Juan Ojeda

Biodesulfurization of gas oil using inorganic supports biomodified with metabolically active cells immobilized by adsorption.

The immobilization of Pseudomonas stutzeri using adsorption on different inorganic supports was studied in relation to the number of adsorbed cells, metabolic activity and biodesulfurization (BDS). The electrophoretic migration (EM) measurements and Tetrazolioum (TTC) method were used to evaluate adsorption and metabolic activity. Results indicate that maximal immobilization was obtained with an initial load of 14 x 10(8) cells mL(-1) for Al and Sep, whereas Ti requires 20 x 10(8) cells mL(-1). The highest interaction was observed in the P. stutzeri/Si and P. stutzeri/Sep biocatalysts. The IEP values and metabolic activities indicate that P. stutzeri change the surface of supports and maintains metabolic activity. A direct relation between BDS activity and the adsorption capacity of the bacterial cells was observed at the adsorption/desorption equilibrium level. The biomodification of inorganic supports by the adsorption process increases the bioavailability of sulphur substrates for bacterial cells, improving BDS activity.

Biodesulfurization of dibenzothiophene and gas oil using a bioreactor containing a catalytic bed with Rhodococcus rhodochrous immobilized on silica.

Abstract Biodesulfurization (BDS) in a bioreactor packed with a catalytic bed of silica containing immobilized Rhodococcus rhodochrous was studied. Various bed lengths and support particle sizes were evaluated for BDS of dibenzothiophene (DBT) and gas oil. The sulfur-containing substrates were introduced separately into the bioreactor at different feed flows. Higher removal of sulfur from DBT and gas oil was achieved with a long bed, lower substrate flow, and larger sizes of immobilization particles. The packed bed bioreactor containing metabolic active cells was recycled and maintained BDS activity.

Effects of UV Radiation on Usnic Acid in Xanthoparmelia microspora (Müll. Arg. Hale)

An important decrease in the level of stratospheric ozone has been observed during the past decade (1), with accompanying increases in UV-B radiation (2) and some UV-A radiation (3), thus leading to probable damage to aquatic and terrestrial ecosystems (4–7). Inhabitants of terrestrial and aquatic ecosystems have developed strategies to cope with the potential stress induced by UV radiation. One of these strategies is the synthesis of photoprotector compounds derived mainly from the biosynthetic route of the polymalonate acetate (8–13). As levels of UV radiation increase, accumulation rates of some photoprotective compounds in lichen species from the Chilean Alpine zones also increase (14). Photodegradation of depsides may have accounted for the low levels of phenolics in lichens at higher elevations (15). It was observed that, in Xanthoparmelia lichens from the Alpine regions of Chile, the higher the altitude where the lichen was found, the greater amount of usnic acid it produced (16). This increase of usnic acid is the result of the lichen’s ability to adapt to radiation, which ensures its survival in extreme environmental conditions. In thalli from Xanthoparmelia oleosa collected at 4690 m no usnic acid was detected, which could be proof of the presence of a photodegradation product of usnic acid (17) but which has not been identified to date. In growth-chamber experiments lasting 1 week, thalli of Umbilicaria americana always produced smaller amounts of phenolic residue when exposed to both UV-B and UV-A radiation, compared with exposure to UV-A alone. In one field experiment exclusion of UV-B by light filtration produced significant increases in phenolic compounds. This increase occurs only during spring and autumn, when lichens are metabolically more active (18). In this article we evaluated the accumulation rates of usnic acid in Xanthoparmelia microspora (Mull. Arg. Hale) exposed to doses of solar radiation and to additional doses of UV-A and UV-B radiation. Furthermore, we report on the photolysis of usnic acid in nonnucleofilic solvents during exposure to higher doses of UV-A and UV-B radiation.

