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Molecular filtration: the study of adsorbents
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Adsorbent materials for gas purification have been studied and developed for application in many areas. It is known that a single adsorbent may not adequately control multiple contaminants. Therefore, the development of adsorbent materials has accelerated over the past two decades, and is today an area attracting a lot of attention. In view of the global environmental movement for clean air, the development of improved sorbents will help address new challenges that cannot efficiently be met with the generic sorbents that are presently commercially available. On the other hand, the utilization of these new sorbents for specific applications within the area of molecular filtration remains largely unexplored. This thesis presents a synthesis of new sorbent materials, and the characterization and application of these materials for molecular filtration. Commercial adsorbents have been used for benchmarking for the pore properties, the applicability, and the performance of these new adsorbents. 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. The effect of thermal treatment on pore parameters of these adsorbents has been investigated. The results show that heat treatment had a notable effect on the pore parameters, and that the pore structure was thermally stable even at 600°C.

 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 also before coagulation. The routes presented here leads to carbon-silica composites possessing high micro porosity, meso porosity as well as large surface areas. The increase in micro porosity and surface areas was linear with carbon content. The results shows further 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 (1-30nm) was obtained where as by route II a narrow pore size (1-4nm) was observed. KOH or KMnO4 modified MgCa adsorbent varieties were also prepared. The impregnationwas performed by either a direct synthesis or post-synthesis procedure. Potassium hydroxide and potassium permanganate have been chosen as impregnate chemicals. Results revealed that theimpregnate amount significantly affected both the structural and the gas adsorption characteristics of the impregnated MgCa adsorbents. The properties of double- metal adsorbents, impregnated adsorbents and carbon-silica composites were characterized by various methods (X-ray diffraction, scanning electron microscopy, thermo gravimetric analysis, and nitrogen adsorption at 77K) to study the material structure and morphology, thermal stability, ignition temperature and porous parameters with regard to surface area, pore size, pore size distribution and porosity volume, which is important for optimizing their use in many practical application. The up-take performance of adsorbents for dynamic adsorption of SO2, H2S and toluene was performed in a system similar to the setup usedin ASHRAE 145.1. Finally the applicability and performance of the impregnated modified MgCa-silica adsorbents and composites have been evaluated for H2S, SO2 and toluene adsorption and compared to some commercial adsorbent materials. Results revealed that a potassium permanganate modified MgCa-adsorbent has a H2S adsorption capacity in the range of 0.08-3.19 wt % at 50% efficiency, and that the uptake capacity was relative to the amount of potassiumpermanganate loading. Moreover, KOH modified MgCa-adsorbent shows highest SO2 adsorption capacity (1.7 wt %) which is 3.47 times higher than commercial alumina impregnate with potassium permanganate (0.49 wt %). Carbon-silica composites on the other hand shows adsorption of toluene and high adsorption capacity was obtained when carbon content was 45 wt %. The results further shows that a composite with 45 wt % carbon and obtained via route I present the highest toluene adsorption capacity ( 27.6 wt % relative to carbon content) at 0% efficiency. The large uptake capacity of this composite was attributed to the presence of high microporosity volume and a wide (1-30nm) bimodal pore system consisting of extensive mesopore channels (2-30nm) 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , v, 38 p.
Series
Trita-BYMA, ISSN 0349-5752 ; 2011:1
Keyword [en]
adsorbents, activated carbon, alumina, MgCa-silica, carbon-silica composite, characterization, porous parameters, molecular filtration
National Category
Other Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-32075OAI: oai:DiVA.org:kth-32075DiVA: diva2:408548
Presentation
2011-03-17, Gävle Teknikpark, Nobelvägen 2, Gävle, 10:00 (English)
Opponent
Supervisors
Note
QC 20110405Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-04-07Bibliographically 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 (ScopusID)
Note

QC 20130318. Updated from submitted to published.

Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2013-04-08Bibliographically approved
2. Effects of heat treatment and impregnation on the textural properties and H2S uptake of a new precipitated silica adsorbent
Open this publication in new window or tab >>Effects of heat treatment and impregnation on the textural properties and H2S uptake of a new precipitated silica adsorbent
(English)In: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757Article in journal (Other academic) Submitted
Keyword
H2S adsorption, pore structure, pore size distribution, heat treatment
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-32072 (URN)
Note
QS 20120327Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2012-03-27Bibliographically 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 (ScopusID)
Note
QC 20120613Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2013-04-08Bibliographically approved

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