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TEMPLATE DESIGN © 2008
www.PosterPresentations.com
DEVELOPMENT OF NOVEL ADSORBENTS FOR WASTEWATER TREATMENT
Raman Talwar
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  1. 1. TEMPLATE DESIGN © 2008 www.PosterPresentations.com DEVELOPMENT OF NOVEL ADSORBENTS FOR WASTEWATER TREATMENT Raman Talwar Supervisor: Dr. E.P.L Roberts School of Chemical Engineering and Analytical Sciences, The University of Manchester Introduction and Project Background Wastewater treatment using adsorbents is increasingly gaining dominance owing to their environment friendliness and cost- effectiveness. After adsorbing pollutants to their saturation capacity, they lose their ability to adsorb further and consequently have to be regenerated. Adsorbent Synthesis, Properties and Kinetics Adsorbent Synthesis The adsorbent (CEG) was prepared using the following scheme: Adsorbent Properties Stability of Nyex®Regeneration Characteristics Experiments Electrochemical regeneration was performed in a Y-cell (Figure 9): Conclusions and Future Work References a) Sieving Using a Sieve Tower to get particles in the range of 250 – 425 microns b) Expansion Heating Nyex particles to 800 – 850 °C for 60 seconds c) Compression Compression in a hydraulic press at 2500 kgf using a 4 cm2 die d) Crushing Crushing using a blender at 18000 rpm Figure 8: Adsorbate loading over time for Nyex and compressed expanded graphite (CEG). The initial concentration of AV 17 was taken as 100 mg l-1 in both cases with 20 gm Nyex and 10 gm CEG. It can be seen that steady equilibrium is reached after 60 minutes for both the adsorbents with about 50 – 60 % adsorption taking place within 20 minutes in both cases. Figure 4: Surface morphology of Nyex® particles (left) at 100 times magnification. The non- porous structure of Nyex® particles can be seen which leads to a low adsorption capacity. A schematic (right) of the intercalated structure showing low inter-planar Van der Waals forces. Figure 6: Procedure for adsorbent synthesis 1. Brown, N.W., et al., (2004). Electrochemical regeneration of a carbon-based adsorbent loaded with crystal violet dye. Electro Acta, 49: 3269-3281. 2. Celzard, A., et al., (2002). Preparation, electrical and elastic properties of new anisotropic expanded graphite- based composites. Carbon, 40: 557-566. Figure 9: Y-cell equipment used for regeneration. Regeneration was performed for 40 minutes at 1 A current for adsorbents (110 gm Nyex and 50 gm CEG) over 4 adsorption/regeneration cycles. In each cycle, a fresh batch of AV 17 dye (500 mg l-1 for Nyex and 800 mg l-1 for CEG) was taken and replaced after every adsorption cycle which lasted for 1 hour. Adsorbent Kinetics Adsorption experiments were performed in flasks using Acid Violet 17 (AV 17) dye solutions as the adsorbate loading. The saturation adsorption capacity (Figure 8) for CEG (8 mg g-1) was found to be twice that of Nyex® particles (4 mg g-1) due to a higher surface area and pore volume of CEG particles (17 m2 g-1 and 0.07 cm3 g-1 respectively) as compared to Nyex particles (1 m2 g-1 and 0.004 cm3 g-1 respectively). This finding marked a significant breakthrough in improving the adsorption properties of Nyex®. Compression Regeneration Efficiencies The regeneration efficiencies (ratio of loaded capacity to fresh capacity) for both CEG and Nyex® particles (Figure 10) were found to be around 100%, suggesting that the synthesised adsorbent (CEG) displayed good regeneration behaviour. Figure 10: Regeneration efficiencies for both Nyex and CEG were found to be similar and above 100% for theoretical charge passes (21.8 C g-1 for 110 gm Nyex and 48 C g-1 for 50 gm CEG, implying 1 A for 40 minutes in each case) calculated using Faraday’s Laws. Marginal decrease in efficiencies below 100% can be attributed to inefficient current passage through the cell. Cell Potentials CEG bed required half the cell voltage (Figure 11) for the same treatment time (40 minutes) over 4 cycles, leading to a lower power consumption due to a higher electrical conductivity (1.6 S cm-1) than