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Green chemistry is increasingly seen as a powerful tool that researchers must use to evaluate the environmental impact of nanotechnology. As nanomaterials are developed, the environmental and human health impacts of both the products themselves and the processes to make them must be considered to ensure their long-term economic viability.

(Sandy) Dasgupta is a native of India and was educated in a college founded by Irish missionaries where he got his bachelor’s degree with honors in Chemistry and was recognized as a National Science talent Search Scholar. Peterson's Stress Concentration Factors establishes and maintains a system of data classification for all of the applications of stress and strain analysis and expedites their synthesis into CAD applications. Substantially revised and completely updated, this book presents stress concentration factors both graphically and with formulas. It also employs computer-generated art in its portrayal. Abstract Adsorption–desorption processes of Pb at contaminated levels in two variable charge soils were investigated. The red soil (RAR) developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) adsorbed more Pb2+ than the red soil (REQ) derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult). Assuming equilibrium partitioning between the gas and particle phases has been shown to overestimate the fraction of low-volatility chemicals in the particle phase. Here, we present a new steady-state mass balance model that includes separate compartments for fine and coarse aerosols and the gas phase and study its sensitivity to the input parameters. We apply the new model to investigate.

Tetraacetylethylenediamine, commonly abbreviated as TAED, is an organic compound with the formula (CH₃C(O))₂NCH₂CH₂N(C(O)CH₃)₂. This white solid is commonly used as a bleach activator in laundry detergents and for paper pulp. It is produced by acetylation of ethylenediamine.

Use and mechanism of action[edit]

TAED is an important component of laundry detergents that use 'active oxygen' bleaching agents. Active oxygen bleaching agents include sodium perborate, sodium percarbonate, sodium perphosphate, sodium persulfate, and urea peroxide. These compounds release hydrogen peroxide during the wash cycle, but Hydrogen peroxide is inefficient when used in temperatures below 60 °C (140 °F). TAED and hydrogen peroxide react to form peroxyacetic acid, a more efficient bleach, allowing lower temperature wash cycles, around 40 °C (104 °F). TAED was first used in a commercial laundry detergent in 1978 (Skip by Unilever).^[1] Currently, TAED is the main bleach activator used in European laundry detergents and has an estimated annual consumption of 75 kt.^[2]

Perhydrolysis[edit]

TAED reacts with alkaline peroxide via the process called perhydrolysis releasing of peracetic acid. The first perhydrolysis gives triacetylethylenediamine (TriAED) and the second gives diacetylethylenediamine (DAED):^[3]

TAED typically provides only two equivalents of peracetic acid, although four are theoretically possible.^[4]Competing with perhydrolysis, TAED also undergoes some hydrolysis, which is an unproductive pathway.^[5][6]

Preparation[edit]

TAED is prepared in a two-stage process from ethylenediamine and acetic anhydride. The process is nearly quantitative.^[7][8][9]

The acetic acid by-product is recycled as acetic anhydride.

Properties[edit]

Powdered TAED is stabilized by granulation with the aid of the sodium salt of carboxymethylcellulose (Na-CMC),^[10] which are sometimes additionally coated blue or green. Despite the relatively low solubility of TAED in cool water, (1 g/l at 20 °C), the granulate dissolves rapidly in the washing liquor.

The peroxyacetic acid formed has bactericidal, virucidal and fungicidal properties, thereby enabling TAED with percarbonate to disinfect and deodorize.^[11]

Ecology[edit]

Triacetylethylenediamine is mostly non-toxic and easily biodegradable. TAED and its byproduct DAED have low aquatic ecotoxicity. Triacetylethylenediamine shows a very low toxicity in all exposure routes, is practically non-irritating effect on skin and eye, and does not give any indication of skin sensitization. Triacetylethylenediamine is not mutagenic and not teratogenic.^[12] TAED, TriAED and DAED are all completely biodegradable and substantially removed during wastewater treatment.^[13]

References[edit]

