1,720,977 research outputs found
Geopolymers: A new and smart way for a sustainable development
Full text link“Geopolymers” is a general term that describes a wide variety of inorganic and composite materials with limited restrictions on alumina and silica content. In the last decades, they have been also defined as “low-temperature aluminosilicate glasses”, “hydroceramics”, “inorganic polymer concrete” or “alkali bonded ceramics”. Recently, an updated definition has been proposed by the RILEM Technical Committee 224-AAM: “geopolymer materials are essential aluminosilicates activated with alkaline solution, excluding any other alkali-activated materials that should be classified apart” [1]
Production and characterization of geopolymers based on mixed compositions of metakaolin and coal ashes
No full textMixtures of coal ashes from pulverized coal combustion (PCC) or fluidized bed combustion (FBC) and metakaolin were used to synthetize geopolymers. Upon full characterization of the raw powders (chemical and mineralogical composition), geopolymerization tests were conducted using an alkali aqueous solution of NaOH / Na 2 SiO 3 at different dilutions. The produced geopolymers were subjected to SEM analysis, as well as to leaching, thermal and mechanical tests. The final microstructure and the properties of the geopoly- mers indicate that FBC ash can be conveniently used as a partially reactive filler in combination with the metakaolin powder. The composite material has good thermal performance and compressive strength ( ∼30 MPa) suitable for the building sector
New hybrid unit operation for gas separation membranes application
No full textAn innovative membrane-based process for the separation of gaseous streams has been developed and tested at lab-scale. The new process can be conveniently carried out on the same modules currently employed for conventional gas separation membrane systems, and it relies on periodic swing of the downstream pressure, while upstream conditions are kept constant. Such new unit operation is run with no need of switching streams, and it allows to process constant flow rate and composition of both feed and retentate, while permeate is collected at assigned frequency, resulting in an overall on-average steady state process. An on-off control strategy over time of permeate collection produces alternate sorption/desorption steps in the membrane, associated to increase/decrease cycles of downstream pressure in the process, in a similar fashion to pressure swing adsorption (PSA). Indeed, consistently with the hybrid nature of the new process, the specific dynamic control of downstream pressure allows the exploitation of both resistive (permeation) and capacitive (adsorption) properties of the membrane, and the associated characteristics in terms of selectivity. By changing the duration of pressure swing period, the resistive or capacitive properties of the membrane can be conveniently tuned in order to explore different performances of the process, in terms of key component recovery and separation facto
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Development of an ion exchange process for ammonium removal and recovery from municipal wastewater using a metakaolin K-based geopolymer
Full text linkIon exchange represents a promising process for ammonium removal from municipal wastewater (MWW), in order to recover it for fertilizer production. Previous studies on ammonium ion exchange neglected the assessment of process robustness and the optimization the desorption/recovery step. This study aimed at developing a continuous-flow process of ammonium removal/recovery based on a metakaolin K-based geopolymer, named G13. Process robustness was assessed by operating 7 adsorption/desorption cycles with two types of MWW. These tests resulted in satisfactory and constant performances: operating capacity at 40 mgN L-1 in the inlet = 12 mgN gdry sorbent-1, bed volumes of treated MWW at the selected breakpoint = 199-226, ammonium adsorption yield = 88-91%. Empty bed contact time (EBCT) was decreased from 10 to 5 min without any reduction in performances. The NH4+ adsorption process was effectively simulated by the Thomas model, allowing a model-based assessment of the effect of EBCT reductions on process performances. An innovative desorption procedure led to high ammonium recovery yields (86-100%) and to a desorbed product composed primarily of KNO3 (54%w) and NH4NO3 (39%w), two salts largely used in commercial fertilizers. The energy consumption of ammonium removal/recovery with G13 resulted 0.027 kWh m-3treated WW, with a relevant reduction in comparison to traditional nitrification/denitrification, whereas the operational cost resulted equal to 60-110% of the cost of the benchmark process. These results show that G13 is a promising material to recover ammonium in a circular economy approach.Ion exchange represents a promising process for ammonium removal from municipal wastewater (MWW), in order to recover it for fertilizer production. Previous studies on ammonium ion exchange neglected the assessment of process robustness and the