KR20060136454A - Process for preparing dialkyl carbonate - Google Patents

Abstract

A method of producing dialkyl carbonates by reacting an alcohol, for example C ₁ -C ₃ alcohol, with urea is disclosed, wherein water and ammonium carbamate impurities in the feed are removed in a prereactor. Water reacts with urea in the feed to produce ammonium carbamate, which is broken down into ammonia and carbon dioxide along with the ammonium carbamate originally present in the feed. In addition, some urea reacts with the alcohol in the first reactor to produce alkyl carbamate, a precursor of dialkyl carbonate. Dialkyl carbonate is produced in the second reaction zone. Undesired by-product, N-alkyl alkyl carbamate, is continuously distilled off in the second reaction zone with ammonia, alcohol and dialkyl carbonate under steady state reactor operation. N-alkyl alkyl carbamates can be converted to heterocyclic compounds in the third reaction zone to remove as solids in the system.

Urea, Alkyl Carbamate, Dialkyl Carbonate, Main Reactor, Prereactor

Description

Process for producing dialkyl carbonate {PROCESS FOR MAKING DIALKYL CARBONATES}

The present invention relates to a process for the production of dialkyl carbonates, in particular C ₁ -C ₃ dialkyl carbonates, wherein the reaction takes place simultaneously with the separation of the reactants and the carbonate product. 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 catalyst. More specifically, the present invention relates to a method for removing impurities in a feed stream to provide stable catalyst performance, improved reaction rates and trouble-free downstream operation of the apparatus.

  Dialkyl carbonates are important commercial compounds, the most important of which is dimethyl carbonate (DMC). Dimethyl carbonate is used as the methylating agent and carbonylating agent, and is used as a raw material for the production of polycarbonate (polycarboante). Dimethyl carbonate can also be used as a solvent to replace halogenated solvents such as chlorobenzene. Although the current prices of both dimethyl carbonate and diethyl carbonate are enormously expensive to use as fuel additives, they can be used as oxygenates in the combined gasoline and octane components. Dimethyl carbonate has a much higher oxygen content (53%) than MTBE (methyl tertiary butyl ether) or TAME (tertiary amyl methyl ether) and therefore has the same effect Less amount is needed. Dimethyl carbonate has a RON of 130 and is less volatile than MTBE or TAME. Dimethyl carbonate has an aromatic odor and, unlike ether, is more readily biodegradable.

In old commercial methods, dimethyl carbonate was produced from methanol and phosgene. Because of the tremendous toxicity and price of phosgene, efforts have been made to develop better methods that do not use phosgene.

In one of the new commercial methods, dimethyl carbonate is prepared via oxidative carbonylation from methanol, carbon monoxide, oxygen molecules and cuprous chloride in a two step slurry process. Such a method is disclosed in EP 0 460 735 A2. The main drawbacks of this process are low production rates, high costs for separation of product and reactants, formation of by-products, high recovery requirements, and the need for corrosion resistant reactors and process lines.

Another new process is disclosed in EP 0 742 198 A2 and EP 0 505 374 B1, wherein dimethyl carbonate is produced via methyl nitrite instead of the above mentioned cuprous methoxychloride. By-products are nitric oxide, carbon dioxide, methylformate and the like. Dimethyl carbonate is separated from the reactor in the product stream by solvent extractive distillation with dimethyl oxalate as solvent for separating azeotrope. Although the chemistry for this seems straightforward and production rates have improved, this method can be achieved by separating multiple materials, balancing the materials in various flow sections in the process, complex process controls and hazardous chemicals. It is very complicated because of handling methylnitrile.

In another commercial process, dimethyl carbonate is produced in a two-step process from methanol and carbon dioxide. In the first step, the cyclic carbonate is disclosed in US Pat. No. 4,786,741; Produced by the reaction of epoxides with carbon dioxide as disclosed in 4,851,555 and 4,400,559. In the second step, dimethyl carbonate is produced with glycol by exchange of cyclic carbonate with methanol. For example, Y. Y. Okada et al., "Dimethyl Carbonate Production For Fuel Additives", ACS, Div. Fuel Chem., Preprint , 41 (3), 868, 1996] and John F. John F. Knifton et al., "Ethylene Glycol-Dimethyl Carbonate Cogeneration", Journal of Molecular Chemistry , vol. 67, pp 389-399, 1991. This method is advantageous, but the reaction between epoxide and carbon dioxide is slow and requires high pressure. In addition, the exchange reaction between the cyclic carbonate and methanol is limited by equilibrium, and methanol and dimethyl carbonate form an azeotrope that is difficult to separate.

Dialkyl carbonate is prepared by reacting a primary aliphatic alcohol such as methanol with urea (1) in the presence of various homogeneous and homogeneous catalysts, that is, dibutyltin dimethoxide, tetraphenyltin, and the like. It is known to be possible. For example blood. P. Ball et al., "Synthesis of Carbonates and Polycarbonates by Reaction of Urea with Hydroxy Compounds", C1 Mol. Chem. , vol. 1, pp 95-108, 1984. Ammonia is a coproduct and can be recovered to urea (2) as in the following reaction sequence.

Carbamate is produced at low temperatures followed by the formation of ammonia in both stages and at the same time dialkyl carbonate at high temperatures.

As described the two reactions are reversible under the reaction conditions. The order of catalytic activity of the organotin compound is R ₄ Sn <R ₃ SnX << R ₂ SnX ₂ , where X is C, RO, RCOO, RCOS. Maximum reaction rates and minimum byproduct formation have been reported for dialkyl tin (IV) compounds. For most catalysts (Lewis acids), higher catalytic activity is required if the reaction is carried out in the presence of a suitable cocatalyst (Lewis base). For example, preferred cocatalysts for organotin (IV) catalysts such as dibutyltin dimethoxide, dibutyltin oxide and the like are triphenylphosphine and 4-dimethylaminopyridine. However, dibutyl pyrolysis of intermediate alkyl carbamate and urea with isocyanic acid (HNCO) or isocyanuric acid ((HNCO) ₃ ) and alcohol or ammonia (a coproduct of urea decomposition) was used in the synthesis of dialkyl carbamate. It may also be promoted by organotin compounds such as tin dimethoxide or dibutyltin oxide. WO 95/17369 discloses dialkyl carbonates such as dimethyl carbonate, p. Disclosed is a two-step production from alcohols and urea using chemistry and catalysts disclosed by Vol. In the first step, the alcohol reacts with urea to produce alkyl carbamate. In the second stage, dialkyl carbonate is produced by reacting alkyl carbamate with alcohol at a higher temperature than the first stage. This reaction is carried out using an autoclave reactor. However, when methanol reacts with methyl carbamate or urea, N-alkyl byproducts such as N-methyl methyl carbamate (N-MMC) and N-alkyl urea are also produced according to the following reaction:

This dialkyl carbonate is present in the reactor in an amount of 1 to 3% by weight based on the total carbamate and alcohol content of the reactor solution to minimize the formation of byproducts.

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

The ether solvent also functions as a complexing agent for forming a homogeneous complex catalyst in situ from dibutyltin dimethoxide or oxide.

The separation of substances involved in the DMC method is very important for the commercial production of DMC for economic reasons. EP 0 742 198 A1 and US 5,214,185 disclose the separation of DMC in a distillation mixture of methanol and DMC using dimethyl oxalate (DMOX) as the extraction solvent. Because of the high melting point (54 ° C.) of DMOX, using DMOX is not convenient and requires additional costs for separation.

