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Preparation and Evaluation of New Nanoporous Silica Materials for Molecular Filtration and for Core Materials in Vacuum Insulation Panels
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology. (Folke Björk)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanoporous materials for gas purification and thermal insulation have been studied and developed for application in many areas. It is known that a single adsorbent may not adequately control multiple contaminants. Further the utilization of nanoporous material as thermal insulator in building applications is limited due to high cost. Moreover, in view of the global environmental movement for clean air and reduction of heating energy consumption in built environment, the development of new and better nanoporous materials will not only facilitate major advances in gas adsorption and thermal insulation technology, but also meet the new challenges that cannot be met with the nanoporous materials that are currently available. This thesis presents a synthesis of new nanoporous silica based materials, and the characterization and application of these materials for molecular filtration and thermal insulation. Commercial nanoporous materials have been used for benchmarking for the pore properties, the applicability, and the performance of these new materials.

First a double metal-silica adsorbent has been synthesized. The preparation procedure is based on the use of sodium silicate coagulated with various ratios of magnesium and calcium salts which yields micro-meso porous structures in the resulting material. The results show that molar ratios of Mg/Ca influence the pore parameters as well as the structure and morphology. The bimodal pore size can be tailored by controlling the Mg/Ca ratio.

In the second synthesis, pure mesoporous silica, SNP has been prepared using glycerol as pore forming agent and monovalent salts as coagulant. This leads to material with large surface area and uniformed pore size centred at 43 or 47 nm.  The materials further exhibits a low bulk density in the range of 0.077 to 0.122 g/ml and possess a high porosity in the range of 95-97%. The influence of acid type (organic or inorganic) on the pore parameters and on the tapped density has also been investigated.  

A synthesis method has also been developed for the preparation of carbon-silica composites. The method involves a number of routes, which can be summarised as addition of activated carbon particles to (I) the paste, (II) the salt solution, or (III) with the sodium silicate solution. In route II and III the activated carbon is present before coagulation. The routes presented here leads to carbon-silica composites possessing high micro porosity, meso porosity as well as large surface areas. The results further shows that pore size distribution may be tailored based on the route of addition of the carbon particles. Following route I and III a wide pore size (1-30 nm) was obtained whereas by route II a narrow pore size (1-4 nm) was observed.    

MgCa-silica chemisorbents were also developed using either potassium hydroxide or potassium permanganate as impregnate chemicals. A direct or post-impregnation procedure was employed. The results revealed that the impregnate route and amount cause a reduction in both specific surface area and pore volume.

Finally the thermal conductivity and dynamic adsorption of H2S, SO2 andtoluene were measured. Results show that at room temperature and atmospheric pressure, a thermal conductivity of 28.4 and 29.6 mW/m.K were obtained for the SNP mesoporous silicas. The dynamic adsorption behaviour of the chemisorbents and composites indicate their ability to absorbed H2S, SO2 andtoluene respectively. The highest H2S uptake corresponds to chemisorbents with 11.2-13.6 wt% KMnO4. The effect of impregnation route, amount of KMnO4 and its location in the pore system are likely the key factors in achieving a large H2S uptake. For SO2 adsorption, the highest uptake capacity was observed for MgCa-68/32-KOH. The results further suggest that the key to large SO2 uptake is as a result of the synergetic effect between large mesopore diameter and extensive mesopore volumes. Carbon-silica composites with carbon content 45 wt % exhibits high toluene adsorption with composite via route I having the highest toluene adsorption capacity (27.6 wt % relative to carbon content). The large uptake capacity of this composite was attributed to the presence of high microporosity volume and a wide (1-30 nm) bimodal pore system consisting of extensive mesopore channels (2-30 nm) as well as large surface area. These capacity values of carbon-silica composites are competitive to results obtained for commercial coconut based carbon (31 wt %), and better than commercial alumina-carbon composite (9.5 wt %).

