DE19930732A1 - Process for the controlled production of spherical activated carbon - Google Patents

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 DEG 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 DEG C and pyrolised by heating the product to a temperature of 250 DEG C with a heating rate of 5 to 15 K/min. The temperature is maintained at 250 DEG C for 30 minutes. The product is then further heated to 330 DEG C with a heating rate of 2 to 10 K/min, and subsequently to a temperature of 750 to 900 DEG C with a heating rate of 50 K/min. The product is maintained at the maximum temperature for 5 to 10 minutes.

Description

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

Due to the comparatively large surface of Activated carbon and the resulting large Adsorption capacity, activated carbon has been in for a long time the different areas for cleaning tasks used. Activated carbon is found on many use in different areas, such as cleaning Flue gases or cleaning liquids, the Activated carbon in the latter case often also as Filtration aid is used.

In recent times, more and more activated carbons have been used special, tailor-made properties. This applies particularly in the field of motor vehicle Interior air filter, which has a high adsorption capacity often should show very small dimensions. Farther special filters are to be mentioned that are for very special ones  Purpose created and partly only for Adsorption of a certain substance are provided.

Main area of use for the use of carbonaceous Adsorbents has been the air and Gas cleaning and gas separation. Such Adsorbents have many variations a wide range of uses. Except the conventional one Use of activated carbon in the bed or in the Fluid bed have changed over the past 20 years Filter systems established on the market where the Adsorbents on textile supports, on PU foam, metal or similar 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 one textile outer fabric with an activated carbon filter material is connected. Spherical adsorbents come as filters in question as a monolayer on a textile backing are fixed. Powdered activated carbon on fine-pored Find polyurethane foam or pure activated carbon fabric also use. These materials that are are at least partially composite materials made up to suits that are in the Use as protective clothing over the permanently worn Clothes are pulled. Except for those Protective clothing is also a single-layer filter composite known that are wearable as underwear in a suit.

The area of application for filter systems in motor vehicles for Protection of passengers from harmful emissions and Comfort has had an improvement in recent years  undergo dynamic development so that on the European market today with about 80% of all commercial vehicles are equipped with a particle filter.

So-called combination filters are increasingly being used Use that from a composite of textile particle filter and activated carbon medium. Because, as already mentioned, the construction volume is often very limited, arise sometimes extreme requirements regarding Flow resistance, particle separation performance and Adsorption capacity.

The activated carbon volume of the combination filter and the resulting one resulting adsorption capacity is relatively low. The However, the pore structure of the activated carbon is such that a good one even in the low partial pressure range (<100 ppm) Adsorption kinetics is given. Combination filters can therefore excellent for reducing short-term Concentration peaks are used, d. H. for the Smoothing. A significant improvement in comfort achieved by using high-odor components of the Supply air flow can be reduced below the odor threshold. As key substances for the determination of such activated carbon or filter properties are n-butane, toluene, Sulfur dioxide and nitrogen oxide are used.

Already found in various vehicle types so-called upper middle and upper class Activated carbon matrix filter that has an essential have higher activated carbon volume. These so-called "Extended bed" filters are too classic Bed filter comparable adsorption characteristics, however with greatly reduced flow resistance. This  Effect is achieved by using a open-pore polyurethane foam activated carbon is fixed. If a ball of equal grain size in the sense of a Random pack over an activated carbon volume of approx. 62.5% and a resulting gap volume of 37.5% values for matrix filters are from 35 to 40%. It is therefore obvious that to achieve the Bulk bed adsorption characteristics (no immediate breakthrough and long breakthrough times followed by a steep climb the breakthrough curve) a targeted selection of activated carbon must be made.

Due to the increased demands on the properties such activated carbon is understandable that such Activated carbons are no longer used with conventional methods Production of activated carbon can be produced in a simple manner are. The prior art has been around for some time isolated attempts for targeted and if necessary controlled production of activated carbons.

In this context, e.g. B. EP 0 326 271 B1 name from which the production of activated carbon, especially known from styrene-divinylbenzene copolymers is. In the process disclosed, the copolymer first with a large excess of smoking Sulfuric acid or oleum for a long period of time treated. After sulfonation is done polysulfonated copolymer to remove excess Acid washed extensively and then dried. This procedure is due to the high Use of sulfuric acid and the energy-intensive Drying step and with regard to the resulting Process wastewater extremely uneconomical.  

