Niobia supported on silica as a catalyst for Biodiesel production from waste oil

The activity and stability of niobia supported on silica catalyst have been tested in continuous micro-pilot reactors, for biodiesel production starting from acid vegetable oils. A catalyst was prepared by the impregnation of silica pellets with a loading of 12% of Nb and was extensively characterized. The activity of this catalyst in both esterification and transesterification was tested in a continuous micro-pilot laboratory plant in which acid oil was fed (FFA 10% w/w) at a temperature of 220°C and at a pressure of 60 bar. The niobia based catalyst resulted in a very active catalyst in both esterification (FFA conversion = 95-90%) and transesterification reactions (FAME yield = 80-90%), and the activity remained quite constant for more than 100 h on stream. Notwithstanding this stability, a non-negligible leaching phenomena has been detected, in the case of long-time continuous runs, as the Nb concentration on the spent catalyst resulted lower than that on the fresh one. The obtained result confirms that the leaching of the active specie is one of the most strong problem in heterogeneous catalysis for biodiesel production.

Predictors of poliomyelitis case confirmation at initial clinical evaluation: implications for poliomyelitis eradication in the Americas

In 1985, the Pan American Health Organization adopted the goal of eradication of poliomyelitis from the Americas by 1990. Strategies to accomplish this included high vaccination coverage, aggressive outbreak control, and active surveillance for acute flaccid paralysis (AFP). Although the sensitivity of AFP surveillance for detecting paralytic poliomyelitis cases is high, studies have shown the specificity to be low. In 1990, 2497 notified cases of AFP were investigated in the Americas of which 2146 had stool specimens collected. However, only 18 were confirmed as poliomyelitis by isolation of wild poliovirus from stool specimens, 71 were classified as being compatible with poliomyelitis. Cases of AFP due to causes other than poliomyelitis result in extensive but unnecessary outbreak control measures. To predict, at initial clinical evaluation, the likelihood of future confirmation as a case of poliomyelitis, likelihood ratios (LR) were calculated for different combinations of clinical characteristics of AFP cases (249) from Mexico in 1989 and 1990. The best predictors in a child with AFP were proximal muscle involvement which progressed '4 days together with fever at onset of paralysis, and proximal and unilateral involvement with either fever at onset or paralysis which progressed '4 days. The odds would increase by 12 that the child would eventually be confirmed as poliomyelitis (19), based on a stool culture positive for wild poliovirus (95% confidence interval (CI) 2.6-55.9). A guide for use in the field is proposed whereby local health officials, often with little training in neurological evaluation, can predict at initial clinical examination the likelihood that an AFP case will subsequently be confirmed as poliomyelitis.(ABSTRACT TRUNCATED AT 250 WORDS)