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Thermodynamics and Reaction Mechanism of Urea Decomposition† Cite This: Phys
PCCP View Article Online PAPER View Journal | View Issue Thermodynamics and reaction mechanism of urea decomposition† Cite this: Phys. Chem. Chem. Phys., 2019, 21,16785 a b b b Steffen Tischer, * Marion Bo¨rnhorst, Jonas Amsler, Gu¨nter Schoch and Olaf Deutschmann ab The selective catalytic reduction technique for automotive applications depends on ammonia production from a urea–water solution via thermolysis and hydrolysis. In this process, undesired liquid and solid by-products are formed in the exhaust pipe. The formation and decomposition of these Received 18th March 2019, by-products have been studied by thermogravimetric analysis and differential scanning calorimetry. Accepted 5th July 2019 A new reaction scheme is proposed that emphasizes the role of thermodynamic equilibrium of the DOI: 10.1039/c9cp01529a reactants in liquid and solid phases. Thermodynamic data for triuret have been refined. The observed phenomenon of liquefaction and re-solidification of biuret in the temperature range of 193–230 1Cis rsc.li/pccp explained by formation of a eutectic mixture with urea. Creative Commons Attribution-NonCommercial 3.0 Unported Licence. 1 Introduction and ammonium ISE (ion-selective electrode) measurements. Concluding from experimental results and literature data, 23 Air pollution by nitrogen oxides from Diesel engines is a major possible reactions including urea and its by-products biuret, problem concerning the environment and society. Therefore, cyanuric acid, ammelide, ammeline and melamine are presented. governments follow the need to regulate emissions by law (e.g., Further, cyanate and cyanurate salts and cyanamide are 715/2007/EG, ‘‘Euro 5 and Euro 6’’).1 The favored method to proposed as possible intermediates of high temperature urea reduce nitrogen oxides is selective catalytic reduction (SCR) decomposition. -
SODIUM HYPOCHLORITE, AKA “LIQUID CHLORINE” in Other Words, Bleach by the PHTA Recreational Water Quality Committee
TECH NOTES SODIUM HYPOCHLORITE, AKA “LIQUID CHLORINE” In other words, bleach By the PHTA Recreational Water Quality Committee IN THE SWIMMING pool industry, one gallon of 12.5% sodium hypochlorite a corrosive. As such, a maximum of of the most popularly chosen forms for provides approximately 12.5 ppm of 500 gallons can be stored in a non-fire, sanitizing and superchlorinating water free chlorine per 10,000 gallons of sprinkler-protected room and 1,000 is sodium hypochlorite. Commonly pool water. It takes 10.6 fl. oz of 12.5% gallons in a fire, sprinkler-protected known as “liquid chlorine” or bleach, sodium hypochlorite to get roughly room as maximum exempt quantities. sodium hypochlorite is widely used 1 ppm of free chlorine in 10,000 gallons Quantities beyond this create an “H” in both commercial and residential of pool water. The pH of pool grade Hazardous Occupancy and require swimming pools. Sodium hypochlorite sodium hypochlorite is 13. special fire protection. effectively destroys bacteria and Sodium hypochlorite is Sodium hypochlorite reacts prevents algae in swimming pools. classified as an inorganic sanitizer; in water to create hypochlorous This edition of Tech Notes provides it does not contain cyanuric acid. information on the characteristics, Sodium hypochlorite is a primary effects and proper application of sanitizer because of its ability to SODIUM HYPOCHLORITE: THE sodium hypochlorite. kill microorganisms, oxidize non- living contaminants like ammonia BASIC FACTS WHAT IT IS and swimmers’ waste and provide • Clear yellow liquid with a Sodium hypochlorite (NaOCl), a protective residual in the water. chlorine odor commonly referred to as “liquid Sodium hypochlorite is non-flammable, • A solution containing chlorine” or liquid bleach, is an non-combustible and non-explosive, water, hypochlorite, sodium aqueous solution created by and containers under 1.3 gallons hydroxide and a trace amount mixing chlorine gas in water with aretransported as “Limited Quantities” of sodium chloride concentrations of sodium hydroxide. -
Title Synthesis of Melamine from Urea, II Author(S)
