DD245646A5 - PROCESS FOR THE PREPARATION OF ACTIVATED CARBON - Google Patents

Abstract

A process for producing charcoal from upgraded lignite prepared by subjecting the lignite to shear forces, solidifying the mass thus produced, and drying the mass to form a hard, relatively dense product comprises the steps of: (a) pyrolyzing the lignite treated lignite, preferably at a temperature of 350 to 500C; (b) activating the pyrolyzed product of step (a) by treatment with steam at elevated temperature, preferably 700 to 800 ° C; and (c) cooling the activated carbon product of step (b) in an inert atmosphere.

Description

Field of application of the invention

The invention relates to the production of activated carbon with a large effective surface of lignite.

Characteristic of the known technical solutions

Suitable reclaimed lignite can be obtained by the densification-hardening process of co-pending Australian application 24294/84 and application for a patent supplement thereto, No. PG 9283, filed February 14, 1985, a process in which U.S.P. Coal shear and extrusion in continuous form, for example, in a Sigma kneading machine HKS 50, manufactured by Janke & Dunkel GmbH & Co, KG IKA Biengen plant.

The above densification-hardening process provides a possibility to convert crude soft lignite into comparatively hard, abrasion-resistant solids. Briefly, in the notified process, lignite is subjected to shearing forces to produce a wet plastic mass which, for example, is solidified into pellets by extrusion subsequently dried to form a hard, relatively dense product which can be produced in any granular size and finish. Such solid granules or pellets, which are composed of treated lignite, are the most suitable starting materials for the production of activated carbons with great efficiency

Surface with the aid of the method according to the invention. The properties of the pellets used can be varied to suit the various quality requirements by the right choice of coals or by appropriate additives.

Although the raw lignite has a relatively high content of oxygen and hydrogen, the ratios of these elements to the carbon during pyrolysis, which is a part of the thermal activation process for producing activated carbons, can be substantially altered. At this stage, the chemical exclusion of water results in a final product having a comparatively high carbon content (of the order of 85%). The low ash content of many lignite from Victoria is also advantageous, so that the finished activated carbons have a relatively small proportion of inorganic elements. With existing processes activated carbon by the pyrolysis and subsequent steam activation of expensive starting materials, eg. B. high quality carbon, which are inherently strong and coherent, or made of coconut shells or peat. Lignite is not used. The cost of the materials used or certain prior art processing conditions are generally much higher than that of the brown coal processed by the above process. It has also been found that in the process according to the invention activation temperatures can be successfully applied which are some 50 to 100 ^° C. lower than those used in conventional processes.

Object of the invention

The invention provides a process comprising the pyrolysis of treated lignite and the subsequent activation to produce the required activated carbon and having technical-economical advantages over the prior art processes.

Explanation of the essence of the invention

The object of the invention is to develop a process for the production of activated carbon with a large effective surface of lignite.

According to one aspect of the present invention, starting materials are first obtained by processing lignite using the above-mentioned densification hardening method, or alternatively by a method in which only a part of the coal is kneaded (shear) and then the rest of the coal is put into this way obtained plastic mass is mixed in briefly.

According to another aspect of the invention, selected lignites are prepared by the above method. A starting pellet size of 2 to 3mm diameter is generally suitable.

The freshly extruded pellets are then allowed to dry at or near ambient temperature either in still air or with moderately agitated air (of the order of 0.1 m / s) to increase the drying rate. After 24 hours, about 80% of the moisture contained will have been removed by evaporation to the atmosphere. After a further two or three days, the pellets will reach approximately equilibrium water content (10 to 15%) and maximum strength. The latter varies greatly depending on the nature of the coal and the additives used during the preparation.

The dry pellets are then available for pyrolysis and activation to produce the desired effective surface area required for the intended applications.

According to a further aspect of the invention, the first process step consists of pyrolysis at temperatures ranging from 350 to 500 ° C in an inert gas stream (normally nitrogen), residual water, chemically developed water, low molecular weight organic compounds (predominantly phenols) and gases such as carbon dioxide To remove carbon monoxide and hydrogen. Negligible amounts of tar are generated.

After this pyrolysis treatment, further heating of the pellets to higher temperatures will only produce the gases hydrogen and carbon monoxide.

