Title of Invention

"A PROCESS FOR PREPARATION OF ACTIVATED CARBON SPHERES

Abstract

This invention relates to a process for the preparation of activated carbon spheres. According to the process the precursor (styrene divenyl benzene) is dried in the precursor of Co2 gas. The dried precursor is subjected to the step of corbonisation in a plurality of stages followed by the step of activation. And then the activated precursor is subjected to the step of cooling in the precursor of nitrogen gas.

Full Text

FIELD OF INVENTION This invention relates to a process for preparation activated carbon spheres. INTRODUCTION Activated carbon spheres find applications in the field of pollution control, treatment of potable water, purification of chemicals and drugs, solvent recovery, protective uniforms and respirators meant for removal or toxic chemicals. Generally, activated carbon spheres are available in granular, powder or fabric forms. However, the active carbon sphere form has certain advantages over powdered active carbon like low resistance to flow, batter recovery and its reproducible properties by using polymeric precursor. The mechanical strength of the carbon sphere become critical in dynamic systems as granular and fabric forms, tend to lose structural integrity in dynamic systems due to abrasion and attrition. According to one of the process, known in the art, the activated carbon spheres are prepared using petroleum/coal tar pitch as precursor material. According to this process, a process for the preparation of activated carbon spheres comprises in the steps of drying the precursor, styrene divenyl benzene in the presence of Co2 gas , maintaining the flow of said Co2 at 1000 ml per minute and temperature between 110-130°C, raising the temperature at the rate of 1-2°C per minute, subjecting the said dried precursor to the step of carbonisation in a plurality of stages followed by the step of activation as herein described and then said activated precursor being subjected to the step of cooling as herein described. One of the main disadvantage is that the properties of precursor material varies depending the grade and composition of the crude oil or coal thus affecting the properties of end product also. In this known process, it is difficult to control the properties of the finally obtained active carbon spheres. Another disadvantage is that this process is quite cumbersome and requires an elaborate plant and machinery. Yet another disadvantage is that this process is not easy to adopt. According to another known process activated carbon spheres is prepared by spheronisation of pressure extruded pellets in a special plant. Tha extrusion compound consists of a mixture of fine powder of activated carbon sphere and a binder resin. Using the precursor material such as coal or activated carbon in finely divided form a paste is prepared by mixing the binder (pitch or resin) in a suitable quantity. This is then extruded as extruded cylinder cut in known lengths which are spheronized in a drum or disc granulator in a moist state. The spheres are then dried carbonized and activated if required. However, this process of preparing active carbon spheres, known in the art, also suffers from following disadvantages. Primary disadvantage of this known process is that the use of binder material adversely affects the surface properties of activated carbon. Yet another disadvantage of above process is that abrasion resistance of activated carbon spheres obtained by this process is lower than those achieved by pitch process. OBJECTS OF THE INVENTION Primary object of this invention is to provide a process for preparing activated carbon spheres from polymeric materials and which is a simple and easy process. Another object of this invention is to provide a process for preparing active carbon spheres which allows in situ carbonisation and activation of the precursor material. Yet another object of this invention is to provide a process for preparing activated carbon spheres, which have very high level of mechanical strength and high abrasion resistance. Still another object of this invention is to provide a process for preparing activated carbon spheres, which have higher adhesion to base fabric in case it is utilised for preparing protective uniforms. A further object of this invention is to provide a process of preparing activated carbon spheres, which have high efficiency of absorption and reproducible properties. STATEMENT OF THE INVENTION A process for the preparation of activated