RU2149159C1 - Method of continuously preparing 3-(methylthio) propanal (variants) - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: described is method of continuously preparing 3-(methylthio) propanal which comprises contacting gaseous stream of acrolein-containing stock with liquid reaction medium in gas and liquid contacting zone. Said reaction zone contains 3-(methylthio) propanal, methylmercaptan and catalyst of reaction between mercaptan and acrolein, and gaseous stream of acrolein-containing stock contains acrolein vapors and uncondensable gas, relative amounts of acrolein and methylmercaptan present in containing one being substantially stoichiometrically equivalent due to which fact acrolein is transferred from stream of stock into reaction medium and is directly reacted with methylmercaptan without formation of intermediate hemi(methylthio)acetal of 3-(methylthio) propanal to give liquid reaction product comprising 3-(methylthio) propanal; uncondensable gas is separated from liquid reaction product; said reaction product is separated into product fraction and circulating fraction; and circulating fraction is recycled into gas and liquid contacting zone. Acrolein and methylmercaptan are reacted in liquid medium in reaction zone which includes gas and liquid contacting zone and circulation zone which admits liquid reaction product from gas and liquid contacting zone and through which zone circulating fraction is recycled into gas and liquid contacting zone; mercaptan is admitted into said reaction zone over such area or areas not to allow excessive amount of methylmercaptan of promote any substantial formation of intermediate hemi(methylthio)acetal in any sector of reaction zone for sufficiently prolonged period of time. EFFECT: simplified process and high-grade desired product which need not be purified. 14 cl, 8 dwg, 30 ex, 5 tbl

Description

 The invention relates to the production of 3- (methylthio) propanal, in particular to a method for the continuous direct production of 3- (methylthio) propanal in a gas-liquid reaction medium.

 3- (methyl) thiopropanal (hereinafter referred to as “MMP”) is an intermediate product for the preparation of both d, 1-methionine and 2-hydroxy-4- (methylthio) butyric acid (“HMMC”). Methionine is an essential amino acid, a deficiency of which is usually observed in the components of animal feed. GMMC serves as a source of methionine and is widely used as a methionine supplement to animal feed mixtures. To obtain GMMC or methionine, as a rule, MMP is required, which is relatively free of impurities.

 MMPs are prepared by reacting acrolein with methyl mercaptan. In a conventional MMP process, liquid acrolein and methyl mercaptan are introduced into a reactor containing a liquid phase MMP product. The reaction proceeds in the liquid phase. To obtain the MMP of the required quality during such a process, purified acrolein and / or the MMP product are used before distillation to obtain either GMMC or methionine.

 Acrolein is a highly toxic and combustible material. It is usually obtained by the vapor-phase oxidation of propylene over a solid-phase catalyst, providing the formation of a crude gaseous reaction product, which contains water vapor, acrylic acid, acetaldehyde and other organic by-products. This gas is typically treated to remove acrylic acid and then brought into contact with chilled water to absorb acrolein. The final aqueous solution is distilled with the release of absorbed acrolein and other organic components. The crude acrolein is then purified by removing low boiling impurities such as acetaldehyde to obtain a purified liquid acrolein product. This purified liquid acrolein is stored for use in the preparation of MMPs.

 Storage of liquid acrolein is complicated by significant toxicity, fire and explosion hazard. Therefore, the creation of conditions for the safe handling of this material is associated with large capital and technological costs. The costs associated with working with acrolein could be significantly reduced if acrolein in the gas phase from the process of producing acrolein is continuously sent directly to the MMP reactor without storage or condensation. However, since liquid-phase reactions are provided for in conventional industrial processes for the production of MMPs, the need for condensation of the gaseous acrolein product is considered inevitable. Moreover, since in a normal process, as a rule, a batch reaction system is used, condensation and storage of liquid acrolein along the process in a temporary storage device between the process of producing acrolein and the MMP reactor are necessary.

 Dutch patent 6809647 describes a process in which acrolein is produced by catalytic oxidation of propylene and an acrolein-containing reaction gas mixture is sent to a vertical reaction column in which MMP is formed. MMP is circulated through the reaction column and both acrolein-containing gas and methyl mercaptan are introduced into its lower part. The MMP leaving the column contains a separate aqueous phase, which is removed in a separator. MMP discharged from the separator is partially returned to the reaction column. Sodium bicarbonate solution is added to the circulating MMP. The MMP product removed from the circulating reaction system is distilled under a pressure of 100 mmHg.

US Pat. No. 4,225,516 describes a process for continuously producing MMP from an acrolein gaseous product of catalytic oxidation of propylene. In this method, the gas is first treated to remove acrylic acid, and then cooled to condense water vapor. To reduce the water vapor content to a level acceptable for the MMP reaction, the final condensation temperature is maintained at a level of from 0 to -5 ^° C. The treated and cooled acrolein gas stream is brought into contact with the liquid MMP stream in a countercurrent absorption tower, which results in absorption acrolein MMP. A stream of liquid MMP containing dissolved acrolein is sent to the MMP reactor to which methyl mercaptan is added. When implementing this method, the interaction of methyl mercaptan with MMP proceeds with the formation of hemimercaptal MMP, and this hemimercaptal in turn interacts with acrolein in the liquid phase with the formation of an additional amount of MMP. Thus, the implementation of this method requires the presence in the reaction mixture of up to 1 weight. % hemimercaptal. The MMP product is withdrawn from the system at a rate equivalent to that of the MMP in the reactor, while the bulk of the MMP stream is returned to the acrolein absorber.

In order to ensure quantitative absorption of acrolein using the MMP according to the '516 patent, it is necessary to cool the circulating MMP to a temperature of from 0 to -15 ^° C until it enters the absorber. The cooling required for condensation of water vapor at a temperature of from 0 to -5 ^o C, and the cooling of the MMP to -15 ^o C comprise a considerable share of capital and operating costs when implementing the method according to the patent '516. Moreover, since such a reaction proceeds through the hemimercaptal formation stage, the kinetics of this conversion reaction is relatively low, which results in lower productivity than is necessary and, thus, exacerbates operating costs in the practical implementation of this method.

 Although absorption at a temperature below zero increases the recovery of acrolein in equilibrium, the absorption of impurities such as acetic aldehyde also increases under these conditions. Moreover, since the scrubber is separated from the reactor, acrolein absorbed in the scrubber is not immediately consumed in the absorption zone. The consequence of this is the tendency of acrolein to accumulate in the liquid phase, which weakens the driving force of mass transfer. The high concentration of acrolein in the MMP fluid also increases the possibility of the formation of by-products of the interactions between acrolein and MMP.

 The present invention is the creation of an improved method for the production of MMP, which can be carried out during the continuous process and which can be carried out with high productivity. Another objective is to develop a method that can be carried out using relatively crude acrolein as raw material; as well as the development of a method in which cooling is not required for the absorption or condensation of acrolein and which eliminates the need to store liquid acrolein, in particular, the creation of such a method that can be carried out using gaseous acrolein raw materials obtained directly from the continuous oxidation of propylene or other suitable for this purpose a hydrocarbon. The task also consists in creating such a method that can be carried out without the formation of a separate aqueous phase in the reaction MMP mixture, as well as in creating a method in which it is possible to obtain high-quality MMP for direct use in the production of methionine or MMC without the need for further purification.

The problem is solved by the method of continuous production of 3- (methylthio) propanal, including contacting a gaseous stream of acrolein-containing raw materials with a liquid reaction medium in the gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and the gaseous stream of acrolein-containing feed contains acrolein vapors and non-condensable gas, while the relative amounts of acrolein and methyl mercaptan, inlet which enter the contact zone are essentially stoichiometrically equivalent, as a result of which acrolein passes from the feed stream to the reaction medium and directly interacts with methyl mercaptan in this medium without the formation of intermediate hemi (methylthio) acetal 3- (methylthio) propanal, resulting in a liquid reaction product is formed containing 3- (methylthio) propanal;
separating non-condensable gas from the liquid reaction product;
separating this reaction product into a product fraction and a circulating fraction; and
returning the circulating fraction to the gas-liquid contacting zone, wherein acrolein and methyl mercaptan interact in a liquid medium in the reaction zone, which includes the gas-liquid contacting zone and the circulation zone, into which the liquid reaction product enters from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone, moreover, methyl mercaptan is introduced into such a reaction zone at such a site or sites so that in no sector of the reaction zone and an excess of methyl mercaptan did not contribute to a substantial formation of intermediate hemi (methylthio) acetal over a sufficiently long period of time.

The problem is also solved by the method of continuous production of 3- (methylthio) propanal, including
contacting a gaseous stream of acrolein-containing raw materials with a liquid reaction medium in a gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and a gaseous stream of acrolein-containing raw materials contains acrolein vapor and non-condensable passes from the feed stream to the reaction medium;
the interaction in this liquid reaction medium of acrolein with methyl mercaptan in the first reaction zone, including the gas-liquid contacting zone, with the formation of an intermediate liquid reaction product;
separating non-condensable gas from the intermediate liquid reaction product;
separating this intermediate liquid reaction product into an intermediate product fraction and a circulating fraction;
returning the circulating fraction to the gas-liquid contacting zone, wherein the first reaction zone includes a gas-liquid contacting zone and a circulation zone into which the liquid reaction product enters from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone; and
passing the intermediate product fraction through a piston flow reactor to convert residual acrolein and methyl mercaptan to 3- (methylthio) propanal.

 In this method, the preferred length of stay in the first reaction zone, based on the ratio between the reaction volume and the total production rate, is in the range of about 0.2 to about 1 hour.

 The feed stream and the liquid reaction medium are preferably passed countercurrently through the gas-liquid contacting zone, whereby the liquid retention time in the gas-liquid contacting zone is sufficient so that the residence time of the liquid in the gas-liquid contacting zone, based on the ratio between the volume of the liquid being retained and the total production rate, is in ranging from about 0.5 to about 0.75 hours

The problem is also solved by the method of continuous production of 3- (methylthio) propanal, including
cooling the crude gaseous reaction product stream resulting from the catalytic oxidation of a hydrocarbon to thereby produce a cooled gaseous stream including acrolein and a condensate containing water, acrylic acid and a residual fraction of acrolein;
separating condensate from the cooled gaseous stream;
fractional distillation of the condensate to obtain a head fraction comprising acrolein and a fraction of bottoms, which practically does not contain acrolein;
mixing the head fraction with a cooled gaseous stream to form a combined gaseous acrolein stream;
contacting the gaseous stream of acrolein-containing raw materials with a liquid reaction medium in the gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and the gaseous stream of acrolein-containing raw materials includes a combined acrolein vapor stream and acrolein and non-condensable gas and water vapor, as a result of which acrolein passes from the feed stream to the reaction medium and enters into this medium reaction with methyl mercaptan to form a liquid reaction product containing 3- (methylthio) propanal;
separating non-condensable gas from the liquid reaction product;
separating this reaction product into a product fraction and a circulating fraction; and
return of the circulating fraction to the gas-liquid contacting zone.

 In a preferred embodiment, the bottoms fraction contains less than about 1 weight. % acrolein, more preferably less than about 0.1 wt.% acrolein.

