DE2436153A1 - PLASTIC FILLING BODY FOR SUBSTANCE TRANSFER DEVICES - Google Patents

Description

Plastic filler for material transfer devices

The specific interface and its dependence on the sprinkling or throughput speed is of particular importance in determining and determining the effectiveness of the phase contact in absorption columns, Extractors, distillation plants and similar devices. Usually, effective contact will prevail by using fillers of suitable shape, e.g. oriented spirals, expanded metals, plates etc. achieved.

An optimal filling material is cheap, has a low specific weight, is easy to process to the optimal shape, mechanically strong, thermally and chemically stable and easily wettable, especially in the presence of the heaviest existing liquid phase. It is difficult to meet all of these requirements at the same time.

(S 8277) -SdSF-Bk

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The most widespread fillers are made of ceramic material, because they are easily wettable by water, which is often an essential component of one of the phases, and because it is exposed to high temperatures and chemicals are extraordinarily stable. Serious disadvantages are the high specific weight, which is why the interior an exchanger must be provided with relief plates, in their fragility, because broken filler bodies the columns can become clogged and therefore regular cleaning is required, and in their view high price due to the service life, which is due, among other things, to the complex shaping steps.

Because of their high mechanical and thermal resistance and their good machinability, metals are also used, but in addition to the high price are even heavier than ceramic fillers and are often at risk of corrosion. Lately plastics are also becoming Often used for packing because they have a low specific weight and high impact resistance (they are difficult to break) and are easy to work with. The applicability of plastic fillers however, is limited by their behavior towards the processed liquids: Either they are towards resistant to the liquid phase, but are not wetted by this and consequently have a low specificity Interface, or they are easily wettable, but swell up due to the liquid and lose their mechanical, thermal and chemical resistance. Hydrophobic polymers such as polyethylene, polypropylene, Polystyrene, polyvinyl chloride or polyacrylonitrile are resistant to water or aqueous solutions, are not wetted by these, so that

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Fillers made from these substances have much smaller active interface areas than geometrically similar ones Have ceramic fillers. In contrast, hydrophilic polymers such. B. polyhydroxyethyl methacrylate, partially hydrolyzed polyacrylonitrile, polyvinyl alcohol, Polyvinylpyrrolidone, sulfonated polystyrene or the like. very easily wettable, but they also swell with water in a strongly networked state. Some water-wettable polymers, because of their crystallinity in water only lower sources, such as B. polyamides, polyesters or polyurethanes show up easily in contact with water Signs of degradation, especially at higher temperatures and in the presence of electrolytes.

Similar disadvantages occur when processing non-polar liquids, for example aliphatic liquids Hydrocarbons or their halogenated derivatives, being hydrophilic polymers resistant, but not wettable, hydrophobic polymers are wettable but not resistant.

In some cases, for example during extraction or rectification, the filler material comes both in contact with polar as well as non-polar liquids and is attacked by one phase, and only slightly wetted by the other. For example, an aqueous solution of crude 2-hydroxyethyl methacrylate (with a small amount of dimethacrylate to be removed) with an aliphatic hydrocarbon in one Columns with polypropylene packing are extracted, the latter are made by the lighter one instead of the heavier one Phase wets, which has a very disadvantageous effect.

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This can hardly be prevented when using a single material, because of the two phenomena - wetting and swelling - are of the same physical nature.

It has been found that the above-mentioned disadvantages can be avoided if the plastic filler material consists of an organic polymer which is neither swellable nor wettable by the heaviest liquid phase present, and if this filler material has a surface layer made of a liquid phase wettable, but not soluble therein polymer is coated. The term "swellable polymer" means a polymer that in equilibrium more than 5 wt -% contains liquid, the contact angle between 0 and 25 ° lies. the term "non-swellable polymer" means that the related properties are outside these limits. The term "surface layer" here means the outer part of the filling body which is in contact with the liquid to be processed and is not more than 0.5 mm thick. If this surface layer is thicker, the two layers do not show adequate adhesion due to their different swelling capacities.

The combination of two such materials results in a density, strength and thermal resistance and formability optimal packing materialj, in which the desired wettability - and to a certain extent also the chemical resistance through the surface layer is reached.

