WO2001049604A1

WO2001049604A1 - A process for preparing activated carbon from urban waste

Info

Publication number: WO2001049604A1
Application number: PCT/IL2000/000001
Authority: WO
Inventors: Yaakov Berman
Original assignee: Katz, Raul; Maavar K.B. Recycling And Production Of Carbon Ltd.
Priority date: 2000-01-03
Filing date: 2000-01-03
Publication date: 2001-07-12
Also published as: AU1887500A

Abstract

A process for the preparation of activated carbon from urban waste comprising: a) sorting the waste to remove foreign materials; b) reducing the size of the waste particles; c) drying the waste under anaerobic conditions at a temperature comprised between about 100 °C - 150 °C; d) pyrolysing the waste of step (c) at a temperature of 110 °C and above whereby to obtain a powdery charcoal product; e) Agglomerating the powdery product obtained in step (d); f) carbonizing the agglomerated particles obtained in step (e) above under anaerobic conditions at a temperature of about 110 °C and above; g) activating the agglomerated particles of step (f) above by contacting the same with steam and CO2 at a temperature in the range of 750 °C-900 °C; h) purifying the particles of step (g) above by rinsing the same in an aqueous acidic solution and subsequently with water; and i) drying the activated carbon particles to reduce their water content to a value not higher than 8 %.

Description

A PROCESS FOR PREPARING ACTIVATED CARBON FROM

URBAN WASTE

The present invention relates to an improved process for preparing activated carbon from urban waste, and to activated carbon prepared thereby.

Background of the Invention

The increasing amount of urban waste produced daily has brought forth the need to find improved solutions to the conventional waste disposal methods of lanclfilling and incineration.

A large scale improved solution currently applied is the recycling for re-use of certain components of the waste, such as metals, glass and plastics. However, this type of recycling does not provide a solution for a major component of the waste, viz., waste from botanical sources (wood scrap, fruits, vegetables, food, vegetation etc.) -and paper product waste, which together with plastic waste constitute the organic fraction of urban waste. An effective solution for the recycling of the organic fraction of urban waste is the use of said fraction as raw material in conversion processes which convert organic waste into economically valuable products. Such a process is a pyrolysis which thermally converts organic waste to charcoal, as a primary product, and to other by-products known as pyrolytic gases and liquids, which have a low commercial value.

U.S. patent 4,077,847 discloses a solid waste disposal system which sorts urban waste and produces via flash pyrolysis char and pyrolytic oils from the organic fraction of the waste. EP 69,159 discloses a pyrolysis process for organic waste which produces charcoal and pyrolytic products, which are recycled for use in the pyrolytic process. The charcoal produced in pyrolytic processes can be used as raw material for preparing activated carbon. The charcoal produced in the aforementioned processes, however, has a high ash content, and therefore the activated carbon produced from such charcoal is characteristically soft and brittle and of poor quality.

Among the characteristics which determine the quahty of activated carbon are the ash content, the pore volume and the hardness. Activated carbon which is hard, contains a low percentage of ash and has high pore volume is considered to be of high quahty. The ash content of the charcoal produced by pyrolysis directly influences the quality of the activated carbon prepared from the charcoal. Charcoal containing 10-20% ash is considered to be excellent quahty charcoal. Thus, the activated carbon prepared from this charcoal is also of prime quahty.

It is a purpose of the present invention to provide an improved pyrolytic process of urban waste.

It is a further purpose of this invention to introduce an improved process for the preparation of charcoal of low ash content, from urban waste.

It is a further purpose of this invention to provide an improved process for the preparation of activated carbon.

It is still a further purpose of this invention to provide an improved process for the preparation of granulated activated carbon of low ash content, from urban waste.

It is yet another purpose of this invention to provide an improved process for the preparation of granulated activated carbon of high quality, from urban waste. Other objects of the invention will become apparent as the description proceeds.

Summary of the Invention

According to the present invention the organic fraction of urban waste is converted to activated carbon via an improved pyrolytic process. The activated carbon produced has a low ash content, high pore volume and improved hardness. Hence, the activated carbon of the present invention possesses superior characteristics.

