Low-Cost Methods for Sweetening Gas Condensates for Small Atmospheric Distillation Units: A Case Study of South Pars Gas Condensates
Collecting & Editing by: Meysam Azizi Kouchaksaraei, [email protected], Abadan Institute of Technology, Petroleum University of Technology, Abadan, Iran
Abstract
Sweetening of gas condensates, especially the naphtha fraction, is essential in modern refineries to achieve product quality standards, prevent equipment corrosion, and comply with environmental regulations. This study examines the specific challenges of naphtha sweetening in small units with limited budgets, focusing on an atmospheric distillation unit with a capacity of 1200 tons per day of South Pars gas condensates. The aim of this research is to identify and recommend the most cost-effective methods for sulfur removal for this specific scenario, with a particular emphasis on chemical sweetening methods. Common sweetening methods, including chemical absorption (amine treating), physical absorption, adsorption, oxidation, and caustic treating, were reviewed. Considering the budget and capacity limitations of the unit in question, adsorption methods with metal oxides, oxidative sweetening with air and catalyst, and regenerative caustic treating (such as the Merox process) were identified as the most suitable options. Taking into account the characteristics of South Pars gas condensates, particularly its high mercaptan content, indicates that methods specifically targeting mercaptans will be highly effective. Finally, recommendations tailored to different budget levels and sulfur removal needs are provided, and the importance of conducting more detailed feasibility studies and complying with safety and environmental regulations is emphasized.
Keywords: Gas condensate sweetening, Naphtha, Limited budget, South Pars gas condensates, Mercaptan, Adsorption, Oxidation, Caustic treating
Introduction
In the oil refining industry, the sweetening of gas condensates is a vital process carried out to remove sulfur compounds, particularly hydrogen sulfide (H2S) and mercaptans. The presence of these compounds in petroleum products can lead to equipment corrosion, reduced product quality, and the release of environmental pollutants. The naphtha fraction, a valuable product obtained from the atmospheric distillation of gas condensates, is primarily used as feedstock in gasoline production and the petrochemical industry. Therefore, the sweetening of this fraction is of particular importance.
This report examines the challenges faced by small refineries with limited budgets in sweetening the naphtha fraction derived from gas condensates. The specific case is an atmospheric distillation unit with a capacity of 1200 tons per day of South Pars gas condensates, seeking a cost-effective and efficient method to reduce the level of sulfur compounds in the naphtha fraction. The relatively small scale of this unit limits the use of complex and expensive technologies.
The main objective of this research is to identify and propose the most cost-effective chemical sweetening methods for this particular unit. To this end, the following objectives are pursued:
1. Identify common sweetening methods used in small refineries.
2. Analyze the advantages and disadvantages of each method in terms of initial cost, operating cost, complexity, and the extent of sulfur compound removal.
3. Specifically examine chemical sweetening methods such as the use of adsorbents and oxidizers for units with limited budgets.
4. Consider the characteristics of South Pars gas condensates.
5. Review simple and low-cost pretreatment options.
6. Provide a list of required chemicals and equipment with preliminary cost estimates (based on available data and industry knowledge).
7. Discuss the safety and environmental considerations related to each method.
8. Review relevant case studies of low-cost sweetening in similar units.
Common Sweetening Methods Applicable in Small Refineries
Various technologies exist for gas sweetening that can be adapted for smaller processing capacities. The following outlines some of the most common methods:
Chemical Absorption (Amine Treating)
This method uses amine solutions (such as MEA, DEA, MDEA) for chemical reaction and removal of acid gases (H2S, CO2) and some sulfur compounds from gas streams. It can also be used for liquid hydrocarbons like LPG. The overall process involves absorption in a contact tower and amine regeneration in a regenerator tower. Amine treating is a common method in refineries for removing H2S and CO2 and can be cost-effective in the long term due to the ability to regenerate the amine. Amine systems offer flexibility, low cost, and high reliability for sulfur removal, especially at low pressures. However, the initial capital investment for a complete amine unit may be high for a small refinery with a very limited budget.
Physical Absorption
This method uses physical solvents (such as sulfolane, selexol) to dissolve acid gases based on their partial pressure and is more effective at higher pressures. Regeneration is usually done by reducing pressure or increasing temperature. Physical absorption is not economical at lower partial pressures. Given the small scale and potentially lower operating pressures of the unit in question, physical absorption may not be the most economically competitive option compared to chemical methods or adsorbents.
