Formate-acetate ratio, precipitation

Statistical analysis of precipitation chemistry data collected at three sites in the United States indicates that the inorganic and organic analytes show little or no correlation. In contrast, formate and acetate concentrations are highly correlated (r> 0.89) and consistently produce a formate/acetate ratio of approximately 2. 

An assessment of the plausibility of various pathways that could introduce the organic compounds into precipitation suggests aqueous-phase oxidation of aldehydes is probably not a major contributor because of the large atmospheric acetaldehyde concentration that must be postulated to produce the observed formate/acetate ratio. Alternatively, potential gas-phase formic and acetic acid... 

Case b In various cases, we observed the formation of large crystals at the bottom of the windowed precipitator. For example, we found large crystals of Prednisolone (corticosteroid) precipitated from Methanol (Figure 1) and of Prednisolone acetate (corticosteroid) precipitated from Tetrahydrofuran, in both cases operating at 150 bar, 40 °C. We also observed that a relative control of the crystal size down to some microns is also possible, in addition to decreasing the concentration in the liquid solution or increasing the ratio between the antisolvent and the liquid solution flow rates. 

This possibility takes on greater credence upon re-examination of the approximately 2 1 ratio of formate to acetate concentrations consistently observed in the Wisconsin and Virginia precipitation samples. As derived from thermodynamic data (12, 14). the effective Kpj for formaldehyde is approximately 7000 M/atm at 25°C the effective Kpj for acetaldehyde is on the order of 11 M/atm. Assuming that aqueous-phase oxidation of the two aldehydes occurs at approximately the same rate, typical gas-phase concentrations of acetaldehyde would have to be about 300 times greater than corresponding formaldehyde concentrations to account for the observed... 

Reynen et al. [164] published a seminal account of the synthesis of ceramic powders by the emulsion technique, in which detailed comments were made on the synthesis of Mg-Al spinel particles. Special attention has been paid in this work on the mode of removal of water from ordinary precipitates or emulsions for preparation of particles. In the emulsion method, salts of Mg and Al in the desired molar ratio were dissolved in water, and the solution mixed with an equal amount of alkanes which, depending on the drying method, could be low or high boiling. For ensuring some stability of the emulsion, a surfactant (Span 80 for sulfate solutions and Bry for acetate and formate solutions 0.1-1%) was added. The necessary stirring was accomplished by very high shear forces. 

Binary systems synthesized consisted of Cu/Fe, Ni/Fe, Cu/Al and Ni/Al and Cu/Cr for 4-10 wt percent Cu or Ni in the calcined mixed oxide. Anionic complexing agents acetic, citric and oxalic acids and EDTA were used in molar ratios of 1 1 with the initial copper or nickel. Two stage precipitations were used starting with an initial formation of aluminum, chromium or ferric hydroxide by addition of NaOH to an aqueous solution of A1 nitrate, Cr nitrate or Fe chloride. In the second stage aqueous solutions of Cu sulfate or Ni nitrate were mixed with the initial precipitate with or without the presence of a 1 1 mole ratio of selected anionic complexing agents to complete the precipitation. A second mode of coprecipitation used was to preadsorb oxalic acid on the initially precipitated AI, Cr or Fe hydroxide. 

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