A method is known from WO 96/21616 in which a Styrene-divinylbenzene copolymer with 5 to 50% by weight Sulfuric acid at a temperature up to 750 ° C or pyrolyzed. Because of the already for one Monosulfonation of the aromatic nuclei inadequate The amount of sulfuric acid is comparatively high Mass loss during pyrolysis. This procedure too is not due to the loss of mass mentioned to perform economically.

From DE 197 52 593.8, which is the same applicant as the the present invention goes back is already a process for the production of activated carbon from polymers with aromatic kernels known in which the used Polymer sulfonated with concentrated sulfuric acid, filtered off, pyrolyzed and activated. Although the the aforementioned patent application already a substantial Progress over the previously mentioned publications because the disclosed method controls the Activated carbon properties, especially the pore size and Pore size distribution, by changing the individual Process parameters enabled, there is still a need other bespoke activated carbons with whole individual properties and also with the broadening the raw material base.

It is therefore an object of the present invention at least another method for the controlled production of Activated carbon to indicate that at least part of the from the Avoids known disadvantages.  

This task is accomplished in the present case by a method with the Process steps of claim 1 solved. Beneficial Refinements of this method are the subject of Subclaims.

The method according to the invention enables in addition to Use of styrene-divinylbenzene polymers advantageously the use of divinylbenzene polymers for the production of activated carbon, which in terms of Starting material for the production of special Activated carbons the base is widened and also activated carbons can be obtained with changed properties.

Another advantage of the method according to the invention lies in streamlining the overall process, in particular also activation only for a special one Design of the method according to the invention provided is.

The sulfonation of the starting polymer is related to that Properties of the final product, i.e. H. the number and Distribution of the pores in the activated carbon according to their size as well as in relation to the total pore volume of particular Importance. Here, the present invention is based on Part of the realization that a high sulfur content in the Coke framework is particularly advantageous.

It is well known that the sulfonation of Polymers leads to infusible products. Surprised however, it was further found that an increase the sulfur content has particular advantages in terms of available pore structure results. The one in the Sulfur contained in the coke structure is used in the  Pyrolysis and / or the possibly taking place Activation detached from the coke structure and forms "Voids" in the form of micropores. The one in the form of Sulfonic or sulfuric acid groups in the starting polymer the sulfur introduced is therefore essential for the relevant characteristics of the end product.

For the mechanism it is currently assumed that the Sulphonation even at relatively low temperatures begins, almost at temperatures up to about 200 ° C exclusively through the formation of sulfonic acid groups electrophilic substitution on those contained in the polymer aromatic seeds. At temperatures above 200 ° C then preferably the formation of sulfone groups occurs a crosslinking of one already by a sulfonic acid group substituted aromatic nucleus with another aromatic nucleus over the same sulfo group below Elimination of water corresponds.

In the event of a further temperature increase, the fundamentally is possible, the effect of hot sulfuric acid occurs Oxidants increasingly in the foreground, which is why a temperature increase to over 300 ° C a strong reduced yield of sulfonated product results.

A special procedural measure within the present invention is the implementation of the Sulphonation of the polymer with sulfuric acid with agitation of the reaction material. It should be noted that a stationary sulfonation only leads to a sintered product, that cannot be used for any of the intended areas of application is. Only when there is sufficient mixing of the  Reaction material takes place, becomes a free-flowing Obtained sulfonation product.

Of course, the heating up regime also plays at Sulfonation plays a crucial role in that Product qualities can also be influenced by this factor are. A heating rate in the range is therefore required from 5 to 20 Kelvin to choose the reaction material Bring sulfonation temperature. At a heating rate under 5 K./Min. the procedural section of the Heating and sulfonation unnecessary. At a Heating rate of more than 20 K./min. it can be too local overheats come up that have negative influences have the end product, as this in particular the Sintering tendency of the starting polymer is increased.

Another way of influencing the end product is to vary the ratio of H ₂ SO ₄ 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 the excess to a maximum of three. This limits the excessive use of sulfuric acid, which further increases the economics of the process.

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

The usual procedure for sulfonation is that Sulfuric acid and polymer in one Reaction container submitted and then on Sulfonation temperature to be heated. In a special embodiment of the method according to the invention however, the sulfuric acid is first introduced and on Sulphonation temperature heated. Following that the polymer to be sulfonated added. Because the temperature in the reaction vessel sinks due to the polymer input again until the sulfonation temperature is reached in the Reaction vessel heated, the heating rate also in the range of 5 to 20 K / min. lies.

