ZA200407487B - (Meth)acryclic acid crystal and method for the production and purification of aqueous (meth)acrylic acid - Google Patents
(Meth)acryclic acid crystal and method for the production and purification of aqueous (meth)acrylic acid Download PDFInfo
- Publication number
- ZA200407487B ZA200407487B ZA200407487A ZA200407487A ZA200407487B ZA 200407487 B ZA200407487 B ZA 200407487B ZA 200407487 A ZA200407487 A ZA 200407487A ZA 200407487 A ZA200407487 A ZA 200407487A ZA 200407487 B ZA200407487 B ZA 200407487B
- Authority
- ZA
- South Africa
- Prior art keywords
- acrylic acid
- meth
- stage
- mother liquor
- region
- Prior art date
Links
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 title claims description 225
- 238000000034 method Methods 0.000 title claims description 190
- 239000013078 crystal Substances 0.000 title claims description 123
- 238000000746 purification Methods 0.000 title claims description 57
- 238000004519 manufacturing process Methods 0.000 title claims description 28
- 239000002253 acid Substances 0.000 title description 5
- 238000002425 crystallisation Methods 0.000 claims description 83
- 239000012452 mother liquor Substances 0.000 claims description 80
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 73
- 239000000725 suspension Substances 0.000 claims description 59
- 239000000203 mixture Substances 0.000 claims description 52
- 239000003795 chemical substances by application Substances 0.000 claims description 40
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 39
- 229920000642 polymer Polymers 0.000 claims description 31
- 238000010791 quenching Methods 0.000 claims description 25
- 239000006096 absorbing agent Substances 0.000 claims description 22
- 239000012535 impurity Substances 0.000 claims description 21
- 239000000155 melt Substances 0.000 claims description 21
- 238000004821 distillation Methods 0.000 claims description 19
- 230000015572 biosynthetic process Effects 0.000 claims description 15
- 238000003786 synthesis reaction Methods 0.000 claims description 12
- 229920000247 superabsorbent polymer Polymers 0.000 claims description 11
- 239000004583 superabsorbent polymers (SAPs) Substances 0.000 claims description 9
- 239000010408 film Substances 0.000 claims description 6
- 239000006260 foam Substances 0.000 claims description 6
- 239000010985 leather Substances 0.000 claims description 6
- 238000011282 treatment Methods 0.000 claims description 6
- 238000004065 wastewater treatment Methods 0.000 claims description 6
- 239000002537 cosmetic Substances 0.000 claims description 5
- 239000006185 dispersion Substances 0.000 claims description 5
- 239000000975 dye Substances 0.000 claims description 5
- 239000004753 textile Substances 0.000 claims description 5
- 239000003599 detergent Substances 0.000 claims description 2
- 238000002447 crystallographic data Methods 0.000 claims 1
- 238000009740 moulding (composite fabrication) Methods 0.000 claims 1
- 239000000047 product Substances 0.000 description 66
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 57
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 56
- 238000005406 washing Methods 0.000 description 31
- 239000012071 phase Substances 0.000 description 27
- 230000003197 catalytic effect Effects 0.000 description 13
- 238000001816 cooling Methods 0.000 description 13
- 238000000926 separation method Methods 0.000 description 13
- 230000003647 oxidation Effects 0.000 description 11
- 238000007254 oxidation reaction Methods 0.000 description 11
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 9
- 239000012530 fluid Substances 0.000 description 9
- 239000007788 liquid Substances 0.000 description 9
- 238000010586 diagram Methods 0.000 description 8
- 230000002829 reductive effect Effects 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- 239000000706 filtrate Substances 0.000 description 7
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 6
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 239000007792 gaseous phase Substances 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- 239000006227 byproduct Substances 0.000 description 4
- 239000000470 constituent Substances 0.000 description 4
- 230000000875 corresponding effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000005265 energy consumption Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 238000000605 extraction Methods 0.000 description 4
- HYBBIBNJHNGZAN-UHFFFAOYSA-N furfural Chemical compound O=CC1=CC=CO1 HYBBIBNJHNGZAN-UHFFFAOYSA-N 0.000 description 4
- 238000007790 scraping Methods 0.000 description 4
- 239000002250 absorbent Substances 0.000 description 3
- 230000002745 absorbent Effects 0.000 description 3
- 150000001253 acrylic acids Chemical class 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 239000000839 emulsion Substances 0.000 description 3
- 238000005755 formation reaction Methods 0.000 description 3
- 239000003112 inhibitor Substances 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- QIGBRXMKCJKVMJ-UHFFFAOYSA-N Hydroquinone Chemical compound OC1=CC=C(O)C=C1 QIGBRXMKCJKVMJ-UHFFFAOYSA-N 0.000 description 2
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical compound CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 description 2
- AMIMRNSIRUDHCM-UHFFFAOYSA-N Isopropylaldehyde Chemical compound CC(C)C=O AMIMRNSIRUDHCM-UHFFFAOYSA-N 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 239000008346 aqueous phase Substances 0.000 description 2
- 239000012431 aqueous reaction media Substances 0.000 description 2
- HUMNYLRZRPPJDN-UHFFFAOYSA-N benzaldehyde Chemical compound O=CC1=CC=CC=C1 HUMNYLRZRPPJDN-UHFFFAOYSA-N 0.000 description 2
- 238000007084 catalytic combustion reaction Methods 0.000 description 2
- 239000000567 combustion gas Substances 0.000 description 2
- XBDQKXXYIPTUBI-UHFFFAOYSA-N dimethylselenoniopropionate Natural products CCC(O)=O XBDQKXXYIPTUBI-UHFFFAOYSA-N 0.000 description 2
- 230000005496 eutectics Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000010191 image analysis Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- 230000036961 partial effect Effects 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 239000007790 solid phase Substances 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 238000005719 Graham synthesis reaction Methods 0.000 description 1
- 208000008454 Hyperhidrosis Diseases 0.000 description 1
- 206010021639 Incontinence Diseases 0.000 description 1
- STNJBCKSHOAVAJ-UHFFFAOYSA-N Methacrolein Chemical compound CC(=C)C=O STNJBCKSHOAVAJ-UHFFFAOYSA-N 0.000 description 1
- NTIZESTWPVYFNL-UHFFFAOYSA-N Methyl isobutyl ketone Chemical compound CC(C)CC(C)=O NTIZESTWPVYFNL-UHFFFAOYSA-N 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 150000001299 aldehydes Chemical class 0.000 description 1
- -1 ali- phatic alcohols Chemical class 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 150000001722 carbon compounds Chemical class 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 229940000425 combination drug Drugs 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000007859 condensation product Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000011552 falling film Substances 0.000 description 1
- 239000012065 filter cake Substances 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 230000035876 healing Effects 0.000 description 1
- 238000007172 homogeneous catalysis Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000007373 indentation Methods 0.000 description 1
- 238000011081 inoculation Methods 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 239000001282 iso-butane Substances 0.000 description 1
- 235000013847 iso-butane Nutrition 0.000 description 1
- 229940035415 isobutane Drugs 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
- 239000011976 maleic acid Substances 0.000 description 1
- FPYJFEHAWHCUMM-UHFFFAOYSA-N maleic anhydride Chemical compound O=C1OC(=O)C=C1 FPYJFEHAWHCUMM-UHFFFAOYSA-N 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- NWVVVBRKAWDGAB-UHFFFAOYSA-N p-methoxyphenol Chemical compound COC1=CC=C(O)C=C1 NWVVVBRKAWDGAB-UHFFFAOYSA-N 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- QNGNSVIICDLXHT-UHFFFAOYSA-N para-ethylbenzaldehyde Natural products CCC1=CC=C(C=O)C=C1 QNGNSVIICDLXHT-UHFFFAOYSA-N 0.000 description 1
- 238000005373 pervaporation Methods 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 238000004094 preconcentration Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 235000019260 propionic acid Nutrition 0.000 description 1
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 1
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 1
- 239000012264 purified product Substances 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- IUVKMZGDUIUOCP-BTNSXGMBSA-N quinbolone Chemical compound O([C@H]1CC[C@H]2[C@H]3[C@@H]([C@]4(C=CC(=O)C=C4CC3)C)CC[C@@]21C)C1=CCCC1 IUVKMZGDUIUOCP-BTNSXGMBSA-N 0.000 description 1
- 230000036647 reaction Effects 0.000 description 1
- 238000001577 simple distillation Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000000638 solvent extraction Methods 0.000 description 1
- 239000003381 stabilizer Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 238000010626 work up procedure Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60N—SEATS SPECIALLY ADAPTED FOR VEHICLES; VEHICLE PASSENGER ACCOMMODATION NOT OTHERWISE PROVIDED FOR
- B60N2/00—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles
- B60N2/75—Arm-rests
- B60N2/78—Arm-rests post or panel mounted
Description
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
The present invention relates to a process for purifying a composition containing (meth)acrylic acid, to an apparatus for producing pure (meth)acrylic acid, an appa- ratus for polymerising (meth)acrylic acid, (meth)acrylic acid and polymers ob- tainable by these processes, their use and substances containing them. "(Meth)acrylic acid" is used in this text for compounds having the nomenclature names "methacrylic acid" and "acrylic acid”. Of the two compounds, acrylic acid is preferred according to the invention.
It is often desirable to work up {meth)acrylic acid to high purities of up to > 99.9 % by weight for their use in polymers. In the hygiene industry, for example, su- perabsorbers based on polyacrylates may contain specific by-products only below the detection limit.
Crystallisation is mentioned as an alternative to the production of high-purity or- ganic substances. The two particular processes which are used industrially are suspension crystallisation and layer crystallisation (Wintermantel et al, Chem. Ing.
Tech. 1991, 63, 881-891; Steiner et al, Chem. Ing. Tech. 1985, 57, 91-102).
However, a crystallisation step alone is often insufficient to remove by-products sufficiently well from the crystals as microinclusions of mother liquors or the in- corporation of impurities at crystal defects, etc. cannot be ruled out under finite crystal growth conditions. The adhesion of mother liquor to the crystal can also impair the purity of the products.