carbon spheres comprises in the steps of drying the precursor, styrene divenyl benzene in the presence of Co2 gas, maintaining the flow of said Co2 at 1000 ml per minute and temperature between 110-130°C, raising the temperature at the rate of 1-2°C per minute, subjecting the said dried precursor to the step of carbonisation in a plurality of stages followed by the step of activation as herein described and then said activated precursor being subjected to the step of cooling as herein described. DESCRIPTION OF THE PROCESS In accordance with the present invention the process of preparing activated carbon spheres comprises following steps. i) Drying of the precursor, polystyrene sulfonate The precursor material, styrene divenyl benzene copolymer (polystyrene sulfonate) is filled in a quartz tube fitted with standard B-19 fitting for passing CO2 gas. The average particle size of the chosen material is from 0.25mm to 1.50mm with average moisture content from 47-54%. The tube is pushed in a tubular roicroprocessor controlled furnace having heating capability from room temperature to 1000°C, The CCO2 gas flow is controlled using needle valve and digital mass flow meter. The CO2 flow is maintained at around 1000 ml per min-tte. The temperature of the furnace is raised at the rate of 1-2ºC per minute to cut off temperature of 110-130ºc. This higher cutoff temperature is maintained for about 30 minutes which results in removal of moisture. The drying is carried out in static bed condition. ii) Carbonisation of dried resin The dried resin is carbonised in two stages. In first step, the temperature is raised to 300—350°C at the rate of 2—4°C per minute. During this period, the bond moisture goes off and material gets partially carbonised. This higher temperature 300—350°C is maintained for about 30 to 60 minutes. In the second step of carbonisation, the temperature is raised to highest treatment temperature of 700—1000°C at the rate of 3—4°C per minute. In this step, the resin gets completely carbonised, tar formation takes place and micro pores are created in the resin. iii) Activation of the carbonised resin In this step, the carbonised resin is finally activated. During this process, tar is removed and new pores are created in addition to widening of the pores. The highest treatment temperature for activation process varies from 700 to 1000°C. The weight time ratio from resin to CO2, is varied from .004 to .4 kg. hour per mole and the residence time from two hours to 66 hours. The surface properties of the finally produced active carbon spheres can be controlled by optimising the process parameters like temperature, flow rate of CO2 and the residence time of CO2, flow. The activation is carried out in CO2 atmosphere in fluidised and static bed condition. Again the activation time can be optimised by controlling the flow rate of CO2, gas. A higher flow rate of the gas will require less activation time while a lower flow rate of CO2 will require higher activation time. iv) Cooling of the activated material The activated resin is suddenly cooled to room temperature by pulling the tubular reactor out of the heating zone. The cooling is done in the atmosphere of Nitrogen gas. The cooling is done for about half an hour till room temperature is achieved. The end product is characterised by utilising standard techniques by measuring CTC adsorption capacity, BET surface area and pour volume. The CTC adsorption capacity is defined by measuring amount of carbon tetra chloride absorbed per gram of activated resin at saturation. BET (Bruner, Emmett and Teller) surface area is measured using nitrogen as adsorbate at —196°C. Pore volume is measured in cm3 per gram by measuring the liquid nitrogen adsorbed at 0.95 of the saturation pressure. The process of present invention will now be illustrated with working examples which are intended to be typical examples to illustrate the working of the inventions and are not intended to be taken restrictively to imply any limitation on the scope of the present invention. WORKING EXAMPLES Example 1. 