The sulfonation is preferred for 20 to 40 minutes carried out, in a special process variant the sulfonation takes place under negative pressure. The negative pressure in the reaction vessel is such that the Pressure difference to the environment is about 50 to 550 mbar.

In particular, by applying negative pressure Response time advantageously to 20 to 40 minutes restrict because in the sulfonation as a reaction product formed water is removed from the equilibrium and thus 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 SO ₄ 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 one and free-flowing product is also in sulfonation, that the reaction material is sufficiently moved and mixed is because otherwise, possibly due to local Overheating, the tendency of the starting polymer to sinter increases significantly. It is particularly preferred if the reaction material by rotating the reaction container is moved. Compared to using one with one Stir is provided rigid reaction container performing sulfonation in a rotating Reaction container advantageous in that the Free flow of the sulfonation product better preserved remains. The reason for this is assumed that the mechanical and possibly thermal load of the starting polymer in a rotating reaction vessel is less.

The pyrolysis in process step b) is generally carried out under a nitrogen atmosphere. In a special one The method according to the invention is designed Pyrolysis in one of nitrogen and hydrogen compound atmosphere that in another Training also contains carbon dioxide. Depending on prior conduct of sulfonation, d. H.  e.g. B. when sulfonation under normal pressure the water content of the Pyrolysis atmosphere not necessarily metered in from the outside but will be due to the water content of the sulfonated Polymers introduced. Of course it is also an addition of water vapor into the pyrolysis atmosphere possible.

Because the pyrolysis atmosphere in addition to nitrogen Contains hydrogen and / or carbon dioxide advantageously on a special activation to be dispensed with. This is a shortening of the procedure and particularly high energy savings possible. On the other hand, a further activation is a additional adjustment of the adsorption properties of the manufactured activated carbon to the expected Requirements of the area of application possible.

The composition of the activation atmosphere or special activation procedures, such as B. impregnation with salt solutions are generally familiar to the person skilled in the art and are chosen according to requirements.

Serve to further explain the present invention the following examples, from which also further advantages of the invention will become apparent.

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

A macroporous polymer was used for the sulfonation experiments used in trade z. B. under the name "LEWATIT" available as pure dinvinylbenzene polymer, and a gel polymer, commercially available as Styrene-divinylbenzene polymer under the name "LEWAPOL" available with varying divinylbenzene (DVB) content.

40 g of the polymer are introduced into a reaction vessel of 0.5 l capacity with the amount of H ₂ SO ₄ (96% by weight) calculated according to the application ratio 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 released during sulfonation Reaction water vapor is pumped (e.g. Water jet pump) removed from the reaction vessel.

After the respective sulfonation time, the heating switched off and the reaction mixture to room temperature allowed to cool while the reaction vessel continues rotates.

The free-flowing, sulfonated product is then coked in a quiescent bed in accordance with the specified values in an N ₂ atmosphere.

The coke cooled to room temperature is then on it in a fluidized layer to the desired one  Burning activated. Alternatively, the activation of the sulfonated product during pyrolysis and without Intermediate cooling.

Results

When using a macroporous polymer, mesopore-rich activates are obtained under otherwise identical conditions during 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, was used to determine the pore volumes and other measured values used methods as they already disclosed in DE 19 75 293.8 by the applicant are.

About the mass ratio of sulfuric acid too Macroporous polymer can also influence the Take the percentage of macropores (absolutely non-percentage) (Examples 1 to 4).

As a comparative example, Example 5 shows that a Mass usage ratio of 1: 1 a significant decrease the coke and activates yield as well as the volume-related BET surface results.  

The sulfonation is governed by the process conditions Heating rate, temperature and holding time still of the reactor type and influenced the type of mechanical energy input. It were 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 used for corresponding tests.

In the former variant, the polymer is in the fixed reaction flask poured and with the appropriate amount of sulfuric acid contacted. The Reaction mixture is with a mechanical stirrer homogenized. However, this only works as long as the mixture is in suspension. Once the sulfonation process uses d. H. the liquid content decreases, the comes Mixing to a halt. In the further course of the Sulfonation no longer takes place in product movement. in the The course of the sulfonation continues to be strong Sintering takes place and it cannot be pourable Reaction product can be obtained.

