In North America, approximately 1 billion gallons of used oil are collected annually from generators such as quick lubes, truck fleets, and manufacturers. Several companies have begun the process of re-refining this hydrocarbon-rich waste product. Re-refining allows the lubricating oil to be repeatedly re-used as a higher value product.
Re-refining involves operations which will separate and remove contaminants in the used oil so that this oil becomes suitable for reuse. The re-refining process is much like that of a traditional refinery with similar waste treatment requirements. Such was the case for a major used oil re-refinery facility in the mid-west. They had a "sour water" treatment system that was not performing as designed, resulting in operational problems and safety concerns. Sour water is hydrogen sulfide rich wastewater water that is generated from a variety of sources including hydrotreaters, reformers and hydrocrackers.
The re-refinery's sour water scrubber was experiencing extreme pH swings and generating precipitate. The scrubber was being fed with sodium hydroxide (NaOH), aka, caustic and hydrogen peroxide (H2O2) to remove the hydrogen sulfide (H2S). The hydrogen peroxide was being supplied from totes, causing safety issues with their handling within the refinery. Working with the re-refinery operations group, US Peroxide's engineering and applications team performed a thorough review of the scrubber system.
US Peroxide identified the sources of the operational problems then designed a turnkey hydrogen peroxide treatment program. Using the re-refinery's existing equipment the new treatment program would effectively treat the hydrogen sulfide, reduce the wide pH swings, eliminate the generation of precipitate, and eliminate the safety risks connected to the handling of the many totes of peroxide by the operations group.
Hydrogen peroxide has been shown to be a convenient, cost effective and environmentally friendly part of hydrogen sulfide gas scrubbing technologies. Scrubbing of hydrogen sulfide using sodium hydroxide and hydrogen peroxide is a well-established technology.
A typical scrubbing solution consists of dilute sodium hydroxide to which enough hydrogen peroxide is added to react with the hydrogen sulfide according to the equation:
4H2O2 + H2S → H2SO4 + 4H2O
The above reaction predominates at pH > 9.2, and yields soluble sulfate as the reaction product. The stoichiometry calls for 4.25 lbs H2O2 per lb S 2- and it is not unusual for reaction efficiencies to approach 100%, provided that the H2O2 is added in a controlled fashion and the reaction medium is thoroughly mixed.
Enough sodium hydroxide must be present to neutralize the sulfuric acid formed according to the equation:
2NaOH + H2SO4 → Na2SO4 + 2H2O
This indicates that for each weight part of hydrogen sulfide, approximately 2½ weight parts of sodium hydroxide are needed.
Following implementation of the US Peroxide treatment solution the previous operational problems were eliminated and the safety of the sour water scrubber system was increased. The re-refinery facility has continued to rely on the new program to continue to meet their sour water treatment needs.
US Peroxide provides a full scope of supply (chemicals, equipment and services) to support emergency and ongoing applications for hydrogen peroxide and a range of water and wastewater treatment chemicals.