In one aspect, the invention is directed to a process for the preparation of activated carbon from urban waste comprising the steps of:

a) Sorting the waste to remove foreign materials;

b) Reducing the size of the waste particles;

c) Drying the waste under anaerobic conditions at a temperature comprised between about 100°C - 150°C;

d) Pyrolysing the waste of step (c) at a temperature of 110°C and above whereby to obtain a powdery product;

e) Agglomerating the powdery product obtained in step (d);

f) Carbonizing the agglomerated particles obtained in step (e) above under anaerobic conditions at a temperature of about 110°C and above;

g) Activating the particles of step (£) above by contacting the same with steam and CO2 at a temperature in the range of 750°C-900°C; h) Purifying the particles of step (g) above by rinsing the same in an aqueous acidic solution and subsequently with water; and

i) drying the activated carbon particles to reduce their water content to a value not higher than 8%.

Unless otherwise specifically indicated, all percentages given herein are by weight, and all ratios between various process components are also by weight.

The urban waste referred to herein includes various types of waste produced in the urban environment. For the purpose of this invention urban waste is defined as waste which includes domestic waste and commercial waste but does not include industrial waste. In this context, domestic waste includes waste produced in an average normal household which comprises food waste, paper products and packaging, plastic products, wood, glass and metal. Commercial waste is the waste produced by the commercial sector, including food establishments, markets, grocery stores and the like.

The term "foreign materials" is meant to indicate non-pyrolyzable materials, such as metal and glass, that may interfere with the process.

Brief Description of the Drawings

Fig. 1 is a block diagram of a preferred embodiment of the process according to the present invention.

Detailed Description of the Invention

According to the initial stage of the process according to the present invention, the waste is sorted to remove foreign materials therefrom. The waste is then shredded to particle size which is generally of about 2cm x 2cm x 2cm. Particles having smaller dimensions are also suitable according to the present invention, and may be preferred as they allow the subsequent drying step to be completed more rapidly.

The particulate waste is dried at a temperature of about 110°C and is subsequently transferred to the pyrolysis vessel. The pyrolysis temperature is at least 110 °C, and preferably above 140 °C, the lower value being suitable to convert waste products made of carton and the like into charcoal. According to one variant of the present invention, the pyrolysis is a two stage process conducted at a temperature, preferably, in the range of 140°C to 500°C, in which primary pyrolysis takes place at about 160°C and in the second stage the temperature reaches 390°C. The total duration of the pyrolysis stage depends on the method of heating the pyrolysis vessel. When the vessel is heated by means of a heating jacket, the pyrolysis generally lasts between 50 minutes to 2 hours. Internal heating, by means of direct contact with gases, may also be employed according to the present invention.

Optionally, matter made of polymeric materials, typically, plastics and rubbers, are removed prior to and/or subsequent to any one of the pyrolysis stages.

The charcoal produced in the pyrolysis is crushed to a mean particle size up to about 0.01mm to yield a powdery product. The ash content of said charcoal is between 9-20%. According to one embodiment of the invention, the charcoal powder obtained may be treated by methods known in the art to decrease its ash content.

The charcoal powder obtained is subjected to an agglomeration process, to obtain compact particles of larger dimensions. The agglomeration process is generally accomplished by either a granulation procedure or an extrusion procedure, the latter being the preferred mode of agglomeration. According to a preferred embodiment of the invention, a mixture of the charcoal powder, water and oil is extruded, the weight ratio between the ingredients being about 1:0.7:0.15, respectively. Particularly suitable oils according to the present invention are oils derived from coal or oils that are produced by the pyrolysis of wooden material. These oils are identified by the Russian standard TOCT 22989-78, which provides the specification of binders for the manufacture of activated carbon.

The subsequent stage according to the process of the present invention is the carbonization of the agglomerated particles, which is carried out under anaerobic conditions at temperatures of 110°C and above, and preferably, in the range of 110°C to 600°C, most preferably about 180 °C. The duration of the carbonization stage is preferably between 50 minutes to 90 minutes.

According to the process of the present invention, the following stage is the activation of the agglomerated particles, which is carried out at a temperature in the range between 750 °C to 900 °C, preferably between 780°C to 850 °C, by contacting said particles with steam and CO₂, preferably under anaerobic conditions.

