Influence of osmotic distillation on membrane absorption for the treatment of high strength ammonia wastewater

Osmotic distillation(OD) was found to be a coupled process in membrane absorption(MA) for the treatment of high strength ammonia wastewater. As a result, ammonia could not be concentrated in absorption solution(AS) as expected. The inhibition of the coupled OD in MA process was investigated as well as various factors affecting the inhibition. The results indicated that the coupled OD can be effectively inhibited by heating concentrated solution and cooling dilute solution. It was also found that experimental minimum inhibition temperature difference(MITD) between concentrated and dilute solutions was different when using polyvinylidene fluoride(PVDF) and polypropylene(PP) membranes respectively, which could be ascribed to material properties, such as OD and membrane distillation(MD) coefficients of the membranes. Experimental MITDs were found to be higher than theoretical MITDs which were calculated using a simplified method.

Experimental studies on the influence of porosity on membrane absorption process

Eight kinds of flat membranes with different micro-structures were chosen to carry out the membrane absorption experiments with CO_(2) and de-ionized water or 0.1 mol·L^(−1) NaOH solution as the experimental system.According to experimental results,the membrane pores shape(stretched pore and cylinder pore)and membrane thickness do not affect the membrane absorption process,and the membrane porosity has only little influence on membrane absorption process for slow mass transfer system.However,the influence of porosity on the membrane absorption process became visible for fast mass transfer system.Moreover,the mass transfer behavior near the membrane surface on liquid side was studied.The results show that the influence of membrane porosity on mass transfer relates to flow condition,absorption system and distance between micro-pores,etc.

Unexpected Selective Absorption of Lithium in Thermally Reduced Graphene Oxide Membranes

Lithium plays an increasingly important role in scientific and industrial processes, and it is extremely important to extract lithium from a high Mg^(2+)/Li^(+) mass ratio brine or to recover lithium from the leachate of spent lithiumion batteries. Conventional wisdom shows that Li^(+) with low valence states has a much weaker adsorption(and absorption energy) with graphene than multivalent ions such as Mg^(2+). Here, we show the selective adsorption of Li^(+) in thermally reduced graphene oxide(rGO) membranes over other metal ions such as Mg^(2+), Co^(2+), Mn^(2+),Ni^(2+), or Fe^(2+). Interestingly, the adsorption strength of Li^(+) reaches up to 5 times the adsorption strength of Mg^(2+),and the mass ratio of a mixed Mg^(2+)/Li^(+) solution at a very high value of 500 : 1 can be effectively reduced to 0.7 : 1 within only six experimental treatment cycles, demonstrating the excellent applicability of the rGO membranes in the Mg^(2+)/Li^(+) separation. A theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cation–π interaction and steric exclusion when hydrated cations enter the confined space of the rGO membranes.

Preparation of Calcium Carbonate Nanoparticles with a Continuous Gas-liquid Membrane Contactor： Particles Morphology and Membrane Fouling

Nanosized calcium carbonate particles were prepared with a continuous gas-liquid membrane contactor. The effects of Ca(OH)2 concentration, CO2 pressure and liquid flow velocity on the particles morphology, pressure drop and membrane fouling were studied. With rising Ca(OH)2 concentrations, the average size of the particles increased. The effects of Ca(OH)2 concentration and CO2 pressure on particles were not apparent under the experimental conditions. When the Ca(OH)2 concentration and liquid flow velocity were high, or the CO2 pressure was low, the fouling on the membrane external surface at the contactor entrance was serious due to liquid leakage, whereas the fouling was slight at exit. The fouling on the membrane inner-surface at entrance was apparent due to adsorption of raw materials. The membrane can be recovered by washing with dilute hydrochloric acid and reused for at least 6 times without performance deterioration.

Permeation properties of CO2 and CH4 in asymmetric polyethersulfone/ polyesterurethane and polyethersulfone/polyetherurethane blend membranes

The transport performances of carbon dioxide and methane were studied in polyethersulfone, polyethersulfone/polyeterurethane(PES–ETPU) and polyethersulfone/polyestherurethane(PES–ESPU) blend membranes separately with different compositions. The variations in the structural characteristics of PES membrane after incorporation of ESPU and ETPU were investigated by different techniques. Additionally, the effect of pressure and composition on the permeance of CO_2, CH_4 and ideal selectivity of CO_2/CH_4 were checked on the membranes.The results revealed that the morphology of the blend membranes was affected by two opposite factors: thermodynamic enhancement and kinetic hindrance. The membranes with denser sponge layers were formed at lower ratio of PU/PES, while more porous structure with enlarged macrovoids membranes were observed at higher PU content. The results indicated that adding PU to PES membrane, caused permeance improvement of the gases with nearly no change and/or reduction in ideal selectivity of CO_2/CH_4. Moreover, PES–ETPU membranes showed higher permeability and less CO_2/CH_4 selectivity in comparison with PES–ESPU samples. For PES–ESPU membrane containing 1.5% ESPU, CO_2 permeance at 10 bar was improved up to 20% with almost no change in CO_2/CH_4 selectivity with respect to PES. Finally, response surface methodology was used to evaluate the effects of the operating parameters on the permeance and ideal selectivity.

VALORIZATION OF BIOGAS THROUGH SIMULTANEOUS CO_(2) AND H_(2)S REMOVAL BY RENEWABLE AQUEOUS AMMONIA SOLUTION IN MEMBRANE CONTACTOR

Upgrading biogas into biomethane not only improves the biogas utilization as vehicle fuel or natural gas substitute,but also reduces the greenhouse gases emissions.Considering the principle of engineering green energy process,the renewable aqueous ammonia(RAA)solution obtained from biogas slurry was used to remove H_(2)S and CO_(2) simultaneously in the hollow fiber membrane contactor.RAA was mimicked in this study using the ammonia aqueous solution mixed with some typical impurities including ethanol,acetic acid,propionic acid,butyric acid and NH4HCO_(3).Compared with the typical physical absorption(i.e.,pure water)removing 48%of H_(2)S from biogas,RAA with 0.1 mol·L^(−1) NH_(3) could remove 97%of H_(2)S.Increasing the NH3 concentration from 0.1 to 0.5 mol·L^(−1) could elevate the CO_(2) absorption flux from 0.97 to 1.72 mol·m^(−2)·h^(−1) by 77.3%.Among the impurities contained in RAA,ethanol has a less impact on CO_(2) absorption,while other impurities like CO_(2) and acetic acid have significant negative impacts on CO_(2) absorption.Fortunately,the impurities have a less influence on H_(2)S removal efficiency,with more than 98%of H_(2)S could be removed by RAA.Also,the influences of operating parameters on acid gases removal were investigated to provide some engineering suggestions.