Title Synthesis of melamine from urea, II Author(s) Kinoshita, Hideo The Review of Physical Chemistry of Japan (1954), 24(1): 19- Citation 27 Issue Date 1954-09-10 URL http://hdl.handle.net/2433/46705 Right Type Departmental Bulletin Paper Textversion publisher Kyoto University The Review of Physical Chemistry of Japan Vol. 24 No. 1 (1954) SYNTHESIS OF MELAMINE FROM UREA, II BS' HILan 1{IYU$H IT Ai it Introduction It was reportedil that the reaction of yielding melamine from urea begins from 275'G, reaches equi]ibrium within 6 hours at 325`C and there is no considerable change in the quantity and the yield of melamine above 325°C. And it was recognized that the reaction velocity is faster, as the packing ratioisgreater and so the pressure of gas phase is-higher. The yield of melamine was calculated from the following equation and the maximum yield was 99.4b. 6NH,CONH_ _ (NH_CN), + 6NH, + 3C0. (1) Moreover, as the intermediate products of this reaction, biuret, cyanuric acid and the water insoluble were obtained. The nitrogen content of this water insoluble ~cas dis- tributedbetween 45.4 and 55.7%. For the purpose of studying the process of this reaction, the author experimented the following cases, the reaction of urea under the condition of existing excess ammonia, the reaction between cyanuric acid and ammonia, the reaction between the water Insoluble and ammonia, and the reaction between melamine and water. These results are compared with those of the previous paper, and moreover the author makes clear that the water insoluble consists of ammelide and ammeline. -
Chlorinated Cyanurates (Dichlor & Trichlor)
Chlorinated Cyanurates (Dichlor & Trichlor) Water Chemistry Implications David G. Wahman Research Environmental Engineer National Risk Management Research Laboratory U.S. Environmental Protection Agency Cincinnati, Ohio, United States EPA Small Systems Webinar Series January 30, 2018 1 OEPA After this presentation: 1. Familiar with chlorinated cyanurates & use 2. Understand water chemistry & implications 3. Aware of things to consider in practice 4. Aware of application & future updates Free Chlorine & Sunlight . Free chlorine . Hypochlorous acid (HOCl) + hypochlorite ion (OCl–) . Absorbs ultraviolet (UV) light decomposes . Wavelengths > ~280 nm reach Earth’s surface – . Peak absorbance (λmax): OCl = 292 nm & HOCl = 235 nm . 30 minute half–life Source: Zayat et al. (2007) Cyanuric Acid Addition . Cyanuric acid (CYA) . Not related to cyanide . Outdoor pools since 1958 . Added to “stabilize” free chlorine . Forms chlorinated cyanurates . Lowers free chlorine concentration . “Reservoir” of free chlorine releases back into water . λmax = 215–220 nm more stable in sunlight . Public pool concentrations (ANSI/APSP 2009) Parameter Minimum Ideal Maximum Total (Available) Chlorine (mg Cl2/L) 1 2–4 4 Cyanuric Acid (mg/L) N/A 30–50 100 CYA Stabilization (Concentration) 100 . ↑ CYA ↑ Stability 90 80 70 60 50 40 30 pH 7 0 mg/L CYA Percent of Total Chlorine Remaining Chlorine Total Percent of 20 84–90 °F 25 mg/L CYA 10 2.5 mg Cl2/L Total Chlorine Sunlight Exposed 100 mg/L CYA 0 0 1 2 3 4 Source: Wojtowicz (2004) Time (hours) Cyanuric Acid (H3Cy) ⇌ Cyanuric Acid Isocyanuric Acid (enol form) (keto form) . “Cy” = Cyanurate structure H3Cy Chlorinated Cyanurates Trichlor Cl3Cy – Chlorinated HCl2Cy Cl2Cy Dichlor Cyanurates + Free ⇌ ⇌ Chlorine – 2– H2ClCy HClCy ClCy ⇌ ⇌ ⇌ ⇌ ⇌ ⇌ ⇌ – 2– 3– Cyanuric H3Cy H2Cy HCy Cy Acid ↑ pH . -
Analysis of Melamine and Cyanuric Acid by Liquid Chromatography with Diode Array Detection and Tandem Mass Spectrometry Byungchul Kim
The University of Maine DigitalCommons@UMaine Electronic Theses and Dissertations Fogler Library 5-2009 Analysis of Melamine and Cyanuric Acid by Liquid Chromatography with Diode Array Detection and Tandem Mass Spectrometry Byungchul Kim Follow this and additional works at: http://digitalcommons.library.umaine.edu/etd Part of the Food Chemistry Commons Recommended Citation Kim, Byungchul, "Analysis of Melamine and Cyanuric Acid by Liquid Chromatography with Diode Array Detection and Tandem Mass Spectrometry" (2009). Electronic Theses and Dissertations. 12. http://digitalcommons.library.umaine.edu/etd/12 This Open-Access Dissertation is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of DigitalCommons@UMaine. ANALYSIS OF MELAMINE AND CYANURIC ACID BY LIQUID CHROMATOGRAPHY WITH DIODE ARRAY DETECTION AND TANDEM MASS SPECTROMETRY By Byungchul Kim B.E. Pukyong National University, 1998 M.S. Pukyong National University, 2000 M.S. University of Arkansas, 2004 A THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy (in Food and Nutrition Sciences) The Graduate School The University of Maine May, 2009 Advisory Committee: Rodney J. Bushway, Professor of Food Science & Human Nutrition-Co chair L. Brian Perkins, Assistant Research Professor of Food Science-Co chair Alfred A. Bushway, Professor of Food Science & Human Nutrition Beth Calder, Extension Food Science Specialist and Assistant Professor of Food Science & Human Nutrition Lawrence A. LeBlanc, Assistant Research Professor of Food Science Titan Fan, President of Beacon Analytical Systems, Inc. © 2009 Byungchul Kim All Rights Reserved ii LIBRARY RIGHTS STATEMENT In presenting this thesis in partial fulfillment of the requirements for an advanced degree at The University of Maine, I agree that the Library shall make it freely available for inspection. -
