Development of A Batch Reactor For The Production Of A Activated Carbon From Coconut Shells

ABSTRACT

Nigeria currently imports large quantities of Activated Carbon (AC), for its domestic usage, despite abundance of agricultural wastes (coconut shells, palm kernel shells, etc), that can be used as raw materials. Short-circuiting of heating elements and absence of inert gases inlet have been identified as major challenges associated with AC production in Nigeria. This work was designed to develop a batch reactor incorporating functional materials for production of AC using locally sourced materials. 

Design parameters (refractory and insulator thicknesses, thermal stress and strain,  heat loss and heating rate) for 800g batch reactor with 32-1200 oC temperature range were obtained using standard heat conduction equations. Materials were selected for reactor shell, refractory lining, thermal insulation and heating elements.  Heating elements were fully embedded in refractories to avoid short–circuiting due to activation fumes. Tuyere was incorporated into the charging inlet for passage of inert gas (Nitrogen) into the reactor. Reactor was constructed and temperature profiles were obtained at different loading conditions (0, 25, 50, 85 and 100%) by charging it with prepared dried samples of powdered coconut shell, carbonised to 1000 oC. Validation of produced AC was by chemical activation using 200 g of coconut shell, crushed, milled into powder, oven dried for 48 hours at 110 oC and impregnated with Potassium hydroxide at (KOH : sample) ratio 3:2, as recommended. Impregnated samples were heated in flowing stream of Nitrogen (15 l/min) till 450 oC activation temperature. Samples (AC), were held at this temperature for 1-hour and 3-hour activation times. Experimental results were characterised by X-ray diffraction and scanning electron microscopy and compared with descriptive statistics and chi-squared required standard values.  

Refractory lining and insulator thicknesses were 0.3 and 0.2 m respectively. Thermal stress and strain were 166.9 MN/m2, and 5.6, respectively. Heat loss through wall of reactor was 912.92 W/K and heating rate was 10 oC/min. Materials for shell, refractory lining, thermal insulation and heating element were galvanised steel plate, aluminosilicate bricks, fibre glass and nichrome respectively. Temperature drop across aluminosilicate bricks and fibre glass were 168 and 299 K, respectively. Peak temperatures were attained in 9.0, 35.8, 108.6, 174.6 and 218.3 minutes at 0, 25.0, 50.0, 85.0 and 100.0% loading respectively. Production time and efficiency were 5 hours and 80% respectively. X-ray diffraction pattern showed that the major part of the AC produced were amorphous with small amount of crystalline matter. Scanning electron microscope at 1 hour activation showed a few micropores with not well- developed pores of sizes 0.58 nm, while well- formed elliptical micropores of sizes 1.8 nm were observed at 3 hours activation time. There is no significant difference (.) between experimental pore sizes of 1.8 and standards for 2 nm.

 A batch reactor, suitable for the production of Activated Carbon from coconut shell was developed.