Activation consists of steaming, usually in the temperature range of 700 to 800 ^° C. For this purpose, steam is added to or injected into the nitrogen stream at a controlled rate by water at a temperature below the boiling point (usually 95 ° C) to thereby ensure the required partial pressure of water in the nitrogen. The mixed gas stream now has the ability to selectively erode portions of the pyrolyzed pellets to thereby provide very large internal surfaces and a microporous structure. Water gas reaction may play a role, and possibly other processes as well. The steaming is continued for several hours until the required inner surface has been developed. The carbon is cooled in the inert atmosphere.

The properties of granular activated carbons are usually evaluated in terms of nitrogen adsorption of the effective surface, iodine adsorption from aqueous medium, and drumming resistance in an aqueous phase. Table 1 shows a wide range of values of such properties obtained from samples prepared by the method of the invention.

Table 1 Comparative measurements of the effective surface of activated carbons

Sample (coals ausdem LatrobeTal) (4 h activation at 800 ⁰ C) unless otherwise indicated

Loy Yang, medium-dark 250-500 μη \ 150-250 μ, ιη

Low I ₂ -ZaM sample High I ₂ -ZaM _t sample prepared from 1 h of kneaded carbon

Loy Yang, medium dark - + 5% Mg (OH) ₂ , whole granules Morwell C92 (Maryvale)

The pH produced by an activated carbon when placed in an aqueous medium has some significance in determining the extent of adsorption of metal ions by the carbon. (See Table 2).

Effective surface iodine BET Nitrogen adsorption mg / g m ² / g 652 578 652 573 461st 459 901 800 764 679 1049 865 456 668 786 728 538 403

Table 2

pH measurements of water-dispersed coals and activated carbons

PH value

sample

coal

activated carbon

Loy Yang, pale-bright 3.8 Loy Yang, medium dark 3.0 + 2% NaOH and 5% HCHO + 5% Mg (OH) ₂ 3.0 Loy Yang, dark 3.2 + 10% Fe ₂ O ₃ 3.2 Morwell 5.4 Maddingley 7.1 + 5% Mg (OH) ₂ + 0.1% NaOH + 0.4% Na ₂ CO ₃

9.6

9.6

10.4

9.4

8.9

8.3

11.0

11.2

11.8

10.6

11.2

A variant of the method according to the invention relates to a procedure in which a magnetic activated carbon is produced, i. one in which the granules respond to an applied magnetic field so that efficient recovery can be made from a heterogeneous system.

According to another aspect of the present invention, the total energy consumed for grinding the coal can be reduced by kneading only a part of the coal and mixing the non-kneaded residue therewith.

As set forth in our co-pending Australian application PG 9107, there are opportunities to improve the compressive strength and abrasion resistance of dried compacted carbon granules with appropriate additives. The possible degree of improvement varies depending on the origin of the coal and its natural pH.

In general, minor effects achieved by additives are not manifest as significant improvements in breaking strength or total effective surface area of activated carbons.

However, when significant effects have been achieved by suitable additives, they are also transferred to the final products and provide significant improvements.

embodiments

Preferred embodiments of the invention are illustrated by the following non-limiting examples.

example 1 Improvements made in terms of the strength of activated carbons by suitable additives

A series of activated carbon samples were prepared using the following detailed procedure. 200 g of slush-wet coal was kneaded for 5 hours in a slow-speed kneading machine to obtain a wet plastic mass, which was then extruded through a 3 mm diameter die attached to a hand-operated screw extruder. In cases where an additive was required, it was added at the beginning of the attrition period. The amount of addition was calculated in terms of% by mass with respect to the dry matter of the coal. The extruded pellets (cut into appropriate lengths) were allowed to sit in a quiescent atmosphere at 20 ^° C. for one week

dry to develop their maximum strength and reach the moisture balance with the atmosphere (usually in the range of 10 to 15%).

The pellets were next pyrolyzed at 400 to 450 ^° C. and the resulting water and the low molecular weight organic compounds developed were removed using a blanket gas stream (usually nitrogen). The activation process consisted of erosion in the steam-enriched nitrogen stream at a temperature approaching 750 ° C. The partial pressure of the vapor was determined by saturating the flow of nitrogen while passing through water maintained at a temperature of 95 ° C. The activation was continued for a period of four hours and the pellets were cooled in an inert atmosphere.

The pellets were tested by determining their compressive strength in the initial dried state and after activation, and measuring the uptake of iodine from aqueous medium (the iodine value). The iodine value is the number of milligrams of iodine adsorbed by a gram of carbon from a 0.05N aqueous iodine solution when the iodine content of the remaining filtrate is not less than 0.02N. For the measurement, the carbon is finely ground, a sieved fraction taken and the contact with the iodine solution limited to a fixed short period of time. The values of iodine number are said to be numerically approximately the same as the effective surface area (in m ² / g) as determined by BET nitrogen adsorption method.

