Acetone steady-state concentration

Acetone steady-state concentrations are maintained at a low level through subsequent side reactions involving formation of heavy ends by condensation of acetone and through its removal from streams of light ends using countercurrent dis-tillation/extraction methods [64a-cj. The formation of azeotropes of acetone, methyl acetate and methyl iodide preclude the separation of acetone by conventional distillation techniques. 

A study of oxidation of HMSA was done relative to pinacol to estimate the absolute rate of oxidation of HMSA with OH radicals in solution. Pinacol was oxidized to acetone in Fenton s oxidation. Anbar and Neta (1967) reported reaction rates of OH radicals with pinacol and acetone of 3.2 x 108 Mr1 s 1 and 4.3 x 107 Mr1 s, respectively. Table 6.1 presents the oxidation rates of pinacol (10-2 M) and pinacol-HMSA (10-2 M each). The concentrations of the reactants were Fe2+ = 104 M, H202 = 0.1 M, and pH 2. Oxidation rates for each molecule were different in separated and mixed reactions, as the steady-state concentration of free radicals depends on the chemistry of organic substrates in solution. HMSA is more reactive than pinacol by a factor of 3.9 0.8. If the absolute rate of reaction of pinacol with OH radicals was calculated to be 3.2 x 108 M 1 s, then ... 

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

Figure 5.7. Steady-state fluorescence polarization versus temperature over viscosity ratio for Trp residues of human aj -acid glycoprotein prepared by acetonic precipitation. Data were obtained by thermal variations in the range 7-35" C. Xex = 300 nm. Xem = 330 nm. Protein concentration is equal to 10 pM. The rotational correlation time determined from the Perrin plot is equal to 13 ns at 20°C is in the same range as that (17 ns) expected for the protein at the same temperature, indicates the presence of residual motions. Also, the extrapolated anisotropy (0.264) is equal to that measured at -35 C (0.267). Source Albani, J. R. 1998, Spectrochimica Acta, Part A. 54, 173-183.

X 10 m s ) of 2.4 x 10 ° dm mol s and in substantial agreement with a similar determination by Aldrich et al. [117]. Both groups found that the rate coefficient was independent of acetone concentration. It is substantially activation-limited. With nitromethane, the operational rate coefficient increased with concentration from 2.9 x 10 in dilute solutions to 4.3 X 10 dm mol" s at O.Smoldm" nitromethane. Such an increase would be expected for reactions occurring before the steady-state is established. Wolff et al. [118] found that the rate coefficients for hydrated electrons reacting with NOJ, H, acetone and NO2 was independent of concentration of scavenger above 0.1 mol dm , though only nitrate reacts at the diffusion-limited rate, even if hydro-dynamic corrections are applied (Chap. 9, Sect. 4). 

Other Oxygenated Hydrocarbons Reductants. Other oxygenated hydrocarbons— 2-propanol, ethanol, methanol, iso-butanol, ethyl ether—were also tested. The inlet carbon atom concentration of these hydrocarbons was calculated to be equal to that of acetone in the tests reported above, e.g., equivalent to 1,300 ppm acetone. The NO conversion at steady state for each reductant is shown in Table II. All reductants showed 100% selectivity to N2. Since the carbon concentration of all reductants was the same, the activity of the reductants can be compared by comparing the NO conversion. The only reductant with activity close to acetone is 2-propanol with 31% conversion. Others showed much less activity than acetone. Specifically, methanol showed negligible NO reduction activity. It is speculated that the NO selective reduction activity is closely related to the ability of hydrocarbons to form oxygenated surface intermediates at these reaction conditions. This is being investigated further. 

---