The swellable surface layer protects the filler material against physical and chemical penetration the processed liquids as one

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one of them is incapable of swelling, the other being separated by the swollen surface layer. Through this a material can be chosen regardless of its chemical resistance, while the On the other hand, the surface layer does not have to have a greater mechanical strength. Is the latter mechanical or chemically attacked, it can usually be easily renewed.

Another essential advantage of the filler material according to the invention is its compared to ceramic fillers significantly increased effectiveness. As indicated in the examples, the effective interface is in one Column with plastic packing with a hydrophilic surface layer larger than in the same column with comparable ceramic packings, especially in higher sprinkling speeds or throughputs. This is surprising in that ceramics are common is considered a more or less optimal material from this point of view.

The surface layer must be swellable by at least one of the liquid phases present without, however, dissolving in one phase. For this reason it is sometimes necessary to create chemical bonds between the polymer chains (e.g. -CO-O-CH ₂ -, -CH ₂ -O-CO-, -0-CH ₂ -O-, -NH-CO- Of course, there are also various polymers that are swellable but insoluble even in the uncrosslinked state, for example poly-2-hydroxyethyl methacrylate in water, partially hydrolyzed polyacrylonitrile in water and aqueous solutions, as well as numerous copolymers (especially block or graft copolymers that are both hydrophilic and

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also contain hydrophobic groups.

"If the heaviest liquid phase present is polar, such as water or an aqueous solution, an alcohol or the like. the inner part of the filling material can for example made of polyethylene, polypropylene, polystyrene, polyisobutylene, polyvinyl chloride, polyamide, polyester, cellulose acetate, an epoxy resin, a phenol-formaldehyde, urea-formaldehyde or melamine-formaldehyde resin, made of polycarbonate, polyurethane, high molecular weight formaldehyde, polyalkyl acrylate or polyalkyl methacrylate, a coumarone resin, made of polydivinylbenzene, polyvinyl acetate, poly-glycol-bis-methacrylate, polyacrylonitrile and consist of various copolymers of these and other hydrophobic monomers.

The hydrophilic surface layer can be made of polyglycolraonomethacrylate, partially hydrolyzed polyacrylonitrile, polyvinylpyrrolidone, copolymers of acrylic acid, Methacrylic acid, maleic acid, itaconic acid, vinylsulfonic acid or their salts as well as vinylpyridine, Glyceryl methacrylate, vinyl alcohol, sulfonated! Polystyrene, sulfonated or chlorosulfonated polyolefins, oxidized Polyethylene, polypropylene, polyvinyl chloride, polystyrene or the like. exist. In addition, the hydroxyl, a'ther- or the surface layer containing ester groups is additionally hydropholized by introducing -O SO, -groups (GB-PS 1,357,989 and CS-PS 154 36l).

When the heaviest liquid phase is non-polar, such as an aliphatic, aromatic or hydroaromatic one The fillers consist of hydrocarbons, an olefin, an ether or halogenated derivatives thereof usually from a polymer containing some of the above-mentioned polar groups or from polyamide, polyester,

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Polyacrylonitrile, polyvinyl chloride, polyformaldehyde or the like. The surface layer made of polyethylene, polypropylene, polybutadiene, polyisoprene, polyisobutylene, polychloroprene, polystyrene, polydivinylbenzene, polyalkyl acrylate or methacrylate C ₁ -C ₂ ^ or the like polysiloxane or the like. (and of course also from the corresponding copolymers), depending on the type of non-polar phase. If necessary, the surface layer can be crosslinked.

The combination of swellable and non-swellable materials also depends on the cohesion of both Layers off. The volume change caused by the swelling leads to shear stresses, so that the Boundary layer must be bridged by sufficiently strong chemical bonds. Such interlayer chemical bonds can be formed by chain transfer towards the polymer when the surface layer by polymerizing a hydrophilic monomer on the surface of the hydrophobic polymer or vice versa was formed, provided that the latter contains a sufficient amount of groups associated with one growing macro radical such as -Br, -CH-CHp, -CH = CHp, -CH = CH-CH. ,, -CH or the like. can react. It is very advantageous if the swellability gradually decreases from the outer layer towards the inside. This can e.g. B. by polymerizing the surface layer in the presence of a suitable swelling agent that prevents the diffusion of the Monomers in the polymer allows (see. US-PS J5 625 For the same reason, the surface layer as thin as possible, preferably less than 0.01 mm. One way of making such a fine one The layer is the radiation-initiated graft or the radicals formed on the hydrophobic surface initiated polymerization.

