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Membranes 2021, 11, 575 24 of 29 solutions up to 0.18 M presents an SEC of up to 20.4 kWh·kg−1 of LiOH [31], depending on operating conditions. On the other hand, LiOH production by membrane electrolysis has reported an SEC of 6.1–14.6 kWh·kg−1 LiOH using initial LiOH solutions between 4 and 8 wt% as the initial catholyte [66] and 7.25 kWh·kg−1 of LiOH for an initial catholyte of 2.3 wt% [29]. For conventional industrial process of obtaining lithium hydroxide from Li2CO3 by chemical reaction with lime slurry, the specific energy consumption is 14.04 kWh·kg−1 of LiOH·H2O (or 24.6 kWh·kg−1 of LiOH) [67], of which electricity, fuel, and natural gas consumption represent 17.3%, 10.3%, and 72.4% of the total energy required, respectively. High natural gas consumption can be attributed to the thermal energy required for the evaporation and crystallization stages of the process to obtain lithium hydroxide monohy- drate, in which a lithium hydroxide solution of approximately 3 wt% must be evaporated to saturation. The BMED process of obtaining LiOH does not eliminate the need to evaporate LiOH solution to crystallize LiOH·H2O; however, it is expected that obtaining LiOH concentra- tions higher than 3 wt% would contribute to reduce heat requirements in these stages. Thus, if the LiOH solution is evaporated to saturation at 70◦C, initial LiOH concentrations of 4 wt% and 5 wt% would allow the thermal energy requirement to be reduced by 9.4% and 18.9%, respectively, compared to using a 3 wt% LiOH solution. Obtaining LiOH via the chemical reaction of Li2CO3 with lime slurry presents a conver- sion efficiency of 59.0–59.5% after one hour of processing at 60–100 ◦C [68], which, based on mass and energy balances, allows the estimation of a theoretical SEC of 1.27–2.84 kWh·kg−1 of LiOH. This required energy is lower than that obtained in this work by BMED. However, membrane processes could become competitive if process sustainability is considered by reducing the use of chemical reagents, reducing waste generation, and potential coupling with non-conventional renewable energies. 4. Future Challenges The results in this work present the current scope of obtaining high concentrations of LiOH by BMED, variation of electrical energy consumption with concentration, and salt leakage related to Cl− ion contamination of LiOH solution. The results of this work suggest that from an initial LiOH concentration of 0.5 wt%, it is possible to obtain con- centrated LiOH solutions in the range of 3.34–4.35 wt%, with 96.0–95.4% purity and a specific electricity consumption between 7.57 and 9.45 kWh per kilogram of LiOH. After this point, current efficiency tends to decrease below 0.50, significantly increasing the specific energy consumption of the process. This is associated with high OH− ion leakage in the cation-exchange membrane [40,53] and salt leakage in the bipolar membrane [44,69], which causes undesired Cl− transport into the LiOH compartment. In the production of LiOH by membrane electrolysis, energy consumption can be reduced in a concentra- tion range between 40 and 50 g·L−1 [30], which is approximately 3.5 wt% and4.3 wt% LiOH, respectively. For the implementation of a lithium hydroxide production process by electrodialysis with bipolar membranes, there exist limitations related to membrane performance, affecting final product purity and energy efficiency. For the use of lithium hydroxide as a precursor for lithium batteries, work must be done to reduce the transport of impurities in membranes. Both monopolar and bipolar membranes are not 100% permselective. Thus, as LiOH and HCl concentrations increase, LiOH solution purity and process efficiency are affected. Implementation-related challenges for this technology in LiOH production involve aspects such as the performance of monopolar membranes and bipolar membranes, stack design related to the optimal number of unit cells, membrane lifetime, and technology implementation coupled with renewable energy sources. In this work, evidence is shown that process efficiency is mainly established by membrane performance. To date, several investigations have been carried out in order to improve cationic membranes’ selective transport [70–72]. In the case of bipolar membranes,PDF Image | Bipolar Membrane Electrodialysis for LiOH Production
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