RU2367648C2 - Method for dialkylcarbonate preparation - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention refers to the improved method of dialkylcarbonate preparation due to interreaction of an alcohol, e.g. C1-C3 alcohols, with carbamide including removal in the prereactor of the water and ammonium carbamates admixture in starting materials. The water reacts with initial carbamide generating ammonium carbamate which is destructed together with present in starting materials ammonium carbamates to ammonia and carbon dioxide. Besides some amount of carbamide reacts with alcohol in the first reactor generating alkylcarbamate which is dialkylcarbonate precursor. Dialkylcarbonates are obtained in the second reaction zone. Undesirable side-products - alkyl-N-alkylcarbamates are continuously distilled off from second reaction zone together with ammonia, alcohol and dialkylcarbonates in steady mode of reactor operation. Alkyl-N-alkylcarbamate can be transformed to heterocyclic compounds in the third reaction zone in order to remove the solid material from the system. Admixtures removal from raw material flow is the main object of prereactor use. The additional improvement is made due to partial transformation of carbamide to alkylcarbamate proceeding in the prereactor which leads to increase of dialkylcarbonate formation rate in the primary reactor and to the decrease of alcohol recycle to the primary reactor. ^ EFFECT: increased dialkylcarbonate concentration in the upper flow from primary reactor reduces the dialkylcarbonate separation cost. ^ 23 cl, 5 dwg, 3 tbl, 5 ex

Description

FIELD OF THE INVENTION

The present invention relates to a method for producing dialkyl carbonates, in particular C ₁ -C ₃ dialkyl carbonates, in which the reaction occurs simultaneously with the separation of the reactants and carbonate products. More specifically, the invention relates to a method in which the alcohol is reacted with urea and / or alkyl carbamate in the presence of a complex compound catalyst. More specifically, the invention relates to a method in which impurities are removed from a feed stream in order to achieve stable catalyst operation, increase reaction rates and trouble-free operation of the equipment following the scheme.

State of the art

Dialkyl carbonates are important commercially available compounds, the most important of which is dimethyl carbonate (DMC). Dimethyl carbonate is used as a methylating and carbonylating agent and as a raw material for producing polycarbonates. It can also be used as a solvent to replace chlorinated solvents such as chlorobenzene.

Despite the fact that the prices of both dimethyl carbonate and diethyl carbonate are currently too high for their use as a fuel additive, both can be used as oxygenate in reformed gasoline and a high-octane component. Dimethyl carbonate contains significantly more oxygen (53%) than MTBE (methyl tert-butyl ether) or TAME (tertamyl methyl ether), and therefore less is required to achieve the same effect. It has an octane number of 130, and it is less volatile than both MTBE and TAME.

It has a pleasant smell, unlike esters, and is more easily biodegradable.

In old industrial processes, dimethyl carbonate was obtained from methanol and phosgene. Due to the extreme toxicity and high cost of phosgene, attempts have been made to develop improved methods without using the latter.

In one new industrial process, dimethyl carbonate is prepared from methanol, carbon monoxide, molecular oxygen and copper chloride by oxidative carbonylation in a two-step process in suspension. Such a method is disclosed in European Patent EP 0460735A2. The main disadvantages of this method are low productivity, high costs for the isolation of products, the formation of by-products, high processing requirements and the need for corrosion-resistant reactors and pipelines.

Another new method is disclosed in European Patents EP 0742198A2 and EP 0505374B1, in which dimethyl carbonate is obtained through the formation of methyl nitrite instead of copper (I) methoxychloride above. By-products are nitrogen oxides, carbon dioxide, methyl formate and others. Dimethyl carbonate from the reactor product stream is isolated by solvent extractive distillation using dimethyl oxalate as a solvent to break the azeotropic mixture. Despite the fact that the chemistry of the process is simple and productivity is increased, the method is very complicated due to the separation of a number of materials, the observance of the material balance in different parts of the process stream, complicated process control and the need to deal with methyl nitrite, a dangerous chemical compound.

In another industrial process, dimethyl carbonate is prepared from methanol and carbon dioxide in a two-step process. As disclosed in US Patents 4,786,741, 4,851,555, and 4,400,559, cyclic carbonates are prepared in the first step by reacting epoxides with carbon dioxide. In the second stage, dimethyl carbonate is produced together with glycol by the exchange of cyclic carbonates with methanol. See, for example, Y. Okada, et al "Dimethyl Carbonate Production for Fuel Additives", ACS, Div. Fuel Chem., Preprint, 41 (3), 1996, and John F. Knifton, et al, "Ethylene Glycol-Dimethyl Carbonate Cogeneration", Journal of Molecular Chemistry, vol. 67, pp. 389-399, 1991. Although this method has advantages, the reaction rate of epoxides with carbon dioxide is low and high pressure is required. In addition, the exchange reaction of a cyclic carbonate with methanol is limited by equilibrium conditions, and methanol and dimethyl carbonate form an azeotrope, which complicates their separation.

It has long been known that dialkyl carbonates can be obtained by reacting primary aliphatic alcohols such as methanol with urea (1) in the presence of various heterogeneous and homogeneous catalysts, such as dibutyltin dimethoxide, tetraphenyltin, and others. See, for example, 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 byproduct and can be processed into urea (2), as shown by the following reaction sequence.

Carbamates are obtained at a lower temperature, followed by dialkyl carbonates at a higher temperature, with ammonia being formed in both stages.

As noted above, two reactions are reversible under the required conditions. According to their catalytic activity, organotin compounds are arranged in the series R ₄ Sn <R ₃ SnX << R ₂ SnX ₂ , where X = Cl, RO, RCOO, RCOS. The maximum reaction rate and the minimum formation of by-products are observed for tin (IV) dialkyl compounds. For most catalysts (Lewis acids), a higher catalytic activity is claimed if the reaction is carried out in the presence of an appropriate co-catalyst (Lewis base). For example, triphenylphosphine and 4-dimethylaminopyridine are the preferred co-catalyst for catalysts based on organic tin (IV) compounds, such as dibutyltin dimethoxide, dibutyltin oxide and others. However, the thermal decomposition of the intermediate alkyl carbamates and urea into isocyanic acid (HNCO) or isocyanuric acid ((HNCO) ₃ ) and alcohol or ammonia (a co-product of the decomposition of urea) is also accelerated by organotin compounds such as dibutyltin dimethoxide or dibutyltin amide synthesis used. WO 95/17369 discloses a method for producing a dialkyl carbonate, such as dimethyl carbonate, in two stages from alcohols and urea, based on the chemistry and catalysts described by P. Ball et al. In the first step, the alcohol interacts with urea to produce alkyl carbamate. In the second stage, dialkyl carbonate is obtained by subsequent reaction of the alkyl carbamate with alcohol at higher temperatures than in the first stage. Reactions are carried out in an autoclave. However, when methanol reacts with methyl carbamate or urea, N-alkyl by-products, such as methyl N-methyl carbamate (N-MMK) and N-alkyl urea, also form according to the following reactions:

In order to minimize the formation of by-products, the content of dialkyl carbonate in the reactor is maintained from 1 to 3 wt.% Of the total content of carbamate and alcohol in the solution in the reactor.

In US Pat. No. 6010976, dimethyl carbonate (DMC) is synthesized from urea and methanol in a high yield in a single step in the presence of high boiling esters and a homogeneous tin complex catalyst.

The ether as a solvent also serves as a complexing agent in the formation of a homogeneous complex catalyst from dimethoxide or dibutyltin oxide in situ.

The separation of materials associated with the methods for producing DMK is very important for its industrial production for economic reasons. EP 0742198A1 and US Pat. No. 5,214,185 disclose the separation of DMC from a steam mixture of methanol and DMC using dimethyl oxalate (DMOX) as an extraction solvent. Due to the high melting point of DMOKS (54 ° C), the use of DMKS is inconvenient and leads to additional separation costs.

