Influence of the composition and structure of the glass-crystalline shell of cenospheres on helium permeability

Abstract

INTRODUCTIONMembrane technologies of gas mixture separation are a steadily developing research area [1] and require the creation of selective membranes possessing high permeability, increased mechanical strength, and thermal and chemical resistance. The membranes are manufactured from polymeric and nonorganic mate rials in the form of planar, tubular, and spiral elements [2]. Any damage to such constructions in the process of their use leads to a drastic quality drop of the gas mixture separation.Increasing the effectiveness of gas mixture separa tion is achieved by the use of hollow closed membrane elements. In this area, expensive synthetic glass microspheres based on borosilicate glass are used [3,4], which are subjected to additional processing to improve their permeability (acid etching, doping with rare earth and transition metals).The promising prospects of using silicate glasses as membranes are due to the combination of their high permeability to helium and hydrogen with an extremely low permeability to the heavier gases (oxy gen, nitrogen, methane); moreover, the selectivity of separation of helium-nitrogen and helium-methane gas mixtures reaches the values of 10 5 -10 6 . This is one of the significant technological advantages of silicate glass membranes over polymeric ones [5].An essential influence on the diffusive properties is exerted by phase transformations in the glasses, accompanied by crystallization of phases. For the glass crystalline materials, helium diffusion occurs along two routes: through the anionic lattice of the glass and along the interphase "glass-crystal" bound aries. The contribution of each route to the total diffu sion process depends on temperature. For example, for the quartz glass samples containing cristobalite crystals, at temperatures above 300°C, the preferable route is lattice diffusion of helium with an activation energy of 24 kJ/mol; in the low temperature interval 0-110°C, diffusion along the interphase "glass-cris tobalite" boundaries becomes predominant, for which the activation energy amounts to 18 kJ/mol [6].In the creation of selectively permeable mem branes for gas mixture separation, as well as in the sorption and storage of the desired components (e.g., helium and hydrogen), of special interest are hollow microspheres with a thin glass crystalline shell, which provide increased permeability and mechanic strength. Such microspherical membranes can be made of glass crystalline cenospheres of fly ash, whose special features of morphology and phase composition suggest promising prospects for obtaining certain modern functional materials.Cenospheres, or aluminosilicate hollow micro spheres, are one of the microspherical components of fly ashes of the sialic type [7]; they are characterized by a low (0.2-0.8 g/cm 3 ) bulk density and can be easily isolated in concentrated form by gravitational meth Abstract-We studied the interrelation between the composition, morphology, and helium permeability of the shell of narrow fractions of nonmagnetic nonperforated cenosph...

Characterization of Fly Ash Cenospheres Produced from the Combustion of Ekibastuz Coal

“…53 As a result, the cenospheres have an additional advantage in the development of functional materials, such as microspherical membranes, 15,16 composite sorbents, 18,19 and supported catalysts. 23 Table 4.…”

“…27 In the design and preparation of microspherical glass-crystalline materials for highly selective separation of helium, the determining factors are the shell thickness and the content of crystalline phases. 15 Our previous study 16 indicated that, as the content of the mullite phase in the shells of the cenospheres increases in the range from 4 wt % to 48 wt %, the helium permeability coefficient at 25°C increases by 2 orders of magnitude and exceeds, by approximately the same value, the corresponding coefficient for synthetic hollow glass microspheres 3 M Scotchlite K37 glass bubbles. For the cenospheres containing 48 wt % mullite and 14 wt % cristobalite, the separation factors of the helium−hydrogen and helium−neon mixtures at a temperature of 280°C are equal to 32 and 221, respectively, which are considerably higher than the corresponding values for polymeric membrane materials He/ H 2 = 1−4 (ref 29) and He/Ne = 5 (ref 30).…”

Influence of chemical composition of fly-ash cenospheres on their grains size

“…One of the key parameters determining the possible use of waste is the chemical composition (Uliasz-Bocheńczyk and Mokrzycki 2018). The largest part is constituted by SiO 2 silica (45-60%) and Al 2 O 3 white clay (20-30%) (Żyrkowski et al 2016;Haustein and Quant 2011;Kapuściński and Strzałkowska 2008;Senthamarai Kannan et al 2016;Fomenko et al 2012), which ensures their high mechanical strength (Żyrkowski et al 2016;Dey and Pandey 2016). The remaining components: Fe 2 O 3 and CaO, MgO, SO 3 , K 2 O, Na 2 O and TiO 2 , occur in low concentrations (Vassilev et al 2004;Strzałkowska 2017;Ngu et al 2007).…”

Characterization of Aerodynamically Separated Products of Fly Ash Produced via the Pulverized Combustion of Coal from Kuznetsk Basin

“…В последние годы повышенный интерес вызывают разработки на основе отдельных компонентов зол функциональных материалов с заданными свойствами (адсорбентов, катализаторов, носителей, керамических материалов, цеолитов) [4,6]. Так, вы-деление из зол-уноса узких фракций микросфер определенного размера в интервале 50-250 мкм с постоянным химическим и минерально-фазовым составом [18][19][20][21] позволило получить высокоселективные мембраны для диффузионного выделения гелия и контейнеры для хра-нения водорода [22][23][24], эффективные катализаторы для процессов окисления метана [25,26], крекинга тяжелой нефти, мазутов и битумов [27,28], сенсибилизаторы эмульсионных взрывча-тых веществ [29], магнитоуправляемые капсулированные рН-чувствительные спиновые зонды для исследования биологических объектов [30], магнитные аффинные сорбенты типа «ядро-оболочка» для выделения рекомбинантных белков [31,32], композитные сорбенты для извле-чения радионуклидов из жидких радиоактивных отходов [33][34][35].…”