Stockbausen GmbH DAOG1206 HZHR
Degussa AG . For this reason, the crystals produced, particularly in the case of a crystal suspen- sion, are frequently washed with washing fluids after separation from the mother liquor and/or the crystals are subjected, during layer or suspension crystallisation, to an exudation process during which impurities of any type may optionally be depleted. A process of this type may be carried out continuously in what are known as wash columns. The dissertation by Poschmann (Zur Suspensionskristal- lisation organischer Schmelzen und Nachbehandlung der Kristalle durch Schwit- zen und Waschen, Diss. Uni. Bremen, Shaker Verlag Aachen 1996) provides an overview.
EP 0616998 discloses a process for producing > 99.9 % by weight acrylic acid starting from previously purified product having an acrylic acid content of 97.771 % by weight. The effect of purification is achieved by the cooperation of dynamic and static layer crystallisation processes. What is known as falling film crystallisa- tion is adopted as the final means of crystallisation. An apparatus of this type may only be operated discontinuously and necessitates complex apparatus and logistics and comparatively high energy consumption owing to the many process cycles required to obtain the necessary purities.
It is known from WO 99/14181 to crystallise crude (meth)acrylic acid for purifi- cation in a first step and to work it up in a second step, optionally using wash col- umns. The process disclosed therein starts directly with the condensation products of catalytic gaseous phase oxidation for the production of (meth)acrylic acid. With this process, it is disclosed that the mother liquor produced after washing and separating the crystals is recycled into the condensation stage. With this process, a . product having a purity of 98.8816 % by weight was obtained from 90.972 % by weight acrylic acid. However, this is not sufficient for some industrial applica- tions. For example, the content of inhibitors and aldehydes in the pure
4 PCT/EP03/02753 25. August 2004
Siocktmusen GmbH D80612PC HZ/HR (meth)acrylic acid is a critical variable which, if exceeded, may lead to draw- backs, for example in the subsequent polymerisation process.
Nienrood et al have described how acrylic acid may be well purified by suspen- sion crystallisation and subsequent treatment in a hydraulic wash column (so- called TNO process; Proc. Bremer International Workshop on Industrial Crystalli- zation, Bremen, 1994, Ed.: J. Ulrich, p. 4-11; Purification Potential of Suspension
Growth Melt Crystallization, Proc. 4th International Workshop on Crystal Growth of Organic Materials, Bremen, 1997, Ed.: J. Ulrich, Aachen Shaker Verlag, p. 139-145). The acrylic acid used in these experiments was obtained from Aldrich and had a purity of 99.75 % by weight. It could be purified to a purity of 99.97 % by weight by this process. However, the use of lower-purity, acrylic acid has not been disclosed.
With former processes for producing (meth)acrylic acid, the {meth)acrylic acid obtained in a (meth)acrylic acid reactor and subsequently dissclved in water in a quench absorber is usually subjected to a complex distillation process which sometimes necessitates the use of entrainers such as toluene so that high degrees of purity are then obtained by a crystallisation process. Distillation processes for (meth)acrylic acid have the drawback that the (meth)acrylic acid is exposed to heat during the distillation process, through which its properties change, for ex- ample due to partial (pre)polymerisation.
The object of the present invention is generally to overcome the drawbacks of the prior art by providing appropriate technical teaching.
According to a further object of the invention, a process for producing high-purity (meth)acrylic acid from an impure crude (meth)acrylic acid stream from a process for producing (meth)acrylic acid is to be provided. The process should be harm-
’ PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG less to the (meth)acrylic acid, industrially practicable and therefore superior to processes of the prior art from the economic and ecological point of view. In this connection, an excellent purification capacity and compliance with stringent eco- logical and economic requirements should be mentioned in this connection.
A further object of the invention was to provide an apparatus for producing high- purity (meth)acrylic acid which allows the purification of impure (meth)acrylic acid to maximum purity with low energy consumption and uninterrupted, envi- ronmentally sound operation.
A further object of the invention was to provide a process and an apparatus with which the risk of uncontrolled polymerisation of (meth)acrylic acid during the production and, in particular, during the purification of (meth)acrylic acid is re- duced.
An object of the inventicn was also to reduce the quantity ot stabilisers required to stabilise the (meth)acrylic acid between production and further processing of the (meth)acrylic acid.
A further object was to provide a further use of the apparatus for producing the (meth)acrylic acid or one of its components in which the risk of undesirable, un- : controlled polymerisation of the (meth)acrylic acid is slight.
A further object was to provide a process and an apparatus for producing aqueous solutions of (meth)acrylic acid which is as pure as possible. This object stands against a background, in particular, where aqueous (meth)acrylic acids are often used in solution, suspension or emulsion polymerisation during the production of (meth)acrylic acid-containing polymers. It is of particular interest here that the
»
Stockhausen Grab DROS 26 HLIR
Degussa AG energy consumption associated with exchanges of solvent in the individual steps of synthesis from monomer synthesis to polymerisation is kept as low as possible.
An additional object according to the invention was to provide an aqueous (meth)acrylic acid phase which has a comparably high water concentration at as high a purity of (meth)acrylic acid as possible. Aqueous acrylic acid phases of this type are in this respect advantageous because they can be used directly in the aqueous polymerisation of absorbent polymers without a further dilution step. In this way, the until now common removal of water by distillation, followed by the purification of the acrylic acid and by a readdition of water for the polymerisation of the water-absorbing polymer, is shortened by a step.
These objects are achieved with a process for purifying a composition containing (meth)acrylic acid, at least one impurity and water, wherein the composition has a water content in the range of 0.55 to 90, preferably 7 to 50 and particularly pref- erably 10 to 25, or alsc of 10 to 85, preferably of 15 to 80, particularly preferably 25 to 75 % by weight, respectively based on the composition, to a purified phase containing (meth)acrylic acid and at least one impurity, wherein, in the purified phase, the quantity of at least one impurity is less than 7 % by weight, preferably less than 5 % by weight, more preferably less than 3 % by weight and particularly preferably less than 1 % by weight, based on the (meth)acrylic acid in the purified : phase, comprising a stage of the process which includes the following process steps: a) (meth)acrylic acid is crystallised from the composition while forming a suspension containing a mother liquor and (meth)acrylic acid crystals; b) (meth)acrylic acid crystals are separated from the mother liquor;
»
Stockhausen GmbH DSO 12°C HZ
Degussa AG c) at least a portion of the separated (meth)acrylic acid crystals is melted to form a melt; and d) a portion of the melt is recycled to step a) or step b), preferably step b), - and wherein the portion of melt which is not recycled is in the form of a separated (meth)acrylic acid.
Provided that d) is not followed by further stages or steps of the process, the sepa- rated (meth)acrylic acid forms a component of the purified phase.
According to an embodiment of the process according to the invention, the com- position, as a composition which is rich in water, has a concentration of (meth)acrylic acid with up to 10 % by weight of impurities in the range of 45 to 80 % by weight and water in the range of 20 to 55 % by weight, based on the re- spective composition. The aqueous compositions may originate from a quench absorber. The aqueous compositions may also be a mother liquor depleted in (meth)acrylic acid or the filtrate from a crystallisation, of which the (meth)acrylic acid is still to be purified.
In the case of the composition which is rich in water, the suspension formed in step a) preferably contains water crystals in addition to (meth)acrylic acid crystals.
It is also preferred if the melt contains 10 to 90 % by weight, preferably 15 to 70 % by weight and particularly preferably 25 to 55 % by weight, based on the melt, of water in the case of the composition which is rich in water.
According to a further embodiment of the process according to the invention, the composition, as a composition which is depleted in water, has a concentration of (meth)acrylic acid with up to 10 % by weight of impurities in the range of more than 80 % by weight and water in the range of < 20 to 0.55 % by weight, respec-
? PCT/EP03/02753 25. August 2004
Siocknausen GmbH D80612PC HZ/HR tively based on the composition. These compositions which are depleted in water preferably originate from thermal depletion, preferably distillation, of (meth)acrylic acid or from a previous crystallisation step which preferably corre- sponds to the process according to the invention.
In a further embodiment of the process according to the invention, it is preferred if the purified phase, as a phase which is depleted in water, contains at least 30 % by weight, preferably at least 55 % by weight and particularly preferably at least 75 % by weight of (meth)acrylic acid and less than 5 % by weight, preferably less than 2 % by weight, particularly preferably less than 1 % by weight and more par- ticularly preferably less than 0.5 % by weight of water, based on the respective purified phase.
In a further embodiment of the process according to the invention, it is preferred if the purified phase, as a phase which is rich in water, contains at least 20 % by weight, preferably at least 3C % by weight and particularly preferably at least 70 % by weight of (meth)acrylic acid and in the range of 5 to 80 % by weight, pref- erably in the range of 10 to 70 % by weight, particularly preferably in the range of 15 to 30 % by weight of water, based on the respective purified phase.
The phase which is depleted in water may be supplied, for example, to a solvent- free polymerisation process or a polymerisation process in which the solvent is added only before or during the polymerisation process. On the other hand, the phase which is rich in water may be added directly to a solution, suspension or emulsion polymerisation process in which water is used as a solvent. (Meth)acrylic acid may be obtained in the desired purities by appropriate combi- nation of the process according to the invention, optionally in a plurality of stages.
x
Stockhausen GmbH DAOS1206 HIHR
Degussa AG
For example, the (meth)acrylic acid obtained from the crystallisation of an aque- ous composition may be further purified as (meth)acrylic acid which Is depleted in water. The mother liquor thus formed as an aqueous composition may be further processed to a phase which is depleted in water or is aqueous by the process ac- cording to the invention.
With the process according to the invention, it is preferred to crystallise (meth)acrylic acid in step a) at least in part, preferably to at least 5 % by weight, particularly preferably at least 40 % by weight and more preferably at least 70 % by weight of the crystals, to form a crystal with a crystal structure having a sur- face with at least one recess located on the surface, the crystal structure having an orthorhombic Bravais crystal lattice with an Ibam space group, crystallographic dataa=9.952 A,b=11.767 A and ¢c = 6.206 A (cf. R. Boese, D. Blaser, L. Steller,
R. Latz, A. Baumen Acta Crystallogr., Sect (Cr. Str. Comm.), 55, 9900006, 1999).
It is also preferred with the process according to the inventicn if, in step aj, the mother liquor comprises at least 95 % by weight of (meth)acrylic acid and water, the water concentration of the mother liquor being in the range of 10 and 90 % by weight, in particular 15 and 70 % by weight, preferably 20 and 40 % by weight.
