it into ammonia and carbon dioxide in the pre-reactor, while reacting water and urea in the pre-reactor. Remove. The pre-reactor must be operated under conditions that favor decomposition, so that ammonia and carbon dioxide can be removed as vapors. If the decomposition is incomplete, unconverted ammonium carbamate flows into the main reactor and is converted to urea and water when it decomposes into ammonia and carbon dioxide, thus causing deactivation of the catalyst. Urea is partially converted to alkyl carbamate in the prereactor. The following required reactions occur in the prereactor:

Since the above four reactions are equilibrium reactions and must occur simultaneously in the pre-reactor pre-reaction zone, it is important to control the temperature and pressure of the pre-reactor and the main reactor. Reactions (1), (2), (3), and (4) are conducted in the pre-reactor in the liquid phase at a temperature of 200-380 ° F. (preferably 250-350 ° F.). A preferred range for the prereactor overhead pressure is about 30-300 psig. However, the overhead pressure mainly depends on the desired temperature of the prereactor column and the composition of the liquid in the reactor. Reaction (4) proceeds to an equilibrium state in the absence of a catalyst, but the catalyst [for example, dibutyltin dialkoxide catalyst or weakly acidic or weakly basic heterogeneous catalyst (for example, silica or high temperature (> 850 ° C.) Zinc oxide, tin oxide, titanium oxide, zirconium oxide, molybdenum oxide, talcite, calcium carbonate, zinc hydroxide carbonate, zirconium hydroxide carbonate, etc.) supported on an inert carrier such as calcined alumina) The reaction is faster. The preferred concentration of urea in the liquid phase in the pre-reaction zone under certain conditions is less than about 80% by weight, preferably less than 50% by weight. The partial pressure of ammonia and carbon dioxide must be kept below the decomposition pressure of ammonium carbamate to allow decomposition of ammonium carbamate. Furthermore, it is highly desirable to efficiently remove product, ammonia, and carbon dioxide from the prereactor zone of the prereactor, preferably as a vapor mixture, along with alcohol and optionally an inert stripping gas. If necessary, alcohol vapor can be used as the sole stripping gas. Accordingly, the present invention is an improved process for producing dialkyl carbonates by reaction of a reactant comprising urea and an alcohol and containing water and ammonium carbamate as impurities,
(a) supplying a reactant containing urea and alcohol to the main reaction zone;
(b) supplying a high-boiling solvent containing an electron-donating atom and an organotin compound to the main reaction zone; and
(c) in the main reaction zone,
(i) reacting an alcohol and urea in the presence of the high-boiling solvent containing an electron-donating atom and the organotin compound to produce a dialkyl carbonate; and
(ii) removing the dialkyl carbonate and ammonia from the main reaction zone as vapor;
Performing simultaneously;
Wherein the improvement is such that the water and urea are reacted to form ammonium carbamate and the reactants are first reacted in a pre-reaction zone under conditions such that the ammonium carbamate is decomposed into ammonia and carbon dioxide. And before supplying the reactants in step (a), ammonia and carbon dioxide from the reactants, preferably in the range of 200-380 ° F (more preferably 250-350 ° F). The use of a pre-reaction zone before the main reaction zone to remove water and ammonium carbamate from the reactants by removal at temperature, preferably in the liquid phase. In the preliminary reaction zone, it is preferable that urea and a part of the alcohol react to form an alkyl carbamate.

A preferred embodiment of the process for producing dialkyl carbonate is:
(a) supplying urea and C ₁ -C ₃ alcohol to the preliminary reaction zone;
(i) purify impurities in the feed in the pre-reactor;
(ii) removing ammonia, carbon dioxide, and alcohol as a vapor stream;
(iii) reacting urea with a portion of the alcohol to form an alkyl carbamate; and
(iv) withdrawing a liquid stream containing alkyl carbamate, urea and alcohol and introducing it into the main reaction zone;
(b) supplying a high-boiling solvent containing an electron-donating atom and an organotin compound to the main reaction zone;
(c) in the main reaction zone,
(i) C ₁ -C ₃ alcohol, urea, and the alkyl carbamate is reacted with the high boiling solvent containing the electron donor atom in the presence of said organotin compound, thereby generating a dialkyl carbonate; and
(ii) removing dialkyl carbonate, ammonia, ether, carbon dioxide, alkyl N-alkyl carbamate, and alkyl carbamate as vapor from the main reaction zone;
Performing simultaneously; and
(d) the alkyl N-alkylcarbamate separated from the vapor stream from the main reactor and the alkyl N-alkylcarbamate in the slight slip stream of the liquid reaction medium from the main reaction zone, In the third purification reaction zone, the heterocyclic compound ((RNCO) ₃ (wherein R is H or C _n H _{2n + 1} , and n is 1, 2, or 3)) is converted to Converting the alkyl carbamate to a dialkyl carbonate;
(i) removing the heterocyclic compound in the stream as a solid from the third reaction zone;
(ii) returning the reaming liquid stream to the main and purification reaction zones; and removing ammonia, alcohol, and dialkyl carbonate as overhead vapor streams;
including.

  This embodiment is for removing water and ammonium carbamate from the urea and alcohol, preferably at a temperature in the range of 200-380 ° F (more preferably 250-350 ° F), preferably in the liquid phase. Use a pre-reaction zone and a purification reaction zone to remove the by-product alkyl N-alkylcarbamate in the liquid phase at a temperature in the range of 300-400 ° F. and remove it as a solid from the system. Bring improvements including using.

  A preferred pre-reactor is a double diameter tower reactor. A feed solution obtained by dissolving urea in alcohol is introduced into the column prereactor in the middle section of the narrower diameter upper section. Decompose ammonium carbamate in urea feed into ammonia and carbon dioxide. The tower temperature is maintained at a temperature of about 200 ° F. to about 380 ° F. at a pressure of 50 to 350 psig. Light reaction products, ammonia and carbon dioxide, are removed from the tower as an overhead vapor stream along with alcohol vapor. Urea in the feed stream is at least partially converted to alkyl carbamate in the prereactor. This reaction is an exothermic reaction. The conversion rate of urea is 10% or more, preferably 50% or more. The conversion of urea to alkyl carbamate can be performed without the presence of a complex catalyst, but the conversion rate is faster when a catalyst is used.

  Removing water and ammonium carbamate impurities in the feed stream has some inherent problems in keeping the catalyst active (the problem of controlling distillation tower overhead pressure and cooling of the overhead vapor stream from the main reactor). The problem of clogging in the area caused by the accumulation of ammonium carbamate is eliminated. Purification of impurities in the feed takes place in a pre-reactor, which is a double diameter distillation tower reactor. Removing the impurities in the feed stream is the main purpose of the pre-reactor. Further improvements are achieved by converting at least a portion of the urea to alkyl carbamate in the prereactor. Because of this conversion, the reaction rate to produce dialkyl carbonate in the main reactor is faster and less alcohol is recycled from the dialkyl carbonate recovery unit to the main reactor (dialkyl carbonate in the overhead stream from the main reactor). (Because the concentration of is higher). When producing dialkyl carbonate, the higher concentration of dialkyl carbonate in the overhead stream from the main reactor reduces the cost of separating the dialkyl carbonate.