According to a preferred variant of the present invention, the agglomerated particles are first brought into contact with steam the temperature of which is between 300 °C to 500 °C. Subsequently, the particles and the steam are introduced into an activation zone, together with CO₂. Preferably, nitrogen is also fed into the activation zone. Quantitatively, the preferred ratio between the weight of the agglomerated particles (as weighed prior to the carbonization stage) and the weight of steam used in the activation stage is 1:1. Preferably, the CO₂ gas is introduced into the activation zone at temperature between 300°C to 500 °C, at a rate of about 15 liter/hour, per 1 kg of agglomerated particles, as weighted prior to the carbonation stage. Preferably, nitrogen is introduced into the activation zone at temperature of about 300°C to 500 °C, at a rate of about 60 liter/hour, per 1 kg of agglomerated particles, as weighed prior to the carbonation stage.

The activation zone is provided by any acceptable drier, such as drum drier, continuous drum drier, a fluidized bed or spouted bed. The heat required for this stage may be provided, according to one embodiment of the invention, by electrical means, in which case the temperature of the activation will preferably be in the range of 820 °C to 850 °C and its duration will be about 140 to 160 minutes. Alternatively, the combustion gases that are emitted from previous stages are fed into the activation zone, either as a co-current flow or a counter-current flow, to heat said activation zone. In this case the temperature of the activation will preferably be in the range of 780 °C to 850 °C and its duration will be about 80 to 100 minutes The latter variant renders the addition of the nitrogen redundant, and also reduces the amounts of CO₂ which should be introduced into to the activation zone.

The final purification of the activated carbon is carried out by rinsing the same with an aqueous acidic solution that is preferably HC1 solution at a concentration of 5%-37%, more preferably 20%, which solution is heated to a temperature of about 60 °C. The purification results in reducing the ash content of the agglomerated particles to a value in the range of 2%-7%. Subsequently, the particles are washed in water until the pH of the aqueous extract is between 3.5-7, as desired.

Preferably, the agglomerated particles of the activated charcoal are finally dried at a temperature of about 100°C to reduce the water content in said particles to a desired value which is typically in the range of 4%-8%, although lower values, such as 0.5%, are also obtainable.

In another aspect, the present invention provides particles of activated carbon having an ash content of 2%-7%, a mean pore volume in the range of 0.95-1.2 ml/g as determined according to Kuleshkin, D. A. and Michaelova, C.C, "Activated Carbon", Leningrad Che ., 1972, BET surface area between 1200 to 1500 m²/g, a hardness in the range 85-95 as determined according to the method of Russian standard TOST 16188-70 and Iodine number above 1150mg/g, and preferably between 1200 to 1250 mg/g.

Examples Example 1

The following example is illustrative of a preferred embodiment of the invention, with reference to Fig. 1, which is a block diagram of the process.

Urban waste (1500 kg) were sorted to remove foreign material (Fig. 1, stage 1). The weight after the sorting was 1100 kg. The remaining waste was then shredded to pieces approximately 2cm x 2cm x 2cm (Fig. 1, stage 2). The shredded waste was then introduced into a rotating drum which was heated to 110°C through an external heating jacket under anaerobic conditions for 90 minutes (Fig. 1, stage 3). The partially dried waste was pyrolized initially at about 160°C and then at about 390°C for about 2 hours (Fig. 1, stage 4). The pyrolysis product, charcoal, weighed 100 Kg and was loaded into an extruder (model: LUK 2.5 K, manufactured by WERNER & PFLEIDERER, Germany) together with 70 kg of oil and 14 liters of water (Fig. 1, stage 5). 184 kg of the agglomerated particles having a mean particle diameter of 1.2 mm were obtained. These particles were then carbonized at about 180°C for about 50-75 minutes, under anaerobic conditions to yield 110 kg of dried particles (Fig. 1, stage 6). The activation was conducted at about 790 °C in the presence of steam and combustion gases for about 80 to 110 minutes. The combustion gases were mixed with gases emitted during the initial drying stage (Fig. 1, stage 7). 70 Kg of activated particles were obtained. The activated carbon granules were then washed in an aqueous 10% HC1 solution until the ash content was 2.1%-4.5% (Fig. 1, stage 8). The granules were then rinsed with water until the water extract had a pH of 3.5-5 (Fig. 1, stage 8). Finally the activated carbon was dried at about 100°C until the water content of the particles was 4%-8% (Fig. 1, stage 9). 55 kg of activated carbon were produced possessing the following characteristics:

