DE2642241A1 - Recovering halogen from soln. - by adsorption onto hydrophobic nonionic polymer with exclusion of light - Google Patents

Abstract

Halogen-contg. plastics materials are made by contacting hydrophobic polymers contg. no ionic or ionisable gps. and which are free from ion exchange activity, with a soln. of a halogen with the exclusion of light. Suitable polymers include polyolefins (polyethylene, polypropylene, polyisobutylene etc.), polystyrene, polyacrylonitrile, polyacrylates, polymethacrylates, PVC, PTFE and other polyesters, polyamides, polyacetals, etc., in the form of powders, granules, foams, fibres, films, fabrics, gels, etc. Plastics scrap is an esp. economical material. The plastic is pref. contacted with a soln. of the halogen, esp. at a pH of 0-3. Lower pH's give gaster rates of halogen extn. The halogen is adsorbed reversibly from the soln. to give a stable material which can be transported and used later as a halogen source. Process can be used e.g. for recovering Br2 from salt solns. such as sea water, e.g. after oxidn. of bromide present in the soln. to Br2 e.g. using Cl2 gas.

Description

description

to the patent application relating to "Process for the production of halogen-containing Plastics and their use "The invention relates to halogen-containing compounds, which are suitable for the recovery of halogens or halides after a previous one Suitable for oxidation from solutions.

In addition, they are suitable for safe storage and transport of halogens and as a halogen source for a wide variety of halogenation reactions.

The masses according to the invention are plastics, containing halogen. How this bonding of the halogen to or in the polymer takes place, is not yet fully understood. It is therefore referred to in the following as a "sorption" of the halogen spoken on the plastic, although this term is nothing about the Binding mechanism. The bond between halogen and plastic is reversible, so that the halogen can be recovered from the plastic material can.

According to the invention, it is possible to obtain the bromine from aqueous solutions or of bromides from salt solutions, such as seawater. It is known to be bromides to oxidize to bromine in aqueous solution in order to then be able to obtain bromine, e.g.

with chlorine gas. Bromine is blown out of the solution with supply air or steam, so that it can e.g. win condensation in a cold trap.

There are various anion exchangers containing amino groups known to have a reversible bond of halogen in ionic (as polyhalide ion) or in complex form. Such anion exchange resins that can be used for recovery of halogen from solutions are highly specific substances whose large-scale Application is very expensive.

It was previously of the opinion that the ability of a plastic to bind a halogen, the presence of a functional halogen-binding group, such as an amino group, a quaternary ammonium group or an amido group. It has now surprisingly been found according to the invention that such functional Groups are not required and that halogen can be reversibly introduced into a variety of readily available plastics that do not have such groups contain. Furthermore it was found that you can use these plastics advantageously, inter alia, for easy and efficient recovery of halogen use from solutions even with comparatively low concentrations ka.nn.

According to the invention, a halogen-containing composition is now obtained by a solution of a halogen (chlorine, bromine, iodine, bromine chloride, iodine chloride, bromine iodide) with a plastic that reversibly sorbs the halogen verma.g. The plastic is essentially hydrophobic and does not contain any significant number of ionized or easily ionizable functional groups and thus does not work as an ion exchanger. He is in the absence of light against chemical attack inert to halogens and can easily be obtained from the solution.

The term "halogen" is used herein to denote molecular chlorine, bromine or Iodine or the heterogeneous halogen molecules or mixed halides bromine chloride, Understood iodine chloride or iodine bromide and their mixtures.

According to the invention, the most diverse synthetic plastics can be used as plastics Use polymers, preferably solid or semi-solid, such as in gel form. As mentioned, however, if the plastic is to be essentially hydrophobic, block polymers are used or graft polymers are used, it is sufficient if they are essentially hydrophobic Own blocks or chains. Examples are polyolefins (such as polyethylene, Polypropylene, polyisobutylene), substituted polyethylene (such as polystyrene, polyacrylonitrile, Polyacrylates, polymethacrylates, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene), Polyesters (such as polyethylene terephthalate), polyamides (such as nylon), polyimides, and polyacetals including copolymers and terpolymers as well as block polymers and graft polymers.

Are plastics used according to the invention, which under the action If you suffer a chemical attack by halogen from light, you can start the reaction Perform in the absence of light to avoid such an attack. A An example of this is polystyrene, whose aromatic core is a light-catalyzed one Halogen substitution reaction is accessible, e.g. a bromination with bromine.

According to the invention, the plastic with the above properties is brought together with a solution - aqueous or non-aqueous - containing halogen, the Polymer that picks up halogen from solution. Discolored with increasing halogen uptake the polymer. The initially colorless polymer turns yellowish-green when chlorine is absorbed and reddish-brown when bromine is absorbed. The speed and extent of the You can see the log uptake through the plastic by determining the change in color follow. The halogen uptake by the plastic is reversible, so that a.from this - as will be explained in more detail - the halogen is always light can recover.

