Grantee Research Project Results

2021 Progress Report: Single-Stage Process for Biogas Purification

EPA Grant Number: SU840141
Title: Single-Stage Process for Biogas Purification
Investigators: Lashaki, Masoud Jahandar , Meeroff, Daniel , Bloetscher, Fred , Ayub, Ali , Ahsan, Sara , Li, Diego , Thomas, Ryan , Lam, Dung , Deshommes, Julie , McFadden, Megan , Owen, Tyler
Current Investigators: Lashaki, Masoud Jahandar , Meeroff, Daniel , Bloetscher, Fred
Institution: Florida Atlantic University - Boca Raton
EPA Project Officer: Spatz, Kyle
Phase: I
Project Period: December 1, 2020 through November 30, 2021 (Extended to June 30, 2022)
Project Period Covered by this Report: December 1, 2020 through November 30,2021
Project Amount: $25,000
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2020) RFA Text |  Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Air Quality

Objective:

Landfill gas is a natural by-product of the anaerobic decomposition of organic waste in landfills. Similarly, biogas may be produced in farming communities or commercial facilities by anaerobic digestion of agricultural and municipal organic waste or dedicated crops. