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Recovery of acid and base from brackish water by bipolar membrane electrodialysis
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Authors
Abstract(s)
Nesta dissertação pretendeu-se estudar a viabilidade do uso de eletrodiálise com
membranas bipolares (BM) na recuperação de ácido clorídrico e de hidróxido de sódio a
partir de um efluente industrial que contém 1.4 mol/L de
cloreto de sódio. Estas membranas mostraram ser uma ferramenta eficiente para a
produção de ácidos e bases a partir do respetivo sal.
Foi feita uma seleção de diferentes membranas bipolares (Neosepta, Fumatech e PCA) e
aniónicas (PC-SA e PC-ACID 60) na tentativa de encontrar a combinação mais adequada
para o tratamento do efluente. Dependendo do critério, o melhor arranjo de membranas é o
uso de PC-ACID 60 (membrana aniónica), PC-SK (membrana catiónica) e membranas
bipolares do tipo Neosepta para maior pureza dos produtos; membranas bipolares
Fumatech para maior eficiência de dessalinização e membranas bipolares PCA para um
maior grau de dessalinização. Tecnologicamente foi possível obter uma dessalinização de
99.8% em quatro horas de funcionamento em modo batch com recirculação de todas as
correntes.
Independentemente da combinação usada é recomendável que o processo seja parado
quando a densidade de corrente deixa de ser máxima, 781 A/m2. Assim é possível evitar o
aumento de impurezas nos produtos, contra difusão, descida instantânea do pH e uma
dessalinização pouco eficiente.
A nível piloto o principal fornecedor de membranas e unidade de tratamento “stack” é a
marca alemã PCA. Sendo assim realizaram-se ensaios de repetibilidade, contra difusão,
avaliação económica e upscaling utilizando as membranas bipolares PCA. A nível
económico estudou-se o uso de dois tipos de unidades de tratamento; EDQ 380 e EDQ
1600, para diferentes níveis de dessalinização (50, 75 e 80%). Tendo em conta a otimização
económica, é recomendável uma dessalinização máxima de 80%, uma vez que a eficiência
de processo a este ponto é de 40%.
A aplicação do método com a unidade EDQ 1600 para uma dessalinização de 50% é a mais
vantajosa economicamente, com custos de 16 €/m3 de efluente tratado ou 0,78 €/kg Cl-
removido. O número de unidades necessárias é 4 posicionados em série.
The purpose of this thesis is the recovery and reuse of valuable chemicals from an industrial salt effluent. An acid solution, hydrochloric acid, and a base, sodium hydroxide, were produced from a brackish waste water containing 1.4 mol/L of sodium chloride. The method used was bipolar membranes electrodialysis. A method that looks very promising, particularly when environmental oriented laws will be introduced and technological changes will take place. Furthermore, bipolar membranes are an efficient tool for the production of acids and bases from their corresponding salt. Experimentally, a screening of different types of bipolar membranes (Neosepta, Fumatech and PCA) and anion exchange membranes (PC-SA and PC-ACID 60) was carried out in an attempt to find out which one is best suited for the treatment of the stream. The most suitable combination is a cation exchange membrane PC-SK from PCA, an anion exchange membrane PC-ACID 60 from PCA and a Neosepta Bipolar Membrane for purest products, Fumatech for highest efficiency and PCA for highest degree of desalination. Ii is strictly recommended to stop the experiment at a current density of 781 A/m2 to avoid back diffusion, a drop in pH, the increase of impurities, the possibility to work over the limiting current and very low efficiencies. Technologically it was possible to have a desalination of 99.8% after four hours of recirculation, however this is not recommended because of economical reasons. The main supplier for the pilot scale installation is PCA, so the study was focused on using a combination of PCA bipolar membrane, PC ACID 60 and PC-SK. A first economical evaluation estimate was done for this combination. Two stacks from PCA were studied; EDQ 380 and EDQ 1600, as well as different degrees of desalination (50, 75 and 80%). The most attractive results were obtained using 4 stacks in series EDQ 1600 for 50% desalination. The cost is 16 €/m3 of treated water or 0.78 €/kg of Cl- removed.
The purpose of this thesis is the recovery and reuse of valuable chemicals from an industrial salt effluent. An acid solution, hydrochloric acid, and a base, sodium hydroxide, were produced from a brackish waste water containing 1.4 mol/L of sodium chloride. The method used was bipolar membranes electrodialysis. A method that looks very promising, particularly when environmental oriented laws will be introduced and technological changes will take place. Furthermore, bipolar membranes are an efficient tool for the production of acids and bases from their corresponding salt. Experimentally, a screening of different types of bipolar membranes (Neosepta, Fumatech and PCA) and anion exchange membranes (PC-SA and PC-ACID 60) was carried out in an attempt to find out which one is best suited for the treatment of the stream. The most suitable combination is a cation exchange membrane PC-SK from PCA, an anion exchange membrane PC-ACID 60 from PCA and a Neosepta Bipolar Membrane for purest products, Fumatech for highest efficiency and PCA for highest degree of desalination. Ii is strictly recommended to stop the experiment at a current density of 781 A/m2 to avoid back diffusion, a drop in pH, the increase of impurities, the possibility to work over the limiting current and very low efficiencies. Technologically it was possible to have a desalination of 99.8% after four hours of recirculation, however this is not recommended because of economical reasons. The main supplier for the pilot scale installation is PCA, so the study was focused on using a combination of PCA bipolar membrane, PC ACID 60 and PC-SK. A first economical evaluation estimate was done for this combination. Two stacks from PCA were studied; EDQ 380 and EDQ 1600, as well as different degrees of desalination (50, 75 and 80%). The most attractive results were obtained using 4 stacks in series EDQ 1600 for 50% desalination. The cost is 16 €/m3 of treated water or 0.78 €/kg of Cl- removed.
Description
Keywords
Eletrodiálise Membranas bipolares Corrente limitante Análise económica Electrodialysis Bipolar Membranes Limiting Current Economic Evaluation