Processes, systems, and associated control methodologies are disclosed that control the flow of biogas during the biogas cleanup process to create a more consistent flow of biogas through the digester, while also optimizing the output and efficiency of the overall renewable natural gas facility. In representative embodiments, a biogas buffer storage system may be used during the cleanup process to control the pressure and flow rate of biogas. The biogas buffer storage system may monitor and control the biogas flow rate to either bring down or increase the digester pressure, thereby maintaining a normalized biogas flow rate.

A process for selectively separating H.sub.2S from a gas mixture which also comprises CO.sub.2is disclosed. A stream of the gas mixture is contacted with an absorbent solution comprising one or more amines, alkanolamines, hindered alkanolamines, capped alkanolamines, or mixtures thereof. The H.sub.2S/CO.sub.2 selectivity of the absorbent solution is preferably greater than about 4.0 for an acid gas loading [mol(CO.sub.2+H.sub.2S)/mol(amine)] between about 0.2 and about 0.6, and is achieved by reducing pH of the absorbent solution.

This disclosure relates to CO.sub.2-philic crosslinked polyethylene glycol membranes useful for natural gas purification processes. Also provided are methods of using the membranes to remove CO.sub.2 and H.sub.2S from natural gas.

A process and apparatus for removing hydrogen sulphide from a gas is disclosed. The process comprises the steps of: providing a gas comprising hydrogen sulphide; supplying oxygen for the process if the gas does not comprise oxygen, or does not comprise sufficient oxygen for converting hydrogen sulphide to elementary sulphur; leading the mixture of gas and, if supplied, oxygen to a tank comprising i) a foam forming liquid, such as a scrubber liquid and ii) a foam layer made from said foam forming liquid on the top of the foam forming liquid where the hydrogen sulphide in the gas is oxidized to elementary sulphur to form a cleaned gas removed from hydrogen sulphide.

A process for selectively separating H.sub.2S from a gas mixture which also comprises CO.sub.2 is disclosed. A stream of the gas mixture is contacted with an absorbent solution comprising one or more amines, alkanolamines, hindered alkanolamines, capped alkanolamines, or mixtures thereof. The H.sub.2S/CO.sub.2 selectivity of the absorbent solution is preferably greater than about 4.0 for an acid gas loading [mol(CO.sub.2+H.sub.2S)/mol(amine)] between about 0.2 and about 0.6, and is achieved by reducing pH of the absorbent solution.

The present invention relates to a composition for scavenging hydrogen sulphide and/or mercaptans in hydrocarbon streams, the composition comprising an oxazolidine compound and a synergistic additive.

A scavenger comprising a formaldehyde sulfoxylate may be used to scavenge hydrogen sulfide (H.sub.2S) from systems that are brine or mixed production. Suitable formaldehyde sulfoxylates include, but are not necessarily limited to, sodium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, and calcium formaldehyde sulfoxylate, potassium formaldehyde sulfoxylate, magnesium formaldehyde sulfoxylate, iron formaldehyde sulfoxylate, copper formaldehyde sulfoxylate, alkene aldehyde sulfoxylates, and combinations thereof.

Systems and methods for selectively removing hydrogen sulfide from a feed gas stream. The systems include an absorber-heat exchanger (ABHEX) assembly configured to exchange thermal energy between a mixed stream and a thermal management fluid stream. The ABHEX assembly defines a mixed stream volume and a thermal management fluid stream volume. The ABHEX assembly includes an isolation structure that maintains fluid separation between the mixed stream and the thermal management fluid stream and facilitates thermal communication between the mixed stream and the thermal management fluid stream. The ABHEX assembly is configured to receive and to mix the feed gas stream and a lean solvent stream to generate the mixed stream, to separate the mixed stream into a product gas stream and a rich solvent stream, and to cool the mixed stream. The methods include methods of operating the systems.

An integrated refinery process for removing mercaptans from a hydrocarbon stream containing mercaptans and converting by-product disulfide oil to useful products. The process includes introducing the hydrocarbon stream containing mercaptans into an extraction vessel containing an alkaline solution and passing the hydrocarbon stream through an extraction section of the extraction vessel which includes one or more liquid-liquid contacting decks for reaction to convert the mercaptans to alkali metal alkanethiolates. Further, the process includes withdrawing a hydrocarbon product stream free of mercaptans from the extraction vessel and recovering spent caustic containing alkali metal alkanethiolates from the extraction vessel. Additionally, the process includes subjecting the spent caustic containing alkali metal alkanethiolates to air oxidation to produce a by-product stream containing disulfide oils (DSO) and sulfides and processing the by-product stream in a steam cracking unit to produce a DSO free product stream.

Embodiments of a composition of the present invention for scavenging sulfides from hydrocarbon fluids and water generally include diaminol/diaminacetal provided in a chemical system, wherein the diaminol/diaminacetal is prepared by reacting one molar equivalent of glyoxal and two molar equivalents of a primary amine functionality. In various embodiments, the chemical system includes at least one component selected from surfactants, hydrotropes, alcohols, amines, amino acids, and ethers. Embodiments of a method for scavenging sulfides from hydrocarbon fluids and water is also provided.