Sulfur continued handling

For the process step involving handling of spent sulfuric acid, several patents have been issued in which improvements in this step were a main claim. The azeotropic nitration of benzene essentially eliminates the need to reconcentrate sulfuric acid (10,11). The nitration step is carried out at higher than usual temperatures (120—160°C). Because excess benzene is used, the higher temperature allows water to be removed as a water—benzene azeotrope. The water is separated and the benzene phase, containing approximately 8% nitrobenzene, is recycled back into the reactor. The dry sulfuric acid is then reused continuously. 

Sodium sulfate. A single-hearth furnace like that shown in Fig. 19-24g is used. Sodium chloride and sulfuric acid are charged continuously to the center of the pan, and the rotating scrapers gradually work the reacting mass to the periphery, where the sodium sulfate is discharged at 540°C (1000°). Pans are 3.3 to 5.5 m (11 to 18 ft) in diameter and can handle 5500 to 9000 kg/d (12,000 to 20,000 lbm/d) of salt. Rotary kilns also are used for this purpose. Such a unit 1.5 m (4.9 ft) in diameter by 6.7 m (22 ft) has a capacity of... 

Chlorinated polyether can be used continuously up to 125°C, intermittently up to 150°C. Chemical resistance is between polyvinyl chloride and the fluorocarbons. Dilute acids, alkalies, and salts have no effect. Hydrochloric, hydrofluoric, and phosphoric acids can be handled at all concentrations up to 105°C. Sulfuric acid over 60 percent and nitric over 25 percent cause degradation, as do aromatics and ketones. 

A sharp increase in price and decrease in availability of sulfur reduced the experimental effort temporarily, but laboratory work based on the above findings continued. Pourable paving mixes were developed containing one-sized sands which could be cast in place without rolling, much as portland cement concrete is handled. Based on satisfactory laboratory findings, a test road was constructed in Richmond, British Columbia in 1970, where a sand—asphalt—sulfur mix was cast between forms (5). The success of this trial, coupled with a decrease in the price of sulfur and the forecast for a long-term world sulfur surplus, led us to initiate an extensive research and development program to exploit sand-asphalt-sulfur mixes as road base and surface materials. 

Mix Handling Trials. The general objective in conducting field trials was to use, with minimum modification, conventional asphalt equipment for processing, transporting, and placing sand-asphalt-sulfur mixes. To date, the mixes have been processed in batch-type hot-mix asphalt plants. Details of the processing steps were published in a previous report (4). In 1975, we intend to evaluate a continuous-type hot-mix... 

---