Ricardo J. Grau

Liquid phase hydrogenation, isomerization and dehydrogenation of limonene and derivatives with supported palladium catalysts

Abstract The hydrogenation of limonene, using 5% Pd/C, 5% Pd/Al 2 O 3 and 0.5% Pd/Al 2 O 3 catalysts, was studied in a stirred slurry minireactor in a temperature range of 273–323 K, at 106.65 kPa of hydrogen pressure. In the absence of extraparticle and intraparticle mass transfer effects, side products, such as terpinolene, γ-terpinene and p -cymene, were formed besides p -menthene and p -menthane. A significant presence of terpinolene and γ-terpinene indicates that an extensive isomerization precedes hydrogenation, while the presence of p -cymene shows that a dehydrogenation occurs simultaneously. The virtual absence of intermediates, such as α-phellandrene, β-phellandrene and α-terpinene, can be attributed to the fact that conjugated cyclic dienes are too strongly adsorbed to desorb before reacting further. Possible mechanisms of reaction are discussed: the involvement of π-allyl-adsorbed species explains the isomerization process over palladium, but greater isomerization activity observed for alumina-supported catalysts is explained by mechanisms involving Lewis acid sites provided by the alumina. Two possible pathways for isomerization on alumina are recognized: one of them involves the formation of carbonium ions and the other may comprise double-bond migration via allyl route including carbanions. The results suggest that, over alumina, limonene isomerizes via the π-allylic mechanism, whereas terpinolene and terpinene isomerize via the carbonium ion mechanism.

Catalysts and network modeling in vegetable oil hydrogenation processes

Abstract Hydrogenation of vegetable oils is one of the earliest commercial gas-liquid- solid heterogeneous catalytic processes. usually employed to reduce the degree of unsaturation of the naturally occurring triglycerides so as to obtain new, attractive organoleptic changes, and a greater chemical stability. Due to its intrinsic challenge and to its commercial importance, the process has drawn the attention of numerous scholars. Accordingly, there exists a great deal of work which has both generated empirical rules and allowed us to tackle many of the theoretical aspects of the problem as well.

Volatile Constituents of Leaf Oils from the Cupressacea Family: Part I. Cupressus macrocarpa Hartw., C. arizonica Greene and C. torulosa Don Species Growing in Argentina

Abstract Volatile compounds from Cupressus macrocarpa Hartw., C. arizonica Greene and C. torulosa Don. leaves collected in the Argentinian Patagonia were isolated by steam distillation yielding 0.78%, 1.01% and 0.61% of essential oils, respectively. Leaf oils were analyzed by GC and GC/MS. The main constituents of each oil were: (i) C. macrocarpa oil: α-pinene (20.2%), sabinene (12.0%), p-cymene (7.0%) and terpinen-4-ol (29.6%); (ii) C. arizonica oil: α-pinene (22.9%), limonene (8.5%), umbellulone (16.5%), terpinen-4-ol (5.5%) and cis-muurola-4(14), 5-diene (90%); and (iii) C. torulosa oil: α-thujene (4.2%), α-pinene (25.8%), sabinene (22.3%), myrcene (4.7%) and terpinen-4-ol (9.3%).

Essential Oil of Hop Cones (Humulus lupulus L.)

Abstract The essential oil from hop cones (Humulus lupulus L.), which was obtained by steam distillation, was analyzed by GC and GC/MS. The major constituents obtained were: myrcene (25.4%), β-caryophyllene (9.8%), α-humulene (36.7%), α-muurulene (3.0%), γ-cadinene (5.5%) and δ-cadinene (4.1%). Fifteen minor components were also identified. The yield of oil relative to dried hop cones was 0.3%.

Dynamic optimization of bioreactors using probabilistic tendency models and Bayesian active learning

Abstract First-principles models of fermentation processes typically have built-in errors in the form of structural mismatch and parametric uncertainty. A model-based optimization approach for run-to-run improvement under uncertainty of fed-batch bioreactors by integrating probabilistic tendency models with Bayesian inference is proposed. Probabilistic models grounded on first principles are used in the design of dynamic experiments to bias data gathering towards the subspace of most promising operating conditions. Results obtained in the fed-batch fermentation of penicillin G are presented.