  The main reactor (where dialkyl carbonate is formed) is a tank reactor with a stirrer equipped with a heat exchanger to recover the latent heat of the product vapor stream from the main reactor. The recovered heat is used to recycle the alcohol from the alcohol recovery tower to the main reactor. Although mechanically stirring the liquid reaction medium is not necessary, it may be performed. In the present invention, the reaction / distillation column of the main reactor is operated in a different manner so that unwanted N-alkylation by-products are removed from the liquid reaction zone as part of the overhead product stream. The This makes it possible to keep the by-products as low as possible, thus keeping the reactor at a constant liquid level without filling the liquid reaction zone with undesired by-products without any interruption of the reactor operation for a long time. Can be operated. This is highly desirable for the successful commercial production of dialkyl carbonates. In order to minimize the rate of formation of N-alkylated by-products, lower concentrations of urea, alkyl carbamate, and dialkyl carbonate in liquid media are used. Minimizing the production rate is accomplished by using a higher concentration of high boiling solvent (eg, triglyme). However, if the concentration of alkyl carbamate is too low, DMC's unacceptably low space yield may occur.

  Simultaneously with continuous distillation of alkyl N-alkylcarbamate from the liquid reaction medium to prevent the accumulation of by-products (e.g. alkyl N-alkylcarbamates and heterocyclic compounds) in the main reactor. In particular, by adjusting the temperature and pressure of the vapor stream from the main reactor in the distillation column, the formation reaction of dialkyl carbonate can be achieved, and the alkyl N-alkylcarbamate can be converted into a heterocyclic compound. It has been found that this can be removed from the system as a solid. In other words, a constant concentration of alkyl N-alkylcarbamate and a heterocyclic compound in a given liquid reaction volume in the main reaction zone provides stable operating conditions for the station reactor. It was found that it can be held below. In addition, maintaining the surface temperature of all interiors of the main reactor below about 550 ° F (preferably below 450 ° F) minimizes the formation of heterocyclic compounds in the main reaction zone. It has been found very desirable. Conversion of the alkyl N-alkylcarbamate to the heterocyclic compound is performed by using a third purification reaction zone.

  A preferred clean-up reactor for this purpose is an agitated tank reactor equipped with an attached distillation column, a condenser, and a reflux drum. The by-product alkyl N-alkylcarbamate produced by alkylation of alkyl carbamate with dialkyl carbonate in the main reaction zone has a vapor temperature from the main reaction zone higher than about 255 ° F (preferably higher than 265 ° F). By operating at column temperature, it is continuously removed along with other products as part of the overhead vapor stream.

  The alkyl N-alkylcarbamate is separated from the overhead stream from the main reactor and introduced into the purification reactor. The purification reactor is preferably operated at a liquid reaction medium temperature in the range of 330-400 ° F. It is important to control the tower temperature and tower overhead pressure so that the overhead vapor stream does not contain alkyl N-alkyl carbamates. The purification reactor is generally operated at a reaction temperature that is at least 2 ° F. higher than the main reactor, and at an overhead pressure that is at least 5 psig higher.

  The method of removing by-products disclosed in the present invention is based on the prior art for producing dialkyl carbonate from urea and alcohol, regardless of whether a solvent is used in the main reactor and the purification reactor [eg, US Pat. No. 6,359,163B2]. No. (2002), WO95 / 17369 (1995), US Pat. No. 6,031,122 (2000), and EP1167339 (2002)].

  When producing heavier dialkyl carbonates, such as dipropyl carbonate or dibutyl carbonate, it is difficult to remove the alkyl N-alkylcarbamate from the main reactor as part of the overhead stream. Thus, a large amount of liquid slip stream is removed from the main reactor and sent to the purification reactor. The alkyl N-alkylcarbamate in this slip stream is converted to a high-boiling material that can be separated in a purification reactor as disclosed in the present invention. After removing the high boiling waste material in the bottom stream from the purification reactor, the remaining liquid stream can be returned to the main reactor and the purification reactor.

  A variety of physical devices can be used as the pre-reactor. Such physical devices include distillation column reactors, tank reactors with stirrers, bubble reactors, tubular reactors, boiling point reactors, or any combination thereof. A preferred apparatus is a distillation column reactor, in which the reaction takes place under reaction / distillation conditions. Despite the equilibrium properties of reactions (1), (2), and (3), using a distillation column reactor will drive these three reactions to the right (i.e., water and carbamic acid in the feed stream). Complete removal of the ammonium). Urea is partially converted to alkyl carbamate in a pre-reactor according to equilibrium reaction (4). By removing ammonia from the reaction zone as an overhead gas mixture, reaction (4) can be allowed to proceed to the right side of the reaction as well. Converting some of the urea to alkyl carbamate increases the rate of conversion of alkyl carbamate to dialkyl carbonate in the main reactor, resulting in a higher concentration of dialkyl carbonate in the overhead stream from the main reactor. Become. This is because the reaction between urea and alcohol to produce dialkyl carbonate occurs in two stages, and reaction (4) is the first stage.

  The reaction to produce dialkyl carbonate is as follows:

  Reaction (5) is carried out in a reaction / distillation mode in the main reactor in the presence of a high boiling solvent so as to create favorable conditions for the rapid removal of the dialkyl carbonate from the reaction medium as soon as the dialkyl carbonate is produced. Is called. The rate of producing dialkyl carbonate in the main reactor is more sensitive to the concentration of ammonia in the reaction medium in the main reactor than the rate of producing alkyl carbamate in the pre-reactor due to chemical thermodynamics. The rate of formation of the dialkyl carbonate is faster at lower concentrations of ammonia in the liquid reaction medium in the main reactor at a given concentration of alkyl carbamate. The temperature of the reaction medium in the main reactor is about 300 ° F. to about 450 ° F. (preferably about 320 ° F. to about 400 ° F.) under a pressure of about ambient pressure to 150 psig (preferably 30 to 120 psig). Most preferably from about 330 ° F. to about 360 ° F.). By selecting the appropriate high boiling solvent and by adjusting the concentration of the high boiling solvent in the main reactor, the desired temperature and pressure combination can be obtained that results in a high selectivity for dialkyl carbonate. . In order to recover the latent heat of the overhead vapor stream to be used to recycle the alcohol as superheated alcohol vapor to the main reactor and the pre-reactor, the main reactor is at least about 300 ° F (preferably about 320 ° F). It is highly desirable to operate with an overhead vapor temperature of

