STORAGE MATERIAL AND METHOD FOR CHLORINE STORAGE

Abstract

The invention relates to a novel storage material on the basis of nanoporous silicon dioxide particles for the adsorption of chlorine, to the use of said storage material for chlorine recovery and for chlorine liquefaction for the purpose of storing, transport and cleaning.

Claims

1.-16. (canceled)

17. A porous storage material for the reversible storage of chlorine in liquid phase based on particles of silicon dioxide, in which the particles have pores with a pore diameter of <10 nm, with a maximum in the pore diameter distribution in the range of from 1 nm to 8 nm, and the silicon dioxide is present with a degree of condensation, determined by means of silicon-29 solid-state NMR spectroscopy, of at least 0.91.

18. The storage material as claimed in claim 17, wherein the particles have a particle diameter in the range of from 30 nm to 2 m.

19. The storage material as claimed in claim 17, wherein the particles have a mean particle diameter of from 200 nm to 1 m.

20. The storage material as claimed in claim 17, wherein the particles, measured at 0 C. and not more than 3 bar, preferably measured at 0 C. and not more than 2 bar, have a loading capacity of at least 0.4 g of chlorine/g of storage material.

21. The storage material as claimed in claim 17, wherein the time taken to load the storage material is <40 minutes (based on 1 g of chlorine per g of material) and the time taken for unloading is <60 minutes (based on 1 g of chlorine per g of material).

22. A storage body comprising a storage material as claimed in claim 17, wherein the particles are packed 3-dimensionally in the storage body.

23. The storage body as claimed in claim 22, wherein the storage body has additional pores with a pore diameter of at least 20 nm.

24. A storage system for the reversible storage of chlorine in liquid phase, at least comprising a feed pipe for a chlorine-containing gas, a discharge pipe for chlorine-containing gas, optionally a discharge pipe for residual gas separated from the chlorine, a thermally insulated pressure vessel which is filled with a storage material based on silicon dioxide for the adsorption of chlorine, wherein there is present as the storage material a storage material as claimed in claim 17.

25. A method for the reversible storage of chlorine in liquid phase, comprising at least the following method steps: feeding of a chlorine-containing process gas to a storage material which is maintained at a temperature of not more than 40 C. at a pressure of from 0.25 bar to 10 bar, then either desorption of the stored chlorine by the passage of inert gas through the storage material or desorption of the stored chlorine by either reducing the pressure across the storage material or by increasing the temperature of the storage material, wherein there is used as the storage material a storage material as claimed in claim 17.

26. The method as claimed in claim 25, wherein the method is carried out in a storage system as claimed in claim 24.

27. The use of the porous storage material as claimed in claim 17 or of a storage body as claimed in claim 22 for the adsorption of chlorine for the purpose of separating chlorine from chlorine-containing process gases.

28. The use as claimed in claim 27, wherein the process gas, in addition to chlorine, contains gases such as hydrogen, oxygen, nitrogen or inert gases such as argon and helium.

29. The use as claimed in claim 27, wherein the process gas is the residual gas, containing at least hydrogen, chlorine and oxygen, of a chlorine liquefaction.

30. The use as claimed in claim 27, wherein the process gas is the gas, containing at least hydrogen and chlorine, from the catholyte chamber of an HCl diaphragm electrolysis.

31. The use as claimed in claim 27, wherein the process gas is the waste gas, containing at least oxygen and chlorine, from a gas-phase oxidation process for the reaction of hydrogen chloride with oxygen.

32. The use of the porous storage material as claimed in claim 17 or of a storage body as claimed in claim 22 for the liquefaction of chlorine for the purification, storage or operationally safe transport of liquid chlorine.

Description

[0037] The invention is explained in greater detail below with reference to the examples and figures, which, however, are not intended to limit the invention.

[0038] In the Figures:

[0039] FIG. 1 shows the chlorine storage isotherms of silicon dioxide storage material A according to the invention at 26 C., 0 C. and 30 C. Storage material A consists of SiO.sub.2 with a mean pore diameter of between 1.4 nm and 3.4 nm, and a particle diameter of approximately from 100 nm to 800 nm.

[0040] FIG. 2 shows the chlorine storage isotherms of silicon dioxide storage material B according to the invention at 26 C., 0 C. and 30 C. Storage material B consists of SiO.sub.2 with a mean particle diameter of between 1.8 nm and 3.2 nm, and a particle diameter of approximately from 300 nm to 1 m.

