Preparation of carbon molecular sieve membranes from an optimized ionic liquid-regenerated cellulose precursor

Abstract

Novel carbon molecular sieve membranes with high separation performance and stability in the presence of humidified streams were prepared from an optimized ionic liquid-regenerated cellulose precursor, in a single carbonization step. Membranes prepared at two different carbonization end temperatures (550°C and 600°C) were analyzed through scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, carbon dioxide adsorption and permeation experiments. The prepared membranes exhibited uniform thickness of approximately 20 µm and a well-developed microporous structure. The permeation performance of these carbon molecular sieve membranes was above the Robeson upper bound curve for polymeric membranes. In particular, the membrane prepared at 550°C end temperature exhibited permeability to oxygen of 5.16 barrer and O 2 /N 2 ideal selectivity of 32.3 and permeability to helium of 126 barrer and He/N 2 ideal selectivity of 788; besides, permeation experiments performed in the presence of ca. 80% relative humidity showed that humidity does not originate pore blockage. These results open the door for the preparation of tailor made precursors that originate carbon molecular sieve membranes with extraordinary separation performances, mechanical resistance and stability. [21], poly(furfuryl alcohol) [22,23], phenolic resins [24-28], resorcinol-formaldehyde resin [29][30][31][32] and cellulose [16,[33][34][35]. Recently, our group applied for a patent of a process for obtaining, in a single carbonization step, CMSM that display no pore blockage effect in

Cellulose-Based Carbon Molecular Sieve Membranes for Gas Separation: A Review

“…These CMSM present a better permeability/selectivity balance when compared with the other cellulose-based CMSM with O 2 /N 2 ideal selectivity well above the Robeson upper bound for the two temperatures. The CMSM carbonized at 600 • C presents a larger volume of micropores but with smaller length resulting in lower permeability than the CMSM prepared at 550 • C [30]. The permeability of CO 2 decreased from 13 barrer to 4 barrer due to the tighter carbon structure induced by the sintering mechanism [30].…”

“…Despite the great expectation of the cellophane-based paper carbon membranes [75], such as its very high selectivity, >800 for O 2 /N 2 , the permeability of O 2 is low (1 barrer). To overcome this limitation, Rodrigues et al developed a high-performance cellulose-based CMSM prepared from an optimized ionic liquid-regenerated cellulose precursor [30]. In this work, 9.2 wt% of wood pulp was dissolved in DMSO and 1-ethyl-3-methyl imidazolium acetate (EMIMAc) to obtain a homogeneous solution.…”

“…Rodrigues et al [30], studying the preparation of CMSM from an optimized ionic liquid-regenerated cellulose precursor, immersed the precursor films in a softener bath with 5 wt% of propylene glycol for 1 min; the precursor films were then dried in an oven at 100 • C for 10 min. Propylene glycol was added to act as a molecular spacer, preserve the pores, reduce the warpage, improve the mechanical properties of the carbonized membranes and improve the membrane permeability [30].…”

“…Therefore, typically, lower permeability and higher selectivity is achieved increasing the end carbonization temperature. However, the mechanical stability is also influenced by the carbonization end temperature [30,75], and CMSMs carbonized at higher temperatures are usually more brittle. Therefore, a compromise between membrane performance and mechanical stability should be attained.…”

“…In 2019, the same authors prepared an ionic liquid-regenerated cellulose-based CMSM prepared at 550 • C and 600 • C [30]. These CMSM present a better permeability/selectivity balance when compared with the other cellulose-based CMSM with O 2 /N 2 ideal selectivity well above the Robeson upper bound for the two temperatures.…”