 The source gas may contain less than about 0.1 vol.% Acrylic acid.

 Fractional separation can be carried out in a distillation column comprising at least about two theoretical plates and operating at an absolute pressure in the head of not more than about 30 psi and with an irrigation coefficient of at least about 0.5.

 The preferred absolute pressure in the head does not exceed about 20 psi, and the acrolein content in the bottoms fraction is less than about 0.1 wt.%.

 The crude gaseous acrolein reaction product is preferably cooled by heat exchange with a cooling fluid in a recuperative heat exchanger, thereby causing condensation of water and acrylic acid to produce a two-phase gas-liquid stream of the crude acrolein product, this two-phase gas-liquid stream of acrolein product passing through an instant vaporization unit and in which such a two-phase flow is further cooled in order to provide additional condensation condensation from the cooled stream of gaseous acrolein and this condensate are sent from the flash unit and the vapor-liquid separator to a distillation column for fractionation.

The problem is also solved by the method of continuous production of 3- (methylthio) propanal, including
contacting a gaseous stream of acrolein-containing feed with a liquid reaction medium in a gas-liquid contact zone of the reaction zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and an interaction catalyst between methyl mercaptan and acrolein, and the gaseous stream of acrolein raw material contains acrolein vapor and non-condensable;
passing parallel streams of raw materials and the reaction medium through the contact zone, whereby acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing 3- (methylthio) propanal;
separating non-condensable gas from the liquid reaction product;
separating this reaction product into a product fraction and a circulating fraction;
return of the circulating fraction to the gas-liquid contacting zone; and
heat removal of the reaction from the reaction zone by recuperative heat exchange of the liquid reaction medium with another fluid, the flow rate of the circulating liquid medium and the portion in which heat is removed from the reaction zone are such that the temperature of the liquid reaction medium in the entire reaction zone ranges within no more than approximately ± 5 ^o C.

The reaction zone preferably includes a gas-liquid contacting zone and a circulation zone into which the liquid reaction product comes from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone, the temperature of the liquid reaction medium in this circulation zone being within no more than ± 2 ^° C.

 In general, in a continuous MMP process, a liquid reaction medium is brought into contact with a gaseous stream of acrolein feed in a gas-liquid contact zone. This reaction medium includes MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapors and non-condensable gas. The relative amounts of acrolein and methyl mercaptan entering the contact zone are essentially stoichiometrically equivalent. Acrolein passes from the feed stream to the reaction mixture and reacts directly with methyl mercaptan in this mixture without significant formation of the intermediate hemi (methylthio) acetal of MMP, resulting in a liquid reaction product containing MMP. The non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and the circulating fraction and the circulating fraction are returned to the gas-liquid contacting zone. Acrolein and methyl mercaptan interact in a liquid medium in a reaction zone that includes a gas-liquid contact zone and a circulation zone into which a liquid reaction product is discharged from the gas-liquid contact zone and through which the circulating fraction is returned to the gas-liquid contact zone. Methyl mercaptan is introduced into the reaction zone at a point or several points so that excess methyl mercaptan cannot prevail in any part of the reaction zone for a period of time long enough to form a noticeable amount of intermediate hemi (methylthio) acetal.

 A variant of the method for continuous production of MMP is a method in which a liquid reaction medium is contacted with a gaseous stream of acrolein feed in a gas-liquid contacting zone. Such a reaction medium contains MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapor, non-condensable gas and water vapor. Acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing MMP. The ratio between water vapor and acrolein in the acrolein feed stream is such that the liquid reaction product, due to condensation of water in the feed stream, does not contain any significant amount of the second liquid phase. Non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 The invention also provides a method for continuously producing MMP in which a liquid reaction medium is contacted with a gaseous stream of acrolein feed in a gas-liquid contacting zone, which reaction medium includes MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapor, non-condensable gas and water vapor. Acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing MMP. The molar ratio between water vapor and acrolein in the acrolein feed stream does not exceed about 0.3. Non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 The invention also provides a method for the continuous production of MMP in which a liquid reaction medium is brought into contact with a gaseous stream of acrolein feed in a gas-liquid contacting zone, through which this feed stream and reaction medium are passed in a countercurrent manner. The reaction medium includes MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapor and non-condensable gas, as a result of which acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing MMP. The delay of such a liquid in the zone of countercurrent gas-liquid contacting is sufficient to convert at least 90% of acrolein contained in the gaseous feedstock in this gas-liquid contacting zone. Non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 In addition, according to the invention, there is provided a method for continuously producing MMP in which a liquid reaction medium is brought into contact with a gaseous stream of acrolein feed in a gas-liquid contacting zone, this reaction mixture comprising MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapors and non-condensable gas. Acrolein passes from the feed stream to the reaction medium, and this acrolein reacts with methyl mercaptan in such a medium in the first reaction zone, including the gas-liquid contacting zone, to form an intermediate liquid reaction product. Non-condensable gas is separated from the intermediate liquid reaction product, this intermediate liquid reaction product is separated into an intermediate product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone. The first reaction zone includes a gas-liquid contact zone and a circulation zone into which a liquid reaction product is discharged from the gas-liquid contact zone and through which the circulation fraction is returned to the gas-liquid contact zone. A fraction of the intermediate product is passed through a piston stream reactor to convert residual acrolein and methyl mercaptan to MMP.

 The invention also provides a process for the continuous production of MMPs in which a liquid reaction medium in a gas-liquid contacting zone is brought into contact with a gaseous stream of acrolein feed. Such a reaction medium contains MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapors, non-condensable gas and acrylic acid vapors. Acrolein passes from the feed stream to the liquid reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing MMP. The molar ratio between the pairs of acrylic acid and acrolein in the stream of acrolein feed does not exceed approximately 0.1. Non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 The present invention also provides a process for the continuous production of MMPs in which acrolein vapors are prepared by vapor-phase catalytic oxidation of a hydrocarbon to form a crude acrolein reaction product stream. This crude acrolein reaction product stream is cooled to condense water vapor and acrylic acid from it and produce a cooled acrolein gas stream for conversion to MMP, which feed stream includes acrolein and non-condensable gas. The liquid reaction medium is brought into contact with a gaseous stream of acrolein feed, representing the aforementioned cooled acrolein gaseous stream, in a gas-liquid contacting zone in which the total pressure does not exceed about 3 atm. The reaction medium contains MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. Acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing MMP. Non-condensable gas is separated from the liquid reaction product, this reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 In addition, according to the invention, there is provided a method for continuously producing MMP in which a gaseous stream of a crude reaction product obtained by catalytic oxidation of a hydrocarbon is cooled, as a result of which a cooled gaseous stream comprising acrolein and a condensate comprising water, acrylic acid and a residual portion of acrolein are obtained. The condensate is separated from the cooled gas stream and the condensate is subjected to fractional distillation to obtain an overhead fraction comprising acrolein and bottoms fractions which are substantially free of acrolein. The head fraction is mixed with a cooled gaseous stream to produce a combined acrolein stream. The liquid reaction medium in the gas-liquid contacting zone is brought into contact with a gaseous stream of acrolein feed. The reaction medium includes MMP, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous acrolein feed stream is a combined acrolein gaseous stream and includes acrolein, non-condensable gas and water vapor. Acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in such a medium to form a liquid reaction product containing MMP. Non-condensable gas is separated from this liquid reaction product, the reaction product is separated into a product fraction and a circulating fraction, and this circulating fraction is returned to the gas-liquid contacting zone.

 The present invention also provides a process for the continuous production of 3- (methylthio) propanal. This method involves contacting a liquid reaction medium with a gaseous stream of acrolein feed in a gas-liquid contacting zone of the reaction zone. Such a reaction medium contains 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein. The gaseous stream of acrolein feed includes acrolein vapors and non-condensable gas. A gaseous stream of acrolein feed and a reaction medium are passed through a counter-current gas-liquid contacting zone. Acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in such a medium to form a liquid reaction product containing MMP. Non-condensable gas is separated from this liquid reaction product, and the reaction product is separated into a product fraction and a circulating fraction.

 Other objects and features of the invention are partially apparent and partially described in more detail below.

 In FIG. 1 is a flow chart of an embodiment of the method of the invention illustrating the continuous production of MMP from a crude gaseous acrolein product resulting from the continuous catalytic oxidation of propylene.

 In FIG. 2 schematically illustrates a preferred method according to the invention, in which the MMP is obtained from methyl mercaptan and acrolein in a turbulent gas-lift reactor.

 In FIG. 3 schematically illustrates a gas lift reactor adapted to operate at low pressure drop.

 In FIG. 4 schematically illustrates a gas lift reactor such as a chimney adapted for operation at a low pressure drop.

 In FIG. 5 is a schematic representation of a column type plate reactor for the conversion of methyl mercaptan and acrolein to MMP.

 In FIG. 6 is a schematic illustration of the method of the invention, in which a column type column reactor is used, followed by a piston flow reactor.

 In FIG. 7 schematically illustrates the method according to the invention, in which the crude gaseous acrolein reaction product is treated to remove a significant amount of acrylic acid before introducing this gas into a countercurrent gas lift reactor to react acrolein with methyl mercaptan.

 In FIG. 8 schematically illustrates the method of the invention in which the crude gaseous acrolein reaction product is treated to remove a significant amount of acrylic acid before introducing this gas into a column-type countercurrent plate reactor for reacting acrolein with methyl mercaptan.

 In accordance with the present invention, MMPs are prepared from methyl mercaptan and a gaseous stream of acrolein feed in a gas-liquid reaction system including liquid MMP. In the gas-liquid contacting zone, the liquid phase, including the MMP and the catalyst, is brought into contact with methyl mercaptan and a gas containing acrolein and non-condensable gas. Acrolein passes from the gas phase to the liquid phase and interacts in the liquid phase directly with methyl mercaptan to form an additional amount of MMP. The heat of the exothermic reaction is removed using a heat carrier flowing through a heat transfer device, such as a shirt or a coil in contact with the gas-liquid contact zone, or in the circulation circuit of the IMF between the outlet and the liquid inlet of this contact zone.

 In the gas-liquid contacting zone, high mass transfer coefficients are provided by homogeneous gas-liquid contacting, and the driving force for the mass transfer is preferably maximized by maintaining a substantially piston flow in the gas phase. Uniform gas-liquid contacting can be achieved by carrying out the process in a turbulent flow regime, which can be characterized, for example, by relatively high reduced velocities of gas and liquid in a bubble flow regime in which bubbles actively coalesce and collapse due to turbulence. Such turbulent conditions also accelerate heat transfer from the gas-liquid contacting zone to the jacket or coil, which are in communication with the contacting zone to ensure heat transfer. In another embodiment, gas-liquid contacting can be accomplished by passing gas and liquid countercurrently in the contacting zone. In this latter embodiment, it is advisable to transfer the heat of reaction to the cooling fluid in an external heat exchanger through which the reaction MMP is circulated.