Modeling of dispersed-drug delivery from planar polymeric systems: optimizing analytical solutions.

Analytical solutions for the case of controlled dispersed-drug release from planar non-erodible polymeric matrices, based on Refined Integral Method, are presented. A new adjusting equation is used for the dissolved drug concentration profile in the depletion zone. The set of equations match the available exact solution. In order to illustrate the usefulness of this model, comparisons with experimental profiles reported in the literature are presented. The obtained results show that the model can be employed in a broad range of applicability.

Large-scale patterns of turnover and Basal area change in Andean forests.

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.

Volatile Constituents of Leaf Oils from the Genus Baccharis. Part I: B. racemosa (Ruiz et Pav.) DC and B. linearis (Ruiz et Pav.) Pers. Species from Argentina

Abstract Volatile compounds from Baccharis racemosa (Ruiz et Pav.) DC and two samples of B. linearis (Ruiz et Pav.) Pers. leaves collected in the Argentinean Patagonia were isolated by steam distillation. Yields on the oils were 2.50% for B. racemosa; 0.92% for B. linearis (sample A) and 1.91% for B. linearis (sample B). The leaf oils were analyzed by GC and GC/MS. The main constituents of each oil were: (i) B. racemosa oil: sabinene (13.6%), β-pinene (2.8%), myrcene (2.0%), limonene (13.3%), δ-cadinene (5.3%), (E)-nerolidol (5.0%), viridiflorol (2.6%), α-muurolol (9.7%) and α-cadinol (3.1%); (ii) B. linearis (sample A) oil: α-pinene (6.5%), β-pinene (14.9%), myrcene (2.2%), limonene (27.6%), bicyclogermacrene (2.7%), δ-cadinene (3.9%), caryophyllene oxide (3.1%), cubenol (4.7%) and α-cadinol (4.7%); and (iii) B. linearis (sample B) oil: α-pinene (2.5%), β-pinene (6.5%), limonene (27.7%), β-caryophyllene (2.0%), germacrene D (4.7%), bicyclogermacrene (5.4%), δ-cadinene (6.7%), cubenol (6.0%) and α-cadinol (3.0%).

Shunt reactions in methyl linolenate hydrogenation using a supported Ni catalyst

Abstract A study of the kinetics of methyl linolenate catalytic hydrogenation in liquid phase with a Ni catalyst at 398–443 K and 370–645 kPa, focusing on the proper modelling of the shunt reactions in the network—simultaneous cohydrogenation of double bonds—is presented. A reliable estimation of the corresponding kinetic parameters using pseudo first order rate expressions is made, based on the strategy of analysing subsystems with increasing degress of complexity. The study demonstrates that the linear, consecutive sequence of irreversible hydrogenations from tri-unsaturated to linear methyl esters does not provide a correct description of the kinetic process. Bulk and surface shunt reactions contribute significantly to the net hydrogenation of tri- and di-unsaturates.

Volatile Constituents of Leaf Oils from the Genus Baccharis. Part II: Baccharis obovata Hooker et Arnott and B. salicifolia (Ruiz et Pav.) Pers. Species from Argentina

Abstract Volatile compounds from Baccharis obovata Hooker et Arnott and B. salicifolia (Ruiz et Pav.) Pers. leaves collected in the Argentinean Patagonia were isolated by steam distillation. Yields on the essential oils were 2.81% for B. obovata and 1.50% for B. salicifolia. The oils were analyzed by GC and GC/MS. The main constituents of each oil were: (i) B. obovata oil: a-thujene (5.8%), α-pinene (9.2%), sabinene (23.2%), β-pinene (9.9%), myrcene (3.7%), limonene (10.7%), terpinen-4-ol (5.9%); and (ii) B. salicifolia oil: α-thujene (2.1%), α-pinene (4.4%), sabinene (2.9%), β-pinene (5.5%), myrcene (2.2%), α-phellandrene (3.2%), limonene (8.1%), (Z)-(3-ocimene (4.6%), terpinen-4-ol (5.9%), γ-ca-dinene (2.3%), elemol (2.7%), cis-α-copaen-8-ol (2.3%), α-muurolol (5.5%), α-eudesmol (2.7%), verboccidentafuran (2.8%), chromolaenin (3.1%) and dihydroisochromolaenin (2.9%).