Читать книгу Concise Handbook of Fluorocarbon Gases - Sina Ebnesajjad - Страница 39
3.4.1 Manufacturing Hydrofluoric Acid
ОглавлениеHydrofluoric acid is manufactured by the reaction of acid-grade fluorspar (≥97% CaF2) with sulfuric acid (H2SO4). The basic reaction is shown in Eq. (3.1).
Figure 3.6 displays a process diagram for commercial production of HF [14]. In the first step fluorspar is dried for 30-60 minutes in a horizontal rotary kiln that is heated to 200-250°C. Dry fluorspar and a small excess of sulfuric acid are fed continuously to the front end of a stationary pre-reactor or directly to the kiln by a screw conveyor. The pre-reactor mixes the components prior to charging to the rotary kiln. Calcium sulfate (CaSO4) is removed through an air lock at the opposite end of the kiln. The gaseous reaction mixture - HF and the excess H2SO4 from the primary reaction are removed at the front end of the kiln along with entrained particulates. Silicon tetrafluoride (SiF4), sulfur dioxide (SO2), carbon dioxide (CO2), and water produced in secondary reactions are also removed along with the HF.
Table 3.3 Typical physical properties of hydrogen fluoride and hydrofluoric acid [13].
| Concentration | 49% HF | 70% HF | 100% HF (AHF) |
| Freezing Point | -33°F (-36°C) | -95°F (-71°C) | -118°F (-84°C) |
| Boiling Point | 223°F (106°C) | 146°F (63°C) | 67.1°F (19.5°C) |
| Density (68°F) | 9.6 lbs/gal | 10.1 lbs/gal | 8.3 lbs/gal |
| pH | <3.4 | <3.0 | <1.0 (10% solution) |
| Flash Point | Not Flammable | ||
| Vapor Pressure (68°F) | 23 mm Hg | 132 mm Hg | 771 mm Hg |
| Vapor Density | 2.4 (air = 1.0) |
Figure 3.6 Hydrofluoric acid manufacturing process flow diagram [14].
The particulates are separated from the gas stream using a dust separator and returned to the kiln. Sulfuric acid and water are removed using a pre-condenser. HF vapors are next condensed in refrigerated condensers forming crude HF (impure) sent to storage tanks. The remaining gas stream passes through a sulfuric acid absorption tower or acid scrubber, to take out most of the residual HF and H2SO4. The gases exiting the scrubber are passed through water scrubbers to recover SiF4 and HF as fluosilicic acid (H2SiF6). The water scrubber gases are passed through a caustic scrubber before release to the atmosphere. Stored HF and H2SO4 are distilled to obtain HF at 99.98% purity. Lower concentration HF are prepared by water dilution [14].