TABLE I

Example 2

Urban waste was sorted to remove foreign material. The remaining waste was then shredded to pieces approximately 2cm x 2cm x 2cm. The shredded waste was then introduced into a rotating drum which was heated to 110°C through an external heating jacket under anaerobic conditions for 90 minutes. The partially dried waste was pyrolized initially at about 160°C and then at about 390°C for about 2 hours, under anaerobic conditions. The pyrolysis product, charcoal, weighed 2.6 Kg and was loaded into an extruder (model: LUK 2.5 K, manufactured by WERNER & PFLEIDERER, Germany) together with 1.4 Kg of oil (product of wood pyrolysis, according to TOCT 22989-78) and 300 ml of water. 4.3 Kg of the agglomerated particles having a mean particle diameter of 1.2 mm were obtained. These particles were then carbonized, under anaerobic conditions, in electrically heated drier at temperature of about 180°C for about 50-75 minutes. The particles leaving said drier were fed into a small vessel, into which steam was introduced at a rate of 0.4 kg/hour at temperature of 400°C. This mixture was subsequently fed into a drier which was electrically heated to a temperature of 820 °C. CO₂ (temperature: 300°, feed rate: 0.9 liter/min) and N₂ (temperature: 300°, feed rate: 4 liter/min) were also added to said drier, to accomplish the activation, which lasts 150 minutes 1.6 Kg of activated particles were obtained. The activated carbon granules were then washed in an aqueous 20% HC1 solution until the ash content was 3.0%. The granules were then rinsed with water until the water extract had a pH of 6. Finally the activated carbon was dried at about 100°C until the water content of the particles was 1.3%, to yield 1100 g activated carbon.

All the above descriptions of preferred embodiments and examples of the invention have been provided for the purpose of illustration and are not intended to limit the invention in any way.

Claims

1. A process for the preparation of activated carbon from urban waste comprising : a) Sorting the waste to remove foreign materials; b) Reducing the size of the waste particles; c) Drying the waste under anaerobic conditions at a temperature comprised between about 100°C - 150°C; d) Pyrolysing the waste of step (c) at a temperature of 110°C and above whereby to obtain a powdery charcoal product; e) Agglomerating the powdery product obtained in step (d); f) Carbonizing the agglomerated particles obtained in step (e) above under anaerobic conditions at a temperature of about 110°C and above; g) Activating the agglomerated particles of step (f) above by contacting the same with steam and CO₂ at a temperature in the range of 750°C-900°C; h) Purifying the particles of step (g) above by rinsing the same in an aqueous acidic solution and subsequently with water; and i) Drying the activated carbon particles to reduce their water content to a value not higher than 8%.

2. A process according to claim 1, wherein the waste is dried at a temperature of about 110°C.

3. A process according to claim 1, wherein the pyrolysis is a two stage process in which primary pyrolysis takes place at about 160°C and in the second stage the temperature reaches up to 390°C for about 2 hours.

4. A process according to claim 1, wherein the powdery, charcoal is obtained by crushing the pyrolysis product to particles having a mean particle size of up to about 0.01mm. -12-

5. A process according to claim 1, wherein the charcoal produced in the pyrolysis stage having an ash content in the range 9-20% is treated to reduce its ash content.

6. A process according to claim 1, wherein agglomeration is carried out in an extruder with a charcoal:water:oil weight ratio of about 1:0.7:0.15.

7. A process according to claim 1, wherein carbonization is carried out at about 180°C under anaerobic conditions.

8. A process according to claim 1, wherein activation is carried out at a temperature between 780 to 850 for 80 to 150 minutes.

9. A process according to claim 8, wherein the activation is carried out by contacting the agglomerated particles with steam at temperature between 300°C to 500°C and subsequently introducing the same into an activation zone together with CO2 and nitrogen, said activation zone being electrically heated.

10. A process according to claim 8, wherein the activation is carried out by contacting the agglomerated particles with steam at temperature between 300°C to 500°C and subsequently introducing the same into an activation zone together with combustion gases that were emitted from the pyrolysis and carbonization stages, which gases contain CO₂ and nitrogen, said activation zone being heated by said combustion gases.

11. A process according to claim 1, wherein the rinsing aqueous acidic solution is a 5%-37% HC1 solution in water.

12. A process according to claim 1, wherein the activated carbon of step (h) is dried until the water content of the particles is in the range 4%-8%.

13. Activated carbon having an ash content of 2%-7%, a mean pore volume in the range of 0.95-1.2 ml/g, BET surface area between 1200 to 1500 m²/g, a hardness in the range 85-95 and Iodine number above 1150mg/g.