Urea and alcohol are both quite hygroscopic. Urea contains ammonium carbamate impurities. Thus, water and ammonium carbamate are impurities in urea and alcohol feeds. It is known that impurities such as water and ammonium carbamate in the urea and alcohol feed cause line plugging at the cooling point in the cooling section (condenser) for catalyst inactivation and overhead vapor stream from the reactor. have. Water causes inactivation of the catalyst containing an alkoxy group, for example the methoxy group on the organotin complex molecule is very reactive with the water molecule resulting in hydrolysis of the bond between the tin atom and the oxygen atom of the methoxy group. Ammonium carbamate causes problems in controlling the backpressure in the dialkyl carbonate production reactor and plugging the cooling system (condenser) of the product distillation stream from the dialkyl reactor due to precipitation of the ammonium carbamate.

Summary of the Invention

In short, the present invention is an improved process for preparing dialkyl carbonates comprising the following steps:

(a) feeding a stream containing urea, alcohol, water and ammonium carbamate to the first reaction zone:

(b) simultaneously in the first reaction zone,

(i) reacting water with urea to form ammonium carbamate,

(ii) decomposing ammonium carbamate in the feed and ammonium carbamate derived from the reaction of water and urea with ammonia and carbon dioxide; And

(c) removing ammonia, carbon dioxide and the alcohol from the first reaction zone as first overhead;

(d) removing urea and the alcohol from the first reaction zone;

(e) feeding the urea and the alcohol to a second reaction zone;

(f) reacting the alcohol and urea to form a dialkyl carbonate in the presence of a homogeneous catalyst containing an organotin complex of dialkylalkoxide in a high boiling solvent; And

(g) removing dialkyl carbonate and the alcohol from the second reaction zone.

The dialkyl carbonate is an alcohol, preferably C ₁ −, in the presence of a complex of a high boiling point electron donor compound and an organotin compound, preferably a dibutyltin dialkoxide complex and a high boiling point oxygen-containing organic solvent that functions as a solvent. Prepared by reacting C ₃ alcohol with urea or alkyl carbamate or both, wherein the reaction is preferably carried out simultaneously with the distillation of the dialkyl carbonate in a reboiler of a distillation still or a stirred tank reactor. Is performed. Urea and alcohol feeds are purified by removing trace fractions of water and ammonium carbamate, N-alkylation by-products and alkyl carbamate.

Water is removed by reaction with urea in a prereactor having a preliminary reaction zone. Ammonium carbamate is removed by decomposition into ammonia and carbon dioxide in a prereactor. In addition, urea is partially and optionally converted to alkyl carbamate in the pre-reactor for faster reaction rates in the primary reactor, the reduction of alcohol recycled to the main reactor in the dialkyl carbonate unit or column, and the main reactor The result is a high concentration of dialkyl carbonate in the overhead stream from which it originates.

1 is a simplified flow diagram of one embodiment for producing a DMC in accordance with the present invention.

2 is a simplified flow diagram of a DMC separation unit.

3 is a schematic representation of one embodiment of producing DEC in accordance with the present invention.

4 is a simplified flowchart of a reaction / distillation column reactor embodiment for the present method.

5 is a simplified flow diagram of a catalytic stirred tank reactor embodiment with a distillation column for the process.

Detailed Description of the Preferred Embodiments

Water impurities in the urea and alcohol feed are removed by reacting water with urea in the prereactor, while ammonium carbamate is removed by decomposition with ammonia and carbon dioxide in the prereactor. The prereactor must be operated under favorable conditions for decomposition so that ammonia and carbon dioxide are removed with steam. If the decomposition is not complete, the unconverted ammonium carbamate will enter the main reactor and will be converted to urea and water, and will also be broken down to ammonia and carbon dioxide causing inactivation of the catalyst. Urea is partially converted to alkyl carbamate in the prereactor. The following essential reactions take place in the prereactor:

Since the four reactions are equilibrium reactions and must occur simultaneously in the pre-reaction zone in the pre-reactor, it is important to control the temperature and pressure of the pre- and main reactors. Reactions (1), (2), (3) and (4) are carried out in a pre-reactor at temperatures between 200 and 380 ° F, preferably between 250 and 350 ° F, in the liquid phase. The preferred range of overhead pressure of the prereactor is about 30 to 300 psig. However, this overhead pressure is mainly determined by the desired temperature of the prereactor column and the composition of the liquid in the reactor. Reaction (4) proceeds to equilibrium in the absence of a catalyst, but zinc oxide supported on a catalyst such as a dibutyltin dialkyloxide complex catalyst and an inert carrier such as silica, alumina calcined at high temperature (> 850 ° C.), The reaction rate is faster in the presence of weakly acidic or weakly basic heterogeneous catalysts such as tin oxide, titanium oxide, zirconium oxide, molybdenum oxide, talcite, calcium carbonate, zinc hydroxide, zirconium hydroxide and the like. The preferred concentration of urea in the liquid phase in the pre-reaction zone under given conditions is about 80% by weight, preferably less than 50% by weight. The partial pressures of ammonia and carbon dioxide should be kept below the decomposition pressure of the ammonium carbamate causing the ammonium carbamate to degrade. It is highly desirable to remove the product, ammonia and carbon dioxide in the prereaction zone of the prereactor effectively, preferably as a vapor with alcohol and any inert stripping gas used as an option. If desired, alcohol may be used as the only stripping gas. Thus, by the reaction of a reactant containing water and ammonium carbamate as impurities and containing urea and alcohols, dialkyl carbonates are produced in an improved manner comprising the following steps:

(a) feeding a reactant containing urea and an alcohol to the main reaction zone;

(b) supplying a solvent containing an organotin compound and a high boiling point electron donor atom to the main reaction zone; And

(c) simultaneously in the main reaction zone

(i) reacting an alcohol and urea in the presence of the organotin compound and a solvent containing the high boiling electron donor atom to produce a dialcohol carbonate,

(ii) removing dialkyl carbonate and ammonia as steam in said main reaction zone,

The improvement here is that the water is reacted with urea to form ammonium carbamate, preferably at a temperature in the range from 200 to 380 ° F., more preferably at 250 to 350 ° F. and preferably in the liquid phase, and the ammonium carbamate is ammonia and Under conditions of decomposition with carbon dioxide, water and ammonium carbamate are removed from the reactants by first feeding the reactants to the pre-reaction zone and removing ammonia and carbon dioxide from the reactants before feeding the reactants according to step (b). The preliminary reaction zone can be used before the main reaction zone. Preferably, urea and a portion of the alcohol react to form an alkyl carbamate in the prereaction zone.

Preferred embodiments of the process for the production of dialkyl carbonates comprise the following steps:

(a) feeding urea, C ₁ -C ₃ alcohol to the pre-reaction zone;

(i) purifying impurities in the feed in a prereactor;

(ii) removing ammonia, carbon dioxide and alcohol as a vapor stream;

(iii) reacting a portion of the urea and alcohol with an alkyl carbamate; And

(iv) removing the liquid stream containing alkyl carbamate, urea and alcohol and injecting into the main reaction zone;

(b) supplying a solvent containing an organotin compound and a high boiling point electron donor atom to the main reaction zone;

(c) at the same time in the main reaction zone,

(i) reacting C ₁ -C ₃ alcohol, urea and alkyl carbamate in the presence of the organotin compound and a solvent containing the high boiling electron donor atom to produce a dialkyl carbonate,

(ii) removing dialkyl carbonate and ammonia, ether, carbon dioxide, N-alkyl alkyl carbamate and alkyl carbamate as vapor in the main reaction zone; And

(d) N-alkyl alkyl carbamate separated from the vapor stream in a small slipstream of the liquid reaction medium from the pre-reactor and from the pre-reaction zone with a heterocyclic compound (RNCO) in the third clean-up zone. ₃ , wherein R is H or C _n H _{2n +1} and n = 1, 2, or 3) and converting the alkyl carbamate to dialkyl carbonate;

(i) removing the heterocyclic compound in the stream as a solid in a third reaction zone;

(ii) returning the reaming liquid stream to the main reaction zone and the purification reaction zone;

(iii) removing ammonia, alcohol and dialkyl carbonate as overhead vapor stream.