Both urea and alcohols are highly hygroscopic. Urea contains an admixture of ammonium carbamate. Therefore, water and ammonium carbamate are impurities in the initial urea and alcohol. It was found that these impurities cause catalyst deactivation and clogging of the pipeline in cold areas in the cooling system (cooler) of the upper vapor stream from the reactor. Water causes the deactivation of a catalyst containing alkoxyl groups, for example, methoxyl groups of an organotin complex, whose molecules actively react with water molecules, which leads to hydrolysis of the bond between the tin atom and the oxygen atom of the methoxy group. Ammonium carbamate causes problems in controlling the back pressure in the dialkyl carbonate reactor and clogging the cooling system (refrigerator) of the product stream in the vapor state from the dialkylation reactor due to the precipitation of ammonium carbamate.

SUMMARY OF THE INVENTION

Briefly, the present invention is an improved method for producing dialkyl carbonate, comprising the steps of:

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

(b) simultaneously in said first reaction zone

(i) the interaction of water with urea with the formation of ammonium carbamate,

(ii) the decomposition of ammonium carbamate present in the feed and ammonium carbamate resulting from the reaction of water with urea to ammonia and carbon dioxide, and

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

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

(e) supplying said urea and said alcohol to a second reaction zone;

(f) reacting said alcohol and urea in the presence of a homogeneous catalyst containing an organotin complex compound of dialkyl methoxide in a high boiling solvent to form dialkyl carbonate, and

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

Dialkyl carbonates are prepared by the reaction of alcohols, preferably C ₁ -C ₃ alcohols, with urea or alkyl carbamate, or both in the presence of a complex organotin compound with a high boiling electron-donor compound acting as a solvent, preferably dibutyltin dialkoxide and a high boiling oxygen-containing organic solvent, when the reaction is preferably carried out in reba a distillation apparatus or in a stirred reactor with simultaneous distillation of dialkyl carbonate. Water and ammonium carbamates, N-alkylated by-products and a minimal portion of alkyl carbamate are removed from the feed urea and alcohol feed.

Water is removed by reaction with urea in a prereactor having a preliminary reaction zone. Ammonium carbamate is removed by decomposition to ammonia and carbon dioxide in the prereactor. In addition, in the prereactor, urea is partially and selectively converted to alkyl carbamate, which leads to a higher reaction rate in the primary reactor, a decrease in alcohol recycle to the primary reactor from the dialkyl carbonate recovery unit or column, and a higher concentration of dialkyl carbonate in the overhead stream from the primary reactor. A higher concentration of dialkyl carbonate in the overhead stream from the primary reactor reduces the cost of separation of the dialkyl carbonate.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a schematic flow chart of one embodiment of the production of DMC according to the present invention.

In FIG. 2 is a schematic diagram of a DMK separation unit.

In FIG. 3 schematically illustrates one embodiment of the production of a DEC according to the present invention.

In FIG. 4 is a schematic diagram of an embodiment of a reactive distillation column reactor for the present method.

In FIG. 5 is a schematic diagram of an embodiment of a catalytic stirred tank reactor with a distillation column connected for the present method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An admixture of water from the introduced initial urea and alcohol is removed by the interaction of water with urea in the prereactor, while ammonium carbamate is removed in the prereactor by decomposing it to ammonia and carbon dioxide. The prereactor must be operated under favorable conditions for decomposition, so that ammonia and carbon dioxide can be removed as vapors. If the decomposition does not pass completely, unreacted ammonium carbamate will enter the primary reactor and turn into urea and water, and urea in turn decomposes into ammonia and carbon dioxide, causing catalyst deactivation. Urea is partially converted in the prereactor to alkyl carbamate. The following main reactions proceed in the prereactor:

Since the above four reactions are reversible and occur simultaneously in the preliminary reaction zone in the prereactor, it is important to control the temperature and pressures in the prereactor and the primary reactor. Reactions (1), (2), (3) and (4) proceed in the prereactor at a temperature of from 200 to 380 ° F, preferably from 250 to 350 ° F in the liquid phase in the prereactor. A preferred pressure range at the top of the pre-reactor is from 30 to 300 psig. However, the pressure in the upper part is determined mainly by the required temperature in the pre-reactor column and the composition of the liquid in the reactor. Reaction (4) reaches equilibrium even in the absence of a catalyst, but it proceeds much faster in the presence of a catalyst such as a complex catalyst based on dibutyltin dialkoxide and a slightly acidic or basic heterogeneous catalyst such as zinc oxide, tin oxide, titanium oxide, zirconium oxide, molybdenum oxide, talcite, calcium carbonate, zinc hydroxide carbonate, zirconium carbonate and the like, supported on an inert carrier such as silica, calcined at high temperature (> 850 ° C) alumina. The preferred concentration of urea in the liquid phase in the preliminary reaction zone under these conditions is less than 80 wt.%, Preferably 50 wt.%. In order for decomposition of ammonium carbamate to occur, the partial pressures of ammonia and carbon dioxide must be kept below the decomposition pressure of ammonium carbamate. It is also highly desirable to efficiently remove products, ammonia and carbon dioxide, from the pre-reaction zone of the pre-reactor, preferably, as an option, in the form of a vapor mixture together with alcohol and any inert gas that is removed. Alcohol vapors, if desired, can be used as the sole gas for removal. Thus, the improvement lies in the method for producing dialkyl carbonates by reacting reagents, including urea and alcohol, containing water and ammonium carbamate as impurities, comprising the steps of:

(a) feeding reactants containing urea and alcohol to the primary reaction zone;

(b) feeding the organotin compound and the high boiling solvent containing electron donor atom to said primary reaction zone; and

(c) simultaneously in the specified primary reaction zone

(i) the interaction of alcohol and urea in the presence of said organotin compound and said high boiling point electron-donating atom-containing solvent to produce a dialkyl carbonate; and

(ii) removing the dialkyl carbonate and ammonia from said primary reaction zone as vapors,

in which the improvement is the use of a preliminary reaction zone in front of the primary reaction zone to remove water and ammonium carbamate from these reagents by feeding the reagents first to the preliminary reaction zone under conditions under which said water reacts with urea to form ammonium carbamate, and decomposition of ammonium carbamate to ammonia and carbon dioxide, and removing ammonia and carbon dioxide from said reagents before feeding the reagents to step (b), preferably at temperatures in the range of 200 to 380 ° F, more preferably 250 to 350 ° F, and preferably in the liquid phase. Preferably, part of the urea and the alcohol are reacted to form alkyl carbamate in the pre-reaction zone.

A preferred embodiment of the method for producing dialkyl carbonates includes the steps of:

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

(i) purification from impurities of raw materials in the prereactor;

(ii) removing ammonia, carbon dioxide and alcohol as vapors;

(iii) the interaction of a portion of urea and alcohol in an alkyl carbamate; and

(iv) removing a liquid stream containing alkyl carbamate, urea and alcohol for introduction into the primary reaction zone;

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

(c) simultaneously in the specified primary reaction zone

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

(ii) removing dialkyl carbonate and ammonia, ether, carbon dioxide, alkyl-N-alkyl carbamate and alkyl carbamate from the above primary reaction zone in the form of vapors; and

(d) converting the alkyl N-alkyl carbamate separated from the steam stream and in a small stream transferring the liquid reaction medium from the primary reaction zone to said heterocyclic compound ((RNCO) ₃ , where R is H or

C _n H _{2n + 1} and n = 1, 2 or 3) in said third reaction zone of purification, and conversion of alkyl carbamate to dialkyl carbonate;

(i) removing heterocyclic compounds in a stream from the third reaction zone in the form of solid materials;

(ii) returning the redirected fluid stream to the primary reaction zone and the purification reaction zone, and

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

This embodiment offers improvements that include the use of a preliminary reaction zone to remove water and ammonium carbamate from said urea and alcohol, preferably at a temperature in the range of 200 to 380 ° F, more preferably 250 to 350 ° F, and preferably in liquid phase, and using the purification reaction zone to convert the alkyl N-alkyl carbamate by-product to heterocyclic compounds at a temperature in the range of 300 to 400 ° F. in the liquid phase to remove from the system as a solid th substance.