Adsorption
In this method, solid materials (adsorbents) are used to adsorb sulfur compounds through physical or chemical bonding. Examples include activated carbon, molecular sieves , and metal oxides. This method can be non-regenerative (guard beds) or regenerative. Various adsorbents exist for sulfur removal, including AxTrap™ and SULFURTRAP®, which are effective in removing H2S and mercaptans. Some sources state that PURASPEC adsorbents are the “most cost-effective solution in terms of cost per kilogram of sulfur removed”. Adsorption, especially using non-regenerative adsorbents, can be a suitable low-cost option for a small refinery due to its simplicity and potentially lower initial capital cost. The adsorbent capacity and the frequency of its replacement will be key factors in the operating cost.
Oxidation (Oxidative Desulfurization – ODS)
This method involves oxidizing sulfur compounds to sulfoxides and sulfones, which have higher boiling points and can be separated by distillation or extraction. Common oxidants include hydrogen peroxide and air. The process can be catalytic or non-catalytic. ODS has been suggested as a potentially cost-effective method, especially when using atmospheric oxygen as the oxidant. This method is carried out at atmospheric pressure and temperatures up to 100°C, which potentially simplifies equipment requirements. ODS appears promising for a small refinery with a limited budget, especially for removing mercaptans, which are abundant in South Pars gas condensates.
Membrane Separation
This method uses semi-permeable membranes to selectively separate acid gases (H2S, CO2) from the hydrocarbon stream. The efficiency of this method depends on the membrane properties and operating conditions (pressure, temperature). Membrane technology offers simplicity and modularity, making it suitable for small-scale applications. Membrane systems are lightweight, have no moving parts, require little supporting equipment, and do not need regeneration. However, the potential for higher costs compared to other methods may make it less suitable for a very budget-limited operation.
Caustic Treating
In this method, alkaline solutions (such as sodium hydroxide) are used to react with acidic sulfur compounds like H2S and mercaptans. This can be a simple once-through process or involve caustic regeneration. Caustic treating is particularly economical for removing mercaptans in naphtha and gas condensate streams. Some sources state that caustic treating remains the most cost-effective process for mercaptan removal. Regenerative caustic treating, such as the Merox process, can further enhance its economic viability.
In-Depth Analysis of Chemical Sweetening Methods for Budget-Limited Units
Considering the budget and capacity limitations of the unit in question, the following chemical sweetening methods are examined in more detail as potentially low-cost options:
Adsorption
Adsorption involves the physical or chemical attraction of sulfur compounds to the surface of an adsorbent material. Types of adsorbents relevant to gas condensate sweetening include:
• Activated carbon: Effective for removing various impurities, including some sulfur compounds, and is relatively low in cost.
• Metal oxides (e.g., zinc oxide, copper oxide): Specifically designed for removing H2S and mercaptans. Examples include AxTrap™ (Axens) and PURASPEC (Johnson Matthey). Metal oxide-based adsorbents appear very suitable for the user’s needs due to their targeted removal of sulfur compounds and the availability of non-regenerative options.
• Molecular sieves: Primarily used for dehydration but can also adsorb H2S and CO2, although they require regeneration.
Adsorption offers advantages for small units such as simpler operation and potentially lower initial capital cost. However, limited adsorption capacity and the need for periodic replacement or regeneration of the adsorbent are its drawbacks. The feasibility and cost-effectiveness of this method for a unit with a capacity of 1200 tons per day depend on the amount of sulfur present in the naphtha.
Oxidation (Oxidative Desulfurization – ODS)
The principles of ODS involve the oxidation of sulfur compounds, particularly mercaptans in South Pars gas condensates , to less harmful disulfides or to sulfoxides/sulfones for removal. Common oxidants include:
• Air/oxygen: Readily available and low-cost, often used in the presence of a catalyst (such as phthalocyanine) for mercaptan sweetening. Mercaptan sweetening with air appears to be a very cost-effective option for South Pars gas condensates.
• Hydrogen peroxide (H2O2): Can oxidize a wider range of sulfur compounds and, when combined with a separation step, can achieve lower total sulfur levels.
ODS can operate under relatively mild conditions for small units and has a potentially lower initial capital cost. However, handling oxidizing agents requires safety measures, and it may produce oxidized byproducts.