18 gm of precursor material, styrene divenyl benzene copolymer (polystyrene sulphonate) is taken in a tubular flow reactor. The tube is pushed in the microprocessor controlled oven and the temperature of the oven is raised up to 120°C at the rate of l.5ºC during drying process. The flow rate of the CO2 is maintained at the rate of 300 ml/minute. In the next step, during carbonisation process, the temperature is raised up to ml/minute. In the next step, during carbonisation process, the temperature is raised up to 300° C and the temperature is maintained for about one hour. Finally during activation step, the temperature is raised up to 850DC and the temperature is maintained for about six hours. The activation cycle is carried out in static bed conditions. Finally 4 gm active carbon spheres are achieved after cooling of the activated material under the presence of nitrogen gas. The properties of the active carbon spheres, thus achieved, are as follows: PROPERTIES OF THE ACTIVE CARBON SPHERES CTC adsorption capacity 70X BET surface area 700 m2/gm Bulk density 0.73 gm/cm3 Total pore volume 0.43 cm3/gm Yield on carbonised resin basis 40% EXAMPLE 2 The reactor is charged with 10 gm of precursor material Styrene divenyl benzene copolymer (polystyrene sulphonate) resin. The reactor is pushed into microprocessor controlled furnace and the temperature is raised to 125°C at the rate of 1.2°C/min. The flow rate of CO0 is maintained at the rate of 500 ml/min. In the next step, the temperature is raised upto 325°C and maintained for 45 mins. Finally during activation step the temperature is raised to 850°C at the rate of 3°C/min and the raised temperature is maintained for 24 hours. During this step, the resin is treated with CGU> at the rate of 80 ml/minute. Finally 1.1 gm of active carbon spheres are achieved after completion of the cooling of the activated material under the presence of nitrogen gas. The properties of the active carbon spheres thus achieved are as follows: PROPERTIES OF THE ACTIVE CARBON SPHERES CTC adsorption capacity 400/C BET surface area 2000 m2 /gm.. Bulk density 0.23 gm/cm0 Total pore volume 2.3 cm /gm Yield on carbonised resin basis 5.5% EXAMPLE 3 The reac tor is charqed with 58 gm of precursor material and is pushed into microprocessor controlled furnace. The temperature of the furnace is raised to 130ºC at the rat of .1 . 5ºC/m.in. The flow rate of CO2 is maintained at 1000 ml/min. In the next step, the temperature is raised to 340ºC and this raised temperature i» maintained for i hour. Finally, during activation step, the temperature is raised at 850°C at the rate of 4aC/min and maintained for 7, hours. The CO2 flow rate in activation step is maintained at 500 ml/min. At the end of the process, 24 gm active carbon spheres are achieved after completion of cooling of the activated material under the presence of nitrogen gas. The properties of active carbon spheres thus achieved are as follows: CTC adsorption capacity 55% BET surface area 600 m2/gm Bulk density 0.73 gm/cm3 Total pore volume 0.43 cm /gm Yield on carbonised resin basis 48% It is to be understood that the process of present invention is susceptible to adaptations, changes, and modifications by those skilled in the art. Such adaptations, changes, and modifications are intended to be within the scope of the present invention, which is further set forth by the following claims. I CLAIM: 1. A process for the preparation cf activated carbon spheres characterized by the step of drying the precursor (styrene divenyl benzene) of particle size of .25 mm to 1.50 mm., in the presence of CO2 gas, maintaining the flow of said CO2 at 1000 ml per minute and temperature between 110-130°C, raising the temperature at the rate of l.-2°C per minute, subjecting the said dried precursor to the step of carbonisation wherein first step of carbonisation is carried at a temperature of 300-350°C and raising the temperature at the rate of 2-4°C per minute arid the second step of the carbonisation is completed at the temperature of 700-1000°C, and raising the temperature at the rate of 3-4°C per minute in the presence of CO2 gas wherein said step of activation, weight and time ratio as herein described of resin to CO2 is maintained from .004 to .04 kg hour per mole and is maintained for a period of 2-66 hours, the said activated precursor is subjected to the step of cooling as herein described. 2. A process for preparing activated carbon spheres as claimed in claim 1 wherein the said step of cooling is carried out in the presence of nitrogen gas. 3. A process for preparing activated carbon spheres substantially as described herein.

Documents:

1212-del-1999-abstract.pdf

1212-del-1999-claims.pdf

1212-del-1999-correspondence-others.pdf

1212-del-1999-correspondence-po.pdf

1212-del-1999-description (complete).pdf

1212-del-1999-form-1.pdf

1212-del-1999-form-19.pdf

1212-del-1999-form-2.pdf

1212-del-1999-form-3.pdf

1212-del-1999-form-5.pdf

1212-del-1999-gpa.pdf