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vii, 57 p.
Series
Meddelande. Institutionen för byggvetenskap, ISSN 1651-5536 ; 211
Keyword [en]
Adsorbents, activated carbon, MgCa-silica, carbon-silica composite, characterization, porous parameters, molecular filtration, thermal conductivity, thermal insulation
National Category
Architectural Engineering Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-120330ISBN: 978-91-7501-701-3 (print)OAI: oai:DiVA.org:kth-120330DiVA: diva2:614405
Public defence
2013-04-16, Sal B2, Brinellvägen 23, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Formas
Note

QC 20130408

Available from: 2013-04-08 Created: 2013-04-04 Last updated: 2013-04-08Bibliographically approved
List of papers
1. Preparation and characterization of double metal-silica sorbent for gas filtration
Open this publication in new window or tab >>Preparation and characterization of double metal-silica sorbent for gas filtration
2013 (English)In: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 19, no 1, 49-61 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents the preparation of a porous (Mg, Ca) silicate structure, which could be employed as sorbent filter media. The sorbents have been prepared using sodium silicate precipitated with various ratios of magnesium and calcium salts. The sorbents obtained were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen physisorption isotherm. Further, the applicability and performance of the sorbent impregnate with potassium hydroxide for removal of sulphur dioxide (SO2) has been demonstrated. From the isotherms, specific surface area, pore diameter and volume of pores were estimated. Results show that the chemical composition and textural properties of the resultant sorbents were highly dependent on Mg/Ca molar ratio. It was found that sorbents made with 68 mol% Mg and 32 mol% Ca (PSS-MgCa-68/32); and 75 mol% Mg and 25 mol% Ca (PSS-MgCa-75/25) exhibited even higher specific surface area and pore volume than the sorbents containing a single metal. The Mg/Ca-silica sorbents obtained contains interconnected bimodal porosity with large portions being mesopores of varied sizes. The pore size distribution (PSD) results further indicate that PSS-MgCa-68/32 sorbent exhibits wide PSD of interconnected pores in the size range of 1 to 32 nm while PSS-MgCa-50/50 and PSS-MgCa-75/25 exhibits narrow PSD of 1 to 5 nm. Using SO2 as model contaminate gas, it was shown that the dynamic adsorption performance of the PSS-MgCa-sorbents impregnated with 8 wt% KOH exhibits SO2 uptake, with impregnated PSS-MgCa-68/32 showing better performance. This shows that the materials prepared can be used as adsorbent for gas filtration.

Keyword
Mg/Ca-silica sorbent, gas filtration, characterization, textural properties
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-32071 (URN)10.1007/s10450-012-9411-5 (DOI)000314766700005 ()2-s2.0-84873735711 (Scopus ID)
Note

QC 20130318. Updated from submitted to published.

Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2017-12-11Bibliographically approved
2. Textural and hydrogen sulphide adsorption behaviour of double metal-silica modified with potassium permanganate
Open this publication in new window or tab >>Textural and hydrogen sulphide adsorption behaviour of double metal-silica modified with potassium permanganate
2013 (English)In: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 20, no 3, 447-455 p.Article in journal (Refereed) Published
Abstract [en]

A new MgCa-silica material with bimodal pore size is impregnated with KMnO4 for dynamic adsorption of H2S. The MgCa-silica was synthesized using sodium silicate and calcium and magnesium salts as precipitating agents. The KMnO4 impregnation onto MgCa-silica was obtained through either direct addition into MgCa-silica wet coagulum or doping of dried MgCa-silica pellets into KMnO4 solution. These chemisorbents were characterized by nitrogen physisorption, spectrophotometer, microscopy and dynamic H2S adsorption test setup similar to ASHRAE standard I45.I. The results show that impregnation route and KMnO4 wt% cause a reduction of surface area and total pore volume. The decrease in pore volume was slightly more in chemisorbents obtained via post doping compared to direct impregnation. Regardless of pore volume reduction the pore size range, 1-32 nm, was as in the parent MgCa-silica with micro and meso-pore diameter centered at 1.4 and 5.4 nm respectively. Thus obtained chemisorbents have their pore entrances neither blocked nor shifted. The MgCa-silica/KMnO4 chemisorbents exhibits good H2S uptake performance. The chemisorbent with 11.4 wt% KMnO4 and obtained via direct impregnation possesses the highest uptake capacity. The lowest capacity was observed for chemisorbent with 8 wt% KMnO4 and made by direct impregnation. The variations in uptake capacity are likely due to impregnation route, the KMnO4 content and its location in the pore system. The results suggest that the MgCa-silica/KMnO4 chemisorbents can remove H2S from indoor air at room temperature.