 Due to the maintenance of almost equimolar amounts of methyl mercaptan and acrolein added to the reaction medium, the formation of hematioacetal MMP is substantially prevented. As a result, methyl mercaptan and acrolein directly interact with the formation of MMP. Since such a reaction scheme is much shorter than that carried out through the formation of hemithioacetal, the reaction rate is 3-10 times higher than that achieved in the method described in the '516 patent. At the reaction rates achieved by the new method, the conversion rate is limited by the rate of mass transfer of acrolein from the gas phase to the liquid phase. However, it has been found that when turbulent conditions are maintained in accordance with preferred embodiments of the invention, high mass transfer coefficients are achieved. Moreover, due to the direct rapid interaction between acrolein and methyl mercaptan in the liquid phase, acrolein entering the liquid phase is consumed immediately, thereby increasing the driving force of mass transfer. Thus, the overall mass transfer rates are high. The combined effect of the direct reaction and high mass transfer rates determines the high productivity of the reaction system according to the invention.

 As shown in FIG. 1, acrolein is continuously produced in the acrolein reactor 1 by catalytic oxidation of propylene, propane or other suitable hydrocarbon feed in the presence of water vapor and non-condensable gas. When propylene is used as a feed, the crude gaseous acrolein product leaving this reactor contains from about 4 to about 10 vol.% Acrolein, from about 0.3 to about 1.0 vol.% Acrylic acid, to about 1.0 vol. % propylene, to about 1.0 vol.% propane, to about 0.5 vol.% propionic aldehyde, from about 0.1 to about 0.4 vol.% acetic aldehyde and from about 30 to about 50 vol.% water steam, as well as from about 40 to about 55 vol.% non-condensable gases, including oxygen, nitrogen, carbon monoxide and carbon dioxide. The crude gaseous product is then treated to substantially reduce its water vapor and acrylic acid content. In a preferred embodiment, this crude product is treated by cooling it in a regenerative heat exchanger 3, causing condensation of acrylic acid and water from the crude gaseous product. Although water cooled by a refrigerator can be used as a cooling fluid in the heat exchanger 3, it is economically feasible to use room temperature water, for example tap water, artesian water or cooling tower water. By condensing acrylic acid and water in a heat exchanger using room temperature water as a cooling medium, a cooled gaseous stream of acrolein feed is obtained containing from about 5 to about 25 vol.%, Mainly from about 7 to about 15 vol.% Acrolein; up to about 0.1 vol.%, more preferably up to about 0.01 vol.% acrylic acid; up to about 2.0 vol.% propylene; up to about 1.0 vol.% propane; up to about 1.0 vol.% propionic aldehyde; up to about 0.5 vol.% acetic aldehyde; from about 1 to about 8 vol.%, more preferably from about 1 to about 3 vol.% water vapor and from about 60 to about 80 vol. % non-condensable gases. In a preferred embodiment, the molar ratio between water vapor and acrolein in the cooled gaseous stream is from about 0.05 to about 0.3, more preferably from about 0.05 to about 0.15, and the molar ratio between acrylic acid and acrolein is from 0 to about 0.01, more preferably 0 to about 0.001. Acrylic acid may optionally first be removed from the crude gaseous acrolein product by contacting this gas with a conventional absorbent agent in a countercurrent contacting device such as a packed column. The gas leaving the absorber can then be cooled to condense water vapor by passing this gas through a recuperative heat exchanger located downstream of the absorber.

 Then, the cooled gaseous stream of acrolein feed is introduced into the continuous flow reactor 5, in which the reaction medium, which is a circulating MMP stream, is located. The reactor 5 is equipped with a cooling jacket 7. The circulating MMP contains a catalyst for the interaction of methyl mercaptan with acrolein. The catalyst can be injected continuously or periodically at any suitable point in the circuit. Methyl mercaptan is introduced into the circulating MMP stream at any suitable point, however, it is preferable to introduce it together with acrolein or slightly higher than that point during the process at which acrolein is introduced. In this way, a two-phase mixture of reagents is prepared in which acrolein is distributed between a liquid phase containing MMP and a catalyst and a gas phase containing non-condensable products. Methyl mercaptan can also be distributed between the two phases, however, according to observations, it is significantly dissolved in the liquid phase. The catalyst, as a rule, is a salt of an organic acid and an amine. In the gas-liquid contacting zone, which is lower than the acrolein injection point during the process, acrolein gradually transfers from the gas phase to the liquid phase and in the liquid phase enters into direct and continuous interaction with methyl mercaptan with the formation of IMF. To the extent that methyl mercaptan is initially distributed between the phases, it also gradually passes into the liquid to interact with acrolein.

 Water vapor contained in gaseous acrolein feedstocks in the gas-liquid contacting zone can also condense in the IMF stream. By cooling the gaseous stream of the crude acrolein reaction product in front of the reactor 5 during the process for partial condensation of water vapor, the molar ratio between water vapor and acrolein is kept low enough to prevent the formation of any significant amount of a second (aqueous) liquid phase in the gas-liquid contacting zone or to avoid the presence of any second liquid phase in the gas-liquid contacting zone or liquid reaction product due to the separation occurrence at any point in the reaction system of the aqueous phase from the reaction MMP environment. In a preferred embodiment, the water content in the circulating MMP medium does not exceed about 6 wt.%, And usually it is in the range from about 1 to about 6 wt.%. At a temperature preferable for the reaction, water in such concentrations remains, as described below, completely dissolved in the MMP phase. As indicated above, the molar ratio between water vapor and acrolein in the gaseous feed stream does not exceed approximately 0.3. It was found that this ratio is sufficient to maintain the concentration of water in the circulating MMP medium at a level low enough to avoid the formation of a separate aqueous phase at temperatures prevailing when the liquid exits the gas-liquid contact zone.

 Excessive amounts of acrylic acid in the MMP product are also avoided by cooling the crude gaseous acrolein product with room temperature water. By condensation of acrylic acid from a gaseous stream of raw materials in the refrigerator, a gaseous stream of acrolein feed is sent to the MMP reactor, in which the molar ratio between acrylic acid and acrolein in the feed stream does not exceed about 0.01, preferably does not exceed about 0.001, and the vapor concentration of acrylic acid does not exceed about 0.1%, preferably does not exceed about 0.01%.

 The turbulent flow conditions in the gas-liquid contacting zone are preferably maintained by setting the speed of the two-phase flow in the turbulent range, as defined above. The reaction proceeds rapidly with the formation of a two-phase mixture of reaction products, including a liquid phase containing an MMP product and a catalyst, and a gaseous phase containing non-condensable products. The reaction product exiting the reactor is introduced into a separator 9, in which it is separated into gas and liquid phases. The gas phase, which contains propane, propylene, propionic aldehyde, acetic aldehyde and water vapor, is discharged from the separator into an emission control unit, such as an incinerator. In the case where the discharged gas contains a substantial amount of unabsorbed acrolein or unreacted propylene, a portion of the discharged gas can be returned to the reactor for the oxidation of propylene. However, the combination of high mass transfer rates in the gas-liquid contact zone with the addition of acrolein and methyl mercaptan to the reaction system in practically equimolar amounts gives a discharged gaseous stream, which usually contains from about 90 to about 97 vol.% Non-condensable products and a total of about 0 01 to about 0.03 vol.% Acrolein. The discharged gas usually contains from about 1 to about 2% propylene, that is, an amount that is acceptable for flaring through which non-condensable products and vapors of residual organic substances from the combined acrolein / MMP unit can be passed. Alternatively, part of the discharged gaseous stream can be returned to the process in which it serves as a source of water vapor and non-condensable gas in the reactor for the oxidation of propylene.

 All obtained MMP are removed from the separator through the opening 10 for product withdrawal, although the bulk of the MMP is returned from the separator to the reactor. Such an MMP product practically does not contain methyl mercaptan, acrolein and impurities present in gaseous acrolein raw materials. Without the need for further purification, the MMP product can be used as an intermediate in the production of GMMCs.

The reaction can be carried out at a temperature in the range from about 30 to about 70 ^° C., preferably in the range from about 40 to about 50 ^° C., and under a total pressure in the range from about 1 to about 3 atm, preferably in the range from about 1.5 up to about 2 atm. Methyl mercaptan and acrolein are introduced into the reaction medium at a molar ratio between mercaptan and acrolein in the range of about 0.95 to about 1.2, more preferably in the range of about 1.00 to about 1.02. As indicated above, the acrolein feed contains from about 5 to about 25 vol.%, Typically from about 7 to about 15 vol.% Acrolein. In a most preferred embodiment, the vaporous stream of acrolein feed contains from about 10 to about 15 vol.% Acrolein.

At a reaction temperature below about 50 ^° C, the favorable equilibrium state of acrolein between the liquid and gaseous phases creates a particularly effective driving force for mass transfer to the liquid phase, however, at temperatures that are noticeably lower than 40 ^° C, refrigerant-cooled refrigerant may be required, and reaction kinetics may begin limit performance. Moreover, at a lower reaction temperature, the equilibrium distribution of acetic aldehyde between the gas and liquid phases also becomes unfavorable, which leads to an increase in the concentration of acetic aldehyde in the product leaving the separator. A particularly preferred reaction temperature is in the range of from about 40 ^° C. to about 45 ^° C. In this range, the reaction temperature can be easily controlled by heat transfer from the reaction mixture to cooling tower water at a temperature of up to 35 ^° C. through a jacket covering the gas-liquid contacting zone. As the dissolved acrolein is consumed from the gas in response to an imbalance caused by the consumption of acrolein, an additional amount of acrolein gradually passes into the liquid phase. Thus, in most embodiments of the present invention, cooling either to control the reaction temperature or to accelerate the transition of acrolein from the gas to the liquid phase is not necessary.

 Although mass transfer is also promoted by high pressure, rapid mass transfer in the zone of turbulent gas-liquid contact is achieved at atmospheric pressure or close to it, as a result of which it is not necessary to use high pressure reactors. Moreover, while maintaining the pressure in the reactor at a moderate level, the prevailing pressure in the reactor for the oxidation of propylene may be sufficient to introduce a gaseous acrolein product into the MMP reactor without the need for mechanical compression of this gas.

 Despite the possibility of carrying out the process using a gaseous feed stream, the acrolein content of which is in the range of from about 5 to about 25 vol.%, The mass transfer rate is increased if the gas feed contains at least about 10 vol.% Acrolein. On the other hand, too high an acrolein content can cause an overload of the gas-liquid contacting zone with its existing absorption capacity and can cause the opposite effect with respect to both recovery of acrolein from the gas phase and the MMP yield in terms of acrolein. Taking into account the results of an additional study of factors that affect the process in a typical reactor for producing acrolein and which are directly necessary for the implementation of the proposed method, the concentration of acrolein in the gaseous feedstock in the range from about 10 to about 15 vol.% Can be considered optimal.

 The creation of a very small excess of mercaptan in the reaction mixture allows to maximize the conversion of acrolein and significantly eliminate the need for dumping unreacted acrolein into waste. In cases where the molar ratio between the reactants is maintained in the range of from about 1.00 to about 1.02 moles of methyl mercaptan per mole of acrolein, it is preferable to conduct a direct interaction between mercaptan and acrolein until the formation of intermediate hemi (methylthio) acetal MMP. As a result, high interaction speeds are achieved with high productivity and relatively low capital and technological costs. The ratio between the reagents can be adjusted using various means known in the art. In a preferred embodiment, the circulating MMP stream is periodically analyzed using a gas chromatograph installed during the process after the gas-liquid contact zone, and all the necessary adjusting actions are carried out related to the consumption of acrolein and methyl mercaptan raw materials in order to maintain a corresponding excess of methyl mercaptan and to prevent the formation of hemi-acetal. For this purpose, an analyzer installed on the production line can be used. Excluding the initial stage, the process is carried out in a stationary mode of a continuously recirculating stream. Thus, after reaching the stationary mode, the ratio between the added methyl mercaptan and acrolein can be maintained at substantially 1.0.

