Effect of temperature and reaction time

The reaction temperature, mainly for exothermic reactions, affects the structure and textural properties of the catalysts which cause deactivation. The consequences are structural modifications or sintering of the catalyst. The most important identification of sintering is the analysis of crystal sizes or particle sizes before and after reaction. 

Catalyst, % Pt (weight) TPR, ixmo/ of l-12/gat Chemisorption Dynamic, [imol 0fH2lgcM H/m 

However, the Pt/Ti02 catalyst exhibits reduction at room temperature and at 112°C, 372°C, and above 500°C, besides peak shift to lower temperatures due to the reduction of PtO. Partial reduction of Ti02 to Ti02- occurs at higher temperatures which are attributed to SMSI. The presence of Pt atoms promoted the reduction of titanium which in turn facilitates the reduction of platinum at the surface. 

The calculated dispersion of Pt atoms at the surface of alumina was 54%, considering the reduction degree of 82% of platinum oxide (Table 13.8). On the other hand, the Pt/Ti02 catalyst has two times more hydrogen consumption than the alumina-supported catalyst, indicating reduction of Ti02 and thus interaction with metallic Pt°. The H2 chemisorption is three times less (17%) than the Pt/Al203 catalyst and confirms SMSI effect after reduction at 500°C. 

Jiang and collegues claim that the Ti + cations may adsorb hydrogen and then diffuse through the support, decreasing the adsorption rate of hydrogen dissociation. 

The influence of steam on the reduction of nickel supported catalysts is shown in Fig. 8.12. The reduction was performed with steam and 10 % H2/Ar. The reduction temperature with steam shifts the maximum peak to higher temperature but is not signiflcant. 

The first peak is associated to the reduction of NiO without interaction with the support, while the second and third peaks are associated to the reduction of NiO interacting with the support, probably due to the reduction of nickel aluminate. The reduction degree was 100 % and the particle sizes of the order of 200 A.  

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E Billa, M-T Tollier, B Monties. Characterization of the monomeric composition of in situ wheat straw lignins by alkaline nitrobenzene oxidation Effect of temperature and reaction time. J Sci FoodAgric 72 250-256, 1996. 

Table I. Effect of Temperature and Reaction Time on Ethyl Levulinate Yields...

Research described in this paper focuses on the second step of the gasification process, and details the effects of temperature and residence time on product gas formation. Cellulose is used as a feedstock for pyrolytic volatiles formation. Earlier papers (JS.M) have discussed the effect of steam on cellulose pyrolysis kinetics. Two recent papers (1, 1 6) presented early results on pelletized red alder wood pyrolysis/gasification in steam. Future papers will discuss results using other woody materials, crop residues, and manures (17,1 ). Research to date indicates that all biomass materials produce qualitatively similar results in the gasification reactor described in the following section of this paper. Effects of pressure on the heat of pyrolysis of cellulose are also discussed as a prelude to future papers detailing the more general effects of pressure on reaction rates and product slates. 

EFFECTS OF TEMPERATURE AND RESIDENCE TIME ON THE SECONDARY, GAS-PHASE REACTIONS... 

PEN/PET Deuterated PET/small-angle neutron scattering/effects of temperature and heating time/reaction kinetics/NMR Collins et al. 2001... 

The model considers the activities of the chemicals to evaluate the driving force of the permeation and the kinetics of the reaction. Satisfactory agreement is obtained between experimental data and model results.The effects of temperature and space time in the reactor are studied. 

The effects of temperature and heating time on the formation of the coloured complex were also studied. The reaction of ETD with both reagents proceeded... 

In a study by Rahman et al. (2007), the selectivity and xylose yield were developed to study individual and combined effect of parameters such as temperature, retention time and acid concentration at five different levels. The feedstock under study was oil palm empty fruit bunch fiber which is a lignocellulosic waste from palm oil mills and a potential source of xylose that can be used as a raw material for production of xylitol. It was found that under optimum conditions (i.e., temperature 119°C, reaction time 60 min and H SO concentration 2%), the xylose yield and selectivity were 91.3% and 18 g/g, respectively. The combined effect of temperature with reaction time and temperature with acid concentration was found to be more prominent than combined effect of reaction time and acid concentration. 

FIGURE 6.3. Graph to illustrate effect of temperature and residence time on the reaction. 

Cotton linters and viscose grade wood pulp were grafted with acrylamide using the xanthate method. The effects of monomer concentration, reaction time, hydrogen peroxide concentration, reaction temperature, and liquor ratio on the grafting process were studied. Optimum conditions for the grafting reaction were established [26]. 

Enzymatic hydrolysis is affected by numerous process factors including pH, temperature, reaction time, and enzyme loading. These factors often interact with one another. In the current study the main and interactive effects of four factors (reaction time, enzyme to... 

Figures 1-3 demonstrate the effect of KOH/precursor ratio, reaction temperature and reaction time, respectively, on porous structure parameters of carbon produced by KOH activation. While the presented relationships concern mostly carbonaceous mesophase, basically they are typical of all coal and pitch-derived materials of the study.

The reaction ordinate is utilized here as a means of combining the effects of temperature and time. In presenting and discussing our results, the data is presented on plots of the derived data versus logio Reconversion of lignin to liquid and gaseous products was determined as follows ... 

Effect of temperature. The reaction was conducted by changing the temperature and the contact time, while fixing the other conditions. In order to compare the selectivity at the same level of the toluene conversion, the yields of benzaldehyde are plotted as a function of the conversion in Fig. 3. The selectivity increases with raising the temperature. This finding is in conformity with that obtained with V- and Mo-P-based oxide catalysts [19-21]. 

An interesting feature of the conversion profile is the existence of a maximum located between the wall and the axis of the mold. This effect is explained by the superposition of the influence of temperature and residence time on the kinetics of the reaction a liquid moves faster in the central zone than at the wall, therefore the residence time is longer near the walls, but temperature is higher in the center therefore the reaction rate of the material near the walls is lower than in the center. As a result, there is a point between the center and a wall where the degree of conversion is maximum. The results in Fig. 4.55, also answer the question about the role of the fountain effect ... 

In the batch-type reaction system, however, the pressure cannot be controlled during the treatment. Table 1 shows a maximum pressure for various supercritical alcohols at 300 and 350°C. It can be observed that at the same temperature, they gave different maximum pressure and that the pressure tended to be lower as the alkyl chain of the alcohol became longer. Previously, it was found that the reaction pressure is an important reaction parameter in enhancing the reaction rate (11). Therefore, the flow-type reaction system, which can control the reaction pressure up to 50 MPa, was used to study the effect of the reaction pressure on the formation of alkyl esters. Reaction temperature and reaction time were set at 300°C and 20... 

When optimizing the reaction of trichlorosilane with silica gel, the first important factor to consider is the effectiveness. The pretreatment temperature of the silica, the reaction temperature and reaction time must be controlled to yield an effectiveness of... 

Even though it is generally admitted that both the reaction temperature and the substrate/AA ratio have a positive effect on the production of acetylated phenyl ethers,[3] there are no papers describing the effect of temperature and in only one study is the effect of the anisole/AA ratio in fixed bed reactor experiments described.191 At 363 K, for a contact time x > 0.05 h (t is taken as the inverse of the weight hour space velocity for anisole), anisole is almost completely acetylated initially [time on stream (TOS) of 10 min] when anisole/AA is 5, whereas less than 50 % of anisole is transformed with an equimolar ratio. Moreover with higher ratio... 

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