scholarly journals KINETICS OF PALM OIL TRANSESTERIFICATION IN METHANOL WITH POTASSIUM HYDROXIDE AS A CATALYST

2010 ◽  
Vol 8 (2) ◽  
pp. 219-225
Author(s):  
Yoeswono Yoeswono ◽  
Triyono Triyono ◽  
Iqmal Tahir
Keyword(s):  
Activation Energy ◽  
Palm Oil ◽  
Rate Constants ◽  
Potassium Hydroxide ◽  
Catalyst Concentration ◽  
Time Interval ◽  
Pseudo First Order Reaction ◽  
Exponential Factor ◽  
Potassium Methoxide ◽  
First Order

A study on palm oil transesterification to evaluate the effect of some parameters in the reaction on the reaction kinetics has been carried out. Transesterification was started by preparing potassium methoxide from potassium hydroxide and methanol and then mixed it with the palm oil. An aliquot was taken at certain time interval during transesterification and poured into test tube filled with distilled water to stop the reaction immediately. The oil phase that separated from the glycerol phase by centrifugation was analyzed by 1H-NMR spectrometer to determine the percentage of methyl ester conversion. Temperature and catalyst concentration were varied in order to determine the reaction rate constants, activation energies, pre-exponential factors, and effective collisions. The results showed that palm oil transesterification in methanol with 0.5 and 1 % w/w KOH/palm oil catalyst concentration appeared to follow pseudo-first order reaction. The rate constants increase with temperature. After 13 min of reaction, More methyl esters were formed using KOH 1 % than using 0.5 % w/w KOH/palm oil catalyst concentration. The activation energy (Ea) and pre-exponential factor (A) for reaction using 1 % w/w KOH was lower than those using 0.5 % w/w KOH.   Keywords: palm oil, transesterification, catalyst, first order kinetics, activation energy, pre-exponential factor

On the Chemical Reactivity of the Phytochrome Chromophore in the Pr and Pfr Form

1985 ◽  
Vol 40 (3-4) ◽  
pp. 215-218 ◽  
Author(s):  
Fritz Thümmler ◽  
Peter Eilfeld ◽  
Wolfhart Rüdiger ◽  
Doo-Khil Moon ◽  
Pill-Soon Song
Keyword(s):  
Reaction Kinetics ◽  
Rate Constants ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order Reaction ◽  
Limiting Factor ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
The Difference

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

Kinetics and Activation Parameters for the Alkaline Aqueous Rearrangement of Trichorfon [O,O-Dimethyl-(2,2,2-Trichloro-1-Hydroxyethyl) Phosphonate] to Dichlorvos [O,O-Dimethyl-O-(2,2-Dichloroethenyl)Phosphate]

2001 ◽  
Vol 36 (3) ◽  
pp. 589-604 ◽  
Author(s):  
Julian M. Dust ◽  
Christopher S. Warren
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Activation Parameters ◽  
Base Catalysis ◽  
Rearrangement Product ◽  
Exponential Factor ◽  
First Order ◽  
Pseudo First Order ◽  
Order Plot ◽  
Kinetics Of

Abstract The kinetics of the alkaline rearrangement of O,O-dimethyl-(2,2,2-trichloro-1- hydroxyethyl)phosphonate, (trichlorfon, 1), the active insecticidal component in such formulations as Dylox, was followed at 25±0.5°C by high pressure liquid chromatography (UV-vis detector, 210 nm). The rearrangement product, O,Odimethyl- O-(2,2-dichloroethenyl)phosphate (dichlorovos, 2), which is a more potent biocide than trichlorfon, undergoes further reaction, and the kinetics, consequently, cannot be treated by a standard pseudo-first-order plot. A two-point van't Hoff (initial rates) method was used to obtain pseudo-first-order rate constants (kѱ) at 25, 35 and 45°C: 2.6 × 10-6, 7.4 × 10-6 and 2.5 × 10-5 s-1, respectively. Arrhenius treatment of this data gave an activation energy (Ea) of 88 kJ·mol-1 with a pre-exponential factor (A) of 5.5 × 109 s-1. Kinetic trials at pH 8.0 using phosphate and tris buffer systems show no buffer catalysis in this reaction and indicate that the rearrangement is subject to specific base catalysis. Estimates are reported for pseudo-first-order half-lives for trichlorfon at pH 8.0 for environmental conditions in aqueous systems in the Corner Brook region of western Newfoundland, part of the site of a recent trichlorfon aerial spray program.

scholarly journals Microwave-Assisted Transesterification of Kusum Oil: Parametric, Kinetic and Thermodynamic Studies