 The reaction can be carried out using conventional catalysts and at a conventional catalyst concentration. Such catalysts include a wide variety of organic amines, such as, for example, pyridine, hexamethylenetetramine and triethylamine. Organic acids are typically added to inhibit the polymerization of acrolein. In the case where, for example, a pyridinium acetate catalyst is used, the concentration is maintained in the range of about 0.2 to about 1.0%, preferably in the range of about 0.35 to about 0.5%, by continuously or periodically adding the catalyst to the liquid phase.

 The flow rate of the circulating MMP is at least approximately equal to a value in excess of the flow rate of the resulting MMP, preferably in excess of about 20 to about 50 times, as a result of which a direct-flow reactor of the type shown in FIG. 1 is an axial mixing reactor in a liquid phase. For carrying out such a reaction, any of a variety of two-phase reactors can be used, for example, a straight-through flow reactor, a stirred reactor or a counter-flow reactor, such as a column with an irrigated wall, a bubbler column, a packed column, or a plate column. To increase the mass transfer rate, it is preferable to keep the gas phase in the piston stream. In the piston flow, a concentration gradient of acrolein in the gas phase is established and is maintained along the path of the reactants in the gas-liquid contact zone, as a result of which the combined average driving mass transfer force is maintained, significantly exceeding that prevailing during gas-phase axial mixing. A gas-lift reactor is particularly preferred because it is capable of operating with a gas-phase piston stream and since a substantial amount of non-condensable products in a gaseous stream of acrolein feed can be successfully used both for circulating the liquid MMP phase and for achieving extremely efficient mixing of the liquid in the reactor. This eliminates the need for mechanical equipment with moving parts, such as pumps or mixers. In another embodiment, a countercurrent column can be successfully used, especially where there is a need to minimize the pressure drop across the gas-liquid contacting zone.

 In FIG. 2 illustrates the gas-lift type reactor of the circulating type according to the invention and its use in a combined process in which the crude gas-phase acrolein is cooled and introduced directly into the MMP reactor. In this combined process, as shown in the drawing, propylene (or another suitable hydrocarbon for this purpose) is mixed with air and introduced together with a diluent stream and / or non-condensable gases into a reactor 101 containing a catalyst suitable for oxidizing a hydrocarbon to acrolein. The feed stream for the reactor is prepared by mixing air with propylene and a diluent, as described above, and this mixture is preheated in a recuperative heat exchanger 111 by removing heat from the crude gaseous acrolein product. In a countercurrent absorber 113 in the form of a flow packing column, a partially cooled gaseous product is brought into contact with a liquid absorbent medium to remove acrylic acid from the gas stream. The gas leaving the absorber is passed through another recuperative heat exchanger 103 to further cool the gaseous product and condense acrylic acid and water vapor from it. In an optimal and preferred embodiment, acrylic acid and excess water vapor are removed by condensation alone, avoiding the need for an acrylic acid absorber and the pressure drop required to allow a gaseous stream to pass through this absorber. Next, the cooled gaseous acrolein product is introduced into the gas-lift reactor 105.

The reactor 105 includes an upflow tube 117 (“upstream elbow”) provided with a jacket 107 through which cooling fluid can circulate. Such a reactor further includes a downflow pipe 119 (“downstream elbow”), which, through the lower circuit 121, is in fluid communication with the upward elbow. The ascending elbow 117 is a gas-liquid contacting zone. A separator 109 communicating with the fluid stream is provided between the upper ends of both knees. The downward elbow 119, the lower loop 121 and the separator 109 together form a circulation zone in which the interaction between acrolein and methyl mercaptan can continue after the reaction medium leaves the gas-liquid contact zone. Thus, the reaction zone includes both a gas-liquid contacting zone and a circulation zone. The circulation speed and location of the jacket 107 are such that the temperature of the liquid MMP reaction medium ranges from not more than approximately ± 5 ^° C throughout the reaction zone, preferably not more than approximately ± 2 ^° C in the upstream bend of the reactor.

 In an industrial installation, targeted performance can be achieved through the use of several reactor loops in combination with a single separator. A gas inlet 123 is provided at the bottom of the ascending elbow 117 to allow for the introduction of chilled gaseous acrolein feedstock, and a downstream elbow 119 is provided with a fluid inlet 125 for allowing the introduction of vaporous or liquid methyl mercaptan. In another embodiment, this methyl mercaptan can be introduced at or near the gaseous feed of acrolein feed. The catalyst can be introduced continuously or intermittently at any suitable point. In a preferred embodiment, the entry points of acrolein and methyl mercaptan are close enough to each other; as a result, in any part of the reaction zone between the entry points where the MMP medium may contain an excess of methyl mercaptan, the residence time of the circulating MMP medium is insufficient for the formation of significant amounts of hemimercaptal at this ratio between methyl mercaptan and acrolein and the absolute concentration of methyl mercaptan prevailing in this part. In a gas-lift reactor, the concentration of methyl mercaptan and any excess compared to this concentration of acrolein are negligible due to the diluting action of the large recirculation MMP stream in the circuit. The ascending knee is a gas-liquid contacting zone, and its size is such that the two-phase flow is in the bubble flow regime in which the gas is dispersed in the form of discrete bubbles inside the continuous liquid phase or at the interface between the bubble flow regime and the piston flow. Fluid circulation is initiated by the difference between the fluid heads due to the reduced density of the biphasic fluid contained in the ascending knee compared to the density of the fluid in the descending knee. To establish the preferred flow conditions, the reduced gas velocity in the ascending knee is maintained in the range of about 0.1 to about 0.5 m / s. With this combination of gas velocity and reactor height, the gas delay in the ascending knee is from about 5 to about 20%, and the reduced fluid velocity in the ascending knee is from about 0.3 to about 3.0 m / s. To achieve the target circulation rate, the preferred gas lift circuit height is from about 20 to about 30 feet, which requires excess gas pressure at the inlet of the acrolein feed gas to the reactor in the range of about 10 to about 15 psi. inch, i.e. from about 67 to about 100 kPa. In the lower circuit 121, a circulation pump can optionally be provided and can reduce the required height of the ascending knee 117.

 The most satisfactory mass transfer from the gas to the liquid phase is achieved by controlling the reduced velocity of the gaseous and liquid phases in the ascending knee so that the two-phase flow moves in the bubble flow mode. In the bubble flow regime, gas dispersion in the form of small bubbles in the continuous liquid phase creates the maximum surface area for mass transfer. An appropriate balance between the liquid and gas velocities maintains stable conditions for the bubble flow regime and eliminates the coalescence of bubbles and the occurrence of piston gas motion. The intervals of speeds effective for this purpose can be predicted with a certain accuracy, based on the principles illustrated, for example, by Govier and Aziz in "The Flow of Complex Mixtures in Pipes", Van Nostrand Reinhold Company, New York, 1972 (see, in particular, p. 324-325, which describes the dependence of the flow pattern on fluid velocities for air / water systems). Since the flow pattern depends on the properties of the fluids and the diameters of the tube, some routine experiments may be required to confirm optimal velocities in a particular system. It should be noted that the method according to the invention can also be carried out in a mode with a piston flow, however, mass transfer is maximized during the process in a turbulent mode of bubble flow.

To start the reactor of FIG. 2, the circulation loop is essentially filled with MMP, immediately after which gaseous acrolein feed and methyl mercaptan can be introduced. Even at room temperature, the reaction proceeds at a sufficiently high speed, as a result of which the heat of the exothermic reaction quickly brings the temperature of the reaction mixture to a preferred level of about 40 ^° C. or higher, at which the process proceeds in a stationary mode.

 Using a gas lift reactor, the method of the invention can be carried out providing recovery of acrolein of at least about 98%, conversion of at least about 97%, and yield in terms of acrolein of at least about 95%. Recovery is defined as the fraction of acrolein entering the process in the gaseous feed, which goes into the liquid phase; conversion is defined as the proportion of acrolein entering the process that is spent on the reaction; and the yield is defined as the fraction of acrolein in the gaseous feedstock, which is converted to the total MMP product.

 When the method according to the invention is carried out in combination with an installation in which acrolein is produced by catalytic oxidation of propylene, impurities such as propylene, propane, acetic aldehyde, propionic aldehyde, oxygen, carbon monoxide, carbon dioxide are not present in the gaseous acrolein feedstock no increase in the formation of by-products or the destruction of the MMP product. Thus, in order to avoid the need for condensation of acrolein, purification of acrolein or storage of acrolein in liquid form, the proposed method can be economically feasible in combination with an installation for producing acrolein.

 This method is most suitable for use in combination with the acrolein production process, in which the crude gaseous acrolein product is a mixture of acrolein vapors with inert gases containing water vapor and organic impurities in a low concentration.

 In the case of using a gas-lift reactor of the circulation type, the back pressure caused by the pressure drop in the ascending knee may tend to increase the pressure in the acrolein reactor to a level that exceeds the optimum. This back pressure is at least partially compensated by the exclusion from the process of an acrolein absorber used in the preparation of purified liquid acrolein. During a typical acrolein production process, the drop in the absorber is transmitted in conjunction with backpressure to the reactor to oxidize propylene or another hydrocarbon. Moreover, any undesirable effect of a pressure drop in a gas-lift reactor can be eliminated by any technical measures. So, for example, by placing the compressor on the gas discharge line from the separator, it is possible to provide moderate negative pressure to the separator 109. As indicated above, the necessary height of the gas-liquid contacting zone can be reduced due to the mechanical circulation of the reaction MMP medium.

 In FIG. 3 shows another embodiment of a gas lift reaction system that is adapted to carry out the process at a particularly low pressure drop. Instead of introducing gaseous acrolein near the lower part of the ascending knee, as shown in FIG. 2, a gaseous stream of acrolein feed is introduced through the downstream elbow 221 inlet device 219. At start-up, circulation in the gas-lift reactor circuit is initiated by introducing a “starting” gas through the upstream elbow 214 inlet. The starting inlet is located at least slightly below the inlet 221 , but both devices can be at any desired height of the gas circuit, as a result of which the pressure of the liquid in the circuit does not create excessive back pressure at the point of entry a. To start, either gaseous acrolein feedstock or an inert gas can be used. After the circulation of the MMP reaction medium is established, the introduction of gaseous acrolein feed can begin through the inlet device 221, and after the two-phase flow propagates from the inlet device 221 to the inlet device 224 or higher, the start gas input is stopped. Methyl mercaptan can be introduced at any suitable point, for example, at or near the point of entry of acrolein feedstock, or via a starting gas supply line. The catalyst can be introduced anywhere in the loop. The gas-liquid contacting zone includes a section of the descending elbow 219 below the inlet device 221 plus the entire ascending elbow 217. The rest of the circulation loop is a circulation zone, and the gas-liquid contacting zone and the circulation zone together form a reaction zone. Since the component of the two-phase zone in the elbow 217 is longer than such a component in the elbow 219, the downward flow of the two-phase mixture of reagents is held in the elbow 219. Further, the reactor continues to operate with the difference in fluid pressure determined by the liquid column above the inlet device 221. When such a liquid column is moderate, the pressure drop reduced to the minimum. If the limitations of the allowable difference in pressure of the liquid caused by the pressure drop cause a reduction in the reduced liquid velocity below the optimum for effective mass transfer, this can be compensated by increasing the vertical size below the gas inlet point in order to increase the residence time for the mass transfer.

