PROCESS FOR THE PRODUCTION OF HIGH-QUALITY ACTIVATED CARBONS AS WELL AS ACTIVATED CARBONS PRODUCED ACCORDING TO THE PROCESS

Abstract

A process for the production of high-quality activated carbons from carbonized, self-regenerating, carbon-containing biomasses selects the carbonized biomasses from HTC carbon from fruit stones and HTC carbon from nut shells. The carbonized biomasses together with potassium hydroxide, sodium hydroxide or a mixture of both hydroxides as activator are subjected to a heat treatment at temperatures at which the activator exists in the form of a melt. The activator and the carbonized biomasses are present in a weight ratio of 0.5:1 to 6:1 at the beginning of the heat treatment.

Claims

1. An activated carbon produced by a process for producing activated carbons from carbonized, self-generating carbon-containing biomasses, the process comprising: (a) selecting the biomasses from hydrothermal carbonized (HTC) carbon from fruit stores or hydrothermal carbonized (HTC) carbon from nut shells; and (b) subjecting the biomasses together with potassium hydroxide, sodium hydroxide, or a mixture of potassium hydroxide and sodium hydroxide as activator to a heat treatment at temperatures where the activator exists in a form of a melt; wherein the activator and the biomasses are present in a weight ratio of 0.5:1 to 6:1 at commencement of the heat treatment according to claim 1.

2. The activated carbon according to claim 1, wherein the activated carbon has a specific surface of greater than 700 m.sup.2/g.

3. The activated carbon according to claim 2, wherein the specific surface is greater than 1,000 m.sup.2/g.

4. The activated carbon according to claim 2, wherein the specific surface is greater than 2,000 m.sup.2/g.

5. The activated carbon according to claim 2, wherein the specific surface is greater than 2,500 m.sup.2/g.

6. The activated carbon according to claim 1, wherein the activated carbon has a pronounced micropore structure.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] Further advantages and advantageous configurations may be inferred from the examples hereinafter and the claims. The examples serve for explanation of the invention and are not intended to limit it in any way.

EXAMPLES

Example 1

[0031] HTC carbon from cherry stones was introduced together with pure potassium hydroxide in a weight ratio of 4:1 potassium hydroxide to HTC carbon into an activation reactor and homogenized. Both the HTC carbon and the potassium hydroxide had been previously ground in a mill. The particle size of the HTC carbon was approximately 1 mm on the average. The mixture was heat-treated at 600 C. in a furnace for 2 hours. The activation conditions were selected in such a way that the potassium hydroxide was completely melted within the shortest time, so that the heat treatment took place in the presence of the melt for approximately 2 hours. After the cooling, the obtained activated carbon was rinsed with deionized water and dried for several hours in an oven at 105 C. The yield of activated carbon was approximately 20%, starting from the HTC carbon.

[0032] The activated carbon was investigated with respect to its physical properties and its adsorption capacity. The specific surface, the bulk density and the ash content were determined. In addition, the adsorption capacities for heavy metals, phenol and chloroform as well as the iodine number were determined. The following values were obtained:

TABLE-US-00001 specific (BET) surface 2,910 m.sup.2/g bulk density 0.16 g/mL ash content 5 wt % maximum chloroform load 0.97 g/g maximum Cu.sup.2+ load 47.8 mg/g maximum phenol load 50.1 mg/g iodine number 1,016 mg/g

[0033] The obtained activated carbon has not only a very large specific surface of 2,910 m.sup.2/g with a value of 0.97 g/g for the maximum chloroform load, but also a very large capacity for adsorption of chloroform. Comparison measurements undertaken on a commercial activated carbon, which was produced by means of pyrolytic carbonization of the biomasses and subsequent gas activation, yielded only a specific (BET) surface of 1,100 m.sub.2/g and a maximum chloroform load of 0.43 g/g. The capacity for the adsorption of copper, with a maximum load of 47.8 mg/g, was also higher in the comparison with the 12.1 mg/g for the commercial activated carbon.

[0034] In addition, the porosity of the obtained activated carbon was determined. For this determination, it was found that approximately two thirds of the pore volume consists of micropores, which essentially have a diameter between 0.7 and 2 nm. With a proportion of more than 60%, the obtained activated carbon has a pronounced micropore structure. Thin structure is very advantageous, because the micropores are available for the adsorption of a large number of molecules and substances.