  When a high boiling point solvent is used in the main reactor, the reaction can be carried out in a liquid reaction medium under low pressure and low concentration of a carbamate. The lower the pressure, the faster the transfer of dialkyl carbonate from the liquid reaction medium to the gas phase, resulting in a lower concentration of dialkyl carbonate in the liquid reaction medium. The lower the concentration of dialkyl carbonate and carbamate / urea in the liquid reaction medium, the undesirable by-products associated with N-alkylation and the presence of urea, alkyl carbamate, and N-alkylated products in the main reactor. The amount of decomposition products is also reduced. Preferred solvents for synthesizing dialkyl carbonate must have the following properties: (1) the boiling point must be at least 20 ° F. higher than the boiling point of the dialkyl carbonate product; and (2) Do not form azeotropes with dialkyl carbonates. Examples of such solvents include high boiling ethers, ketones, hydrocarbons, esters, or mixtures thereof; triethylene glycol dimethyl ether; tetraethylene glycol dialkyl ether; anisole; dimethoxybenzene; dimethoxytoluene; alkyl oxalate; decalin Tetralin; xylene; decane; or a mixture thereof;

  As soon as the dialkyl carbonate is produced, the superheated alcohol vapor stream is introduced directly into the liquid reaction zone to provide reaction heat to convert the alkyl carbamate to dialkyl carbonate (this conversion reaction is somewhat endothermic). Remove dialkyl carbonate and ammonia from the liquid reaction medium. The desired total concentration of alkyl carbamate and urea in the reaction medium is about 10 to about 60% by weight (preferably about 15 to about 50% by weight) of the total material in the liquid reaction medium. The desired concentration of dialkyl carbonate in the reaction medium is about 0.5 to about 12% by weight (preferably about 2 to about 9% by weight) based on the total content of the liquid reaction medium. The molar ratio of alkyl carbamate to alcohol in the liquid reaction medium is 0.2: 1 to 2: 1 (preferably 0.3: 1 to 1.5: 1). The concentration of organotin complex catalyst is from about 2 to about 20% by weight as tin (preferably from about 5 to about 17% by weight as tin), based on the total content of all materials in the liquid reaction zone in the main reactor. . It should be noted that this catalyst also catalyzes the aforementioned unwanted side reactions. If the reaction is carried out at a lower temperature, there will be fewer side reactions. However, the rate of production of dialkyl carbonate is also slow, which is unacceptable for commercial production of DMC. The desired concentration of the high boiling point solvent in the reaction medium in the main reactor is about 2 to about 65% by weight (preferably about 2.5 to about 55% by weight) based on the total material in the reaction medium.

The catalyst that acts under steady-state reaction conditions is an organotin complex compound of dialkyltin dialkoxide R ′ _4-n Sn (OR) _n · xL (where R ′ is an alkyl group, aryl group, or aralkyl group) R is alkyl; n is 1 or 2; x is 1 or 2; L is a monodentate or bidentate ligand containing an electron-donating atom) Is an organotin complex catalyst system. Examples of L are ethers, esters, ketones, aldehydes, organic phosphines, or mixtures thereof; triethylene glycol dimethyl ether; tetraethylene glycol dimethyl ether; dimethyl oxalate; dimethyl malonate; dimethyl succinate; anisole; dimethoxybenzene; Ethylene glycol; catechol; 1,4-dioxane-2,3-diol; 2-methyltetrahydrofuran-3-one; 2,3-pentanedione; 2,4-pentanedione; 3-methyltetrahydropyran; or triphenyl An electron-donating ligand molecule such as phosphine; A homogeneous catalyst system is a quasi-equilibrium mixture of various organotin species. Suitable catalysts of this type and their preparation are described in US Pat. Nos. 6,010,976 and 6,392,078, the entire disclosures of these patents are hereby incorporated by reference.

  The catalyst system operating under steady state reaction conditions is a mixture of various soluble organotin monomer species, organotin dimer species, and organotin oligomer species. These various organotin catalyst species are in a quasi-equilibrium state to some extent under the given reaction conditions. Dialkyltin oxide, dialkyltin halide, dialkyltin bis (acetylacetonate), and dialkyltin carboxylate (for example, dibutyltin diacetate, dialkyltin oxalate, dibutyltin malonate, dibutyltin diacetate, or dibutyltin bis (acetylacetonate) Etc.] can be used to react with alcohol in the presence of a high boiling solvent (eg, triglyme) to produce in situ soluble tin complex catalyst species at the start of the main reactor. The alkyl groups bonded to the tin atom may be the same or different. For example, the catalyst precursor may be a dialkoxide, dihalide, hydroxyhalide, diacetate, or oxide of dibutyltin, butylbenzyltin, butylphenyltin, butyloctyltin, or di-2-phenylethyltin. By-products such as water, carboxylic acid, or hydrochloric acid are continuously removed as an overhead vapor stream from the liquid reaction medium in the presence of a high boiling solvent at low pressure. A suitable temperature for the catalyst formation reaction is about 200 to about 400 ° F. and a suitable pressure is 150 psig from ambient pressure. In a preferred embodiment, methanol, ethanol, or propanol is continuously pumped into the main reactor, depending on the intended dialkyl carbonate product type. For the production of MEC, methanol or ethanol can be used. The catalyst formation reaction is advantageously carried out in the main reactor in the presence of a dilute solution of alkyl carbamate, alkyl N-alkyl carbamate, or dialkyl carbonate. Needless to say, during this catalyst formation reaction, the operation of the distillation column allows the removal of by-products water, carboxylic acid, or hydrogen chloride as an overhead stream with alcohol as overhead product from the reaction zone. Must be operated under such conditions. In the case of dimethyl carbonate production, the soluble organotin complex catalyst system forms dibutyltin dimethoxide and triglyme (organotin complex catalyst in the main reactor) before initiating the dialkyl carbonate formation reaction in the presence of a high boiling solvent. As a complexing agent) and methanol. For the production of diethyl carbonate, the soluble organotin complex catalyst system is preferably made by using dibutyltin dimethoxide with triglyme and ethanol in the main reactor. As the reaction proceeds, the catalyst replaces the methoxy group with an ethoxy group.

