EP1204590A2

EP1204590A2 - Method for the controlled production of spherical activated carbon

Info

Publication number: EP1204590A2
Application number: EP00958108A
Authority: EP
Inventors: Wolfgang Heschel; Dirk MÜLLER; Thorsten Keibel; Marlen Kolinke
Original assignee: Helsa Werke Helmut Sandler GmbH and Co KG
Current assignee: Helsa Werke Helmut Sandler GmbH and Co KG
Priority date: 1999-07-05
Filing date: 2000-07-01
Publication date: 2002-05-15
Also published as: WO2001002295A3; AU6979200A; DE19930732A1; WO2001002295A2

Abstract

The invention relates to a method for producing spherical activated carbon from divinyl-benzene or styrene-divinyl-benzene polymer-based polymers in gel or macroporous form, by sulfonating the polymer with sulfuric acid and stirring the reaction material at a sulfonating temperature of 200 to 250 °C, for 20 to 90 minutes. The ratio H2SO4:polymer, calculated as pure substances, is 1.4:1 to 3:1 at the beginning of the sulfonation. The heating rate until the sulfonating temperature is reached is 5 to 20 K/min. The sulfonated polymer is then cooled to a temperature of < 50 °C and pyrolised by heating the product to a temperature of 250 °C with a heating rate of 5 to 15 K/min. The temperature is maintained at 250 °C for 30 minutes. The product is then further heated to 330 °C with a heating rate of 2 to 10 K/min, and subsequently to a temperature of 750 to 900 °C with a heating rate of 50 K/min. The product is maintained at the maximum temperature for 5 to 10 minutes.

Description

Process for the controlled production of spherical activated carbon

The present invention relates to the controlled production of spherical activated carbon, in particular the controlled production of spherical activated carbon from gel-like or macroporous polymers.

Due to the comparatively large surface area of activated carbon and the resulting large adsorption capacity, activated carbon has long been used in various areas for cleaning tasks. Activated carbon is used in many different areas, such as the cleaning of flue gases or the cleaning of liquids, the activated carbon often being used as a filtration aid in the latter case.

In recent times, more and more activated carbons with special, tailor-made properties have been requested. This is particularly true in the field of automotive cabin air filters, which are said to have a high adsorption capacity with often very small dimensions. Furthermore, special filters are to be mentioned, which are created for very special purposes and some are only intended for the adsorption of a certain substance.

The main area of application for the use of carbon-containing adsorbents has been air and gas purification and gas separation for decades. Such adsorbents have a wide range of uses due to numerous variations. In addition to the conventional use of activated carbon in the packed bed or in the fluidized bed, filter systems have become established in the past 20 years, in which the adsorbents on textile carriers, on PU Foam, metal or the like are applied. Applications in

Protective suits or as an activated carbon filter for the passenger compartment in vehicles have emerged in recent years.

ABC protective suits essentially consist of a textile outer fabric that is connected to an activated carbon filter material. Spherical adsorbents that are fixed as a monolayer on a textile support are suitable as filters. Powdered activated carbon on fine-pored polyurethane foam or pure activated carbon fabric are also used. These materials, which are at least partially composite materials, are assembled into appropriate suits that are pulled over the permanently worn clothing when used as protective clothing. In addition to such protective clothing, single-layer filter composites are also known, which can be worn as underwear in a suit.

The area of application for filter systems in motor vehicles to protect passengers from harmful emissions and to improve comfort has undergone a dynamic development in recent years, so that about 80% of all commercial vehicles on the European market today are equipped with a particle filter.

So-called combination filters are increasingly being used, which consist of a combination of textile particle filter and activated carbon medium. Because, as already mentioned, the construction volume is often very limited, there are sometimes extreme requirements with regard to flow resistance, particle separation performance and adsorption capacity.

The activated carbon volume of the combination filter and the resulting adsorption capacity is relatively low. However, the pore structure of the activated carbon is such that there is good adsorption kinetics even in the low partial pressure range (<100 ppm). Combination filters can therefore be used excellently for reducing short-term concentration peaks, ie for smoothing. A significant improvement in comfort is achieved by lowering odor-intensive components of the supply air flow below the odor threshold. N-butane, toluene, sulfur dioxide and nitrogen oxide are used as key substances for determining such activated carbon or filter properties.