2020 ◽  
Vol 32 (11) ◽  
pp. 2893-2903
Author(s):  
SHEETAL N. NAYAK ◽  
MILAP G. NAYAK ◽  
CHANDRAKANT P. BHASIN
Keyword(s):  
Activation Energy ◽  
Reaction Rate ◽  
Frequency Factor ◽  
Molar Ratio ◽  
Pseudo First Order Reaction ◽  
Time Intervals ◽  
First Order ◽  
Microwave Assisted ◽  
Lower Heat ◽  
Kinetic And Thermodynamic Studies

Microwave-assisted transesterification of non-edible oil to produce biodiesel is gaining attention due to lower heat loss as well as rapid conversion. In this study, esterified kusum oil as a feedstock was transesterified in the presence of Ba(OH)2. At 800 W microwave power and constant magnetic stirring the effect of important process parameters such as solvent methanol molar ratio, Ba(OH)2, temperature, and time on biodiesel yield were evaluated. The parametric study suggested that 9:1 M methanol, 65 ºC reaction temperature, 2.5 wt% Ba(OH)2 catalyst and 3.5 min of transesterification time gave close to 96% biodiesel yield. At the above conditions of methanol and catalyst, the reaction kinetics and thermodynamic study were performed using different time intervals. The microwave-assisted transesterification followed pseudo-first-order reaction rate with 34.57 kJ/mol K activation energy and 205664 min-1 frequency factor. The reduction in activation energy and increase in the frequency factor reveal the non-thermal effect associated with microwave heating. The thermodynamic properties evaluated using the Eyring equation suggests non-spontaneity and endothermic nature of transesterification.

Hydrothermal Transformation of Inorganic and Biogenic Silica as Studied Using in Situ Hydrothermal Infrared Microspectroscopy

2018 ◽  
Vol 72 (10) ◽  
pp. 1487-1497
Author(s):  
Naoto Morifuji ◽  
Satoru Nakashima
Keyword(s):  
Activation Energy ◽  
Rate Constants ◽  
Biogenic Silica ◽  
Zero Order ◽  
Silica Gels ◽  
Dissolution Rates ◽  
First Order ◽  
Order Rate ◽  
Hydrothermal Transformation

Infrared (IR) spectral changes with time of biogenic and inorganic silica have been examined using in situ IR micro-spectroscopy by using an original hydrothermal diamond cell. Centric diatoms (diameters = 100–350 µm) and silica gels (C-300, Wako Chemicals) were heated at 125–185 ℃ range with a pressure of 3 MPa. Decreases of 950 cm−1 (Si–OH) peak heights could be fitted by a combination of exponential and linear decreases (y = A1 exp (−k1t) − k0 t + A0). The first-order rate constants k1 [s−1] for Si–OH decreases of diatoms and silica gels are similar but the activation energy was lower for diatoms (61 kJċmol−1 < 106 kJċmol−1). The first-order rate constants k1 [s−1] for Si–OH decreases of diatoms and silica gels are much faster than reported hydrothermal transformation rates of silica (Opal A to Opal CT and Opal CT to quartz). These results indicate that the exponential Si–OH decreases observed in biogenic and inorganic silica during hydrothermal reactions are considered to correspond to dehydration–condensation reactions in the amorphous states (Si–OH + HO–Si → Si–O–Si). In fact, band area ratios 1220 cm−1/1120 cm−1 increased exponentially indicating more bridging of Si–O–Si. On the other hand, the linear decreases of Si–OH of silica gels (k0 [s−1]) were considered to be due to dissolution of silica. By using the grain size and density of silica gels, the zero-order dissolution rate constants k0* [molċm−2ċs−1] were calculated from k0 [s−1]. The obtained dissolution rates k0* are larger than reported values for silica glass and quartz. The zero-order dissolution rates k0 [s−1] for diatoms are similar to those for silica gels but with a lower activation energy (32 kJċmol−1 < 60 kJċmol−1). The smaller activation energy values for diatoms than silica gels both for the first and zero-order decrease rates of Si–OH might indicate catalytic effects of organic components bound to biogenic silica for the dehydration–condensation reaction and dissolution. The present in situ hydrothermal IR micro-spectroscopy is useful for characterizing transformation of amorphous materials including inorganic–organic composites.