Example 2

[0035] The process was carried out as described under Example 1, except for the temperature of the heat treatment, which was 450 C. The yield was approximately 40%. For the obtained activated carbon, the following values were determined:

TABLE-US-00002 specific (BET) surface 1,140 m.sup.2/g maximum chloroform load 0.48 g/g maximum Cu.sup.2+ load 19 mg/g maximum phenol load 52.6 mg/g

Example 3

[0036] The process was carried out as described under Example 1, except for the temperature of the heat treatment, which was 500 C. For the obtained activated carbon, the following values were determined:

TABLE-US-00003 specific (BET) surface 1,290 m.sup.2/g maximum chloroform load 0.56 g/g

Example 4

[0037] The process was carried out as described under Example 1. Instead of HTC carbon from cherry stones, HTC carbon from hazelnut shells was used. The yield was approximately 12%. For the obtained activated carbon, the following values were determined:

TABLE-US-00004 specific (BET) surface 1,998 m.sup.2/g maximum chloroform load 0.90 g/g

Example 5

[0038] The process was carried out as described under Example 1. Instead of HTC carbon from cherry stones, HTC carbon from coconut shells was used. The yield was approximately 30%. The specific (BET) surface reached 2,579 m.sup.2/g.

Comparison Example

[0039] HTC carbon from cherry stones was activated in an aqueous solution of 0.5 M, 1 M or 2 M potassium hydroxide at 30 C. Then the potassium hydroxide solution was filtered off. The reaction product was washed with deionized water and dried in an oven at 105 C. for several hours. In a determination of the specific surface according to the BET method, the obtained reaction produce did not exhibit any significant increase of the specific surface.

Example for HTC Carbon from Cherry Stones

[0040] Cherry stones with a water content of approximately 60% relative to the dry substance were used for the production of the HTC carbon. The Table 1 shows the composition of the cherry stones:

TABLE-US-00005 TABLE 1 Composition of the cherry stones Proportion by mass, relative to dry substance (mass %) Starting Hemicellulose substance Lignin and cellulose* Ash C H N S O Cherry 19.67 79.93 0.4 54.5 6.9 1 0.2 37 stones *Hemicellulose and cellulose together constitute 79.93%; only lignin and ash (inorganic content) were determined

[0041] The cherry stones were subjected to a hydrothermal carbonization with water and under pressure for one hour at 160 C. and then for 5 hours at 220 C. The yield after the hydrothermal carbonization was approximately 80%. An HTC carbon with a specific surface of approximately 20 m.sup.2/g was obtained, and its calorific value of approximately 25 MJ/kg is in the range of the fossil lignite.

[0042] The determination of the properties of the activated carbons was carried out according to the methods presented hereinafter.

Determination of the Specific Surface According to the BET Method:

[0043] The specific surface was determined via gas adsorption according to the BET method. For this purpose a multi-point BET instrument for recording the adsorption-desorption isotherms by means of nitrogen was used.

Measurement of the Chloroform Adsorption:

[0044] The determination of the capacity for the chloroform adsorption was carried out by means of gas flow through a glass cylinder that contained 0.3 g of the obtained activated carbon. A chloroform-enriched nitrogen, which was passed with a flow rate of 25 L/hour through the glass cylinder, was used as the flow medium. The change in the mass of the activated carbon was observed and the maximum chloroform load was determined by means of a balance.

Measurement of the Heavy Metal and Phenol Adsorption:

[0045] The determination of the maximum loading capacity was carried out respectively by means of aqueous solutions of copper sulfate and phenol in a concentration of 100 mg/L heavy metal sulfate or phenol. The obtained activated carbon was shaken for 24 hours in concentrations between 0.5 and 5 g/L in the aqueous copper sulfate or phenol solution in an overhead shaker at room temperature. Then the loading capacity was determined by optical emission spectrometry with inductively coupled plasma (ICP-OES).

Determination of the Porosity:

[0046] The characterization of the pore distribution was carried out by the variation profile of the isothermal nitrogen sorption at 77 K in the relative pressure range p/p.sub.0 between 0.0001 and 1. The absolute pore volume and, on the basis of the DR model (Dubinin Radushkevich), the total pore volume of pores with a diameter smaller than 2 mm were determined from the measured data. Then the isotherms of the CO.sub.2 sorption at 273 K in the relative pressure range p/p.sub.0 from 0.01 to 0.03 were determined. The measured data from the isothermal CO.sub.2 sorption were also evaluated on the basis of the DR model and yielded the pore volume proportion of pores with a diameter smaller than 0.7 nm.

[0047] All features of the invention can be essential to the invention both individually and also in any combination with one another.

[0048] Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.