OCR Text |
Show In procedure C a converter was used, i.e. the setup shown in Figure 1 was changed so that on exiting the reactor the flowing gas mixture could be sent either to the SOe meter as shown in Figure 1, or sent via heated lines to a converter, a tube packed with platinum catalyst and heated to 1000o C, and then sent to the S02 meter. In this manner it was possible to measure both [SO.] in the post reaction gases and the sum of [SOe] and [S03]. Also in procedure C the metering pump and boiler shown in Figure 1 were replaced with a unit that allowed the flowing gas mixture . to . ~ass . over concentrated HeSO. at elevated temperatures. By controlling the temperature the amount of acid vaporized into the gas mixture could be controlled. This allowed doing experiments with gas mixtures that contain no water vapor other than that which was formed by reaction. As discussed in detail below, computer modeling studies showed that when methanol oxidizes in mixtures containing NO and S03 the NO is converted to N02 while the S03 is reduced to SO., and that the optimum conditions for the two reactions tended to be the same. Since the measurement of NO to N02 conversion is much easier than SOa to SO. conversion, this fact was useful in choosing experimental conditions for measuring S03 reduction. In addition to the above described laboratory scale experiments done with synthetic gas mixtures a limited set of experiments were done with a 1S.2 cm ID by 2.4 meter long refractory lined tunnel furnace fired with either natural gas or coal at IS kW (Figure 2). The temperature profile in this unit matches the profiles typically found in utility boilers. Modeling Procedures Calculations were done using the set of rate constants given in reference 12 with the addition of the reactions 0+SOa=02+S0e , O+SO.+M=SOa+M, H+S03=OH+SOe , OH+SOe+M=HSOa+M, HSOa+Oe =HOe +S03 , with rate constants from references 13, 13, 13, 14 and 14 respectively. Thermochemical data from the JANAF tables was used an~ for the specie HSOa Benson's estimate was accepted (IS). Experimental Results Figure 3 shows the results of a series of experiments in which methanol was oxidized at varying reaction times and temperatures in the presence of NO while Table 2 shows the results of a series of experiments in which_ various gas mixtures were passed through the reactor, and the concentration of S02 in the post reaction gas mixture was measured by procedure A. Two sets of experiments were done in which mixtures containing both NO and Sea were reacted with CH30H and the amounts of NO converted to NOe and SOa reduced to So. were measured as a function of the input CHaOH concentration. One of these sets of experiments was done using procedure B and the other with procedure C. Figure 4 is a relative rate plot for the oxidation of NO to NOe and the reduction of SOa to SOe, i.e. a log log plot of the NO and SOa conversions observed in these experiments. Another set of experiments was done in which the NO to NOe conversion was measured for a gas mixture containing 22S ppm NO, 4.6X Oe, varying amounts of CHaOH, either 0 or 2600 ppm S02, and balance inert, reacting for 0.S9 sec. at 601°C. The presence or absence of the SOe was found to have no effect on the NO to NOe conversion. A qualitative observation is also to be reported: as one might -expect from the reaction mechanism it was found under a variety of conditions that the conversion of NO and S03 to NOe and SOe produces at least one mole of CO per mole of NO and/or SOa converted. |