FIG. 1 shows a simplified flow diagram of one embodiment of the present invention. Figure 1 is an improved process flow diagram with the DMC separation unit removed. The DMC separation unit is shown in FIG. The reaction / distillation column reactor 111 is used as a pre-reactor to remove impurities in the feed stream and to partially convert urea to methyl carbamate. The urea solution is made by mixing urea feed 1 and methanol stream 3 in drum 131. The methanol stream consists of a fresh methanol feed stream 2 and a methanol recycle stream 4 (part of the methanol recycle stream 30 from the DMC separation unit). The methanol recycle stream 30 from the DMC separation unit (shown in FIG. 2) is divided into three streams (4, 33 and 32 via 31), drum for making urea solution, main reactor 112. , And sent to the purification reactor 113. The urea solution feed 5 from the drum 131 is introduced into the center of the narrower column section above the double diameter distillation column reactor 111. Reactor 111 acts as a pre-reactor to purify impurities (water and ammonium carbamate) in the methanol and urea feeds and to convert some of the urea to MC. The vapor stream 6 from the pre-reactor 111 contains ammonia, carbon dioxide, and methanol. The purified mixed solution in which MC and urea are dissolved in methanol is removed from the pre-reactor 111 as a bottoms liquid stream 7, which is connected via line 20 to the recirculated liquid stream 22 from the cooling / filter system 133. Merge to flow 8. The liquid recycle stream 20 from the chiller / filter system 133 is split into two streams (21 and 22) and recycled to the main reactor 112 and the purification reactor 113. The combined stream 8 is introduced into the main reactor 112 (reactor with stirrer or bubble column reactor if necessary) 112. Recycled methanol stream 33 from the DMC separation unit is introduced into main reactor 112 as superheated methanol vapor. Overhead recycle stream 14 from flash column 132 is introduced into the main reactor. Stream 14 contains the majority of MC, a small amount of N-MMC, and a small amount of methanol. Overhead vapor stream 9 from the primary reactor 112 includes ammonia, CO _2, dimethyl ether, methanol, DMC, MC, N-MMC , TG, and a small amount of organotin catalyst. Overhead stream 9 from main reactor 112 is combined with overhead stream 17 from clarified tank reactor 113 with stirrer to stream 10. Stream 17, comprising ammonia, CO _2, dimethyl ether, methanol, and DMC. Combined stream 10 is introduced into distillation column 151 to separate the components ammonia, CO ₂ , dimethyl ether, methanol, and DMC from the remaining heavy components in the stream. Overhead stream 12 from column 151 is combined with overhead stream 6 from prereactor 111 to stream 23. This combined stream 23 is introduced into the distillation column 134. Overhead stream 25 from column 134 is sent to an ammonium carbamate removal system 135 where stream 25 is appropriately cooled to react CO ₂ and ammonia to ammonium carbamate and precipitate solid ammonium carbamate. Solid ammonium carbamate can be removed by using a filter or a hydroclone. Stream 27 from ammonium carbamate removal system 135 is introduced into distillation column 136 to recover ammonia. Overhead stream 28 from tower 136 is sent to an ammonia storage tank. The bottom liquid stream 29 from the column 136 is organic waste and is composed almost of dimethyl ether. The bottom liquid stream 24 from the column 134 is sent to the DMC separation unit shown in FIG. Stream 24 contains DMC and methanol. The bottom liquid stream 13 from the column 151 is sent to the flash column 132. Stream 13 contains methanol, MC, N-MMC, TG, and a small amount of catalyst. The bottoms liquid stream 15 from the flash column 132 contains N-NMC, MC (small amount), TG, and a small amount of organotin catalyst. Stream 15 is combined with a small amount of liquid slip stream 11 from the main reactor 112 to form stream 16. A combined stream 16 is introduced into the purification reactor 113 (if desired, a small amount of slip stream 11 from the main reactor 112 can be introduced into the lower section of either column 151 or 132). Cool the bottoms liquid stream 18 from the purification reactor 113 to precipitate the heterocyclic compound in the stream (for example, isocyanuric acid, 1,3,5-trimethyltriazine-2,4,6-trione, etc.). This precipitate is removed from the filtration system 133 as a solid via line 19. Filtrate stream 20 from filtration system 133 is split into two streams 21 and 22 and recycled to main reactor 112 and purification reactor 113.

  Depending on the production capacity of the dialkyl carbonate, the main reactor may be a tank reactor equipped with a single stirrer or a tank reactor equipped with a plurality of stirrers. For example, if the main reactor consists of a series of three tank reactors with stirrers, the purified alkyl carbamate / urea feed stream 7 from the pre-reactor 111 is divided into three streams, It is appropriate to introduce the stream directly into the three reactors. A liquid reaction stream is removed from each reactor and introduced into the next reactor. The liquid reaction stream from the third reactor is sent to the first reactor. A small amount of slip stream from the liquid reaction stream from the third reactor is combined with the bottom liquid stream 15 from column 132 to form stream 16 and this stream 16 is sent to purification reactor 113. An alcohol recycle stream (eg, methanol recycle stream 33 from the DMC separation unit) is introduced into the first reactor as superheated alcohol vapor. The overhead vapor stream from the tank reactor with the first stirrer is introduced into the second reactor. An overhead vapor stream from the second reactor is introduced into the third reactor. The content of dialkyl carbonate in the overhead stream from each reactor increases as the vapor stream moves from the first reactor to the third reactor, resulting in the overhead stream from the third reactor. DMC concentration is highest. Overhead stream 9 from the third reactor is combined with overhead stream 17 from purification reactor 113 to form stream 10, which is introduced into distillation column 151.

  The bottoms liquid stream 24 from the distillation column 134 is sent to a DMC separation unit (see FIG. 2). This stream contains about 28% by weight of DMC. Stream 24 from column 134 is introduced into extractive distillation column 137 via line 34. Overhead stream 35 (containing about 98 wt% methanol and about 2 wt% DMC) is recycled through line 30 in FIG. Column bottom liquid stream 36 is introduced into an extractive solvent recovery column 138. Anisole, the extraction solvent, is recovered from column 138 as a bottoms liquid stream 38 and recycled to column 137 via line 38. Overhead stream 37 from column 138 is DMC product, which is sent to the DMC storage tank.

  Diethyl carbonate (DEC) can be produced in a manner similar to that described for the production of DMC. Since the mixture of ethanol and DEC does not form an azeotrope, separation of DEC from ethanol can be performed in a single distillation column.

