scholarly journals Role of Water in Diethyl Ether Dehydration Reaction

2017 ◽  
Vol 15 (1-2) ◽  
Author(s):  
Rada Petrović ◽  
Jelena Penavin-Škundrić ◽  
Branko Škundrić ◽  
Bogoljub Antonić ◽  
Zora Levi
Keyword(s):  
Diethyl Ether ◽  
Initial Period ◽  
Initial Reaction ◽  
Static System ◽  
Dehydration Reaction ◽  
Reaction Products ◽  
Active Centers ◽  
Temperature Growth ◽  
Cobalt Cation

The study examined catalytic conversion of diethyl ether in a gas phase in the static system on the synthetic mordenite (NaM) and the mordenite which the bivalent cobalt cation was introduced into (CoM). The reaction was observed in the temperature range from 424 K to 653 K, and the reaction products on both catalysts were ethene and water, and on NaM a small quantity of butene.The reaction of diethyl ether dehydration in the observed temperature interval is accelerate in time. The initial reaction is registered at the very beginning of the reaction followed by the water occurrence. The water originating from the reaction is generated on the surface of the zeolite catalyst the active centers that is favorable for the dehydration reaction. With the temperature growth the initial period on NaM catalyst gradually disappears and the reaction becomes the first order reaction (temperature is 653 K), while on CoM catalyst the initial period is registered at all observed temperatures. The explanation of the role of water in the occurrence of active centers needed for diethyl ether hydrolysis was obtained by experiments in which water was also added to the reaction mixture of diethyl ether – catalyst.

scholarly journals TEXTURAL AND CATALYTIC CHARACTERISTICS OF DECATIONIZED MORDENITE AND ZSM-5 ZEOLITE

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Jelena Penavin Škundrić ◽  
Branko Škundric ◽  
Rada Petrović ◽  
Dragica Lazić ◽  
Zora Levi ◽  
...  
Keyword(s):  
Specific Surface ◽  
Gas Phase ◽  
Temperature Interval ◽  
Diethyl Ether ◽  
Initial Period ◽  
Order Reaction ◽  
Dehydration Reaction ◽  
First Order ◽  
Adsorption Of Nitrogen ◽  
Acid Centers

The textural characteristics of acid forms of mordenite and ZSM-5 zeolite (HM and HZSM-5) were described based on the experiments of adsorption of nitrogen at 77 K in a specially constructed apparatus. The specific surface (SP) of catalysts was determined by applying BET-equation (SPBET), Langmuir adsorption isotherm (SPLANG) and t-method. The „t-method” was used to determine the outer specific surface (SPextt) and the volume of micropores (Vμpt) of zeolite. The volume of micropores (VμpDR) was additionally determined also based on Dubinin-Radushkevich method. The reactions of diethyl ether dehydration in the temperature interval from 400 to 480 K got sped up in time on both zeolites (HM and HZSM-5) and did not fully follow the kinetics of the first order reaction. The initial period registered by the experiment (increase of reaction rate in time) is interpreted by the slow reaction of water occurrence in the reaction of dehydration, which is necessary for the occurrence of Brönsted acid centers, where diethyl ether dehydration takes place. Now the overall rate of the dehydration reaction is determined by the rate of water occurrence. When there is a sufficient number of acid centers, the rate of diethyl ether dehydration is determined by the surface reaction and the „initial period“ gradually disappears. In the reaction of diethyl ether dehydration on HZSM-5 catalyst, the reaction is slower, even water (which is a product of dehydration) occurs more slowly, and therefore in the observed temperature interval the reaction was not transferred to the first order reaction. By the adsorption of diethyl ether from gas phase on HM and HZSM-5 zeolite at 300 K, the insight was provided into hydrophilic-hydrophobic characteristics of the surface, as well as the insight into the character and strength of active centers of these zeolites. As the test reaction for determining acidity of the catalyst, the one selected was the reaction of isomerization of 3,3-dimethyl butene-1 (3,3-DMB-1), which takes place on Brönsted acid centers by the mechanism of carbonium ion. The results obtained by the experiments of adsorption of nitrogen and diethyl ether from gas phase are in accordance with the kinetic data of the diethyl ether dehydration reaction.