Adsorption of 4,6-Dimethyldibenzothiophene over Cu/ZrO2

The adsorption of refractory sulfur molecule 4,6-Dimethyldibenzothiophene (4,6-DMDBT) over copper supported on zirconia, using different copper loadings (2-10% w/w) and a zirconia support with a high specific surface area, was studied. The results showed that the adsorption capacity of 4,6-DMDBT over Cu/ZrO2 increased with copper content, reaching a maximum at around 8% Cu (0.58 mmol 4,6-DMDBT per gram of adsorbent). The results of characterizations with H2-TPR, Electrophoretic Migration, and XRD demonstrated that this Cu loading (8%) also corresponds to a maximum copper dispersion capacity for ZrO2 support. Also, these absorbents showed considerable selectivity toward the adsorption of 4,6-DMDBT in a feed stream also containing Quinoline, decreasing adsorption capacity of 4,6-DMDBT by only 35%, despite both molecules being present in the same concentrations. The results of this work showed that desulfurization adsorption using Cu/ZrO2 adsorbents can be an effective method to remove this type of refractory sulfur molecules, and an excellent alternative as a complementary process for deep desulfurization in the fuel industry.

STUDY OF THE REMOVAL OF 4–NITROPHENOL FROM AQUEOUS MEDIA BY ADSORPTION ON DIFFERENT MATERIALS

The removal of 4–Nitrophenol (4–NP) from aqueous media by adsorption is studied in a batch system using different porous materials: activated carbon, zirconia, alumina, sepiolite, natural zeolite and 13X zeolite. Depending on their adsorption capacities, the best adsorbent was chosen to be impregnated with different levels of nickel (Ni) in order to study the adsorption by π-complexation in batch and continuous systems. The samples of Ni(x)/support (x= 2, 4, 6%) were prepared by wet impregnation and were characterised using the same method as with all the materials, by N2 adsorption-desorption using the BET method, surface acidity and Z potential measurements by electrophoretic migration. The samples were measured in a UV-Vis electrophotometer at a wavelength of 318 nm, while the adsorption capacity of the material in the batch system was determined by calculating the difference in concentration once the adsorbent became saturated after an initial concentration of ~20 ppm, and in the continuous system this was done by integrating the area under the adsorption curve. The results suggest that adsorption capacity depends on the specific BET area, apparent acid strength and the IEP of each support, and that it varies with the addition of Ni.

Spectroscopic and photochemical properties of some annulated boldine derivatives

The aim of this study was to determine the influence of the substituent groups on the photostability of eight boldine derivatives, including some oxazole and oxazinone derivatives, in order to increase the sunscreen protection properties previously demonstrated for boldine. Such derivatives showed bands similar to those of boldine in the absorption and emission spectrum. The spectroscopic properties are pH dependent. The photostability of the derivative compounds was higher than that of boldine, in accordance with the low value of the photoconsumption quantum yield determined. The low fluorescence quantum yield values observed for boldine 1 and 4 as both base and hydrochloride derivative compounds led us to postulate that these compounds are deactivated by a mechanism different to the fluorescence pathway, probably due to the electron-withdrawing inductive effect of NO for boldine 1, and to the increase of the aromatic framework for boldine 4.

A new functional biofilm biocatalyst for the simultaneous removal of dibenzothiophene and quinoline using Rhodococcus rhodochrous and curli amyloid overproducer mutants derived from Cobetia sp. strain MM1IDA2H-1

Highlights • Two mutants strains were generated by mutagenesis of Cobetia sp MM1IDA2H-1.• A functional biofilm of R. rhodochrous and a Curli over producer mutants was formed.• DBT and QN were simultaneous removal by the biofilm functional by co-metabolism.

DENITROGENATION BY ADSORPTION OF PYRIDINE ON NI/SUPPORT ADSORBENTS

In this work we have carried out the adsorption of pyridine using three different supports (activated carbon, SiO2 and γ-Al2O3). After choosing the best support, due to its higher adsorption capacity, we have impregnated the support with nickel at three different concentrations (2, 4 and 6% w/w) by wet impregnation to study the adsorption of pyridine by π-complexation. All the samples (supports and adsorbents) were characterized by N2 adsorption-desorption by the BET method and electrophoretic migration. The experimental results, for the three different supports, show that the adsorption capacity is better for γ-Al2O3, due to its higher isoelectric point. With the incorporation of nickel, no better adsorption capacities are observed, due that the nickel incorporation diminish the zero point charges of the adsorbents.