PROCESS FOR PREPARING 3-METHYLTHIOPROPIONALDEHYDE

Abstract

A process for preparing 3-methylthiopropionaldehyde, by a) providing a liquid stream with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan; b) providing an acrolein with a vapor stream, where the major part of the vapor stream is acrolein, and the pressure of the vapor stream is lower than atmospheric pressure; c) introducing the liquid stream with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) and the acrolein with a vapor stream of b) into a reaction unit with a vapor-liquid mixing device, and d) reacting acrolein with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan in the reaction unit of c) to give a 3-metyhlthiopropionaldehyde product mixture.

Claims

1. A process for preparing 3-methylthiopropionaldehyde, comprising: a) providing a liquid stream comprising methyl mercaptan and/or a hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan; b) providing an acrolein comprising vapor stream, wherein a major part of the stream is acrolein, and a pressure of the stream is lower than atmospheric pressure; c) introducing the liquid stream comprising the methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) and the acrolein comprising vapor stream of b) into a reaction unit with a vapor-liquid mixing device; and d) reacting acrolein with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan in the reaction unit of c) to give a 3-metyhlthiopropionaldehyde comprising product mixture.

2. The process according to claim 1, wherein the acrolein comprising vapor stream of b) comprises at least 70 wt.-% of acrolein.

3. The process according to claim 1, wherein the pressure of the acrolein comprising vapor stream of b) ranges from 300 to 950 mbara.

4. The process according to claim 1, wherein c) comprises mixing the liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) and the acrolein comprising vapor stream of b) in the vapor-liquid mixing device of c).

5. The process according to claim 1, wherein the pressure of the acrolein comprising vapor stream of b) is generated in the vapor-liquid mixing device of c) and/or by a vacuum generating device downstream of the reaction unit of c).

6. The process according to claim 1, wherein a temperature in d) is higher than a condensation temperature of acrolein in the vapor stream of b).

7. The process according to claim 1, wherein a temperature of the liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan in d) ranges from 50 to 90° C.

8. The process according to claim 1, wherein a temperature of the acrolein comprising vapor stream in b) ranges from 20 to less than 50° C.

9. The process according to claim 1, wherein the liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) further comprises a solvent having a boiling temperature which is at least 20° C. higher than a boiling temperature of acrolein.

10. The process according to claim 1, wherein the process further comprises: e1) scrubbing acrolein and/or methyl mercaptan, if contained in an off-gas from the reaction of d), with a solvent having a boiling temperature which is at least 20° C. higher than a boiling temperature of acrolein, to give an acrolein and/or methyl mercaptan comprising liquid stream; and e2) feeding the acrolein and/or methyl mercaptan comprising liquid stream obtained in e1) to c) and/or to d).

11. The process according to claim 1, wherein the liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) further comprises a solvents; wherein the solvent is 3-methylthiopropionaldehyde.

12. The process according to claim 1, wherein the process further comprises: f1) withdrawing a 3-methylthiopropionaldehyde comprising product mixture obtained in d) as 3-methylthiopropionaldehyde comprising stream from the reaction unit; f2) feeding a complete or at least a part of the 3-methylthiopropionaldehyde comprising stream from f1) to a heat exchanger to provide a tempered 3-methylthiopropionalydhe comprising stream; and f3) feeding a part of the tempered 3-methylthiopropionalydhe comprising stream of f2) to the reaction unit or mixing a part of the tempered 3-methylthiopropionalydhe comprising stream of f2) with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan to provide the methyl mercaptan comprising liquid stream.

13. The process according to claim 12, wherein the 3-methylthiopropionalydhe comprising stream is tempered in 12) to a temperature in a range from 20 to 40° C.

14. The process according to claim 1, wherein, when the liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan of a) comprises a solvent which is different from 3-methylthiopropionaldehyde, the process further comprises separating the solvent from the 3-methylthiopropionaldehyde comprising product mixture obtained from d).

15. The process according to claim any of claim 1, wherein a molar ratio of methyl mercaptan and/or the hemi thioacetal formed from methyl mercaptan and 3-methylthiopropionaldehyde to acrolein in c) and/or d) is less than 1.

Description

FIGURES

[0070] FIG. 1 shows a process according to the present invention, in which the numbers denote the following items [0071] (1) liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan, [0072] (2) acrolein comprising vapor stream, [0073] (3) vapor-liquid mixing device, [0074] (4) reaction unit, [0075] (5) 3-methylthiopropionaldehyde comprising product stream, [0076] (6) scrubber, [0077] (7) off-gas stream

[0078] FIG. 2 shows an embodiment of the process according to the present invention, in the meaning of the numbers (1) to (7) is identical with FIG. 1, and the additional numbers denote the following items [0079] (8) partial MMP recycle stream, [0080] (9) process MMP stream, [0081] (10) bottom pump-around MMP recycle stream, [0082] (11) partial MMP recycle stream, [0083] (12) heat exchanger, [0084] (13) cooled partial MMP recycle stream, [0085] (14) liquid stream comprising methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan

[0086] FIG. 3 shows a comparison between the process of the prior art, US 2012/0165573 A1, (above) and the process according to the present invention (below).