Caustic Treating
The reaction of sodium hydroxide (NaOH) with H2S and mercaptans results in the formation of sodium sulfide and sodium mercaptides. Different approaches include:
• Once-through caustic wash: Simple but produces spent caustic that requires disposal and can be costly.
• Regenerative caustic treating (Merox process): Involves re-oxidizing the extracted mercaptides to disulfides using air and a catalyst, allowing for the reuse of the caustic. The Merox process appears to be an established and potentially cost-effective solution for mercaptan removal from gas condensates.
Caustic treating is effective for removing H2S and mercaptans, and regenerative options reduce operating costs. However, regenerative systems have higher initial capital costs.
Considerations for South Pars Gas Condensates
South Pars gas condensates have the following characteristics:
• Paraffinic crude oil with a relatively low total sulfur content (around 0.26 weight percent).
• High mercaptan content (mercaptan sulfur around 1865 micrograms per gram).
• Low nitrogen content.
• Density of about 0.72-0.74 grams per cubic centimeter.
The high mercaptan content suggests that sweetening methods specifically targeting mercaptans, such as oxidation with air and a catalyst or caustic treating (Merox), will be very effective for this feedstock. The relatively low total sulfur content may make simpler sweetening methods sufficient without the need for deep desulfurization. For oxidation with air, a phthalocyanine catalyst is typically used. For Merox, a specific organometallic catalyst is required. The choice of adsorbent depends on the specific sulfur compounds that need to be removed.
Low-Cost Pretreatment Options for Sulfur Reduction
Pretreatment can reduce the sulfur load on the main sweetening unit, potentially improving its efficiency and reducing operating costs. Simple and inexpensive methods include:
• Guard beds with non-regenerative adsorbents: Small fixed beds containing an adsorbent (such as activated carbon, zinc oxide) for the selective removal of H2S or other highly reactive sulfur compounds before the main sweetening stage.
• Oxidation with air in a simple reactor: Can partially oxidize some mercaptans to disulfides, reducing the load on the subsequent caustic treating or adsorption unit.
• Extraction with a low-cost solvent: Some sulfur compounds may be preferentially soluble in an inexpensive and readily available solvent, allowing for a simple liquid-liquid extraction step. Extraction with a strong alkaline liquid (NaOH solution) is a common method.
Pretreatment can lead to reduced chemical consumption, increased efficiency of the main sweetening unit, and lower operating costs.
Required Equipment and Chemicals and Preliminary Cost Estimates
Specific costs will vary depending on the vendor, scale, and customization. The following table provides a preliminary cost comparison of potential sweetening methods for a naphtha unit with a capacity of 1200 tons per day:
Sweetening Method Initial Capital Cost Operating Cost Complexity Main Sulfur Target Potential Suitability for 1200 Tons/Day Unit
Adsorption (Non-regenerative Adsorbent) Low Medium Low Mercaptans, H2S High
Mercaptan Sweetening with Air Oxidation & Catalyst Low Low Low Mercaptans High
Desulfurization with Hydrogen Peroxide Oxidation Medium Medium Medium Total Sulfur Medium
Caustic Treating (Merox – Regenerative) Medium Low Medium Mercaptans High
Safety and Environmental Aspects
Each sweetening method has its own specific safety and environmental considerations. For example, handling spent adsorbent materials in adsorption and oxidizing agents in oxidation requires safety precautions. Caustic treating can also lead to wastewater that needs to be managed. Compliance with local environmental regulations regarding emissions and waste disposal is crucial for all methods.
Case Studies on Low-Cost Sweetening in Similar Units
Case studies indicate that demercaptanization units are of high importance in South Pars refineries. Various processes such as amine treating and the Merox process have been used in this region. Merichem’s MERICAT™ technology is also highlighted as an effective process for mercaptan sweetening in gas condensates and naphtha using caustic/catalyst/air. Additionally, a feasibility study of a low-capacity gas sweetening unit in Iran suggests that research into optimizing existing sweetening technologies can lead to cost reduction.
Conclusion and Recommendations
Based on the analysis, several low-cost sweetening methods appear promising for the unit in question. The high mercaptan content in South Pars gas condensates makes methods that target these compounds particularly relevant.
Tailored Recommendations:
• For immediate budget constraints and a primary focus on mercaptan reduction: Sweetening with air oxidation using an alkaline solution and a phthalocyanine catalyst appears to be the most cost-effective option.