This embodiment preferably utilizes a pre-reaction zone for removing water, and ammonium carbamate from the urea and alcohol, in a temperature in the range 200 to 380 ° F., more preferably 250 to 350 ° F. and preferably in the liquid phase. And the use of a purification zone to convert N-alkyl alkyl carbamate by-products into heterocyclic compounds at temperatures ranging from 300 to 400 ° F. in the liquid phase for removal as solids from the system.

Preferred pre-reactors are double diameter tower reactors (the diameter of the lower layer is wider). The urea feed solution in alcohol is injected into the columnar prereactor in a middle layer of narrower diameter than the upper layer. Ammonium carbamate in the urea feed is broken down into ammonia and carbon dioxide. The temperature of the column under 50 to 350 psig is maintained at a temperature of about 200 to about 380 ° F. The photoreaction products, ammonia and carbon dioxide, together with the alcohol vapors are removed as overhead vapor streams in the column. In this prereactor the urea in the feed stream is at least partially converted to alkyl carbamate. This reaction is exothermic. The conversion rate of urea is higher than 10%, preferably higher than 50%. The conversion of urea to alkyl carbamate can be carried out in the absence of a complex catalyst. However, the conversion is faster when using a catalyst.

Removal of water and ammonium carbamate impurities from the feed stream is characterized by maintaining the catalyst active, controlling the overhead pressure of the distillation column, and overhead steam stream from the main reactor by precipitation of ammonium carbamate. Solve the problems associated with plugging the cooling unit. Purification of impurities in the feed is carried out in a prereactor, which is a double diameter distillation column type reactor. Removing impurities in the feed stream is the primary purpose of the prereactor. Further improvements are made by the conversion of urea to alkyl carbamate, at least in part, in the prereactor, which results in faster reaction rates of dialkyl carbonate production in the main reactor and dialkyl carbonate in the overhead stream from the main reactor. Higher concentrations of reduced alcohol recycled from the dialkyl carbonate recovery unit to the main reactor. In the preparation of dialkyl carbonates, the high concentration of dialkyl carbonates in the overhead stream from the main reactor reduces the cost of separation of the dialkyl carbonates.

The main reactor in which the dialkyl carbonate is formed is a stirred tank reactor 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 column to the main reactor. Mechanical stirring of the liquid reaction medium is not essential but optional. In the present invention, the reaction / distillation column of the main reactor operates differently from the conventional way in which unwanted N-alkylated byproducts are removed from the liquid reaction zone as part of the overhead product stream, which process is to a minimum level. This allows the reactor to be operated at a constant liquid level without filling the liquid reaction zone with unwanted byproducts for extended reactor operating time without any obstructions. This is highly desirable for the successful commercial production of dialkyl carbonates. Low concentrations of urea, alkyl carbamate and dialkyl carbonates in the liquid medium minimize the rate of formation of N-alkylated byproducts, which are achieved by the use of high concentrations of high boiling solvents such as triglyme. Such, if the concentration of alkyl carbamate is too low, an unacceptably low space yield of DMC may occur.

In order to avoid accumulation of by-products such as N-alkyl alkyl carbamate and heterocyclic compounds in the main reactor, by controlling both the temperature and the pressure of the distillation column of the main reactor vapor stream, the dialkyl carbonate production reaction is carried out, It has been found that -alkyl alkyl carbamates can be continuously distilled off from the liquid reaction medium and that N-alkyl alkyl carbamates can be converted to heterocyclic compounds that can be removed as solids in the system. In other words, it has been found that the normal concentration of N-alkyl alkyl carbamate and heterocyclic compounds in a given liquid reaction volume in the main reaction zone can be maintained under steady-state reactor operating conditions. It has been found that maintaining the surface temperature of any point within the main reactor at temperatures below about 550 ° F., preferably below 450 ° F., is highly desirable to minimize the formation of heterocyclic compounds in the main reaction zone. The conversion of the N-alkyl alkyl carbamate to the heterocyclic compound is carried out by using the third purification reaction zone.

Preferred purification reactors for this purpose are stirred tank reactors equipped with a connected distillation column, condenser and reflux drum. The N-alkyl alkyl carbamate by-products produced by the alkylation of alkyl carbamate and dialkyl carbonates in the main reaction zone produce vapor temperatures derived from the main reaction zone at column temperatures above about 255 ° F., preferably above 265 ° F. By operation it is continuously removed as part of the overhead vapor stream along with other products.

N-alkyl alkyl carbamate is separated from the overhead stream from the main reactor and injected into the purification reactor. This purification reactor is preferably operated at a temperature of the liquid reaction medium in the range from 330 to 400 ° F. It is important that the column temperature and column overhead pressure be controlled so that the overhead vapor stream does not contain N-alkyl alkyl carbamate. Generally, the refinery reactor operates at least 2 ° F. and 5 psig higher than the reaction temperature and overhead pressure of the main reactor.

The technique of by-product removal disclosed in the present invention is described in U.S. Pat. 6,359,163 B2 (2002) and WO 95/17369 (1995), U.S. 6,031,122 (2000), and EP 1167339 (2002) can be extended to the prior art, which produces dialkyl carbonates from urea and alcohol, regardless of whether solvents are used in the main reactor and in the purification reactor.

When producing heavier alkyl carbonates such as dipropyl carbonate, dibutyl carbonate and the like, it is difficult to remove N-alkyl alkyl carbamate from the main reactor as part of the overhead stream. Thus, a liquid slip stream is taken in the main reactor in a greater amount than for the purification reactor. The N-alkyl alkyl carbamates in the slip stream are converted to high boiling point separable materials in the purification reactor as disclosed herein. After removal of the high boiling point of unwanted material in the bed stream from the purification reactor, the remaining liquid stream can be returned to the main reactor and the purification reactor.

Various physical devices can be used as the prereactor. These include distillation column reactors, stirred tank reactors, bubble reactors, tubular reactors, boiling point reactors or any combination thereof. Preferred apparatus is a distillation column reactor, in which the reaction is carried out under reaction / distillation conditions. Despite the equilibrium nature of reactions (1), (2) and (3), the use of a distillation column reactor allows all three reactions to proceed to the right, i.e. complete removal of water and ammonium carbamate from the feed stream. Means that. Urea is partially converted to alkyl carbamate in the prereactor following the equilibrium reaction (4). By removing ammonia from the reaction zone as an overhead gas mixture, reaction (4) can also proceed to the right side of the reaction. Partial conversion of urea to alkyl carbamate increases the rate at which alkyl carbamate converts to dialkyl carbonate in the main reactor, resulting in higher concentrations of dialkyl carbonate in the overhead stream of the main reactor urethane. This is because the reaction of urea with alcohol to produce dialkyl carbonate takes place in two steps and reaction (4) is the first step.