It is particularly preferred if the crystals have a tubular recess in their longitudinal direction, this recess preferably being dumb-bell-shaped, the openings of the tubu- lar recess being greater on the end faces of the approximately square crystals than in the sectional face of the crystal lying parallel to the end faces.
It is also preferred with the process according to the invention if crystallisation takes places in a suspension and not by the formation of layers in which a plural- ity of individual crystals are connected to one another to form a compact layer which is rigid in comparison with a crystal suspension. This is preferably i PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ'HR achieved in that crystallisation does not take place on a surface with correspond- ing temperature control — for example the wall of a layer crystalliser — with forma- tion of a crystal layer. Instead, the crystals formed in the suspension are freely mobile in the liquid phase, such as the mother liquor, containing them.
The above-described recess advantageously complicates the inclusion of impuri- ties such as mother liquor inside the crystal. The impurities are able to flow out or be washed out through the open recesses.
Even a high water content in the (meth)acrylic acid does not lead to an otherwise conventional increase in inclusions but to cavities which are open on both sides. If a water-containing suspension with such crystals is subjected to liquid/separation, the adhering mother liquor can advantageously flow away. This purification effect may be used, in particular, to considerably simplify the production of (meth)acrylic acid, to improve the quality of the (meth)acrylic acid produced in this way and thus to obtain pure, optionally aqueous {meth)acrylic acids.
Aqueous (meth)acrylic acids of which the water content is generally in the range of 10 and 90, preferably 11 and 50, particularly preferably 12 to 40 % by weight and more particularly preferably of 25 to 35 % by weight, based on the total quan- tity of water and (meth)acrylic acid, are produced by quenching the (meth)acrylic } acid obtained by catalytic gaseous phase reaction with water in a quench absorber.
In the past, water concentrations of this type had to be reduced almost completely in order to achieve sufficiently pure (meth)acrylic acid by crystallisation. This necessitated, in particular, at least one distillation step which impaired the quality of the (meth)acrylic acid owing to incipient polymerisation caused by exposure to heat.
’ PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
In one embodiment, the volume of the recess is at least 5 % by volume, in particu- lar at least 10 % by volume, preferably 20 % by volume, particularly preferably 50 % by volume, of the volume of the crystal. These large volumes of the recesses ensure that only comparatively few impurities can appear inside the crystal.
In a further embodiment of the invention, the crystal comprises at least one inclu- sion, the sum of the volumes of inclusions being less than 30 % by volume, pref- erably less than 15 % by volume and particularly preferably less than 5 % by vol- ume and more preferably less than 1 % by volume, of the volume of the crystal.
Owing to the small volume of impure mother liquor in the inclusions, impurities which are unable to flow away or be removed by a washing process, in the (meth)acrylic acid, based on the volume of the crystal, are limited.
In a further embodiment, the crystal has a length of between 0.001 and 5 mm, in particular between 0.05 and 0.5 mm, preferably between 0.1 and 0.2 mm, on aver- age. The length is determined by an image analysis system from 500 crystals se- lected at random from photographs obtained using a light microscope. An image analysis system consisting of a light microscope with attached CCD camera and a
PC evaluating unit is used for this purpose, whereby a PC programme from Soft
Imaging System (SIS, V3.1) is employed.
The composition used in the process according to the invention, in particular for crystallising a crystal according to the invention, is made up of at least 60 % by weight, preferably 80 % by weight and particularly preferably 95 % by weight of (methacrylic acid and water, the remainder being other substances, for example by-products produced during the synthesis of (meth)acrylic acid, wherein the wa- ter concentration is between 0.5 and 60 % by weight, in particular between 5 and 40 % by weight, preferably between 15 and 35 % by weight.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
This process surprisingly, but no less advantageously, leads to high-purity prod- ucts which are also suitable for use in polymers, for exampie in the hygiene indus- try.
The process preferably takes place continuously. It is preferable to use a wash column to separate the (meth)acrylic acid crystals from the mother liquor. For this purpose, the wash column comprises a separating region in which the (meth)acrylic acid crystals are washed. For successful operation of a wash col- umn, it is advantageous if the crystals to be washed are hard enough and have a specific narrow size distribution in order to guarantee appropriate porosity and stability of the resultant packed or unpacked filter bed.
It is also preferred that the process according to the invention is characterised by a crystallisation outlay (Wellinghof, Wintermantel, CIT 63 (1991) 9, p. 805, section 3.2.1) of 1 to 4.5, preferably less than 1 to 3.5 and particularly preferably of 1 to 2.5 and more preferably of 1 tc 1.5.
The process according to the invention may be carried out with impure crude (meth)acrylic acid containing < 99.5 % by weight of (meth)acrylic acid. The crude (meth)acrylic acid used preferably has a purity of 50 % by weight to 95 % by weight, preferably 75 % by weight to 90 % by weight of (meth)acrylic acid.
More preferably, the condensed mixture of a catalytic gaseous phase oxidation for the production of (meth)acrylic acid may be introduced directly as a composition into the process according to the invention, preferably into step a).
Accordingly, (meth)acrylic acid, usually originating from a corresponding olefin, is generated in a reactor, then brought into an aqueous composition in a quench absorber, whereupon the (meth)acrylic acid may be distilled to a composition yr
PCT/EP03/02753 25. August 2004
Stockhausen GrubH D80612PC HZ/HR
Degussa AG which is depleted in water in a distillation apparatus. The resultant crude (meth)acrylic acid stream 1s suppiled to the purification apparatus. The process allows the production of very pure (meth)acrylic acid from comparatively impure crude (methacrylic acid.
Crystallising agents which allow the purification process according to the inven- tion to be carried out continuously should be used during crystallisation. Suspen- sion crystallisation is preferably employed. This may be carried out advanta- geously in a stirred tank crystalliser, scraper crystalliser, cooling plate crystalliser, crystallising worm, drum crystalliser, multitube crystalliser or the like. In particu- lar, the vanations of crystallisation mentioned in WO 99/1418] may be used for this purpose. Crystallisers which may be operated continuously are again particu- larly advantageous. Cooling plate crystallisers or scraper coolers are preferred (Diss. Poschmann, p. 14). A scraper cooler is preferably used for crystallisation.
In principle, any wash column which allows continuous implementation of the purification according to the invention may be used for the process according to the invention. With a conventional embodiment, the suspension in a hydraulic wash column is introduced in the upper part of the column; the mother liquor is removed from the column via a filter so that a close-packed crystal bed is formed.
The crystal bed is permeated by the mother liquor in the direction of the base of the column and pressed downward by the fluid resistance. On the base of the col- umn is a moving, preferably rotating, scraping device or scraper which produces a suspension again from the close-packed crystal bed and the washing melt intro- duced at the lower part of the wash column. This suspension is preferably pumped through a melter, preferably a heat exchanger, and melted. A portion of the melt may be used, for example, as washing melt; this is then recirculated into the col- umn and preferably washes out the crystal bed which is migrating in the opposite direction, 1.e. the crystallised (meth)acrylic acid is washed in the countercurrent of
¥
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZHR the recycled (meth)acrylic acid. On the one hand, the washing melt brings about washing of the crystals, on the other hand, the melt crvstallises at least in part onto the crystals. The liberated crystallisation enthalpy heats the crystal bed in the washing region of the column. A purification effect similar to the exudation of the crystals is thus achieved. On the one hand, purification is therefore brought about by washing the surface of the (meth)acrylic acid crystals with molten, and there- fore already purified, (meth)acrylic acid and, on the other hand, healing or exuda- tion of impurities is achieved by crystallisation of the molten purified (meth)acrylic acid on the existing (meth)acrylic acid crystals. This allows produc- tion of high-purity (meth)acrylic acid.
In a specific embodiment of the process according to the invention, the return flow resulting from the recycling of the molten (meth)acrylic acid from step c) into step a) or into step b) is greater than a feed flow of the composition which is continuously supplied to step a) from the exterior.
In particular, the return flow is at least twice and preferably at least ten times as great as the feed flow. The great return flow ensures that the exposure of the (meth)acrylic acid to heat on the melter is reduced.
For inoculation of the (meth)acrylic acid to be crystallised, it is advantageous to supply the separated crystallised (meth)acrylic acid from step b) at least in part to step a). The recirculated (meth)acrylic acid crystals simplify crystal growth in step a) and therefore assist separation of the (meth)acrylic acid from the mother liquor.
This is advantageous, particularly with an aqueous composition.
From the energy point of view, a single-stage purification process with a single stage of the process is particularly advantageous and therefore particularly pre-
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZHR
Degussa AG ferred. However, a two-stage purification process may be appropriate under cer- tain circumstances.
To increase the yield, it is expedient to recycle the mother liquor separated in step b) at least in part to step a). (Meth)acrylic acid which has remained in the mother liquor may therefore be further crystallised with appropriate spatial temperature profiles, preferably to the thermodynamic limit (for example eutectic). i. In an advantageous group of embodiments, the process according to the invention comprises at least two stages of the process, which each include steps a) to d), wherein at least one of the following features (al) to (a4) is fulfilled: (al) separated, in particular crystalline and/or molten, (meth)acrylic acid from a first stage of the process is supplied at least in part to a second stage of the process; (02) separated, in particular crystalline and/or molten, (meth)acrylic acid from a second stage of the process is supplied at least in part to a first stage of the process; (03) mother liquor, in particular mother liquor separated in step b), from a first stage of the process is supplied at least in part to a second stage of the process; (04) mother liquor, in particular mother liquor separated in step b), from a sec- ond stage of the process is supplied at least in part to a first stage of the
Process.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZHR
Degussa AG
From this group of advantageous embodiments with at least one of the features (al) to (04) of the invention, the embodiments in which at least one of the follow- ing features (B1) and (P6) is fulfilled, are preferred: (Bl) crystalline (meth)acrylic acid from the first stage of the process is supplied to at least one of steps a) and b) of the second stage of the process; (B2) molten (meth)acrylic acid from the first stage of the process is supplied to at least one of steps a) and b) of the second stage of the process; (B3) crystalline (meth)acrylic acid from the second stage of the process is sup- plied to at least one of steps a), b) and c) of the first stage of the process; (B4) molten (meth)acrylic acid from the second stage of the process is supplied to at least one of steps a), b) and c) of the first stage of the process; (B5) mother liquid separated in step b) from the first stage of the process is supplied at least in part to step a) of the second stage of the process; (P6) mother liquid separated in step b) from the second stage of the process is supplied at least in part to step a) of the first stage of the process.