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Both polymers can therefore be bonded to one another after the polymerization if they are suitably reactive Groups such as B. -OH, -NHg- or -COOH on the have one side and epoxy, -COCl or isocyanate groups on the other side «

The surface layer can be very expediently formed by a suitable polymer-analogous reaction, for example by converting the hydrophobic groups into hydrophilic groups and vice versa, since the surface layer thus formed can be made extremely thin and anchored very firmly to the substrate. Examples of polar groups which allow a polymer-analogous reaction are, for example, the hydrolysis of polyacrylonitrile, polyalkyl acrylate or methacrylate, polyvinyl acetate, polyglycidyl methacrylate or cellulose derivatives; the sulfonation of polystyrene; the chlorosulfonation of polyolefins; the sulfation of polyglycol methacrylate or cellulose acetate; nitration with subsequent reduction to amino groups; the oxidation or ozonization of polyolefins, polyvinyl chloride or the like. The surface oxidation of polyethylene, polypropylene, polyvinyl chloride or polyacrylonitrile can with a mixture of sulfuric acid and K ₂ Cr ₂ Og, with KMnO ₂ ,, with peroxides, nitric acid, nitrogen oxides, chlorine oxides or the like. be performed. The oxidation can also be carried out by brief flame exposure, by an electric arc or by corona discharges or the like, advantageously in the presence of an oxidizing medium such as oxygen-containing vapors or gases.

On the other hand, many hydrophobic groups can be introduced into the polymer chain instead of hydrophilic groups are, for example, by a long aliphatic or polysiloxane chain-producing reaction.

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The methods described above for producing hydrophilic or hydrophobic surface layers are, as well as numerous others, known for themselves.

The terms "filler body" or "filler material" used here are to be understood in their broadest sense. It is not just Raschig rings and other loose packing of any shape, but also sheets of various shapes, oriented spirals, stretched or stretched plastics (analogous to stretched Metals), including any internal parts of an absorber or a rectifying or extracting apparatus, designed to achieve intimate contact between the processed fluid phases are. The plastic filling material can be reinforced, foamed or the like. be.

A completely wetted filling material also enables an increase in the efficiency of the Device by reducing the wall flow. The conditions for mass transfer are in the immediate vicinity of the wall inconvenient, and the liquid on the wall cannot easily be brought back to the filler material. According to the invention, the wall flow should therefore also be reduced when the wall passes through the heaviest existing one fluid phase is less wetted than the filler material, the wall can advantageously be hydrophobized if the heaviest phase is a polar liquid, or hydrophilized if it is a non-polar liquid is. The wall flow can be further reduced if a layer of different filler material is used is arranged along the wall with much lower wettability.

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Exemplary embodiments of the invention are described below:

■ Example 1

A column consisting of a polymethyl methacrylate cylinder with an internal diameter of 143 mm and a height of 715 mm was filled with Raschig rings made of ceramic (industrial porcelain) up to a height of 680 mm. The rings of 15x15x2 had a specific surface area of a = 330 m / xo? . An aqueous solution of sodium sulfite (0.5 kmol / m ² , pH = 8.5, with 10 "^ kmol.n" ⁵ CoSO ^ as catalyst) was through 64 openings evenly distributed over the entire cross section in the uppermost part of the column introduced. The solution left the column through a siphon that closed off in such a way that the gas phase could not escape. Pure oxygen saturated with water vapor was introduced into the column foot. The 'temperature of the beiden.eintretenden streams was 20 ⁰ C. The rate of absorption into the column at a constant rate of