1. ^Smulders E.; von Rybinski W.; Sung E.; Rähse W.; Steber J.; Wiebel F.; Nordskog A. (2002). 'Laundry Detergents'. Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH.
2. ^Reinhardt, G.; Borchers, G. (2009). 'Application of Bleaching Detergent Formulations'. In Zoller, Uri (ed.). Handbook of Detergents Part E: Applications. USA: CRC Press. ISBN9781574447576.
3. ^D. Martin Davies and Michael E. Deary 'Kinetics of the hydrolysis and perhydrolysis of tetraacetylethylenediamine, a peroxide bleach activator' J. Chem. Soc., Perkin Trans. 2, 1991, pages 1549 - 1552. doi:10.1039/P29910001549.
4. ^Farr, J. P.; Smith, W. L.; Steichen, D. S. (1992). 'Bleaching Agents'. Kirk-Othmer Encyclopedia of Chemical Technology Vol. 4 (4th ed.). John Wiley & Sons, Inc. pp. 271–299.CS1 maint: multiple names: authors list (link)
5. ^Hauthal, G. H., Schmidt, H., Scholz, J., Hofmann, J. and Pritzkow W. (1990). 'Studies concerning the mechanism of bleach activation'. Tenside Surf. Det. 27 (3).CS1 maint: multiple names: authors list (link)
6. ^Hofmann, J., Just, G., Pritzkow, W. and Schmidt, H. (1992). 'Bleaching activators and the mechanism of bleaching activation'. Journal für Praktische Chemie/Chemiker-Zeitung. 334 (4): 293–297. doi:10.1002/prac.19923340402.CS1 maint: multiple names: authors list (link)
7. ^Europäische Patentanmeldung EPA 004 919, Verfahren zur Herstellung von N,N,N’,N’-Tetraacetyl-ethylendiamin, Erfinder: G. Müller-Schiedmayer, R. Aigner, Anmelder: Hoechst AG, veröffentlicht am 31. Oktober 1979
8. ^Europäische Patentanmeldung EPA 0 051 739 A1, Verfahren zur Herstellung von N,N,N’,N’-Tetraacetylethylendiamin, Erfinder: W. Köhler et al., Anmelder: BASF AG, veröffentlicht am 19. Mai 1982
9. ^Europäisches Patent EP 0 238 958 B1, Verfahren zur Reinigung von Tetraacetylethylendiamin, Erfinder: K. Köster, F.-J. Carduck, Anmelder: Henkel KG aA, veröffentlicht am 12. Juni 1991
10. ^US-Patent US 5,100,576, Process for the preparation of a readily soluble bleach activator granulate with a long shelf life, Erfinder: J. Cramer et al., Anmelder: Hoechst AG, erteilt am 31. März 1992.
11. ^Clariant Surfactant Division: The Clean and Clever Way of Bleaching - PERACTIVEArchived 2013-07-17 at the Wayback Machine (PDF; 865 kB), 08.99
12. ^HERA Human & Environmental Risk Assessment on ingredients of European household cleaning products: Tetraacetylethylenediamine (TAED), CAS 10543-57-4 (PDF; 666 kB), Draft, DECEMBER 2002.
13. ^Gilbert, P. A. (1992). 'TAED-Tetraacetylethylenediamine'. In de Oude, N. T. (ed.). The Handbook of Environmental Chemistry, Vol. 3 Part F Antropogenic Compounds: Detergents. Berlin: Springer-Verlag. ISBN354053797X.

External links[edit]

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Water purification, process by which undesired chemical compounds, organic and inorganic materials, and biological contaminants are removed from water. That process also includes distillation (the conversion of a liquid into vapour to condense it back to liquid form) and deionization (ion removal through the extraction of dissolved salts). One major purpose of water purification is to provide clean drinking water. Water purification also meets the needs of medical, pharmacological, chemical, and industrial applications for clean and potable water. The purification procedure reduces the concentration of contaminants such as suspended particles, parasites, bacteria, algae, viruses, and fungi. Water purification takes place on scales from the large (e.g., for an entire city) to the small (e.g., for individual households).