The Vulcanization of Elastomers. XI. The Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. I

1957 ◽  
Vol 30 (3) ◽  
pp. 911-927 ◽  
Author(s):  
Otto Lorenz ◽  
Elisabeth Echte
Keyword(s):  
Activation Energy ◽  
Zinc Oxide ◽  
Natural Rubber ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Network Formation ◽  
Zinc Salt ◽  
Kcal Mole ◽  
Minimum Quantity ◽  
First Order

Abstract 1. The decrease of free sulfur occurs according to the first order law during the vulcanization of natural rubber accelerated by mercaptobenzothiazole in the presence of zinc oxide. The activating energy for this reaction amounts to 30.5 kcal./mole. 2. If zinc benzothiazolylmercaptide is used as an accelerator, one obtains the same rate constants for the sulfur decrease as in the presence of mercaptobenzothiazole. These seem to be equivalent as regards their effectiveness of acceleration. 3. A kinetic analysis of the reciprocal swelling, which represents a measure of network formation, indicates that the reaction is first order. Sulfur decrease and reciprocal swelling prove to be equal processes as regards rate. This is true where vulcanization is accelerated with mercaptobenzothiazole or with the zinc salt. 4. During vulcanization there occurs a decrease of accelerator concentration. This is dependent upon the temperature and is tied in with the combination sulfur with rubber. 5. If the quantity of the accelerator added is changed, the rate constants for sulfur decrease and for reciprocal swelling do not change, provided that a minimum quantity of accelerator is present. 6. In vulcanization accelerated with zinc benzothiazolylmercaptide, zinc oxide being absent, sulfur decrease again occurs according to the first order law but considerably faster, without thereby changing the activation energy. These investigations are being continued and the results will be discussed in detail in relation to other published contributions in this field.

THE ISOLATION, IDENTIFICATION, AND PROPERTIES OF DINUCLEOTIDES FROM ALKALI HYDROLYZATES OF RIBONUCLEIC ACIDS

1959 ◽  
Vol 37 (11) ◽  
pp. 1329-1350 ◽  
Author(s):  
B. G. Lane ◽  
G. C. Butler
Keyword(s):  
Rate Constants ◽  
Potassium Hydroxide ◽  
Ribonucleic Acids ◽  
Pancreatic Ribonuclease ◽  
Preliminary Characterization ◽  
First Order

The isolation, identification, and properties of dinucleotides from alkali hydrolyzates of RNA are described. Preparative methods for obtaining the alkali-labile dinucleotides which were found in our 18-hour hydrolyzates of RNA in 1 M potassium hydroxide are described, and it is noted that all of them (ApAp, ApGp, ApUp, GpAp, and GpCp) are not susceptible to pancreatic ribonuclease at the concentrations of the enzyme which are customarily employed for hydrolytic degradations. It has been found, however, that two of these dinucleotides (ApAp and ApUp) are susceptible to pancreatic ribonuclease at concentrations of the enzyme which are about five thousand times greater than those customarily employed. The rate constants of first order hydrolysis in alkali of ApAp, ApGp, ApUp, GpAp, and GpCp are found to be correspondingly lower than the rate constants for two dinucleotides which were not found in our 18-hour hydrolyzates, and which are susceptible to pancreatic ribonuclease. Furthermore, it is reported that the eight possible diribonucleotides which are not susceptible to pancreatic ribonuclease (ApAp, ApGp, ApCp, ApUp, GpGp, GpAp, GpCp, and GpUp) are found in roughly equivalent amounts in a 2-hour alkali hydrolyzate of a preparation of yeast RNA, and account for 80–90% of the dinucleotides present.In addition to the alkali-labile dinucleotides found in alkali hydrolyzates of RNA, the isolation and preliminary characterization of five alkali-stable compounds are reported.

Gas Phase Adduct Reactions in MOCVD Growth of GaN

1995 ◽  
Vol 395 ◽  
Author(s):  
A. Thon ◽  
T.F. Kuech
Keyword(s):  
Activation Energy ◽  
Gas Phase ◽  
Decomposition Temperature ◽  
Adduct Formation ◽  
Gas Phase Reactions ◽  
Flow Tube ◽  
Exponential Factor ◽  
First Order ◽  
Mocvd Growth ◽  
Tube Reactor

ABSTRACTGas phase reactions between trimethylgallium (TMG) and ammonia were studied at high temperatures, characteristic to MOCVD of GaN reactors, by means of insitu mass spectroscopy in a flow tube reactor. It is shown, that a very fast adduct formation followed by elimination of methane occurs. The decomposition of TMG and the adduct - derived compounds are both first order and have similar apparent activation energy. The pre-exponential factor of the adduct decomposition is smaller, and hence is responsible for the higher full decomposition temperature of the adduct relative to that of TMG.

