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Twumasi, Ebenezer
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Publications (7 of 7) Show all publications
Twumasi Afriyie, E., Norberg, P., Sjöström, C. & Forslund, M. (2013). Preparation and characterization of double metal-silica sorbent for gas filtration. Adsorption, 19(1), 49-61
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, p. 49-61Article 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.

Keywords
Mg/Ca-silica sorbent, Gas filtration, Characterization, Textural properties, Impregnated Mg/Ca. silca sorbents
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-13782 (URN)10.1007/s10450-012-9411-5 (DOI)000314766700005 ()2-s2.0-84873735711 (Scopus ID)
Available from: 2013-03-04 Created: 2013-02-04 Last updated: 2018-12-03Bibliographically approved
Twumasi Afriyie, E., Norberg, P., Sjöström, C. & Forslund, M. (2013). Textural and hydrogen sulphide adsorption behaviour of double metal-silca modified with potassium permanganate. Journal of porous materials, 20(3), 447-455
Open this publication in new window or tab >>Textural and hydrogen sulphide adsorption behaviour of double metal-silca modified with potassium permanganate
2013 (English)In: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 20, no 3, p. 447-455Article 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/KMnO4chemisorbents can remove H2S from indoor air at room temperature.

Keywords
Hydrogen sulphide, KMnO4 impreganation, H2S adsorption, Textural properties, Pore size
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hig:diva-13783 (URN)10.1007/s10934-012-9614-x (DOI)000318369400001 ()2-s2.0-84877827331 (Scopus ID)
Available from: 2013-02-04 Created: 2013-02-04 Last updated: 2018-12-03Bibliographically approved
Twumasi, E., Norberg, P., Forslund, M. & Sjöström, C. (2012). Carbon–silica composites prepared by the precipitation method: Effect of the synthesis parameters on textural characteristics and toluene dynamic adsorption. Journal of porous materials, 19(3), 333-343
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, p. 333-343Article 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.

Place, publisher, year, edition, pages
US: , 2012
Keywords
Carbon–silica composites, Synthesis parameters, Textural characteristics, Dynamic adsorption
National Category
Materials Engineering Chemical Sciences
Identifiers
urn:nbn:se:hig:diva-9334 (URN)10.1007/s10934-011-9479-4 (DOI)000304100100009 ()2-s2.0-84861958897 (Scopus ID)
Projects
Molecular Filtration
Available from: 2013-03-04 Created: 2011-06-07 Last updated: 2018-03-13Bibliographically approved
Gudmundsson, K., Sjöström, C., Norberg, P., Trinius, W. & Twumasi, E. (2011). Durable and robust vacuum insulation technology for buildings. In: Michael A. Lacasse, Vasco Peixoto de Freitas, Helena Corvacho (Ed.), XII DBMC: 12th International Conference on Durability of Building Materials and Components (Vol. 4): . Paper presented at 12th International Conference on Durability of Building Materials and Components (XII DBMC), Porto - Portugal, April 12th -15th, 2011. Porto: FEUP Edições
Open this publication in new window or tab >>Durable and robust vacuum insulation technology for buildings
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2011 (English)In: XII DBMC: 12th International Conference on Durability of Building Materials and Components (Vol. 4) / [ed] Michael A. Lacasse, Vasco Peixoto de Freitas, Helena Corvacho, Porto: FEUP Edições , 2011, , p. 8Conference paper, Published paper (Refereed)
Abstract [en]

Vacuum insulation panels (VIPs) provide unprecedented opportunities for obtaining excellent thermal insulation with light and slender constructions. This article discusses the performance over time of VIPs, and the possibilities to overcome the current problems related to fragility and limited durability. Aerogels are together with fumed silica among the most competitive core materials for VIP's. The use of classical aerogels, as produced in autoclaves is, however, limited due to the high production costs. The fumed silica on the other hand requires vacuum levels that are difficult to maintain with the currently available vacuum envelopes. A material with comparatively smaller pores will on the other hand allow obtaining low thermal conductivity at higher pressure (less vacuum) and will therefore reduce the pressure difference over the envelope. There is therefore much to be gained by reducing the pore size. New cost and performance efficient silica aerogels offers opportunities to enhance the properties of the panels by customizing the pore structure and pore size distribution. Building technologies and how the panels are applied in a manner that improves the structural, thermal and hygroscopic performances of vacuum insulated constructions have been studied and are discussed.