The dialkyl carbonate formation reaction is as follows:

Reaction (5) is carried out in the main reactor in the presence of a high boiling point solvent in a reaction / distillation mode to create favorable conditions for the rapid removal of dialkyl carbonate from the reaction medium as soon as the dialkyl carbonate is produced. The rate of formation of dialkyl carbonate in the main reactor is more sensitive to the concentration of ammonia in the reaction medium in the main reactor than to the rate of alkyl carbamate in the prereactor due to chemical thermodynamics. If at a given concentration of alkyl carbamate, the ammonia concentration of the liquid reaction medium in the main reactor is lower, the rate of formation of the dialkyl carbonate will be faster. Under a pressure between about atmospheric pressure and 150 psig, preferably between 30 and 120 psig, the temperature of the reaction medium in the main reactor is about 300 to about 450 degrees F., preferably about 320 to 400 degrees F. and most preferably about 330 to 360 degrees F. Any combination of preferred temperatures and pressures that exhibit high selectivity of dialkyl carbonates can be obtained by the selection of appropriate high boiling point solvents and control of the solvent concentration in the main reactor. The main reactor is operated to have a temperature higher than at least about 300 ° F., preferably higher than about 320 ° F. for recovery of latent heat of the overhead vapor stream used to recycle the alcohol as alcohol vapor superheated to the main reactor and the pre-reactor. Very preferred.

The use of high boiling solvents in the main reactor allows the reaction to be carried out under low pressure and low concentrations of carbamate in the liquid reaction medium. Low pressures are suitable for faster removal of dialkyl carbonate from the liquid reaction medium into the vapor phase, resulting in a lower concentration of dialkyl carbonate in the reaction medium. The lower the concentration of dialkyl carbonate and carbamate / urea in the liquid reaction medium, the lower the concentration of unwanted by-products and degradation products of urea, alkyl carbamate and N-alkylated products associated with N-alkylation in the main reactor. . Preferred solvents for the synthesis of dialkyl carbonates should have the following properties: (1) The solvent must boil at a temperature 20 ° F. above the boiling point of the dialkyl carbonate product; And (2) the solvent should not form an azeotrope with the dialkyl carbonate. Examples of such solvents are high boiling ethers, ketones, hydrocarbons and esters or mixtures thereof; For example triethylene glycol dimethyl ether, tetraethylene glycol dialkyl ether, anisole, dimethoxy benzene, dimethoxy toluene, alkyl oxalate, decalin, tetralin, xylene, decane and the like, or mixtures thereof There is this.

The superheated alcohol vapor stream is injected directly into the liquid reaction zone to provide the heat of reaction for the conversion of the slightly exothermic alkyl carbamate to the dialkyl carbonate, and as soon as the dialkyl carbonate is produced, the dialkyl carbonate and Remove ammonia Preferred total concentrations of alkyl carbamate and urea mixed in the reaction medium are from about 10% to about 60%, preferably from about 15% to 50% by weight of the total material in the liquid reaction medium. The preferred concentration of dialkyl carbonate in the reaction medium is from about 0.5 to about 12% by weight, preferably from 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 from 0.2: 1 to 2: 1, preferably from 0.3: 1 to 1.5: 1. The concentration of the organotin complex catalyst is from about 2 to about 20 weight percent tin, preferably from about 5 to about 17 weight percent tin, based on the total content of all materials in the liquid reaction zone in the main reactor. Note that this catalyst promotes the unwanted side reactions discussed above. Performing the reaction at low temperatures reduces side reactions. However, the rate of production of dialkyl carbonates is also lowered, which may be undesirable for commercial production of DMC. Preferred concentrations of the high boiling solvent in the reaction medium in the preliminary reactor are about 2 to about 65 weight percent, preferably 2.5 to 55 weight percent of the total material in the reaction medium.

Catalyst operating under steady-state reaction conditions, dibutyltin alkoxide yugiju seat complex, R _{'4 - n} Sn (OR) _n and xL (wherein R' is an alkyl group, an aryl or an aralkyl group and; R = alkyl; n = 1 or 2; x = 1 or 2; L is an organotin complex catalyst system derived from an electron donor atom containing a monodentate or bidentate ligand. Examples of L are electron donor ligand molecules such as ethers, esters, ketones, aldehydes, organic phosphines or mixtures thereof; Triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethyl oxalate, dimethyl malonate, dimethyl rosinate, anisole, dimethoxy benzene, dimethoxy toluene, ethylene glycol, catecol, 1,4 -Dioxane-2,3-diol, 2-methyltetrahydrofuran-3-one, 2,3-pentanedione, 2,4-pentanedione, 3-methyltetrahydropyran, triphenylphosphine and the like. Homogeneous catalyst systems are quasi-equilibrium mixtures of various organotin species. Suitable catalysts of this type and methods for their preparation are described in US Pat. Nos. 6,010,976 and 6,392,078, which are incorporated herein by reference in their entirety.

Catalyst systems operating under steady state reaction conditions are mixtures of various soluble organotin monomers, dimers and oligomer species, which are produced by a number of possible reactions. These various organotin catalytic species are present in somewhat quasi-equilibrium under given reaction conditions. Dialkyltin oxide, dialkyltin halide, dialkyltin bis (acetylacetonate) and dialkyltin carboxylates such as dibutyltin diacetate, dialkyltin oxalate, dibutyltin malonate, dibutyltin Diacetate, dibutyltin bis (acetylacetonate) and the like can be used to form species of soluble tin complex catalyst in the field in the presence of a high boiling point solvent such as triglyme. The alkyl groups linked to the tin atoms can be the same or different. For example, the catalyst precursor is a dialkoxide, dihalide, hydroxyhalide, diacetate or oxide of dibutyltin, butylbenzyltin, butylphenyltin, butyloctyltin or di-2-phenylethyltin. Water, carboxylic acid or hydrochloric acid coproducts are continuously removed from the liquid reaction medium as an overhead vapor stream in the presence of a high boiling solvent under low pressure. Suitable temperatures for the catalyst formation reaction are about 200 to about 400 ° F., and pressures are about atmospheric pressure to about 150 psig. In a preferred embodiment, methanol, ethanol or propanol are continuously injected into the main reactor depending on the intended dialkyl carbonate. Either methanol or ethanol is suitable for the production of MEC. This catalyst formation reaction is advantageously carried out in the presence of dilute alkyl carbamate, N-alkyl alkyl carbamate or dialkyl solution in the main reactor. It will be appreciated that during this catalyst formation reaction the operation of the distillation column should be operated under conditions such that co-product water, carboxylic acid or hydrogen chloride can be removed from the reaction zone with the alcohol as overhead in the overhead stream. For the production of dimethyl carbonate, the soluble organotin complex catalyst system allows the formation of dibutyltin dimethoxide and triglyme (organic tin complex catalyst) in the main reactor prior to initiating the dialkyl carbonate formation reaction in the presence of a high boiling solvent. As a complexing agent) and methanol. For diethyl carbonate production, soluble organotin complex catalyst systems are preferably formed using triglyme and ethanol with dibutyltin dimethoxide in the main reactor. As the reaction proceeds, the methoxy group on the catalyst is replaced by an ethoxy group.

