Electrochemical acidification of Kraft black liquor by electrodialysis with bipolar membrane: Ion exchange membrane fouling identification and mechanisms.
Integrated forest biorefinery offers promising pathways to sustainably diversify the revenue of pulp and paper industry. In this context, lignin can be extracted from a residual stream of Kraft pulping process, called black liquor, and subsequently converted into a wide spectrum of bio-based products. Electrochemical acidification of Kraft black liquor by electrodialysis with bipolar membrane results in lignin extraction and caustic soda production. Even though the implementation of this method requires less chemicals than the chemical acidification process, fouling of the ion exchange membranes and especially bipolar membrane impairs its productivity. Membrane thickness and ash content measurements along with scanning electron microscopy (SEM), elemental analysis (EDX) and X-ray photoelectron spectrometry (XPS) analysis were performed to identify the nature and mechanisms of the membrane fouling. The results revealed that the fouling layer mostly consisted of organic components and particularly lignin. Based on our proposed fouling mechanisms, throughout the electrodialysis process the pH of the black liquor gradually decreased and as a result more proton ions were available to trigger protonation reaction of lignin phenolic groups and decrease the lignin solubility. Due to the abundance of the proton ions on the surface of the cation exchange layers of the bipolar membrane, destabilized lignin macro-molecules started to self-aggregate and formed lignin clusters on its surface. Over the time, these lignin clusters covered the entire surface of the bipolar membrane and the spaces between the membranes and, eventually, attached to the surface of the cation exchange membrane.
Research Unit on Energy Efficiency and Sustainable Implementation of the Forest Biorefinery (E(2)D(2)BF), Department of Chemical Engineering, Polytechnique de Montréal, Canada. Electronic address: maryam.haddad@polymtl.ca.
Maryam
M
Haddad
Institute of Nutrition and Functional Foods (INAF), Laboratory of Food Processing and Electromembrane Processes (LTAPEM), Department of Food Sciences, Université Laval, Canada.
Sergey
S
Mikhaylin
Institute of Nutrition and Functional Foods (INAF), Laboratory of Food Processing and Electromembrane Processes (LTAPEM), Department of Food Sciences, Université Laval, Canada.
Laurent
L
Bazinet
Research Unit on Energy Efficiency and Sustainable Implementation of the Forest Biorefinery (E(2)D(2)BF), Department of Chemical Engineering, Polytechnique de Montréal, Canada.
Oumarou
O
Savadogo
Research Unit on Energy Efficiency and Sustainable Implementation of the Forest Biorefinery (E(2)D(2)BF), Department of Chemical Engineering, Polytechnique de Montréal, Canada.
Jean
J
Paris
D003956:Dialysis / Q000295:instrumentation*; D055664:Electrochemical Techniques / Q000295:instrumentation*; D019544:Equipment Failure Analysis; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008031:Lignin / Q000737:chemistry*; D008567:Membranes, Artificial; D010209:Paper; D011522:Protons; D012972:Sodium Hydroxide / Q000737:chemistry
D008567:Membranes, Artificial; D011522:Protons; D012972:Sodium Hydroxide; D008031:Lignin
Bipolar membrane fouling; Colloidal lignin; Electrodialysis; Fouling analyses; Integrated forest biorefinery; Kraft black liquor