The extraction kinetics of the essential oil of Xylopia aethiopica (Dunal) A. Rich by hydrodistillation was studied for modeling its process and optimizing its yield. The oils obtained, analyzed by GC/MS, consists mainly of pinenes, sabinene, myrenal, terpinene-4-ol, limonene. Experimental data were fitted into first and second order kinetics for a 2-steps extraction, washing and diffusion, of the phenomenological model, according to the hypothesis used. The essential oil which moves inner vegetable cells by diffusion and is extracted at the surface of the particle by washing with an extraction solvent. When the washing step is instantaneous compared to that of diffusion, the mechanism, which is under diffusion control, admits first order. Considering both washing and diffusion steps, kinetic order became 2, in agreement with the Peleg model. The Monod and Langmuir models also fitted experimental data. All these models validated by the experimental data with determination coefficients R2> 0.96 can be used for optimizing the extraction of the essential oil of Xylopia aethiopica (Dunal) A. Rich.
The hydrodistillation extraction kinetics of Xylopia aethiopica fruit essential oil were modeled according to the phenomenological approach applied to Fick diffusion model, Peleg sorption model and Michaelis-Menton enzymatic model. All these models fitted experimental data. The assumptions underpining each model highlight the understanding of the process. It emerges that the essential oil releases completely at the washing step (> 90 %) with a rate constant 105 higher than those of diffusion step. This latter is the limiting step of the process. The end of the process can be estimated at 18.4 min (10t1/2) or at 36.8 min (20 t1/2) with a maximum yield varying between 3.84 and 5.09 % for the 3 studied samples. Exploring the mechanism of extraction by different complementary models improves significantly the understanding of the process and reinforces the predictive goal of this study.
In the literature, the drying mechanism were generally analyzed in terms of effective diffusivity through the pseudo first order diffusion model. This process was revisited through the modified Peleg model, assuming the drying as a moisture desorption versus drying time. The leaves of Corymbia citriodora acclimatized in the Congo Brazzaville “Plateau des Cataractes” were dried in open air and under shade thanks to a domestic scale of essential oil production. One obtains following model parameters: kinetic constant k1: 0.8555 - 2.1355 d.(g/g)-1, extraction capacity constant K2: 1.5255 - 1.8733 (g/g)-1; end equilibrium moisture X∞ = 0.53 - 0.66 g/g. and first order drying kinetic constant k = K2/k1: 1.71 - 1.78 d-1. Pseudo first order diffusion model fits experimental data with k = 0.368 - 0.587 d-1 and t1/2 = 1,18 - 1,88 d.. These results needed for the optimization of proccess and sizing equipments came from a fast graphic data processing, with low computer inputs.
Acacia mangium Willd est une espèce à croissance rapide, fixatrice d’azote, capable de restituer au sol des éléments minéraux par chute de litière. Elle est actuellement très utilisée dans les programmes de reboisement. L’effet substrat sur la biomasse des plants, à l’âge de plantation, a été estimé dans le but d’optimiser les conditions de production des plants. Un dispositif en blocs complets randomisés comprenant six types de substrats à base de terre noire, charbon et sciure de bois, a été mis en place. Des jeunes plants âgés de trois semaines ont été transplantés dans des plaques alvéolées comprenant différents substrats puis élevés jusqu’à l’âge de plantation. Une dose de 30 g d’engrais NPK dilués dans 10 l d’eau a été apportée quotidiennement aux plants. Les résultats obtenus montrent un effet substrat sur la biomasse et la croissance. Les plants issus des substrats 6 (75% terre+25% charbon) et 4 (50% terre+50% charbon) présentent les meilleures performances de croissance. L’Activité Réductrice d’Acétylène (ARA) réalisée a été influencée par le substrat. La dose de fertilisation apportée n’a pas engendré l’avortement des nodules. Le substrat 5 (50% de terre noire, 25% de charbon et 25% de sciure de bois) offre les conditions optimales de développement des nodules.Mots clés : Substrat, Acacia mangium, biomasse, ARA. English Title: Effect of substrate on the biomass and the symbiotic fixing of nitrogen by Acacia mangium willd. (Fabaceae) seedlings in the nurseryAcacia mangium Willd is a rapid growth species, fixing of nitrogen and able to restore on the ground biogenic salts through the fall of litter. It’s currently very used in the afforestation programs. The effect of substrate on the seedlings biomass at the plantation age was estimated with the aim of optimizing the seedlings production conditions. A randomized complete blocks of six types of substrate containing black soil, charcoal and sawdust, was set up. Seedlings of three weeks old were transplanted in the alveolate plates with various substrates during the education phase until the age of plantation. 30 g of a mineral fertilizer NPK (20-20-20) diluted in 10 l of water was brought daily to the seedlings. The results showed a substrate effect on the biomass and the plants growth. Seeedlings which growed on the substrate 6 (75% black soil + 25% charcoal) and 4 (50% black soil + 50% charcoal) present the best growth performances. The Acetylene Reduction Assay (ARA) realized was significantly influenced by the types of substrate. Mineral fertilizer brought does not generate the abortion of the nodules. The substrate 5 (black soil 50%, charcoal 25% and sawdust 25%) offered the optimum conditions of nodules development.Keywords: Substrate, Acacia mangium, biomass, ARA.
The Cymbopogon flexuosus species introduced in Congo-Brazzaville (equatorial climate) to solve the low production problem of Cymbopogon citratus, a source of citral, was acclimatized in Chad (subtropical climate) for the same reasons. The plant was perfectly adapted with a very high production of biomass. Its low essential oil extraction yield (0.89% DM) compared to the Cymbopogon citratus local species (1.26%) is very largely balanced by its very high biomass productivity. The extraction of essential oil fits Milojevic's pseudo first order model with rate constant k = 0.0087 min-1 (R2 = 0.9816) for Cymbopogon flexuosus vs k = 0.0109 min-1 (R² = 0.922), for local C. citratus. It also fits Peleg's model with a kinetic constant k1 = 217.94 min %-1 and an extraction capacity constant K2 = 0.6022%-1, which leads to a pseudo first order kinetic constant of hydrodistillation k = k1/K2 = 0.0028 min-1. For local C. citratus, these values are respectively k1 = 108.94 min %-1; K2 = 0.4971%-1 and k = 0.0046 min-1 with R² = 0.9885. Michael Menton's model, which is also fitted, leads to the kinetic constant Km/Ymax = 237 min %-1 and the yield Ymax = 1.9% with R² = 0.9862, for C. flexuosus and Km/Ymax = 113.12 min %-1, Ymax = 2.1% (R² = 0.9952) for C. citratus. These results corroborate those obtained on the same species acclimatized in Congo-Brazzaville.
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