| 摘要 |
Liquid sulphur trioxide is produced by distilling oleum and controlling the distillation according to the dielectric constant of the product or the liquor remaining during the distillation. The distillation is preferably done in at least two stages, the dielectric constant of the product or liquor remaining in the second stage being used for control purposes. The control may be effected by running off the liquor remaining in the distillation or second distillation stage or by altering the temperature of the distillation. The measurements may be made continuously or intermittently. The free sulphur trioxide content of the oleum may be between 5 and 65% by weight and the temperature of the distillant coolant is between 28 DEG and 37 DEG C. A stabilizer may be added to the liquor or product, e.g. a carbonyl halide or carbon tetrachloride. Sulphur trioxide of very low acid content, e.g. down to 20 to 30 p.p.m., is obtained.ALSO:Liquid sulphur trioxide, mixed with a small proportion of sulphuric acid, is produced by distilling oleum, and the impure sulphur trioxide is then re-distilled in a second still which is controlled by a device for measuring the dielectric constant of the liquid in the second still, or of the final product. The control prevents the accumulation of acid in the second still, and is effected either by running off the liquid from the second still, or by varying the heat input to the still. The measuring device preferably comprises a pair of platinum electrodes, immersed in the liquid, which are connected to a relay via a variable frequency oscillator circuit adjusted to operate the relay at a given dielectric constant. |