Nyex® particles (0.8 S cm-1). Figure 11: Cell potentials for the two adsorbent beds over 4 cycles. Values were recorded over 40 minutes and the error bars show the standard deviation of multiple readings from mean. Methodology Nyex® particles have been observed to break down in solution during adsorption. To characterise this breakdown, turbidity measurements were taken to account for the generation of fines. Figure 12: Turbidimeter (left) used to assess Nyex® attrition and its working principle (right) Figure 13: Turbidity values after adsorption/regeneration cycles (left) and with/without current passage (right). Error bars show standard deviation of multiple readings from mean. Turbidity Results Adsorption and regeneration cycles were mimicked with Nyex® and water solution in a Y-cell to study the fines generation upon current passage (Figure 13). During regeneration, more fines were produced and when current was passed, turbidity was observed to be 30% higher. Composite Development The expanded graphite particles can be impregnated and polymerised with a conductive furan based resin to obtain composites (Figure 14) with a higher adsorption capacity, which can be subsequently, carbonised and activated to increase micro- porosity – a feature lacking in both Nyex® and CEG particles. a) Sieving Particles b) Liquid impregnation c) Polymerise on surface d) Carbonisation e) Chemical Activation and final washing Figure 7: Surface morphology of expanded graphite (left) and compressed expanded graphite (CEG, right) at 200 and 100 times magnification respectively. The expansion of the graphite layers can be observed in the morphology (SEM) of expanded graphite. The roughness of edges which lead to enhanced adsorption can be observed on the surface of CEG particles. Property Nyex® CEG Activated Carbon BET Surface Area 1 m2 g-1 17 m2 g-1 2000 m2 g-1 Specific Pore Volume 0.004 cm3 g-1 0.07 cm3 g-1 0.70 cm3 g-1 Bulk Density 0.80 g cm-3 0.19 g cm-3 0.30 g cm-3 Electrical Conductivity 0.8 S cm-1 1.6 S cm-1 0.012 S cm-1 Project Objectives a) Sieving Particles b) Expansion of Nyex c) Compression of expansion graphite (CEG) d) Crushing of CEG Figure 2: Thermal regeneration drawbacks Industrially, thermal regeneration is commonly practised but has its drawbacks (Figure 2) whereas electrochemical regeneration is an alternative technique which offers many advantages (Figure 3) Figure 1: Activated Carbon, common adsorbents for wastewater treatment Thermal Regeneration Energy and Capital Intensive Environ- mental Issues 5 – 10% Material Losses Electro- chemical Regeneration Low Energy Usage Environ- mentally Safe No Material Losses Figure 3: Electrochemical regeneration advantages Earlier methods of electrochemical regeneration were less efficient, made use of high charge passes and required long treatment times. In 2004, using a non-porous graphite intercalated compound called Nyex® (Figure 4), Brown et al.[1] achieved over 100% regeneration efficiencies within 20 minutes of treatment and complete adsorption equilibrium within 60 minutes Basic Methodology Idea is to expand the Nyex structure by lowering the Van der Waals forces between the layered structure, develop expanded graphite and compress it to form compressed expanded graphite (CEG)[2]. Characterise the attrition behaviour of Nyex® particles as they have been found to breakdown in solution during regeneration. Increase the adsorption capacity of Nyex® particles whilst maintaining similar regeneration efficiencies. Figure 5: Scheme for the development of compressed expanded graphite Conclusions The synthesised adsorbent showed an increased adsorption capacity due to a higher surface area and consumed lesser power during regeneration due to a higher electrical conductivity. Figure 14: Composite synthesis process Material Modelling Many options for the synthesis of composites can be screened and explored by building a framework for material modelling of intercalated compounds at a molecular level using molecular dynamics (MD) and Monte-Carlo simulations.

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