A preferred prereactor is a column reactor with two diameters in height (a larger diameter at the bottom). The initial solution of urea in alcohol is introduced into the column prereactor in the middle part of the upper section with a smaller diameter. Ammonium carbamate in the initial urea decomposes into ammonia and carbon dioxide. The temperature in the column is maintained at 200 to 380 ° F at a pressure of 50 to 350 psig. The light reaction products, ammonia and carbon dioxide, are removed from the column as an overhead vapor stream along with alcohol vapors. Urea in the feed stream is at least partially converted into alkyl carbamate in this prereactor. This reaction is exothermic. The conversion of urea is more than 10%, preferably more than 50%. The conversion of urea to alkyl carbamate can also be carried out in the absence of a complex catalyst. But with a catalyst, the conversion rate is higher.

Removing impurities of water and ammonium carbamate from the feed stream solves the problems associated with maintaining the catalyst in an active state, controlling the pressure in the upper part of the distillation column, and clogging the cooling surface of the upper vapor stream from the primary reactor due to the precipitation of ammonium carbamate. Purification of raw materials from impurities is carried out in a pre-reactor, which is a reactor with a distillation column with two different diameters in height. Removing impurities from the feed stream is the main purpose of using a pre-reactor. Further improvement was made due to at least partial conversion of urea into an alkyl carbamate in the prereactor, which leads to a higher reaction rate of dialkyl carbonate production in the primary reactor, a decrease in alcohol recycle to the primary reactor from the dialkyl carbonate recovery unit, due to the higher concentration of dialkyl carbonate in the upper flow from the primary reactor. In the production of dialkyl carbonate, a higher concentration of dialkyl carbonate in the overhead stream from the primary reactor reduces the costs of the isolation of the dialkyl carbonate.

The primary reactor in which the dialkyl carbonate is formed is a stirred reactor equipped with a heat exchanger to extract the latent heat of the product vapor stream from the primary reactor. The recovered heat is used to recycle the alcohol from the alcohol recovery column to the primary reactor. This is not necessary, but it is not necessary that the liquid reaction medium is mechanically mixed. In the present invention, the primary distillation reactor distillation column operates unusually, as a result of which undesired N-alkylated by-products are removed from the liquid reaction zone as part of the overhead product stream, which allows the by-product content to be kept to a minimum, so that the reactor can be operated at a constant liquid level without filling the liquid reaction zone with undesirable by-products for a long period of reactor operation without interruptions. This is extremely important for the industrial production of dialkyl carbonate. Lower concentrations of urea, alkyl carbamate, and dialkyl carbonate in the liquid medium are used to minimize the rate of formation of N-alkylated by-products by using a higher concentration of a high boiling solvent such as triglyme. However, if the concentration of the alkyl carbamate is too low, an unacceptably low DMC reactor productivity may occur.

It was found that in order to prevent the accumulation of such by-products, such as alkyl-N-alkyl carbamate and heterocyclic compounds, in the primary reactor, alkyl-N-alkyl carbamate should be continuously distilled from the liquid reaction medium, while the dialkyl carbonate production reaction is carried out while controlling the temperature and flow pressure steam the distillation column of the primary reactor, and turn into heterocyclic compounds that can be removed from the system in solid form. In other words, it was found that constant concentrations of alkyl-N-alkyl carbamate and heterocyclic compounds in a given liquid reaction volume of the primary reaction zone can be maintained under constant operating conditions of the reactor. It has also been found that the surface temperature of any interior of the primary reactor at temperatures below 550 ° F, preferably below 450 ° F, is highly desirable to minimize the formation of heterocyclic compounds in the primary reaction zone. The conversion of alkyl N-alkyl carbamates to heterocyclic compounds is carried out using a third purification reaction zone.

A preferred purification reactor for this purpose is a stirred reactor equipped with an attached distillation column, condenser and reflux collector. The alkyl N-alkyl carbamate by-product obtained by alkylating the alkyl carbamate with the dialkyl carbonate in the primary reaction zone is continuously removed as part of the overhead vapor stream along with other products by controlling the temperature of the vapor from the primary reaction zone at a column temperature higher than 255 ° F, preferably higher 265 ° F.

Alkyl-N-alkylcarbamate is recovered from the overhead stream from the primary reactor and introduced into the purification reactor. The purification reactor is preferably operated at a temperature of the liquid reaction medium in the range of 330 to 400 ° F. It is important that the temperature in the column and the pressure at the top of the column are controlled so that the top steam stream does not contain alkyl-N-alkyl carbamate. Typically, the purification reactor is operated at a temperature and pressure at the top of at least 2 ° F and 5 psig higher than in the primary reactor.

The by-product removal method disclosed in this invention can be extended to prototypes such as US Pat. No. 6,359,163 B2 (2002) and WO 95/17369 (1995), US Pat. No. 6,031,122 (2000), and European Patent EP 1167339 (2002). devoted to the production of dialkyl carbonate from urea and alcohol, regardless of whether the solvent is used or not in the primary reactor and purification reactor.

To obtain a higher molecular weight alkyl carbonate such as dipropyl carbonate, dibutyl carbonate and so on, removing the alkyl N-alkyl carbamate from the primary reactor as parts of the overhead stream becomes difficult. Therefore, the liquid portion of the stream is withdrawn from the primary reactor in larger quantities to the purification reactor. The alkyl-N-alkyl carbamate in this transition stream is converted to separable high boiling materials in a purification reactor as disclosed in this invention. After the removal of high boiling waste in the lower stream from the purification reactor, the remaining liquid stream can be returned to the primary reactor and purification reactor.

Various physical devices can be used as a prereactor. These include a distillation column reactor, a stirred reactor, a bubble reactor, a tubular reactor, a fluidized bed reactor, or any combination thereof. A preferred apparatus is a distillation column reactor in which reactions are carried out under reaction-distillation conditions. Despite the reversibility of reactions (1), (2), and (3), the use of a reactor with a distillation column allows one to shift the equilibrium of the three reactions to the right, i.e., to completely remove water and ammonium carbamate from the feed stream. Urea is partially converted in the prereactor to alkyl carbamate according to the reversible reaction (4). By removing ammonia from the reaction zone in the form of an upper gas mixture, the equilibrium of reaction (4) can also be shifted to the right. Partial conversion of urea to alkyl carbamate increases the rate of conversion of alkyl carbamate to dialkyl carbonate in the primary reactor and provides a higher concentration of dialkyl carbonate in the overhead stream from the primary reactor, since the interaction of urea with alcohol to produce dialkyl carbonate proceeds in two stages, and reaction (4) is the first stage.

The reaction of the formation of dialkyl carbonate proceeds as follows:

The reaction (5) is carried out in a primary reactor in the presence of a high boiling solvent in the reaction-distillation mode to create a favorable condition for the rapid removal of dialkyl carbonate from the reaction medium at the time of its formation.

The rate of formation of dialkyl carbonate in the primary reactor is more sensitive to the concentration of ammonia in the reaction medium in the primary reactor than the rate of formation of alkyl carbamate in the prereactor due to chemical thermodynamics. The rate of formation of dialkyl carbonate becomes higher if, at a given concentration of alkyl carbamate, there is a lower concentration of ammonia in the liquid reaction medium in the primary reactor. The temperature of the reaction medium in the primary reactor is from 300 to 450 ° F, preferably from 320 to 400 ° F, most preferably from 330 to 360 ° F at atmospheric pressure to 150 psig, preferably from 30 to 120 psig. Any combination of the required temperature and pressure, which leads to high selectivity for dialkyl carbonate, can be obtained by selecting the appropriate high boiling solvent and controlling the concentration of the solvent in the primary reactor. It is highly desirable that, during operation, the primary reactor has an upper vapor temperature of at least about 300 ° F, preferably higher than 320 ° F, to extract the latent heat of the upper vapor stream used to recycle the alcohol in the form of superheated alcohol vapor in the primary reactor and prereactor.