So-called activated carbon matrix filters, which have a significantly higher volume of activated carbon, are already used in various vehicle types in the upper middle and upper class. These so-called "extended bed" filters have an adsorption characteristic comparable to classic packed bed filters, but with a greatly reduced flow resistance. This effect is achieved by fixing activated carbon on the carrier walls of an open-pore polyurethane foam. If a spherical equilibrium fill in the sense of a random packing has an activated carbon volume of approx. 62.5% and a resulting gap volume of 37.5%, values of 35 to 40% result for matrix filters. It is therefore obvious that in order to achieve the bed bed adsorption characteristics (no immediate breakthrough and long breakthrough time followed by a steep increase in the breakthrough curve), a specific selection of the activated carbon must be made.

Due to the increased demands on the properties of such activated carbons, it is understandable that such activated carbons can no longer be produced in a simple manner using the conventional processes for producing activated carbon. For some time now there have been isolated attempts in the prior art for the targeted and optionally controlled production of activated carbons.

In this connection, EP 0 326 271 B1, for example, is to be mentioned, from which the production of activated carbon, in particular from styrene-divinylbenzene copolymers, is known. In the disclosed process, the copolymer is first used with a large excess of fuming sulfuric acid or oleum for a longer period Period treated. After sulfonation, the polysulfonated copolymer is washed extensively to remove excess acid and then dried. This process is extremely uneconomical due to the high use of sulfuric acid and the energy-intensive drying step, and with regard to the process wastewater that arises.

A method is known from WO 96/21616 in which a styrene-divinylbenzene copolymer with 5 to 50% by weight sulfuric acid is carbonized or pyrolyzed at a temperature of up to 750 ° C. Because the amount of sulfuric acid, which is already insufficient for monosulfonation of the aromatic nuclei, there is a comparatively high loss of mass during the pyrolysis. This method, too, cannot be carried out economically due to the loss of mass mentioned.

From DE 197 52 593.8, which goes back to the same applicant as the present invention, a process for the production of activated carbon from polymers with aromatic nuclei is already known, in which the polymer used is sulfonated, filtered off, pyrolyzed and activated with concentrated sulfuric acid. Although the aforementioned patent application already represents a significant advance over the aforementioned publications, because the disclosed method enables the activated carbon properties, in particular the pore size and pore size distribution, to be controlled by changing the individual process parameters, there is still a need for further tailored activated carbons with very individual properties and also at broadening the raw material base.

It is therefore an object of the present invention to provide at least one further method for the controlled production of activated carbon which avoids at least some of the disadvantages known from the prior art.

This object is achieved in the present case by a method having the method steps of claim 1. Advantageous embodiments of this method are Subject of the subclaims.

In addition to the use of styrene-divinylbenzene polymers, the process according to the invention advantageously enables the use of divinylbenzene polymers for the production of activated carbon, as a result of which the base is widened with respect to the starting material for the production of special activated carbon and activated carbon with modified properties is also obtained.

Another advantage of the method according to the invention lies in the streamlining of the overall method, in particular activation being provided only in the case of a special embodiment of the method according to the invention.

The sulfonation of the starting polymer is related to the properties of the final product, i.e. the number and distribution of the pores in the activated carbon according to their size and in relation to the total pore volume are of particular importance. The present invention is based in part on the knowledge that a high sulfur content in the coke structure is particularly advantageous.

It is well known that sulfonation of polymers leads to infusible products. Surprisingly, however, it was also found that an increase in the sulfur content has particular advantages with regard to the available pore structure. The sulfur contained in the coke skeleton is in fact released from the coke skeleton during pyrolysis and / or the activation that may take place and forms “defects” in the form of micropores. The sulfur introduced into the starting polymer in the form of sulfonic or sulfuric acid groups is therefore of essential importance for the relevant characteristics of the end product.

For the mechanism, it is currently assumed that the sulfonation begins at relatively low temperatures, with the formation of sulfonic acid groups almost exclusively at temperatures up to about 200 ° C. electrophilic substitution takes place on the aromatic nuclei contained in the polymer. The formation of sulfone groups then preferably takes place at temperatures above 200 ° C., which corresponds to a crosslinking of an aromatic nucleus already substituted by a sulfonic acid group with a further aromatic nucleus via the same sulfo group with the elimination of water.

With a further increase in temperature, which is fundamentally possible, the effect of hot sulfuric acid as an oxidizing agent comes to the fore, which is why an increase in temperature to above 300 ° C. results in a greatly reduced yield of sulfonated product.

A special process measure in the context of the present invention is to carry out the sulfonation of the polymer with sulfuric acid with agitation of the reaction mixture. It should be noted here that stationary sulfonation only leads to a sintered product which cannot be used for any of the intended areas of use. A free-flowing sulfonation product is only obtained when the reaction mixture has been thoroughly mixed.