Table 3 shows the measurements made on samples made from a selection of Victoria lignites, Loy Yang, Morwell and Maddingley.

Table 3 pH additive Compressive strength MPa after 4 h of steam iodine Dimensions coal getrockn. activation number loss getrockn. granules mg / g % 56 Loy Yang borehole 47 (1276) - 10 67 832 63 pale light - 12 901 63 medium-dunkel3,2 - 20 76 841 60 dark 2% NaOH + 5% 75 medium-dunke! HCHO 60 690 59 5% hexamine 29 649 59 • (NH ₄ OH + 60 HCHO) 49 0.4% Na ₂ CO ₃ -13 10 840 62 - 57 786 70 Morwell 5.4 - 29 568 94 Maddingley 7.1

The above table shows the range of compressive strengths (10 to 60 MPa) found on dried granules which had not been modified with any additive. While the weaker (acid) coals show a significant improvement in strength after pyrolysis and steam activation, the more solid coals seem to lose strength after these treatments.

Double acting additives, as shown in Table 3 (i.e., pH enhancers and additional bridging-bonding species), not only improve the strength of the dried granules, but also result in very marked improvements in steam-activated strength Granules (Loy Yang, medium-dark). The improvement in strength is usually accompanied by a reduction in the effective surface area (as evidenced by lower iodine adsorption), but this can be tolerated in cases where unusually strong granules are required.

Suitable additives not only improve the compressive strength of activated carbons (see Table 3), but they can also significantly increase the abrasion resistance of activated carbon granules, as can be seen from the information in Table 4. In this case, the single additive ammonium hydroxide has achieved a significant improvement in the abrasion resistance of a relatively weak carbon derived from medium-dark Loy Yang coal.

1 mm 1-0.21 mm 0.21-0.075 mm 0.075 mm (1000 yams) (210-1000 atm) (75-21 Ομητι) (75 / Lim) 90.1 0.2 0.1 9.6 93.7 0.5 0.1 5.8 93.3 0.5 0.2 5.9 73.5 1.4 0.2 24.9 80.9 1.3 0.3 '17.5 89.5 1.0 0.2 9.4

Table 4 Comparative abrasion tests on activated carbon

5g sample, 30ml of water were spun in a 250ml cylinder over the ends for 8 hours at 40rpm. sample

Loy Yang, medium dark

(a) low I ₂ -ZaIiI

(b) hohel _2- number Loy Yang, pale-light Loy Yang, medium-dark

(a) 1: 1 kneaded: not kneaded

(b) 1: 1 kneaded: unkneaded + 0.5 ⁰ ANH ₄ OH + 1.0% NH ₄ OH

Example 2. Improvements resulting from partial attrition

As modifications can be achieved by additives, it is also possible to vary the properties of dried granules and the activated carbons produced therefrom by varying the frying conditions. As already stated, such a change can consist in a prolonged kneading of only a part of the coal and a subsequent brief mixing in of the remainder of the coal in the plastic mass created in this way. Alternatively, the kneading time of the total mass of the coal can be varied considerably while still producing satisfactory end products. In either case, the energy spent for grinding the coal can be advantageously reduced in conjunction with other useful results (discussed in detail below).

The following procedure was used to study the effects of kneading only a portion of the coal: 200g of flooded coal, which had been reduced in size by passing once through a hammer mill, was divided into two equal parts of which one was kneaded for five hours in a sigma kneader, while the other was held until the end of this period and then blended briefly (2 minutes) in the plastic mass in the kneading machine. The extrusion and the subsequent treatment of the granules were carried out according to the procedure described in Example 1. The measurements made on these granules are shown in Table 5.

Table 5

sample Compressive strength, MPa iodine nach4h mg / g Dimensions % number steam activation loss getrockn. 832 65 granules 29 619 62 Loy Yang pale-bright 30 (a) 1: 1 kneaded: not kneaded 7 634 60 (b) 1: 1 kneaded: not kneaded 13 58 + 0.5% NH ₄ OH (c) 1: 1 kneaded: not kneaded 36 + 1% NH ₄ OH

It turns out that activated carbons of adequate strength can be obtained with large effective surfaces if only a part of the original coal is kneaded and this kneaded part is used as a binding phase for the remaining coal.

