Kraft lignin adsorbents
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Waste water could contain polyaromatic hydrocarbons (PAH) up to concentrations of 30mg/l. Due to their carcinogenic nature, long term persistent, and high mobility in the environment PAHs are considered primary pollutants. Removal of these organic contaminants is highly desirable.
Lignin has so far not been commercially utilized as adsorbent. A low surface area and detectable water solubility are considered as the main drawbacks hindering its direct application as an efficient adsorbent for environmentally hazardous organic molecules present in contaminated water.
In this project softwood kraft lignin have been modified using different modification methods for the purpose of adsorption of PAH. The modification techniques were physical and chemical. The properties of the treated lignins were evaluated with respect to the Brunauer-Emmett-Teller (BET) surface area measurement, water solubility and ability to adsorb naphthalene from water solutions.
The physical modification involved thermal treatments of lignin. The effect of three different heating rates and different target temperatures were evaluated. It was shown that slower heating rates rendered in higher BET surface area of the thermally treated lignin. It was found that the total BET surface area was smaller than commercially activated carbon (650m2/g). However, the thermally treated softwood kraft lignins had a higher micro-pore area (around 300m2/g). BET surface area of up to 430 m2/g has been achieved. This is a remarkable increment for a normal untreated lignin which can be considered non porous to undergo to a surface area increments well enough comparable as that of commercially available activated carbon (650m2/g). The thermal treatments did not involve activation of lignin only heating up to the carbonization temperature.
The chemical modification involved cross linking of lignin, using paraformaldehyde under alkaline condition at elevated temperature followed by thermal treatment.
Naphthalene, which is water soluble PAH, was used as a representative model compound for evaluation of the adsorbing efficiency of the modified lignin adsorbents. The results of the adsorption efficiencies of modified lignins were compared with the adsorption efficiency of commercially activated carbon. The cross-linked lignin showed better adsorption efficiency than thermally treated lignins for naphthalene.
Place, publisher, year, edition, pages
2012. , 43 p.
Lignin, Adsorption, PAH, Thermal treatment, Cross linked lignin, Activated Carbon
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-156179OAI: oai:DiVA.org:kth-156179DiVA: diva2:765504