A novel method for the extraction of cellulose fibers from Spanish broom (Spartium junceum L.) is based on the sequential combination of an initial chemical stage (alkaline digestion) followed by a subsequent physical-chemical stage, consisting of compression with hot air in an autoclave followed by rapid decompression (DiCoDe process, digestion-compression-decompression). The proposed methodology is characterized by rapid production times and fibers with excellent physical-chemical properties, such as high mechanical resistance and high elasticity. However, the disposal of the alkaline solution used in the digestion step raises serious problems of environmental impact due to its high polluting load. The development of a system for recovering and recycling the extracting solution is an interesting perspective to rationalize and optimize the whole extraction cycle: it allows to recover a solution that can be used for subsequent extraction cycles and secondly to reduce strongly the pollution load of the wastewater. Membrane technology could be a viable method for recycling and reusing the alkaline liquor mother thus making the overall process economically convenient. In this work the use of ceramic microfiltration (MF) and ultrafiltration (UF) membranes in tubular configuration was investigated for the treatment of spent alkaline solutions coming from the extraction of cellulose fibers in order to obtain a suitable solution reusable for new extraction cycles. For UF membranes with molecular weight cut-off of 1 and 3 kDa the effect of transmembrane pressure (TMP) and axial feed flow rate (Qf) on the permeate flux and total organic carbon (TOC) was investigated. An integrated membrane process was developed on the basis of experimental results. It includes a preliminary treatment of MF devoted to the removal of suspended solids from the spent solution, followed by a UF treatment of the microfiltered spent solution with 1 kDa tubular membranes. The UF membrane showed a maximum rejection towards TOC (74%) in optimized operating conditions (TMP, 4 bar; Qf, 90 L/h; temperature, 25°C) and a steady-state permeate flux of about 20 L/m2h. The integrated process permitted to reduce the initial TOC of the spent solution of 80%, producing a final permeate stream that can be reused for new extraction cycles. A significant positive impact is obtained in terms of reduction of polluting load and consumption of water and chemicals.
Recovery of spent alkaline solutions in the production of cellulose fibres from Spanish broom by MF and UF processes
A Cassano;
2014
Abstract
A novel method for the extraction of cellulose fibers from Spanish broom (Spartium junceum L.) is based on the sequential combination of an initial chemical stage (alkaline digestion) followed by a subsequent physical-chemical stage, consisting of compression with hot air in an autoclave followed by rapid decompression (DiCoDe process, digestion-compression-decompression). The proposed methodology is characterized by rapid production times and fibers with excellent physical-chemical properties, such as high mechanical resistance and high elasticity. However, the disposal of the alkaline solution used in the digestion step raises serious problems of environmental impact due to its high polluting load. The development of a system for recovering and recycling the extracting solution is an interesting perspective to rationalize and optimize the whole extraction cycle: it allows to recover a solution that can be used for subsequent extraction cycles and secondly to reduce strongly the pollution load of the wastewater. Membrane technology could be a viable method for recycling and reusing the alkaline liquor mother thus making the overall process economically convenient. In this work the use of ceramic microfiltration (MF) and ultrafiltration (UF) membranes in tubular configuration was investigated for the treatment of spent alkaline solutions coming from the extraction of cellulose fibers in order to obtain a suitable solution reusable for new extraction cycles. For UF membranes with molecular weight cut-off of 1 and 3 kDa the effect of transmembrane pressure (TMP) and axial feed flow rate (Qf) on the permeate flux and total organic carbon (TOC) was investigated. An integrated membrane process was developed on the basis of experimental results. It includes a preliminary treatment of MF devoted to the removal of suspended solids from the spent solution, followed by a UF treatment of the microfiltered spent solution with 1 kDa tubular membranes. The UF membrane showed a maximum rejection towards TOC (74%) in optimized operating conditions (TMP, 4 bar; Qf, 90 L/h; temperature, 25°C) and a steady-state permeate flux of about 20 L/m2h. The integrated process permitted to reduce the initial TOC of the spent solution of 80%, producing a final permeate stream that can be reused for new extraction cycles. A significant positive impact is obtained in terms of reduction of polluting load and consumption of water and chemicals.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