FIG. 3 is a simplified flow diagram of the DEC manufacturing process. A urea solution is made by mixing urea feed 101 and ethanol stream 103 in drum 141. Ethanol stream 103 includes fresh ethanol feed 102 and ethanol recycle stream 155 (which is part of ethanol recycle stream 130). The ethanol recycle stream 130 includes an overhead stream 117 from the distillation tower 146 and a bottoms liquid stream 129 from the distillation tower 145 (ethanol recovery tower). The ethanol recycle stream 130 is split into two streams 152 and 156. Stream 152 is recycled to purification reactor 123. Stream 156 is also divided into two streams 155 and 157 which are recycled to drum 141 and main reactor 122, respectively. Ethanol recycle stream 157 is introduced into main reactor 122. The urea solution 104 from the drum 141 is introduced into the center of the upper narrower section of the double diameter column reactor 121. The reactor 121 acts as a preliminary reactor for purifying impurities (water and ammonium carbamate) in the feed ethanol and urea, and for converting part of the urea into EC. The vapor stream 105 from the pre-reactor 121 contains ammonia, carbon dioxide, and ethanol. The purified mixed solution is withdrawn from the preliminary reactor 121 as a bottom liquid stream 106. Stream 106 is introduced into a main reactor 122 (tank reactor with stirrer or bubble column reactor as required) 122. A recirculated ethanol stream 157 (which is the main part of the ethanol recycle stream 130) is introduced into the main reactor 122 as superheated ethanol vapor. A small amount of slip stream 108 from the main reactor 122 is combined with the bottoms liquid stream 120 from the DEC recovery tower 147 to form a stream 161, which is introduced into the purification reactor 123. Slip stream 108 is ethanol, ammonia, diethyl ether, DEC, ethyl carbamate, ethyl N-ethyl carbamate, TG, heterocyclic compounds (e.g. isocyanuric acid or 1,3,5-triethyltriazine-2,4, 6-trionto etc.), and organotin complex catalysts. Stream 120 contains ethanol, ethyl carbamate, ethyl N-ethyl carbamate, TG, and traces of catalyst. Overhead stream 160 from clean-up reactor 123 includes ammonia, CO _2, diethyl ether, ethanol, and DEC. The bottoms liquid stream 159 from the purification reactor 123 contains ethyl carbamate, triglyme, ethyl N-ethylcarbamate, ethanol, a heterocyclic compound, and a homogeneous organotin catalyst. The bottoms liquid stream 159 from the reactor 123 is cooled in a cooling / filter system 148 to precipitate the heterocyclic compound. Precipitated solid by-products are removed from system 148 via line 124. Liquid stream 125 from system 148 is split into two streams 126 and 127 and recycled to main reactor 122 and purification reactor 123. Overhead stream 107 from main reactor 122 is merged with overhead stream 160 from purification reactor 123 into stream 109. Overhead vapor stream 107 from primary reactor 122, ammonia, CO _2, diethyl ether, ethanol, ethyl carbamate, ethyl N- ethyl carbamate, DEC, TG, and a trace amount of catalyst, the flow 107 clean-up reactor Merge with overhead stream 160 from 123 into stream 109. Overhead stream 160 includes ammonia, CO _2, diethyl ether, ethanol, and DEC. Combined stream 109 is introduced into distillation column 142. An overhead stream from column 142 (containing ammonia, CO ₂ , diethyl ether, and ethanol) is introduced into distillation column 143. Overhead stream 154 from column 143 is cooled to cause the reaction of CO ₂ and ammonia to produce ammonium carbamate. Ammonium carbamate is precipitated in liquid ammonia and removed as a solid via line 115 from the chiller / filter system 144. Liquid ammonia stream 116 from cooling / filter system 144 is sent to an ammonia storage tank. The bottoms liquid stream 150 from column 142 contains DEC, ethanol, ethyl carbamate, ethyl N-ethyl carbamate, TG, and traces of catalyst. Stream 150 is introduced into distillation column 146 (first ethanol recovery column). Overhead ethanol stream 117 from column 146 is combined with ethanol bottoms stream 129 from distillation column 145 (second ethanol recovery column) to form ethanol recycle stream 130. Column bottom liquid stream 118 from column 146 is introduced into distillation column 147 (DEC recovery column). Overhead stream 119 is product DEC, which is sent to the DEC storage tank. The bottoms liquid stream 120 from the column 147 is merged with a small amount of slip stream 108 from the main reactor 122 and the merged stream 161 is introduced into the tank purification reactor 123 with stirrer. Overhead stream 160 (containing ammonia, CO ₂ , diethyl ether, ethanol, and DEC) is sent to column 142 via line 109. A bottoms liquid stream 114 from column 143 is sent to distillation column 145 to separate diethyl ether from ethanol in the stream. Overhead ether by-product stream 128 is sent to an ether storage tank. The bottoms liquid stream 129 from column 145 is ethanol which is recycled to purification reactor 123 and main reactor 122 via line 130.

  Instead of methanol feed or ethanol feed to the drum to prepare the urea solution, mixed dialkyl carbonates such as methyl ethyl carbonate (MEC) can be obtained by using a suitable mixture of methanol and ethanol as the feed stream. can get. However, the overhead stream from the main reactor and the purification reactor contains some DMC and DEC in addition to MEC. DEC and DMC are separated from the mixture, and DEC and DMC are exchanged into MEC in a separation reactor (not shown). This exchange reaction can be carried out in the presence or absence of a solvent in the presence of a heterogeneous base catalyst (eg, an alkaline form of zeolite or basic talcite), a homogeneous catalyst (eg, IVB By using a group element compound (eg, titanium tetraethoxide or titanium ethoxycarbonate), a dialkyltin compound (eg, alkoxide, dialkyltin methoxyalkyl carbonate, or dialkyltin carbonate), or the organotin complex catalyst described above Suitable solvents are those having a boiling point above about 265 ° F. Examples of such solvents include decalin, decane, xylene, diglyme, triglyme, or mixtures thereof.

  FIG. 4 shows a reaction / distillation column reactor using a basic heterogeneous catalyst. The DEC feed is introduced into the reaction / distillation column reactor 153 via line 221 at the location of the upper section of the catalyst bed. DMC feed is introduced into column 153 via line 222 at a position below the catalyst bed. Overhead stream 223 is mostly composed of DMC and MRC. Stream 223 is sent to the MEC separation unit. The temperature of the liquid catalytic reaction zone is maintained at a temperature in the range of about 200 ° F. to about 450 ° F. (preferably 235 ° F. to 380 ° F.). A small amount of bottom liquid is withdrawn from line 224 to prevent heavy material from accumulating in the reboiler of column reactor 153.

  FIG. 5 shows a tank catalyst reactor 158 with a stirrer fitted with a distillation column 162. A homogeneous catalyst such as dibutyltin dimethoxide is used. A predetermined amount of homogeneous catalyst is charged into the reactor 158 before the reaction. The DEC / DMC mixed feed is introduced into reactor 158 via line 301. Overhead stream 303 from column 162 is mostly composed of DMC and a small amount of MEC is recycled to reactor 158. A side draw stream 302 (concentrated with MEC) from distillation column 162 is sent to distillation column 163 to separate MEC from DMC. Overhead stream 304 from column 163 is recycled to reactor 158. MEC bottoms stream 305 from column 163 is sent to the MEC storage tank. The temperature of the liquid catalytic reaction zone is maintained at a temperature in the range of about 200 ° F. to about 450 ° F. (preferably 235 ° F. to 380 ° F.). The overhead pressure range for column 162 is from about 20 psig to about 150 psig (preferably from about 25 psig to about 120 psig). However, the overhead pressure of column 162 depends on the intended temperature of the liquid reaction medium in reactor 158, the composition of the reaction medium, and whether a solvent is used.