[0041] FIG. 3 shows the time-dependent chlorine adsorption on silicon dioxide storage materials A and B according to the invention at 26 C.

[0042] FIG. 4 shows the time-dependent chlorine adsorption on a comparative silicon dioxide storage material C with larger particles than materials A and B, Comparative material C consists of SiO.sub.2 with a mean pore diameter of between 5.5 nm and 8 nm, and a particle diameter of approximately from 1 nm to 1.5 m.

[0043] FIG. 5 shows the time-dependent chlorine desorption of silicon dioxide storage materials A and B according to the invention at 26 C.

EXAMPLES

Example 1

[0044] Two storage materials which permit higher loading than in the prior art were produced as follows:

[0045] Material A: Material A consists of SiO.sub.2 with a mean pore diameter of between 1.4 nm and 3.4 nm, and a particle diameter of approximately from 100 nm to 800 nm.

[0046] Production was carried out according to the following formulation: With stirring at room temperature, 87.5 ml of ethanol and 70.3 ml of deionized water were mixed with 7.9 ml of aqueous ammonia solution (25% by weight). 2.83 g of cetyltrimethylammonium bromide were added and dissolved by stirring for 10 minutes at room temperature. With stirring, 5.42 g of tetraethyl orthosilicate were added quickly and stirred for a further 2 hours. The colorless solid which formed was separated off by centrifugation (10 min at 6000 min.sup.1). The solid was redispersed in 40 ml of ethanol and separated off by centrifugation (10 min at 6000 min.sup.1). Then the solid was stored in air for 16 hours at 50 C. and then calcined in air for 15 hours at 500 C. The resulting storage material consisted of spherical particles with particle diameters of approximately from 100 nm to 800 nm. It had an internal surface area of A.sub.BET=116123 m.sup.2/g and a pore volume of V.sub.p=0.83 cm.sup.3/g. The diameter of the pores was between 1.4 nm and 3.4 nm, with a maximum of the pore diameter distribution at 2.30.5 nm. A further batch of the material had, divergently, an internal surface area of A.sub.BET=153697 m.sup.2/g and a pore volume of V.sub.p=0.70 cm.sup.3/g.

[0047] Material B: Material B consists of SiO.sub.2 with a mean pore diameter of between 1.8 nm and 3.2 nm, and a particle diameter of approximately from 300 nm to 1 m.

[0048] Production was carried out according to the following formulation: With stirring at room temperature, 1.75 g of cetyltrimethylammonium bromide were dissolved in 411.6 ml of deionized water. To the solution there were added 31.6 ml of aqueous ammonia solution (25% by weight), and stirring was carried out for 20 minutes at room temperature. With stirring, 8.33 g of tetraethyl orthosilicate were added quickly. Stirring was carried out for 5 hours at room temperature. The resulting colorless solid was separated off by filtration, washed with 50 ml of water and dried for 24 hours at 105 C. It was then calcined in air for 15 hours at 500 C. The resulting storage material consisted of particles with particle diameters of approximately from 300 nm to 1 m. It had an internal surface area of A.sub.BET=10365 m.sup.2/g and a pore volume of V.sub.p=0.78 cm.sup.3/g. The diameter of the pores was between 1.8 nm and 3.2 nm, with a maximum of the pore diameter distribution at 2.50.3 nm.

[0049] In order to study the chlorine storage capacity of the storage materials, chlorine adsorption isotherms were recorded. In order to measure the adsorption of chlorine on the material, approximately 200 mg of storage material were heated thoroughly at 210.sup.3 bar and 150 C. in a magnetic suspension balance. For defined temperatures and chlorine pressures, the increase in mass of the sample was measured, whereby adsorption isotherms were obtained.

[0050] FIG. 1 shows the adsorption and desorption isotherms of chlorine on material A at 26 C., 0 C. and 30 C. FIG. 2 shows the adsorption and desorption isotherms of chlorine on material B at 26 C., 0 C. and 30 C. It can be seen from the isotherms that the materials have a chlorine storage capacity of over 1 g of chlorine per 1 g of storage material. They are thus significantly superior to the materials described in the prior art having a storage capacity of up to 0.26 g of chlorine per 1 g of material. The storage isotherms additionally show that, even at low pressures, considerable chlorine adsorption takes place. The materials exhibit, for example, at a temperature of 0 C. and a pressure of 3 bar, a load of more than 0.4 g of chlorine per 1 g of storage material. Under the same conditions, the load of chlorine on SiO.sub.2 materials in [W. Q. Xiao, dissertation, Chlorine Adsorption Properties of NaX, NaY, MCM-41, MCM-48 and Mordenite Molecular Sieves, Taiyuan University of Technology, China, 2010] is below 0.2 g of chlorine per 1 g of material.