In the variant with the moving reaction vessel, this is approximately at an angle of 30 to 45 ° against the Horizontal arranged inclined and rotating around its Longitudinal axis with 1 to 30 revolutions / min. On the inside wall the reaction vessel can be built-in, which in promote the mixing of the type of lifting blades. This will result in a certain reaction stage Occasional solidification of the reaction product, which is also known as cake formation, avoided and the Water vapor is evacuated evenly from the Dissipated reaction mixture. The result of this design advantages of the reactor are on the one hand  free-flowing sulfonation product and a substantial one Saving sulfuric acid because compared to fixed reactor, a much smaller one Amount of sulfuric acid for a corresponding sulfonation is sufficient.

Compared to an essentially horizontal one Rotary tube is the exploitation of the reaction space in the inclined reactor better by more than twice as Fill levels up to 60% are possible. It has surprisingly shown that for the inclined Reactor typical mixing movements in which the radial Good movement by rolling on the reactor wall through a Good movement is superimposed in the axial direction Homogenization of the reaction mixture promote this Way shorten the response time and thus to Contribute energy saving.

From embodiment 11, a reaction vessel with 2 Liter capacity used, in which 300 g of each Polymers were introduced.

As can be seen from Examples 37 to 40, this has Applying a negative pressure has no direct influence the coke yield and the pore structure of the coke. At sufficient vacuum, d. H. at a Differential pressure of at least 50 mbar is possible Reaction product, however, rather in the free-flowing state about what's overall favorable in terms of Mixing of the reaction material and shortening the Process time affects. Excessive negative pressure, i. H. at Differential pressures from about 550 to 700 mbar lead to  Loss of sulfuric acid due to 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 H ₂ SO _{4 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 dilute sulfuric acid.

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

Since the crosslinking of the styrene-divinylbenzene used Polymers based on their degree of crosslinking and therefore yours Divinylbenzene content depends, further research has been done regarding the influence of the degree of networking in relation performed on the properties of the process product.

Examples include styrene-divinylbenzene copolymers a divinylbenzene content of 2 and 4 wt .-% and a so-called monodisperse styrene-divinylbenzene polymer a divinylbenzene content of about 8%, which with a Swelling agent was added, examined, the holding time sulfonation, d. H. the response time and that Mass ratio of sulfuric acid to polymer varies were.

Basically, the result is that the Divinylbenzene content in the range between 2 and 8% by weight no significant influence on the quality of the activates and Yield. Both over the sulfonation period as well The pore structure can be targeted via the acid content to be changed. With short sulfonation times and comparatively low acid-polymer ratios are used when using styrene-divinylbenzene gel Polymer microporous activates with an increased Macro pore volume obtained. By changing these two Activated carbons can be used to control the process a deliberately different macroporous structure, however approximate match of the BET surface area and consequently generate appropriate adsorption capacity. About the Macroporous structure allows the adsorption rate Taxes. In the sulfonation of macroporous polymer,  d. H. of divinylbenzene polymer, especially that Mesopore volume of the activated spherical carbon to be produced can be set. A short hold time of about 20 min. during sulfonation extremely mesopore-rich Coke and activates with the same BET surface area, while a long hold time of about 90 minutes the mesopore fraction down to 1/3.

Claims (10)

1. Process for producing spherical activated carbon from gel-like or macroporous polymers based on divinylbenzene 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 of H ₂ SO ₄ : polymer calculated as pure substances at the start of sulfonation in the range of 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, that in step a) sulfuric acid and polymer for Sulfonation submitted together and on Sulfonation temperature to be heated. 3. The method according to claim 1, characterized, that in step a) the sulfuric acid initially submitted, heated to sulfonation temperature and the polymer to be sulfonated subsequently added becomes. 4. The method according to any one of the preceding claims, characterized, that the sulfonation for 20 to 40 minutes is carried out. 5. The method according to any one of the preceding claims, characterized, that the sulfonation takes place under negative pressure, especially with a pressure difference to the environment from 50 to 550 mbar. 6. The method according to any one of the preceding claims, characterized,  that the sulfuric acid used in step a) a Has a concentration between 54 and 96%. 7. The method according to any one of the preceding claims, characterized, that agitation of the reactant by moving in particular rotation of the reaction vessel takes place. 8. The method according to any one of the preceding claims, characterized, that the pyrolysis in step b) under a Nitrogen atmosphere takes place. 9. The method according to any one of claims 1 to 7, characterized, that the pyrolysis in step b) under one Compound nitrogen and water vapor Atmosphere. 10. The method according to claim 9, characterized in that the atmosphere in the pyrolysis in step b) further contains CO ₂ .