The exact mechanism by which halogen enters the plastic and remains in it has not yet been fully elucidated, but shows the complete Reversibility of the process and the diversity of the plastics that can be used, that the mechanism is similar to a dissolution or a sorption of the halogen in or the plastic runs off. The process can be characterized by sight the distribution of the halogen between the solution phase and the plastic phase in this two-phase system. As with solvent extraction, the partition coefficient depends in the present Pall on the type of halogen, solvent and plastic away. Aqueous halogen solutions are preferred according to the invention, because they result in higher distribution coefficients and thus the speed and the amount of halogen introduced can be increased. Halogen solutions in organic Solvent can also be used if the extraction rate is slower be compensated by longer contact times and / or countercurrent technology.

It was found that the rate of halogen extraction from the aqueous solutions to the plastics increases as the pH value of the halogen solution falls, which is achieved by adding an inorganic acid such as halogenic acid. The preferred pH is between 0 and 4, in particular between 0 and 3.

The physical form of the plastic is not of great importance for the method according to the invention. It can be in the form of granules, powder, in Porm of pellets, foamed particles, fibers, sheets and films or fabrics are present. However, the plastic particles should have such a shape and size that that the halogen solution as large a surface as possible is presented to the halogen uptake to accelerate through the plastic. An important advantage lies in the fact that recycled according to the invention, the most diverse types of plastic waste can be.

You do not need any to carry out the process according to the invention special facilities or conditions. The contact of the plastic with the halogen solution can be done in any way, so in countercurrent or cocurrent, as in usual Ion exchange systems under normal conditions.

So you can get the halogen solution through one packed with plastic beads Column guide, with the flow rate for optimal speed and amount of halogen uptake set by the plastic shall be. But you can also in a continuous manner in a Make a system with several columns.

The recovery of the halogen from the plastic containing halo happens, for example, by displacement with a gas flow, such as air, whose flow velocity, Pressure and temperature with regard to the desired rate of halogen release is set. The halogen-containing gas is then condensed in the usual way, absorbed or dissolved. ifiri a high halogen concentration in the gas stream obtained aimed at, the flushing gas and / or the halogen-containing plastic will be used Heat the container containing it. Halogen can also be obtained from the gas stream as a halide by chemical reduction, e.g.

with sis scrap or ammonia.

Another way to recover the halogen from the Plastic is the application of negative pressure, which releases the halogen can be caught in a condenser.

But you can also mix the halogen-laden plastic with an organic one Wash solvent to achieve a halogen solution.

The halogen-laden plastic can be used directly as a halogen source use for various chemical reactions. To do this, he will talk to the reaction partner brought into contact for the halogen, optionally the reactant is dissolved. For example, a plastic loaded with bromine will give ammonium bromide with ammonia respectively.

with a liquid monoolefin da.s corresponding dibromo addition product. However, if the halogen is displaced from the plastic with a purge gas, then ka.nn one then the halogen-containing gas stream directly from a chemical reaction feed, e.g. as a reaction partner for the production of lead tetrabromide.

Finally, those obtained according to the invention are loaded with halogen Plastics very simple and safe means of storing and transporting halogen, without the otherwise associated problems and dangers due to toxicity and Corrosiveness of the halogens. The halogen remains in a closed container in the plastic for a long time and can be released if necessary.

Once all of the halogen has been recovered from the plastic, so can one this again for the extraction of the halogen from a solution or the like without having a reduced sorption capacity for extracted halogen observed. In some cases the extraction capacity even increases after an or several cycles of extraction and recovery of the halogen.

The selective and reversible introduction of halogens into plastics can also be carried out in cyclic processes in which the first stage is halogen extraction from an aqueous solution into the plastic and the second stage the release of the halogen from the plastic or direct recycling. The so released Halogens are completely pure because the plastics used are essentially solid and are hydrophobic and therefore no water or ionic substances from the solution able to absorb. This is particularly useful when producing halogens or their extraction from natural salt solutions or industrial wastewater. One Particularly important application is the recovery of bromine from aqueous solutions or bromide solutions.

The invention is further illustrated by the following examples.

Example 1 62 cm3 of an aqueous solution of 23 mmol / l Br2 (3.24 g / l) were made into 1 g of polystyrene foam beads approximately 5 mm in diameter given to a sealed glass tube at room temperature. The pH of the bromine solution was around 3.5. After 2 hours the aqueous solution was removed from the glass tube. This solution now only contained 9.4 mmol / l Br (1.5 g / l). The originally colorless Polystyrene beads were now colored brown like bromine.