(Example 1)
In this embodiment, the reaction between water and urea is performed. In a 500 ml three-necked flask equipped with a magnetic stirrer and a water-cooled reflux condenser, charge the following materials: 229.67 g triethylene glycol dimethyl ether (triglyme), 1.58 g water, 2.06 g methanol, and 15.89 g urea. . When the reaction temperature of the mixture in the flask reaches about 100 ° C., an additional 3.2 g of methanol is added. The reaction between water and urea is carried out at a temperature of 128 ° C. to 140 ° C. for 0.92 hours under a nitrogen atmosphere. A sample is removed from the flask and analyzed by GC and HPLC. The analysis results show that the conversion rate of urea is 22.4% and the conversion rate of water is 45.2%.

(Example 2)
General description of the experiment
A 1 liter autoclave with stirrer serves as the reaction zone and reboiler for the reaction / distillation column reactor, which is connected to a 1 inch diameter by 3.5 foot long distillation column. The distillation column has three zone heaters, which are independently controlled. The overhead vapor stream from the distillation column is diluted with a nitrogen stream (800 cc / min) and then cooled to some 200 ° F. with warm water in a condenser. Cool the vapor stream from the condenser to ambient temperature to prevent clogging problems with cold spots and overhead back pressure regulators. The liquid stream from the condenser flows to a small overhead liquid reflux drum. Maintain the temperature of the liquid reflux drum at ambient temperature. The liquid product flow from the overhead reflux drum is monitored with an LFM (liquid flow meter). The liquid stream from the overhead reflux drum and the cooled vapor stream are combined as the product stream from the reaction / distillation reactor. A sample for analysis is taken to examine the composition of the overhead vapor stream exiting the tower. In addition, samples are sometimes taken from the reboiler to monitor the composition of the liquid reaction medium. Whenever a sample is taken from the reboiler, the make-up solution is pumped to compensate for the loss of triglyme and catalyst. During the operation of the reactor, the liquid level in the reboiler is maintained at a constant level. A vertical viewing window is attached to the reboiler to visually observe the liquid level inside the reboiler during operation. In addition, a liquid level digital monitor is attached to the reboiler to automatically control the reactor during unattended operation at night and on weekends.

To operate the main reactor to produce DMC, the MC feed solution (methyl carbamate in methanol) and the methanol feed are pumped and merged into a single stream. The combined feed stream is passed through a pre-reactor (vertically attached tubular reactor upflow) at 300 ° F. and 230 psig to remove water in the feed stream and then introduced into the main reactor. The temperature of the liquid reaction medium is controlled by adjusting the overhead pressure of the distillation column and the concentration of the high-boiling solvent in the reboiler of the distillation column. The products DMC, ammonia, and other light products (eg, dimethyl ether and CO ₂ ) are distilled off from the liquid medium and carried away with methanol vapor. The operation of the distillation column is performed in a different manner so as to achieve partial condensation of the vapor coming out of the liquid medium in the reboiler without controlling the liquid temperature from the overhead reflux drum by controlling the temperature of the vapor. . The steam temperature is controlled by controlling the zone temperature of the tower with three tower zone heaters as the steam is coming up the distillation tower. This unusual tower operation keeps the triglyme solvent in the reactor and removes the by-product N-MMC along with the MC from the liquid reaction medium as part of the overhead stream, thereby allowing the reactor to remain in the reactor for an extended period of time. It was found that driving is possible. It has been found that the absence of liquid reflux from the overhead reflux drum is highly preferred in order to minimize the formation of by-products N-MMC and heterocyclic compounds. The reaction / distillation column reactor could be operated for more than 1000 hours without interruption until the high pressure nitrogen valve to the reboiler was accidentally opened. When the distillation column is operated in a conventional manner, reboiler formation due to deposition of reaction byproducts (eg, N-MMC, cyanuric acid, and TTT (1,3,5-trimethyltriazine-2,4,6-trione), etc.) Overflow causes shutdown and removal of material from the reboiler.

Other important factors to minimize side reactions while maintaining an acceptable DMC production rate are solvent and catalyst concentrations, liquid medium temperature, and overhead column pressure. Reboiler temperature and overhead tower pressure ranges for optimum operation are about 330 ° F to about 355 ° and about 80 psig to about 110 psig, respectively.

Detailed description of the experiment The reboiler of the distillation column was charged with the following materials: 285 g of triglyme, 100 g of methanol, and 100 g of dibutyltin dimethoxide. A 13.3% wt methanol solution of MC (approximately 280 ppm H ₂ O) is applied to the liquid reaction medium in the reboiler at a constant rate of 3.01 ml / min and methanol (approximately 80 ppm H ₂ O) at approximately 1.92 ml / min. Reaction / distillation column reactor, pumping at 345 ° F, 260 ° F for the vapor temperature of the upper section of the distillation column, and 90.8 psig for the column overhead pressure Steady-state operation was obtained. The methanol flow rate was adjusted to maintain a constant temperature of 345 ° F. with respect to the liquid reaction medium. The stirring speed of the reboiler was 300 rpm. Under this operating condition, the overhead product stream contained ammonia, dimethyl ether, carbon dioxide, DMC, MC, N-MMC, water, unknowns, and traces (about 1000 ppb) of catalyst. An overhead sample and a bottom liquid sample were collected at a flow time of 926 hours. Table 1 shows the analysis results of these samples. Interestingly, the DMC weight percent based on the MC / CH ₃ OH molar ratio and the total weight of MC and CH ₃ OH in the reactor liquid medium is 1.01 and 4.49 weight percent, respectively, These values are comparable to 2-10 and 1-3% by weight claimed in US Pat. No. 5,561,094 (1996, EXXON Chem). The result of this experiment corresponds to a conversion of MC to DMC of 95 mol% or more. This experimental data is used to perform computer simulations for process design.

(Example 3)
Using a 1 liter reactor equipped with a distillation column (autoclave) with a stirrer, impurities in the 8.03% by weight methanol solution of urea were removed, and urea was converted to methyl carbamate. The reactor was not charged with catalyst. The experiment was conducted by pumping the urea solution into the reactor at a rate of 4 ml / min for 27 hours at a constant bottom liquid flow rate of 2 ml / min and at a constant bottom liquid flow rate of 1.5 ml / min. Experiments were conducted at 315 ° F. at 200 psig and 328 ° F. at 230 psig by pumping the urea solution through the reactor at a rate of 3 ml / min to the end (146 hours for flow time). The distillation column was operated with the overhead refluxed. During operation, the overhead flow was adjusted to keep the liquid level in the autoclave constant (50% of the total). The tower was operated using overhead reflux from an overhead reflux drum. The average MC concentration in the bottoms stream from the autoclave is about 20%, which corresponds to a conversion of urea to MC of about 97%. The urea feed contained about 2000 ppm water. The bottoms product on average contained 375 ppm water at 315 ° F and 300 ppm water at 328 ° F.