Cyanuric Acid in Commercial Swimming Pools and Its Effects on Chlorine's
Cyanuric Acid in Commercial Swimming Pools and its Effects on Chlorine’s “Staying Power” And Oxidation Reduction Potentials By Aaron Askins Submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Environmental Assessment Raleigh, North Carolina 2013 Approved by advisory committee: Committee Chair: Linda R. Taylor, PE Abstract Cyanuric acid levels in commercial swimming pools has been a controversial topic in the swimming pool industry in the past few years. This chemical is known for its stabilizing abilities by protecting chlorine from the ultraviolet rays of the sun which cause photolysis. Cyanuric acid has received recognition for this ability, but has also received blame for over stabilization which reduces the effectiveness of sanitization and oxidation reduction potential (ORP) of chlorine. This loss in effectiveness could possibly result in recreational water illnesses arising due to water quality standards being compromised. Local and state regulations can make it unclear on what parameters cyanuric acid levels should be in commercial swimming pools due to its inconsistencies across the United States. These variances are wide and could possibly lead to confusion amongst pool professionals to exactly where they should be when applying this chemical. In this project a look at the “staying power” of chlorine and its oxidation reduction potential at various levels of cyanuric acid will hopefully develop an understanding on where the ideal range of this chemical should be kept. This along with surveys from North Carolina professional pool companies and an interview with a local official who oversees commercial pool inspections in Wake County will develop a foundation on the perception of how pool professionals view this chemical and its capabilities along with testing for its levels. -
The Chlorine / Cyanuric Acid Relationship and Implications for Nitrogen Trichloride by Richard A
The Chlorine / Cyanuric Acid Relationship and Implications for Nitrogen Trichloride by Richard A. Falk Abstract The amount of hypochlorous acid (HOCl) in water with Cyanuric Acid (CYA) at typical pool pH is proportional to the FC/CYA ratio and is orders of magnitude lower than the FC level itself. The primary oxidizing and sanitizing compound is hypochlorous acid while hypochlorite ion and the chlorinated isocyanurate compounds (chlorine attached to CYA) have orders of magnitude lower oxidizing or sanitizing capability. The rate of production and total amount of nitrogen trichloride produced from the oxidation of ammonia by chlorine is related to the hypochlorous acid concentration and not to the FC level directly. Though the precise mechanism of oxidation of urea by chlorine is unknown, proposed mechanisms lead to the same conclusion of nitrogen trichloride quantities being proportional to the hypochlorous acid level, all else equal. Therefore, the use of a small amount of CYA in indoor pools should significantly lower the amount of nitrogen trichloride produced in such pools and result in lower rates of outgassing of chlorine, corrosion of metal directly exposed to water and oxidation of skin, swimsuits and hair. The Hypochlorous Acid / Cyanuric Acid Equilibrium Cyanuric Acid (CYA, aka stabilizer or conditioner) is used in pools to protect chlorine breakdown from sunlight. Though CYA absorbs ultraviolet (UV) radiation directly thus shielding the lower depths of water and protecting chlorine in those depths from breakdown, the primary result of having CYA in the water with chlorine (hypochlorous acid) is that it combines with chlorine to form a set of chemical species collectively called chlorinated isocyanurates. -
Evaluation of Manufacturing Processes for the Production of Atrazine