Most communities rely on natural bodies of water as intake sources for water purification and for day-to-day use. In general, these resources can be classified as groundwater or surface water and commonly include underground aquifers, creeks, streams, rivers, and lakes. With recent technological advancements, oceans and saltwater seas have also been used as alternative water sources for drinking and domestic use.

Determining water quality

Historical evidence suggests that water treatment was recognized and practiced by ancient civilizations. Basic treatments for water purification have been documented in Greek and Sanskrit writings, and Egyptians used alum for precipitation as early as 1500 bce.

In modern times, the quality to which water must be purified is typically set by government agencies. Whether set locally, nationally, or internationally, government standards typically set maximum concentrations of harmful contaminants that can be allowed in safe water. Since it is nearly impossible to examine water simply on the basis of appearance, multiple processes, such as physical, chemical, or biological analyses, have been developed to test contamination levels. Levels of organic and inorganic chemicals, such as chloride, copper, manganese, sulfates, and zinc, microbial pathogens, radioactive materials, and dissolved and suspended solids, as well as pH, odour, colour, and taste, are some of the common parameters analyzed to assess water quality and contamination levels.

Regular household methods such as boiling water or using an activated-carbon filter can remove some water contaminants. Although those methods are popular because they can be used widely and inexpensively, they often do not remove more dangerous contaminants. For example, natural spring water from artesian wells was historically considered clean for all practical purposes, but it came under scrutiny during the first decade of the 21st century because of worries over pesticides, fertilizers, and other chemicals from the surface entering wells. As a result, artesian wells were subjected to treatment and batteries of tests, including tests for the parasite Cryptosporidium.

Not all people have access to safe drinking water. According to a 2017 report by the United Nations (UN) World Health Organization (WHO), 2.1 billion people lack access to a safe and reliable drinking water supply at home. Eighty-eight percent of the four billion annual cases of diarrhea reported worldwide have been attributed to a lack of sanitary drinking water. Each year approximately 525,000 children under age five die from diarrhea, the second leading cause of death, and 1.7 million are sickened by diarrheal diseases caused by unsafe water, coupled with inadequate sanitation and hygiene.

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Process

Most water used in industrialized countries is treated at water treatment plants. Although the methods those plants use in pretreatment depend on their size and the severity of the contamination, those practices have been standardized to ensure general compliance with national and international regulations. The majority of water is purified after it has been pumped from its natural source or directed via pipelines into holding tanks. After the water has been transported to a central location, the process of purification begins.

Pretreatment

In pretreatment, biological contaminants, chemicals, and other materials are removed from water. The first step in that process is screening, which removes large debris such as sticks and trash from the water to be treated. Screening is generally used when purifying surface water such as that from lakes and rivers. Surface water presents a greater risk of having been polluted with large amounts of contaminants. Pretreatment may include the addition of chemicals to control the growth of bacteria in pipes and tanks (prechlorination) and a stage that incorporates sandfiltration, which helps suspended solids settle to the bottom of a storage tank.

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Preconditioning, in which water with high mineral content (hard water) is treated with sodium carbonate (soda ash), is also part of the pretreatment process. During that step, sodium carbonate is added to the water to force out calciumcarbonate, which is one of the main components in shells of marine life and is an active ingredient in agricultural lime. Preconditioning ensures that hard water, which leaves mineral deposits behind that can clog pipes, is altered to achieve the same consistency as soft water.

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Prechlorination, which is often the final step of pretreatment and a standard practice in many parts of the world, has been questioned by scientists. During the prechlorination process, chlorine is applied to raw water that may contain high concentrations of natural organic matter. This organic matter reacts with chlorine during the disinfection process and can result in the formation of disinfection by-products (DBPs), such as trihalomethanes, haloacetic acids, chlorite, and bromate. Exposure to DBPs in drinking water can lead to health issues. Worries stem from the practice’s possible association with stomach and bladdercancer and the hazards of releasing chlorine into the environment.

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