• For a slightly higher budget and the need for deeper sulfur removal (desulfurization): Oxidation with hydrogen peroxide followed by a simple separation step (such as distillation, using existing refinery equipment) could be considered.
• For a more established and potentially scalable solution, with a slightly higher initial investment: A regenerative caustic treating process like Merox, specifically designed for mercaptan removal from gas condensates, offers a robust option with lower long-term operating costs.
• As a simple pretreatment step: Using a small guard bed with a metal oxide adsorbent or extraction with a low-cost alkaline solution could be explored.
It is recommended to conduct a more detailed feasibility study, including pilot tests if possible, to evaluate the performance and cost-effectiveness of the chosen method under the specific operating conditions of the 1200 tons per day unit. Obtaining quotes from vendors for specific equipment and chemicals is also essential for accurate cost estimation. Finally, considering safety and environmental regulations in the final selection and implementation of the sweetening method is of utmost importance.
Refrences
South Pars Gas Complex. (n.d.). South Pars Gas Condensate Storage Facilities. https://www.pogc.ir/Default.aspx?tabid=134 Gas Sweetening. (n.d.). Axens. https://www.axens.net/markets/natural-gas/gas-sweetening Towler, G. P., Shethna, H. K., Cole, B., & Hajdik, B. (1997). Improved Absorber-Stripper Technology for Gas Sweetening to Ultra-Low H2S Concentrations. Gas Processors Association.(https://www.bre.com/PDF/Improved-Absorber-Stripper-Technology-for-Gas-Sweetening-to-Ultra-Low-H2S-Concentrations.pdf) Adsorbents. (n.d.). Axens. https://www.axens.net/solutions/catalysts-adsorbents-grading-supply/sulfur-removal-adsorbents-oil-gas-petrochemicals Khajehpour, M., Amidpour, M., & Sadeghipour, S. (2012). Development of South Pars gas field phase 14, onshore facilities. Petroleum & Coal, 54(4), 333-342. https://pomc.ir/en/portfolio/development-of-south-pars-gas-field-phase-14-onshore-facilities/ Hosseini, G. A. (2024, May 27). South Pars Will Reduce Burning Gases by 1.2 bcm Annually. SHANA (Tehran).(https://en.shana.ir/news/649191/South-Pars-Complex-Producing-613-mcm-d-of-Gas) Hatibi, R. R. (n.d.). Gas Sweetening Processes. SlideShare. https://www.slideshare.net/slideshow/gas-sweetening-processes/77152253 Sweetn G®. (n.d.). Axens. https://www.axens.net/expertise/oil-refining/fcc-naphtha-sweetening Natural gas sweetening. (n.d.). Gazpack. https://gazpack.nl/en/natural-gas-sweetening/ AxTrap™. (n.d.). Axens. https://www.axens.net/markets/natural-gas/gas-sweetening Membrane Gas Sweetening Process. (2019, June 11). GENERON. https://www.generon.com/amine-gas-sweetening-process/ Oxidation (Sweetening). (n.d.). ScienceDirect. https://www.sciencedirect.com/topics/engineering/sweetening PURASPEC™ Absorbents. (n.d.). Johnson Matthey. https://matthey.com/products-and-markets/chemicals/sulphur-removal-absorbents Southern Pars 1 Condensate. (2017, March 15). National Iranian Oil Company.((https://www.nioc-intl.ir/NEW-PDF/Condensate/SouthPars.pdf)) Characteristic of sulfur containing compounds in South Pars condensate and its corrosion behavior. (2016). ResearchGate.