EVALUATION OF MANUFACTURING PROCESSES FOR THE PRODUCTION OF ATRAZINE by Melissa Claire Schaefer Baccalaureus Technologiae: Chemistry A dissertation submitted in fulfilment of the requirements for the Magister Technologiae : Chemistry In the Faculty of Applied Science at the PORT ELIZABETH TECHNIKON January 2002 Promoter: Prof. B. Zeelie View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by South East Academic Libraries System (SEALS) Look thoroughly inside yourself; there is a source of strength that will always issue forth should you seek it. ~ Marcus Aurelius ~ ACKNOWLEDGEMENTS • Professor Ben Zeelie for his input and valued advice. • Dr. Benita Barton for proofreading this dissertation. • Dr. Babrie Schoonees for her guidance. • Staff and students at the PE Technikon chemistry department. • My closest friend and confidant, Dr. Shawn Gouws for unconditional support and encouragement. • Mom, Dad and Selwyn, for endless love and motivation to strive for a dream. SUMMARY This report describes the results of investigations carried out with the view to find an alternative for MIBK as solvent for the production of atrazine as currently practised by Dow AgroSciences in South Africa. The main motivating factors for the said investigation was: • to increase the yield of atrazine produced, • to reduce the amount of organics, consisting essentially of reaction solvent containing dissolved product, in the aqueous process effluent, and • to improve the properties of the solid (crystalline) product to enable easier product formulation. Synthetic reactions carried out in the absence of organic solvent, i.e. in essentially a 10% NaCl solution containing a surfactant, proved rather disappointing. Low yields of atrazine were obtained together with relatively large amounts of by-products such as propazine and simazine, irrespective of the nature of the surfactant. -
Residue Findings of Melamine and Its Structural Analogues in Food Using LC-MS/MS E
Residue findings of melamine and its structural analogues in food using LC-MS/MS E. Eichhorn, H. Marks, C. Wildgrube, D. Stanislawczyk, E. Scherbaum and M. Anastassiades E-Mail: [email protected] Introduction Results Melamine and its structural analogue cyanuric acid Between July 2013 and May 2020 CVUA Stuttgart entered the spotlight of food control labs in 2007 analyzed more than 15,000 samples of plant origin for following severe adulterations cases of animal feed, the presence of melamine, cyanuric acid and various milk powder and infant formulae, which aimed at triazine pesticides (Table 1). Ammeline and Ammelide fraudulently increasing the apparent protein content in were included to the scope only recently (approx. 300 those products. Whereas food of animal origin has total samples analyzed). been regularly monitored for melamine and cyromazine Table 1: Findings of cyromazine, other triazine pesticides and their possible degradation products melamine, ammeline, ammelide and following these incidences, food of plant origin initially cyanuric acid in conventional and organic samples (07/2013-05/2020). remained out of the focus. *Maximum Residue Limit (MRL) exceedances according to Reg. Numerous pathways exist through which food of plant 396/2005/EC and Reg. 1881/2006/EC (Melamine) after deducting the origin may be contaminated with melamine and its measurement uncertainty of ±50 % according to SANTE/12682/2019. downstream hydrolysis products ammeline, ammelide Conventional samples and cyanuric acid (Figure 1). Ammeline, ammelide and Findings (above limit of Quantitation) cyanuric acid are reported as metabolites of the Samples MRL triazine insecticide cyromazine, the triazine fungicide analyzed Total Findings <0.01 ppm >0.01 ppm exceedances* anilazine and numerous triazine herbicides, including Cyromazine 13320 76 0.6 % 31 0.2 % 45 0.3 % 5 0.04 % terbuthylazine, prometryn, simazine, atrazine, ametryn Other triazine and cyanazine. -
Cyanuric Acid Technology John A
Cyanuric Acid Technology John A. Wojtowicz Chemcon Cyanuric acid was identified as a chemical Cyanuric Acid >99% substance over two centuries ago. However, it was not until the late 1950’s that it attained industrial Ammelide and Ammeline ≤0.5% significance with the introduction of chlorinated Water ~0.1%* isocyanurates by Monsanto and FMC. Although the pH of saturated solution at 25°C 4.5-5.0 majority of cyanuric acid production is used in the manufacture of chlorinated isocyanurates, some of it *Water content will vary with manufacturer; some is also used as a swimming pool available chlorine products can contain up to 4% water. stabilizer. Cyanuric acid is also used in the manu- facture of specialty intermediates used in the pro- Table 1 – Typical Analysis of duction of plastics and coatings. The properties, chemistry, uses, etc. of