If the second or further stage of the process brings about additional purification of the (meth)acrylic acid, i.e. (meth)acrylic acid already purified in a first stage of the process is further purified in a second (further) stage of the process, the fol- lowing embodiments from this group of preferred embodiments of the invention are particularly preferred:
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG 0) for achieving high-purity (meth)acrylic acid, molten (meth)acrylic acid from the first stage of the process is supplied to step a) of the second stage of the process; 2 for achieving high-purity (meth)acrylic acid, crystalline (meth)acrylic acid from the first stage of the process is supplied to step a) of the second stage of the process; 3) to allow thorough washing of the (meth)acrylic acid crystals from the first : 10 stage, molten (meth)acrylic acid from the second stage of the process is supplied to step b) of the first stage of the process; or 4) in order to provide particularly pure seed crystals, crystalline (meth)acrylic acid from the second stage of the process is supplied to step a) of the first stage of the process.
A combination of the respective embodiments (1) or (2) with (3) is most particu- larly preferred.
If the second stage of the process is used to increase the yield, the following em- bodiments from the group of preferred embodiments of the invention are particu- larly preferred: (D crystalline (meth)acrylic acid from the first stage of the process is supplied to step a) of the second stage of the process as seed crystals for crystallisa- tion; 2) to increase the yield, the mother liquor separated in step b) of the first stage of the process is supplied at least in part to step a) of the second stage of the process;
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG 3) to increase the purity, molten (methlacrvlic acid from the second step of the process is supplied to step a) of the first stage of the process; or 4) to minimise energy consumption, crystalline (meth)acrylic acid from the second step of the process is supplied to step a) of the first stage of the
Process.
A combination of embodiments (2) and (4) is most particularly preferred.
Advantageously, at least two stages of the process are provided in series. “In se- ries" can refer both to the separated (meth)acrylic acid, i.e. to the crystalline or molten (meth)acrylic acid, and to the separated mother liquor.
It is also advantageous to nest at least two stages of the process with one another.
As a result, the number of melters which are required for melting and consume a large amount of energy during operation as heat exchangers or heaters, is smaller than the number of stages. For example, a simple nesting of two stages of the process can lead to a saving of one melter. Operation therefore becomes much more cost efficient with an identical yield and identical purity. ) The number of stages of the process is based on the purity and economic effi- ciency to be achieved by the process. The achievable purity of (meth)acrylic acid is basically limited by the thermodynamic limit (for example eutectic) for a crys- tallisation capability of (meth)acrylic acid from the mother liquor.
A specific embodiment of the process according to the invention is characterised by the following features (y1) and (y2):
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG (yl) crystallisation of (meth)acrylic acid from an impure crude (meth)acrylic acid stream from a process of producing (meth)acryiic acid, (2) separation of the (meth)acrylic acid crystals from the mother liquor using a wash column, wherein the mother liquor from step (y2) is recycled at least in part to step (yl), the crude (meth)acrylic acid stream having a purity of < 99.5 % by weight of (meth)acrylic acid.
The apparatus according to the invention for producing (meth)acrylic acid com- prises as components which are connected to one another in a fluid-conveying manner, a (meth)acrylic acid synthesis unit, which preferably includes a (meth)acrylic acid reactor and a quench absorber, a distillation apparatus and a purification apparatus, the purification apparatus including an apparatus unit com- prising features (81) to (64): (81) the apparatus unit comprises a crystallisation region, a separating region, a melter and at least three guides; (62) the crystallisation region is connected to the separating region by a first guide; (83) the separating region is connected to the melter by a second guide; (84) the melter is connected to the crystallisation region by a third guide or to the separating region by a fourth guide; wherein the purification apparatus comprises an inlet which guides a composition containing {meth)acrylic acid, at least one impurity and water, the composition
>
PCT/EP03/02753 25 August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG having a water content in the range of 0.55 to 90, preferably of 7 to 50 and par- ticularly preferably of 10 to 25 % by weight. based on the composition.
According to the invention, the expression "in a fluid-conveying manner" means that gases or liquids, including suspensions, or mixtures thereof are guided through corresponding lines. In particular, pipes, pumps and the like may be used for this purpose.
Owing to the low degree of distillation, the (meth)acrylic acid produced in this way is treated particularly carefully, whereby its quality is improved. In addition, the pure aqueous (meth)acrylic acid obtained in this way may be used in solution, emulsion or suspension polymerisation processes so that a detrimental exchange of solvent from identical or different solvents may be avoided, in contrast to con- ventional reaction control.
L5
In an embodiment of the apparatus according to the invention, it is preferred if the (meth)acrylic acid synthesis unit and the purification apparatus are connected to one another without a distillation apparatus.
In a further embodiment of the apparatus according to the invention, it is preferred if the quench absorber and the purification apparatus are connected to one another ) without a distillation apparatus.
An apparatus for producing acrylic acid which is preferred according to the inven- tion preferably has the following construction in the region comprising a (methacrylic acid reactor and a quench absorber during the synthesis of acrylic acid: propylene and optionally further inert gases such as nitrogen or combustion gases such as CO; or nitrogen oxides are fed into a first reactor for initial catalytic oxidation via an educt inlet which opens into the first reactor. The first reactor is
Stockbatsen Gb DR061256 HZHR
Degussa AG connected by a further line to a second reactor into which the product of the first catalytic oxidation process from the first reactor is introduced for second catalytic oxidation. The acrylic acid-containing product of the second catalytic oxidation is fed via a line located between the second reactor and quench absorber to the lower half of the quench absorber. In the quench absorber, the product of second cata- lytic oxidation is brought into contact with water, the water being introduced into the quench absorber above the supply of the product of the second catalytic oxida- tion. On the one hand, a first phase which contains acrylic acid and water is dis- charged from the quench absorber below the supply of the product of second cata- lytic oxidation. This first phase may be recycled into the quench absorber again at least in part above the supply of the product of second catalytic oxidation. The first phase not recycled into the quench absorber is supplied to the distillation ap- paratus and subjected, for example, to azeotropic separation during which the acrylic acid is concentrated and purified. A second phase which contains acrylic acid and water may be discharged from the quench absorber above the return of the first phase and below the introduction of water into the quench absorber. This second phase, like the first phase, may be supplied to the distillation apparatus and be subjected, for example, to azeotropic separation during which the acrylic acid is concentrated and purified. The exhaust gases discharged from the quench ab- sorber may be supplied to a catalytic combustion process. The combustion gases from catalytic combustion may be introduced into the first reactor as inert gases.
The water recovered during the concentration of acrylic acid may be recycled into the quench absorber. Further details of the production of acrylic acid are disclosed in DE 197 40 252 Al, of which the content is referred to as part of this disclosure.
According to the invention, acrylic acid may also be synthesised in a synthesis unit which converts propane directly into acrylic acid. Acrylic acid may addition- ally be synthesised in aqueous reaction media, preferably as homogeneous cataly- sis. During a reaction in aqueous reaction media, the acrylic acid would be pro-
¥
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ HR duced in the form of the composition which is rich in water without the need to add water in 2 quench absorber.
An apparatus for the production of (meth)acrylic acid which is preferred accord- ing to the invention comprises the (meth)acrylic acid reactor and a quench ab- sorber during the synthesis of (meth)acrylic acid by catalytic gaseous phase reac- tion of C4 starting compounds with oxygen. (Meth)acrylic acid may be obtained particularly preferably by catalytic gaseous phase oxidation of isobutene, isobu- tane, tert.-butanol, iso-butyraldehyde, methacrolein or meth-tert.-butylether. Fur- ther details on the production of (meth)acrylic acid are disclosed in EP 0 092 097
B1, EP 0 058 927 and EP 0 608 838, of which the content will be referred to as part of this disclosure.
The purification apparatus is capable of obtaining very pure (meth)acrylic acid with degrees of purity over 99.5 % by weight from a comparatively impure crude (meth)acrylic acid stream containing approximately 85 % by weight of (meth)acrylic acid. According to the invention, it is possible efficiently to purify impure crude (meth)acrylic acid stream with 50 % by weight to 95 % by weight (meth)acrylic acid, preferably 75 % by weight to 90 % by weight (meth)acrylic acid. This effective purification allows preliminary purification of the crude (meth)acrylic acid stream using the distillation apparatus to be reduced, so the heat exposure of the (meth)acrylic acid is reduced. The quality of the (meth)acrylic acid is therefore improved.
The apparatus unit comprises a separate purification apparatus for a further in- crease in the purity of the (meth)acrylic acid. This separate purification apparatus may be used for the further purification of the end product, in particular for the further purification of the (meth)acrylic acid leaving the melter.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZHR
Degussa AG
To improve crystallisation, the separating region is preferably connected to the crystallisation region by a first return for separated (meth)acrylic acid.
To increase the yield, the separating region is advantageously connected to the crystallisation region by a second return for separated mother liquor.
In terms of energy, a single-stage purification apparatus with a single apparatus unit is basically particularly advantageous and therefore particularly preferred.
However, a two-stage purification apparatus may be appropriate under certain circumstances.
To increase the efficacy of purification, in particular to increase the purty and yield, the apparatus according to the invention contains at least two apparatus units according to features (81) to (84), which are connected by at least one con- necting line, the connecting line being a feed line or a return line and at least one of the following features {€1) to (€4) being fulfilled: (e1) the separating region of a first apparatus unit is connected via the connect- ing line to the crystallisation region of a second apparatus unit; (€2) the melter of a first apparatus unit is connected via the connecting line to the crystallisation region of a second apparatus unit; (e3) the separating region of a second apparatus unit is connected via the con- necting line to the crystallisation region of a first apparatus unit; (4) the melter of a second apparatus unit is connected via the connecting line to the crystallisation region of a first apparatus unit. The connecting lines may be a feed line as well as a return line.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
For example, it is expedient with the process according tc the invention tc provide a feed line from the separating region of the first apparatus unit (first stage of the process) to the crystallisation region of the second apparatus unit (second stage of the process) in order to increase the yield. A return between the separating region of the second stage and the crystallisation region of the first stage, on the other hand, is expedient for the preparation of seed crystals.
Therefore, at least two apparatus units may advantageously be connected in series to improve the purity and yield.
The number of melters required and therefore the energy required to operate the apparatus may be reduced by nesting at least two apparatus units.