scholarly journals Catalytic conversion of ethanol on H-Y zeolite

2005 ◽  
Vol 59 (9-10) ◽  
pp. 267-269
Author(s):  
Nedeljko Cegar ◽  
Jelena Penavin-Skundric ◽  
Branko Skundric ◽  
Rada Petrovic
Keyword(s):  
Catalytic Activity ◽  
Diethyl Ether ◽  
Ethanol Conversion ◽  
Static System ◽  
Nay Zeolite ◽  
Y Zeolite ◽  
Active Centers ◽  
Zeolite Nay ◽  
Catalytically Active ◽  
Lower Temperature

The catalytic activity of the H-form of synthetic zeolite NaY was examined in this study. The catalytic activity was determined according to the rate of ethanol conversion in a gas phase in the static system. In the conversion of ethanol on synthetic NaY zeolite at 585, 595, and 610 K, on which the reaction develops at an optimal rate, ethene and diethyl ether are evolved in approximately the same quantity. After transforming the NaY zeolite into the H-form, its catalytic activity was extremely increases so, the reaction develops at a significantly lower temperature with a very large increase in the reaction rate. The distribution of the products also changes, so that at lower temperatures diethyl ether is elvolved in most cases, and the development of ethene is favored at higher ones, and after a certain period of time there is almost complete conversion of ethanol into ethene. The increase in catalytic activity, as well as the change of selectivity of conversion of ethanol on the H-form of zeolite, is the result of removing Na+ cations in the NaY zeolite, so that more acidic catalyst is obtained which contains a number of acidic catalytically active centers, as well as a more powerful one compared to the original NaY zeolite.

Platelet Accumulation on Fibrin-coated Polyethylene: Role of Platelet Activation and Factor XIII

1995 ◽  
Vol 73 (05) ◽  
pp. 850-856 ◽  
Author(s):  
F D Rubens ◽  
D W Perry ◽  
M W C Hatton ◽  
P D Bishop ◽  
M A Packham ◽  
...  
Keyword(s):  
Factor Xiii ◽  
Cross Linking ◽  
Internal Diameter ◽  
Static System ◽  
Graft Occlusion ◽  
Platelet Binding ◽  
Coated Surface ◽  
Platelet Accumulation ◽  
Polyethylene Tubing

SummaryPlatelet accumulation on small- and medium-calibre vascular grafts plays a significant role in graft occlusion. We examined platelet accumulation on the surface of fibrin-coated polyethylene tubing (internal diameter 0.17 cm) during 10 min of flow (l0ml/min) at high wall shear rate (764 s-1). Washed platelets labelled with 51Cr were resuspended in Tyrode solution containing albumin, apyrase and red blood cells (hematocrit 40%). When the thrombin that was used to form the fibrin-coated surface was inactivated with FPRCH2C1 before perfusion of the tubes with the platelet:red blood cell suspension, the accumulation of platelets was 59,840 ± 27,960 platelets per mm2, whereas accumulation on fibrin with residual active thrombin was 316,750 ± 32,560 platelets per mm2 (n = 4). When the fibrin on the surface was cross-linked by including recombinant factor XIII (rFXIII) in the fibrinogen solution used to prepare the fibrin-coated surface, platelet accumulation, after thrombin neutralization, was reduced by the cross-linking from 46,974 ± 9702 to 36,818 ± 7964 platelets per mm2 (n = 12, p <0.01). Platelet accumulation on tubes coated with D-dimer was ten times less than on tubes coated with D-domain; this finding also supports the observation that cross-linking of fibrin with the formation of γ-γ dimers reduces platelet accumulation on the fibrin-coated surface. Thrombin-activated platelets themselves were shown to cross-link fibrin when they had adhered to it during perfusion, or in a static system in which thrombin was used to form clots from FXIII-free fibrinogen in the presence of platelets. Thus, cross-linking of fibrin by FXIII in plasma or from platelets probably decreases the reactivity of the fibrin-containing thrombi to platelets by altering the lysine residue at or near the platelet-binding site of each of the γ-chains of the fibrinogen which was converted into the fibrin of these thrombi.

