Preparation Of Formed Activated Carbon With Composite Adhesive And Its Adsorption Properties

The formed activated carbon avoids the dust pollution and the loss of carbon comparing with powdered activated carbon.It increases the specific surface area of carbon per unit volume,which is convenient for loading adsorption equipment.The selection of suitable adhesives and forming processes is an important factor affecting the performance of formed activated carbon.Polyvinyl alcohol(PVA)is a common organic adhesive with excellent bonding properties,but its water resistance is poor.In addition,sodium silicate is an inorganic adhesive with good heat resistance,but it has poor cohesiveness.These two adhesives have their own disadvantages.Therefore,an environmentally friendly adhesive with both advantages of PVA and sodium silicate in an acidic environment was synthesized.The formed activated carbon has great comprehensive properties such as adsorption performance and compressive strength.Accordingly,the prepared experimental activated carbon is used to adsorb formaldehyde aqueous solution and hexavalent chromium ion.The specific contents and research results are listed as following.Firstly,a series of adhesives were prepared by changing the concentration of PVA,the amount of sodium silicate,the choice of acid,the amount of acid and the reaction temperature.And the adhesives were characterized by Fourier infrared analyzer,comprehensive thermal analyzer,X-ray and water resistance test.The results showed that the adhesive prepared by reaction of 8wt%PVA and 3.0wt%sodium silicate under acidic environment at 70? had the suitable comprehensive properties.In addition,infrared analysis displayed that PVA and sodium silicate were crosslinked by Si-O-C bond under acidic conditions,forming an interpenetrating network structure,which improved the water resistance and thermal stability.Thermal gravimetric analysis showed that the temperature of the first major decomposition weight loss peak of the adhesive film reached 365.9?,which was 106.6? higher than that of pure PVA.Secondly,a series of formed activated carbon were prepared by changing the ratio of adhesive to carbon,forming pressure and time,post-treatment temperature and time.The microstructure of the materials was characterized by scanning electron microscope and gas adsorption instrument.The experimental results displayed that the shaped activated carbon had abundant mesopores and micropores below 10 nm.Moreover,its pore distribution was mainly micropores below 2 nm.When the ratio of adhesive to carbon was 40:60,the forming pressure was 80 MPa,the forming time was 4 min,the post-treatment temperature was 190?,and the post-treatment time was 90 min,the performance of the formed activated carbon was excellent.Its iodine adsorption value could be 930 mg/g,and the maximum compressive strength was 12 MPa.The formaldehyde aqueous solution and hexavalent chromium ion was adsorbed by activated carbon under suitable forming process.The result reflected that the diffusion rate of formaldehyde in formed carbon was lower than that of powdered carbon at the initial stage of adsorption,while the formaldehyde adsorption rate of formed carbon was higher than that of powdered carbon at the equilibrium of adsorption.Therefore,the formed activated carbon was more favorable for the adsorption of formaldehyde comparing with powdered activated carbon.On the other hand,adsorption rate of hexavalent chromium in aqueous solution was close to 90%by adding proper amount of formed activated carbon.And the decrease of pH value was beneficial to the adsorption of chromium ion by activated carbon.While pH value was less than 2,the adsorption rate could be 80%.In addition,when the initial concentration of chromium solution was 0.5 to 2.5mg/L,the adsorption rate of hexavalent chromium was 84.93 to 90.3%.Therefore,the appropriate pH value and initial concentration was beneficial to the adsorption reaction,and the adsorption effect was excellent..