Abstract
Choline chloride-based deep eutectic solvents are widely used in biomass processing. In this work, four different green solvent mixtures were used as pre-treatment of acid sulphite dissolving pulp with the hypothesis of increasing the possibilities to produce viscose fibres and decreasing the use of the harmful and toxic carbon disulphide in the process. The experiments were performed at two different pulp to solvent mass ratios. Pulp quality parameters were also measured to determine the suitability of the pre-treatment: α-cellulose, viscosity, lignin and pentosan content. In addition, X-ray diffraction analysis of pulps at the best solid to liquid ratio was performed to obtain the influence of the crystallinity index. Best results were obtained with the use of lactic acid, with reactivity values close to 94%, giving a reduction of CS2 usage of 15.83%. Furthermore, a linear relationship between the crystallinity index calculated by the XRD and reactivity with a regression factor of 0.87 was found.
Highlights
Choline chloride-based deep eutectic solvents are widely used in biomass processing
Lignin content, pentosan content and reactivity of the pulp were analysed to evaluate the effects of the pre-treatment α-cellulose content
At 1/20 solid to liquid ratio, cellulose content increases slightly when the system is formed by ChCl:LA (1.65 %), ChCl:MA (0.29 %) and ChCl:Ur (0.94 %), showing that the solubility of cellulose in the deep eutectic solvents (DES) used in this work is almost negligible as stated by
Summary
Choline chloride-based deep eutectic solvents are widely used in biomass processing. In this work, four different green solvent mixtures were used as pre-treatment of acid sulphite dissolving pulp with the hypothesis of increasing the possibilities to produce viscose fibres and decreasing the use of the harmful and toxic carbon disulphide in the process. DES systems are a mixture of two or more components with a final melting point much lower than the individual components (Kumar et al 2016) which makes it liquid at room temperature (Procentese and Rehmann 2018) These solvents are usually composed by a quaternary ammonium, phosphonium or sulfonium cation or a metal chloride (Smith et al 2014), defined as Hydrogen Bond Acceptor (HBA) and a Hydrogen Bond Donor (HBD). Depending on the components employed to form the solvent, DES can be classified in four types (Zdanowicz et al 2018): (1) Organic salts and metal chlorides; (2) Organic salts and metal hydrates; (3) Organic salts and organic compounds (carboxylic acids, alcohols, or amides); and (4) Metal chlorides and organic compounds (amides, alcohols) These solvents have similar properties to Ionic Liquids (IL): low vapour pressure, chemical and thermal stability, non-flammability and can be tailored (Wilpiszewska and Spychaj 2011).
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