Influnces Of Membrane Fouling And Uphill Transport On Reverse Electrodialysis Performance

The implementation of the green transformation strategy of energy and electric power under the goal of"double carbon"provides a vital opportunity for the exploitation and utilization of Marine renewable energy resources.Salt difference energy is a kind of renewable energy produced when two solutions of different salt concentrations are mixed.As a kind of Marine energy,it has a large amount of resources,but low utilization rate and immature utilization way.Reverse electrodialysis（RED）,which has converted salt difference into electric energy through ion-exchange membrane,has a huge potential for development as a new green and recyclable energy technology.RED has achieved considerable electricity generation efficiency in the laboratory stage with pure sodium chloride solution as the feed solution.However,in practice,the presence of organic matter and a variety of polyvalent ions in natural water will affect the ion exchange capacity and membrane resistance of the ion exchange membrane,thus affecting the electricity generation efficiency of the RED device.Based on this,this paper mainly studied the influence of ion exchange membrane pollution and polyvalent ion reverse slope transport on the electrochemical characteristics of RED device,and explored the influence law of operating conditions on the electrochemical characteristics of RED device.In the experiment,an electrochemical workstation was used to monitor the changes in the electrochemical characteristics of RED device under different polyvalent ion feeding solutions.The results show that the polyvalent ions will not only have the phenomenon of inverse slope transport,but also increase the resistance of the ion exchange membrane and reduce the generation voltage,thus reducing the power density of the RED device.Therefore,on the one hand,the reverse slope transport phenomenon was explored.The test results showed that when MgCl₂ solution was added only in RED dilute test,the Mg²⁺content in dilute measured water was less than that in influent water,indicating that the reverse slope transport phenomenon occurred.On the other hand,the influence of MgCl₂,CaCl₂ and Na₂SO₄ polyvalent ions as feed salt solution on the electrochemical characteristics of RED was explored.The test results showed that with the addition of three polyvalent ions and the increase of their concentration,the voltage,resistance and power density of RED device all showed a decrease.High ion valence leads to low voltage and high resistance.The influence of the addition of polyvalent ions on RED power density is Na₂SO₄>CaCl₂>MgCl₂.Secondly,sodium alginate（SA）was used as a typical natural organic matter to explore the effect of interaction between SA and polyvalent ions on the electrochemical characteristics of RED.The experimental results showed that when SA was added only on one side,the power density of RED device increased when pure Na Cl and polyvalent ions were used as salt solution and SA concentration was lower than 30 mg/L.When the SA concentration is greater than30mg/L,the power density decreases.When SA was added on both sides,the power density changed similarly with SA concentration,but the power density level was higher.When the feed salt solution was CaCl₂ and SA was added,the power density did not increase significantly,which might be due to the chelation reaction between Ca²⁺and SA.When pure Na Cl is used as salt solution and SA is added,the power density generated by RED is greater than the power density of MgCl₂,CaCl₂,Na₂SO₄ interacting with SA,indicating that the addition of polyvalent ions will decrease the voltage and increase the resistance of RED device,which is consistent with the reasons described before.Based on the XDLVO theory,the interfacial free energy between the membrane and the pollutant was calculated,and the interaction between SA and the ion exchange membrane was analyzed to reveal the interfacial thermodynamic principle of SA’s influence on the efficiency of RED power generation.SA can spontaneously adsorb to the anion exchange membrane,resulting in the increase of the membrane resistance and the decrease of the power density of the RED device.The effect of salt difference ratio and solution flow rate on the electrochemical characteristics of RED was further studied.The experimental results show that the RED voltage and power density increase and the resistance decreases with the increase of salt difference ratio when the mixed solution of polyvalent ions and Na Cl is used as the feed solution,and the RED voltage and power density tend to be stable when the salt difference ratio is 30.When salt difference ratio and flow velocity interact with RED,with the increase of salt difference ratio and flow velocity on both sides,the RED voltage and power density increase rapidly and then slowly,and the resistance increases rapidly and then slowly,and tends to be stable when the final flow rate is 200 m L/min.The change of RED voltage is not obvious only by changing the thick side velocity.Therefore,the effect of salt difference ratio and dilute flow rate on the electrochemical characteristics of RED was studied.The experimental results show that the RED voltage,resistance and power density change similarly with dilute flow rate compared with the increase of flow rate on both sides,and the maximum power density is obtained when the salt difference is 30 and the flow rate is 400 m L/min.To sum up,membrane pollution and polyvalent ion reverse slope transport reduce the voltage and power density of RED device,and increase the resistance.With the increase of salt difference ratio and solution flow rate,the voltage and power density of RED device increase and the resistance decreases.This study provides data support for the improvement of RED electricity generation efficiency and theoretical basis for its application in practical engineering.