Study On Preparation,Structure And Properties Of The Anion Exchange Membranes For Recovery Of Waste Acid By Diffusion Dialysis

A large amount of acid-rich wastewater is produced in various industrial production processes such as metal pickling,electroplating,etching,mining and bacterial fermentation engineering.The resource utilization of acid-rich wastewater is a great challenge to the sustainable development of modern industry.Acid recovery by diffusion dialysis(DD)can simultaneously realize the separation and recovery of acid and metal resources in acid-rich wastewater.Anion exchange membrane(AEM)is the core component of acid recovery via DD.Using the existing commercial membranes to solve the problem of resource utilization of massive acid wastewater will cost huge amounts of membrane area and equipment volume resulting extremely high project cost due to their limited acid diffusion coefficients(+)and separation factors(S).The present situation of acid recovery by DD urgently needs to develop AEMs with high values of+and S.In this paper,anion exchange membranes with different local high fixed charge density afforded by the fixed cations of biquaternary ammoniums,hexaquaternary ammonium and different hydrophobic backbones were designed according the orientations of functionalities.The designed AEMs were fabricated by the designing of molecular structures and processes.The effects of varying structures and distributions of different fixed cations on the DD performances of acid recovery of the AEMs were studied.The main research contents are as follows:(1)Using 1,4-Diazabicyclo[2.2.2]octane;triethylenediamine(DABCO)and poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)as the core units,a series of PPO-based DABCO double fixed cations functioning AEMs with the various auxiliary side groups having different hydrogen bond forming abilities were designed and prepared.The effects of different auxiliary side groups on the basic structure and DD performance of the series of AEM were studied.It is found that this series of AEMs have obvious microphase structure and strong Donnan repulsion effect.The membrane PPO-DABCO-Hex125 with hydrophobic side group gives full play to the advantage of high fixed charge density of DABCO double cations,and has a very high S value.But the very low+of PPO-DABCO-Hex125 makes itself losing utilization chance.The double hydrogen bond center side group of hydroxyethyl with active hydrogen and the single hydrogen bond center side group of furan-2-methyl have strong abilities to regulate the interstitial phase structures.The fluxes of hydrogen ion of these two kinds of AEMs can be enhanced by the Gr?tthuss mechanism.The PPO-DABCO-Et OH125 membrane with hydroxyethyl side groups has the highest values of+and S simultaneously,and the PPO-DABCO-MTHF125 membrane with furan-2-methyl side groups has a relatively balanced DD performances.The diffusion dialysis performances of these two kinds of membranes are much higher than those of the commercial membrane TWDDA1(+=9 mm·h^-1,+_/0)2+=19.51).(2)A series of AEMs with double hydrogen bonding center auxiliary hydroxyethyl side groups(PPO-DABCO-Et OH50-125)having different ion exchange capacities(IEC)were designed and prepared.The effects of distribution of hydroxyethyl DABCO double cations on the structures and performances of the AEMs were studied systematically.The effective mechanisms of the active hydrogen and double hydrogen bond centers on the DD performance of the AEMs were explored.The continuity of the active regions resulting from the cation groups has a great influence on the performance of the type of cation channel.The channels with high hydrogen ion flux and high selectivity can be achieved only if enough continuity is achieved.With a small increase of IEC,the+of the channel is doubled,and the separation factor is only reduced by 14.16%.The PPO-DABCO-Et OH125 membrane has excellent DD performance.The+value is 24.31 mm·h^-1 and the S value is 71.48.At the same time,the membrane has good thermal,dimensional,acid stability and mechanical properties,which can meet the long-term working requirements of DD process.(3)A series of DABCO double fixed cations type AEMs with single hydrogen bonding center auxiliary hydroxyethyl side group(PPO-DABCO-MTHF100-150)and different IECs are prepared from PPO and MTHF-DABCO.The effect of distribution of furan-2-methyl DABCO double cations on the structures and performances of the AEMs were studied systematically.The effecting mechanism of the side group with mono strong hydrogen bond center of non-hydrogen on the DD behavior is firstly revealed in the thesis.The tetrahydrofuran-2-methyl side groups can fix free waters close to the active regions of the biquaternary ammonium ions to make full use of the Donnan repulsion effect,and improve the selectivity of the cations channels.This type of cation channel is characterized by synchronous enhancements of cation fluxes by the continuity of the active regions,which results in a larger decrease of S than that of PPO-DABCO-Et OH50?125 series.However,the PPO-DABCO-MTHF150membrane still has a high S value(43.11)companying the highest+value(+=24.0mm·h-1)and good basic performances.(4)In order to give full play to the high Donnan repulsion effect of DABCO multi-quaternary ammonium ions,a series of DABCO six-ion series-connected crosslinked AEMs based on poly(aryl ether sulfone)(PAES)(QPAES-DB25?75)were designed and prepared with DABCO,tetramethylbiphenyl bisphenol,9-bis(4-hydroxyphenyl)fluorene and 4-fluorophenyl sulfone as the core units.The structures and performances of the membranes were studied systematically.This series of membranes have obvious microphase separation structures and high fixed charge densities to afford strong Donnan effects.However,too high cross-linking density gives a rigid spatial network structure to limit the Donnan effect of the ion structure,and lead to a decrease of separation ability.Only at moderate ion crosslinking,the resulting QPAES-DB50 membrane gives full play to the advantage of series-connected multi-quaternary ammonium cations structure and show good DD performances in the conventional single metal waste acid system and multi-metal ions chloride waste acid system.QPAES-DB50 membrane with the excellent comprehensive performances shows a strong application prospect in DD acid recovery.