 Alternatively, a gas lift reactor such as a draft tube reactor may be used in which gaseous acrolein feed is introduced into the draft pipe. Such a system is illustrated in FIG. 4. The reactor 305 includes a traction pipe 319 radially centered in a cylindrical reaction vessel 309 and representing a descending elbow of the gas-lift reactor system. The annular zone between the traction pipe 319 and the inner wall of the reaction vessel is an ascending elbow 317, and together the traction pipe and the annular zone are a circuit for the circulation of IMF. A gaseous stream of acrolein feed is introduced through the inlet fixture 321 of the immersion tube in the traction tube 319. As is apparent to any person skilled in the art and described above with reference to FIG. 3, methyl mercaptan and the catalyst can be introduced at any suitable point in the loop. The circulation in the gas lift reactor loop is initiated initially by introducing start gas through the inlet device 324 in the annular ascending elbow 317. Although this device is shown as an immersion tube with a single outlet, the preferred inlet device 324 is a ring type bubbler surrounding the traction pipe, with outlets placed at a certain pitch along its entire periphery. As with the reactor of FIG. 3, the placement level of the inlet launcher is at least slightly lower than the level of the inlet 321, and both can be provided at any levels that are necessary to minimize backpressure. The circulation begins in the same way as described for FIG. 3, after which the gaseous acrolein feed can be started through the inlet 321, and the start gas is stopped as soon as the two-phase flow propagates from the inlet 321 to the inlet 324. The longer two-phase zone in the ring elbow 317 maintains a downward flow of the two-phase mixture of reagents in traction pipe. Further, the reactor continues to operate with the difference between the liquid columns, which is determined by the liquid column above the inlet 321. Without a noticeable effect on the gas pressure drop, the vertical size of the traction pipe below the outlet of the immersion tube can be as large as necessary to ensure adequate residence time for mass transfer . The heat of reaction can be removed from the reactor of FIG. 3 by means of a jacket enclosing the reactor 305, a coil, or other device with a heat transfer surface located inside the reactor. Excluding the reduced fluid velocity and residence time, in cases where the difference in liquid columns is minimized in order to avoid the effect of excessive backpressure on the acrolein reactor, the preferred operating conditions for the reactor of FIG. 3 are substantially the same as for the reactor of FIG. 2.

 Another preferred embodiment of the invention is shown in FIG. 5. In this embodiment, the reaction is carried out in a plate column 405, which circulates the liquid reaction MMP-environment. Liquid MMP is introduced through a liquid inlet 406 at the top of the column, and gaseous acrolein feed is introduced through a gas inlet 421. Methyl mercaptan is also introduced through or near the bottom of the column, preferably through the same inlet 421. A gas-liquid contact zone is provided inside the column through which the gaseous and liquid phases are passed in countercurrent relative to each other, and mass transfer from the gaseous to the liquid phase occurs primarily on plates of the column. The reaction proceeds in the liquid phase on the plates, in the drain pipes between the plates and in the circulation zone, including the settling zone in the bottom of the column and the recirculation path to the fluid inlet 406. As the gas flows in the column from the bottom up, acrolein gradually passes into the liquid phase, as a result of which the gas leaving the top of the column contains almost no acrolein and is discharged into the atmosphere through an incinerator, torch, or similar installation to control emissions.

In contrast to the substantially isothermal gas lift reactors of FIG. The 2-4 plate column reactor itself operates essentially adiabatically. The resulting liquid reaction mixture leaves the bottom of the column and is separated into a product fraction which is removed from the process and a recycle fraction which is cooled and returned to the column. The pump 430 creates the recirculation driving force. The heat of reaction is removed by transferring it to the water from the cooling tower in the recuperative heat exchanger 407. In order to ensure that the acrolein is completely absorbed by the liquid phase, the recirculating MMP exiting the heat exchanger 407 is preferably passed through the second recuperative heat exchanger 408, where the recirculation flow is cooled approximately to 10 ^° C. or lower, preferably to a temperature of from about 0 to about 10 ^° C., by transferring heat to the cooled brine. A portion of the MMP fraction exiting the refrigerator 407 may optionally be returned through opening 422 to a plate at the bottom of the column, for example, to the sixth or eighth actual plate of a 20-plate column. Although a partial return to the lower part of the column changes its temperature profile, the reaction proceeds throughout the column both in this embodiment and in the variant in which the entire recirculation reaction MMP medium is returned to the upper part of the column.

Thanks to operation under practically adiabatic conditions, a temperature gradient is maintained inside the column. The liquid stream within the column at a temperature of from about 0 to about 10 ^° C. at the top of the column is preferably heated to a temperature of from about 50 to about 60 ^° C. at the bottom of the column. Since the gas leaving the column is in contact with the IMF at a low temperature, a favorable equilibrium prevails and an acrolein recovery rate> 99% can be achieved. To accelerate the reaction in the gas-liquid contacting zone, the temperature of the liquid medium at the inlet of the liquid from the column is preferably raised to at least about 40 ^° C. This increase in the temperature of the liquid medium as it passes through the gas-liquid contacting zone is preferably in the range of from about 20 to about 80 ^° C Since the pressure drop of the gas occurs essentially only when the gas passes through the liquid, which is trapped on the plates, the plate column reactor can be designed as so that the acrolein reactor is affected by a very moderate backpressure.

 In the system of FIG. 5 instead of plates, a nozzle can serve as a means of accelerating mass transfer between the gaseous and liquid phases. However, a tray column is preferred due to counterflow conditions in the gas-liquid contacting zone, which approach the conditions of the piston flow. The packed column may be more susceptible to channel formation and vortex formation, which eliminate the positive effect of the piston flow with respect to the driving force of absorption and reaction, and in the future can become a hindrance to the task of ensuring sufficient fluid retention for the reaction to proceed until it is practically completed in the liquid phase in the gas-liquid contacting zone. The incompleteness of the reaction in the liquid phase also weakens the driving force of mass transfer, thereby reducing the overall reaction rate in the gas-liquid contact zone and increasing the length of stay in the reaction zone (including the gas-liquid contact zone and the circulation zone), which is necessary to achieve the desired conversion of acrolein.

 In a preferred embodiment, the fluid retention is sufficient to ensure a conversion in the gas-liquid contacting zone of at least about 95%, preferably at least 99%, most preferably at least about 99.5%. For this purpose, in a preferred embodiment, the delay should be sufficient to provide an effective residence time in the gas-liquid contacting zone from about 2 to about 5 hours, more preferably from about 3 to about 4 hours, based on the total receipt of the IMF. In a tray column of known design, at least 99.5% conversion can be achieved with a fluid retention that provides an effective residence time of not more than about 4 hours. This corresponds to acrolein and methyl mercaptan concentrations of not more than about 0.5 wt.% In the fraction of the MMP product . Due to the limitation of the reaction rate by mass transfer, it is not necessary to provide a significant additional reaction volume in the circulation zone, for example, in the settling zone of the column or in the reservoir for MMP circulation. Thus, the preferred ratio between the volume of liquid trapped in the gas-liquid contacting zone and the working volume of the circulation zone is at least about 2, preferably at least about 5, most preferably at least about 15 or even more. From a practical point of view, the length of stay in the circulation zone is so short that it does not matter in comparison with the gas-liquid contacting zone of the column. For effective mass transfer and heat removal of the reaction, the circulation rate through the column and heat exchanger (s) is usually at least several times higher than the actual rate of MMP production. Thus, it is obvious that the length of stay per passage, based on the relationship between the volume of fluid retained and the rate of circulation, should only be in the range of about 0.5 to about 1 hour, even though the effective length of stay in the column if based on the relationship between the volume of the retained liquid and the actual production rate, it is preferably in the above ranges.

 An additional advantage of carrying out the process in a countercurrent dish column is the achievement of a high mass transfer rate with a low pressure drop. It has been found that satisfactory mass transfer rates can be achieved with a pressure drop of not more than about 2 to about 5 psi.

 In yet another embodiment, the system of FIG. 5 can operate as a column with a bubble flow. However, the pressure drop in the bubble column significantly exceeds the pressure drop in both the poppet and packed columns. In those cases where a relatively high pressure drop is permissible, a gas-lift reactor is preferable due to the turbulence that is created in the upward bend of the reactor.

 Particularly preferred embodiments of the combined process of the invention are illustrated in FIG. 7 and 8. In each of these preferred embodiments, the crude gaseous acrolein product is treated to remove a substantial amount of acrylic acid from the gas, while at the same time recovering substantially all of the acrolein. In FIG. 7 illustrates a processing process carried out in combination with a gas-lift-type MMP reaction system, while in FIG. 8 illustrates a processing process in combination with a countercurrent plate-shaped column low-pressure MMP reactor.

 When carrying out the process according to the scheme of FIG. 7, a mixture of propylene or other suitable hydrocarbon, water vapor, oxygen and non-condensable products is passed over an appropriate catalyst in an acrolein reactor 601 to produce a crude reaction gas of acrolein, the composition of which is described above. This initial mixture is preheated by transferring heat from the crude reaction gas to it in a feed preheater, which is a recuperative heat exchanger 611. The crude product is processed by further cooling it in a recuperative heat exchanger 603, causing condensation from the crude gaseous product of acrylic acid and water. The gas phase leaving the refrigerator could be introduced directly into the continuous MMP reactor 605. However, the condensate formed in the capacitor 603 typically contains acrolein in an amount sufficient to ensure its recovery. Thus, in the process of FIG. 7, the condensate leaving the condenser is distilled to separate residual acrolein from it to produce a vapor phase, which can be combined with the gas phase leaving the condenser to obtain feed for the reactor, and containing the acrylic acid liquid phase, which is removed from the process. In particular, as shown in the drawing, a two-phase gas-liquid stream exits the condenser 603 and is supplied to the flash unit 627, where it is further cooled, for example, by transferring heat to the cooling fluid in the coil inside the flash unit. Next, the flash installation serves as a vapor-liquid separator, and the condensate is drained from its lower part and the gas phase is removed from the upper part. The condensate is sent to a fractional distillation column 629, equipped with a boiler, which is a recuperative heat exchanger 631, and a condenser, which is a recuperative heat exchanger 633. This column is usually designed for at least 2, preferably 4-6 theoretical plates. The steam discharged from the top plate of the column is partially condensed in the heat exchanger 633. The condensate is returned to the column for irrigation, and the vapor phase is mixed with the cooled acrolein gas phase leaving the flash unit 627. In a preferred embodiment, the vapor fraction condensed in the heat exchanger 633 is such that the column operates at a molar reflux ratio of at least about 0.5, preferably in the range of about 1 to about 2. The bottoms from column 629 contain from about 3 to about 5 % acrylic acid in water, and the content of acrolein in it is less than 1 wt.%, preferably not more than about 0.1 wt.%. Head overheads from the column include predominantly acrolein, typically in an amount of over 75 mol%, usually in excess of about 90 mol%.