The use of a high boiling solvent in the primary reactor allows the reaction to be carried out at low pressure and a low concentration of carbamate in the liquid reaction medium. Lower pressure promotes faster removal of dialkyl carbonate from the liquid reaction medium to the vapor phase, resulting in lower concentrations of dialkyl carbonate in the liquid reaction medium. The lower the concentrations of dialkyl carbonate and carbamate / urea in the liquid reaction medium, the lower the amount of undesirable by-products associated with N-alkylation and decomposition of products, urea, alkyl carbamate and N-alkylated products in the primary reactor. A preferred solvent for the synthesis of dialkyl carbonates should have the following properties: (1) the solvent should have a boiling point at least 20 ° F higher than the boiling point of the product, dialkyl carbonate; and (2) It should not form an azeotropic mixture with dialkyl carbonate. Examples of such a solvent are high boiling ethers, ketones, hydrocarbons, and their esters and mixtures; triethylene glycol dimethyl ether, tetraethylene glycol dialkyl ether, anisole, dimethoxybenzene, thimethoxytoluene, alkyloxalate, decalin, tetraline, xylene, decane and so on, or mixtures thereof.

A stream of superheated alcohol vapor is directly introduced into the liquid reaction zone to provide heat for the reaction of converting the alkyl carbamate to a dialkyl carbonate, which is weakly endothermic, and dialkyl carbonate and ammonia are removed from the liquid reaction medium as soon as the dialkyl carbonate is formed. The required total concentration of alkyl carbamate and urea combined in the reaction medium is from 10 to 60 wt.%, Preferably from 15 to 50 wt.% Of the total amount of materials in the liquid reaction medium. The desired concentration of dialkyl carbonate in the reaction medium is from 0.5 to 12 wt.%, Preferably from 2 to 9 wt.% Of the total content of materials in 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 2 to 20 wt.% Tin, preferably from 5 to 17 wt.% Tin of the total content of all materials in the liquid reaction zone in the primary reactor. It should be noted that the catalyst also accelerates the undesirable side reactions discussed above. Carrying out the reaction at a lower temperature reduces side reactions. However, the rate of production of dialkyl carbonate is also reduced, which may not be acceptable for the industrial production of DMC. The desired concentration of high boiling solvent in the reaction medium in the primary reactor is from 2 to 65 wt.%, Preferably from 2.5 to 55 wt.% Of the total amount of materials in the reaction medium.

The catalyst used under steady conditions is a catalytic system based on an organotin complex obtained from an organotin complex compound of dialkyltin dialkoxide,

R ' _4-n Sn (OR) _n · xL (where R' is an alkyl group, an aryl or aralkyl group; R = alkyl; n = 1 or 2; x = 1 or 2; L is an electron-donating 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 succinate, anisole, dimethoxybenzene, dimethoxytoluene, ethylene glycol, catechin, 1,4-dioxane-2,3-diol, 2-methyl-tetrahydrofu 2,4-pentanedione, 3-methyltetrahydropyran, triphenylphosphine and others. A homogeneous catalytic system is a quasi-equilibrium mixture of various organotin compounds. Suitable catalysts of this type and method for their preparation are described in US Pat.

The applied catalytic system under steady-state reaction conditions is a mixture of various soluble organotin monomeric, dimeric and oligomeric compounds, which are obtained by a number of possible reactions. These various organotin compounds are to a greater or lesser extent in a quasi-equilibrium state under the given reaction conditions. Dialkyltin oxide, dialkyltin halides, dialkyltin bis (acetylacetonate) and dialkyltin carboxylates such as dibutyltin diacetate, dibutyltin oxalate, dibutyltin malonate, dibutyltin diacetate can be used to react with as a result of reaction with alcohol in the presence of a high boiling solvent such as triglyme. Alkyl groups attached to the tin atom may be the same or different. For example, the catalyst precursor may be dibutyltin, butylbenzyltin, butylphenyltin, butylctyltin or di-2-phenylethyltin dialkoxide, dihalides, hydroxyhalide, diacetate or oxide. Associated products, water, carboxylic acid, or salic acid, are continuously removed from the liquid reaction medium as an overhead stream of steam in the presence of a high boiling solvent at low pressure. The appropriate temperature for the catalyst formation reaction is 200 to 400 ° F and the pressure is atmospheric to 150 psig. In a preferred embodiment, methanol, ethanol or propanol, depending on the intended dialkyl carbonate product, is continuously pumped to the primary reactor. Either methanol or ethanol are acceptable for the preparation of IEC. The catalyst formation reaction is preferably carried out in the presence of dilute alkyl carbamate, alkyl N-alkyl carbamate, or a dialkyl solution in a primary reactor. It is assumed that during this catalyst formation reaction, the distillation column should operate under conditions that allow the removal of related products, water, carboxylic acid or hydrogen chloride, as an overhead stream together with alcohol as an overhead from the reaction zone. To obtain dimethyl carbonate, a soluble complex organotin catalyst system is prepared by simply mixing dibutyltin dimethoxide with triglyme (as a complexing agent to form an organotin complex catalyst) and methanol in a primary reactor before initiating a dialkyl carbonate formation reaction in the presence of a high boiling solvent. To obtain diethyl carbonate, a soluble complex organotin catalyst system is preferably prepared using dibutyltin dimethoxide with triglyme and ethanol in a primary reactor. As the reaction proceeds, the methoxyl groups in the catalyst are replaced by ethoxyl groups.

Let us now consider FIG. 1, where a flow chart of one embodiment of the invention is schematically shown. In FIG. 1 is a flow chart of an improved method without installing a DMK separation. The DMC separation unit is shown in FIG. 2. The reaction-distillation column reactor 111 is used as a prereactor to remove impurities from the feed stream and to partially convert urea to methyl carbamate. The urea solution is obtained in tank 131 by mixing the initial urea 1 and methanol stream 3. The methanol stream consists of a fresh methanol stream 2 and a methanol stream 4, which is part of the methanol stream 30 from the DMC separation unit. The methanol recycle stream 30 from the DMC separation unit (see FIG. 2) is divided into three streams (4 and 33 through 31, and 32) for use in the preparation of the urea solution, into the primary reactor 112 and the purification reactor 113. The urea stock solution 5 of tank 131 is introduced in the middle of a narrower section of the column with two different diameters in height of the column reactor 111. The reactor 111 serves as a prereactor for purification of the initial methanol and urea from impurities (water and ammonium carbamate), and for the partial conversion of urea to MK. The vapor stream 6 from the prereactor 111 consists of ammonia, carbon dioxide and methanol. The purified solution of a mixture of MK and urea in methanol is removed from the prereactor 111 in the form of a bottom stream 7 and combined with the stream of recirculated liquid 22 from the cooling / filtration system 133 through line 20 to stream 8. The stream of recycle liquid 20 from the cooling / filtration system 133 is divided into two stream (21 and 22) for recycling to primary reactor 112 and purification reactor 113. Combined stream 8 is introduced into the primary reactor (stirred reactor or optionally bubble column reactor) 112. Methanol recycle stream 33 from the DMC separation unit is introduced to primary reactor 112 in the form of superheated methanol vapor. The top stream of recycle 14 from the evaporation column 132 is introduced into the primary reactor. Stream 14 consists mainly of MK and minor amounts of N-MMK and methanol. The overhead vapor stream 9 from primary reactor 112 consists of ammonia, CO ₂ , dimethyl ether, methanol, DMK, MK, N-MMK, TG and a small amount of organotin catalyst. This overhead stream 9 from the primary reactor 112 is combined with the overhead stream 17 from the purification reactor with stirrer 113 into stream 10. Stream 17 consists of ammonia, CO ₂ , dimethyl ether, methanol and DMC. The combined stream 10 is introduced into the distillation column 151 to separate the components, ammonia, CO ₂ , dimethyl ether, methanol and DMC from the remainder of the heavier components in the stream. The overhead stream 12 from the column 151 is combined with the overhead stream 6 from the prereactor 111 into the stream 23. The combined stream 23 is introduced into the distillation column 134. The overhead stream 25 from the column 134 is directed to an ammonium carbamate removal system 135, where the stream 25 is suitably cooled so that initiate the reaction of CO ₂ and ammonia into ammonium carbamate and precipitation of solid ammonium carbamate. Solid ammonium carbamate can be removed using filtration or a hydrocyclone. Stream 27 from ammonium carbamate removal system 135 is introduced into distillation column 136 to recover ammonia. An overhead stream 28 from column 136 is directed to an ammonia storage tank. The bottom stream 29 from column 136 is an organic waste, mainly consisting of dimethyl ether. The bottom stream 24 from the column 134 is directed to the DMC separation unit shown in FIG. 2. Stream 24 consists of DMC and methanol. The bottom stream 13 from the column 151 is directed to the evaporation column 132.

