PTQ Q2 2024 Issue

Sulphur reduction, sulphur removal, and spent caustic reuse

Demand for flexible sulphur recovery solutions is increasing, including wet air oxidation, deep neutral i sation, incineration, and processes that need sustainable strategies

Richard Stambaugh Merichem Technologies

M ore than a hundred different crude oils are traded on the market today. The most desirable crudes are light and sweet, containing less than 0.5% (by weight) sulphur. They are highly efficient, leave minimal residue in the refinement process, and the low density makes them easy to distil and transport. Demand for light, sweet crude grades rose exponentially across Europe, Africa, and the US as refineries adjusted their slates ahead of the International Maritime Organization (IMO) 2020 lower sulphur cap. In contrast, heavy, sour crudes contain more than 0.5% sulphur. They are generally extracted from the Gulf of Mexico, Mexico, South America, Canada, and the 24 OPEC Member Nations. Sour crudes are more complicated to refine into lower-sulphur fuels, and the refiners who can process them have a distinct advantage over those who cannot, particularly considering IMO 2020. The impetus has been on refineries to determine the best methods of separating sulphur compounds from sour crude. In doing so, US refineries can take in almost any crude oil and turn it into clean-burning fuel. The problem Sitting midway to 2030 net zero goals, it has become clear to scientists and environmentalists that incremen- tal and fragmented change is insufficient to achieve the Sustainable Development Goals (SDGs) in the seven years remaining. Meeting (net zero goals) requires transforma - tive and accelerated actions, outlined in the 2023 Global Sustainable Development Report (GSDR), a new phase of accelerated progress by UN member states towards the Sustainable Development Goals leading up to 2030. It out- lines the shifts required to transform the energy sector, and the increasingly stringent fuel specifications have made crude oil desulphurisation obligatory. The sulphur-containing compounds in sour crudes are among the most undesirable. Hydrogen sulphide (H 2 S) is toxic to humans and particularly dangerous because, at suf - ficiently high concentrations, it paralyses olfactory nerves even when exposed to it for only a few minutes. According to the National Institute for Occupational Safety and Health (NIOSH), H2S environmental concentrations of 100 ppm are immediately dangerous to life or health. Concentrations greater than 500 ppm can cause a person to collapse

within five minutes, and concentrations exceeding 700 ppm can cause immediate collapse and death within just one or two breaths. Spent caustics When the malodorous and potentially dangerous sulphides and mercaptans are expended from sweetened hydro - carbons, the residual caustics are considered spent. The complexities and numerous processes involved in treating spent caustic are challenging. It is one of the most prob- lematic industrial wastes in terms of disposal. When man - aged poorly, spent caustic can cause significant harm to health and the environment. Since 1997, the Environmental Protection Agency (EPA), under the Resource Conservation The complexities and numerous processes involved in treating spent caustic are challenging. It is one of the most problematic industrial wastes in terms of disposal and Recovery Act (RCRA), has classified spent caustics as hazardous waste, with strict handling and disposal require - ments because of the high levels of contaminants. Spent caustics typically have a high pH value (>12) and high sulphide concentrations (2-3% w/w), not accounting for the phenols, mercaptans, amines, or other organic compounds that are emulsified in the caustic. Spent caustic is classified as an EPA Hazardous Waste Number of DOO3, hazardous waste under the US Resource Conservation and Recovery Act (RCRA), and a Class 8 (corrosive) hazard throughout United Nations (UN) participating countries use the UN Globally Harmonized System of Classification and Labeling of Chemicals (GHS), which is defined as substances that can cause significant harm to living tissue and/or corrode steel and aluminium upon contact. Spent caustic is also on the Right to Know Hazardous Substance List cited by the Occupational Safety and Health Administration (OSHA), American Conference of Governmental Industrial Hygienists

PTQ Q2 2024