An air stream was passed through the tube with the loaded polystyrene spheres of 70 C. The bromine-containing gas mixture that escaped was placed in a cold trap from -180C (cold mixture). This was continued 1 until the foam styrene beads were completely discolored. Most of the bromine from the original aqueous The solution was now found in the Kühlfais.

Example 2 The measures of Example 1 were repeated, each.

but in this case a saline solution containing 10 g / l KOl, 10 g / l NaCl, 100 g / l Ca.Cl2, 350 g / l MgCl2 and 1.4 g / l Br2. The remaining saline solution contained only 0.544 after the treatment according to the invention with polystyrene beads g / l Br2.

Example 3 720 cm3 of an aqueous bromine solution containing 5 mmol / l (0.8 g / l) Br2 at a pH of 3.5 became 40 g of polyethylene terephthalate fibers - 4 den - put in a closed glass tube and the whole thing for 24 hours at room temperature ditched. The solution was then drawn off; it now only contains 1.2 mmol / l Br2 (0.0192 g / L).

Similar results are obtained with analogous chlorine solutions.

Example 4 10 1 of a saline solution containing 10 g / l KCl, 10 g / l NaCl, 100 g / l Carl2, 350 g / l MgCl2 and 10 g / l Br2 of pH 3 were repeated through a vertika.le closed glass column containing 1 kg of polystyrene foam beads with a diameter of about 5 mm and a density of 0.16 g / cm31. To a calculated contact time of 1 h, the concentration of the effluent was 0.1 g / l Br2. Thus 99 g of bromine had entered the plastic from the solution.

The solution was then drained off the column and transferred to the column Vacuum applied, the released bromine vapor was collected in a cold trap and gave 95 even2.

Example 5 The procedures of Example 3 were repeated, namely with the following plastics as fibers or films with bromine or. Chlorine solutions: polyethylene, Polypropylene, polyisobutylene, polyvinyl acetal, polymethyl styrene, polyvinyl chloride, Polyvinylidene chloride, polytetrafluoroethylene, polycaprolcatam and polyhexamethylene acipamide.

In all of these attempts one could get an excellent extraction the halogens from their solutions and a release of the halogens from the plastic determine with the help of preheated air.

Example 6 Polypropylene Shrimp 855 den 1 were saturated with one Combined chlorine solution with pH O in the dark, the solution was drawn off after 6 h and let the fiber material run off. The originally colorless fibers were turned yellow-green. The chlorine could now get out of the fibers with preheated supply air be driven out.

Example 7 According to Example 1, bromine was made into polystyrene foam beads introduced, this then drained from the solution and into the column Hexen-1 brought in. The solvent remained with the bromine-laden plastic 1 h in contact, after which the solution was drawn off and fractionally distilled into a low-boiling praction made from unreacted hexene-1 and a higher-boiling one Residue of 1,2-dibromohexane nD20 1.5060.

Example 8 A sample of a knitted fabric made from polypropylene and Polyester fibers dipped in a carbon tetrachloride solution containing 10 g / l Br2l for 2 h. Then the solution was stripped from the fabric, which was brown had become. He could dry in a glass tube in a stream of warm air.

The gas mixture flowing off was passed into a cold trap at −1 ° C. The amount of bromine collected showed that much less was in the plastic fabric Bromine penetrated as from an aqueous bromine solution.

Example 9 Polypropylene fibers were placed in a 0.1N iodine solution 2 g / l potassium iodide, immersed and the iodine uptake determined. The attempt was made repeated with polyethylene terephthalate yarn material.

If the iodine solution containing potassium iodide is replaced by an ethanol one Iodine solution, so iodine is only slowly absorbed into the two plastics instead of.

- patent claims -

Claims (6)

R a t e n t a n s p r ü c h e 1. Process for the production of halogenated Plastics, noting that one is essentially one hydrophobic, practically no ionic or easily ionizable functional groups containing plastic that does not act as an ion exchanger with the exclusion of light treated with a halogen solution. 2. The method according to claim 1, characterized in that g e k e n n -z ei c h n e t that an aqueous halogen solution is used. 3. The method according to claim 1 or 2, characterized in that g e -k e n n z e i c It should be noted that a solution with a pH value below about 4, preferably about. used between 0 and 3. 4. The method according to claim 1 to 3, characterized in that g e -k e n n z e i c h n e t that one treats polystyrene, polyolefin or polyester. 5. Use of the halogen-containing plastics according to claim 1 to 4 for the production of pure halogens from their solutions. 6. Use according to claim 5 for obtaining the halogen content of aqueous Solutions.