دانلود رایگان مقاله لاتین کاتالیزور keggin heteropolyacids از سایت الزویر
عنوان فارسی مقاله:
درک نقش کاتالیزور نوع Keggin heteropolyacids برای استیله گلیسرول با استفاده از تولوئن به عنوان یک entrainer
عنوان انگلیسی مقاله:
Understanding the role of Keggin type heteropolyacid catalysts for glycerol acetylation using toluene as an entrainer
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Glycerol is inevitably produced in the biodiesel production from transesterification of vegetable oil or animal fats and has led to a drastic surplus in chemical market. Global production of biodiesel market is estimated to reach 36.9millionmetric tons in 2020, which will give approximately 3.7 million metric tons of crude glycerol [1–3]. The current use of glycerol in pharmaceuticals, food and cosmetics consumes only a small part and hence, demand is somehow limited. To sustain chemical market and industry, it is important to convert glycerol into value added chemicals by several catalytic processes, such as selective oxidation to glyceric acid or hydroxyacetone [4], dehydration to acrolein [5–7], hydrogenolysis to 1,2- or 1,3-propanediol [8], etherification to alkyl ether [9,10], condensation to dimers or higher oligomers [11] and many others [3,12]. Another interesting approach to convert glycerol into monoacetyl glycerol (MAG, monoacetin), diacetyl glycerol (DAG, diacetin) andtriacetyl glycerol (TAG, triacetin) by means of esterification with acetic acid (acetylation) as shown in Fig. 1. These products have application in food and leather industry, as plasticizers and also they may serve as solvent and fuel additive [13–15]. Glycerol acetylation is an acid catalyzed reaction with equimolar formation of water as by-product at every consecutive step and the chemical equilibrium limits the extent of the esterification. In addition, Gibbs free energies of the firsttwo acetylation steps (MAG and DAG) are 19.15 and 17.80 kJ/mol, respectively, whereas this value for the third step (TAG) is relatively high (55.58 kJ/mol) and thus, the third step should be the most difficult one [16]. Beyond that, elevated temperatures are necessary to obtain high reaction rates. Generally the reaction is performed using homogeneous catalysts like sulfuric acid and paratoluene sulfonic acid [17] or heterogeneous catalysts such as sulphated mesoporous silica [18], sulphated zirconia [19,20], sulphated activated carbon [21,22], double SO3Hfunctionalized ionic liquids [23] and acid ion exchange resins like Amberlyst-15 or Amberlyst-36 [24–26]. On the other side, use of acetic anhydride as acetylation agent instead of acetic acid boosts the selectivity to TAG close to 100% as no water is formed, and the reaction rates are high even in the absence of catalysts. However,
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کلمات کلیدی:
Catalysis in Application - Issue 289 - Page 261 - Google Books Result https://books.google.com/books?isbn=0854046089 S. David Jackson, Justin S. J. Hargreaves, David Lennon - 2003 - Science Keggin-type and Dawson-type heteropolyanion salts have been proved to be inactive ... so demonstrating that only Brensted acidity plays a fundamental role for the ... reactions have been investigated mainly with Keggin-type heteropolyacids, ... Emerging Fields in Sol-Gel Science and Technology https://books.google.com/books?isbn=146150449X Tessy Maria Lopez, David Avnir, Michel A. Aegerter - 2013 - Technology & Engineering In all cases, it was found that hydroxyl groups developed an important role in the ... which is a Keggin type heteropolyacid) for 2-butanol dehydration, the last ... Factors Affecting the Removal of Ammonia from Air on Carbonaceous ... https://books.google.com/books?isbn=1461433924 Camille Petit - 2012 - Nature C. Petit and T. J . Bandosz, “Role of Aluminum Oxycations in Retention of Ammonia ... B. B. Bardin, et al., “Ammonia Adsorption on Keggin-Type Heteropolyacid ... [PDF]structure and texture of some keggin type heteropolyacids supported ... https://joam.inoe.ro/arhiva/pdf7_6/Popa.pdf 2005 - Cited by 21 - Related articles Keggin type heteropolyacids (HPAs) have been widely used in .... for Aerosil supported HPAs and 1.2-4.7 nm for titania supported HPAs in function of different. Acid-Base Catalysis II - Page 1 - Google Books Result https://books.google.com/books?isbn=008088752X H. Hattori, M. Misono, Y. Ono - 1994 - Technology & Engineering The present paper describes acidic salts of heteropolyacid and their ... Recently, we demonstrated that acidic salts of the Keggin—type heteropolytungstic acids ... Searches related to Understanding the role of Keggin type heteropolyacid keggin structure polyoxometalate chemistry keggin isomers keggin unit isomers dawson structure heteropoly acids of molybdenum wells dawson isopoly and heteropoly acids