Stream 13 consists of methanol, MK, N-MMK, TG and a small amount of catalyst. The bottom stream 15 of the evaporation column 132 consists of N-MMK, MK (a small amount), TG and a small amount of organotin catalyst. Stream 15 is combined with a small liquid stream of transition 11 from the primary reactor 112 to stream 16. The combined stream 16 is introduced into the purification reactor 113 (optionally a small dilute stream 11 from the primary reactor 112 can be introduced into the lower section or columns 151 or 132). Bottom stream 18 from purification reactor 113 is cooled to precipitate heterocyclic compounds such as isocyanuric acid, 1,3,5-trimethyltriazine-2,4,6-trion and others in the stream, and the precipitate is removed from filtration system 133 as a solid along line 19. The stream of liquid filtrate 20 from the filtration system 133 is divided into two streams 21 and 22 for recycling back to the primary reactor 112 and the purification reactor 113.

The primary reactor may be a single stirred reactor or a system with several stirred reactors, depending on the dialkyl carbonate production capacity. For example, if the primary reactor consists of three reactors with a stirrer connected in series, the purified alkyl carbamate / urea feed stream 7 from the prereactor 111 is respectively divided into three streams, and each stream is introduced directly into the three reactors.

The liquid reaction stream is withdrawn from one reactor and introduced into the next reactor. The liquid reaction stream from the third reactor is sent to the first reactor. The small dilute stream from the liquid reaction stream from the third reactor is combined with the bottom stream 15 from column 132 to stream 16, which is sent to purification reactor 113. The alcohol recycle stream, such as methanol recycle stream 33 from the DMC separation unit, is introduced into the first reactor as superheated alcohol vapors. An overhead stream of steam from the first stirred reactor is introduced into the second reactor. The upper vapor stream from the second reactor is introduced into the third reactor. The dialkyl carbonate content in the overhead stream from each reactor increases as the vapor stream moves from the first reactor to the third reactor, resulting in the highest DMC concentration in the overhead stream from the third reactor. The overhead stream 9 from the third reactor is combined with the overhead stream 17 from the purification reactor 113 into a stream 10 that is introduced into the distillation column 151.

The bottom stream 24 from the distillation column 134 is sent to the installation separation of DMK (see Fig. 2). This stream contains about 28 wt.% DMC. Stream 24 from column 134 is introduced into extractive distillation column 137 through line 34.

An overhead stream 35, which consists of 98% by weight methanol and 2% by weight DMC, is recycled along line 30 of FIG. 1. The bottom stream 36 is introduced into the extraction solvent extraction column 138. The extraction solvent, anisole, is recovered as the bottom stream 38 from the column 138 and recycled back to the column 137 through line 38. The upper stream 37 from the column 138 is a DMC product that is sent into the storage tank for DMK.

Diethyl carbonate (DEC) can be obtained in a similar manner as described above to obtain DMC. Since the mixture of ethanol and DEC does not form an azeotrope, the separation of DEC from ethanol can be carried out in a single distillation column.

In FIG. 3 schematically shows a flow chart of a method for producing a DEC. A urea solution is prepared in a tank 141 by mixing the starting urea 101 and the ethanol stream 103. The ethanol stream 103 consists of fresh starting ethanol 102 and ethanol recycle stream 155, which is part of the ethanol recycle stream 130.

The ethanol recycle stream 130 consists of an upper stream 117 from a distillation column 146 and a lower stream 129 from a distillation column 145 (ethanol recovery column). The ethanol recycle stream 130 is divided into two streams 152 and 156. The stream 152 is recycled to the purification reactor 123. The stream 156 is again divided into two streams 155 and 157 for recycling to the tank 141 and primary reactor 122, respectively. The ethanol recycle stream 157 is introduced into the primary reactor 122. The urea solution 104 from the tank 141 is introduced into the middle of the upper narrower section of the column of the column reactor with two different diameters in height 121. The reactor 121 serves as a prereactor for purification of impurities (water and ammonium carbamate) raw materials, ethanol and urea, and for the partial conversion of urea into EC. The vapor stream 105 from prereactor 121 consists of ammonia, carbon dioxide and ethanol. The purified solution of the mixture is removed from the prereactor 121 as a bottom stream 106. Stream 106 is introduced into the primary reactor (a stirred reactor or optionally a bubble column reactor) 122. The recycle stream of ethanol 157 (this stream is the main part of the ethanol recycle stream 130) is introduced into primary reactor 122 in the form of superheated ethanol vapor. The small dilute stream 108 from the primary reactor 122 is combined with the bottom stream 120 from the recovery column of the DEK 147 to form stream 161 and the combined stream 161 is introduced into the purification reactor 123. The diluted stream 108 consists of ethanol, ammonia, diethyl ether, DES, ethyl carbamate, ethyl- N-ethyl carbamate, TG, heterocyclic compounds such as isocyanuric acid, 1,3,5-triethyltriazine-2,4,6-trion and others, and an organotin complex catalyst. Stream 120 consists of ethanol, ethyl carbamate, N-ethyl carbamate, TG, and trace amounts of catalyst. Overhead stream 160 from purification reactor 123 consists of ammonia, CO ₂ , diethyl ether, ethanol, and DEC. The bottom stream 159 from purification reactor 123 consists of ethyl carbamate, triglyme, ethyl N-ethyl carbamate, ethanol, heterocyclic compounds and a homogeneous organotin catalyst. The bottom stream 159 from reactor 123 is cooled to precipitate heterocyclic compounds in the cooling / filtration system 148.

The precipitated solid by-product is removed from system 148 via line 124.

The liquid stream 125 from the system 148 is divided into two streams 126 and 127 for recycling to the primary reactor 122 and the purification reactor 123. The upper stream 107 from the primary reactor 122 is combined with the upper stream 160 from the purification reactor 123 to the stream 109. The upper vapor stream 107 from the primary reactor 122 consists of ammonia, CO ₂ , diethyl ether, ethanol, ethyl carbamate, ethyl N-ethyl carbamate, DEK, TG and trace amounts of catalyst. Stream 107 is combined with overhead stream 160 from purification reactor 123 to stream 109. Overhead stream 160 consists of ammonia, CO ₂ , diethyl ether, ethanol and DEC. The combined stream 109 is introduced into the distillation column 142. The upper stream 110 from the column 142, which consists of ammonia, CO ₂ , diethyl ether and ethanol, is introduced into the distillation column 143. The upper stream 154 from the column 143 is cooled to cause the reaction of CO ₂ with ammonia with the receipt of ammonium carbamate. Ammonium carbamate is precipitated in liquid ammonia and removed as a solid through line 115 from the cooling / filtration system 144. The flow of liquid ammonia 116 from the cooling / filtration system 144 is directed to an ammonia storage tank. The bottom stream 150 from column 142 consists of DEC, ethanol, ethyl carbamate, ethyl N-ethyl carbamate, TG and trace amounts of catalyst. Stream 150 is introduced into distillation column 146 (first ethanol recovery column). The upper ethanol stream 117 from column 146 is combined with the lower ethanol stream 129 from distillation column 145 (second ethanol recovery column) to ethanol recycle stream 130.

