In this study, bipolar membrane electrodialysis (BMED) was implemented for cleaner production of L-10-camphorsulfonic acid (L-CSA) to lower the environmental impact.Under the current density of 300-400 A/m 2 and feed salt concentration of 6-10 wt. %, the energy consumption and current efficiency were 2.24-2.70 kWh/kg and 20.89-29.5%, respectively. Positron annihilation lifetime spectroscopy, x-ray photoelectron spectroscopy with ion beam etching, and other characterizations were used to elucidate the transport behaviors of large-sized anions across the membranes. It was speculated that the large-sized camphor sulfonate ions were more likely to deposit on the surface of the anion-exchange membrane to form a deposition layer under a direct current electric field. The appearance of water splitting at this deposition layer would offset the water dissociation in the bipolar membrane. Nevertheless, the successful commissioning of industrial-scale stack proved the feasibility and sustainability of BMED technique for a closed loop L-CSA production.

In the papermaking industry (reconstituted tobacco), a large number of tobacco stems, dust, and fines are discharged in the wastewater. This high salinity wastewater rich in ionic constituents and nicotine is difficult to be degraded by conventional biological treatment and is a serious threat that needs to be overcome. Electrodialysis (ED) has proved a feasible technique to remove the inorganic components in the papermaking wastewater. However, the fouling in ion exchange membranes causes deterioration of membranes, which causes a decrease in the flux and an increase in the electrical resistance of the membranes. In this study, the fouling potential of the membranes was analyzed by comparing the properties of the pristine and fouled ion exchange membranes. The physical and chemical properties of the ion exchange membranes were investigated in terms of electrical resistance, water content, and ion exchange capacity, as well as studied by infrared spectroscopy (IR) spectra, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The results indicated that the membrane fouling is caused by two different mechanisms. For the anion exchange membranes, the fouling is mainly caused by the charged organic anions. For the cation exchange membrane, the fouling is caused by minerals such as Ca2+ and Mg2+. These metal ions reacted with OH− ions generated by water dissociation and precipitated on the membrane surface. The chemical cleaning with alkaline and acid could mitigate the fouling potential of the ion exchange membranes.

Bipolar membrane electrodialysis (BMED) is a promising technique for upgrading traditional manufacturing procedures and achieving a circular economy. However, the industrial applications of BMED technology have been restricted by the large consumption of expensive bipolar membranes and the unmatching behavior between water splitting and ion migration. Herein, we proposed a novel asymmetric bipolar membrane electrodialysis (ABMED) to regulate the water splitting in the bipolar membrane and orientational ion migration in the electrodialysis (ED). It was found that the ABMED exhibited comparable performances to BMED for acid/base production when the area of the bipolar membrane was reduced to 50% of the monopolar membrane.

Bipolar membrane electrodialysis (BMED) is an environmentally friendly, high-effective technique for the cleaner production of gluconic acid. However, the unsatisfactory purity and low concentration of the regenerated base limit the applicable field of the byproduct for further utilization. In this study, BMED was applied for the cleaner production of gluconic acid from the perspective of the regenerated base. First, four types of cation-exchange membrane were screened for the BMED process by evaluating the performances of current efficiency, purity of regenerated base, and energy consumption. The BMED performances follow the order of CMX > TWEDC > CJMC-5 > CJMC-3. Furthermore, the effects of current density, the volume ratio between salt and base compartment on the BMED performances were optimized. A high base purity of 96.6% was obtained at a current density of 40 mA/cm 2 , while a high base concentration of 4.58 mol/L could be reached by applying a high volume ratio of 5:1 between the salt and base compartment. Moreover, the mechanism on the leakage of organic salts into the regenerated base was elucidated. The purity of the regenerated base was attributed to diffusion and electromigration. Diffusion dialysis experiments demonstrated that the permeability of gluconate through the CMX was 4.7 times of that through the BP-1. It was also found that the leakage of gluconate into the base could be alleviated at a low current density ranging from 20 to 50 mA/cm 2 . Finally, the regenerated base was subjected to the enzyme catalyst experiment for conversion of glucose into gluconate. This proof-of-concept study demonstrates that the regenerated base from the BMED process could be valorized to the upstream route for a closed-loop cleaner production.

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