Referring now to FIG. 1, a simplified flow diagram of one embodiment of the present invention is shown. 1 shows a flowchart of an improved method excluding the DMC separation unit. The DMC separation unit is shown in FIG. Reaction / distillation column reactor 111 is used as a pre-reactor for removing impurities in the feed stream and for partial conversion of urea to methyl carbamate. The urea solution is prepared by mixing the urea feed 1 and the methanol stream 3 in the drum 131. The methanol stream consists of a fresh methanol feed stream 2 and a methanol recycle stream 4 which is 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 split into three streams (33 and 32 through 4 and 31) to prepare the urea solution, the main reactor 112 and the purification reactor ( 113). The urea solution feed 5 from the drum 131 is injected in the middle of the narrow column portion of the upper layer of the double diameter tower reactor 111. Reactor 111 serves as a pre-reactor for purifying impurities (water and ammonium carbamate) in methanol and urea feeds and partially converting urea to MC. The vapor stream 6 from the prereactor 111 contains ammonia, carbon dioxide and methanol. The purified mixed solution of MC and urea in methanol is removed in prereactor 111 as bed stream 7 and recycle stream 22 and recycle liquid stream 22 from cooling / filtration system 133 via line 20. 8) mixed. The liquid recycle stream 20 from the cooling / filtration system 133 is split into two streams 21 and 22 and recycled to the main reactor 112 and the purification reactor 113. Mixed stream 8 is injected into main reactor 112 (stirring tank reactor or optionally bubble column reactor). The recycle methanol stream 33 from the DMC separation unit is injected into the main reactor 112 as superheated methanol vapor. Overhead recycle stream 14 from flash column 132 is injected into the main reactor. This stream 14 contains primarily MC and small amounts of N-MMC and methanol. Overhead vapor stream 9 from main reactor 112 contains ammonia, CO ₂ , dimethyl ether, methanol, DMC, MC, N-MMC, TG and small amounts of organotin catalyst. The overhead stream 9 from the main reactor 112 is mixed into the overhead stream 17 and stream 10 from the purified stirred tank reactor 113. This stream 17 contains ammonia, CO ₂ , dimethyl ether, methanol and DMC. Mixed stream 10 is injected into distillation column 151 to separate ammonia, CO ₂ , dimethyl ether, methanol and DMC components from the remaining heavy components in the stream. Overhead stream 12 from column 151 is mixed into overhead stream 6 and stream 23 from prereactor 111. This mixed stream 23 is injected into the distillation column 134. Overhead stream 25 from column 134 is sent to an ammonium carbamate removal system 135, where stream 25 is adequately cooled so that the CO ₂ and ammonia precipitates ammonium carbamate and solid ammonium carbamate It causes a reaction to become. Solid ammonium carbamate can be removed using filtration or hydroclone. Stream 27 from ammonium carbamate removal system 135 is injected into distillation column 136 and recovered with ammonia. Overhead stream 28 from column 136 is sent to an ammonia storage tank. The bottoms stream 29 from column 136 is organic waste and contains mainly dimethyl ether. The bottoms stream 24 from column 134 is sent to the DMC separation unit shown in FIG. Stream 24 contains DMC and methanol. The bottoms stream 13 from column 151 is sent to flash column 132. Stream 13 contains methanol, MC, N-MMC, TG and small amounts of catalyst. The bottoms stream 15 from flash column 132 contains N-MMC, MC (trace), TG and a small amount of organotin catalyst. Stream 15 is mixed into a small amount of liquid slipstream 11 and stream 16 from main reactor 112. This mixed stream 16 is injected into the purification reactor 113 (optionally a small amount of slipstream 11 from the pre-reactor 112 can be injected into the bottom of either column 151 or column 132). Can be). The bed stream 18 from the purification reactor 113 is cooled and precipitated in the stream with heterocyclic compounds such as isocyanuric acid, 1,3,5-trimethyl triazine-2,4,6-trione and the like, the precipitate Silver is removed by filtration system 133 as a solid via line 19. Liquid filtration stream 20 from filtration system 133 is separated into two streams 21 and 22 and recycled to main reactor 112 and purification reactor 113.

The main reactor may be a single stirred tank reactor or multiple stirred tank reactor system depending on the production capacity of the dialkyl carbonate. For example, if the main reactor consists of a series of three stirred tank reactors, the purified alkyl carbamate / urea feed stream 7 from the prereactor 111 is suitably separated into three streams, each stream Is injected directly into the three reactors. The liquid reaction stream is withdrawn from each reactor and injected into the next reactor. The liquid reaction stream from the third reactor is sent to the first reactor. A small amount of slipstream from the liquid reaction stream from the third reactor is mixed into the bottoms stream 15 from the column 132 and the stream 16, which is sent to the purification reactor 113. An alcohol recycle stream, such as methanol recycle stream 33 from the DMC separation unit, is injected into the first reactor as superheated alcohol vapor. The overhead vapor stream from the first stirred tank reactor is injected into the second reactor. The overhead vapor stream from the second reactor is injected 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, and consequently, the concentration of DMC in the overhead stream from the third reactor is highest. The overhead stream 9 from the third reactor is mixed into the overhead stream 17 and stream 10 from the purification reactor 113, which is injected into the distillation column 151.

The bottoms 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 injected into extractive distillation column 137 via line 34. Overhead stream 35 containing about 98% methanol and about 2% DMC is recycled through line 30 of FIG. Bed stream 36 is injected into extraction solvent recovery column 138. Extraction solvent, anisole, is recovered from column 138 as bed stream 38 and recycled to column 137 via line 38. Overhead stream 37 from column 138 is product DMC, which is sent to the DMC storage tank.

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

3 shows a simplified flow diagram of a method of producing DEC. Urea solution is prepared in drum 141 by mixing urea feed 101 and ethanol stream 103. Ethanol stream 103 contains ethanol recycle stream 155 which is part of fresh ethanol feed 102 and ethanol recycle stream 130. Ethanol recycle stream 130 contains overhead stream 117 from distillation column 146 and bed stream 129 from distillation column 145 (ethanol recovery column). Ethanol recycle stream 130 is separated into two streams 152 and 156. Stream 152 is recycled to purification reactor 123. Stream 156 is again split into two streams 155 and 157 and recycled to drum 141 and main reactor 122, respectively. Ethanol recycle stream 157 is injected into main reactor 122. The urea solution 104 from the drum 141 is injected into the middle of the upper narrow column portion of the double diameter tower reactor 121. Reactor 121 serves as a pre-reactor for the purification of impurities (water and ammonium carbamate) in the feed, ethanol and urea, and for partially converting urea to EC. Vapor stream 105 from prereactor 121 contains ammonia, carbon dioxide and ethanol. The purified mixed solution is removed in prereactor 121 as bed stream 106. Stream 106 is injected into the main reactor (stirring tank reactor or optionally bubble column reactor) 122. Recycled ethanol stream 157 (most of which is ethanol recycle stream 130) is injected into main reactor 122 as superheated ethanol vapor. A small amount of slipstream 108 from main reactor 122 is mixed with bottoms stream 120 from DEC recovery column 147 to form stream 161, and mixed stream 161 is a refinery reactor ( 123). Slimstream 108 comprises ethanol, ammonia, diethyl ether, DEC, ethyl carbamate, N-ethyl ethyl carbamate, TG, heterocyclic compounds (isocyanuric acid, 1,3,5-triethyl triazine-2, 4,6-trione), and the organotin complex catalyst. Stream 120 contains ethanol, ethyl carbamate, N-ethyl carbamate, TG and traces of catalyst. Overhead stream 160 from purification reactor 123 contains ammonia, CO ₂ , diethyl ether, ethanol and DEC. The bottoms stream 159 from the purification reactor 123 contains ethyl carbamate, triglyme, N-ethylethyl carbamate, ethanol, heterocyclic compounds and homogeneous organotin catalysts. Bed stream 159 from reactor 123 is cooled in cooling / filtration system 148 to precipitate the heterocyclic compound. This precipitated solids by-product 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 vapor stream 107 from main reactor 122 contains ammonia, CO ₂ , diethyl ether, ethanol, ethyl carbamate, N-ethyl ethyl carbamate, DEC, TG and traces of catalyst. Stream 107 is mixed into overhead stream 160 and stream 109 from purification reactor 123. Overhead stream 160 contains ammonia, CO ₂ , diethyl ether, ethanol and DEC. Mixed stream 109 is injected into distillation column 142. Overhead stream 110 from column 142 containing ammonia, CO ₂ , ethyl ether and ethanol is injected into distillation column 143. Overhead stream 154 from column 143 is cooled to cause a reaction of ammonia with CO ₂ to produce ammonium carbamate. Ammonium carbamate is a precipitate in liquid ammonia and is removed from the cooling / filtration system 144 as a solid via line 115. Liquid ammonia stream 116 from cooling / filtration system 144 is directed to an ammonia storage tank. The bottoms stream 150 from column 142 contains DEC, ethanol, ethyl carbamate, N-ethyl ethyl carbamate, TG and traces of catalyst. Stream 150 is injected into distillation column 146 (first ethanol recovery column). Overhead ethanol stream 117 from column 146 is mixed with ethanol bed stream 129 and ethanol recycle stream 130 from distillation column 145 (second ethanol recovery column). Bottom stream 118 from column 146 is injected into distillation column 147 (DEC recovery column). Overhead stream 119 is product DEC, which is sent to the DEC storage tank. The bottoms stream 120 from column 147 is mixed with a small amount of slimstream 108 from main reactor 122, and this mixed stream 161 is injected into stirred tank refinery 123. Overhead stream 160 containing ammonia, CO ₂ , diethyl ether, ethanol and DEC is sent to column 142 via line 109. A bed stream 114 from column 143 is sent to distillation column 145 to separate diethyl ether from ethanol in the stream. Overhead ether byproduct stream 128 is sent to an ether storage tank. The bottoms stream 129 from column 145 is ethanol, which is recycled via line 130 to purification reactor 123 and main reactor 122.