Keyword
Hydrogen sulphide, KMnO4 impregnation, H2S adsorption, Textural properties, Pore size
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-120460 (URN)10.1007/s10934-012-9614-x (DOI)000318369400001 ()2-s2.0-84877827331 (Scopus ID)
Note

QC 20130610

Available from: 2013-04-08 Created: 2013-04-08 Last updated: 2017-12-06Bibliographically approved
3. Textural and adsorption properties of a carbon-silica composite adsorbent for air filtration
Open this publication in new window or tab >>Textural and adsorption properties of a carbon-silica composite adsorbent for air filtration
2010 (English)In: World journal of Engineering, ISSN 1708-5284, Vol. 7, no 2, 227-228 p.Article in journal (Other academic) Published
Keyword
Carbon-silica composite, adsorption properties, Dynamic VOC adsorption
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-32073 (URN)
Note
QC 20110405. Updated from submitted to published, 20120316Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2013-04-08Bibliographically approved
4. Carbon-silica composites prepared by the precipitation method. Effect of the synthesis parameters on textural characteristics and toluene dynamic adsorption
Open this publication in new window or tab >>Carbon-silica composites prepared by the precipitation method. Effect of the synthesis parameters on textural characteristics and toluene dynamic adsorption
2012 (English)In: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 19, no 3, 333-343 p.Article in journal (Refereed) Published
Abstract [en]

Three synthesis routes are presented here that leads to carbon-silica composites. These were characterized by nitrogen physisorption, by thermogravimetric analysis and by dynamic toluene adsorption test similar to Ashrae standard I45.1. The carbon-silica composites possess high microporosity and mesoporosity as well as large surface areas. Furthermore, the control of the microporosity as well as pore size distribution is possible because they depend on the amount of carbon used and of the synthesis route. Following routes I and III a wide micro-mesoporous pore size (1-32 nm) was obtained where as by route II narrow micro-mesoporous pore size (1-4 nm) was observed. In addition, pore diameters center in the range of 1.13-1.17 nm was observed when carbon content was 32 or 45 wt%. The dynamic adsorption of toluene was evaluated for carbon-silica composites obtained by three preparation routes at two different carbon contents, 32 and 45 wt% The results showed that a composite with 45 wt% carbon content and obtained via preparation route I gave the highest toluene adsorption capacity (27.6 wt% relative to carbon content). The large uptake capacity of this composite was attributed to the presence of high microporosity volume and a wide (1-32 nm) bimodal pore system consisting of extensive mesopore channels (2-32 nm) as well as large surface area. These capacity values of carbon-silica composites are by weight relative to carbon content and are competitive to, results obtained for commercial coconut activated carbon (31.1 wt%) and significantly better than a commercial alumina-carbon composite (9.5 wt%) at 0% efficiency.

Keyword
carbon-silica composites, synthesis parameters, textural characteristics, dynamic adsorption
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-32074 (URN)10.1007/s10934-011-9479-4 (DOI)000304100100009 ()2-s2.0-84861958897 (Scopus ID)
Note
QC 20120613Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2017-12-11Bibliographically approved
5. Textural and thermal conductivity properties of a low density mesoporous silica material
Open this publication in new window or tab >>Textural and thermal conductivity properties of a low density mesoporous silica material
2014 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 75, 210-215 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the pore structure, tapped density and thermal conductivity properties of a new type of nanoporous silica material have been studied. We have applied nitrogen physisorption, high resolution scanning microscopy and Transient Plane Source thermal conductivity measurements to investigate these properties. The new mesoporous silica SNP have large BET surface area, 400-439 m2 g-1 and possess high porosity in the range of 95-97%. The results further show pore diameter centred at 43 nm or 47 nm for the two materials studied. Tapped densities as low as 0.077 g/cm3 have so far been obtained and the thermal conductivity of these materials has been measured to 0.0284 and 0.0294 W (m K)-1 at room temperature and atmospheric pressure. The effects of tapped density, pore size diameter and particle morphology on thermal conductivity are discussed.

Keyword
Low density, Nanopore size, Porosity, Thermal conductivity
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-120462 (URN)10.1016/j.enbuild.2014.02.012 (DOI)000337013200021 ()2-s2.0-84896537786 (Scopus ID)
Note

Updated from "Manuscript" to "Journal" QC 20140707

Available from: 2013-04-08 Created: 2013-04-08 Last updated: 2017-12-06Bibliographically approved
6. A comparative study of methods for evaluating the thermal conductivity of nanoporous silica materials for vacuum insulation panels
Open this publication in new window or tab >>A comparative study of methods for evaluating the thermal conductivity of nanoporous silica materials for vacuum insulation panels
(English)Article in journal (Other academic) Submitted
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-120461 (URN)
Note

QS 2013

Available from: 2013-04-08 Created: 2013-04-08 Last updated: 2015-11-12Bibliographically approved

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