_ii -ι ι
5 · 10 nrs of oxygen introduced was determined from the difference in the sulfite ion concentration in the solution at the inlet and outlet of the column. The method for calculating the interface area is described in the literature (Yoshida P., Miura Y .: Ind. Eng. Chem. Proc. Design 196j5, 2, 263; Sharma MM, Danckwerts P .: Brit. Chem. Engng, 1970 , JJ5, 522). The method for determining the kinetic data is described in: Linek V .: Chem. Eng. Sci., 1966, 21, 777; Linek V., Mayerhoferova J .: ibid, 1970, 2% j_ 787. The dependence of the rate constants on the pH value and the temperature of the solution can be found in: Reith T.:.Dissertation, Delft, 1968; de Waal KJΑ., Okezon JC: Chem. Engg. May be. 1966, 21 ^ _ $ 59; Linek V., Tvrdik J .: Biotech. Bioeng. 1971, H ₂ . 353. The values of the constants such as the diffusivity, the solubility of oxygen and the velocity

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constants were used at the mean logarithmic temperature of the solution in the column. The calculated values of the boundary layer areas at different irrigation speeds or throughputs and the ratio of these values to the specific filler surface area are compiled in Table 1.

Example 2

Polyethylene Raschig rings of 15x15x1 * 8 mm with a specific surface area of a = 355 m / nr Provide a hydrophilic layer in the following way:

The rings were 7 min at a temperature of C with a mixture of 95 parts by weight of HpSO ^, 0.8 parts by weight of Cr ₂ (SO ₂₁ U, 1.9 parts by weight of K ₂ Cr ₃ Og and 4 Parts by weight of water brought together. The resulting surface was about 0.1 mm thick (measured microscopically) and consisted of a polymer preferably containing -COOH groups. The layer was partially cross-linked with Cr ^ ions; its equilibrium swelling capacity with water was 52 wt -.% (determined from the weight increase due to swelling and the estimated volume in the swollen state) the related in the manner described in example 1 solution contact angle was less than about 5 °, while the contact angle of the original polyethylene about 8o ° was. The packing elements with and without a hydrophilic surface layer were placed in the column and their effective boundary layer area was measured in the same way as in Example 1. The results of both test series are summarized in Table 1.

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Example 3

Polyvinyl chloride Raschig rings of 15x15x1 * 5 mm with a specific surface area of a = 545 m / nr were coated with a water-swellable layer 0.4 mm thick made of a copolymer consisting of 2-hydroxyethyl methacrylate, methacrylic acid and ethylene glycol dimethacrylate. Consisting of 0.4 wt -.% Dimethacrylate, 3.6 wt .- ^ methacrylic acid and 96 wt -.% Consisting of 2-hydroxyethylmethacrylate monomer mixture was diluted with an equal volume of cyclohexanone and added 1% Dibenzdylperoxid. The Raschig rings were immersed in this solution for 10 minutes. After taking them out, they were ^{dried under a nitrogen protective atmosphere at 35 °} C. under reduced pressure for 4 h. The temperature was then ^{increased to 70 °} C. for 1 hour. The Raschig rings were then treated with a mixture of 10% of the above Monomerengemisehes, 10 wt -% soluble coated poly (2-hydroxyäthylenmethacrylat), 0.1 wt .- ^ dibenzoyl peroxide and 79 * 9 wt .- ^ methanol.. After the excess solution ^{had been removed at 40 °} C. until the rings were no longer sticky, the rings were dried, after which the temperature was increased to 65 ^° C. After swelling in the solution of Example 1 and staining with methylene blue, the determined thickness was 0.4 mm; the contact angle was less than 5 °. The packings with and without a coating were introduced into the column and their effective interface was measured in the same way as in Example 1. The results are summarized in the table.

Example 4

Polypropylene Raschig rings of 15x15x12 with a specific surface area of 330 m ² / m were 6 hours long

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heated at 100 ⁰ C under a pure argon atmosphere, then ^{cooled to -70 0} C and irradiated with gamma rays. After irradiation, they were immersed for 1.5 hours at 30 ⁰ C in pyridine. A hydrophilic surface layer less than 0.01 mm thick formed which could be dyed with acidic dyes. The contact angle based on the solution of Example 1 was 16 °.