The activated carbons produced in this way have the considerable advantage that they absorb solutes much faster than those made from fully-kneaded coal. Obviously, the fragments of raw coal with their high porosity, even after pyrolysis, offer better penetration of solutes to the internal surfaces of the granules. The effect is shown in the following Table 6. ·

Table 6 Loy Yang, pale-light coal

sample

(a) fully kneaded

(b) 1: 1 kneaded: not kneaded

% Iodine absorbs 4h 1h 2h 3h 46.7 27.0 35.8 41.8 58.8 32.4 44.0 52.7

The time for kneading the coal can also be shortened considerably (from 5 h to 1 h), without a noticeable loss of compressive strength or the effective total surface area of the resulting activated carbons, as can be seen from the data in Table 7.

Table 7 Loy Yang, medium-dark coal

Kneading time h

Weight loss% at activation

Iodine number mg / g

Compressive strength MPa

60 64 63

764 860 901

41 58 47

Example 3. Improvements resulting from proper activation

As mentioned in the general description of the process, the activation consists of treating the dried and pyrolyzed granules with high temperature steam, which is a constituent of an otherwise inert atmosphere. Important variables in the activation process are the partial pressure of the water vapor in the activation atmosphere, the temperature at which the activation is carried out and the treatment time. To study these variables, dried granules were prepared using the procedure detailed in Examples 1 and 2. After a preliminary pyrolysis, the granules were activated under varying conditions. The final products were evaluated for iodine value, and in some cases by measuring mass loss during activation, because this can vary quite considerably with the severity of the conditions. The results of the experiments with various lignites from Victoria are shown in Table 8.

Table 8

Lithotyp

Steam partial pressure (Temp

Steam generation ⁰ C

Activator, - (Temp.) ⁰ C

Temp. ⁰ C pH2, mmHg

75,289.1

95 633.9

100 760

Activation time h

iodine

of

production

of

mg / g

(I) LoyYang, pale light 75 800 3 540 100 800 3 1073 (II) LoyYang dark 75 800 3 562 100 800 3 1473 (III) LoyYang dark 95 710 4 837 (64.1% M.-Verl.) 95 800 4 1049 (65.9% M.-Verl.) (Iv) Morwell 95 680 4 690 (89.6% M.-Verl.) 95 800 4 786 (69.9% M.-Verl.) (V) LoyYang medium dark 95 800 1 759 95 800 4 998 (VI) Morwell 95 800 3 270 95 800 6 630 (VIl) Maddingley 95 800 V ₂ 350 + 5% Mg (OH) ₂ 95 800 1 572 95 800 4 507

Items (I) and (II) in Table 8 show the importance that the vapor partial pressure has for achieving effective activation. Increasing the relative partial pressure (see box below Table 8) from the 289 at 75 ° C corresponding to the 760 at 100 ° C, increased the effective surface area of activated samples by 2 to 2.5 times.

It might therefore be an advantage to apply the highest practical vapor partial pressure at which the process can be adequately controlled. If boiling water is used to provide the steam, activation will be very rapid and can lead to serious degradation of the granules. The process will therefore probably be most successful if the shielding gas stream has a relatively high partial pressure of the vapor but is not saturated with that ingredient.

The points (III) and (IV) that activation at temperatures above about 680 ° C can be achieved, but that the best results are obtained at about 800 ⁰ C show in Table 8 below. Under 68O ⁰ C, the activation times become unreasonably long. ,

Within limits, the effective surface area achieved is related to percent mass loss during activation. Too much mass loss can lead to smaller areas because the structure of the carbon is removed. Points (V), (Vl) and (VII) in Table 8 indicate that the effective surfaces are significantly increased by longer exposure times of the activating gas in the range of 1 to 6 hours. However, the effects depend on the origin of the coal. Loy-yang coal, which gave granules that were relatively weak at the beginning, achieves a high effective surface in a relatively short time, but the effects are reduced after a longer exposure time. Morwell coal, which gives solid dried granules, gives low effective surface area with short exposure times, but reacts well for extended exposure. Maddingley coal appears to reach a maximum effective surface area after an activation time of about one hour, with a decrease in the active surface upon prolonged activation. '[