Of course, the heating regime also plays a decisive role in sulfonation, although the product qualities can also be influenced by this factor. It is therefore necessary to choose a heating rate in the range from 5 to 20 Kelvin in order to bring the reaction material to the sulfonation temperature. With a heating rate below 5 K./Min. the heating and sulfonation process section is extended unnecessarily. With a heating rate of more than 20 K./Min. local overheating can occur, which has a negative impact on the end product, since this increases the tendency of the starting polymer to sinter.

Another way to influence the end product is to vary the ratio of H2SO4 to the polymer used. According to the invention, this ratio, calculated as the ratio of the pure substances, is 1.4: 1 to 3: 1. The sulfuric acid used as the sulfonating agent is therefore in principle in excess, and it was possible to limit it to a maximum of three times the excess. This limits the excessive use of sulfuric acid, which further increases the economics of the process.

After completion of the sulfonation with sulfuric acid, the reaction mixture is allowed to cool to a temperature of <50 ° C. Subsequently, the sulfonated polymer by heating the product to a temperature of 250 ° C with a heating rate of 5 to 15 K./Min. and 30 min. hold at 250 ° C, further heating up to 330 ° C with a heating rate of 2 to 10 K / min. and then further heating up to a temperature of 750 to 900 ° C with a heating rate of 30 to 50 K / min. and pyrolyzed at the maximum temperature reached for 5 to 10 minutes.

The sulfonation is usually carried out in such a way that sulfuric acid and polymer are initially introduced into a reaction vessel and then opened

Sulfonation temperature to be heated. In a special embodiment of the process according to the invention, however, the sulfuric acid is initially introduced and heated to the sulfonation temperature. The polymer to be sulfonated is then added. Since the temperature in the reaction vessel drops as a result of the polymer input, the

Sulphonation temperature in the reaction vessel heated, the heating rate likewise in the range from 5 to 20 K / min. lies.

The sulfonation is preferably carried out for 20 to 40 minutes, the sulfonation being carried out under reduced pressure in a special process variant. The vacuum in the reaction vessel is dimensioned so that the pressure difference to the environment is about 50 to 550 mbar.

In particular by applying negative pressure, the reaction time can advantageously be limited to 20 to 40 minutes, since in the sulfonation Reaction product formed water is removed from the equilibrium and thus the further sulfonation is favored.

Surprisingly, the use of dilute sulfuric acid as a sulfonating agent is also possible in the sulfonation of gel-like or macroporous polymers. In principle, it is therefore possible in the process according to the invention to use sulfuric acid with a concentration of about 54 to 96% by weight of H ₂ SO4 as the sulfonating agent. When using dilute sulfuric acid as the sulfonating agent, it is particularly preferred to carry out the process in combination with carrying out the sulfonation under reduced pressure.

Of particular importance for obtaining a non-sintered and free-flowing product in sulfonation is that the reaction material is agitated and mixed sufficiently, because otherwise the tendency towards sintering of the starting polymer increases significantly, possibly due to local overheating. It is particularly preferred if the reaction material by rotating the

Reaction container is moved. Compared to the use of a rigid reaction vessel provided with a stirring device, carrying out the sulfonation in a rotating reaction vessel is advantageous in that the flowability of the sulfonation product is better preserved. The reason for this is assumed to be that the mechanical and possibly also thermal load on the starting polymer in a rotating reaction vessel is lower.

The pyrolysis in process step b) is generally carried out under a nitrogen atmosphere. In a special embodiment of the method according to the invention, the pyrolysis takes place in an atmosphere composed of nitrogen and water vapor, which in a further development also contains carbon dioxide. Depending on the previous procedure in the sulfonation, ie, for example, if the sulfonation was carried out under normal pressure, the water content of the pyrolysis atmosphere does not necessarily have to be metered in from the outside are brought in by the water content of the sulfonated polymer. Of course, water vapor can also be metered into the pyrolysis atmosphere.

Because the pyrolysis atmosphere contains nitrogen and / or carbon dioxide in addition to nitrogen, there is advantageously no need for special activation. This enables a shortening of the process and, in particular, high energy savings. On the other hand, further activation makes it possible to adapt the adsorption properties of the spherical activated carbon produced to the anticipated requirements of the area of use.

The composition of the activation atmosphere or special activation methods, such as. B. impregnation with salt solutions are generally familiar to the expert and are selected depending on the requirement.

The following exemplary embodiments serve to further explain the present invention, from which further advantages of the invention also become apparent.

