چكيده به لاتين
The use of new technologies such as membrane technology in separation process is inevitable for sustainable development, reducing water and wastewater pollution. The main challenge in membrane filtration is to make a balance between the membrane rejection and permeability values to increase its efficiency in water and wastewater industries. The main purpose of this study is to prepare a sustainable hierarchical meso-macroporous alumina membrane with proper mechanical strength for tight ultrafiltration (TUF) to increase the membrane permeability and efficiency with the appropriate membrane rejection value. The controlled existence of macropores in mesoporous material leads to higher liquid transfer to mesoporous sites with high surface area. The goal parameters for achieving TUF membrane with high efficiency are: high surface area (higher than 250 m2/g), pore size distribution in the 1-10 nm range, pore volume higher than 0.4 cm3/g, molecular weight cut off (MWCO) in the 1-10 kDa range, and the permeability value higher than the available permeability for ceramic tight ultrafiltration and fine ultrafiltration (F-UF).
To achieve this purpose, Taguchi method (TM) and response surface methodology (RSM) have been employed to optimize three parameters, including the amounts of P123, the amounts of nitric acid and calcination temperature, in order to define an optimal setting for sol‐gel synthesis of high surface area mesoporous alumina powder. The optimum setting of RSM design was 2.42 g P123, 0.58 ml nitric acid and calcination temperature of 524 °C and RSM statistically predicted high SBET (431.25 m2.g−1) under this optimum condition focused on quadratic model. Conducting confirmation test showed high BET surface (363.4 m2.g−1) assumed optimum setting calculated by RSM. Then, the optimal condition was studied using the gel casting method for preparing the macroporous alumina monolith. For this goal, the density changes, mechanical strength, BET surface area, pore size and pore size distribution were analyzed based on different preparation parameters such as alumina loading, the sintering temperature, the amount of monomer and crosslinker and nano alumina to micron alumina fraction. The optimum condition for providing the alumina macroporous monolith was 15 vol.% of alumina loading with a 60_N/40_M nano alumina to micron alumina fraction, and 18 wt.% monomer and crosslinker. For the prepared macroporous alumina in optimal condition, increasing the sintering temperature to 1600, 1450, 1300, and 1150 °C will lead to a total porosity of 32.99, 42.80, 59.41, and 70.44%, open porosity of 18.11, 67.42, 73.32, and 89.20%, bulk density of 2.86, 2.71, 1.61, and 1.17 g.cm-3, and mechanical strength of 27.18, 19.39, 9.24, and 7.50 MPa, respectively. Afterward, the hierarchical meso-macroporous alumina membrane was provided in optimal conditions for the mesoporous alumina powder and macroporous alumina monolith using a mixture of sol-gel and gel casting methods. The ultrafiltration membrane performance includes the water permeabilty and molecular weight cut off (MWCO) has been analyzed. The hierarchical meso-macroporous alumina membrane includes mesopores with 392.82 m2.g-1, 0.62 cm3.g-1, and 5.82 nm and macropores with a 161.63 nm porosity size, and 42.80% porosity percentage. This membrane has a 7.62 KDa molecular weight cut off at which 90% of the macromolecular solute (higher than 7.62 KDa) is rejected by the prepared membrane. The pure water permeability (PWP) of this membrane is 18.50 L.m-2.h-1.bar-1 that shows a considerable increase compared to the permeability of other similar ceramic tight ultrafiltration membranes.