Example 4. Magnetic activated carbon

The recovery of activated carbon granules (or fragments thereof) from heterogeneous systems, such as suspensions of minerals in water, is facilitated as the carbon responds to an applied magnetic field. An activated carbon having this property was produced from lignite by incorporating fine iron oxide during the preparation of the granules. The manufacturing process was similar in detail to that of Example 1 above using Loy Yang dark lithotype coal. While kneading the coal, 10 mass% of fine iron oxide was added to the wet plastic mass and mixed thoroughly therewith. The granules prepared in this way dry in the normal way, and during the pyrolysis and the activation a sufficient reduction of the iron oxide, so that the granules respond strongly to a magnetic field. The reduction is believed to be due to the hydrogen and carbon monoxide being developed during the heating of the coal. From a functional point of view, the presence of the reduced iron phase does not have serious adverse effects on either the strength or the achievable effective surface area of the granules. The magnetic properties of the activated carbons are not destroyed by immersion in aqueous medium, and in fact it has proved extremely difficult to extract any appreciable portion of the iron with effective metal or oxide solvents. The magnetic properties were perfectly preserved after such extractions

 The properties are shown in Table 9.

Table 9 coal Dimensions Compressive strength MPa after acti four. iodine loss due to activation before acti four. 67 33 number mg / g Loy Yang, dark Loy Yang, dark + 10% Fe ₂ O ₃ 60% 59% O CN CN CN 841 545

Both preparations (with and without Fe ^ O ₃₎ are gaining strength in the activation, the latter slightly less than the former. The erosion during activation is somewhat reduced by the presence of iron, and this is evidenced by a significantly lower effective surface area; however, harder activation conditions could be used to create a larger surface area as needed.

It is to be understood that the invention in its broader aspects is not limited to the specific details set forth therein.

Claims (9)

Invention claim: A process for producing activated carbon from upgraded lignite prepared by subjecting lignite to shearing forces, solidifying the mass so produced, and drying the mass to produce a hard, relatively dense product; characterized in that the method comprises the following steps: (a) Pyrolysis of the processed lignite (b) activating the pyrolyzed product of step (a) by treatment with steam at elevated temperature; and (c) cooling the activated carbon product of step (b) in an inert atmosphere. 2. The method according to item 1, characterized in that the pyrolysis step (a) is carried out at a temperature of 350 to -500 ° C in a protective gas stream. 3. The method according to item 2, characterized in that it is the inert gas is nitrogen. 4. The method according to any one of the items 1,2 and 3, characterized in that the activation step (b) is carried out at a temperature of 700 to 800 ⁰ C. 5. The method according to item 3, characterized in that the pyrolysis step (a) is carried out in a stream of nitrogen and the activation step (b) is carried out in the presence of the nitrogen stream added steam. 6. The method according to item!, Characterized in that it comprises the following steps: (a) treatment of lignite by subjecting it to shearing forces, solidifying the mass thus produced, and drying the mass to form a hard, relatively dense product; (b) pyrolyzing the product of step (a); (c) activating the pyrolyzed product of step (b) by treatment with steam at elevated temperature; , · (d) cooling the activated carbon product of step (c) in an inert atmosphere. 7. Method according to item 1, characterized in that it comprises the following steps: (a) treatment of lignite by subjecting it to shearing forces, solidifying the mass so produced, and drying the mass to form a hard, relatively dense product; (b) pyrolyzing the product of step (a) in a stream of nitrogen at a temperature of 350 to 500 ^° C; (c) activating the pyrolyzed product of step (b) by treatment with the nitrogen stream added steam at a temperature of 700 to 800 ⁰ C; (d) cooling the activated carbon product of step (c) in an inert atmosphere. 8. Method according to item 1, characterized in that it comprises the following steps: (a) treating a quantity of lignite by subjecting a portion of it to shear, then mixing the treated portion with the remainder of the mass to produce a plastic mass, solidifying the mass so produced, and drying the mass to form a hard, relatively dense product; (b) pyrolyzing the product of step (a); (c) activating the pyrolyzed product of step (b) by treatment with steam at elevated temperature; (d) cooling the activated carbon product of step (c) in an inert atmosphere. 9. Method according to item 1, characterized in that it comprises the following steps: (a) treating a quantity of lignite by subjecting a portion of it to shearing forces, then mixing the treated portion with the remainder of the mass to produce a plastic mass, solidifying the mass so produced, and mass to form a hard, relatively dense one Product is dried; (b) pyrolyzing the product of step (a) in a stream of nitrogen at a temperature of 350 to 500 ^° C; (c) activating the pyrolyzed product of step (a) by treatment with the nitrogen stream added steam at a temperature of 700 to 800 ⁰ C; (d) cooling the activated carbon product of step (b) in an inert atmosphere.