Electrochemical Acidification of Kraft Black Liquor: Effect of Fouling and Chemical Cleaning on Ion Exchange Membrane Integrity

Abstract

In the essence of the green biorefinery concept an interest in further implementations of wood compounds has gained a lot of attention. Therefore, it is crucial to identify and develop efficient and eco-friendly extraction processes. In particular in a lignin biorefinery plant, electrochemical acidification of Kraft black liquor via electrodialysis with bipolar membrane is considered as a sustainable avenue to acidify the Kraft black liquor and subsequently extract lignin. Even though the application of this acidification technique results in less chemical consumption than the acid precipitation method, the colloidal fouling of the ion exchange (bipolar and cation exchange) membranes, adversely affects its performance. This study was performed to determine the influence of the colloidal fouling and chemical cleaning process on the integrity of the membranes. Four commercially available cation exchange membranes and one bipolar membrane were examined. Membrane analyses, such as thickness, contact angle, ion exchange capacity and electrical resistance measurements, as well as scanning electron microscopy with energy dispersive X-ray analysis, were carried out. It was found that changing the type of the cation-exchange membrane cannot eliminate the fouling phenomenon and a chemical cleaning cycle is required. Caustic soda and fresh diluted black liquor were tested as the cleaning solutions. The initial properties of the bipolar membrane and two cation-exchange membranes (CMB and Nafion 324) were reestablished after the chemical cleaning step. Furthermore, in terms of sustainability concept, the utilization of in situ and free of charge fresh diluted black liquor, as the cleaning agent, can be an interesting eco-efficient approach.

Lignin recovery from spent alkaline pulping liquors using acidification, membrane separation, and related processing steps: A review

“…In the case of an electrochemical membrane separation process, a pulsed electric field might be used for such cleaning (Haddad et al 2016). Haddad et al (2017c) found that effective cleaning could be achieved with either NaOH solution or fresh diluted black liquor.…”

Developing a novel direct liquid fuel cell based on pulping liquors

“…Moreover, after passing the peak power density, P p , the values decay faster in the experiments using acid oxidant than in alkaline media. This behavior may be justified by the membrane fouling caused by the deposition of kraft lignin [71]. It owes to lignin insolubility at pH < 10.5 [72], leading to its protonation and precipitation upon crossing the membrane to the cathodic compartment.…”

The Role of Ion Exchange Membranes in Membrane Capacitive Deionisation

“…There are five groups of chemicals that can be used as cleaning agents for membrane processes, namely: alkalis, acids, metal chelating agents, surfactants, and enzymes—each targeting different types of deposits. The type of cleaning chemical to be utilized is usually selected based upon the nature of the foulant, the compatibility of the chemical with the processing equipment, chemical availability, cost, and safety [ 88 , 98 ]. However, chemical cleaning has many disadvantages, namely: membrane damage, usage of large quantities of chemicals, and waste generation.…”