Feasibility Study on Conversion of Indian Bamboo to Activated ...

<strong>Feasibility</strong> <strong>Study</strong> on Conversion of Indian Bamboo to Activated Carbon carried out byChemical Engineering Department, Indian Institute of Technology, BombayAbstractActivated carbon can be used for removal of organic chemicals, chlorine, lead, unpleasanttastes and odors in effluent or coloured substances from gas or liquid streams by themechanism of adsorption. Adsorption can be classically defined as absorption on the surfaceof the material due to capillary condensation inside the multitude of pores/active sitesavailable.In its effort to promote value added bamboo based products, the National Mission onBamboo Applications launched an investigation to study the conversion of Indian bamboospecies to activated carbon in association with Indian Institute of Technology – Bombay.Three commonly occurring species has been used in the experimentation. These areMelacona baccifera, Bambosa tulda and Oxycelandra stockii. The study indicating thatIndian bamboo is a good raw material for conversion to activated carbon has laid thefoundation for further activity in this area.In the first step, carbonisation of bamboo has been done in inert atmosphere using ZincChloride promoter. The carbonised product has been activated chemically using CO 2 . Theactivated product obtained has surface area above 1200m 2 /gm. Performance studies carriedout with methylene blue as coloring agent has indicated that the product has betteradsorption indices than that of the standard activated carbon available. The yield ofcarbonisation and activation was observed to be 40% and 75% respectively. Out of the threespecies experimented, activated carbon prepared from Bambusa tulda has been found to bethe best in terms of surface area and adsorption capacity.BackgroundHigh-grade activated carbon can be obtained from woody material like bamboo havinginherent mechanical strength, high carbon and low ash content. Since India is the secondlargest producers of bamboo, there exists an excellent scope for producing bamboo basedhigh-grade activated carbon if appropriate technology is developed and exploited atcommercial level.During assessment of technology needs for bamboo based activated carbon, it was foundthat no such knowledge base currently exists in the country with reference to Indian bamboospecies. While there has been much indigenous effort in converting coconut shell intoactivated carbon, certain initiatives were necessary for an investigative study of conversionof bamboo.Experimental WorkRaw Material

Three bamboo species available in abundance in the country has been used in theexperiment. These are Melacona baccifera, Bambosa tulda and Oxycelandra stockii.Methodology□ Bamboo is crushed either manually or by Lathe machine to a desired mesh size.Particle size of bamboo is 60-80 meshes□ The crushed bamboo pieces are washed with water for the removal of adherentextraneous matter.□ The washed bamboo pieces are dried in oven at 150 0 C for 4 hrs for removal ofmoisture.□ The dried bamboo pieces are treated with carbonizing promoters like phosphoric acid(H 3 PO 4 ) or Zinc chloride (ZnCl 2 ). Then carbonization is carried out in a fixed bedreactor at 400-600 0 C for 4 hrs in the presence of nitrogen gas.□ The carbonized mass was washed with water for the removal of carbonizingpromoter.□ Activation is carried out at 900-1000 0 C in the presence of carbon dioxide (CO 2 ).Experimental setupFig. 2. Experimental set-up for the production of activated carbon. 1. Trap. 2. Cooling bath. 3.Furnace with reactor tube. 4. Carbon sample. 5. Support. 6. Flow meter. 7. Valve. 8. N 2 -cylinder. 9. CO 2 -cylinder.Observations1. CrushingIt is convenient to do crushing of bamboo in two stages, first by lathe machine and then bymanual crushing. Manual crushing alone is not adequate to give the desired size due tofibrous nature of bamboo.2. CarbonizationDuring carbonization, the use of phosphoric acid (H 3 PO 4 ) as a promoter was found to betroublesome because it is an oxidizing and corroding agent, which corrodes the insidesurface of the reactor and causes burning of bamboo particles thereby producing continuousbluish flame at the outlet of the reactor. This phenomenon was quite violent. It is to be notedthat this observation has not been reported in the available literature, but we noticed itseveral times during carbonization using phosphoric acid as a carbonizing promoter for all

uns. On other hand, zinc chloride (ZnCl 2 ) as a carbonizing promoter was friendly to use forcarbonization process. The yield of carbonization was typically 40%.3. ActivationThe yield of activation is typically 75% with respect to the material charged in the fluidizedbed.5. Results and DiscussionProperties of Activated CarbonTable-1 Properties of various activated carbon analyzed by BET apparatusStandardAssam bamboo samplesactivatedcarbon.(ActivatedMelacona BambosaCarbon.coBaccifera Tuldam)Sr.No. Parameters1.23.4.4.5.6.Surface area. (m 2 /g)Pore volume. (cc/g)Avg.Pore diameter. (A)Bulk density (gm/cc)Volatile matterAsh contentIodine No.(ASTM_4607)11000.730.48-3.00900-110012200.499516.52780.21321.33.38950-105013500.961416.63220.23721.33.38950-1100Oxycelandrastockii12800.505716.190.2821.33.38950-11005.1 Effect of particle size and activation temperatureSome exploratory work was performed to investigate the effect of two important processparameters viz particle size and activation temperature. It was observed that if the activatedcarbon is prepared by finely crushed bamboo (particle size < 1 mm) then the surface area isabout 8 to10% more than that observed for the granules of about 3 mm. Activationtemperature is a crucial parameter that mainly determines the fete of the product. Its effectover the range 700-900 0 C studied and it was observed that the surface area at 900 0 C is almostdouble the surface area when the activation was performed at 700 0 C under otherwise similarconditions.5.2 Recovery of Zinc Chloride (ZnCl 2 )As seen from characteristics of the product zinc chloride has given a substantial increase inthe total surface area. However, in order to recommend this agent for carbonization, it isnecessary to look at the economical aspects of its use.

The quantitative analysis of ZnCl 2 in aqueous solution was performed by the standardmethod of titration with 0.1N AgNO 3 solution. The results suggested that 9-10 % of zincchloride is lost during this operation, which is well in limit of economical application. Thepercentage recovery can still be improved by carefully performing more runs. Since the zincchloride solution is more dilute than the initial solution, it is necessary to concentrate thesolution to the required strength prior reuse.5.3 Performance study: Comparison of different activated carbon samplesThe performance studies were conducted for all the activated carbon samples using batchand semi-continuous (column) adsorption for methyl blue dye solutions. The breakthroughcurve for activated carbon from Assam bamboo samples and that of the standard activatedcarbon by contact method using methylene blue dye solution are shown in Fig. 3. Asmentioned before, the performance is well in agreement with the surface areas given inTable-1.Concentration Vs TimeConcentration (gm/lit)0.70.60.50.40.30.20.100 20 40 60 80Time (min)Not SpecifiedBmabossa TuldaStandardTable 3: Performance <strong>Study</strong> using Methylene BlueConclusionA huge amount of waste is generated during processing of bamboo into mat, flooring tilesand sticks. The major portion of the bamboo pole cannot be used for manufacture of suchproducts due to poor machinability. Certain bamboo species such as melocanna bacciferathough abundantly available are not suitable for certain applications due to their poormechanical properties. From the study carried out it can be concluded that:• The performance of bamboo based activated carbon, with methylene blue as coloring agentgives better adsorption indices than that of the standard activated carbon• Activated carbon prepared from Bambusa tulda has been found to be the best in terms ofsurface area and adsorption capacity