EXAMPLES

[0087] The examples herein are performed using a computational model of a process based on the individual processes of the examples. Process modelling is an established and reliable methodology used by engineers to simulate complex chemical processes before building the real plant. In the context of the examples herein the commercial modelling software Aspen Plus® (Aspen Technology, Inc 20 Crosby Roads, Bedford, Mass. 01730, USA) was used in combination with physical property data available from public databases.

1. Comparative Example

[0088] Using the modelling software Aspen Plus@, the preparation of MMP is simulated for a production process according to the technical teaching of US 2012/0165573 A1: A stream of a gaseous mixture comprising acrolein is absorbed in a reactive absorber in a mixture of MMP, methyl mercaptan and the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan, and then reacts with methyl mercaptan to give 3-methylthiopropionaldehyde.

[0089] MMP and reacts with free methyl mercaptan or with methyl mercaptan released from the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan MMP. After being absorbed from the gas phase into the liquid phase, the absorbed acrolein reacts with methyl mercaptan and/or the hemi thioacetal formed from 3-methylthiopropionaldehyde and methyl mercaptan to give MMP. The thus obtained MMP comprising liquid stream is withdrawn from the reaction unit and subjected to a purification to remove gaseous impurities and by-products. The process of said process gives an off-gas of ca. 7400 kg/h per ton acrolein with 50 kg/h of sulfur containing components per ton of acrolein, based on the data in Tables 1 and 4 of US 2012/0165573 A1. The specific composition of this off-gas and the flow rates of its components are given in Table 1 below.

TABLE-US-00001 TABLE 1 composition of the off-gas in a simulation of the process according to US 2012/0165573 A1 Concentration Flow rate Components [wt.-%] [kg/h per ton acrolein] CO.sub.2 1.064 78 CO 0.368 27 O.sub.2 6.079 448 Ar 0.926 68 N.sub.2 89.891 6621 propene 0.254 19 propane 0.049 4 H.sub.2O 0.341 25 acetaldehyde 0.223 16 acrolein 0.000 0 acetic acid 0.014 1 methyl mercaptan 0.356 26 dimethyl sulfide 0.216 16 dimethyl disulfide 0.021 2 MMP 0.150 11 methanol 0.016 1 dimethyl ether 0.034 3 H.sub.2S 0 0 Sum 100 7366

2. Example According to the Invention

[0090] Using the modeling software Aspen Plus®, the preparation of MMP is simulated for a production process shown in FIG. 2: A methyl mercaptan (MC) comprising liquid steam (1), comprising ca. 82 wt.-% of the hemithioacetal of methyl mercaptan and MMP and ca. 3 wt.-% of H.sub.2O, and an acrolein comprising vapor stream (2), having a pressure of ca. 0.60 bara and comprising ca. 92.6 wt.-% acrolein, ca. 2 wt.-% of acetaldehyde, and ca. 5 wt.-% water, are introduced into the reaction unit (4) by means of the vapor-liquid mixing device (3). In the reaction unit (4) acrolein is reacted with methyl mercaptan at a temperature of ca. 6400 to give a 3-methylmercaptopropionaldehyde comprising product mixture. Compared to the process of US 2012/0165573 A1, the process of the present invention gives an off-gas of only ca. 0.8 kg/h per ton acrolein. In other words, the off-gas of the process according to the present invention is only 0.01% of the off-gas of the process of US 2012/0165573 A1. Further, said off-gas only contains 0.05 kg/h of sulfur containing components per ton acrolein, which is only 0.1% of the sulfur containing components in the off-gas of the process of US 2012/0165573 A1. The composition of the off-gas of a process according to the present invention and the flow rates of its components are given in the table 2 below.

TABLE-US-00002 TABLE 2 composition of the off-gas in a simulation of the process according to the present invention Flow rate Components [kg/h per ton acrolein] CO.sub.2 0.000 CO 0.007 O.sub.2 0.077 Ar 0.000 N.sub.2 0.605 propene 0.004 propane 0.003 H.sub.2O 0.026 acetaldehyde 0.022 acrolein 0.005 acetic acid 0.000 methyl mercaptan 0.000 dimethyl sulfide 0.008 dimethyl disulfide 0.000 MMP 0.007 methanol 0.000 dimethyl ether 0.012 H.sub.2S 0.011 Sum 0.788