Bottom stream 118 from column 146 is introduced into distillation column 147 (DEC extraction column). Overhead stream 119 is a product, DEC, which is sent to a storage tank for DEC. The bottom stream 120 from column 147 is combined with a small stream of transition 108 from primary reactor 122, and the combined stream 161 is introduced into the reactor with a purifier 123. The top stream 160, which consists of ammonia, CO ₂ , diethyl ether, ethanol and DES, is sent to column 142 along line 109. The bottom stream 114 from column 143 is sent to a distillation column 145 to separate diethyl ether from ethanol in the stream. The overhead stream of the by-product, ether, 128 is sent to an ether storage tank. The bottom stream 129 from column 145 is ethanol, which is recycled to purification reactor 123 and primary reactor 122 via line 130.

A mixed dialkyl carbonate, such as methyl ethyl carbonate (MEK), is prepared using appropriate mixtures of methanol and ethanol as a feed stream instead of a stream of methanol feed or a stream of ethanol feed in a urea solution tank.

However, the overhead streams from the primary reactor and the purification reactor contain some DMC and DEC in addition to the IEC. DEC and DMK are separated from the mixture and the exchange reaction of DEC and DMC in the MEC is carried out in a separate reactor (not shown). This exchange reaction is carried out using either a basic heterogeneous catalyst such as alkaline zeolites, basic talcite, etc., or a homogeneous catalyst such as Group IVB compounds such as titanium tetraethoxide or ethoxycarbonates or dialkyltin compounds such as alkoxide, methoxyalkyl carbonate dialkyltin, dialkyltin carbonate, or an organotin complex catalyst system discussed above in the absence or presence of a solvent. An appropriate solvent should have a boiling point higher than 265 ° F. Examples of such a solvent are hydrocarbons such as decalin, decane, xylene, diglyme, triglyme, and so on, or mixtures thereof.

In FIG. 4 shows a reactive distillation column reactor using a basic heterogeneous catalyst. The original DEC is introduced into the reaction-distillation column reactor 153 along lines 221 at the position of the upper part of the catalyst layer. The starting DMC is introduced at 153 to a position below the catalyst layer along line 222. The upper stream 223 consists mainly of DMC and MEK. Stream 223 is sent to an IEC separation unit. The temperature of the liquid catalytic reaction zone is maintained between 200 and 450 ° F, preferably between 235 and 380 ° F. To prevent the accumulation of heavy residues in the reboiler of the column reactor 153, a small amount of bottom residue is withdrawn via line 224.

In FIG. 5 shows a catalytic reactor with a stirrer 158 with an attached distillation column 162. A homogeneous catalyst such as dibutyltin dimethoxide is used. A predetermined amount of a homogeneous catalyst is loaded into the reactor 158 before carrying out the reaction. The initial DEK / DMK mixture is introduced into the reactor 158 via line 301. The top stream 303 of 162 consists mainly of DMK, and a small amount of MEK is recycled back to the reactor 158. The stream of side fraction 302, which is enriched in accordance with IEC, from the distillation column 162 is sent to distillation column 163 for separating IEC from DMK. The upper stream 304 from the column 163 is recycled back to the reactor 158. The lower stream of IEC 305 from the column 163 is directed to an IEC storage tank. The temperature of the liquid catalytic reaction zone is maintained between 200 and 450 ° F, preferably between 235 and 380 ° F. The pressure range in the upper part of column 162 is from 20 psig to 150 psig, preferably from 25 to 120 psig. But the pressure in the upper part of column 162 is determined by the estimated temperature of the liquid reaction medium at 158, the composition of the reaction medium, and the fact that a solvent is used or not.

Example 1

In this example, water and urea are reacted. The following materials are charged into a 500 ml three-necked flask equipped with a magnetic stirrer and a water-cooled reflux condenser: 229.67 grams of triethylene glycol dimethyl ether (triglyme), 1.58 grams of water, 2.06 grams of methanol and 15.89 grams of urea. When the reaction temperature of the mixture in the flask reaches 100 ° C, an additional 3.2 grams of methanol is added. The interaction of water with urea is carried out at a temperature of from 128 to 140 ° C for 0.92 hours in a nitrogen atmosphere. The analysis of the sample taken from the flask is carried out using GC and HPLC. The analysis results showed 22.4% urea conversion and 45.2% water conversion.

Example 2

General description of the experiment

A one liter autoclave serves as a reaction zone and a reboiler for a reactive distillation column reactor that is connected to a distillation column with a diameter of 1 inch and a height of 3.5 feet. The distillation column has three heating zones, which are independently regulated. The top steam stream from the distillation column is diluted with a stream of nitrogen (800 cm ³ / min) and then partially cooled to 200 ° F with hot water in a condenser. Steam flow from a refrigerator cooled to room temperature to prevent problems with clogging of cold areas and the upper back pressure regulator. The liquid stream from the condenser enters a small upper reflux tank. The collection of phlegm maintains room temperature. The flow of liquid product from the upper reflux tank is controlled by BCF (liquid flow meter). The liquid stream from the upper reflux tank and the cooled vapor stream are combined as a product stream from a reactive distillation reactor. Samples are taken for analysis to determine the composition of the top stream of steam leaving the column. Samples were also taken periodically from the reboiler to control the composition of the liquid reaction medium. Whenever samples were taken from a reboiler, additional solutions were introduced there to compensate for the loss of triglyme and catalyst.

During the operation of the reactor, the liquid level inside the reboiler was kept constant. The reboiler is equipped with a vertical sight glass for visual observation of the liquid level inside the reboiler during operation. The reboiler is also equipped with a digital liquid level monitor for automatic regulation of the reactor at night and during the weekend for automatic operation.

To carry out the operation of the primary reactor with the production of DMC, the initial MK solution (methyl carbamate in methanol) and the initial methanol are fed and combined into a single stream. The combined feed stream is passed through a prereactor (vertically fixed upstream tubular reactor) at 300 ° F and 230 psig to remove water from the feed stream, and then introduced into the primary reactor. The temperature of the liquid reaction medium is controlled by adjusting the pressure in the upper part of the distillation column and the concentration of high boiling solvent in the reboiler of the distillation column. DMC products, ammonia, and other light by-products, such as dimethyl ether and CO ₂ , are distilled off from the liquid medium and removed together with methanol vapor. The work of the distillation column is carried out in a special mode for partial condensation of the steam leaving the liquid medium in the reboiler without returning the liquid from the upper reflux collector by controlling the temperature of the steam, which is carried out by controlling the temperature of the column with three heating zones of the column when the steam rises through the distillation column. It was found that the operation of the column in a special mode makes it possible to keep the triglyme solvent in the reactor and continuously remove the by-product of N-MMK together with MK from the liquid reaction medium as part of the overhead stream, which allows the reactor to be operated for a long period of time. It was found that the return of liquid from the upper reflux collector is extremely preferable to minimize the formation of a by-product of N-MMK and heterocyclic compounds. It was possible to operate the reactive distillation column reactor for more than 1000 hours without interruption until a high nitrogen pressure regulator for the reboiler was accidentally opened. Normal operation of the distillation column will stop or remove materials from the reboiler due to reboiler overflow due to accumulation of reaction by-products such as N-MMK, cyanuric acid and TTT (1,3,5-trimethyltriazine-2,4,6-trion) and so on.