Examples

Macroporous and gel-like polymer as a starting material for sulfonation

A macroporous polymer was used for the sulfonation experiments, e.g. available under the name "LEWATIT" as pure dinvinylbenzene polymer, and a gel-like polymer, commercially available as styrene-divinylbenzene polymer under the name "LEWAPOL" with varying divinylbenzene (DVB) contents.

40 g of the polymer are with the according to the application ratio The calculated amount of H2SO4 (96% by weight) was introduced into a reaction vessel of 0.5 l capacity and mixed by rotating the reaction vessel. The reaction vessel rotates at 30 revolutions / min. about its longitudinal axis, which is inclined at 30 ° to the horizontal. The reaction vessel is heated on all sides by a fixed electric furnace. The desired temperature regime can be achieved in the reaction mass by setting a specific heating mode.

The water of reaction released during the sulfonation is removed from the reaction vessel by a pump (e.g. water jet pump).

After the respective sulfonation time, the heating is switched off and the reaction mixture is allowed to cool to room temperature, the reaction vessel continuing to rotate.

The free-flowing, sulfonated product is then in a dormant

The bed is coked in an N ₂ atmosphere in accordance with the specified values.

The coke, which has cooled to room temperature, is then activated in a fluidized layer until the desired burn-up. Alternatively, the sulfonated product can be activated during pyrolysis and without intermediate cooling.

Results

When using a macroporous polymer, mesopore-rich activates are obtained under conditions that are otherwise the same for sulfonation, coking and activation compared to a gel-like polymer (Examples 3 and 6). The pore sizes were determined as follows:

Micropores: <7.6 nm Mesopores: 7.6 to 50 nm

Macropores:> 50 nm.

For the rest, methods were used to determine the pore volumes and other measured values, as are already disclosed in DE 197 52 93.8 of the applicant.

The mass ratio of sulfuric acid to macroporous polymer can also have an influence on the proportion of macropores (absolutely non-percentage) (Examples 1 to 4).

As a comparative example, Example 5 shows that a mass use ratio of 1: 1 results in a significant decrease in the coke and activate yield and in the volume-related BET surface area.

In addition to the process conditions heating rate, temperature and holding time, the sulfonation is also influenced by the type of reactor and the type of mechanical energy input. Therefore, sulfonation reactions in a fixed reaction vessel without mechanical stirrer and an inclined, rotating reaction vessel with and without lifting elements on the inner wall were used for corresponding experiments.

In the former variant, the polymer is poured into the fixed reaction flask and brought into contact with the corresponding amount of sulfuric acid. The reaction mixture is homogenized with a mechanical stirrer. However, this is only possible as long as the mixture is in suspension. As soon as the sulfonation process begins, ie the liquid content decreases, the mixing stops. In the further course of the sulfonation, product movement no longer takes place. In the course of the sulfonation sintering continues to take place and a free-flowing reaction product cannot be obtained.

In the variant with the moving reaction vessel, this is arranged at an angle of approximately 30 to 45 ° to the horizontal and rotates about its longitudinal axis at 1 to 30 revolutions / min. On the inner wall of the

Reaction vessels can be installed which promote mixing in the manner of lifting blades. As a result, the temporary solidification of the reaction product, which is also known as cake formation, which occurs at a certain reaction stage is avoided and the water vapor is evacuated uniformly from the reacting reaction mixture. The advantages resulting from this design of the reactor are, on the one hand, a free-flowing sulfonation product and a considerable saving in sulfuric acid, since, compared to the fixed reactor, a significantly lower amount of sulfuric acid is sufficient for a corresponding sulfonation.

Compared to an essentially horizontally mounted rotary tube, the utilization of the reaction space with the inclined recator is more than twice as good, as filling levels of up to 60% are possible. It has surprisingly been found that the mixing movements typical of the inclined reactor, in which the radial material movement is superimposed by rolling on the reactor wall by a material movement in the axial direction, thus promoting the homogenization of the reaction mixture, shortening the reaction time and thus contributing to energy savings ,

From Example 11, a reaction vessel with a 2 liter capacity was used, into which 300 g of the respective polymer were introduced.

As can be seen from Examples 37 to 40, the application of a negative pressure has no direct influence on the coke yield and Pore structure of the coke. With a sufficient negative pressure, ie with a differential pressure of at least 50 mbar, however, the reaction product tends to flow into the free-flowing state, which has an overall favorable effect with regard to the mixing of the reaction mixture and the shortening of the process time. Excessive negative pressures, ie at differential pressures from approximately 550 to 700 mbar, lead to losses of sulfuric acid as a result of partial evaporation and should therefore also be avoided.