With the process according to the invention for purifying acrylic acid, a tempera- ture in the range of -20 to 20°C, preferably -10 to 13°C at a pressure of 1 to 10 bar prevails in the separating region. It is preferred if the temperature and pressure prevailing in the lower region of the separating region are lower than in the upper region of the separating region. Preferably, a temperature of -20 to < 12°C at a pressure of 1 to 2 bar prevails in the lower region of the separating region. A tem- perature of at least 12°C at a pressure of 1 to 10 bar, preferably 3 to 7 bar prevails in the upper region of the separating region.
With the process according to the invention for purifying acrylic acid, a tempera- ture in the range of -20 to 20°C, preferably -12 to 13°C at a pressure of 0.5 to 10 bar, preferably 0.8 to 2 bar prevails in the crystallisation region.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
With the process according to the invention for purifying acrylic acid, a tempera- ture in the range of 10 to S0°C, preferably 11 to 20°C at a pressure of ! tc 10 bar, preferably 3 to 7 bar prevails in the mcltcr.
With the process according to the invention for purifying methacrylic acid, a tem- perature in the range of -5 to 30°C, preferably -3 to 20°C at a pressure of 1 to 10 bar prevail in the separating region. It is preferred that the temperature and pres- sure prevailing in the lower region of the separating region are lower than in the upper region of the separating region. Preferably, a temperature of -16 to < 15°C at a pressure of 1 to 2 bar prevails in the lower region of the separating region. A temperature of at least 15°C and a pressure of 1 to 10 bar, prevail in the upper region of the separating region.
With the apparatus according to the invention for purifying methacrylic acid, a temperature in the range of -5 to 30°C, preferably -3 to 20°C at a pressure of 1 to 10 bar, preferably 1 tc 2 bar prevails in the crystallisation region.
With the apparatus according to the invention for purifying methacrylic acid, a temperature in the range of 10 to 50°C, preferably 11 to 30°C at a pressure of 1 to 10 bar, preferably 3 to 7 bar prevails in the melter.
The temperature and pressure conditions prevailing in the guides allow reliable, uninterrupted transport of the (meth)acrylic acid and the substances possibly ac- companying it in these guides.
The apparatus according to the invention enables a relatively impure (meth)acrylic acid to be used as the starting material, so the preliminary expenditure for distilla- tion of the (meth)acrylic acid originating from synthesis is reduced. Therefore, the
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG exposure of the (meth)acrylic acid to heat, which may lead to undesirable polym- erisation, is reduced.
The invention further relates to an apparatus for polymerising (meth)acrylic acid, comprising an apparatus for producing (meth)acrylic acid and a polymerisation unit, wherein the purification apparatus of the apparatus for producing (meth)acrylic acid is connected to the polymerisation unit.
The invention also relates to a (meth)acrylic acid obtainable by the process of pu- rification according to the invention.
The invention further relates to a process for producing a polymer containing (meth)acrylic acid, wherein a (meth)acrylic acid according to the invention or a purified phase according to the invention, obtainable by the process of purification according to the invention, is polymerised. Polymerisation preferably takes place as solution polymerisation, reaction control in a recessed belt being particularly preferred. In the process, the aqueous phase is used directly or, alternatively, the phase which is depleted in water is correspondingly diluted. Polymerisation gen- erally takes place in a medium having a water content of 20 to 80 % by volume, based on the medium.
The invention also relates to a polymer which may be obtained by the process described in the foregoing paragraph.
The polymer is preferably an absorbent polymer with a maximum absorption of 0.9 % by weight aqueous NaCl solution according to ERT 440.1-99 in a range of 10 to 1,000, preferably 15 to 500 and particularly preferably 20 to 300 ml/g. Fur- ther details about absorbent polymers and their production may be found in "Mod-
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG ern Superabsorbent Polymer Technology", Fredrick L. Buchholz, Andrew T. Gra- ham, Whiley-VCH, 199%
The fibres, shaped articles, films, foams, superabsorbent polymers or hygiene arti- cles according to the invention are based at least on or contain at least the (meth)acrylic acid according to the invention or the polymer according to the in- vention.
The (meth)acrylic acid according to the invention or the polymer according to the invention is used in or for the production of fibres, shaped articles, films, foams, superabsorbent polymers or hygiene articles.
The apparatus according to the invention or the purification apparatus according to the invention or the process according to the invention is used for producing acrylic acid having a purity of more than 90 % by weight, preferably more than 95 % by weight and particularly preferably more than 95.5 % by weight, based on the respective (meth)acrylic acid with impurities.
In a specific embodiment of the process according to the invention for purifying (methacrylic acid, the process comprises two process steps v1) crystallisation of (meth)acrylic acid from an impure crude (meth)acrylic acid stream from a process of producing (meth)acrylic acid; 2) separation of the (meth)acrylic acid crystals from the mother liquor using a wash column, wherein the mother liquor from step (2) is recycled at least in part to step (v1), the crude (meth)acrylic acid stream having a purty of < 99.5 % by weight of (meth)acrylic acid.
y
Stockhausen GmbH D806 276 HOH
Degussa AG
A mechanically operated wash column (Diss. Poschmann, p. 18) is particularly preferred according to the invention.
With a mechanical wash column — reference being made to EP 0 193 226 B and
NL 100 76 87 A for example — a dense crystal bed is produced within the column by means of a piston which is permeable to the melt. The piston may be located at the upper or lower end of the column; in the first case, the suspension is supplied in the upper region of the column and in the second case in the central or lower region. The piston is permeable to the melt so, during compression, melt issues at the back of the piston, where it is removed. In a similar manner to a hydraulic wash column, the mechanical wash column also contains a scraping apparatus, for example a moving, preferably rotating, scraping member for scraping crystals from the crystal bed and transferring them into a suspension with the wash melt.
The wash melt moves countercurrent to the crystal bed. Suspension is removed from the side of the wash column remote from the piston and, after the melting operation, a propostica ¢f the melt may be recycled as wash melt and the remain- der removed from the circuit as extra-pure product.
Embodiments of suspension crystallisation with subsequent washing of the crys- tals in a hydraulic or mechanical wash column can be found in the book "Melt
Crystallisation Technology " by G.F. Arkenbout, Technomic Publishing Co. Inc, : Lancaster-Basel (1995), p. 265-288 and the article about the preconcentration of waste water using the Niro freeze concentration process in Chemie Ingenieur
Technik (72) (10/2000), 1231-1233.
Depending on the application, a washing fluid familiar to a person skilled in the art may be used as the washing fluid (for example water in the case aqueous solu- tions). For washing the crystallised (meth)acrylic acid, as already mentioned, it is most particularly preferred to use a proportion of the molten crystals thereof. This
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D830612PC HZ/HR
Degussa AG ensures, on the one hand, that no further substance has to be introduced into the system for the production of high-purity products and, on the other nand, the mol- ten crystals are also used to force back the mother liquor front in the wash column and simultaneously have a purifying effect similar to exudation on the crystals.
Products are not lost in the process as the washing fluid crystallises again on the crystals to be washed and is therefore found in the product again (for example brochure from Niro Process Technology B.V., Crystallization and wash column separation set new standards in purity of chemical compounds).
It is further preferred in the process according to the invention that the process occurs in a device according to the invention.
In an embodiment of the process according to the invention, the separated, in par- ticular crystalline and/or molten, (meth)acrylic acid is purified in a separate puri- fication process. For example, it is possible to treat the mother liquor from stcp b) prior to the return to step a), at least once by a further purification process. A per- son skilled in the art is sufficiently familiar with such processes. Preferably, the following processes in particular are employed: 1) Simple distillation
Separation into low-boilers (acetic acid, water, etc.), medium-boilers ((meth)acrylic acid) and high-boilers (MSA, PTA, etc.). The purification of impure (meth)acrylic acid (in particular of water and acetic acid) is car- ried out in the majority of cases by azeotrope rectification. Entrainers such as toluene or MIBK, for example, are used (EP 0 695 736 B1). 2) Extraction of acrylic acid
The (meth)acrylic acid may be obtained by extraction with n-butanol. An aqueous phase in which the minor constituents are dissolved remains. The
Y
Stockbausen GmbH DAS L276 HZHR
Degussa AG extraction of (meth)acrylic acid from impure solutions pertains to the prior art similarly te distillation. (Meth)acrylic acid may also be extracted, for example, from aqueous solu- tions with liquid ion exchanges, mixtures of tri-n-alkylamines and ali- phatic alcohols or n-butanol (Vogel et al.: Chem. Eng. Technol. 23 (2000) 1, pp. 70-74; Tamada et al.: in Solvent Extraction 1990, Ed.: T. Sekine, El- sevier Science Publishers B.V. pp. 1791-1796; JP 57 095 938; WO 98/40342; Information brochure from SULZER Chemtech on fractional extraction of (meth)acrylic acid with n-butanol). 3) Dewatering of (meth)acrylic acid by pervaporation
This process is disclosed inter alia in DE 4401405 Al.
Advantageously, the mother liquor from step b), prior to return to step a), may be treated at least once by a process including steps a, and b) and may be recycled to the respectively purer branched partial stream in step a) of the original process or a prior process so that maximum purity may be achieved with the minimum loss of yield.
Fig. 2 illustrates this matter. The mother liquor from crystal separation in the wash column may also be treated in a subsequent crystallisation region. The resultant suspension may then be worked-up in turn in a wash column as usual. The mother liquor now formed may be similarly treated in the following stages. There is a choice between recycling the respective purer streams produced by this procedure into crystallisation of the first purification process or into crystallisation of a prior process. Maximum purity can thus be achieved with a minimum of waste using relatively inexpensive apparatus.
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
The processes according to the invention may be carried out continuously and discontinuously. continuous operation being preferred as such operation is particularly cost effective.
The invention further relates to an apparatus for polymerising (meth)acrylic acid, comprising an apparatus according to the invention for producing (meth)acrylic acid and a polymerisation unit, the purification apparatus of the apparatus for pro- ducing (meth)acrylic acid being connected to the polymerisation unit. This po- lymerisation unit may be a kneaded or stirred-tank reactor or a recessed belt in or on which polymerisation takes place. Recessed belt polymerisation is advanta- geous for the phase which is rich in water. The phase which is rich in water has a water and (meth)acrylic acid concentration which is particularly suitable for the solution polymerisation of polymers based on (meth)acrylic acid, preferably su- perabsorbent polymers and special polymers for leather and paper production and 1S waste water treatment.
