Patent Application
20070270606
Conditions for carrying out the reaction for the direct esterification of (meth)acrylic acid by the corresponding alcohol in the presence of sulphuric acid in order to obtain the C1-C4 alkyl (meth)acrylate and the various stages for the purification of the ester formed are described, for example, in the document EP 609 127, incorporated by reference.
In the process of the invention, the bottom product originates from the bottom of the column for the distillation of the C1-C4 alkyl (meth)acrylate produced, a final distillation generally being carried out in order to isolate the expected product with high purity.
An average composition of the bottom product, in the case of the manufacture of butyl acrylate in the presence of phenothiazine as polymerization inhibitor, is generally as follows:
The bottom product can also comprise other polymerization inhibitors used in combination with phenothiazine, in particular hydroquinone (HQ) and its derivatives, such as hydroquinone methyl ether (HQME), 2,6-di(tert-butyl)-4-methylphenol (BHT) and 2,4-dimethyl-6-(tert-butyl)phenol (Topanol A), salts of thiocarbamic or dithiocarbamic acid, N-oxyl compounds, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine oxyl (4-OH-TEMPO), compounds comprising nitroso groups, such as N-nitrosophenylhydroxylamine and its ammonium salts, quinones, such as benzoquinone, or amino compounds, such as para-phenylenediamine derivatives.
According to the process of the invention, the bottom product is distilled under an inert atmosphere and under reduced pressure.
Use may be made, as inert atmosphere, of a stream of nitrogen or argon, so as to remove the air which may be present in the medium.
The distillation is carried out under a pressure which can range from 133 Pa to 13 300 Pa (1 to 100 mmHg), preferably from 1330 Pa to 6650 Pa (10 to 50 mmHg).
The bottom product is fed to the distillation column at ambient temperature and is brought to a distillation temperature which can range from 50° C. to 150° C.
Preferably, the distillation is carried out at a temperature ranging from 100° C. to 120° C.
The distillation is carried out in a reboiler surmounted by a demister, in order to limit the distillation of the phenothiazine present in the bottom product.
The residence time is suited to the bottom product feed throughput and to the content of phenothiazine present in the distillate. The distillate resulting from the distillation stage comprises less than 100 ppm of phenothiazine, preferably less than 50 ppm.
The bottom product can have a dispersant added to it before being distilled. Mention may in particular be made, as dispersants which can be used, of the phosphoric compounds described in the published international application WO 06/040457, more particularly Beycostat® FB 095. The content of dispersant can vary between 500 and 5000 ppm, more particularly between 1000 and 3000 ppm. The distillate resulting from the distillation stage is composed predominantly of butyl butoxypropionate (BBP), with butyl acrylate and butyl acryloyloxypropionate (AA/BuA).
The distillate is subsequently subjected to a thermal cracking stage at atmospheric pressure. Use is made, for the cracking, of a temperature which can range from 160° C. to 185° C., preferably from 165° C. to 175° C. The thermal cracking is also carried out under an inert atmosphere, which prevents oxidation of the traces of phenothiazine which might be present in the distillate resulting from the first stage.
Use is made of sulphuric acid as catalyst for the thermal cracking, in an amount by weight ranging from 1 to 5% with respect to the feed, more particularly from 3 to 5%. Use may be made of concentrated sulphuric acid, which is introduced into the cracker so as to form the bottoms of the cracker.
The thermal cracking stage can be carried out in the presence of a polymerization inhibitor added to the feed stream of the cracker. Use may be made of conventional polymerization inhibitors other than phenothiazine, such as those mentioned above, in an amount ranging from 200 to 2000 ppm with respect to the feed, preferably from 300 to 1000 ppm.
A dispersant can also be added to the distillate before carrying out the thermal cracking. Mention may be made, as dispersants which can be used, of the same compounds mentioned above for the distillation stage, it being possible for the content of dispersant to vary between 500 and 5000 ppm, more particularly between 1000 and 3000 ppm.
On conclusion of the stage of heat treatment at high temperature, the butyl butoxypropionate (BBP) is decomposed to give butyl acrylate and butanol and the butyl acryloyloxypropionate (AA/BuA) is decomposed to give butyl acrylate and acrylic acid. The decomposition products butanol and acrylic acid are advantageously recycled to the reaction stage. The butyl acrylate thus recovered makes it possible to increase the productive output of the process.
The operating conditions in the process of the invention make it possible to obtain high levels of stripping, expressed as percentages of output throughput with respect to the feed throughput, whether for the distillation stage or thermal cracking stage, which are markedly greater than 60% and which can reach more than 80% during the thermal cracking.
The invention makes it possible to decompose the heavy products generated during the manufacture of C1-C4 alkyl (meth)acrylate to give recyclable products while limiting deposits of solid materials in the plants and thus while reducing the frequency of shutdowns necessary for the cleaning of the items of equipment.
The present invention will now be described with the help of examples which do not limit the scope of the invention.
