A study of the Apollo aqueous redox process for converting hydrogen sulfide in biogas to elemental sulfur

An experimental project is reported that had the overall objective of developing a commercial biogas scrubber for municipal and agricultural applications.; In support of the projects overall objective, the specific objectives of this work were: (1) To provide design and scaling parameters, which can be used to enhance the performance and minimize capital and operating costs of the biogas scrubber. (2) To provide a useful reaction model of the aqueous phase iron chelate catalysed oxidation of hydrogen sulfide to elemental sulfur. (3) To develop hypotheses and determine what data are likely to be of relevance to understanding the interfacial phenomena of colloidal sulfur in aqueous solutions that could lead to unwanted sulfur deposition and poor sulfur quality. (4) To obtain interfacial chemistry data that could enhance the understanding of the behaviour of sulfur particles in forming flocs and depositing on surfaces and the factors that lead to poor sulfur quality. (5) To determine whether crystal size and characteristics of deposited and flocculated sulfur could be modified by surfactants to improve sulfur purity and reduce process operability.; Investigations of interfacial chemistry were conducted to develop a greater understanding of the factors that influence the operating problems and poor quality associated with the sulfur product, and indicated a low foaming nonionic surfactant might improve the quality and processability of the elemental sulfur product. The following conclusions reached: (1) The addition of the surfactant to the redox solution decreased the mean hydrogen sulfide removal efficiency of the process, from 99.2 to 98.3%. (2) The addition of the surfactant to the redox solution decreased the mean particle size of the precipitated sulfur product, from 2.91 to 2.52 Mm diameter. (3) The addition of the surfactant to the redox solution increased the purity of the precipitated sulfur product, from 88.070 to 90.783 wt % sulfur before washing and from 97.781 to 99.872 wt % sulfur after washing.; An understanding of sulfur interfacial chemistry gained in this work allowed Apollo Environmental Systems to design, install, and operate a commercially successful biogas scrubber that is highly resistant to sulfur plugging.