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Biorefineries aim to convert low value biomasses into high value products. The feedstock biomasses are often high-silica agricultural waste products such as rice straw, wheat straw, corn stover, sugarcane bagasse, or empty fruit b...
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Biorefineries aim to convert low value biomasses into high value products. The feedstock biomasses are often high-silica agricultural waste products such as rice straw, wheat straw, corn stover, sugarcane bagasse, or empty fruit bunches. This causes challenges, since silica is problematic in industrial processes, where it forms water-insoluble precipitates that are hard to remove, block filtration systems, and cause instrumental defects. In this paper we review various industries that experience issues with silica. These include paper pulping and waste-water treatment, where they try to solve their problems with silica in different ways. High pH and co-precipitation with mineral elements are some common ways of alleviating silica problems. Reviewing the literature for the fundamentals of silica revealed a complex chemistry that is not yet fully understood. Much is still to be learned about the interactions between silica and organic material as well as the mechanisms of silica precipitation and dissolution. Understanding the fundamental and complex chemistry of silica might help developing better solutions than those existing today, allowing efficient use of high silica biomasses in biorefineries. (c) 2014 Society of Chemical Industry and John Wiley & Sons, Ltd
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The influence of the acid nature on the structure and texture of silica precipitates has been studied. In synthesis of silica precipitates from sodium silicate in hydrochloric acid, twelve variables were modified simultaneously us...
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The influence of the acid nature on the structure and texture of silica precipitates has been studied. In synthesis of silica precipitates from sodium silicate in hydrochloric acid, twelve variables were modified simultaneously using a statistical method based on balanced incomplete blocks. The most important variables controlling the Broensted acidity and specific surface area were identified and compared with those corresponding to silica precipitates obtained in sulphuric acid in the sameconditions, reported in a previous paper [1].The initial concentration of sodium silicate solution is the most significant factor for both acids. The relative significance of some of the other variables is different, suggesting that the acid anion is involved in the complex mechanism of formation of silica precipitates.
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The influence of twelve synthesis variables upon the properties of the silica precipitates was studied using the Plackett and Burman design. The most important variables controlling the Broensted acidity and the specific surface a...
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The influence of twelve synthesis variables upon the properties of the silica precipitates was studied using the Plackett and Burman design. The most important variables controlling the Broensted acidity and the specific surface area wereidentified. For the syntheses of silica precipitates from sodium silicate in acidic media the initial concentration of sodium silicate solution is the most significant factor determining the structure and the texture of the porous silica. A method toevaluate the silanol group surface density was also proposed.
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In order to prepare porous silica that is mesoporous or microporous, the sol-gel process is recommended. Unlike methods that require high temperatures, the sol-gel process produces porous silica more or less at room temperature. T...
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In order to prepare porous silica that is mesoporous or microporous, the sol-gel process is recommended. Unlike methods that require high temperatures, the sol-gel process produces porous silica more or less at room temperature. The process involves the hydrolysis and polycondensation of silicon alkoxides in the majority of cases. Colloidal silica and soluble silicates may be used as well. The processing parameters that influence the porosity are primarily the pH and aging. Applications using porous silica to encapsulate sensor molecules and enzymes are developing rapidly.
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Within each furnace aggregate lining, one or more refractory insulation layers can be found. For this reason all refractory materials producers try to provide both dense and lightweight products. The demand for better thermal insu...
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Within each furnace aggregate lining, one or more refractory insulation layers can be found. For this reason all refractory materials producers try to provide both dense and lightweight products. The demand for better thermal insulation materials grows, due to the efforts of furnace operators to lower energy consumption of firings. Lower density and better insulating materials are in high demand. This paper deals with thermal insulation silica bricks; it describes their application in the glass and smelting industries. It informs about history, up-to-date products and new developing trends at P-D Refractories CZ a.s.
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An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published sili...