cyanuric acid and chloroiso- Commercial Cyanuric Acid cyanurates have been comprehensively reviewed (Wojtowicz 1993a and 1993b). This paper discusses cally referred to as isocyanuric acid whereas the the structure, properties, analysis, chemistry, manu- enol form is simply cyanuric acid. Both forms are facture, and uses of cyanuric acid. collectively referred to as cyanuric acid. Properties Physical Typical Analysis Cyanuric acid is a white crystalline solid. Some of its physical properties are summarized in Typical analysis of commercial cyanuric acid Table 2. The aqueous solubility data for CA in Table (CA) is shown in Table 1. The product also typically 2 refers to distilled water, consequently these solu- contains small amounts of ammonium sulfate or tions have a pH around 4.8. -
GC/MS Analysis of Melamine and Cyanuric Acid Below 1Μg/G in Infant
GC/MS Analysis of Melamine and Cyanuric Acid Below 1 μg/g in Infant Formula Abstract The establishment of a 1 μg/g safety threshold for melamine in infant foods has led to a need for sensitive methods. Here, we established GC/MS conditions for highly reproducible analyses and evaluated the effectiveness of both solvent-based and matrix- matched standards. Using this method, melamine and cyanuric acid were reliably detected at and below 1 μg/g in infant formula. Introduction Reports linking the presence of melamine in pet food and infant formula to illnesses and deaths have led to the recall of a wide variety of tainted food products and to calls for stricter product testing. Melamine is not considered toxic alone at low doses; however, the observed toxicity has been attributed to melamine exposure in the presence of cyanuric acid. In combination, these compounds form insoluble crystals in the kidneys, causing illness and eventual renal failure. Melamine is not a legal food additive; it is a nitrogen-rich industrial compound used for plastics, flame-resistant products, and some cleaning agents. However, melamine and related byproducts have been added illegally to food products in order to falsely represent the amount of protein present, since protein level in many products is determined using nonspecific assays for nitrogen content (Figure 1). Figure 1: Melamine and related compounds are rich in nitrogen and have been used to misrepresent protein levels in some food products. In response to the need for more rigorous melamine and cyanuric acid testing, the U.S. Food and Drug Administration (FDA) has set three different commodity-based minimum reporting levels (MRLs): 10 μg/g for pet food, 2.5 μg/g for human food, and 1 μg/g for infant formula [1,2]. -
The Chemistry of Swimming Pool Maintenance W
Chemistry for Everyone edited by Products of Chemistry George B. Kauffman California State University Fresno, CA 93740 The Chemistry of Swimming Pool Maintenance W Carl Salter* and David L. Langhus Department of Chemistry, Moravian College, Bethlehem, PA 18018; *[email protected] The chemistry involved in swimming pool maintenance Despite the fact that pool chemistry is an interesting provides many potential applications in undergraduate chemi- application of chemical principles, there has been only one cal education. For example, students can learn the importance paper in this Journal about pool maintenance, and its dis- of pH in water chemistry because pH affects chlorine sanita- cussion is outdated (2). There are reports of laboratory ex- tion and calcium balance. Both chlorination and calcium solu- periments designed around certain aspects of pool chemistry bility provide practical examples of chemical equilibrium at (3a–3d), and one recent discussion of chlorination (4), yet work. The reactions of ammonia with chlorine introduce un- none which focus on pool maintenance. usual redox chemistry. There are many obvious applications At the center of pool chemistry is pH, which affects the of pool chemistry in an analytical chemistry course, and the balance of two important processes: the equilibrium between effect of temperature on pool equilibria is a possible physical hypochlorous acid and hypochlorite ion, and the equilibrium chemistry topic. The purpose of this paper is to explain the between calcium ions in solution and calcium carbonate in basic chemistry behind the common practices involved in the cement or plaster liner of many pools. Hypochlorous acid swimming pool maintenance. We hope it stimulates the in- is the most effective antibacterial species formed by chlorine, clusion of pool chemistry throughout the curriculum.