The invention further relates to a process for producing a polymer based on (meth)acrylic acid, whereby a (meth)acrylic acid according to the invention, or a purified phase, obtainable by the process according to the invention for the purifi- cation of (meth)acrylic acid, is polymerised. The polymers obtainable by this process are preferably superabsorbers, special polymers for the waste water treat- ment, dispersion dye, cosmetics, textiles, leather treatment or paper production industry.
The invention also relates to fibres, shaped articles, films, foams, superabsorbers polymers, special polymers for waste water treatment, dispersion dyes, cosmetics, textiles, leather treatment or paper production or hygiene articles, at least based on or containing (meth)acrylic acid purified according to the invention or a polymer according to the invention.
Y
Stockbausen GmbH D806 12C HIHR
Degussa AG
The invention finally relates to the use of the (meth)acrvlic acid produced accord- ing to the invention or a polymer according to the invention in or for the produc- tion of fibres, shaped articles, films, foams, superabsorbent polymers or hygiene articles, detergents or special polymers for the waste water treatment, dispersion dye, cosmetics, textiles, leather treatment or paper production industries. "Superabsorbent polymers" are polymers which absorb water or aqueous fluids in a quantity which is a multiple of their inherent weight. Preferably, more than half of the superabsorbent polymers is based on acrylic acid as a monomer. Further details of superabsorbent polymers, their production and use in hygiene articles may be found in "Modern Superabsorbent Polymer Technology”, Fredrick L.
Buchholz, Andrew T. Graham, Wiley-VCH, 1998, the content of which will be referred to as part of this disclosure. These superabsorbent polymers are prefera- bly incorporated into hygiene articles. Particularly preferred hygiene articles in- clude nappies, incontinence articie for adults and sanitary towels.
Furthermore, the respective combinations of features emerging from the features characterised by numerals hereinbefore represent individual embodiments of the present invention.
Further details and advantageous embodiments will be described in more detail with reference to the following drawings which will illustrate the invention by way of examples.
In the schematic drawings:
Fig. 1 is a further process diagram according to the invention according to Fig. 1:
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG ]
Fig. 2 is a process diagram according to the invention with two process stages connected in series;
Fig. 3 is a process diagram according to the invention with two nested process stages;
Fig. 4 is a process diagram according to the invention with one process stage;
Fig. 5 is a process diagram according to the invention with two process stages;
Fig. 6 shows a crystal habit of pure acrylic acid;
Fig. 7 shows a crystal habit according to the invention of acrylic acid from a 90/10 w/w mixture of acrylic acid and water;
Fig. 8 shows a crystal habit according to the invention of acrylic acid from a 80/20 w/w mixture of acrylic acid and water;
Fig. 9 shows a crystal habit according to the invention of acrylic acid from a 70/30 w/w mixture of acrylic acid and water.
Fig. 1 is a process diagram in which the process (in one stage) will be described in summary:
Stage] 1. storage vessel 2. feed line from 1 to 3 3. suspension producer (e.g. cooling plate crystalliser, scraper cooler)
Y
PCT/EP03/02753 25. August 2004
Stocktausen GmbH D80612PC HZ/HR 4. feed line from 3 to 5 s. wash column, hydraulic or mechanical 6. product circuit 7. product circuit pump 8. product circuit heat exchanger as melter 9. product vessel 10. product return to countercurrent washing wash column 5 11. mother liquor return (optional) 12. mother liquor vessel (reject)
The wash column 5, the suspension generator 3, the product circuit heat ex- changer 8, the feed line 4, the product circuit 6 and the product return 10 corre- spond to the separating region, the crystallisation region, the melter, the first guide, the second guide, the fourth or, if crystal formation takes place in the wash column, the third guide.
The melt which is to be separated and is in the liquid state, in other words con- trolled to a temperature just above equilibrium, is guided from the storage vessel 1 via the feed line 2 into the suspension generator 3. Crystals having a suspension packing of 5 to 50% (preferably 20 to 30%) are formed continuously in the sus- pension generator 3 by cooling below the equilibrium temperature of the melt.
The suspension is guided continuously through the feed line 4 into the wash col- umn 5 where it is separated into a liquid and a solid phase by moving or stationary filters (hydraulic or mechanical (see above)). The filtrate leaves the wash column 5 and is supplied continuously to the mother liquor vessel 12. To increase the yield, at least a portion of the filtrate may optionally also be recycled via the mother liquor return 11 into the suspension generator 3.
¥
Stockhausen GmbH DROS 276 HIHR
Degussa AG
The crystals in the wash column 5 are packed to a crystal bed and, depending on the tvpe of wash column, are shaved off at the top or bottom by rotarv blades. The shaved off product crystals are circulated as a suspension in the product circuit 6 by the circulating pump 7 and melt due to the introduction of the melt enthalpy with the melter or product heat exchanger 8.
A portion is recycled through the product return 10 into the wash column as wash- ing fluid for countercurrent washing. The remainder leaves the apparatus as prod- uct in the vessel 9.
If a minimum loss of product in the reject cannot be achieved with this single- stage procedure, the mother liquor from the first stage of crystallisation may op- tionally be worked-up in one or more further stages of crystallisation or with other purification agents.
Fig. 2 shows an example of implementation in a plurality of crystallisaticn stages.
Stage 2/3 etc. 13. mother liquor vessel from first stage (= 12) 14. feed line from 13 to 15 15. suspension generator stage 2 (e.g. cooling plate crystalliser, scraper cooler) 16. feed line from 15to 17 17. wash column, hydraulic or mechanical 18. product circuit of second stage 19. product circuit pump 20. product circuit heat exchanger as melter 22. product return to 17 23. mother liquor return to second stage crystailiser (optional)
Stockaausen GmbH DROS1256 HZHR
Degussa AG 24. mother liquor vessel of second stage (reject) 25. mother liquor supply from second stage to 26 26. suspension generator stage 3 (e.g. cooling plate crystalliser, scraper cooler) 27. supply of product from 26 to 28 28. wash column, hydraulic or mechanical 29. product circuit of third stage 30. product circuit pump 31. product circuit heat exchanger as a melter 32. product return to 28 33. mother liquor return to crystalliser of third stage (optional) 34. feed line from 28 to 35 35. mother liquor vessel (reject) of third stage 36. optional supply to further purification stages
The suspension generator 15, the wash column 17, the product circuit heat ex- changer 20, the feed line 16, the product circuit 18, product return 20, the mother liquor return 23 each correspond in the first apparatus unit to the crystallisation region, the separating region and the melter, the first guide, the second guide, the third and fourth guide, of the second return.
The suspension generator 26, the wash column 28 and the product circuit heat exchanger 31, the product circuit 32, the product return 29, the mother liquor re- turn 33 each correspond, in the second apparatus unit, to the crystallisation region, the separating region, the melter, the second guide, the third and fourth guide of the second return.
The mother liquor feed line 25 corresponds to a connecting line.
PCT/EP03/02753 25. August 2004
Stockbausen GmbH D80612PC HZ/HR
The mother liquor (12/13) from the first stage is partially or wholly guided into the suspension generator of the second stage 15. Crystals with a suspension den- sity of 5 to 50% (preferably 20 to 30%) are formed continuously in the suspension generator 15 by cooling below the equilibrium temperature of the melt. The sus- pension is guided continuously via the feed line 16 into the wash column of the second stage 17 where it is separated into a liquid and a solid phase by moving or stationary filters (hydraulic or mechanical, see above).
Once the crystals have been densified to a crystal bed, they are shaved with rotary blades at the top or bottom, depending on the type of wash column 17. The shaved off product crystals are optionally (as in the first stage) circulated as a suspension in the product circuit 18 by the circulating pump 19 and melt owing to the introduction of the melt enthalpy with the melter 20. A portion may be recycled 22 into the wash column as washing fluid for countercurrent washing. The remainder may be recycled into the suspension generator of the first stage 3 as a molten product. The filtrate leaves the wash column 17 and is supplied continuously to the mother liquor vessel 24. For a further increase in yield, it 1s optionally possible to recycle at least a portion of the filtrate also via the mother liquor return 23 into the suspension generator 15 and/or to continue working it up in a third stage.
For this purpose, the mother liquor is conveyed via 25 into a further suspension generator 26. The suspension obtained as mentioned hereinbefore is conveyed via 27 into the wash column 28 where it is packed to a crystal bed and shaved off with rotary blades at the top or bottom, depending on the type of wash column 28.
The shaved off product crystals are optionally (as in the first stage) circulated as a suspension in the product circuit 29 by the circulating pump 30 and melt due to the introduction of the melt enthalpy with the heat exchanger 31.
Stocksausen GmbH DAO 127€ HOR
Degussa AG
A portion may be recycled 32 into the wash column as washing fluid for counter- current washing. The remainder may be returned to the suspension generator of the first stage 3 or the second stage 15 as molten product.
Fig. 3 shows a further preferred layout of the working-up process according to the invention. 41. storage vessel 42. suspension generator (e.g. cooling plate crystalliser, scraper cooler) 43. feed line from 42 to 44 44. wash column, hydraulic or mechanical 45. product circuit 46. product circuit pump 47. product circuit heat exchanger as heat exchanger 48. product vessel 49. product retum to countercurrent washing in wash column 44 50. feed line of the second stage = mother liquor from stage 1 (from wash col- umn 44) 51. suspension generator stage 2 (e.g. cooling plate crystalliser, scraper cooler) 52. feed line from 51 to 53 53. wash column, hydraulic or mechanical 54. product from the second stage (suspension, mixed with the original from 41 which is not guided in stage 1, but in stage 2) which is guided in the scraper cooler of the first stage (42) 55. product supply pump 56. supply from the first stage (41) directly to the head of the wash column 53 of the second stage 57. mother liquor return to the crystalliser of the second stage (51) (optional) 58. mother liguer vessel of the secend stage (reject)
( ¥
Stockhausen CoH 8061266 HZMR
Degussa AG
The suspension generater 42, the wash column 44, the product circuit heat ex- changer 47, the product circuit 45, product return 49, the feed linc 43 cach corre- spond, in the first apparatus unit, to the crystallisation region, the separating re- gion, the separating region, the melter of the second guide, the third and fourth guide, the first guide.