Level of stripping: top product throughput (g/h)/feed throughput (g/h)×100
a) Distillation Stage
Use is made of a glass thermosiphon reboiler with a working capacity of 92 cm3. The reboiler is fed continuously, from a receptacle for BuA heavy products, using a membrane pump equipped with a backpressure valve. The feed stream is conveyed into the reboiler at ambient temperature. The feed throughput is regulated by continuously measuring the weight of mixture in the starting receptacle.
The reboiler is heated using 3 ring heaters (electrical resistances) each with a power of 160 W, so as to reduce as much as possible the skin temperature of the ring heaters. These ring heaters, positioned externally, are brought into contact with the wall of the reboiler through an aluminium foil, the role of which is the diffusion of the heat. A thimble with an external diameter of 10 mm is placed at the centre of the heating region in order to reduce as much as possible the volume of the latter and thus to increase the rate of passage of the heavy products to be distilled. The heating power is adjusted so as to have the desired temperature in the reboiler.
A demisting section, composed of a glass component furnished with a piece of multiknit padding with a height of 3 cm, is added at the top of the reboiler. The vapours exiting from the reboiler are directed to a water-cooled condenser and the distillate is taken up by a membrane pump controlled by a float (level regulation) in order to be directed to a recovery receptacle at atmospheric pressure.
The bottoms are recovered by overflowing in the reboiler and then taken up by a membrane pump controlled by a float (level regulation) in order to be directed to a recovery receptacle at atmospheric pressure.
The temperature measurements are carried out in the leg of the thermosiphon equipped with the ring heaters (thimble), in the side leg of the thermosiphon (internal measurement) and at the top of the demisting section (internal measurement). The operations are carried out under a reduced pressure, generally of 1330 Pa (10 mmHg), regulated using a pressure sensor and an electrically-operated valve.
b) Cracking Stage
The arrangement is identical to that used for the distillation but it does not comprise a demisting section and the cracking reaction is carried out at atmospheric pressure. Use is made of a glass thermosiphon reboiler with a working capacity of 92 cm3. The reboiler is fed continuously using a membrane pump from the receptacle containing the distillate from the preceding stage. The feed stream is conveyed into the cracker at ambient temperature and the pressure is maintained at atmospheric pressure. The feed throughput is regulated by continuously measuring the weight of mixture in the starting receptacle.
The cracker is heated using 3 ring heaters (electrical resistances) with a power of 160 W. These ring heaters, positioned externally, are brought into contact with the wall of the reboiler through an aluminium foil. A thimble with an external diameter of 10 mm is placed at the centre of the heating region in order to reduce as much as possible the volume of the latter and thus to increase the rate of passage of the product to be cracked. The heating power is adjusted so as to have the desired temperature in the reboiler.
The vapours exiting from the cracker are directed to a water-cooled condenser and the distillate is directed to a recovery receptacle at atmospheric pressure.
The bottoms are recovered by overflowing in the reboiler.
The temperature measurements are carried out in the leg of the thermosiphon equipped with the ring heaters (thimble), in the side leg of the thermosiphon (internal measurement) and at the top of the reboiler (outlet for the vapours).
BuA heavy products resulting from a process for the esterification of acrylic acid by butanol in which phenothiazine (PTZ) is used as polymerization inhibitor are distilled.
Before the test, 2000 ppm of dispersant (Beycostat® FB095 from Ceca) are added to the feed.
The distillation is carried out under nitrogen, so as to eliminate the air which might be present in the medium.
The BuA heavy products are fed at ambient temperature and the heating is regulated so as to achieve 117° C. in the reboiler (the temperature is adjusted as a function of the level of stripping desired).
The feed throughput is adjusted so as to have a residence time of 15 minutes.
The quality of the distillate is monitored and it is confirmed in particular that it comprises little PTZ (<100 ppm). A simple and rapid test consists in adding a few drops of sulphuric acid to a flask containing distillate. If the distillate instantaneously darkens, there is too much PTZ. If the distillate has a gradual orangey colouring, the concentration of PTZ is correct. The results of the two tests appear in Table 1 below.
Under these conditions, it is found that the wall of the reboiler remains clean.
The distillate resulting from the distillation stage of Example 1 feeds the cracker continuously and at ambient temperature.
The feed throughput is regulated so as to have a residence time of 30 minutes.
The heating power is adjusted so as to have a temperature in the cracker of the order of 170-175° C.
To initiate the cracking, concentrated sulphuric acid is injected at the start so as to constitute the cracker bottoms (the acid concentrates in the bottoms when stripping of the heavy products begins). 2000 ppm of dispersant (Beycostat® FB 095) and 500 ppm of 4-OH-TEMPO (Nalco) are also added.
The cracking is carried out at atmospheric pressure and under nitrogen (bubbling 71 cm3/min), so as to prevent oxidation of the PTZ traces which might be present in the distillate from the 1st stage.
The results of the two tests appear in Table 2 below.
Under these conditions, it is found that the wall of the cracker remains clean.
Table 3 below gives the compositions of the various streams of Test 1, determined by analysis by liquid chromatography (HPLC) and gas chromatography (GC).
| Number | Date | Country | Kind |
|---|---|---|---|
| 06.51820 | May 2006 | FR | national |