[0051] The adsorption of chlorine on the storage materials is wholly reversible, as can be seen from the almost matching curves of the adsorption isotherms (filled symbols in FIGS. 1 and 2) with the corresponding desorption isotherms (unfilled symbols in FIGS. 1 and 2) at maximum and minimum loading.

Example 2

[0052] The storage materials permit liquefaction of chlorine in the pores at a temperature higher than 35 C. at atmospheric pressure, or at a pressure lower than 6.8 bar at room temperature, as can be concluded from a comparison of the density of the adsorbed chlorine with the densities of liquefied and gaseous chlorine under the same conditions:

[0053] At a temperature of T=26 C. and p.sub.chlorine=0.90 bar, an average density of the adsorbed chlorine of =1.47 g/cm.sup.3 is obtained for material A with an adsorbed mass m.sub.ads=1.03 g/g and a pore volume of V.sub.p=0.70 cm.sup.3/g. Under the same conditions, an average density of the adsorbed chlorine of =1.40 g/cm.sup.3 is observed for material B with an adsorbed mass m.sub.ads=1.09 g/g and a pore volume of V.sub.p=0.78 cm.sup.3/g. Since under these conditions liquid chlorine has a density of 1.53 g/cm.sup.3 and gaseous chlorine has a density of 0.003 g/cm.sup.3, the chlorine in the pores is for the most part in liquid form.

[0054] Analogously, for a temperature of T30=30 C. and p.sub.chlorine=6.53 bar, an average density of the adsorbed chlorine of =1.14 g/cm.sup.3 can be observed for material A with an adsorbed mass m.sub.ads=0.95 g/g and a pore volume of V.sub.p=0.83 cm.sup.3/g. For material B, an average density of the adsorbed chlorine of =1.24 g/cm.sup.3 is obtained at T=30 C. and p.sub.chlorine=6.50 bar with an adsorbed mass m.sub.ads=0.97 g/g and a pore volume of V.sub.p=0.78 cm.sup.3/g. The density of liquid chlorine under these conditions is 1.38 g/cm.sup.3, while the density of gaseous chlorine is 0.003 g/cm.sup.3. Consequently, here too a large part of the adsorbed chlorine is in liquid form.

Example 3

[0055] In order to study the kinetics of the loading of the storage materials, approximately 150 mg of storage material were heated thoroughly at 0.01 bar and 150 C. The storage material was introduced into a magnetic suspension balance and nitrogen was circulated around it at T=95 C. and p=1 bar with a gas stream of 150 sccm until a constant weight was obtained. At T=26 C., p=1 bar and a total gas stream of 150 sccm, defined volume fractions of the gas stream were replaced by chlorine. In order to study the adsorption kinetics, the volume fraction of chlorine in the gas stream was increased from 0 vol. % to 88.5 vol. % and the time-dependent increase in mass was measured.

[0056] The loading of materials A and B largely follows a limited linear growth (see FIG. 3). For complete loading with chlorine, lengths of time of approximately from 10 to 20 minutes are required. The rapid loading of the materials is based on the ready accessibility of the storage pores (diameter<10 nm) through additional larger transport pores (diameter>20 nm), for example formed by corresponding particle interspaces in the case of particle diameters below 1 m.

[0057] A material C in which the particle diameters are larger was produced. The number of larger transport pores in relation to the smaller storage pores is thereby reduced significantly.

[0058] Material C: C consisting of SiO.sub.2 with a mean pore diameter of between 5.5 nm and 8 nm, and a particle diameter of approximately from 1 m to 1.5 m.