Other critical factors to minimize adverse reactions while maintaining acceptable DMC performance are matching solvent and catalyst concentrations, liquid temperature, and pressure at the top of the column. The area of optimal operation for the reboiler temperature and the pressure in the upper part of the column is from 330 to 355 ° F for the reboiler temperature and from 80 to 110 psig, respectively.

Detailed experiment description

The following materials were loaded into the reboiler of the distillation column: 285 grams of triglyme, 100 grams of methanol and 100 grams of dibutyltin dimethoxide. The steady-state operation mode of the reaction-distillation column reactor was achieved when a 13.3 wt.% Solution of MK in methanol (≈280 ppm H ₂ O) was supplied at a fixed rate of 3.01 ml / min and about 1.92 ml / min of methanol (≈80 ppm H ₂ O) at 345 ° F for a liquid reaction medium in a reboiler, 260 ° F for the vapor temperature in the upper section of the distillation column, and 90.8 psig for pressure in the upper part of the column. The volumetric rate of methanol was adjusted to maintain a constant temperature of 345 ° F for the liquid reaction medium. The stirring speed in the reboiler was 300 rpm. In this operating mode, the overhead stream of the product consisted of ammonia, dimethyl ether, carbon dioxide, DMK, MK, NMMK, water, unidentified substances and trace amounts (≈1000 ppb) of the catalyst. After 926 hours of continuous operation, samples of distillates and bottoms were taken. The analysis of these samples is given in table 1. The molar ratios MK / CH ₃ OH and DMK wt.%, Based on MK and CH ₃ OH in a liquid medium in the reactor are 1.01 and 4.49 wt.%, Respectively, which are interesting to compare with 2-10 and 1-3 wt.%, as claimed in US Patent 5,561,094 (1996, from EXXON Chem). The experimental result corresponds to better than 95 mol.% Conversion of MK in DMK. These experimental data are used for computer simulation to design the process.

Table 1 Sample analysis (wt.%) Top shoulder strap VAT product CO ₂ 0.10 0.04 NH ₃ 0.73 0.00 (CH ₃ ) ₂ 0 0.04 0.00 Methanol 90.45 11.02 DMK 8.15 1,67 MK 0.36 26.17 N-MMK 0.17 1.88 TG 0.00 40.89 Unidentified 0.01 0.31 TTT 0.00 3.66 Water (ppm) 87 - Sn (ppm) ~ 1 14.35 *

* in the form of dibutyltin dimethoxide

Example 3

To remove impurities from a solution of 8.03 wt.% Urea in methanol and to convert urea to methyl carbamate, a one liter stirred tank reactor (autoclave) with a distillation column was used. The catalyst was not charged to the reactor. The experiment was carried out at 315 ° F and 200 psig and at 328 ° F and 230 psig by adding urea solution to the reactor at 4 ml / min with a constant lower flow rate of 2 ml / min for 27 hours, and at 3 ml / min with a constant speed lower flow 1.5 ml / min until the end (146 hours of continuous operation) of the test. The distillation column was operated with reflux. In the process, the upper flow was adjusted to maintain a constant liquid level (50% filling) in the autoclave. The work of the column was carried out with reflux irrigation from the upper reflux collection. The concentration of MK in the lower stream from the autoclave averaged 20%, which corresponds to about 97% of the conversion of urea to MK. The initial urea contained about 2000 ppm of water. The bottoms contained an average of 375 ppm water at 315 ° F and 300 ppm water at 328 ° F.

Example 4

The purpose of this experiment is to demonstrate the primary reactor system, which consists of several reactors. To demonstrate the operation of the second primary reactor, an experimental setup was used, the same as in example 2. The experiment was carried out as in example 2. This example differs from example 2 in that it uses a solution of 8 wt.% DMC in methanol instead of pure methanol, as in experiment 2, and a slightly lower pressure (88 psig) at the top of the present distillation column.

The following materials were loaded into the reboiler of the distillation column: 285 grams of triglyme, 40 grams of methanol and 100 grams of dibutyltin dimethoxide.

The steady state operation of the reactor with a distillation column was achieved when the MK solution and the DMK-methanol solution were fed into the reactor. The reactor continued to run for more than 1,500 hours without stopping at 345 ° F for the liquid reaction medium in a reboiler, a temperature in the distillation column of ≈278 ° F, and a pressure at the top of the column of 88 psig. The average composition of the distillate and bottoms from the reactor for 54 hours in the range from 1428 to 1482 hours of the working cycle are given in table 2. During this period, a solution feed rate of 22.5 wt.% MK (≈590 ppm H ₂ O) was set to 1.97 ml / min and a solution feed rate of 8 wt.% DMC (80 ppm H ₂ O) was about 3.2 ml / min at 345 ° F. The molar ratios MK / CH ₃ OH and DMK wt.%, Based on MK and CH ₃ OH in a liquid medium in the reactor, are 0.915 and 6.40 wt.%, Respectively. The experimental result corresponds better than 93 mol.% Conversion of MK in DMK.

table 2 Sample analysis (wt.%) Top shoulder strap VAT product CO ₂ traces - NH ₃ 0.89 - (CH ₃ ) ₂ 0 0.06 - Methanol 84.91 13.32 DMK 12.35 2.68 MK 1.41 28.58 N-MMK 0.36 2.28 TG 0 36.55 HS * 0 3.77 Catalyst** 12.83 Water (ppm) 39 - Sn (ppm) 0.6 -

* HS: isocyanic acid and 1,3,5-trimethyltriazine-2,4,6-trion

** in the form of dibutyltin dimethoxide

Example 5

The purpose of this experiment is to demonstrate the production of diethyl carbonate (DEC). DEC was prepared by reacting ethyl carbamate (EC) with ethanol. The experiment was carried out as in example 2.

A solution of ethyl carbamate in ethanol and ethanol were used instead of a solution of MK and methanol, respectively, in contrast to Example 2. The following materials were loaded into the reboiler of the distillation column: 180 grams of triglyme, 100 grams of ethanol and 100 grams of dibutyltin dimethoxide. A steady state operation of the distillation column reactor was achieved by feeding ethyl carbamate (EC) solution at a constant flow rate and adjusting the ethanol feed rate to maintain a constant temperature of the liquid reaction medium. The reactor continued for 340 hours without stopping at ≈345 ° F for the liquid reaction medium in the reboiler, the temperature in the distillation column ≈282 ° F, and a constant pressure in the upper part of the column 66 psig and at a stirrer speed of 300 rpm. A solution feed rate of 15.35 wt.% EC (≈275 ppm H ₂ O) was set to 2.69 ml / min and an average ethanol feed rate (≈106 ppm H ₂ O) was 2.36 ml / min. The upper vapor stream at the top of the column was mixed with diluent gas, nitrogen (600 cm ³ / min) and then cooled to 200 ° F in a water-cooled condenser. The average composition of the overhead and the composition of bottoms during the full cycle of the experiment are given in table.3. At the end of the experiment, 74.2 grams of solid material was removed from the reactor, which was a mixture of heterocyclic compounds and contained 670 ppm Sn by weight. Analysis of the bottoms product in Table 3 shows that the molar ratio of EC / C ₂ H ₅ OH and DEC wt.%, Based on EC and ethanol in a liquid medium in the reactor, was 0.939 and 11.08 wt.%, Respectively. The material balance and the urea molar balance for the full cycle of the experiment were 102% and 101%, respectively. The experimental result shows 57.5% conversion of EC and 91 mol.% Selectivity of conversion of EC in DEC. The experimental result corresponds to a DEC intensity of about 1.60 lb / hr / ft ³ .