Mixed dialkyl carbonates such as methyl ethyl carbonate (MEC) are produced using an appropriate mixture of methanol and ethanol as feed stream instead of feeding the methanol or ethanol feed stream to the drum for the preparation of the urea solution. However, the overhead stream from the main reactor and the purification reactor contains some DMC and DEC in addition to the MEC. DEC and DMC are separated from the mixture and exchange of DEC and DMC to MEC is carried out in a separation reactor (not shown). These exchange reactions are heterogeneous basic catalysts, such as zeolites in the form of alkalis, basic desites, or group IVB compounds such as titanium tetraethoxide or ethoxycarbonate or alkoxides, dialkyltin methoxy alkyl carbonates, dialkyltin carbonates It is carried out in the presence or absence of a solvent using a dialkyltin compound and a homogeneous catalyst such as the organotin complex catalyst discussed above. Suitable solvents will have a boiling point higher than about 265 ° F. Examples of such solvents are decalin, decane, xylene, diglyme, triglyme and the like or mixtures thereof.

4 shows a reaction / distillation column reactor using a basic heterogeneous catalyst. DEC feed is injected into the reaction / distillation column reactor 153 via line 221 at the top of the catalyst bed. The DMC feed is injected into column reactor 153 at the bottom of the catalyst bed via line 222. Overhead stream 223 contains primarily DMC and MEC. This stream 223 is sent to the MEC separation unit. The temperature of the liquid catalytic reaction zone is maintained in the range of about 200 to about 450 ° F., preferably 235 to 380 ° F. In order to prevent the formation of heavy matter in the reboiler of column reactor 153, a small amount of bed phase material is discharged through line 224.

5 shows a stirred tank reactor equipped with a connected distillation column 162. Homogeneous catalysts such as dibutyltin dimethoxide are used. A predetermined amount of homogeneous catalyst is charged to the reactor 158 before carrying out the reaction. Mixed DEC / DMC feed is injected into reactor 158 via line 301. Overhead stream 303 from distillation column 162 contains predominantly DMC and a small amount of MEC is recycled to reactor 158. Side recovery stream 302 from distillation column 162 concentrated in MEC is sent to distillation column 163 to separate the MEC from the DMC. Overhead stream 304 from column 163 is recycled back to reactor 158. The bottoms MEC stream 305 from column 163 is sent to a MEC storage tank. The temperature of the liquid catalytic reaction zone is maintained in the range of about 200 to about 450 ° F., preferably 235 to 380 ° F. The overhead pressure of column 162 ranges from about 20 psig to about 150 psig, preferably from about 25 psig to about 120 psig. However, the overhead pressure of column 162 is determined by the intended temperature of the liquid reaction medium in reactor 158, the composition of the reaction medium, and whether solvents are used.

Example 1

The reaction of water and urea was carried out in this example. The following materials were charged to a 500 ml three neck flask equipped with a magnetic stirrer and a water cooled reflux condenser: 229.67 g of triethylene glycol dimethyl ether (triglyme), 1.58 g of water, 2.06 g of methanol and 15.89 g of urea. When the reaction temperature of the mixture in the flask reached about 100 ° C., additional 3.2 g of methanol was added. The reaction of water and urea was carried out at a temperature of 128-140 ° C. for 0.92 h under nitrogen cover. Analysis of the sample taken from the flask was performed by GC and HPLC. The urea showed 22.4% conversion and water 45.2% conversion.

Example 2

General description of the experiment

A 1 L stirred autoclave was used as the reboiler for the reaction zone and reaction / distillation column reactor, which was connected to a 1 in diameter × 3.5 ft length distillation column. This distillation column had three zone heaters controlled independently. The overhead vapor stream from the distillation column was diluted with a nitrogen stream (800 cc / min) and then partially cooled to about 200 ° F. with hot water in a condenser. The steam stream from the condenser was cooled to room temperature to prevent plugging problems of the cooling point and overhead back pressure regulator. The liquid stream from the condenser flowed into a small overhead liquid reflux drum. The temperature of the liquid reflux drum was kept at room temperature. The flow of liquid product from the overhead reflux drum was monitored by an LFM (liquid flow meter). The liquid stream and the cooled steam stream from the overhead reflux drum were mixed as product stream from the reaction / distillation reactor. Samples were taken for the purpose of analysis to determine the composition of the overhead vapor stream exiting the column. Samples were also taken from the reboiler from time to time to monitor the composition of the liquid reaction medium. Each time a sample was taken from the reboiler, a supplement solution was injected to supplement triglyme and catalyst. While the reactor was running, the liquid level inside the reboiler remained constant. During operation, a vertical sight glass was attached to the reboiler for visual observation of the liquid level inside the reboiler. The reboiler was also equipped with a liquid level digital monitor for automatic control of the reactor for night and weekend absences.

To carry out the operation of the main reactor to produce DMC, the MC feed solution (methyl carbamate in methanol) and methanol feed were injected and mixed in a single stream. At 300 ° F. and 230 psig to remove water from the feed stream, the mixed feed stream was passed through a prereactor (vertically installed tubular up-flow reactor) and then injected into the main reactor. The temperature of the liquid reaction medium was controlled by adjusting the overhead pressure of the distillation column and the concentration of high boiling solvent in the reboiler of the distillation column. The products DMC, ammonia and other light byproducts such as dimethyl ether and CO ₂ were boiled off in the liquid medium and conveyed with methanol vapor. The operation of the distillation column was carried out in an atypical way to effect partial condensation of the vapor exiting the liquid medium in the reboiler without liquid reflux from the overhead reflux drum by controlling the steam temperature, in which the steam was distilled. This was done by controlling the zone temperature of the column with three column zone heaters while exiting the column. It has been found that an atypical operating method retains the triglyme solvent in the reactor and continuously removes by-product N-MMC as part of the overhead stream with MC from the liquid reaction medium, which operates for extended periods of time. To make it possible. It has been found that the absence of liquid reflux from overhead reflux drums is highly desirable in minimizing the formation of by-products N-MMC and heterocyclic compounds. It was possible to operate the reaction / distillation column reactor without failure for more than 1000 hours until the high pressure nitrogen valve of the reboiler was inadvertently opened. Operating the distillation column in a conventional manner has led to the termination of the reaction or removal of material from the reboiler because N-MMC, cyanuric acid and TTT (1,3,5-trimethyl triazine-2,4,6 Due to the overflow of the reboiler due to the accumulation of reaction by-products such as -trione).