The suspension generator 51, the wash column 53, the feed line 52, the mother liquor return 57 each correspond, in the second apparatus unit, to the crystallisa- tion region, the separating region, the first guide, the second return.
The feed lines 54, 50 correspond to connecting lines. The nesting shown here by way of example advantageously eliminates the need for the second apparatus unit to have a melter.
A particularly preferred variation of a two-stage cr multiple-stage design guides the melt to be separated from the first stage 41 via the supply line 56 and the pump 55 to the head of the wash column of the second stage 53 where the shaved off product crystals of the second stage are guided into the suspension generator of the first stage 42 as a suspension 54. This variation has the advantage, in terms of energy, that melting in the second stage may be dispensed with and the crystals now in the first stage do not have to be frozen out again.
The countercurrent washing in the wash column of the second stage 53 is achieved using the melt from 41 via feed line 56 of the first stage which 1s very pure in comparison with the impurity concentration in the second stage and there- fore allows washing which is similarly effective to washing with product.
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
Although a combination of a scraper cooler and a wash column is known for the production of high-purity organic substances, it could not be anticipated that this process is also very suitable for concentrating (meth)acrylic acid with starting purities of < 99.5 % by weight and with a high water content, based on the quan- tity of acrylic acid. It was further surprising that the content of impurities, such as further organic carbon compounds, may be considerably reduced to values by the process according to the invention. Consequently, critical variables such as fur- fural, inhibitors, acetic acid or maleic acid may also be depleted to uncritical val- ues. This could not be inferred from the prior art and is not made obvious thereby either.
Fig. 4 shows a process diagram according to the invention with one process stage and Fig. 5 shows a process diagram according to the invention with two process stages. 60. apparatus unit {first process stage} 61. crystallisation region 62. separating region 63. heat exchanger as melter 64. second guide 65. third guide 66. first guide 67. fourth guide 68. separate purification apparatus 69. first return 70. second return 71. connecting line 72. connecting line 73. connecting line
A
Stockhausen Grab DaO612PE HZHR
Degussa AG 74. (meth)acrylic acid reactor 75. quench absorber 76. distillation apparatus 77. purification apparatus 78. apparatus unit (second process stage) 79. pump 80. residual mother liquor outlet 81. product outlet
Fig. 4 shows an apparatus according to the invention for the production of (meth)acrylic acid with a (meth)acrylic acid reactor 74, a quench absorber 75, a distillation apparatus 76 and a purification apparatus 77, the purification apparatus 77 containing a crystallisation region 61 and a separating region 62. The crystallisation region 61 and the separating region 62 are close together, the crystallisation region 61 and the separating region 62 preferably being connected to one another directly, not by pipes. Preferably, crystal growth also takes place in a single housing during washing of the crystals, in particular separation of the crystals from the mother liquor. The crystallisation region 61 and the separating region 62 are connected to one another by a first guide 66, which may be formed by the common housing. The separating region 62 is connected via a second guide 74 to the melter 63 which melts the (meth)acrylic acid crystals separated from the mother liquor in the separation region. The molten (meth)acrylic acid is conveyed by a pump 79 either via a fourth guide 67 to the separating region 62 or via a third guide 65 to the crystallisation region 61. Advantageously, a separate purification apparatus 68 has the function of increasing the purity of the (meth)acrylic acid. To promote crystallisation in the crystallisation region 61, (meth)acrylic acid crystals are supplied separately as seed crystals to the crystallisation region 61 by means of a first return 69 in the separating region 62. The yield is increased in that the (meth)acrylic acid remaining in the mother liquor after incomplete separation in
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG the separating region 62 is recovered by supplying the mother liquor from the separating region 62 via a second return 70 to the crystallisation regicn £1. The purified (meth)acrylic acid is removed from the circuit by means of a product out- let 81. Residual mother liquor which cannot be utilised is removed by means of a residual mother liquor outlet 80.
Fig. 5 shows a purification apparatus 77 with two apparatus units 60, 78. The pu- rification apparatus 77 comprises two process stages. In order to increase the achievable purity of the (meth)acrylic acid and the yield, the two apparatus units 60 are connected to one another by connecting lines 71, 72, 73.
With respect to the mother liquor, which is supplied from the first apparatus unit 60 via a connecting line 73 to the second apparatus unit 78, the two apparatus units 60 and 78 are connected in series.
To increase the purity of the {meth)acrylic acid which 1s obtained from the second process stage with the second apparatus unit 78, which purity may be lower owing to the lower (meth)acrylic acid concentration in the mother liquor supplied to the second apparatus unit 78, the (meth)acrylic acid obtained in the second process stage is supplied to the crystallisation region 61 of the first apparatus unit 60 via a connecting line 72, for further purification. Improved purity of the (meth)acrylic acid obtained is ensured by this subsequent purification.
With respect to transport of the mother liquor, the second apparatus unit 78 fol- lows the first apparatus unit 60. With respect to transport of the (meth)acrylic acid, the first apparatus unit 60 follows the second apparatus unit 78. The two process apparatus units 78 and 60 therefore nest with one another.
Y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZHR
Degussa AG
Fig. 6 shows a crystal habit of pure acrylic acid at an equilibrium temperature of 12.7°C and a crystallisation temperature of 11.25°C with a crystallisation time of 2h.
Fig. 7 shows a crystal habit of acrylic acid according to the invention from a 90/10 w/w mixture of acrylic acid and water with an equilibrium temperature of 4.5°C, with a starting temperature of 3.1°C and a cooling rate of 1 K/h with a crystallisa- tion time after 1.5 h. As the comparison of Fig. 6 and 7 shows, the crystals accord- ing to the invention have a small number of inclusions but that the habit changes in such a way that recesses from which mother liquor can advantageously flow appear on the respective upper side of the crystals. it can be seen that not all crys- tals are affected by this phenomenon.
Fig. 8 shows a crystal habit of acrylic acid according to the invention consisting of a 80/20 w/w mixture of acrylic acid and water with an equilibrium temperature of -2°C and a starting temperature of -3.5°C with a cooling rate of 1 K/h and a crys- tallisation time of 1.5 h. It can be seen that all crystals are affected and the size of the indentations increases.
Fig. 9 shows a crystal habit of acrylic acid according to the invention consisting of a 70/30 w/w mixture of acrylic acid and water with an equilibrium temperature of -7.5°C and a starting temperature of -8.7°C with a cooling rate of 1 K/h and a crystallisation time of 1.5 h. Fig. 5. It can be seen that general crystal de- fects increase, the actual habit still being clearly discernible. Some of the recesses are so great that the crystals are internally hollow. The discharge of mother liquor is ensured and the washing out of further impurities is permitted also in this case.
The invention will now be described in more detail with reference to non-limiting examples.
JY
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ'HR
Degussa AG
Example I
Crystallisation of acrylic acid which is depleted in water
In an apparatus corresponding to Fig. 1 with a scraper crystalliser for suspension creation and a mechanical wash column with a piston arranged at the bottom and an outlet for the purified melt arranged at the top, acrylic acid having the follow- ing composition (Table 1) was introduced into the scraper cooler.
Table l
Conn [om
Furfural % 0.033
Benzaldehyde 0.038
Propionic acid % 0.018
Acrylic acid % 85.140
Hydroquinone 0.028
Maleic acid anhydride 0.276
CR I RE
Acrylic acid of the composition shown in Table 1 was used as the feedstock (composition which is depleted in water).
Ny
Stockhausen GmbH 8061 2PC HZ HR
Degussa AG
The scraper cocler was cocled, whereby 2 crystal layer was formed in the scraper cooler at approximately -5°C and shaved off by the rotary shavers in thc scraper cooler to form a suspension. The filtered mother liquor was invariable sluiced 5s completely from the process. After about 12 hours’ operation, the liquid phase in the crystalliser (= filtrate from the wash column) had the composition according to
Table 2.
Table 2
ER EE NL
Coie || ew
The crystal suspension removed from the crystalliser was packed in the wash col- umn to form a compact crystal bed. On the upper side of the crystal bed, the crys- tal bed was shaved off using a rotary shaver, pumped in the product circuit as a oy
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR crystal suspension and melted by the heat exchanger. A portion was recycled into the crystal bed for countercurrent washing, ir order to keep the washing font con- stant so that neither product nor mothcr liquor strikes through the crystal bed. The _ remainder was obtained continuously as the product. The mean values from prod- : 5S uct analysis of the acrylic acid which was obtained about 1 to 3 hours later as the sample from Table 2, in other words about 12 to 15 hours after the beginning of the experiment are shown in Table 3 as examples of the product qualities achieved.
Table3
Swe [eee
Ee EC
EC RN
As shown in Table 3, the process according to the invention allows the production of high-purity acrylic acid.
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Degussa AG
The concentrations were determined per GC and the colour index by the DIN-ISO 6271 method. Water was determined to ASTM D 1364 and the inhibitors (MEHQ) to ASTM D 3125.
y
PCT/EP03/02753 25. August 2004
Stockhausen GmbH D80612PC HZ/HR
Example II
Crystallisation of aqueous acrylic acid 760 g of a sample from a quench absorber sump of an acrylic acid apparatus hav- ing a composition according to Table 4 were introduced into a stirred double shell vessel and cooled by a cryostat.
Table 4 _
Total minor constituents | constituents 1 % CC % IEEE T4714
The sample introduced was cooled to 11°C and then cooled further at a cooling rate of 0.1 k/min. It was inoculated with 1 mg of ice and 1 mg of crystalline acrylic acid at -15°C. The solution then became cloudy. After a further 10 min- utes, the suspension was separated into solid and liquid on a vacuum filter con-
\
PCT/EP03/02753 25. August 2004
Stocknausen GmbH D80612PC HZ/HR trolled to a temperature of 0°C with a 250 um propyltex filter cloth. The resultant mother liquor (filtrate, 380 g) has the composition shown in Table 5. This mother liquor is more heavily depleted in acrylic acid than in water.
TableS
Nw [wee]
Two different crystal habits (one clear white and one milky) with different melt- ing temperatures and melting behaviour were observed on the vacuum filter. The crystals, having residual moisture of 214 g, on the vacuum filter have the compo- sition shown in Table 6.
PCT/EP03/02753 25. August 2004
Stockbavsen GmbH D80612PC HZHR
Table 6
Name Crystals prior te
The filter-moist crystals according to Table 6 were washed with a quantity of 200 gof VE water controlled to a temperature of 0°C. The resultant filter cake has the composition shown in Table 7.