 As shown in the drawing, the overhead from column 629 is mixed with the gas phase leaving the flash unit 627 to produce gaseous acrolein feed for reactor 605. The composition of the acrolein gaseous feed is generally described above, however, the acrylic acid content is accordingly below 200 ppm. usually below about 100 ppm. The reactor 605 operates on the same principle as the reactor 105 in FIG. 2, and shirt 607, ascending knee 617, descending knee 619, lower loop 621, acrolein injection point 623, and methyl mercaptan supply means 625 perform the same function and have substantially the same design as all the corresponding reactor components in FIG. 2.

 In the process of the circuit of FIG. 8 use an acrolein reactor 701, a heat exchanger 711 for the reaction gas / feed gas, a refrigerator and a partial condensation unit 703 to remove water and acrylic acid from the raw reaction gas, an flash unit 727 and an acrylic fractional distillation column 729 that perform the same functions. as, respectively, a reactor 601, a heat exchanger 611, a partial condensation unit 603, a flash unit 627, and an acrylic acid column 629 in FIG. 7. The operation of the system for producing acrolein and processing crude acrolein reaction gas according to the scheme in FIG. 8 is also similar to that shown in FIG. 7, except that the preferred operating pressure in the flash unit 727 and fractional distillation column 729 in FIG. 8 is significantly lower than the preferred operating pressure in flash unit 627 and column 629 in FIG. 7. Thus, for example, the preferred operating overpressure in the acrylic acid removal circuit of FIG. 7 ranges from about 20 to about 30 psi. inch, while the preferred operating overpressure in the corresponding circuit of FIG. 8 is only about 15 to about 20 psi. The reduced pressure drop along the disk column 705 compared to the pressure drop in the gas lift reactor 607 allows the acrylic acid removal circuit of FIG. 8 operate under reduced working pressure. Carrying out the process under reduced working pressure makes it possible to remove acrylic acid even more efficiently, as a result of which the treated gaseous acrolein feed entering the reactor 705 typically contains <100 ppm, usually <60 ppm of acrylic acid. Head shoulder straps from column 729 contain at least about 75 mol%, usually at least about 90 mol%, of acrolein. The plate column reactor 705 operates in the same manner as the reactor of FIG. 5, and the inlet fixture 723 for methyl mercaptan and acrolein, the circulation pump 730, heat exchangers 707 and 708, and the means 706 and 722 for returning the liquid MMP medium perform the same functions and have essentially the same design as the corresponding components of the reaction system in FIG. 5.

In FIG. 6, an additional embodiment of the invention is illustrated in which a continuous reaction system 501 with partial or full axial mixing is used, designed or operated in such a way as to provide shorter residence times than necessary for the final target conversion, and the reaction medium discharged from reactor 501, to complete the reaction pass through the reactor 511 with a piston stream. As shown in FIG. 6, the reactor 501 is a plate column reactor. However, the reciprocating post-flow reactor is equally applicable as for the reaction system of FIG. 5 or 8 with countercurrent circulation of gas and liquid flows, and for the gas-lift reactor of FIG. 2 or 7. In the process of FIG. 6, a gaseous stream of acrolein feed comprising acrolein vapors and non-condensable gas and methyl mercaptan through a gas inlet 521 is introduced into the lower portion of a plate column reactor 505 of the reaction system 501, and a liquid reaction medium containing MMP and an interaction catalyst between methyl mercaptan and acrolein is guided for circulation through this system, enters the top of the column through the fluid inlet 506. The column includes a gas-liquid contacting zone through which the gas and liquid phases circulate countercurrently. The gaseous stream of acrolein feed is contacted with a liquid reaction medium containing MMP in the gas-liquid contacting zone, whereby acrolein passes from the feed stream to the liquid reaction medium. Acrolein and methyl mercaptan react in the MMP-containing liquid reaction medium in the first reaction zone to form an intermediate liquid reaction product. This intermediate liquid reaction product before separation into a fraction of the intermediate product and the circulating fraction is removed from the gas-liquid contacting zone and introduced into the lower part of the plate column reactor. The entire circulating fraction is returned to the gas-liquid contacting zone and introduced into the upper part of the column through the liquid inlet 506, or alternatively, a portion of the circulating fraction can be introduced through the opening 522 into the lower part of the column. The first reaction zone includes a gas-liquid contacting zone and a circulation zone into which a liquid reaction medium enters from the gas-liquid contacting zone and through which the circulating fraction is returned back to the gas-liquid contacting zone. The reaction heat is removed from the circulating fraction by heat transfer to the cooling water from the cooling tower in recuperative heat exchangers 507 and 508. Non-condensable gas is separated from the intermediate liquid reaction product. The intermediate fraction containing residual acrolein and methyl mercaptan is removed from the recycle stream of system 501 through aperture 509 and then passed through a piston stream reactor 511 to convert the residual acrolein and methyl mercaptan to MMP. The use of a reactor with a piston flow at a temperature in the range of from about 30 to about 70 ^° C. and a residence time in the range of from about 0.1 to about 0.5 hours can significantly reduce the length of stay in a circulation reaction system with countercurrent flows of gas and liquid in comparison with that which is characteristic of the reaction system of FIG. 5. So, for example, in cases where the length of stay in the reaction system with axial mixing based on the total discharge of the product is only 0.2-1 hours (for example, when the fluid is retained in a plate column reactor 0.2-0.75 hours ), and the liquid fraction of the reaction product leaving this system through opening 509 results in from about 0.5 to about 1% of both acrolein and methyl mercaptan (each), and at the outlet of reactor 511 with a piston stream, it can be obtained final reaction product containing not more than tion of 0.3% acrolein and methyl mercaptan with a total residence time in the plug flow reactor of not more than about 0.5 hours. The reactor is a plug flow 511 operates substantially adiabatically. However, to maintain the temperature in the target range, respectively, by supplying heat or cooling, a shirt 513 is provided.

 The reaction MMP product obtained by the methods illustrated in FIG. 1-8, can be used directly to obtain 2-hydroxy-4- (methylthio) butyronitrile without prior distillation to remove either high-boiling or low-boiling impurities. This not only saves the capital and operating costs of distillation, but also eliminates product losses that are inevitable as a result of the formation of additional quantities of high boiling products in the MMP distillation column. 2-hydroxy-4- (methylthio) butyronitrile (HMBN) can be prepared by reacting the MMP product with hydrogen cyanide. HMBN, in turn, can be converted into 2-hydroxy-4-methylthiobutyric acid (HMMC) by hydrolysis of sulfuric or other mineral acid. Without distillation or other purification of either MMP or GMBN, the latter can be converted to GMMC, which is acceptable for use as an additive to animal feed mixtures and which serves as a source of methionine. The MMP obtained by the method according to the invention can be converted into GMBN according to the method described above, and this GMBN can be successfully converted to GMMK either by the method described by Ruest and others in US Pat. No. 4,524,077, or by the method described by Hernandez in US Pat. No. 4,912,257. B The method according to the Ruest patent GMBN is hydrolyzed in sulfuric acid, the obtained GMMC is extracted from the hydrolyzate using a solvent practically immiscible with water, and the extract is distilled with water vapor to obtain an aqueous solution of GMMC with a concentration of 85-90 wt.%. In the method of the Hernandez patent, such a hydrolyzate is neutralized with ammonia, causing it to separate into two phases, the organic phase being evaporated to give an aqueous solution of GMMC with a concentration of 85-90 wt.%.

 The invention is illustrated below by examples.

Example 1
MMPs were prepared by reacting methyl mercaptan with acrolein in a gas-lift reactor of a type similar to that shown in FIG. 2. The height of this reactor was 3 feet (0.914 m), and the inner diameter of the ascending knee was 0.5 inches (1.27 cm). The gas-liquid separator 109 included a cylinder equipped with a transfer hole for the MMP product, a connecting line below the surface of the liquid to return the circulating MMP to the descending knee of the reactor loop, and a ventilation pipe in the upper part to discharge non-condensable gases. Before introducing the reagents, the reactor loop was filled with MMP containing approximately 0.4 wt.% Of the pyridinium acetate catalyst. The MMP circulation in the reactor was started by bubbling air through a 1/16 inch diameter hole in the device 123 for the inlet of gaseous acrolein feedstock. While air was bubbled in to initiate the circulation of the MMP, hot water was passed through the jacket 107 to bring the temperature of the circulating MMP to a predetermined level of 41 ^° F.

 A synthetic crude acrolein stream was obtained, the composition of which is shown in Table 1. This stream was introduced into the reactor through a bubbler of inlet 123. Methyl mercaptan vapors were introduced through the same opening. Acrolein and methyl mercaptan were introduced via a bubbler at a molar ratio of from about 1.0 to 1.02. The absolute input rates of the reagent fluxes are given in Table 1. Table 1 also shows the reduced gas velocity in the upward bend, the volume of liquid in the reactor, the length of time the liquid product was in the reactor, recovery of the starting reagents, product yield in the reactor, continuous cycle time, average addition rate the initial catalyst and the average rate of input of water with gaseous acrolein feed.

 The bubbler on the inlet 123 dispersed both of the starting reagents in the ascending knee fluid and created an aerated column of fluid in that knee. As a result, the non-aerated fluid in the descending knee was forcedly lowered into the lower part of the ascending knee, where it passed along the bottom of the U-shaped knee and continued to move upward along the ascending knee under the action of dispersed gases.

Inside the biphasic rising knee, a mixture of reagents was formed in the section from the gas bubbler near the bottom to the separator located at the top of the separator, which included the liquid phase containing MMP, methyl mercaptan and the catalyst, and the gaseous phase containing acrolein. Acrolein and methyl mercaptan were rapidly absorbed by the liquid phase, and both absorbed reactants reacted with each other to form a liquid reaction product containing MMP. The interaction rate turned out to be very high, however, it was a factor limiting the speed of the method. A somewhat limited vapor-phase interaction between acrolein and mercaptan also proceeded. The temperature in the gas-liquid contact zone in the riser of the reactor was maintained at about 41 ^° F. by removing heat of the exothermic reaction with cooling water circulating in the jacket 107. The two-phase mixture from the riser of the reactor was fed to a gas-liquid separator 109. In this separator, non-condensable gas was separated from the liquid reaction the product and the liquid reaction product were separated into a product fraction and a circulating fraction. The separated non-condensable gas was removed through the ventilation pipe in the upper part of the separator, the product fraction was removed from the senator through the transfer hole, and the circulating fraction was recycled through the descending knee of the reactor circuit and the connecting line below the surface of the liquid in the separator.