Another important factor in minimizing side reactions while maintaining an adequate DMC production rate is to balance the concentration of solvent and catalyst, the temperature of the liquid medium and the overhead column pressure. The optimum operating range for reboiler temperature and overhead column pressure was about 330 to about 355 ° F. for the reboiler temperature and about 80 to about 110 psig for pressure, respectively.

Detailed description of the experiment

The following materials were loaded into the reboiler of the distillation column; 285 g of triglyme, 100 g of methanol and 100 g of dibutyltin dimethoxide. A 13.3 wt% MC solution in methanol (˜280 ppm H ₂ O) was injected at a fixed rate of 3.01 ml / min, 345 ° F. for the liquid reaction medium in the reboiler, 260 ° F. for the vapor temperature at the top of the distillation column, And steady-state operation of the reaction / distillation column reactor was obtained while injecting about 1.92 ml / min of methanol (˜80 ppm H ₂ O) at 90.8 psig for the overhead column pressure. The flow rate of methanol was adjusted to maintain a constant temperature of 345 ° F. for the liquid reaction medium. The reboiler's stirring speed was 300 rpm. Under these operating conditions, the overhead product stream contained ammonia, dimethyl ether, carbon dioxide, DMC, MC, NMMC, water, unidentified components and traces (˜100 ppb) of catalyst. At 926 hours on stream time, overhead and bed samples were taken. The analysis results of these samples are listed in Table 1. The molar ratio of MC / CH ₃ OH and the DMC weight percent based on MC and CH ₃ OH in the liquid medium in the reactor were 1.01 and 4.49 weight percent, respectively, and interestingly US Pat. No. 5,561,094 (1996, EXXON Chem Compared to 2-10 and 1-3% by weight claimed in)). Experimental results were better than 95 mol% MC to DMC. These experimental data are used to perform computer simulations of the process design.

Sample OVHD BTM Assay (% by weight) CO ₂ 0.10 0.04 NH ₃ 0.73 0.00 (CH ₃ ) ₂ O 0.04 0.00 Methanol 90.45 11.02 DMC 8.15 1.67 MC 0.36 26.17 N-MMC 0.17 1.88 TG 0.00 40.89 Unidentified ingredient 0.01 0.31 TTT 0.00 3.66 Water (ppm) 87 - Sn (ppm) To 1 14.35 * As dibutyltin dimethoxide

Example 3

A 1 L stirred reactor (autoclave) with a distillation column was used to remove impurities in a 8.03 wt% urea solution in methanol and the urea was converted to methyl carbamate. No catalyst was charged to the reactor. The experiment was conducted at 315 ° F. and 200 psig under 200 psig by injecting urea solution into the reactor at a constant bed flow rate of 2 ml / min for 4 hours at 4 ml / min and a constant bed flow rate of 1.5 ml / min at 3 ml / min for 27 hours. It was performed at 328 ° F under 230 psig. The distillation column was operated at overhead reflux. During operation, overhead flow was adjusted to maintain a constant liquid level (50% filled) within the autoclave. Column operation was performed with overhead reflux from an overhead reflux drum. The MC concentration in the bed stream from the autoclave averaged about 20%, corresponding to about 97% conversion of urea to MC. The urea feed contained about 2000 ppm of water. The bed phase product contained an average of 375 ppm of water at 315 ° F. and an average of 300 ppm of water at 328 ° F.

Example 4

The purpose of this experiment is to demonstrate a main reactor system consisting of multiple reactors. The experimental setup as in Example 2 was used to demonstrate the performance of the second main reactor. This experiment was performed in a similar manner to Example 2. This example differs from Example 2 in that Example 2 used 8% by weight of DMC solution in methanol instead of pure methanol and that the distillation column used a slightly lower overhead pressure (88 psig). . The reboiler of the distillation column was loaded with the following material; 285 g of triglyme, 40 g of methanol and 100 g of dibutyltin dimethoxide. While the MC solution and the DMC-methanol solution were injected into the reactor, the steady state of the distillation column reactor was obtained. Reactor operation continued for more than 1500 hours without failure at 345 ° F, distillation column temperature -278 ° F and overhead column pressure at 88 psig for the liquid reaction medium in the reboiler. The composition of the overhead and bedside products from the reactor for 54 hours from 1428 to 1482 hours of time on the stream are listed in Table 2. During this period, the infusion rate of 22.5 wt% MC solution (˜590 ppm H ₂ O) at 345 ° F. was fixed at 1.97 ml / min, and the infusion rate of 8 wt% DMC solution (80 ppm H ₂ O) was about 3.2 ml / fixed to min. The molar ratio of MC / CH ₃ OH and DMC wt% based on MC and CH ₃ OH in the liquid medium in the reactor were 0.915 and 6.40 wt% respectively. The results of the experiment were better than 93 mol% MC to DMC.

Sample OVHD BTM Assay (% by weight) CO ₂ tr - NH ₃ 0.89 - (CH ₃ ) ₂ O 0.06 - Methanol 84.91 13.32 DMC 12.35 2.68 MC 1.41 28.58 N-MMC 0.36 2.28 TG 0 36.55 HC * 0 3.77 catalyst** 12.83 Water (ppm) 39 - Sn (ppm) 0.6 - * HC; Isocyanuric acid and 1,3,5-trimethyl triazine-2,4,6-trione ** as dibutyltin dimethoxide

Example 5

The purpose of this experiment is to demonstrate the production of diethyl carbonate (DEC). DEC was produced by reacting ethyl carbamate (EC) with ethanol. This experiment was performed in a similar manner to Example 2. Ethyl carbamate solution and ethanol in ethanol were used in place of the MC solution and methanol in Example 2, respectively. The reboiler of the distillation column was loaded with the following material; 180 g of triglyme, 100 g of ethanol and 100 g of dibutyltin dimethoxide. Steady state operation of the distillation column reactor was obtained while injecting ethyl carbamate (EC) solution at a constant flow rate and adjusting the ethanol injection rate to maintain a constant temperature of the liquid reaction medium. The reactor operation was continued for 340 hours without disturbing at a constant overhead pressure of 66 psig with autoclave stirring speed of ˜345 ° F., distillation column temperature ˜282 ° F., and 300 rpm for the liquid reaction medium in the reboiler. The injection rate of 15.35 wt% EC solution (˜275 ppm H ₂ O) was fixed at 2.69 ml / min, and the average injection rate of ethanol (˜106 ppm H ₂ O) was 2.36 ml / min. At the top of the column, the overhead vapor stream was mixed with nitrogen diluent gas (600 cc / min) and then cooled to about 200 ° F. in a water-cooled condenser. The average composition of the overhead product and the composition of the bed phase product for the entire run are listed in Table 3. 74.2 g of solids were removed from the reactor at the end of the run, which was a mixture of heterocyclic compounds and contained 670 ppm Sn by weight. The analysis of bed phase products in Table 3 showed that the DEC wt% were 0.939 and 11.08 wt%, respectively, based on the molar ratio of EC / C ₂ H ₅ OH and EC and ethanol in the liquid medium in the reactor. The mass balance and urea molar balance were 102% and 101%, respectively, for the entire run. The run results showed an EC conversion of 57.5% and a selectivity of 91 mol% of EC versus DEC. The experimental results were converted to a DEC space yield of 1.60 lb / h / ft ³ .