optimization the desorption/recovery step. This study aimed at developing a continuous-flow process of ammonium removal/recovery based on a metakaolin K-based geopolymer, named G13. Process robustness was assessed by operating 7 adsorption/desorption cycles with two types of MWW. These tests resulted in satisfactory and constant performances: operating capacity at 40 mgN L−1 in the inlet = 12 mgN gdry sorbent−1, bed volumes of treated MWW at the selected breakpoint = 199–226, ammonium adsorption yield = 88–91%. Empty bed contact time (EBCT) was decreased from 10 to 5 min without any reduction in performances. The NH4+ adsorption process was effectively simulated by the Thomas model, allowing a model-based assessment of the effect of EBCT reductions on process performances. An innovative desorption procedure led to high ammonium recovery yields (86–100%) and to a desorbed product composed primarily of KNO3 (54%w) and NH4NO3 (39%w), two salts largely used in commercial fertilizers. The energy consumption of ammonium removal/recovery with G13 resulted 0.027 kWh m−3treated WW, with a relevant reduction in comparison to traditional nitrification/denitrification, whereas the operational cost resulted equal to 60–110% of the cost of the benchmark process. These results show that G13 is a promising material to recover ammonium in a circular economy approach
CO2 adsorption at intermediate and low temperature by geopolymer-hydrotalcite composites
No full textGeopolymer-hydrotalcites composites have been prepared and compared to explore their use in the field of CO2
adsorption for a wide range of working temperatures and relative applications. Two commercial hydrotalcites,
with different Mg:Al ratio, were tested as fillers for a geopolymer matrix up to the maximum of 37 wt%. A high
compressive strength (25–27 MPa) was retained in composites at 500 C, which is the temperature of hydrotalcites
transformation into amorphous mixed solid oxides able to adsorb CO2. Composites were characterized in
term of working capacity by testing the CO2 adsorption at low (35 C) and intermediate (200 C) temperature,
with cycles of adsorption/desorption and regeneration at 500 C. At 35 C, CO2 physisorption capacity was between
0.079 and 0.154 mmol g1, while at 200 C, the total CO2 capacity value was between 0.114 and 0.141
mmol g1.
1. Introduction
In recent years, the sequestration of CO2 downstream of industrial
processes has been the subject of in-depth investigations [1]. The
adsorption of CO2 is also of great importance for the direct use of biogas
[2] where the methane must be purified before being introduced into the
distribution network, as a renewable alternative to natural gas.
The choice of the separation technology depends on the impact of the
industrial process, on the efficiency of the adsorbent and on economic
factors. Physical adsorption is a less-energy-intensive separation technology
resulting an economic alternative in comparison to others [3]. In
most cases, the solid adsorbents are in the form of monoliths or granules
to facilitate handling and storage [4]. The adsorbent material must have
high resistance to abrasion and withstand rapid changes in temperature
and/or pressure, as the methods of regenerating the adsorbent with the
release of CO2 require fluctuations in pressure and/or temperature [5,6].
The key parameter for assessing the validity of an adsorbent is the specific
adsorption capacity of CO2 (moles of CO2 per kg of material), which
depends o
CO2 adsorption in a geopolymer-zeolite composite: Experimental dynamic tests and modelling insights on related thermal effects
Full text linkCO2 adsorption process in a composite geopolymer/zeolite 13X material has been analysed for post combustion carbon capture application, in dynamic conditions for a CO2/N2 gas mixture. Such composite material represents a valid alternative to conventional sorbents owing to the affinity and synergy between zeolite and the geopolymer binder as well as improved mechanical resistance and lower cost. Experimental analysis has been focused both on complete adsorption tests to determine the material maximum adsorption capacity and on breakthrough tests in transient conditions in (cyclic adsorption/desorption). Particular care has been devoted to thermal effects associated to adsorption and their effect on adsorption capacity and kinetics. Experimental data have been employed to support the development of a novel numerical model, based on Sips adsorption approach for sorbent capacity, and capable to describe the adsorption process, accounting for both mass and energy transport in the sorbent bed. The model proved able to describe well the experimental data at different CO2 feed concentration, and thus it has been employed in a predictive way to inspect process operating parameters and sorbent bed design on the resulting adsorption capacity, breakthrough time, and temperature profile. In particular, the model compared the results obtained in a scaled-up configuration (suitable to an industrial application) with those of the lab-scale system
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