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The metal binding properties of kraft lignin
Mälardalen University, School of Sustainable Development of Society and Technology. Mälardalen University, Department of Biology and Chemical Engineering.
2009 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

There is a strong driving force to increase the competitiveness of the pulping industry by finding new business opportunities. In this context full utilisation of the wood raw material used in conventional pulping mills is of vital importance. One focus area is to increase the utilisation areas of lignin. LignoBoost is a new method to obtain kraft lignin of high purity.

The aim of the project was to investigate and increase the ability of LignoBoost kraft lignins to bind metals in aqueous solutions.

The metal binding property of kraft lignins was evaluated using copper (II) ions. The metal binding capacities were 1.76 mg Cu2+/g LignoBoost softwood kraft lignin, 0.96 mg Cu2+/g LignoBoost hardwood kraft lignin and 1.12 mg Cu2+/g condensed softwood kraft lignin. The metal binding capacities of the softwood and hardwood kraft lignins from LignoBoost were lower than expected, when compared to the metal binding capacities of other lignins found in literature. The highest copper binding capacity of a kraft lignin found in literature was almost 50 times greater than that of the LignoBoost softwood kraft lignin.

 

The Mannich reaction was used to increase the nitrogen content in softwood lignin, and thereby increase its electron-donating capacity. An increase in electron-donating capacity should promote its metal binding capacity.

 

The Mannich reaction occurs in the vacant ortho position of the phenolic groups of lignin, introducing an aminomethyl group at that position. The only vacant ortho position in the phenol unit for reaction is in the guaicyl unit. Softwood lignin underwent a Mannich reaction, since softwood contains a greater number of guaiacyl units than hardwoods.

 

A screening of the products from this Mannich reaction on LignoBoost softwood kraft lignin was performed to optimise the reaction conditions. The reaction time, temperature, amount of formaldehyde and dimethylamine were varied. The Mannich products were evaluated by elemental analysis. The conditions giving the highest nitrogen content in the product were used further in a Mannich reaction of condensed softwood kraft lignin. The condensed softwood kraft lignin (7 g) was treated with dimethylamine (0.35 mol) and formaldehyde (0.35 mol) at 80°C for 24 hours.

 

The metal binding experiment could not be carried out with Mannich-modified condensed softwood kraft lignin since the lignin dissolved in the copper solution.

 

When introducing nitrogen functionalities into lignin the electron-donating capacity should increase. An increase in donor groups should promote the metal binding capacity of the lignin. A problem that occurred when introducing aminomethyl groups was an increase in solubility of the lignin. Water solubility of the lignin derivative is undesirable in the envisaged utilization area, metal binding in, for example mine deposits, from where contaminated water may be a concentrated source of heavy metals.

Place, publisher, year, edition, pages
2009. , 24 p.
Keyword [en]
Lignin
National Category
Chemical Sciences Organic Chemistry Inorganic Chemistry
Identifiers
URN: urn:nbn:se:mdh:diva-9392OAI: oai:DiVA.org:mdh-9392DiVA: diva2:303830
Presentation
(English)
Uppsok
Physics, Chemistry, Mathematics
Supervisors
Examiners
Available from: 2010-03-19 Created: 2010-03-15 Last updated: 2010-03-19Bibliographically approved

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CiteExportLink to record
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