Table 3 Sample analysis (wt.%) Top shoulder strap VAT product CO ₂ traces - 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 0.04 9.34 HS * 0.00 0.95 Catalyst** - 11.70 Water (ppm) 148 - Sn (ppm) 1.7 -

* HS: isocyanic acid and 1,3,5-trimethyltriazine-2,4,6-trion

** in the form of dibutyltin dimethoxide

Claims (23)

1. A method of producing a dialkyl carbonate, comprising the steps of:
(a) feeding a stream comprising urea, alcohol, water and ammonium carbamate to a first distillation column reactor:
(b) simultaneously in said first distillation column reactor
(i) reacting a portion of said urea with a portion of said alcohol to produce an alkyl carbamate,
(ii) the interaction of water with urea with the formation of ammonium carbamate,
(iii) the decomposition of ammonium carbamate contained in the feed and ammonium carbamate formed by the interaction of water and urea into ammonia and carbon dioxide, and
(iv) separating ammonia, carbon dioxide and alcohol from urea and alkyl carbamate by distillation;
(c) removing ammonia, carbon dioxide and alcohol from said first distillation column reactor as a first overhead;
(d) removing urea, alkyl carbamate and alcohol from said distillation column reactor as a first bottoms product;
(e) supplying said first still product to a second distillation column reactor;
(f) simultaneously in said second distillation column reactor
(i) reacting an alcohol, an alkyl carbamate and urea in the presence of a homogeneous catalyst containing an organotin dialkyl dialkoxide complex compound in a high boiling solvent to form a dialkyl carbonate; and
(ii) removing dialkyl carbonate and alcohol from said second distillation column reactor. 2. The method according to claim 1, wherein said alcohol is a C ₁ -C ₃ alcohol. 3. A method of producing dimethyl carbamate, comprising the steps of:
(a) feeding a stream comprising urea, methanol, water and ammonium carbamate to a first distillation column reactor:
(b) simultaneously in the first distillation column reactor
(i) the interaction of water with urea with the formation of ammonium carbamate,
(ii) the decomposition of ammonium carbamate present in the feed and ammonium carbamate resulting from the reaction of water with urea to ammonia and carbon dioxide, and
(iii) separating ammonia, carbon dioxide and methanol from urea by distillation;
(c) removing ammonia, carbon dioxide and methanol from said first distillation column reactor as a first overhead;
(d) removing urea and methanol from said first distillation column reactor as a first bottoms product;
(e) supplying said first bottoms product and methanol to a second distillation column reactor;
(f) simultaneously in said second distillation column reactor
(i) reacting methanol and urea in the presence of a homogeneous catalyst containing an organotin complex compound of dialkyl dimethoxide in a high boiling solvent to form dimethyl carbonate and
(ii) separating dimethyl carbonate and ammonia from a homogeneous catalyst by distillation;
(g) removing dimethyl carbonate and methanol from said second distillation column reactor as a second overhead; and
(h) removing a second bottoms product from said second distillation column reactor. 4. The method according to claim 3, in which dimethyl carbonate in the specified second overhead is separated from methanol by extractive distillation. 5. The method according to claim 3, in which an inert diluent is added to the specified first overhead. 6. The method according to claim 3, in which the methanol in the specified first overhead condensate and part of the specified condensed methanol is returned to the upper part of the specified first reactor with a distillation column as reflux and the remainder of the specified condensed methanol is returned to the lower part of the specified first reactor with a distillation column . 7. The method according to claim 3, in which the first part of the specified second bottoms product is introduced into the specified first reactor with a distillation column, the second part of the specified second bottoms product is recycled to the specified second reactor with a distillation column and the third part of the specified second bottoms product is introduced into the third reactor with a distillation column for regenerating the catalyst and removing heavy residues. 8. The method according to claim 3, wherein said second overhead stream is condensed and a portion of said condensed second overhead is returned to said second reactor with a distillation column as a reflux. 9. A method of producing dimethyl carbonate, comprising the steps of:
(a) feeding a stream containing urea, methanol, water and ammonium carbamate to a first distillation column reactor:
(b) simultaneously in said first distillation column reactor
(i) reacting a portion of said urea with a portion of said methanol to produce methyl carbamate,
(ii) the interaction of water with urea with the formation of ammonium carbamate,
(iii) the decomposition of ammonium carbamate contained in the feed and ammonium carbamate formed by the interaction of water and urea into ammonia and carbon dioxide; and
(iv) separating ammonia, carbon dioxide and methanol from urea and methyl carbamate by distillation;
(c) removing ammonia, carbon dioxide and methanol from said first distillation column reactor as a first overhead;
(d) removing urea and methyl carbamate from said first distillation column reactor as a first bottoms product;
(e) supplying said first bottoms product and methanol to a second distillation column reactor;
(f) simultaneously in said second distillation column reactor
(i) reacting methanol and urea in the presence of a homogeneous catalyst containing an organotin complex compound of dialkyl dimethoxide in a high boiling solvent to form dimethyl carbonate and
(ii) separating dimethyl carbonate, methanol and ammonia from a homogeneous catalyst by distillation;
(g) removing dimethyl carbonate, ammonia and methanol from said second distillation column reactor as a second overhead;
(h) removing a homogeneous catalyst from said second distillation column reactor as a second bottoms product;
(i) separating the second overhead in a distillation column to obtain a third still product containing dimethyl carbonate and methanol;
(j) separating dimethyl carbonate from methanol in said third bottoms by extractive distillation; and
(k) supplying a first portion of said second bottoms product to said first distillation column reactor;
(l) supplying a second part of said second bottoms product to a third distillation column reactor in which the catalyst is regenerated and purified from heavy residues; and
(m) recycling a third part of said second bottoms product to said second distillation column reactor. 10. A method of producing dialkyl carbonates as a result of the interaction of reagents, including urea and alcohol, containing water and ammonium carbonate as impurities, comprising the steps of:
(a) supplying reagents, including urea and alcohol, to the primary reaction zone;
(b) feeding the organotin compound and high boiling solvent to said primary reaction zone; and
(c) simultaneously in the specified primary reaction zone
(i) reacting alcohol and urea in the presence of said organotin compound and said high boiling solvent to obtain a dialkyl carbonate; and
(ii) removing the dialkyl carbonate and ammonia from said primary reaction zone as a vapor,
in which the improvement is the use of a preliminary reaction zone in front of the primary reaction zone to remove water and ammonium carbamate from these reagents by feeding the reactants first to the preliminary reaction zone under the reaction conditions of said water with urea to form ammonium carbamate and decomposition of ammonium carbamate to ammonia and carbon dioxide and removing ammonia and carbon dioxide from these reagents before they are fed to step (a). 11. The method according to claim 10, in which the temperature of the preliminary reaction zone is the temperature of the liquid phase in the range from 200 (93 ° C) to 380 ° F (193 ° C). 12. The method according to claim 11, in which the temperature of the preliminary reaction zone is in the range from 250 (121 ° C) to 350 ° F (177 ° C). 13. The method according to claim 10, in which part of the starting alcohol interacts with part of the starting urea with the formation of alkyl carbamate in the preliminary reaction zone. 14. The method according to claim 10, in which the preliminary reaction zone and the primary reaction zone are operated under distillation conditions. 15. The method according to claim 10, in which water is removed from the feedstock by its interaction with urea with the formation of ammonium carbamate, which in turn decomposes into ammonia and carbon dioxide. 16. The method according to clause 15, in which the temperature of the preliminary reaction zone is the temperature of the liquid phase in the range from 200 (93 ° C) to 380 ° F (193 ° C). 17. The method according to claim 10, in which ammonium carbamates are removed from the raw material by decomposition into ammonia and carbon dioxide. 18. The method according to 17, in which the temperature of the preliminary reaction zone is the temperature of the liquid phase in the range from 200 to 380 ° F. 19. The method of claim 10, wherein said high boiling solvent comprises at least one tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether. 20. The method according to claim 1, wherein said alcohol is a C ₃ alcohol. 21. The method of claim 10, wherein said alcohol contains at least methanol or ethanol. 22. The method according to claim 10, in which the alcohol contains methanol and dialkyl carbonate contains dimethyl carbonate. 23. The method of claim 10, wherein the alcohol contains ethanol and the dialkyl carbonate contains diethyl carbonate.

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