Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2000-05-09
2001-10-09
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S486000, C528S50200C, C528S503000
Reexamination Certificate
active
06300466
ABSTRACT:
BACKGROUND OF INVENTION
The present invention concerns the production of activated carbon from polymers with aromatic nuclei, in particular styrene-divinylbenzene copolymers.
Activated carbons have long been known and have a wide range of uses in the area of cleaning and purifying flue gases and waste water or sewage, such use being based on the high adsorption capability of the activated carbon. In general activated carbons have a wide adsorption spectrum. Such activated carbons are not optimised for a specific situation of use, but instead are to be inexpensively manufactured as a mass-produced product.
In contrast high-efficiency activated carbons are optimised for specific situations of use and involve correspondingly higher production costs.
It has been known for some years, for the production of activated carbons, to use polymers with aromatic nuclei, in particular styrene-divinylbenzene copolymers, as the staring materials.
EP 0 326 271 B1 discloses the production of activated carbon, in particular from styrene-divinylbenzene copolymers, wherein the copolymer is firstly treated with a large excess of fuming sulphuric acid or oleum for a prolonged period of time. After sulphonation has been effected, the polysulphonated copolymer is washed to remove excess acid and then dried. The activated carbons obtained have a multi-mode pore size distribution, that is to say the disclosed activated carbon simultaneously has pores of different pore sizes, although there is no disclosure of controlling the pore size distribution or appropriate influencing thereof.
WO 96/21616 discloses a process in which a styrene-divinylbenzene copolymer is pyrolysed or subjected to low-temperature carbonisation with 5 to 50% sulphuric acid at a temperature of up to 750° C. In contrast to the polysulphonation of the aromatic nuclei, which is the aim in EP 0 326 271 B1, as a preliminary step for the production of activated carbon, the amount of sulphuric acid to be used in accordance with WO 96/21616 is not even sufficient for complete monosulphonation of all aromatic nuclei. That however results in a comparatively high loss of mass during the pyrolysis operation, which means that the process is comparatively cost-intensive by virtue of the low level of yield. The pore size or the pore size distribution in the case of the activated carbon in accordance with WO 96/21616 are not mentioned.
SUMMARY OF THE INVENTION
Now, the object of the present invention is to provide a process for the production of activated carbon from polymers with aromatic nuclei, in particular styrene-divinylbenzene copolymers, which is economical to carry out and which results in activated carbon with improved properties.
DETAILED DESCRIPTION OF THE INVENTION
That object is attained by the process as set forth in the opening part of this specification, with the following steps:
a) sulphonating the polymer with aromatic nuclei with concentrated H
2
SO
4
, wherein the ratio of the mass of the concentrated H
2
SO
4
used to the mass of the polymer used is between 0.5:1 and 4:1,
b) filtering off the excess sulphuric acid after the sulphonation operation and coking or pyrolysing the sulphonated product; and optionally
c) activating the coke obtained by the coking or pyrolysing operation.
In that respect it is particularly preferred if in step a) the ratio of the mass of the concentrated H
2
SO
4
used to the mass of the polymer used is between 1:1 and 4:1.
A particular advantage of the process according to the invention is that, after sulphonation has been effected, the polymer only has to be subjected to the filtration step in respect of the excess sulphuric acid, and the polymer does not have to be washed, while at the same time the total yield of activated carbon obtained is sufficiently high. At the same time it is possible to operate with commercially available sulphuric acid which represents an extremely favourable starting material, while the excess sulphuric acid can be used again for subsequent sulphonation operations. It was surprisingly found that activated carbons with different property profiles can be specifically produced by varying the reaction conditions in the procedure for the production of the activated carbon.
In a preferred embodiment of the process according to the invention the polymer is mixed with concentrated H
2
SO
4
in step a) at ambient temperature for the sulphonation operation and heated to a sulphonation temperature in the range of between 110 and 160° C. In that operation, heating to the sulphonation temperature is effected at a rate of between about 3 and 20 K/min, preferably at a rate of between 10 and 20 K/min and particularly preferably at a rate of 15 K/min. As a result, an activated carbon comprising individual particles which are sintered together, with a comparatively porous structure, is obtained.
It is further preferred if the mixture of polymers and concentrated sulphuric acid is kept at the sulphonation temperature for a period in the range of between 0 and 60 min.
The high degree of sintering can further be influenced by the amount of sulphuric acid used being limited. Therefore, to achieve a high degree of sintering, it is preferred if the ratio of the mass of the concentrated sulphuric acid used to the mass of the polymer employed is between 1:1 and 2:1.
After the excess sulphuric acid has been filtered off from the sulphonated product, it is raised to a temperature of between 650 and 850° C. in step b) for the coking or pyrolysis operation, preferably a temperature in the range of between 700 and 800° C. It is particularly preferred for pyrolysis to be implemented at a temperature of 750° C.
The degree of sintering of the activated carbon is surprisingly also influenced by the speed at which the sulphonated product is heated to the pyrolysis temperature and by the holding time at the pyrolysis temperature. To obtain sintered bodies therefore a comparatively low heating rate and a comparatively short holding time at the pyrolysis temperature are the most appropriate. The sulphonated polymer is therefore raised to the pyrolysis temperature at a rate of between 1 and 10 K/min, preferably at a rate of between 5 and 10 K/min and particularly preferably at a rate in the range of between 8 and 10 K/min. In a preferred embodiment of the process according to the invention the pyrolysis temperature is held for a period of between 2 and 10 min, in particular for a period of between 3 and 7 min.
In a further particularly preferred embodiment of the present invention in step a) the polymer is mixed with concentrated sulphuric acid at ambient temperature for sulphonation and heated to a sulphonation temperature in the range of between 130 and 300° C., preferably sulphonation temperature in the range of between 130 and 200° C. The result obtained was surprisingly an activated carbon which is not sintered together and which is capable of trickle flow and which in addition has pores of extremely small diameter. It was surprisingly found that the condition of trickle flow capability occurs when the sulphur content in the pyrolysis coke is greater than 4%.
In a preferred configuration of this alternative form of the process, the step of heating to the sulphonation temperature is effected at a rate of between about 3 and 20 K/min, preferably at a rate of between 10 and 20 K/min.
To obtain a small pore radius in the activated carbon it is preferable for pyrolysis to be terminated after the pyrolysis temperature is reached. It is further preferable if the ratio of the mass of the concentrated sulphuric acid used to the mass of the polymer used is 2:1. This embodiment of the process according to the invention also provides that pyrolysis is effected at a temperature in the range of between 650 and 850° C., preferably in a temperature range of between 700 and 800° C. and particularly preferably at 750° C. It is however preferred if heating to the pyrolysis temperature is effected at a rate of between 20 and 50 K/min, preferably at a rate of 50 K/min, as the tendency to sintering is less with a higher heating
Heschel Wolfgang
Muller Dirk
Helsa-Werke Helmut Sandler GmbH & Co. KG
Hoffmann & Baron , LLP
Truong Duc
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