THE THERMAL DECOMPOSITION OF METHYL HYDROPEROXIDE

1965 ◽  
Vol 43 (8) ◽  
pp. 2236-2242 ◽  
Author(s):  
Alexander D. Kirk
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Gas Phase ◽  
Rate Constants ◽  
Dimethyl Phthalate ◽  
Kcal Mole ◽  
First Order ◽  
Methyl Hydroperoxide ◽  
Expected Values ◽  
Homogeneous Decomposition

The thermal decomposition of methyl hydroperoxide has been studied in solution and in the gas phase. The decomposition was found to be partly heterogeneous in solution in dimethyl phthalate and no reliable rate constants were obtained. Use of the toluene carrier method for the gas phase work enabled measurement of the rate constant for the homogeneous decomposition. The first order rate constants obtained range from 0.19 s−1 at 292 °C to 1.5 s−1 at 378 °C, leading to log A, 11± 2, and activation energy, 32 ± 5 kcal/mole. These results are compared with the expected values of log A, 13–14, and activation energy, 42 kcal/mole. The significance of these findings is discussed.

scholarly journals Photocatalytic degradation of natural organic matter: Kinetic considerations and light intensity dependence

2004 ◽  
Vol 6 (2) ◽  
pp. 73-80 ◽  
Author(s):  
Ceyda Senem Uyguner ◽  
Miray Bekbolet
Keyword(s):  
Humic Acid ◽  
Light Intensity ◽  
Photocatalytic Degradation ◽  
Rate Constants ◽  
Reaction Rates ◽  
Order Reaction ◽  
First Order Reaction ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order

The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercialTiO2powders. The pseudo first order kinetic model and Langmuir-Hinshelwood (L-H) rate equation in modified forms were used to compare the photocatalytic activities ofTiO2materials as a function of light intensity. Under constant irradiation conditions, the pseudo first order reaction rates as well as L-H rates were found to be decreasing in the following trend; Degussa P-25, Millennium PC-500 and Millennium PC-100. The pseudo first order rate constants showed the same decreasing trend as the pseudo first order reaction rates while L-H rate constants exhibited a light intensity related change in the ordering of the photocatalysts. At the lowest light intensity, L-H rate constants decreased as follows: Millennium PC-500>Millennium PC-100>Degussa P-25. However, increasing the light intensity changed the order to; Millennium PC-100>Millennium PC-500>Degussa P-25 revealing the significance of the L-H adsorption constant. Under constant irradiation conditions, ionic strength dependent changes in the structure of humic acid did not alter degradation efficiency trend of the photocatalyst specimens and they were ordered such as; Degussa P-25>Millennium PC-500>Hombikat UV-100>Millennium PC-100 > Merck. The results presented in this research also confirmed the effectiveness of Degussa P-25 as a photocatalyst for the degradation of humic acid.

scholarly journals Alcoholysis of Nyamplung Seed Oil Using Potassium Carbonate Catalyst

2006 ◽  
Vol 6 (2) ◽  
pp. 66
Author(s):  
Sofiyah Sofiyah
Keyword(s):  
Potassium Carbonate ◽  
Potassium Hydroxide ◽  
Seed Oil ◽  
Catalyst Concentration ◽  
Order Reaction ◽  
First Order ◽  
Rate Of Reaction ◽  
Glycerine Content ◽  
Sodium And Potassium ◽  
Good Agreement

The production of glycerol and ester by alcoholysis of vegetable oils has been widely studied. Various catalysts, such as sodium and potassium hydroxide and sulfuric acid have been used to increase the rate of reaction. This preliminary research studied the possibility of using potassium carbonate catalyst. The experiment was conducted in an autoclave. A certain amount of nyamplung seed oil was poured into the autoclave and then the heater was switched on to heat up the oil to the required temperature of reaction. Besides, a mixture of ethanol and potassium carbonate was heated in a flask equipped with condenser to form ethanolate. As soon as the required temperature was reached, the ethanolate was quickly put into the autoclave containing the nyamplung seed oil. The temperature of the reaction was kept constant for a period of time. At the end of each process, a sample was withdrawn and analyzed for its glycerine content by acetin method. The variables studied were reaction time and catalyst concentration. The experimental data were evaluated by applying pseudo homogeneous approach. It was found that data were in good agreement with first order reaction with respect to nyamplung seed oil. Using an equivalent ratio of 5.1 ethanol to nyamplung seed oil, a temperature of lOQoC,and an agitation speed of 150 rpm, the favorable catalyst concentration was found to be at 0.008 gram of potassium carbonate per gram of nyamplung seed oil. Under this condition, the glyceride conversion was 0.5159 in 75 min.

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