• Journal of Environmental Science International
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• v.17 no.2
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• pp.211-224
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• 2008

Characteristics of the esterification reaction between free fatty acid in rice bran oil and methanol was investigated in the presence of catalysts, such as PTS(p-toluene sulfonic acid), Amberlyst 15 dry and SCX(silica gel based strong cation exchange resin). While reaction temperature was kept constant at $65^{\circ}C$, initial feed content of free fatty acid was varied from 100% to 1% by addition of pure free fatty acid which was previously made from rice bran oil. Also, the effect of mole ratio of methanol to fatty acid on the final conversion was examined. When esterification of pure free fatty acid was catalyzed by several acids, final conversions were increased in order of Amberlyst 15 dry, SCX and PTS. Using PTS catalyst, initially the reaction proceeded in homogeneous 2nd oder reaction mechanism. However, phase of reaction mixture changed from homogeneous to heterogeneous along the reaction time and then reaction rate was retarded by mass transfer resistance of methanol. Final conversion of free fatty acid in reaction mixture was depended on initial feed content of free fatty acid, and had maximum value at 30% of initial feed free fatty acid content for all kinds of catalysts used. And the final conversion was increased with mole ratio of methanol by the improvement of reaction rate. When initial feed free fatty acid content below 10% and the reaction was catalyzed by PTS, concentration of free fatty acid in reaction mixture was increased in the middle of reaction time by hydrolysis of triglyceride in reaction mixture. Also, if silica gel was added into the reaction mixture which had initial feed free fatty acid content below 50%, final conversion was increased by the adsorption of moisture produced. The SCX catalyst made the esterification reaction of free fatty acid to progress like in case of PTS catalyst. However, when initial feed free fatty acid content below 10%, concentration of free fatty acid in. reaction mixture was decreased monotonically and not increased in the middle of reaction time on the contrary to the case of PTS. Thus, SCX catalyst accomplished more high value of final conversion than PTS catalyst for the initial feed fatty acid content range from 50% to 5% In case of initial feed free fatty acid content of 1% and mole ratio of methanol was 2, concentration of free fatty acid in reaction mixture increased over the initial feed free fatty acid content for all kind of catalysts used. Although SCX catalyst was added into reaction mixture which had 1% of initial feed fatty acid content, final conversion was hardly raised by mole ratio of methanol.

• Journal of the Korean Society of Food Science and Nutrition
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• v.19 no.3
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• pp.195-200
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• 1990

Effects of cooking time(5-30 min in a pressure cooker) and HTST air dehydratiion time(0-9min at 15$0^{\circ}C$) on physical properties of dried green peas(3% oisture content wet basis) were investigated by determining rehydration ratio rehydration curve browning reaction and puncture force, The rehydration ratio and curve of dried green peas were increased with increa-sing cooking time and HTST air dehydration time. Preheating of the green peas for 30 min in a pressure cooker or for 9 min of HTST air dehydration time prior to 6$0^{\circ}C$ air dehydration recovered a 87.3% of original moisture content of raw green peas in a boiling water for 5 min. The brownin greaction was gradually decreased up to 15 min of cooking time. Puncture pressure of rehydrated green peas treated in a boiling water for 5 min was decreased as the cooking time and HTST air dehydration time were increased and was highly correlated with rehydration (r=-0.956) The effects of cooking time and HTST air dehydration time on rehydration ratio browning reaction and puncture pressure were significantly different at the a=0.01 level except effect of HTST air dehydration time on browning reaction.

• Elastomers and Composites
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• v.38 no.3
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• pp.235-242
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• 2003

A vulcanization reaction characteristics of an isoprene rubber (IR)-modified natural rubber/carbon black (NR/CB) composite was studied using in-situ electrical property measuring technique. Since the electrical conductivity of the sample composite would be changed continuously during the vulcanization reaction by rearranging of the carbon black particles within the sample, volume resistivity (${\rho}$) might be obtained as a function or reaction time. A stabilization time ($t_i$), maximum reaction speed time ($t_p$), and volume resistivity at that time(${\rho}_p$) were defined from the data for the Arrhenius analysis. Volume resistivity ${\rho}$ showed a comparatively high value of ${\sim}10^8$ order before the reaction started, and dramatically decreased to be stabilized within $1{\sim}2$ minutes as soon as the reaction started. As the more time elapsed, thereafter, ${\rho}$ decreased monotonously to a certain constant value through a peak, ${\rho}_p$ at time $t_p$, which was considered as the maximum reaction rate. As a result, while $t_i$ values were comparatively constant as $1{\sim}2$ minutes, $t_p$ values showed to become shorter and shorter as the reaction temperature.

• Korean Chemical Engineering Research
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• v.52 no.3
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• pp.355-359
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• 2014

Recently, many chemicals produced from renewable resources such as lignocellulosics, micro-algae and marine macro-algae, were introduced to chemical industry. Chitin/chitosan is secondly abundant feedstock on Earth. It is easily obtained from crusraceans' shells such as crab, shrimp and insects. In this work, we performed the acidic-hydrothermal hydrolysis to produce levulinic acid from chitosan using statistical approach. By design of response surface methodology, the effect of reaction temperature, catalyst amount, and reaction time and their reciprocal interactions were investigated. As a result, higher reaction temperature and catalyst amount increased the higher concentration of levulinic acid. However, reaction time did not caused large increase of levulinic acid after some reaction period. Levulinic acid of 2.7 g/L produced from chitosan in the optimized condition of reaction temperature of $175^{\circ}C$, sulfuric acid of 2.4% and reaction time of 40.7 min.