(Example 4)
The purpose of this experiment is to describe a main reactor system composed of a plurality of reactors. To clarify the function of the second main reactor, the same experimental equipment as in Example 2 was used. This experiment was performed in a manner similar to that in Example 2. This example differs from Example 2 in that an 8 wt% methanol solution of DMC is used in place of the simple methanol in Example 2 and the overhead pressure in the distillation column is somewhat lower (88 psig).

The following materials were charged to the reboiler of the distillation column: 285 g triglyme, 40 g methanol, and 100 g dibutyltin dimethoxide. The steady state operation of the distillation column reactor was accomplished while pumping MC solution and DMC-methanol solution into the reactor. The temperature of the liquid reaction medium in the reboiler was 345 ° F, the distillation column temperature was about 278 ° F, and the overhead column pressure was 88 psig, and the reactor was operated for over 1500 hours without interruption. Table 2 shows the average composition of the overhead product from the reactor and the bottom liquid product during the 54-hour on-stream-time from 1428 to 1482 hours. During this time, pumping rate of 22.5 wt.% MC solution (H ₂ O to about 590 ppm) was fixed at 1.97 ml / min at 345 ° F, the feed pump 8 wt% DMC solution (H ₂ O of 80 ppm) The speed was fixed at 3.2 ml / min at 345 ° F. The molar ratio of MC / CH ₃ OH, and DMC wt% when the total weight of the MC and of CH ₃ OH in the reactor liquid medium as a reference were respectively 0.915 and 6.40% by weight. The result of this experiment corresponds to a conversion of MC to DMC of 93 mol% or more.

(Example 5)
The purpose of this experiment is to explain the production of diethyl carbonate (DEC). DEC was prepared by reacting ethyl carbamate (EC) with ethanol. This experiment was performed in a manner similar to that in Example 2. Instead of the MC solution and methanol in Example 2, an ethanol solution of carbamic acid and ethanol were used, respectively. The following materials were charged to the reboiler of the distillation tower: 180 g triglyme, 100 g ethanol, and 100 g dibutyltin dimethoxide. While the ethyl carbamate (EC) solution is pumped at a constant flow rate and the temperature of the liquid reaction medium is kept constant, the ethanol pumping speed is adjusted and steady state operation of the distillation column reactor is achieved. It was done. The reaction in the reboiler is about 345 ° F, the distillation column temperature is about 282 ° F, and the constant overhead pressure of 66 psig with an autoclave stirring speed of 300 ppm for 340 hours without interruption. Continued operation of the vessel. The pumping rate of 15.35 wt% EC solution (about 275 ppm H ₂ O) was fixed at 2.69 ml / min and the average pumping rate of ethanol (about 106 ppm H ₂ O) was fixed at 2.36 ml / min. The overhead vapor stream and nitrogen diluent gas (600 cc / min) were mixed at the top of the column and then cooled to about 200 ° F. in a water cooled condenser. Table 3 shows the average composition of the overhead product and the bottom liquid product for the whole experiment. At the end of the experiment, 74.2 g of solid material was removed from the reactor. This material was a mixture of heterocyclic compounds and contained 670 ppm Sn on a weight basis. From the analysis results of the bottom liquid product in Table 3, the EC / C ₂ H ₅ OH molar ratio and the DEC weight% based on the total weight of EC and ethanol in the liquid medium in the reactor were 0.939, respectively. And 11.08% by weight. The mass balance and urea molar balance for the entire experiment were 102% and 101%, respectively. The experimental results show that the conversion of EC is 57.5% and the selectivity from EC to DEC is 91 mol%. The result of this experiment is, in other words, a DEC space yield of 1.60 lb / hr / ft ³ .

2 is a simplified flow diagram of one embodiment for manufacturing a DMC according to the present invention. 4 is a simplified flow diagram of a DMC separation unit. 1 is a schematic diagram of one embodiment of manufacturing a DEC according to the present invention. 2 is a simplified flow diagram of an embodiment of a reaction / distillation column reactor for the production process of the present invention. 2 is a simplified flow diagram of an embodiment of a catalyst tank reactor with a stirrer fitted with a distillation column for the production process of the present invention.

Claims (20)