Sample OVHD BTM Assay (% by weight) CO ₂ tr - NH ₃ 0.50 - ether 0.02 0.11 ethanol 90.21 17.60 DEC 7.30 5.50 EC 1.74 32.00 N-EEC 0.15 1.75 TG 0.04 21.05 Unidentified substance 0.04 9.34 HC * 0.00 0.95 catalyst** - 11.70 Water (ppm) 148 - Sn (ppm) 1.7 - * HC; Isocyanuric acid and 1,3,5-triethyl triazine-2,4,6-trione ** as dibutyltin dimethoxide

Claims (20)

(a) feeding a stream containing urea, alcohol, water and ammonium carbamate to the first reaction zone; (b) simultaneously in the first reaction zone, (i) reacting water with urea to form ammonium carbamate, (ii) decomposing ammonium carbamate to ammonia and carbon dioxide; And (c) removing ammonia, carbon dioxide, and alcohol from the first reaction zone; (d) removing urea and alcohol from the first reaction zone; (e) feeding the urea and alcohol to a second reaction zone; (f) reacting the alcohol and the urea in the presence of a homogeneous catalyst containing an organotin complex of dialkylalkoxide in a high boiling solvent to form a dialkyl carbonate; And (g) removing dialkyl carbonate and alcohol from said second reaction zone. The method of claim 1 wherein the alcohol and urea react in the first reaction zone to form an alkyl carbamate. The method of claim 1, wherein the alcohol is a C ₁ -C ₃ alcohol. The method of claim 1, (a) feeding said stream containing urea, methanol, water and ammonium carbamate to a first reaction zone; (b) simultaneously in the first reaction / distillation zone, (i) reacting water with urea to form ammonium carbamate, (ii) decomposing ammonium carbamate in the feed and ammonium carbamate derived from the reaction of water and urea to ammonia and carbon dioxide, (iii) separating ammonia, carbon monoxide and methanol from urea by distillation; (c) removing ammonia, carbon dioxide and methanol from the first reaction / distillation zone as first overhead; (d) removing urea and methanol in the first reaction / distillation zone as a first bottoms product; (e) feeding the first bottoms product and methanol to a second reaction / distillation zone; (f) simultaneously in the second reaction / distillation zone, (i) methanol and urea are reacted in the presence of a homogeneous catalyst containing an organotin complex of dialkylmethoxide in a high boiling solvent to form dimethyl carbonate, (ii) separating dimethyl carbonate and ammonia from the homogeneous catalyst by distillation; (g) removing dimethyl carbonate and methanol as a second overhead in the second reaction / distillation zone; And (h) removing the second bottoms product from the second distillation column reactor. 5. The process of claim 4 wherein the 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. The method of claim 4, wherein the methanol in the first overhead is condensed, a portion of the condensed methanol is returned to reflux near the top of the first distillation column reactor and the remainder of the condensed methanol is the first distillation column Returning to the bottom of the reactor. The method of claim 4, wherein the first portion of the second bed phase product is fed to the first distillation column reactor, the second portion of the second bed phase product is recycled to the second distillation column, and the second bed phase product. The third portion of is fed to a third distillation column reactor for catalyst regeneration and heavy purification. 5. The method of claim 4, wherein the second overhead is condensed and a portion of the condensed second overhead is returned to reflux to the second distillation column reactor. (a) feeding a stream containing urea, methanol, water and ammonium carbamate to the first distillation column reactor: (b) simultaneously in the first distillation column reactor; (i) reacting a portion of the urea with a portion of the methanol to produce methyl carbamate, (ii) reacting water with urea to produce ammonium carbamate, (iii) ammonium carbamate in the feed and ammonium carbamate derived from the reaction of water and urea with ammonia and carbon dioxide, (iv) separating ammonia, carbon monoxide and methanol from urea and methyl carbamate by distillation; (c) removing ammonia, carbon dioxide and methanol as a first overhead in the first distillation column reactor; (d) removing urea and methyl carbamate as the first bottoms product in the distillation column reactor; (e) feeding the first bottoms product and methanol to a second distillation column reactor; (f) simultaneously in the second distillation column reactor, (i) methanol and urea are reacted in the presence of a homogeneous catalyst containing an organotin complex of dialkylmethoxide in a high boiling solvent to form dimethyl carbonate, (ii) separating dimethyl carbonate and ammonia from the homogeneous catalyst by distillation; (g) removing dimethyl carbonate and methanol as a second overhead in said second distillation column reactor; (h) removing the homogeneous catalyst as a second bottoms product in the second distillation column reactor; (i) separating dimethyl carbonate in the second overhead from methanol by extractive distillation; (j) feeding a first portion of said second bed phase product to said first distillation column reactor; (k) feeding a second portion of the second bottoms product to a third distillation column reactor in which the catalyst is regenerated and the heavy is purified; And (l) recycling the third portion of the second bed phase product to the second distillation column reactor. (a) feeding a reactant containing urea and an alcohol to the main reaction zone; (b) supplying a solvent containing an organotin compound and a high boiling electron donor atom to the main reaction zone; And (c) at the same time in the main reaction zone, (i) reacting an alcohol and urea in the presence of the organotin compound and a solvent containing the high boiling electron donor atom to form a dialkyl carbonate; (ii) producing a dialkyl carbonate by reaction of a reactant containing urea and an alcohol containing water and ammonium carbonate as impurities, comprising the step of removing dialkyl carbonate and ammonia as vapor in said main reaction zone. In this case, the water is reacted with urea to form ammonium carbamate, and under the conditions of decomposing the ammonium carbamate into ammonia and carbon dioxide, the reactant is first supplied to the preliminary reaction zone, and the reactant is supplied according to step (a). Using a pre-reaction zone prior to the main reaction zone to remove water and ammonium carbamate from the reactant by removing ammonia and carbon dioxide from the reactant prior to the reaction. The method of claim 11, wherein the temperature of the pre-reaction zone is in the range of 200 to 380 ° F. in the liquid phase. 13. The method of claim 12, wherein the temperature of the preliminary reaction zone is in the range of 250 to 350 ° F. 12. The method of claim 11, wherein a portion of the methanol feed in the prereaction zone reacts with a portion of the urea feed to form methyl carbamate. 12. The method of claim 11, wherein the pre-reaction zone and the main reaction zone are operated under distillation conditions. 12. The process of claim 11, wherein water reacts with urea to form ammonium carbamate, which is then removed from the feed by a reaction in which ammonium carbamate is broken down into ammonia and carbon dioxide. The method of claim 16, wherein the temperature of the pre-reaction zone is in the range of 200 to 380 ° F. in the liquid phase. 12. The process of claim 11 wherein ammonium carbamate is removed from the feed by decomposition with ammonia and carbon dioxide. The method of claim 18, wherein the temperature of the pre-reaction zone is in the range of 200 to 380 ° F. in the liquid phase. 12. The method of claim 11, wherein the high boiling electron donor atom compound contains triethylene glycol dimethyl ether.

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