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Feedstock Preparation
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
The Selexol process uses a mixture of the dimethyl ether of propylene glycol as a solvent. It is nontoxic and its boiling point is not high enough for amine formulation. The selectivity of the solvent for hydrogen sulfide (H2S) is much higher than that for carbon dioxide (CO2), so it can be used to selectively remove these different acid gases, minimizing carbon dioxide content in the hydrogen sulfide stream sent to the sulfur recovery unit (SRU) and enabling regeneration of solvent for carbon dioxide recovery by economical flashing. In the process, a stream of natural gas is injected in the bottom of the absorption tower operated at 1,000 psi. The rich solvent is flashed in a flash drum (flash reactor) at 200 psi where methane is flashed and recycled back to the absorber and joins the sweet (low-sulfur or no-sulfur) gas stream. The solvent is then flashed at atmospheric pressure and acid gases are flashed off. The solvent is then stripped by steam to completely regenerate the solvent, which is recycled back to the absorber. Any hydrocarbon derivatives are condensed and any remaining acid gases are flashed from the condenser drum. This process is used when there is a high acid gas partial pressure and no heavy hydrocarbon derivatives. Diisopropanolamine can be added to this solvent to remove carbon dioxide to a level suitable for pipeline transportation.
Hybrid Energy Systems for Hydrogen Production
Published in Yatish T. Shah, Hybrid Energy Systems, 2021
Electrolysis could provide an alternative to air separation units with the added benefit of producing a pure hydrogen stream. Key changes to the plant include replacing the entire ASU with an electrolyzer bank and replacing the LO-CAT (a trademark flexible hydrogen sulfide removal process)/ZnO sulfur removal steps with a two-stage Selexol plant. The sulfur removal change was driven by the need for an inert gas for feed pressurization. Selexol is a well-proven process that uses a dimethyl ether-based solvent to remove both sulfur and CO2 from the gas stream. The plant envisioned by Dean et al. [24] is shown in Figure 11.10.
Review: recent advances in biogas purifying technologies
Published in International Journal of Green Energy, 2019
Francisco M. Baena-Moreno, Mónica Rodríguez-Galán, Fernando Vega, Luis F. Vilches, Benito Navarrete
Selexol has a low freezing point and is not corrosive. The solubility of CO2 and ammonia (NH3) is higher in Selexol than in H2O, being able to absorb three times more CO2. The drawback of this type of organic solvents is that they are more difficult to regenerate than H2O (Marsh et al. 2005; Persson 2003). The solubility of H2S in Selexol is greater than the solubility of CO2. To regenerate the Selexol of H2S and H2O, an increase in temperature is required, which is also of different value for both, so these compounds must be eliminated in different stages before sending the Selexol back to the absorption (Marsh et al. 2005). Figure 4 shows a scheme of an absorption system with Selexol used in a plant in Sweden (Persson 2003).
Feasibility study and economic assessment of changing chemical solvent of a high capacity gas treatment plant into a physical solvent-based process with a correction scheme
Published in Petroleum Science and Technology, 2023
Javad Sadeghi Azizkhani, Afshin Eteghad, Fazlallah Dehghani, Marzieh Bahrami Hidaji
Most of the physical solvent processes are proprietary and are produced by multinational modern corporations. For example, the SELEXOL process is a physical adsorption process that uses DEPG as a solvent to remove acid gases such as CO2, H2S, COS and Mercaptan (Mokhatab and Poe 2012). The chemical formula (DEPG) is [CH3-O-(CH2-CH2-O)n-CH3] where n can be 3 to 10 (McJAnnett 2012). This solvent separates H2S and CO2 from inlet sour gas by weak intermolecular bonds. DEPG is neither toxic nor corrosive and due to its high thermal stability, its operating temperature ranges from −18 to 175 °C (Urech et al. 2014; Carpenter and Long 2017; Guo et al. 2012). Figure 2 provides a very general schematic of the SELEXOL process consisted of an Adsorption Tower, several Flash Tanks at different operating pressures, and a recycled gas from the top of the first flash tank (Im et al. 2015). The SELEXOL process was first used in 1969 to selectively remove H2S from natural gas at the IINEGA plant in West Germany. In 2001, DOW Chemical Company bought the license of the gas process, and today the process is licensed by several engineering companies such as UOP. Approximately 55 units of SELEXOL have been successfully launched for steam reforming, partial oxidation, natural gas and waste gases (Biasca et al. 1987). DEPG is relatively capable of separating acid gases up to the standard specification of pipelines, but it also solves high percentages of C3+ hydrocarbons (Ghanbarabadi and Khoshandam 2015). Therefore, this solvent is mainly used for the removal of acid gases in the processes for Synthesis Gas Production (Shehzad, Bashir, and Sethupathi 2016), Combustion Process in Power Plants (Roussanaly, Anantharaman, and Lindqvist 2014), and Coal Gas Productions.