(https://www.researchgate.net/publication/296094111_Characteristic_of_sulfur_containing_compounds_in_South_Pars_condensate_and_its_corrosion_behavior) Optimizing Natural Gas Sweetening in South Pars Refineries. (n.d.). ChemEngProject. https://www.chemengproj.ir/en/portfolio-item/optimizing-natural-gas-sweetening-in-south-pars-refineries/ Gas Condensate Desulfurization by Oxidation Method in the Presence of Nanoclay and Chitosan Adsorbent: An Experimental Study. (2022). TU Engineering Journal, 10(1), 13-21. https://tuengr.com/V10A/10A13NM.pdf Jonell Systems Revolutionized a Traditionally Complicated and Costly Process of NGL Sweetening. (n.d.). Jonell Systems. https://www.jonellsystems.com/casestudies/jonell-systems-revolutionized-a-traditionally-complicated-and-costly-ngl-sweetening-process/ Jonell Systems Revolutionized a Traditionally Complicated and Costly Process of NGL Sweetening. (n.d.). Jonell Systems. https://www.jonellsystems.com/casestudies/jonell-systems-revolutionized-a-traditionally-complicated-and-costly-ngl-sweetening-process/ South Pars Complex Producing 613 mcm/d of Gas. (2024, May 27). SHANA (Tehran).(https://en.shana.ir/news/649191/South-Pars-Complex-Producing-613-mcm-d-of-Gas) Amine gas treating. (2024, April 11). Wikipedia. https://en.wikipedia.org/wiki/Amine_gas_treating Feasibility study, simulation and…source gas sweetening processes – Part 1: A case study on a low capacity plant in Iran. (2014). Journal of Natural Gas Science and Engineering, 20, 16-22. https://ogst.ifpenergiesnouvelles.fr/articles/ogst/full_html/2021/01/ogst210036/ogst210036.html Sulfolane. (2024, March 23). Wikipedia.((https://en.wikipedia.org/wiki/Sulfolane)) Molecular sieves. (n.d.). PetroWiki.(https://petrowiki.spe.org/Sour_gas_sweetening) AxTrap™ – Sulfur Removal Adsorbents for Oil, Gas & Petrochemicals. (n.d.). Axens. https://www.axens.net/solutions/catalysts-adsorbents-grading-supply/sulfur-removal-adsorbents-oil-gas-petrochemicals PURASPEC™ 1065. (n.d.). Johnson Matthey. https://matthey.com/products-and-markets/chemicals/sulphur-removal-absorbents PURASPEC™ Absorbents. (n.d.). Johnson Matthey. https://matthey.com/products-and-markets/chemicals/sulphur-removal-absorbents Gas Sweetening. (n.d.). CECO Environmental. https://www.cecoenviro.com/products/gas-sweetening/ Gas Sweetening. (n.d.). Axens. https://www.axens.net/markets/natural-gas/gas-sweetening PURASPEC™ Absorbents. (n.d.). Johnson Matthey. https://matthey.com/products-and-markets/chemicals/sulphur-removal-absorbents Gasoline Fraction High-Efficient Sweetening by Gas Condensate Oxidation and Rectification. (2022). Molecules, 27(10), 3017. https://www.mdpi.com/2227-9717/11/10/3017 Membrane Gas Sweetening Process. (2019, June 11). GENERON. https://www.generon.com/amine-gas-sweetening-process/ Caustic Treatment: Design, Integration, and Waste Disposal for Gas Plants. (2021, February 1). Gas Processing News. https://gasprocessingnews.com/articles/2021/02/caustic-treatment-design-integration-and-waste-disposal-for-gas-plants/ Caustic Treating. (n.d.). PetroWiki. https://petrowiki.spe.org/Caustic_treating Gas condensate sweetening. (n.d.). Ahmadullins. https://en.ahmadullins.com/publiclist/mercaptan-removal/gas-condensate-sweetening MERICAT™ | Caustic Sweetening of Mercaptans. (n.d.). Merichem Technologies. https://merichemtech.com/removing-mercaptans-with-mericat/ Oxidative desulfurization process for gas condensate using a mixture of hydrogen peroxide and formic acid have been investigated. (2022). TU Engineering Journal, 10(1), 13-21. https://tuengr.com/V10A/10A13NM.pdf Sulfur Removal. (n.d.). Topsoe. https://www.topsoe.com/processes/sulfur-removal Merox Process. (n.d.). Honeywell UOP. https://uop.honeywell.com/en/technologies/refining/treatment/merox-process MERICAT™ II / J | Heavy Mercaptan Sweetening. (n.d.). Merichem Technologies. https://merichemtech.com/heavy-mercaptan-sweetening-with-mericat-j-and-mericat-ii/ Ghaedian, A. R., & Mohammadi, M. (2012). Demercaptanization of Iranian stabilized gas condensate (South Pars gas field) using DMC process in a pilot plant. Petroleum & Coal, 54(4), 343-352. https://www.vurup.sk/wp-content/uploads/dlm_uploads/2017/07/pc_4_2012_ghaedian_186_0.pdf Merox Process. (n.d.). Honeywell UOP. https://uop.honeywell.com/en/technologies/refining/treatment/merox-process DMC Unit Project – South Pars Phases 2 and 3. (n.d.). Artin Azma Mehr. https://artinazma.net/en/portfolio/dmc-unit-project-south-pars-phases-2-and-3/ South Pars/North Dome Gas-Condensate field. (2024, April 10). Wikipedia.