The polypropylene packings with and without hydrophilic surface layers were packed in the column and their effective interface area was measured in the same manner as in Example 1. The results of both series are shown in Table 1. The percentage dependence of the wetted parts of the geometric area on the sprinkling speed for the examples 1-4 is shown in FIG. Table 1 and FIG. 1 show that the geometric area of the packing elements used was more than 2.5 times higher than that of simple plastic packing elements when the packing elements were provided with the wettable surface layer. The effectiveness also increased in comparison to conventional ceramic fillers, in particular with a high sprinkling speed or high throughput. A comparison with filling materials which consist entirely of the same hydrophilic polymer as the surface layer could not be carried out because such filling materials were destroyed by swelling and the liquid throughput through the column was thereby prevented.

Example 5

Conventional polypropylene Raschig rings were used on the

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Wall of the column of embodiment 1 is arranged and the remaining inner space is filled with surface-coated rings according to example 4. The effective boundary area increased by a further 10 % compared to exemplary embodiment 4.

In Fig. 9 * is a surface with a wettable

chenbesehichtung 1 provided filler body made of a non-wettable plastic 2 shown; Fig. 3 *> shows a packed column with the column wall 3> non-wettable fillers 2a and a plastic filler pack provided with a wettable surface layer 4th

Example 6

A glass column filled with oriented spirals 5 made of polymethyl methacrylate was used to absorb COg from air in a 2 molar aqueous solution of monoethanolamine with 0.02 mol / l sodium arsenate. Thereafter, the column including the filler with a mixture of 90 percent was -.% Sulfuric acid and 10 wt -.% Glycerol at 90 ⁰ C 1 min filled, then with water and with aqueous sodium bicarbonate solution and 1 ^ strength then washed again with water. After this treatment, the oriented spirals (cf. FIG. 4, where the column wall 3 can also be seen) were coated in place with a highly swellable but insoluble surface layer. The absorption carried out with the packings treated in this way was about 50 % more effective than with the original polymethyl methacrylate spirals.

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Table 1

Packing (see example)

Specific surface Specific boundary layer area a [m / nr Y a

wetted part of the surface in $ —-2 .-- ■> »^ S. .100)

Sprinkling speed V, / S [10-2 nr / m °

cn ο co oo

O CR ■ »J

Ceramic

Filler rings (l)

15x15x2 mm

⁽²⁾

mm

335

dtto with surface layer (2)

Polyvinyl chloride rings (3) 15x15x1.5 mm

345

dtto, with surface layer (3)

Polypropylene rings (4) 15x15x2 mm

dtto, with surface layer (4) 0.52

1.56

3.12

6.24

12.48

74.5 ($ 23) 104 (32 %) 134 (4l $) 205 ($ 62) ■ 290 ($ 88)

32.7 (9.8 $) 42.2 (13 $) ⁵⁵ ' ^{8 (16} * ⁷ °' ^{3 (21} 0 ¹⁰⁵ (51 ^)

$ 73 ($ 22) $ 110 ($ 33) 142 ($ 42) 228 ($ 68) 302 ($ 35)

42.3 '($ 12) 6l, l ($ 18) 73 ($ 21) 84 ($ 24) 121 ($ 35)

$ 78.3 ($ 23) 123 ($ 36) 140 ($ 40) 240 ($ 70) 325 ($ 94)

$ 34.2 ( $ 10) $ 40.3 ($ 12) 54 ($ 16) 68.2 ($ 21 $ 102 ( $ 31)

$ 83.1 ( $ 25) 102 ( $ 31) 144 ( 44 %) 227 ($ 69) 315 ($ 96)

Claims (2)

Expectations 1. Plastic filler for devices for mass transfer in the form of Raschig rings, spirals or other shapes, column plates, partitions and intermediate floors Or the like. At least partially processed from one by the heaviest in the device liquid phase non-wettable organic polymer consists, characterized by a surface layer (l) of less than 0.5 mm Starch made from an organic polymer that is easily wettable by the heaviest liquid phase. 2. Device for mass transfer, e.g. B. for absorption through which the liquid to be processed flows is characterized in that in the immediate area of the flow walls (3) a layer (2a) made of non-wettable plastic filler material provided and the interior with a plastic filler pack (4) from a not wettable solid polymer is filled, which has a layer (l) of a wettable polymer on its surface having. 509810/0675 Leerse.ite