(a) supplying a stream comprising urea, alcohol, water, and ammonium carbamate to the first reaction zone;
(b) in the first reaction zone,
(i) reacting water with urea to produce ammonium carbamate; and (ii) decomposing ammonium carbamate into ammonia and carbon dioxide;
Performing simultaneously;
(c) removing ammonia, carbon dioxide and alcohol from the first reaction zone;
(d) removing urea and alcohol from the first reaction zone;
(e) supplying the urea and alcohol to a second reaction zone;
(f) a step of reacting an alcohol with urea in the presence of a homogeneous catalyst containing an organotin complex compound in a high-boiling solvent to produce a dialkyl carbonate , wherein the high-boiling solvent comprises the above-mentioned Boils at a temperature at least 20 ° F. (11.1 ° C.) higher than the boiling point of the dialkyl carbonate, does not form an azeotrope with the dialkyl carbonate, and is selected from ethers, ketones, hydrocarbons, esters, or mixtures thereof And the organotin complex compound is R ′ _4-n Sn (OR) _n · xL (where R ′ is an alkyl group, an aryl group, or an aralkyl group, R is an alkyl, and n is 1 or 2; x is 1 or 2; and L is selected from ethers, esters, ketones, aldehydes, organic phosphines, or mixtures thereof ; And
(g) removing the dialkyl carbonate and alcohol from the second reaction zone;
A process for producing a dialkyl carbonate comprising   The production method according to claim 1, wherein an alcohol and urea react to produce an alkyl carbamate in the first reaction zone. Wherein the alcohol is C ₁ -C ₃ alcohol, the production method according to claim 1. (a) supplying the stream containing urea, methanol, water, and ammonium carbamate to the first reaction zone;
(b) in the first reaction / distillation zone,
(i) reacting water with urea to produce ammonium carbamate;
(ii) decomposing ammonium carbamate from the reaction of ammonium carbamate in the feed with water and urea into ammonia and carbon dioxide; and
(iii) separating ammonia, carbon monoxide and methanol from urea by distillation;
Performing simultaneously;
(c) removing ammonia, carbon dioxide and methanol from the first reaction / distillation zone as a first overhead;
(d) removing urea and methanol from the first reaction / distillation zone as a first bottom liquid;
(e) supplying the first bottom liquid and methanol to a second reaction / distillation zone;
(f) in the second reaction / distillation zone,
(i) reacting methanol and urea in a high boiling point solvent in the presence of a homogeneous catalyst containing an organotin complex compound to form dimethyl carbonate;
and
(ii) separating dimethyl carbonate and ammonia from the homogeneous catalyst by distillation;
Wherein the high boiling solvent boils at a temperature at least 20 ° F. (11.1 ° C.) higher than the boiling point of the dimethyl carbonate and does not form an azeotrope with the dimethyl carbonate; And selected from ethers, ketones, hydrocarbons, esters, or mixtures thereof, and the organotin complex compound is R ′ _4-n Sn (OR) _n · xL (where R ′ is an alkyl group, aryl Or an aralkyl group, R is methyl, n is 1 or 2, x is 1 or 2, and L is an ether, ester, ketone, aldehyde, organic phosphine, or these Selected from a mixture) ;
(g) removing dimethyl carbonate and methanol from the second reaction / distillation zone as a second overhead; and
(h) removing the second bottom liquid from the second distillation column reactor;
The manufacturing method of Claim 1 containing this.   The manufacturing method according to claim, wherein dimethyl carbonate in the second overhead is separated from methanol by extractive distillation.   The method of claim 4, wherein an inert diluent is added to the first overhead.   Methanol in the first overhead is condensed, a portion of the condensed methanol is returned as a reflux near the top of the first distillation column reactor, and the remainder of the condensed methanol is returned to the first The manufacturing method of Claim 4 which returns to the lower part of a distillation column reactor.   Supplying a first portion of the second bottoms liquid to the first distillation column reactor and recirculating a second part of the second bottoms liquid to the second distillation column reactor; And a third portion of the second bottom liquid is fed to a third distillation column reactor for catalyst regeneration and heavy material purification.   The production method according to claim 4, wherein the second overhead is condensed and a part of the condensed second overhead is returned to the second distillation column reactor as a reflux. (a) supplying a stream containing urea, methanol, water, and ammonium carbamate to a first distillation column reactor;
(b) in the first distillation column reactor,
(i) reacting a part of the urea with a part of the methanol to form methyl carbamate;
(ii) reacting water with urea to produce ammonium carbamate;
(iii) decomposing ammonium carbamate from the reaction of ammonium carbamate in the feed with water and urea into ammonia and carbon dioxide; and
(iv) separating ammonia, carbon monoxide and methanol from urea and methyl carbamate by distillation;
Performing simultaneously;
(c) removing ammonia, carbon dioxide and methanol from the first distillation column reactor as a first overhead;
(d) extracting urea and methyl carbamate from the distillation column reactor as a first bottom liquid;
(e) supplying the first bottom liquid and methanol to a second distillation column reactor;
(f) in the second distillation column reactor,
(i) reacting methanol and urea in a high boiling point solvent in the presence of a homogeneous catalyst containing an organotin complex compound to form dimethyl carbonate;
and
(ii) separating dimethyl carbonate and ammonia from the homogeneous catalyst by distillation;
Wherein the high boiling solvent boils at a temperature at least 20 ° F. (11.1 ° C.) higher than the boiling point of the dimethyl carbonate and does not form an azeotrope with the dimethyl carbonate; And selected from ethers, ketones, hydrocarbons, esters, or mixtures thereof, and the organotin complex compound is R ′ _4-n Sn (OR) _n · xL (where R ′ is an alkyl group, aryl Or an aralkyl group, R is methyl, n is 1 or 2, x is 1 or 2, and L is an ether, ester, ketone, aldehyde, organic phosphine, or these Selected from a mixture) ;
(g) removing dimethyl carbonate and methanol from the second distillation column reactor as a second overhead;
(h) removing the homogeneous catalyst from the second distillation column reactor as a second bottom liquid;
(i) separating dimethyl carbonate from methanol by extractive distillation in the second overhead;
(j) supplying a first portion of the second bottoms liquid to the first distillation column reactor;
(k) supplying a second portion of the second bottoms liquid to a third distillation column reactor, wherein the catalyst is regenerated and heavy material is purified; and
(l) recycling a third portion of the second bottoms liquid to the second distillation column reactor;
A process for producing dimethyl carbonate comprising A process for producing a dialkyl carbonate by reaction of a reaction product containing urea and an alcohol and containing water and ammonium carbamate as impurities,
(a) supplying a reactant containing urea and alcohol to the main reaction zone;
(b) a step of supplying a high-boiling solvent containing an electron-donating atom and an organotin compound to the main reaction zone , wherein the high-boiling solvent containing the electron-donating atom is triethylene glycol dimethyl ether, tetraethylene Glycol dimethyl ether, dimethyl oxalate, dimethyl malonate, dimethyl succinate, anisole, dimethoxybenzene, dimethoxytoluene, ethylene glycol, catechol, 1,4-dioxane-2,3-diol, 2-methyltetrahydrofuran-3-one, 2 , 3-pentanedione, 2,4-pentanedione, 3-methyltetrahydropyran, or triphenylphosphine, and the organotin compound is R ′ _4-n Sn (OR) _n (where R ′ is , An alkyl group, an aryl group, or an aralkyl group, and R is Alkyl and, process n is 1 or 2); and
(c) in the main reaction zone,
(i) reacting an alcohol with urea in the presence of the high-boiling solvent containing an electron-donating atom and the organotin compound to form a dialkyl carbonate; and
(ii) removing dialkyl carbonate and ammonia from the main reaction zone as vapor;
Performing simultaneously;
Wherein the improvement is such that the water and urea are reacted to form ammonium carbamate and the reactants are first reacted in a pre-reaction zone under conditions such that the ammonium carbamate is decomposed into ammonia and carbon dioxide. To remove water and ammonium carbamate from the reactant by removing ammonia and carbon dioxide from the reactant by feeding to and before feeding the reactant in step (a). Said production method, which consists in using a pre-reaction zone before the reaction zone. The production method according to claim 11, wherein the temperature of the preliminary reaction zone is a temperature in the range of 200 to 380 ° F (93.3 to 193 ° C) in the liquid phase. The process according to claim 12, wherein the temperature of the pre-reaction zone is in the range of 250-350 ° F (121-177 ° C) .   The process according to claim 11, wherein in the preliminary reaction zone, part of the methanol feed and part of the urea feed react to form methyl carbamate. The process according to claim 11, wherein the pre-reaction zone and the main reaction zone are operated under distillation conditions.   12. The method of claim 11, wherein water is removed from the feed by reacting water and urea to produce ammonium carbamate that decomposes into ammonia and carbon dioxide. The process according to claim 16, wherein the temperature of the preliminary reaction zone is a temperature in the range of 200 to 380 ° F (93.3 to 193 ° C) in the liquid phase.   The process according to claim 11, wherein ammonium carbamate is removed from the feed by decomposing ammonium carbamate into ammonia and carbon dioxide. The process according to claim 18, wherein the temperature of the pre-reaction zone is in the range of 200 to 380 ° F (93.3 to 193 ° C) in the liquid phase.   The production method according to claim 11, wherein the high-boiling compound containing an electron-donating atom contains triethylene glycol dimethyl ether.

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