((https://en.wikipedia.org/wiki/South_Pars/North_Dome_Gas-Condensate_field)) Demercaptanization Unit of South Pars Refinery Phases 2, 3 Online. (2022, August 29). SHANA (Tehran).(https://en.shana.ir/news/461297/Demercaptanization-Unit-of-South-Pars-Refinery-Phases-2-3-Online) MERICAT™ II / J | Heavy Mercaptan Sweetening. (n.d.). Merichem Technologies. https://merichemtech.com/heavy-mercaptan-sweetening-with-mericat-j-and-mericat-ii/ South Pars/North Dome Gas-Condensate field. (2024, April 10). Wikipedia.(https://en.wikipedia.org/wiki/South_Pars/North_Dome_Gas-Condensate_field) Simulation and Optimization of Demercaptanization of Propane and Butane in South Pars Gas Refineries. (2019). Journal of Applied Research of Chemical – Polymer Engineering, 3(2), 3-14. https://arcpe.modares.ac.ir/article-38-28933-en.html Southern Pars 1 Condensate. (2017, March 15). National Iranian Oil Company.(https://www.nioc-intl.ir/NEW-PDF/Condensate/SouthPars.pdf) Gas Condensate Desulfurization by Oxidation Method in the Presence of Nanoclay and Chitosan Adsorbent: An Experimental Study. (2022). TU Engineering Journal, 10(1), 13-21. https://tuengr.com/V10A/10A13NM.pdf Caustic Treatment: Design, Integration, and Waste Disposal for Gas Plants. (2021, February 1). Gas Processing News. https://gasprocessingnews.com/articles/2021/02/caustic-treatment-design-integration-and-waste-disposal-for-gas-plants/ Natural gas sweetening. (n.d.). Wikipedia. https://en.wikipedia.org/wiki/Gas_sweetening 80,000 b/d Growth in Iran Gas Condensate Sweetening Capacity. (2022, August 29). SHANA (Tehran).(https://en.shana.ir/news/461308/80-000-b-d-Growth-in-Iran-Gas-Condensate-Sweetening-Capacity) Simulation and Optimization of Demercaptanization of Propane and Butane in South Pars Gas Refineries. (2019). Journal of Applied Research of Chemical – Polymer Engineering, 3(2), 3-14. https://arcpe.modares.ac.ir/article-38-28933-en.html South Pars/North Dome Gas-Condensate field. (2024, April 10). Wikipedia.(https://en.wikipedia.org/wiki/South_Pars/North_Dome_Gas-Condensate_field) MERICAT™ | Caustic Sweetening of Mercaptans. (n.d.). Merichem Technologies. https://merichemtech.com/removing-mercaptans-with-mericat/ Simulation and Optimization of Demercaptanization of Propane and Butane in South Pars Gas Refineries. (2019). Journal of Applied Research of Chemical – Polymer Engineering, 3(2), 3-14. https://arcpe.modares.ac.ir/article-38-28933-en.html Gas Condensate Desulfurization by Oxidation Method in the Presence of Nanoclay and Chitosan Adsorbent: An Experimental Study. (2022). TU Engineering Journal, 10(1), 13-21. https://tuengr.com/V10A/10A13NM.pdf Gas Condensate Desulfurization by Oxidation Method in the Presence of Nanoclay and Chitosan Adsorbent: An Experimental Study. (2022). TU Engineering Journal, 10(1), 13-21. https://tuengr.com/V10A/10A13NM.pdf Jonell Systems Revolutionized a Traditionally Complicated and Costly Process of NGL Sweetening. (n.d.). Jonell Systems. https://www.jonellsystems.com/casestudies/jonell-systems-revolutionized-a-traditionally-complicated-and-costly-ngl-sweetening-process/ PURASPEC™ Absorbents. (n.d.). Johnson Matthey. https://matthey.com/products-and-markets/chemicals/sulphur-removal-absorbents