S| PCT/EP03/02753 25 August 2004
Stockhausen GmbH D80612PC HZ/HR
Table 7
Name | | Crystals prior to washing (filter moist)
The quantities specified in the foregoing were determined by gas chromatography.
In this example, a significant depletion of the by-products accompanying the aqueous acrylic acid were achieved from synthesis of the acrylic acid, as demon- strated by comparison of the total minor constituents.
Units which are used in this specification and which are not in accordance with the metric system may be converted to the metric system with the aid of the following conversion factors. 1 Angstrom =1 x 10m 1bar=1x 10° Pa -50/57 -
Amended sheet: 2 February 2006
Claims (1)
- A PCT/EP03/02753 25. August 2004 Stockhausen GmbH D80612PC HZ/HR Degussa AG Amended Claims from 4 March 2004 L Process for purifying a composition comprising (meth)acrylic acid, at least one impurity and water, wherein the composition has a water content in the range of 0.55 to 90, based on the composition, to form a purified phase comprising (meth)acrylic acid and at least one impurity, wherein, in the purified phase, the quantity of at least one impurity is less than 7% by weight, based on (meth)acrylic acid in the purified phase, comprising a stage of the process which includes the following process steps: a) (meth)acrylic acid is crystallised from the composition while form- ing a suspension comprising a mother liquor and (meth)acrylic acid crystals; b) (meth)acrylic acid crystals are separated from the mother liquor; c) at least a portion of the separated (meth)acrylic acid crystals is20 . melted to form a melt; and d) a portion of the melt is recycled to step a) or step b) and wherein the portion of melt which is not recycled is in the form of a sepa- rated (meth)acrylic acid.2. Process according to claim 1, wherein, in step a), (meth)acrylic acid crys- tallises at least in part to form a crystal with a crystal structure having a surface with at least one recess located on the surface, the crystal structure - 1/6 - AMENDED SHEETA WO 03/078378 PCT/EP03/02753 having an orthorhombic Bravais crystal lattice with an Ibam space group, crystallographic data a = 9.932 A (0.9952 nm), b = 11.767 A (1.1767 nm) and c =6.206 A (0.6206 nm).3. Process according to either of claims 1 or 2, wherein, in step a), the mother liquor comprises at least 60% by weight of (meth)acrylic acid and water, wherein the water concentration of the mother liquor is in the range of 10 and 90% by weight.4. Process according to any of the preceding claims, wherein the (meth)acrylic acid crystals are washed in the countercurrent of the recycled melt.5. Process according to any of the preceding claims, wherein the melt is purified in a separate purification process.6. Process according to any of the preceding claims, wherein the (meth)acrylic acid crystals from step b) are supplied at least in part to step a).7. Process according to any of the preceding claims, wherein the mother liquor separated in step b) is recycled at least in part to step a).8. Process according to any of the preceding claims, wherein the process comprises at least two stages, which each comprise steps a) to d), wherein at least one of the following features (al) to (a4) is fulfilled: (al) separated (meth)acrylic acid from a first stage of the process is supplied at least in part to a second stage of the process; - 2/6 - Amended sheet: 2 February 2806 v WO 03/078378 PCT/EP03/02753 (a2) separated (meth)acrylic acid from a second stage of the process is supplied at least in part 10 a first stage of the process; (a3) mother liquor from a first stage of the process is supplied at least in part to a second stage of the process; (ad) mother liquor from a second stage of the process is supplied at least in part to a first stage of the process.9. Apparatus for producing (meth)acrylic acid comprising, as components which are connected to one another in a fluid-conveying manner, a (meth)acrylic acid synthesis unit comprising a (meth)acrylic acid reactor and a quench absorber, and a purification apparatus which comprises an apparatus unit comprising features (31) to (84): (81) the apparatus unit comprises a crystallisation region, a separating region, a melter and at least three guides; (82) the crystallisation region is connected to the separating region by a first guide; (83) the separating region is connected to the melter by a second guide; (04) the melter is connected to the crystallisation region by a third guide or to the separating region by a fourth guide; wherein the purification apparatus comprises an inlet which guides a composition comprising (meth)acrylic acid, at least one impurity and water, the composition having a water content in the range of 0.55 to 90% by weight based on the composition. - 3/6 - Amended sheet: 2 February 2006< WO 03/078378 PCT/EP03/0275310. Apparatus according to claim 9, wherein the (meth)acrylic acid synthesis unit and the purification apparatus are connected to one another without a distillation apparatus.11. Apparatus according to either of claims 9 or 10, wherein the apparatus unit comprises a separate purification apparatus.12. Apparatus according to any of claims 9 to 11, wherein the separating region is connected to the crystallisation region by a first return for separated (meth)acrylic acid.13. Apparatus according to any of claims 9 to 12, wherein the separating region is connected to the crystallisation region by a second return for separated mother liquor.14. Apparatus according to any of claims 9 to 13, characterised by at least two apparatus units according to features (81) to (84), which are connected by at least one connecting line, the connecting line being a feed line or a return line and at least one of the following features (el) to (4) being fulfilled: (el) the separating region of a first apparatus unit is connected via the connecting line to the crystallisation region of a second apparatus unit; - 4/6 - Amended sheet: 2 February 2006PCT/EP03/02753 25. August 2004 Stockhausen GmbH D80612PC HZ'HR Degussa AG (2) the melter of a first apparatus unit is connected via the connecting line to the crystallisation region of a second apparatus unit: (e3) the separating region of a second apparatus unit is connected via the connecting line to the crystallisation region of a first apparatus unit; (4) the melter of a second apparatus unit is connected via the connect- ing line to the crystallisation region of a first apparatus unit.15. Apparatus for polymerising (meth)acrylic acid, comprising an apparatus for producing (meth)acrylic acid according tc any of claims 9 to 14 and a polymerisation unit, wherein the purification apparatus of the apparatus for producing (meth)acrylic acid is connected to the polymerisation unit.16. Process according to any one of claims 1 to 8, wherein the process is car- : ried out in an apparatus according to any one of claims 10 to 14.17. (Meth)acrylic acid obtainable by a process according to any of claims 1 to 8 or 16.18. Process for producing a polymer based on (meth)acrylic acid, wherein a (meth)acrylic acid according to claim 17 is polymerised.19. Polymer, obtainable by a process according to claim 18.20. Fibres, shaped articles, films, foams, superabsorbent polymers, special polymers for the areas of waste water treatment, dispersion dyes, cosmet- ics, textiles, leather treatment or paper production or hygiene articles, at AMENDED SHEETA PCT/EP03,02753 25. August 2004 Stockhausen GrabH D80612PC HZ/HR Degussa AG least based on or comprising (meth)acrylic acid according to claim 17 or a polymer according to claim 19.21. Use of the (meth)acrylic acid according to claim 17 or a polymer accord- ing to claim 19 in or for the production of fibres, shaped articles, films, foams, superabsorbent polymers or hygiene articles, detergents or special polymers for the areas of waste water treatment, dispersion dyes, cosmet- ics, textiles, leather treatment or paper production. AMENDED SHEE
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10211685A DE10211685A1 (en) | 2002-03-15 | 2002-03-15 | Arm rest for mounting on inside of vehicle door comprises frame which has transverse slots separated by strips of material, slots being wider than strips |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| ZA200407487B true ZA200407487B (en) | 2006-06-28 |
Family
ID=27815699
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| ZA200407487A ZA200407487B (en) | 2002-03-15 | 2004-09-17 | (Meth)acryclic acid crystal and method for the production and purification of aqueous (meth)acrylic acid |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE10211685A1 (en) |
| ZA (1) | ZA200407487B (en) |
-
2002
- 2002-03-15 DE DE10211685A patent/DE10211685A1/en not_active Withdrawn
-
2004
- 2004-09-17 ZA ZA200407487A patent/ZA200407487B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE10211685A1 (en) | 2003-10-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US7557245B2 (en) | (Meth)acrylic acid crystal and process for producing aqueous (meth)acrylic acid | |
| US7964689B2 (en) | Superabsorbent polymer made from acrylic acid | |
| RU2213725C2 (en) | Purified terephthalic acid production process | |
| US7557246B2 (en) | Method for the purification of (meth)acrylic acid | |
| US8362299B2 (en) | Method for producing and purifying aqueous phases | |
| CA3004802C (en) | Method of reprocessing alkanesulfonic acid | |
| CS216849B2 (en) | Method of making the tereftalon acid from dimethyltereftalate | |
| EP3218359B1 (en) | Preparation of dialkyl esters of 2,5-furandicarboxylic acid | |
| US6051736A (en) | Preparation of (meth)acrylic acid | |
| WO2004022518A1 (en) | Process for producing (meth)acrylic acid compound | |
| KR100580419B1 (en) | Improved Process for Producing Pure Carboxylic Acids | |
| US9458080B2 (en) | Process for obtaining acrylic acid | |
| US8476463B2 (en) | Process for separating off fumaric acid and other minor components during the production of maleic anhydride | |
| ZA200407487B (en) | (Meth)acryclic acid crystal and method for the production and purification of aqueous (meth)acrylic acid | |
| EP1104396B1 (en) | Method for recovering methyl acetate and residual acetic acid in the production of pure terephthalic acid | |
| TWI535696B (en) | Process for preparation of methacrylic acid and methacrylic acid ester | |
| ES2559821T3 (en) | Improved filtration rate of terephthalic acid purge by controlling the% water in the filter feed suspension | |
| FR2494684A1 (en) | Terephthalic acid prepn. from di:methyl terephthalate - by hydrolysis with hot steam and recovery by crystallisation from reaction mixt. | |
| EP2374786A1 (en) | Purification of monochloroacetic acid rich streams | |
| CA2421277C (en) | Coupled production of two esters | |
| JP3981550B2 (en) | Method for producing acrylic ester | |
| JP3890641B2 (en) | Production method of high purity benzyl alcohol | |
| JPH0717901A (en) | Production of high-purity isophthalic acid | |
| WO2009033381A1 (en) | A process of removing heavier hydrocarbons from the reaction products of producing sec-butyl acetate | |
| KR20090082897A (en) | Method of separating the acrylic acid from benzoic acid contained in a product gas mixture from a heterogeneously catalyzed gas phase partial oxidation of c3-precursor compound of acrylic acid |