 Due to the two-phase flow characterized by high turbulence and good dispersibility, obtained using a simple gas-lift system without mechanical stirring or a recirculation pump, more than 95% recovery of the total amount of the starting reagents (i.e., acrolein and methyl mercaptan) was achieved in a single-loop reactor, and essentially all recovered reagents were converted to the target MMP product in the same reactor loop. The composition of the product and the flow of non-condensable gases discharged into the atmosphere are also shown in Table 1.

 Despite the higher than usual content of impurities in the starting materials (propylene, propane, acetic aldehyde, propionic aldehyde and water) in the gaseous stream of acrolein feed, due to the presence of such impurities, there are few by-products or decomposition products, or they are not at all formed. This and other experiments demonstrated, in particular, that the reaction system is capable of exhibiting a tolerance to an aqueous impurity content of more than 3 vol.% In a gaseous stream of acrolein feed and a final water content> 6 wt.%, Which was achieved in a circulating liquid during the stationary process .

 As a result of the intense mixing provided by the turbulent flow in the gas-liquid contact zone and the rapid circulation of the reaction MMP medium, it was possible to avoid the formation of localized hot spots and an imbalance of concentrations. This, in turn, suppressed the formation of unwanted by-products.

Examples 2-23
Using the apparatus of FIG. 2, acrolein was reacted with methyl mercaptan to produce MMP. The process was carried out according to the methodology generally described in Example 1, however, changes were made to the operating temperature, the molar ratio between acrolein and methyl mercaptan in the feed supplied to the reactor, the total volumetric flow rate of the gaseous feed, and the concentration of acrolein in the feed gas mixture. These technological parameters and the yield of products for experiments from examples 2-23 are presented in table 2.

 Measurements or determinations of the reduced gas velocity, the concentration of acrolein at the inlet, the reaction temperature, the concentration of the catalyst, the residence time and the ratio in the feed between acrolein and methyl mercaptan were carried out. To determine the effect of these latter technological variables on productivity, acrolein recovery, yield in terms of acrolein, the concentration of acrolein in the liquid phase and the concentration of methyl mercaptan in the liquid phase, a statistical analysis was performed. The results are presented in table 3.

Example 24
Using the method of FIG. 2, for a period of 50 hours a continuous experiment was carried out using gaseous acrolein feed, which was obtained by catalytic oxidation of propylene in a laboratory reactor. To carry out the process, the procedure described in general example 1 was used. During this experiment, the temperature of the gas-lift circuit was maintained at approximately 40 ^° C and the ratio between acrolein and methyl mercaptan in the feed was constantly monitored by a discrete gas chromatographic analysis of a sample of the reactor liquid carried out every half hour . The final aldehyde product was characterized by the following composition:
acetic aldehyde - 0.11 wt.%
methyl mercaptan - 0.88
acrolein - 0.07
allyl alcohol - 0.29
acetic acid - 0.35
acrylic acid - 0.52
β-hydroxypropionic aldehyde - 0.27
pyridine - 0.19
MMP - 89.02
by-product with MV 190 - 0.18
water - 7.00
In an industrial process in which the water content is maintained at a more typical level, for example, 2%, a sample in the MMP would show more than 94% content. The relatively high content of β-hydroxypropionic aldehyde was the result of the presence of water in an amount that significantly exceeded its concentration, easily achieved by cooling gaseous acrolein feedstock in an industrial process.

Example 25
Using the method of FIG. Scheme 2 carried out comparative tests in a reactor with an irrigated wall and in a horizontal circulation reactor. To carry out the process, the procedure described in General Example 1 was used. Synthetic gaseous acrolein feed was used in these experiments. During the stationary process, samples of the liquid product were analyzed by gas chromatography to determine the content of aldehyde, residual acrolein, methyl mercaptan and by-products as impurities. Based on the results of these analyzes, calculations were made to determine the percentage of recovered acrolein, product yield, and material balance of the reactor for each experiment. The average mass transfer coefficient and the reaction kinetics constant were obtained by bringing the experimental data into line with the model of a two-phase reactor. The gas delay time and the flow rate of the recirculation fluid were also measured and correlated.

 The physical parameters of the reactor systems are presented in table 4 together with the temperature, gas velocity and liquid flow rate for each experiment. Table 5 compares the reaction conditions, raw material consumption, product yield and average mass transfer coefficients.

Example 26
In accordance with the method illustrated in FIG. 5, a reaction medium including MMP, methyl mercaptan and a catalyst is contacted with an acrolein vapor stream in a plate column containing 20 plates. The liquid reaction product containing MMP, before separation into a product fraction and a circulating fraction is removed from the gas-liquid contacting zone and introduced into the lower part of the plate column reactor. No amount of the circulating fraction leaving the refrigerator 407 is returned to the bottom of the column. Instead, the entire circulating fraction is passed through the refrigerator 408 and returned to the process through the top of the column. The cooling stage is carried out due to recuperative heat transfer from the liquid phase in the form of still bottoms and liquid on the fifth plate from the bottom. The vapor stream of acrolein is introduced into the lower part of the column at a rate of 662.4 pound mol per hour; it includes 15 vol.% acrolein, 0.28 vol.% acetic aldehyde, 17 vol.% water vapor and 83 vol.% non-condensable products. Methyl mercaptan is introduced into the bottom of the column at a rate of 100 lb / mol.

 The reaction MMP medium is introduced into the top of the column at a flow rate of approximately 600 lb / mol. An MMP product stream containing 97.3% by weight of MMP is diverted from the column at a flow rate of approximately 110.4 lb / mol.

 The process in conditions similar to example 26, but using a reaction system additionally equipped with a reactor with a piston flow (Fig. 6), significantly reduced the residence time of the reaction product in a circulation system with countercurrent flows of gas and liquid. Moreover, the reduction in the length of stay in the reaction system had practically no effect on the total conversion of the reaction products to the final product.

Example 27
MMP (428.1 g) obtained in Example 24 was charged into a 1000 ml reactor equipped with a cooling jacket and a stirrer. 105.4 g of HCN was added to the same reactor over a period of 50 minutes, during which time the temperature was maintained in the range of 35-40 ^° C. After the addition of HCN was completed, the temperature was raised to 45 ^° C. and the reaction continued for another 30 minutes to the completion of the conversion of MMP to 2-hydroxy-4- (methylthio) butyronitrile (HMBN) (527.7 g), which, according to the analysis, contained 90.8% HMBN, and the rest was mainly water, a catalyst and some impurities in a low concentration .

Example 28
515 g of HMBN obtained according to the procedure of Example 27 at 60 ^° C. were added over a period of 50 minutes to 584.2 g of an aqueous solution of sulfuric acid at a concentration of 65.9 wt.% In a 1000 ml reactor equipped with a jacket and a stirrer. In the resulting mixture, the reaction was allowed to proceed for another 10 minutes at 65 ^° C. to complete the first hydrolysis reaction, during which HMBN was converted to the corresponding amide. Then, 378.5 g of hot water was added to the mixture in the reactor at 80 ^° C and the temperature of the mixture was raised to 82 ^° C in order to induce a second hydrolysis reaction, as a result of which the amide was converted to GMMC and ammonium bisulfate as a by-product. The reaction was allowed to continue for 2.5 hours to complete the second hydrolysis. In another embodiment, the required reaction time can be reduced by approximately 50% by increasing the hydrolysis temperature to 90-100 ^o C. The final hydrolyzate was analyzed, as a result of which it was found that it contained 32.1% GMMK monomer, 0.11% GMMK -dimer and less than 0.02% of amide and nitrile, and the rest accounted for ammonium bisulfate as a by-product and water. To extract the GMMC product, the above hydrolyzate was contacted with a methyl isobutyl ketone (MIBK) solvent. To separate the solvent from HMMC, the extract was evaporated in vacuo at 70 ^° C. The residual, solvent-free product included, as shown by analysis, 74.8% HMMC monomer and 7.0% HMMC dimer, and the rest was mainly water and sulfate ions. This product was characterized by a slightly higher than usual water content. This water content can be reduced to a normal value of 11-12% by additional evaporation.

Example 29
In accordance with the method illustrated in FIG. 7, propylene is catalytically oxidized to produce a crude gaseous acrolein reaction product in a catalyst reactor 601. A mixture of propylene, water vapor and air is sent to the reactor through a heat exchanger 611, where it is preheated by heat transfer from the reaction gaseous product. This reaction gaseous product is cooled, causing partial condensation, in the heat exchanger 603 to obtain a mixed vapor-liquid stream with a temperature of 37.8 ^o C. Then this stream is introduced into the installation 627 flash evaporation, where it is further cooled and separated into a cooled gaseous stream containing 18, 9 wt.% Acrolein, 71.1 wt.% Nitrogen, 2.8 wt.% Oxygen, 2.1 wt.% Propane, 1.8 wt.% Propylene, 0.9 wt. % water vapor, 80 ppm acrylic acid, 0.2 wt.% acetic aldehyde, 0.6 wt.% carbon monoxide, 1.7 wt.% carbon dioxide and 140 ppm formalin, and per condensate stream containing 75.4 wt.% Water, 20.0 wt. % acrolein and 3.1 wt.% acrylic acid. The temperature of both the cooled gaseous stream and the condensate is 23.2 ^° C. and the absolute pressure above them is 26 psi. The condensate is introduced into a distillation column 629, in which it is distilled under a head pressure of 23 psi. The steam discharged from the top of the column is partially condensed and the condensate is returned to the column for irrigation at a molar coefficient of irrigation 1. From the bottom of the column, an aqueous product is discharged, which contains 3.9 wt.% Acrylic acid and 711 parts per million acrolein. The overhead includes 94.2% by weight of acrolein, 1.1% by weight of acetic aldehyde, 4.6% by weight of water vapor and less than 1 part per million acrylic acid. The overhead from this distillation column is mixed with a cooled gaseous stream leaving the flash unit to give a combined acrolein gas stream containing 24.6% by weight of acrolein, 0.3% by weight of acetic aldehyde, 1.2% by weight of aqueous steam, 1.9 wt.% propane, 1.6 wt.% propylene and 76 ppm acrylic acid, at a temperature of 26.5 ^° C. and under a total absolute pressure of 23 psi. This gas is introduced together with methyl mercaptan through the inlet 623 into the circulating MMP reaction medium of the lower return circuit 621 of the gas-lift reactor 605. Acrolein is absorbed and the reaction proceeds in a stream moving along the ascending knee, with the formation of a product that is drained from this ascending knee when temperature of 40 ^o C and at an absolute pressure of 16 psi and which contains 75.9 wt.% MMP, 0.2 wt.% methyl mercaptan, 0.3 wt.% acrolein, 1.5 wt.% water, 0 5 wt.% Propane, 0.5 wt.% Propylene, 19.1 wt. % nitrogen, 0.8 wt.% oxygen, 0.1 wt.% acetic aldehyde; 157 frequent ppm formalin, 126 ppm acrylic acid, 0.2 wt.% pyridine and 0.2 wt.% acetic acid. A two-phase mixture of products from the riser of the reactor is introduced into a gas-liquid separator 609. In this separator, non-condensable gas is separated from the liquid reaction product containing MMP, and the resulting liquid reaction product is separated into a product fraction and a circulating fraction. Separate non-condensable gas is removed through the ventilation pipe in the upper part of the separator, the product fraction is removed from the separator through the overflow hole, and the circulating fraction is recycled along the descending bend and the lower circuit to return to the rising bend of the reactor and mix with additional amounts of gaseous acrolein and methyl mercaptan. The fraction of the product containing the MMP is removed at a temperature of 40 ^° C. and under a pressure of 15 psi; it contains 97.4 wt.% MMP, 0.2 wt.% acetic acid, 0.2 wt.% pyridine, 80 ppm methyl mercaptan, 180 ppm. ppm formalin, 520 ppm acetic aldehyde, 160 ppm acrylic acid, 1.8 wt.% water and 0.2 wt.% acrolein.