[0059] Production of material C takes place analogously to [J. Am. Chem. Soc., 1998, 120 (24), pp. 6024-6036]. With stirring at room temperature, 4.0 g of poly(ethylene glycol)-block-poly-(propylene glycol)-block-poly(ethylene glycol) (M.sub.n5800, trade name Pluronic P123) were dissolved in a mixture of 30 ml of water and 130 ml of aqueous HCl (2.0 M). 8.5 g of tetraethyl orthosilicate were added to the solution, and the solution was stirred for a further 5 minutes at room temperature. Then the solution was heated for 18 hours at 35 C. and then for 24 hours at 80 C. The resulting colorless solid was filtered off, washed twice with 50 ml of water and once with 50 ml of ethanol, and then calcined in air for 30 hours at 500 C. Material C consisted of SiO.sub.2 particles with particle diameters of approximately from 1 m to 1.5 m, an internal surface area of A.sub.BET=6563 m.sup.2/g and a pore volume of V.sub.p=0.77 cm.sup.3/g. The diameter of the storage pores was between 5.5 nm and 8 nm, with a maximum of the pore diameter distribution at 6.61.0 nm.

[0060] The loading kinetics of sample C is shown in FIG. 4. For maximum loading, sample C requires at least 20 minutes, whereas the maximum load in the case of A and B is achieved in a time of approximately 10 minutes. The smaller number of transport pores in relation to the storage pores consequently leads in the case of material C to significantly slower loading of the material.

[0061] The study of the desorption kinetics was carried out analogously to the study of the adsorption kinetics, wherein the volume fraction of chlorine in the gas stream was lowered from 88.5 vol. % to 0 vol. % and the time-dependent increase in mass was measured.

[0062] The unloading of materials A and B corresponds largely to an exponential decrease in the adsorbed chlorine (see FIG. 5). Complete unloading of materials A and B takes place within a period of 20 minutes.

Example 4

[0063] In order to study the structural and chemical stability of the materials towards chlorine, the materials were brought into contact with chlorine and then characterized again. A degree of condensation of greater than 0.91 was thereby identified as an important parameter for high stability. The determination of the degree of condensation of the SiO.sub.2 materials in the examples here took place by silicon-29 solid-state NMR spectroscopy (magic angle spinning at 10 kHz). By deconvolution and integration of the signals of the various Q.sup.n centers (Q.sup.n=Si(OSi).sub.n(OH).sub.4-n), the proportions of the corresponding centers in the materials were determined. The degree of condensation of the materials is given as the proportion of SiOSi bonds in all the SiOR bonds (degree of condensation=(number of SiOSi bonds)/(number of SiOR bonds in total)).

[0064] Material A with a degree of condensation of 0.95 and material B with a degree of condensation of 0.92 did not exhibit any structural changes even after repeated full loading and unloading with chlorine. The absence of chlorine in storage materials A and B after the treatment could be demonstrated by energy-dispersive X-ray spectroscopy. Irreversible reactions of the storage materials with chlorine during the treatment can thus be ruled out.

[0065] A comparative material D which has a lower degree of condensation and as a result does not have sufficient chlorine stability was produced.

[0066] Comparative material D: Material D consists of SiO.sub.2 in the form of aerogel with a degree of condensation of 0.90.

[0067] Production of comparative material D: At room temperature, 4.0 ml of tetramethyl orthosilicate were dissolved in 3 ml of methanol. With vigorous stirring, a solution of 2.0 ml of 0.1 M aqueous ammonia and 3.0 ml of methanol was added quickly, and stirring was carried out for a further 1 minute at room temperature. The gel which had formed after 20 minutes was stored for 1 day at room temperature. Then the solvent in the gel was replaced by covering with a layer of acetone. In an autoclave, the solvent in the gel was replaced by covering with a layer of liquid CO.sub.2 (62 bar, room temperature). By increasing the temperature to over 40 C. (p>80 bar), the CO.sub.2 was brought into the supercritical state. Then the pressure was lowered to normal pressure at approximately 5 bar/h and the material was removed.

[0068] Comparative material D with a degree of condensation of 0.90 exhibited considerable structural changes after only 30 minutes' contact with a chlorine gas stream at room temperature and normal pressure. The internal surface area (A.sub.BET) fell from 8203 m.sup.2/g to 6491 m.sup.2/g, while the pore volume (V.sub.p) increased from 1.95 cm.sup.3/g to 3.14 cm.sup.3/g. By means of IR spectroscopy it was possible to observe inter alia a decrease in OH vibrations relative to SiO vibrations. It follows therefrom that chemical reactions have taken place in the material.