Place, publisher, year, edition, pages
Porto: FEUP Edições, 2011. p. 8
Keywords
Vacuum insulation technologies, Performance over time, Building technology, Aerogel, Core materials
National Category
Materials Engineering Building Technologies
Identifiers
urn:nbn:se:hig:diva-13796 (URN)978-972-752-132-6 (ISBN)
Conference
12th International Conference on Durability of Building Materials and Components (XII DBMC), Porto - Portugal, April 12th -15th, 2011
Available from: 2013-02-05 Created: 2013-02-05 Last updated: 2018-03-13Bibliographically approved
Twumasi, E. (2011). Molecular filtration: the study of adsorbents. (Licentiate dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Molecular filtration: the study of adsorbents
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. p. v, 38
Series
TRITA-BYMA, ISSN 0349-5752 ; 2011:1
Keywords
adsorbents, activated carbon, alumina, MgCa-silica, carbon-silica composite, characterization, porous parameters, molecular filtration
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:hig:diva-18959 (URN)
Presentation
2011-03-17, Gävle Teknikpark, Nobelvägen 2, Gävle, 10:00 (English)
Opponent
Supervisors
Available from: 2015-02-10 Created: 2015-02-10 Last updated: 2018-03-13Bibliographically approved
Twumasi, E., Norberg, P. & Sjöström, C. (2011). Tailored Precipitated Silica Adsorbents for the Built Environment. In: XII DBMC: 12th International Conference on Durability of Building Materials and Components (Vol. 4): Michael A. Lacasse, Vasco Peixoto de Freitas, Helena Corvacho. Paper presented at XII DBMC, 12th International Conference on Durability of Building Materials and Components ; 12-15 April 2011, Porto, Portugal. Porto: FEUP Edições
Open this publication in new window or tab >>Tailored Precipitated Silica Adsorbents for the Built Environment
2011 (English)In: XII DBMC: 12th International Conference on Durability of Building Materials and Components (Vol. 4): Michael A. Lacasse, Vasco Peixoto de Freitas, Helena Corvacho, Porto: FEUP Edições , 2011, , p. 8Conference paper, Published paper (Refereed)
Abstract [en]

The paper provides a review of the synthesis and adsorptive properties of a novel class of precipitated silica materials. To enhance or tailor the adsorption efficiency, various trapping chemicals (potassium hydroxide, potassium permanganate) or co-adsorbents (coconut activated carbon) are incorporated in the structure of the substrate material. Further, it discusses the applicability and performance over time of the material as adsorbents for removal of hydrogen sulphide, sulphur dioxide and toluene contaminants which are potentially hazardous to sensitive equipment and more importantly, human health. Chemical substances in the air are an unavoidable by-product of most human endeavours within industry and transportation. The need for adsorbents to combat Airborne Molecular Contamination (AMC) follows from the continued intensification of the global environmental movement as well as the rapid industrialisation of developing countries. The removal performance of modified precipitated silica adsorbent shows that the new adsorbent can be tailored to remove low concentrations of sulphur dioxide, hydrogen sulphide and toluene contaminants at indoor environment conditions. The results further shows that the new precipitated silica adsorbent impregnated with 8 wt% KOH shows better performance than commercial alumina impregnated with 8 wt% KMnO4.The adsorbent material may find interesting and efficient uses as passive sinks for pollutants incorporated into more traditional building products such as acoustic baffles or as ingredients in various coatings. The filter material is environmentally friendly and consists of benign chemicals that are abundant worldwide. Performance over time aspects, re-use and recycling of exhausted filter materials are key issues addressed.

Place, publisher, year, edition, pages
Porto: FEUP Edições, 2011. p. 8
Keywords
Precipitated Silica, Adsorbents, Molecular Filtration, Indoor Air Quality, Performance over Time
National Category
Environmental Sciences Materials Engineering
Identifiers
urn:nbn:se:hig:diva-9341 (URN)978-972-752-132-6 (ISBN)
Conference
XII DBMC, 12th International Conference on Durability of Building Materials and Components ; 12-15 April 2011, Porto, Portugal
Available from: 2011-06-10 Created: 2011-06-08 Last updated: 2018-03-13Bibliographically approved
Twumasi, E., Forslund, M., Norberg, P. & Sjöström, C. (2010). Textural and adsorption properties of a carbon-silica composite adsorbent for air filtration. World Journal of Engineering, 7(2), 227-228
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, p. 227-228Article in journal (Other academic) Published
Place, publisher, year, edition, pages
Canada: Sun light Publishing, 2010
Keywords
Carbon-silica composite, adsorption properties, Dynamic VOC adsorption
National Category
Materials Engineering Chemical Sciences
Identifiers
urn:nbn:se:hig:diva-9358 (URN)
Available from: 2011-06-08 Created: 2011-06-08 Last updated: 2018-03-13Bibliographically approved
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