Example 30
In accordance with the method illustrated in FIG. 8, propylene is catalytically oxidized to produce a crude gaseous acrolein reaction product in a catalytic reactor 701. A mixture of propylene with steam and air is fed into this reactor through a heat exchanger 711, where it is preheated by heat transfer from the reaction gaseous product. This reaction gaseous product is cooled, causing partial condensation, in the heat exchanger 703 to obtain a mixed vapor-liquid stream with a temperature of 37.8 ^o C. Then this stream is introduced into the installation 727 instantaneous evaporation, where it is further cooled and separated into a cooled gaseous stream containing 19, 1 wt.% Acrolein, 71.0 wt.% Nitrogen, 2.8 wt.% Oxygen, 1.8 wt.% Propylene, 2.1 wt.% Propane, 0.9 wt. % steam, 40 ppm acrylic acid, 0.2 wt.% acetic aldehyde, 0.6 wt.% carbon monoxide, 1.7 wt.% carbon dioxide and 140 ppm. / million formalin, and per condensate stream containing 75.8 wt.% water, 19.5 wt. % acrolein, 0.5 wt.% acetic aldehyde and 3.1 wt.% acrylic acid. The temperature of both the cooled gaseous stream and the condensate is 15.2 ^° C. and the absolute pressure is 17 psi. The condensate is introduced into distillation column 729, in which it is distilled at a head pressure of 15 psi. The steam discharged from the top plate of the column is partially condensed and the condensate is returned to the column for irrigation at a molar coefficient of irrigation 1. From the bottom of the column, an aqueous product is discharged, which contains 3.9 wt.% Acrylic acid and 0.6 wt. % acrolein. The overhead includes 94.0 wt.% Acrolein, 0.2 wt.% Acetic aldehyde, 3.6 wt. % water vapor and less than 1 ppm acrylic acid. The overhead from this distillation column is mixed with a cooled gaseous stream leaving the flash unit to give a combined acrolein gas stream containing 24.5 wt.% Acrolein, 0.3 wt.% Acetic aldehyde, 1.0 wt.% Aqueous a pair of 1.9 weight. % propane, 1.6 weight. % propylene and 76 ppm acrylic acid, with a temperature of 18.2 ^o C and a total absolute pressure of 16 psi. This gas is introduced together with methyl mercaptan through the inlet device 723 at the bottom of the plate-shaped column reactor 705 into the circulating MMP. The gas flows from bottom to top along the column in countercurrent with respect to the downward flow of the liquid reaction MMP medium. The reaction medium, including 96.7 weight. % MMP, 962 frequent / million acrolein and 0.14 wt.% methyl mercaptan, enters the top of the column at a temperature of 0 ^o C. The liquid reaction product exiting the bottom of the column at a temperature of 62 ^o C and containing 0.14 wt.% methyl mercaptan, 960 parts. / million acrolein and 96.8 wt.% MMP, are divided into the product fraction and the circulating fraction. This circulating fraction circulates through a heat exchanger 707, where it is cooled to 32.2 ^° C. due to regenerative heat transfer to the cooling water. Slightly less than two-thirds of the circulating fraction is returned from the outlet of the heat exchanger 707 to the plate located at the midpoint of the reactor 705. The remaining part of the circulating fraction is mixed with the catalyst and passed through the heat exchanger 708, where it is cooled to a temperature of 0 ^o C due to regenerative heat transfer to the cooling brine . A portion of the circulating fraction discharged from the heat exchanger 708 is returned via line 706 to the head of the plate column reactor 705. The product fraction is removed from the circulating MMP reaction medium at the point between the bottom of the plate column reactor 705 and the inlet of the heat exchanger 707. Alternatively, the product fraction release from the outlet device either cooler 707 or cooler 708. The product fraction contains 96.8 wt.% MMP, 0.14 wt.% methyl mercaptan and 960 ppm acrolein. The ratio between the flow rate of the recycle stream of the reaction MMP medium and the flow rate of the withdrawn total product stream is approximately 15: 1.

Claims (13)

 1. The method of continuous production of 3- (methylthio) propanal, characterized in that it involves contacting a gaseous stream of acrolein-containing raw materials with a liquid reaction medium in the gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and the gaseous stream of acrolein-containing raw materials contains acrolein vapors and non-condensable gas, while the relative amounts of acrolein and methyl mercaptan included in the zone contacting, are essentially stoichiometrically equivalent, as a result of which acrolein passes from the feed stream to the reaction medium and directly interacts with methyl mercaptan in this medium without significant formation of intermediate hemi (methylthio) acetal 3- (methylthio) propanal, resulting in a liquid reaction a product containing 3- (methylthio) propanal; separating non-condensable gas from the liquid reaction product; separating this reaction product into a product fraction and a circulating fraction and returning the circulating fraction to a gas-liquid contacting zone, wherein acrolein and methyl mercaptan interact in a liquid medium in the reaction zone, which includes a gas-liquid contacting zone and a circulation zone into which the liquid reaction product comes from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone, wherein methyl mercaptan is introduced into such a reaction zone in such a section or sections so that in no sector of the reaction zone an excess of methyl mercaptan does not contribute to a substantial formation of intermediate hemi (methylthio) acetal over a sufficiently long period of time.  2. A method for the continuous production of 3- (methylthio) propanal, characterized in that it involves contacting a gaseous stream of acrolein-containing raw materials with a liquid reaction medium in a gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and the gaseous stream of acrolein-containing raw materials contains acrolein vapors and non-condensable gas, as a result of which acrolein passes from the feed stream to the reaction medium; the interaction in this liquid reaction medium of acrolein with methyl mercaptan in the first reaction zone, including the gas-liquid contacting zone, with the formation of an intermediate liquid reaction product; separating non-condensable gas from the intermediate liquid reaction product; separating this intermediate liquid reaction product into an intermediate product fraction and a circulating fraction; returning the circulating fraction to the gas-liquid contacting zone, wherein the first reaction zone includes a gas-liquid contacting zone and a circulation zone into which the liquid reaction product enters from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone, and passing the intermediate product fraction through the piston reactor a stream for converting residual acrolein and methyl mercaptan to 3- (methylthio) propanal.  3. The method according to claim 2, characterized in that the length of stay in the first reaction zone, based on the ratio between the reaction volume and the total production rate, is in the range from about 0.2 to 1 hour  4. The method according to claim 3, characterized in that the feed stream and the liquid reaction medium are passed countercurrently through the gas-liquid contacting zone, and the liquid retention time in the gas-liquid contacting zone is sufficient so that the length of the liquid in the gas-liquid contacting zone is based on the ratio between the volume of the retained liquid and the total production rate was in the range from about 0.5 to 0.75 hours  5. A method for the continuous production of 3- (methylthio) propanal, characterized in that it includes cooling the flow of the crude gaseous reaction product resulting from the catalytic oxidation of a hydrocarbon, thereby producing a cooled gaseous stream comprising acrolein and a condensate containing water, acrylic acid and residual acrolein; separating condensate from the cooled gaseous stream; fractional distillation of the condensate to obtain a head fraction comprising acrolein and a fraction of bottoms, which practically does not contain acrolein; mixing the head fraction with a cooled gaseous stream to form a combined gaseous acrolein stream; contacting a gaseous stream of acrolein-containing raw materials with a liquid reaction medium in a gas-liquid contacting zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and a catalyst for the interaction between methyl mercaptan and acrolein, and the gaseous stream of acrolein-containing raw materials comprises a combined acrolein vapor stream and acrolein and non-condensable gas and water vapor, as a result of which acrolein passes from the feed stream to the reaction medium and enters into this medium reaction with methyl mercaptan to form a liquid reaction product containing 3- (methylthio) propanal; separating non-condensable gas from the liquid reaction product; dividing this reaction product into a product fraction and a circulating fraction and returning the circulating fraction to the gas-liquid contacting zone.  6. The method according to claim 5, characterized in that the fraction of bottoms contains less than about 1 wt.% Acrolein.  7. The method according to claim 6, characterized in that the fraction of bottoms contains less than about 0.1 wt.% Acrolein.  8. The method according to claim 5, characterized in that the source gas contains less than about 0.1 vol.% Acrylic acid.  9. The method according to claim 5, characterized in that the fractional separation is carried out in a distillation column comprising at least about two theoretical plates and operating under an absolute pressure in the head of not more than about 30 psi. inch and with an irrigation coefficient of at least about 0.5.  10. The method according to claim 9, characterized in that the absolute pressure in the head does not exceed about 20 psi, and the acrolein content in the fraction of bottoms is less than about 0.1 wt.%.  11. The method according to claim 5, characterized in that the crude gaseous acrolein reaction product is cooled by heat exchange with a cooling fluid in a recuperative heat exchanger, thereby causing condensation of water and acrylic acid and obtaining a two-phase gas-liquid stream of the crude acrolein product, this two-phase gas-liquid the acrolein product stream is passed through a flash unit and a vapor-liquid separator, in which such a two-phase stream is further cooled to provide additional additional condensation and condensate evolution from the cooled stream of gaseous acrolein and this condensate are sent from the flash unit and the vapor-liquid separator to a fractionation distillation column. 12. A method for the continuous production of 3- (methylthio) propanal, characterized in that it comprises contacting a gaseous stream of acrolein-containing feed with a liquid reaction medium in a gas-liquid contacting zone of the reaction zone, this reaction medium containing 3- (methylthio) propanal, methyl mercaptan and an interaction catalyst between methyl mercaptan and acrolein, and the gaseous stream of acrolein feed contains acrolein vapors and non-condensable gas; passing parallel streams of raw materials and the reaction medium through the contact zone, whereby acrolein passes from the feed stream to the reaction medium and reacts with methyl mercaptan in this medium to form a liquid reaction product containing 3- (methylthio) propanal; separating non-condensable gas from the liquid reaction product; separating this reaction product into a product fraction and a circulating fraction; returning the circulating fraction to the gas-liquid contacting zone and removing the reaction heat from the reaction zone by regenerative heat exchange of the liquid reaction medium with another fluid, the flow rate of the circulating liquid medium and the portion in which heat is removed from the reaction zone, such that the temperature of the liquid reaction medium in the whole the reaction zone ranges from not more than approximately ± 5 ^o C. 13. The method according to p. 12, characterized in that the reaction zone includes a gas-liquid contacting zone and a circulation zone into which the liquid reaction product enters from the gas-liquid contacting zone and through which the circulating fraction is returned to the gas-liquid contacting zone, wherein the temperature of the liquid reaction medium in this the circulation zone fluctuates within no more than ± 2 ^o C.

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