The Kinetics of Inhibition of the Action of Thrombin by the Fibrinopeptides Formed during the Clotting of Fibrinogen

1966 ◽  
Vol 16 (01/02) ◽  
pp. 277-295 ◽  
Author(s):  
A Silver ◽  
M Murray
Keyword(s):  
Amino Acids ◽  
Competitive Inhibition ◽  
Amorphous Material ◽  
Peptide Bond ◽  
Initial Reaction ◽  
Reaction Products ◽  
Coagulation Mechanism ◽  
Kinetics Of ◽  
Kinetics Of Inhibition ◽  
Burk Plot

SummaryVarious investigators have separated the coagulation products formed when fibrinogen is clotted with thrombin and identified fibrinopeptides A and B. Two other peaks are observed in the chromatogram of the products of coagulation, but these have mostly been dismissed by other workers. They have been identified by us as amino acids, smaller peptides and amorphous material (37). We have re-chromatographed these peaks and identified several amino acids. In a closed system of fibrinogen and thrombin, the only reaction products should be fibrin and peptide A and peptide B. This reasoning has come about because thrombin has been reported to be specific for the glycyl-arginyl peptide bond. It is suggested that thrombin also breaks other peptide linkages and the Peptide A and Peptide B are attacked by thrombin to yield proteolytic products. Thrombin is therefore probably not specific for the glycyl-arginyl bond but will react on other linkages as well.If the aforementioned is correct then the fibrinopeptides A and B would cause an inhibition with the coagulation mechanism itself. We have shown that an inhibition does occur. We suggest that there is an autoinhibition to the clotting mechanism that might be a control mechanism in the human body.The experiment was designed for coagulation to occur under controlled conditions of temperature and time. Purified reactants were used. We assembled an apparatus to record visually the speed of the initial reaction, the rate of the reaction, and the density of the final clot formed after a specific time.The figures we derived made available to us data whereby we could calculate and plot the information to show the mechanism and suggest that such an inhibition does exist and also further suggest that it might be competitive.In order to prove true competitive inhibition it is necessary to fulfill the criteria of the Lineweaver-Burk plot. This has been done. We have also satisfied other criteria of Dixon (29) and Bergman (31) that suggest true competitive inhibition.

Effect of grain size on the vapour phase hydration of monoclinic and triclinic modifications of tricalcium silicate; role of high temperature activation

1991 ◽  
Vol 56 (10) ◽  
pp. 1993-2008
Author(s):  
S. Hanafi ◽  
G. M. S. El-Shafei ◽  
B. Abd El-Hamid
Keyword(s):  
Particle Size ◽  
Vapour Phase ◽  
Tricalcium Silicate ◽  
Active Centers ◽  
Thermally Activated ◽  
Grain Sizes ◽  
Intermediate Size ◽  
Surface Active ◽  
Temperature Activation

The hydration of tricalcium silicate (C3S) with three grain sizes of monoclinic (M) and triclinic (T) modifications and on their thermally activated samples were investigated by exposure to water vapour at 80°C for 60 days. The products were investigated by XRD, TG and N2 adsorption. The smaller the particle size the greater was the hydration for both dried and activated samples from (M). In the activated samples a hydrate with 2θ values of 38.4°, 44.6° and 48.6° could be identified. Hydration increased with particle size for the unactivated (T) samples but after activation the intermediate size exhibited enhanced hydration. Thermal treatment at 950°C of (T) samples increased the surface active centers on the expense of those in the bulk. Changes produced in surface texture upon activation and/or hydration are discussed.

Involvement of monocytes/macrophages as key factors in the development and progression of cardiovascular diseases

2014 ◽  
Vol 458 (2) ◽  
pp. 187-193 ◽  
Author(s):  
María Fernández-Velasco ◽  
Silvia González-Ramos ◽  
Lisardo Boscá
Keyword(s):  
Myocardial Infarction ◽  
Immune System ◽  
Cardiovascular Diseases ◽  
Cardiac Tissue ◽  
Initial Period ◽  
Cardiac Injury ◽  
Key Factors ◽  
Cardiac Damage ◽  
Inflammatory Profile

Emerging evidence points to the involvement of specialized cells of the immune system as key drivers in the pathophysiology of cardiovascular diseases. Monocytes are an essential cell component of the innate immune system that rapidly mobilize from the bone marrow to wounded tissues where they differentiate into macrophages or dendritic cells and trigger an immune response. In the healthy heart a limited, but near-constant, number of resident macrophages have been detected; however, this number significantly increases during cardiac damage. Shortly after initial cardiac injury, e.g. myocardial infarction, a large number of macrophages harbouring a pro-inflammatory profile (M1) are rapidly recruited to the cardiac tissue, where they contribute to cardiac remodelling. After this initial period, resolution takes place in the wound, and the infiltrated macrophages display a predominant deactivation/pro-resolution profile (M2), promoting cardiac repair by mediating pro-fibrotic responses. In the present review we focus on the role of the immune cells, particularly in the monocyte/macrophage population, in the progression of the major cardiac pathologies myocardial infarction and atherosclerosis.

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