Design, optimization and modelling of a chemical recovery system for wet spinning of cellulose in sodium carbonate solutions

Abstract

The aim of this study is to present the design, optimization and modelling of a chemical recovery system for a novel CS2-free viscose-type process that entails dissolution of pre-treated dissolving pulp in a continuous-flow reactor in cold alkali and wet spinning of cellulose in sodium carbonate solutions. Technologies already known to other industries for the recovery and reuse of chemicals, such as causticizing, recalcination, recarbonization and freeze-separation, were used. Chemical equilibria simulations were performed with OLI Studio 9.5, with the purpose to select experimental conditions which avoid undesired precipitations in each unit operation. Synthetic solutions mimicking the spent coagulation liquor were used in the laboratorial experiments. The proposed chemical recovery system was shown to be technically feasible and reduce chemical make-ups to a minimum of 45 kg/ton of NaOH and 4 kg/ton of H2SO4. Small amounts of Zn are expected to precipitate during recarbonization of the coagulation liquor at 30 °C and causticizing at 98 °C. Thus, a filter for ZnO particles should be included in the design of the recarbonization unit and a continuous purge of lime mud and input of fresh lime make-up should be needed to keep burnt lime availability at an acceptable level. Overall, the results presented in this study portray a solution to reduce operating costs and the environmental impact of novel viscose-type processes with alkaline spin dopes and wet spinning of cellulose in sodium carbonate solutions.

Dissolving-grade pulp: a sustainable source for fiber production

“…Another innovative, technically and economically feasible alternative is the Neo-Cel process, which comprises dissolution of pretreated dissolving pulp in a continuous-flow reactor in cold alkali, aided by Zn and additives, after which the spin dope is coagulated in a sodium carbonate solution. Bialik et al (2020) conducted an investigation which included the design, optimization and modelling of a chemical recovery system for wet spinning of cellulose in sodium carbonate solutions (Neo-Cel). Based on the results, the system was technically feasible and reduced chemical makeup.…”

Lyocell fibre production using NMMO – A simulation-based techno-economic analysis

“…Specifically, no techno-economic assessments of Lyocell fibre production process have been published before. Only a few plant-wide process simulation -based process optimization studies of other fibre production processes have been reported (Bialik et al 2020). Other context utilising NMMO as a lignocellulosic material pre-treatment solvent for production of ethanol or biogas from forest residues, pine or spruce, and food industry side-streams has been examined using process techno-economic analysis (Shafiei et al 2011(Shafiei et al , 2014Teghammar et al 2014;Oliva et al 2022).…”