After 98% concentrated sulfuric acid absorbs hydrogen sulfide and phosphine from acetylene gas, why does the 75% waste acid have a strong hydrogen sulfide odor?

They are all unpleasant gases; converting them into an acidic odor reduces their intensity

In two lines, concentrated sulfuric acid is used to absorb hydrogen sulfide and phosphine from acetylene gas; one of these lines has a strong odor and its color is similar to that of engine oil； A line with a mild odor and a color similar to soy sauce ； The concentration of spent sulfuric acid is kept below 75%.

Hello, do you have any data on the composition of waste sulfuric acid? And what about the disposal of waste sulfuric acid?

This question itself contains too many issues: 1. Are the two sets of absorption lines identical? Are the equipment and facilities, as well as the process operating conditions, all the same? 2. Is the sulfuric acid used the same? Is 98% of the sulfuric acid directly absorbed and 78% discharged? Intermittent or continuous? If the equipment is the same, the operating parameters are the same, and the flow rate is the same, then there must be a problem with one of the sets of equipment. Is it possible that a short circuit occurred in the sulfuric acid during the absorption process, resulting in low absorption efficiency of the entire system? Also, how long has it been since the packing used for washing acetylene with sulfuric acid was replaced? Is the equipment corroded? Has the lining or pipe suffered from lining detachment, and are there any substances such as iron ions that could affect color?

The two production lines have the same equipment; the equipment on one line has been repaired. The filler has been in use for a year without any replacement.

Our factory also uses concentrated sulfuric acid to wash acetylene gas; the concentrated sulfuric acid is added continuously and then discharged, but we keep the concentration of the waste sulfuric acid at 82%-92%. The washing principles are as follows: (1) 3H2S + H2SO4 = 4H2O + 4S; (2) H2S + H2SO4 = S + 2H2O + SO2 (in small amounts); (3) SO2 + 2H2SO4 = 2H2O + 3S; (4) H3P + 2H2SO4 = H3PO4 + 2H2O + 2S. Under normal conditions, the waste sulfuric acid is a black, viscous liquid that does not have the rotten egg smell associated with hydrogen sulfide. It is recommended to examine the packing, process parameters, and analyze the acetylene composition after washing in the two separate lines, and then compare them ； Or increase the amount of concentrated sulfuric acid added to the oil-color production line as well as its discharge volume, replace the sulfuric acid in the scrubber tower, and then observe the effects ； It is recommended to measure the thickness of the equipment again to rule out the impact of iron ions on color intensity.

Now the company requires controlling the consumption of concentrated sulfuric acid; moreover, it is very difficult to dispose of waste sulfuric acid, so the concentration is not kept high. Both the washing tower and the purification tower are made of fiberglass; the side walls don’t serve much purpose. If testing is to be done, it will only involve the pipes and plate heat exchangers. Let’s pay attention to this part and try replacing it again.

A simple and effective method is to add some surfactant to the acid solution; this results in bubbles forming on the surface of the acid during operation, thereby reducing acid mist.

What kind of surfactant should be added? It’s just to mask the acid mist; that doesn’t serve much purpose. What’s needed are fundamental solutions to the acid mist problem