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An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published silica concentrations and fluxes for the period 2003–2005. The annual estuarine DSi mass-balance was established, based on seasonal fluxes estimated using measured DSi concentrations and (fully transient) model simulations of conservative transport. The annual BSi mass-balance was deduced from measured BSi contents in the suspended particulate matter and annual mud fluxes taken from the literature. The Scheldt estuary acted as a net sink not only for the BSi carried by the tidal river as well as that produced by diatoms in the estuary, but also for large amounts of BSi imported from the coastal zone. This results in the retention of dissolved and biogenic silica higher than that of DSi alone, which is in contrast with the classical consideration that rivers act as a source of BSi for the coastal zone. DSi and silica (DSi + BSi) retentions amounted to, respectively, 28 and 64 % in the estuary, and 33 and 66 % in the entire tidal system. This study highlights thus the predominant role of the estuary in the entire Scheldt tidal system when dealing with silica dynamics, as well as the importance of including BSi when investigating estuarine silica retention.
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摘要 :
An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published sili...
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An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published silica concentrations and fluxes for the period 2003-2005. The annual estuarine DSi mass-balance was established, based on seasonal fluxes estimated using measured DSi concentrations and (fully transient) model simulations of conservative transport. The annual BSi mass-balance was deduced from measured BSi contents in the suspended particulate matter and annual mud fluxes taken from the literature. The Scheldt estuary acted as a net sink not only for the BSi carried by the tidal river as well as that produced by diatoms in the estuary, but also for large amounts of BSi imported from the coastal zone. This results in the retention of dissolved and biogenic silica higher than that of DSi alone, which is in contrast with the classical consideration that rivers act as a source of BSi for the coastal zone. DSi and silica (DSi ? BSi) retentions amounted to, respectively, 28 and 64 % in the estuary, and 33 and 66 % in the entire tidal system. This study highlights thus the predominant role of the estuary in the entire Scheldt tidal system when dealing with silica dynamics, as well as the importance of including BSi when investigating estuarine silica retention.
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Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydroph...
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Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydrophobic be reacting with silane, change with time when the substrate is immersed in aqueous solution. Therefore the experimental conditions when such model systems are employed have to be carefully assessed.
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摘要 :
Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydroph...
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Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydrophobic be reacting with silane, change with time when the substrate is immersed in aqueous solution. Therefore the experimental conditions when such model systems are employed have to be carefully assessed. This paper summarizes the findings of the force measurement tests between air bubbles and silica particles hy-drophobized with organosilanes such as trimethylchlorosi-lane and 1,1,1,3,3,3-hexamethyl-disilazane. The results showed that the attractive forces as well as the adhesion between the air bubbles and silica particles decrease with the time of aging in aqueous solution. The silica surfaces rendered hydrophobic with organosilanes become hydrophilic with time due to hydration. The hydrophobicity could be restored by heating the samples at 190 °C. The atomic force microscopy imaging on silica plates revealed that in addition to hydration, decomposition of the organosilane layer also takes place.
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Estuaries are major pathways for silica fluxes towards the ocean and considered to be a sink for dissolved silica (DSi). However, the data basis for DSi, but also biogenic silica (BSi) fluxes through estuaries is relatively thin. ...
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Estuaries are major pathways for silica fluxes towards the ocean and considered to be a sink for dissolved silica (DSi). However, the data basis for DSi, but also biogenic silica (BSi) fluxes through estuaries is relatively thin. To test the hypothesis, a silica budget for the inner Elbe Estuary was constructed, based on 18 cruises between 2009-2011 and historical monitoring data. A strong positive correlation between particulate organic carbon (POC) and BSi concentration was identified, allowing the reconstruction of historical BSi time series from POC monitoring data. The budget revealed that the Elbe Estuary is a source for DSi and a strong sink for BSi, contradicting the general assumption of estuaries being a sink for DSi. The Elbe River delivered 2.8 x 10(9) mol DSi a(-1) and 0.9 x 10(9) mol BSi a(-1) to the estuary. There, 17 % of DSi were added along the inner estuary and 88 % of BSi were lost. Estuarine tributaries represented the largest source of additional DSi to the estuarine waters, while sedimentation was the single largest sink for BSi. It was calculated that large amounts of BSi were removed permanently from the estuarine cycle by sediment dredging. As data on Si transformation in estuaries are scarce and widely underrepresented in global budgets, findings from this study are a valuable contribution, especially since the Elbe Estuary seemed to act contradictory to observed systems so far.RI Hartmann, Jens/A-6306-2008OI Hartmann, Jens/0000-0003-1878-9321
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