No abstract

No abstract

Pine sawdust catalytic steam gasification has been studied in a fluidized bed at a relatively low temperature, 700°C. The Ni-Al catalyst used was prepared by coprecipitation and calcined at 750°C for 3 h. The influence of the catalyst weight/biomass flow rate (W/mb) and steam/ biomass (S/B) ratios on the product distribution and on the quality of the gas product obtained was analyzed. An increase of the W/mb ratio increases the total gas, H 2 , CO, and CO 2 yields, while CH 4 and C 2 yields decrease. An increase of the S/B ratio increases H 2 and CO 2 yields while CO and CH 4 yields decrease. This fact can be explained by steam reforming and water-gas shift reactions. The increase of the S/B ratio also has a positive effect on the life of the catalyst. The gas composition and gas yields at initial time have also been studied. For W/mb ratios > 0.5 h, the gas composition at initial time is similar to that for thermodynamic equilibrium for different S/B ratios. The influence of the S/B ratio on gas yield at initial time is more marked, up to a ratio of 1.5.

Ni-Al coprecipitated catalysts promoted with magnesium have been prepared using the rising and the constant pH techniques, two precipitant agents [(1) KOH and K 2 CO 3 , and (2) NH 4 OH)] and different metal contents. Catalyst characterization by temperature-programmed reduction and CO 2 reforming of methane as a test reaction served to select the appropriate catalysts for use in the steam gasification of biomass. The catalysts selected were NiMgAl 2 O 5 , prepared at constant pH and precipitated with KOH and K 2 CO 3 ; NiMgAl 4 O 8 and NiMgAl 1.24 O 3.86 , both prepared at increasing pH with NH 4 OH. Biomass steam gasification experiments were carried out at 700 °C and at atmospheric pressure using different steam/biomass (S/B) and catalyst weight/ biomass flow rate (W/B) ratios. From an analysis of the results obtained, the initial activity and stability of the catalysts have been studied. The NiMgAl 2 O 5 catalyst presents the best performance showing the highest initial activity and stability. This work evidences an improvement of the NiMgAl 2 O 5 catalyst with respect to the previously studied NiAl 2 O 4 catalyst.

We have found that sequences in the 5' leader of the Chlamydomonas chloroplast rbcL gene, when fused 5' to foreign genes, destabilize transcripts of these chimeric genes in the chloroplast of transgenic Chlamydomonas but that 5' sequences ofthe rbcL structural gene prevent this destabilization. Transcripts of the chloroplast rbcL gene are about equally abundant at all times in Chlinydomonas reinhardij growing on an alternating 12-h light/12-h dark cycle. However, Chlamydomonas chloroplast transformants, harboring chimeric genes containing the same rbcL promoter with 63 or 92 bp of the rbcL 5' leader sequence fused upstream of the Escherichia coli uidA (P-glucuronidase, GUS) gene, accumulated GUS transcripts only in the dark. Transcripts disappeared rapidly upon Mumination of the cells. The same phenomenon was exhibited by transcripts of chimeric genes in which the GUS gene coding sequence was replaced by other unrelated genes. The precipitous light-induced drop in GUS transcript abundance was found to be due to an "16-fold increase in the rate of degradation of GUS transcripts in light rather than to a decrease in the rate of transcription of the GUS gene. Transcripts of a chimeric rbcL-GUS construct in which the leader sequence of the rbcL gene was replaced by 103 bp of the leader sequence of the atpB gene were stable in illuminated cells. The destabilizing effect of the rbcL 5' leader sequence was reversed by adding 257 bp of the 5' coding region of the rbcL gene. The results show that chloroplast transcript levels in illuminated Chiamydomonas cells-and perhaps in other cases-can be determined, at least to some extent, by sequences and interactions of sequences transcribed from the 5' ends of genes.

The aim of this study was to design a modified atmosphere packaging suitable for Tuber melanosporum and Tuber aestivum truffles that extend their shelf life and their availability as a fresh product. Their respiration rates were determined by O(2) depletion and CO(2) formation in closed systems performed at different temperatures: 4, 10, and 23 degrees C. The results were fitted by exponential equations and derivatives of these equations were used to obtain the experimental respiration rates. Our results revealed high respiration rates in both species of truffles and respiratory quotients (RQ) higher than 1 in all the cases studied. A linear dependence of respiration rate, both R(O2) and R(CO2), on O(2) concentration was revealed. A mathematical model was used to predict the evolution of the gaseous composition at 4 degrees C in the interior of polypropylene trays (250 mL) heat sealed with 4 microperforated films of different transmission rates. A microperforated film with 2 holes (90 x 50 microm) was selected to produce an internal atmosphere of 15%CO(2)/7%O(2) at 4 degrees C. The predicted atmosphere composition was confirmed by the experimental results. The quality and microbiological characteristics of fresh truffles, packaged in these conditions, revealed that the microbial counts of pseudomonads and Enterobacteriaceae were decreased, the weight loss was reduced, the typical hard texture was maintained, and the development of mycelium growth was delayed, enabling good scores for aroma and flavor, and therefore prolonging the shelf life of T. melanosporum and T. aestivum truffles to 28 and 21 d, respectively. Practical Application: This study describes the benefits of using MAP with microperforated films in the postharvest storage of Tuber melanosporum and Tuber aestivum fresh truffles. The shelf life of T. aestivum is prolonged to 21 d and of T. melanosporum to beyond 28 d increasing the possibilities for a foreign market.

No abstract

No abstract