• Textile Coloration and Finishing
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• v.16 no.2
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• pp.34-40
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• 2004

This study was conducted to remove the reactive dyes by the Ozone demand flask method which are one of the main pollutants in dye wastewater, Ozone oxidation of three kinds of the reactive dyes was examined to investigate the reactivity of dyes with ozone, Trihalomethane formation potentials(THMFPs), competition reaction and ozone utilization on various conditions for single- and multi-solute dye solution. Concentration of dyes was decreased continuously with increasing ozone dosage in the single-solute dye solutions. THMFPs per unit dye concentration were gradually increased with increase of ozone dosage. By the result of THMFPs change with reaction time, THMFPs were rapidly decreased within 1 minute in single-solute dye solutions. Dey were increased after 1 minute of reaction time, and then they were consistently decreased again after longer reaction time. Competition quotient values were calculated to investigate the preferential oxidation of individual dyes in multi-solute dye solutions. Competition quotients$(CQ_i)$ and values of the overall utilization efficiency, no$_3$, were increased at 40mg/1 of ozone dosage in multi-solute dye solutions.

• Journal of the Korean Ceramic Society
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• v.27 no.8
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• pp.965-970
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• 1990

A nitrogenation of coal ash in the presence of carbon was carried out to examine the effects of reaction temperature, reaction time and carbon composition on the formation of AlN, SiC and Si3N4. Decreasing the particle size increased the formation of AlN and its maximum composition in the product was obtaiend under 1450~150$0^{\circ}C$, 2 hours of reaction time and about 30% of carbon addition(on the basis of sample weight). Compositions of SiC and Si3N4 were distributed to the opposite so that SiC showed a higher composition compared with Si3N4 at a lower temperature, a shorter reaction time and a greater carbon addition.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.182-187
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• 2001

This paper examines the effects on human reaction time and mental fatigue of changes in the intensity of physical activity. A treadmill-equipped instrument and perception tester were used to attain several levels of physical activity. In this paper, in order to determine the individual levels of physical activity of subjects, Borg-RPE scale, Heart Rate(HR) and Respiratory Quotient(RQ) were used. Also, a reaction test in whole-body activity on treadmill-equipped instrument and an addition test as an indicator of mental fatigue were performed. In the above experiments, the scores obtained in addition test administered before and after Physical activity at each intensity level used. Restricted within the limits of this paper, the results of these tests showed that mental fatigue decreased after physical activity.

• Journal of Korean Society on Water Environment
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• v.18 no.2
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• pp.169-187
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• 2002

The effects of important parameters such as reaction time and pH on the Fenton's process were evaluated using a batch reactor. It was proven that organic materials and heavy metals in leachate could be successfully removed by Fenton's reagent. Favorable operation conditions were investigated. It was observed that the reaction between ferrous iron and hydrogen peroxide with the production of hydroxyl radical was almost complete in 10 minutes. That is, the oxidation of organic materials by Fenton's reagent was so fast that it was complete in 30 minutes with batch experiments. With the formation of carbonic acid, pH of the batch reactor decreased to favorable acidic conditions without acid addition. The oxidation of organic materials in the leachate showed a pH dependence and was most efficient in the pH range of 2-3.

• Applied Chemistry for Engineering
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• v.31 no.6
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• pp.630-634
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• 2020

We developed a processing recipe to synthesize flexible polyurethane foam with a pore size of 335 ± 107 ㎛. The gelling reaction time was varied from 0 to 30 minutes and the physical properties of the foam were evaluated. The gelling reaction where the polypropylene glycol and tolylene 2,4-diisocyanate (TDI) were reacted to form urethane prepolymer, proceeded until a chemical blowing agent, deionized water, was introduced. Fourier transform infrared (FT-IR) spectra showed that the composition of the foam did not change but the foam height reached a peak value when the gelling reaction time was 10 minutes. We found that increasing the gelling time lessened the coalescence and helped the formation of cells. Lastly, the repeatability of polyurethane foam was confirmed by one-way analysis of variance (ANOVA) by synthesizing ten identical polyurethane foams under the same experimental conditions, including the gelling reaction time. Overall, the new time parameter in-between the gelling and blowing reactions will give extra stability in manufacturing identical polyurethane foams and can be applied to various polyurethane foam processes.

• Food Science of Animal Resources
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• v.41 no.5
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• pp.894-904
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• 2021

Microencapsulation is a protective process for materials that are sensitive to harsh conditions encounted during food manufacture and storage. The objectives of this research were to manufacture a milk protein-based delivery system (MPDS) containing Lactobacillus rhamnosus GG (LGG) using skim milk powder and to investigate the effects of manufacturing variables, such as reaction temerpature and holding time, on the physiccohemical properties of MPDS and viability of LGG under dairy food processing and storage conditions. MPDS was prepared using chymosin at varing reaction temperatures from 25℃ to 40℃ for 10 min and holding times from 5 to 30 min at 25℃. The morphological and physicochemical properties of MPDS were evaluated using a confocal laser scanning microscope and a particle size analyzer, respectively. The number of viable cells were determined using the standard plate method. Spherical-shaped MPDS particles were successfully manufactured. The particle size of MPDS was increased with a decrease in reaction temperature and an increase in holding time. As reaction temperature and holding time were increased, the encapsulation efficiency of LGG in MPDS was increased. During pasteurization, the use of MPDS resulted in an increase in the LGG viability. The encapsulation of LGG in MPDS led to an increase in the viability of LGG in simulated gastric fluid. In addition, the LGG viability was enhanced with an increase in reaction temperature and holding time. In conclusions, the encapsulation of LGG in MPDS could be an effective way of improving the viability of LGG during pasturization process in various foods.