Drying of cellulose nanocrystal gel beads using supercritical carbon dioxide
7
Citation
30
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract BACKGROUND The effects of the conditions for the supercritical carbon dioxide (scCO 2 ) drying of cellulose nanocrystal (CNC) wet gel were investigated on the residual solvent content, the shrinkage and the microstructure of the ensuing aerogel. RESULTS The scCO 2 drying of CNC wet gel could be divided into a spillage phase and an extraction phase. In the first phase, just a very short time after the beginning of drying, shrinkage occurred and more than half of the solvent was removed. No further shrinkage was observed thereafter, but the solvent continued to be exponentially removed. Increasing pressure, temperature and time were favorable for solvent removal and the reduction of aerogel shrinking. The shrinkage increased the pore size inside the aerogel and made the outer surface of the CNC aerogel much denser than its interior. To preserve the original microstructure of the wet gel, the optimal drying was performed at 11.04 MPa and 40 °C for 120 min. At these conditions, the shrinkage ratio was only inversely proportional to the CNC content in the wet gel. CONCLUSION CNC aerogel was obtained with a shrinkage ratio of 3.1%, a surface area of 387 m 2 g −1 and an average pore size of 7.2 nm using 3.0% (w/w) CNC wet gel. © 2019 Society of Chemical IndustryKeywords:
Shrinkage
Supercritical Carbon Dioxide
Supercritical drying
Supercritical drying
Alkoxide
Cite
Citations (41)
TEOS aerogel a is the most commonly used. a Aerogel has attracted increasing attention from both academic and industries due to its extraordinary performance and potentials. We have systematically studied the relationship between the densification temperature of the synthesis environment of silica aerogels on their resulting morphological, optical and thermal properties. SEM and BET measurements were employed as structural probes to ascertain the structural differences. Lee's disc apparatus was used for determining the thermal conductivity coefficient. There is a systematic correlation between the annealing temperature and the aerogel surface area, porosity, as well as pore size. The implemented autoclave was able to produce aerogel monolith of surface area reaching to 998.25 g/m2 and low electric conductivity arrive to of 1.17*10-4(s/m), associated with density of 0.047 g/cm3.The calculated thermal conductivities were (0.0063, 0.016 and 0.0053 mW m-1 0 C-1) for pH1, pH7 and pH8 samples respectively. The microstructure observed is categorized into three types, namely, open cellular foam (the substance that is formed by trapping pockets of gas in solid), fractal (the structural features it's clearly show the hierarchical repetition) and isotropic morphology (visible spectrum scale). The aerogel properties were are remarkably varied. While the influence of annealing temperature the reaction setting has gradually influence on the final aerogel properties, h However, it is obviously requested for achieving desirable optically and nano-featured products.
Supercritical drying
Specific surface area
Cite
Citations (2)
Supercritical drying
Alkoxide
Cite
Citations (1)
Monolithic silica aerogel is a transparent material with very low thermal conductivity. These properties make the material interesting for use as insulation in, for example, windows, solar collectors, and solar walls. To produce silica aerogel it is necessary to circumvent the high capillary forces working when the solvent is being removed from the gel structure during drying. Supercritical drying has successfully achieved this. However, supercritical drying with an alcohol might be a dangerous and expensive way to produce the aerogel material. In this work we have studied a new type of monolithic silica xerogels made without supercritical drying. The xerogels are produced by strengthening the gel structure before drying, and low densities in the range 0.42 - 0.73 g/cm3 have been obtained. Properties of this new type of silica xerogels have been compared to the properties of silica aerogel made by supercritical drying. Density, pore size, surface area, thermal conductivity, and optical transmittance are reported in this work and some application advantages are discussed.
Supercritical drying
Cite
Citations (2)
A tetramethylorthosilicate(TMOS)/ethanol solution was gelled together with BaTiO3 nanoparticles or carbon nanoparticles. The wet gel was dried in supercritical carbon dioxide, resulting in aerogel nanocomposites with compositions in the range of BaTiO3/SiO2 = 1/100 to 20/100 and C/SiO2 = 20/100 to 80/100. The bulk density of the aerogel obtained was in the range of 0.1 to 0.2 g/cm3, the porosity was about 95%, and the specific surface area was in the range of 400 to 700 m2/g. These values represent the characteristics of the aerogel. The relative permittivity and dielectric loss were respectively approximately 2 and 5 × 10−3 for the BaTiO3-silica aerogel nanocomposite, and in the range of 5 to 10 and 0.012 to 0.4 for the carbon-silica aerogel nanocomposite.
Supercritical drying
Carbon fibers
Cite
Citations (3)
The new supercritical CO_2 drying technology provides a green and safe method to develop these structure-controllable materials.Recent researches on the process parameters and the mechanisms are reviewed.Preparation of superfine ZrO_2 aerogel catalysts using supercritical CO_2 drying is introduced.Application prospects of oxide aerogel catalysts are also discussed.
Supercritical drying
Cite
Citations (0)
Supercritical drying
Nanoporous
BET theory
Specific surface area
Cite
Citations (38)
With tetraethoxysilicane as raw material and by addition of catalyst(dilute hydrochloric and aqueous ammonia),SiO2 alcogel was obtained by sol-gel process.SiO2 alcogel was transformed into SiO2 aerogel via the CO2 supercritical drying technique,which had four parameters—Carbon dioxide flow,supercritical temperature,drying time,and supercritical pressure.A four-factor,three-level orthogonal experiment was designed to investigate the influence of these four parameters on the density and BET of the resultant SiO2 aerogel.In the experiment the microstructure,shape,and composition of SiO2 aerogel were analyzed by SEM,BET,TEM,and FTIR.The experimental results report: the optimized parameters were 12 kg·h-1 of CO2 flow,13 mPa of pressure,45 ℃ of supercritical temperature,and 6 h of supercritical drying time.The prepared SiO2 aerogel was composed of spherical nano-particles with size between 0 nm and 20 nm.Its pore size was around 10 nm,its specific surface area was 927.37 m2·g-1,and its density was 0.195 6 g·cm-3.Therefore,the prepared SiO2 aerogel was a typical nano-mesoporous material.
Supercritical drying
Supercritical Carbon Dioxide
Specific surface area
Supercritical fluid extraction
BET theory
Cite
Citations (0)
Silica aerogels were prepared through a two-step catalyzed sol-gel route and ethanol supercritical drying technique.A four-factor,three-level orthogonal experiment was designed to investigate the influence of technological parameters of ethanol supercritical drying on the density of resulting SiO2 aerogel.The optimized parameters are 400 mL of ethanol,8 MPa of pre-pressure,270 ℃ of supercritical temperature and 12 MPa of supercritical pressure.Density of silica aerogel prepared under this condition is only 0.091 1 g/cm3.The microstructure of the aerogel was investigated by SEM,TEM and FTIR.
Supercritical drying
Supercritical fluid extraction
Cite
Citations (0)
Supercritical drying
Nanoporous
Monolith
Texture (cosmology)
Cite
Citations (12)