Surprisingly, it has also been shown that a dilute sulfuric acid can also be used. In particular, it was found that sulfuric acid with a concentration in the range from 54 to 96% by weight of H2SO4 had no influence on the coke yield and the quality of the activates, provided the other conditions were kept the same. This can be seen from Examples 20 to 32 and Example 42, it also being found that an extension of the sulfonation time may be necessary when using a dilute heavy iron acid.

Tables 1 and 2 below show the results of the tests for the production of spherical activated carbon.

Table 1

Sulfonation CONDITIONS

Table 1 (continued)

Sulfonation CONDITIONS

Table 2 continued

Since the crosslinking of the styrene-divinylbenzene polymers used depends on their degree of crosslinking and thus on their divinylbenzene content, further studies were carried out with regard to the influence of the degree of crosslinking in relation to the properties of the process product.

As examples, styrene-divinylbenzene copolymers with a divinylbenzene content of 2 and 4% by weight and a so-called monodispersed styrene-divinylbenzene polymer with a divinylbenzene content of about 8%, which was mixed with a swelling agent, were investigated, the Sulfonation hold time, d. H. the reaction time and the mass ratio of sulfuric acid to polymer were varied.

Basically, the result is that the divinylbenzene content in the range between 2 and 8% by weight has no significant influence on the

Activat quality and yield possesses. The pore structure can be changed in a targeted manner both via the sulfonation time and via the acid content. With short sulfonation times and comparatively low acid-polymer ratios, when using gel-like styrene-divinylbenzene polymer, microporous activates with an increased macropore volume are obtained. By changing these two control variables of the process, activated carbons can be produced with a deliberately different macro-pore structure, but approximate agreement of the BET surface area and consequently corresponding adsorption capacity. The adsorption rate can be controlled via the macro-pore structure. In the sulfonation of macroporous polymer, i. H. of divinylbenzene polymer, in particular the mesopore volume of the spherical activated carbon to be produced can be adjusted. A short hold time of about 20 minutes during sulfonation provides extremely mesopore-rich coke and activates with the same BET surface area, while a long hold time of about 90 minutes reduces the mesopore content to 1/3.

Claims

Patent claims

1. Process for the preparation of spherical activated carbon from gel-like or macroporous polymers based on divinyibenzene or styrene-divinylbenzene polymers with the following process steps:

a) sulfonation of the polymer with sulfuric acid with agitation of the reaction mixture at a sulfonation temperature of 200 to 250 ° C for a period of 20 to 90 minutes, the ratio calculated as pure substances of

H2SO4: polymer at the start of sulfonation in the

Range from 1, 4: 1 to 3: 1 and the

Heating rate until the sulfonation temperature is reached in the range from 5 to

20 K / min. lies,

b) cooling the sulfonated polymer to a temperature of <50 ° C and pyrolyzing the sulfonated polymer by heating the

Product to a temperature of 250 ° C with a heating rate of 5 to 15 K / min. and 30 min. hold at 250 ° C, further heating up to 330 ° C with a heating rate of 2 to 10 K / min. and then further heating up to a temperature of 750 to 900 ° C with a

Heating rate of 50 K / min. and hold at the maximum temperature reached for 5 to 10 minutes.

2. The method according to claim 1, characterized in that in step a), sulfuric acid and polymer are initially submitted for sulfonation and heated to sulfonation temperature.

3. The method according to claim 1, characterized in that in step a) the sulfuric acid is initially introduced, heated to sulfonation temperature and the polymer to be sulfonated is subsequently added.

4. The method according to any one of the preceding claims, characterized in that the sulfonation is carried out for 20 to 40 minutes.

5. The method according to any one of the preceding claims, characterized in that the sulfonation takes place under reduced pressure, in particular at a pressure difference to the environment of 50 to 550 mbar.

6. The method according to any one of the preceding claims, characterized in that the sulfuric acid used in step a) has a concentration between 54 and 96%.

7. The method according to any one of the preceding claims, characterized in that the agitation of the reaction material takes place by moving, in particular rotation, the reaction container.

8. The method according to any one of the preceding claims, characterized in that the pyrolysis in step b) is carried out under a nitrogen atmosphere.

9. The method according to any one of claims 1 to 7, characterized in that the pyrolysis in step b) is carried out under an atmosphere composed of nitrogen and water vapor.

10. The method according to claim 9, characterized in that the atmosphere in the pyrolysis in step b) further contains CO2.