The use of other catalysts such as H-ZSM-5, H-β, H-ferrierite, silica-alumina mixtures, and supported heteropolyacids gave similar behaviors of the glycerol conversion and acrolein yield with the increase of glycerol concentration [23, 24, 25, 26]. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. The main features of these catalysts that affect the acrolein selectivity are the strength and type of the surface acid sites, which are known to promote the dehydration reactions of alcohols [44, 45, 46]. It was evidenced that the WHSV has significant influence on the catalytic activity. At any temperature, the introduction of La into the HY zeolite improved the glycerol conversion, attributed to the increase of total acidity. Table 2 summarizes this behavior, considering the effect of the water content (from 15.7 to 91.7 mol %) on the glycerol dehydration over H-ZSM-5 (150) with time-on-stream [23]. As a food additive, glycerol is lab… The production of acrolein from glycerine in the presence of hierarchical H-ZSM-5 zeolites has proven to be feasible. Consequently, the catalyst stability with the time-on-stream (TOS) is adversely affected when increasing glycerol content in the feed. The catalytic dehydration of glycerol may also occur on oxides promoted with phosphate. In food and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. [39] got 80% of acrolein yield with complete conversion of glycerol at 573 K using a catalyst of tungstated zirconia promoted with silica (WSi/Zr). Copyright © 2014 Elsevier Ltd. All rights reserved. However, severe catalyst deactivation with TOS occurs at higher temperatures. An improvement of the acrolein selectivity was also observed with the rise of temperature at initial activities, maintaining the trends along the TOS and resulting in a higher acrolein yield at 593 K even after 10 h. Similar behavior has been reported for the glycerol dehydration performed over several catalysts such as H-ZSM-5 (150), H-β (25) and H-ferrierite (55), La-NH4-modified H-β (13) zeolite, and aluminosilicophosphate nanospheres (ASPN-40) [23, 24, 30, 31]. Catalysts, such as zirconium oxide, with HA between −3 and + 7, belong to the second group. Table 3 shows the effect of reaction temperature, between 553 and 593 K, and TOS on the glycerine dehydration in the presence of MCM-22 (molar ratio SiO2/Al2O3 = 30) as catalyst [29].
These catalysts are less selective to acrolein but more stable with TOS than those of group 3 [47]. Real‐time analysis of the product composition indicated the in situ MOF structural evolution. Dalil et al. Effect of the weight hourly space velocity on the glycerol conversion and product selectivity. As a sugar substitute, it has approximately 27 kilocalories per teaspoon (sugar has 20) and is 60% as sweet as sucrose. Besides, the incorporation of Pd to the LaY catalyst resulted in an acrolein yield of 87.6% at the same temperature. [36] investigated a catalyst of tungsten oxide supported on titania (WO3/TiO2) in a fluidized-bed reactor. Since the concentration of Lewis acid sites was also increased after the ion-exchange procedures, the acetol yield followed the order Pd/LaY > HY > LaY with values of 0.07, 0.5, and 2.5%, respectively.

Catalytic Dehydration of Glycerine to Acrolein, Glycerine Production and Transformation - An Innovative Platform for Sustainable Biorefinery and Energy, Marco Frediani, Mattia Bartoli and Luca Rosi, IntechOpen, DOI: 10.5772/intechopen.85751.

[23, 24] as catalysts for the glycerine dehydration in a fixed-bed reactor, taking into account several parameters such as the composition of the catalyst (SiO2/Al2O3 molar ratio), the reaction temperature, and the amount of water in the feed. [43]. Regarding the acrolein yield, it also presents a maximum value of 80% at 0.35 h−1 and decreased with the increase of WHSV because the formed acrolein may further react with unconverted glycerol. These results suggest that at low glycerol concentrations (large amounts of water), the water molecules may modulate side reactions of glycerol and acrolein such as etherification, oxidation, hydrogenolysis, condensation, and polymerization, thus enhancing the acrolein selectivity [23, 27]. The current development of several precursors on suitable support such as heteropoly acids, zeolites, mixed metal oxides, and pyrophosphates in creating superior catalytic properties for both liquid- and gas-phase processes has been discussed. Regarding the effect of space velocity on the glycerol dehydration with TOS, no marked trend was found during 20 h periods resulting in neglectable change in the glycerol conversion and acrolein yield [34].

Care should be taken concerning the choice of the reference conditions, since the three ways of expressing space velocity find extensive use. acrolein glycerol step method characterized Prior art date 2007-12-20 Legal status (The legal status is an assumption and is not a legal conclusion. An increase in the total amount of acid sites was observed after the exchange with La cations, increasing around 1.5 and 2.1 times the concentration of Lewis and Brønsted sites in the LaY catalyst regarding the HY zeolite, at 573 K. A subsequent raise of the total acidity occurred after the impregnation of the LaY solid with Pd, leading to concentrations 2.5 and 3.5 times higher than the acidity of HY zeolite.
Figure 5 presents the influence of temperature on the glycerol conversion and acrolein yield for the gas-phase reaction over catalysts of 20 wt % of phosphomolybdic acid (H3PMo12O40, HPMo), phosphotungstic acid (H3PW12O40, HPW), and silicotungstic acid (H4SiW12O40, HSiW) supported on commercial alumina (Al2O3, A5) in a fixed-bed reactor [28].

When the glycerol concentration in the feed was increased to 20 wt %, the acrolein yield slightly decreased, and the catalyst was stable during a shorter TOS regarding the reaction with 10 wt % of glycerol in the feedstock. [30] studied the dehydration activity of the protonic (H-β) and the ammonium-lanthanum-modified beta zeolites (NH4-La-β). The acidity and textural properties of various catalysts, as significant variables affecting acrolein yield and selectivity, are evaluated separately.

The promoting effect of Lewis acidity on the acetol production was also evidenced since the change from 0.41 to 2.95 μmol m−2 resulted in the enhancement of the acetol selectivity from 5 to 18%, independent of the dispersed phase and the catalytic support. The formation of acrolein from glycerol has … Complete glycerol conversion and acrolein selectivity of 73% were reached after 6 h of TOS at 553 K. Besides the high activity of the catalyst, the authors find that the acrolein selectivity increased from 55 to 73% with the increase in TOS from 1 to 6 h, related to the increase of coke formation over the catalyst. The authors found that the catalytic activity depended on the type of heteropolyacid as well as the size of mesopores in the silica support.

Effect of the glycerol concentration in the feedstock on the glycerol conversion and product yield. However, the highest acrolein yields were 57.3, 75.2, and 87.6% at 573 K, for the HY, LaY, and Pd/LaY, respectively, as a result of the increase of the glycerol conversion.

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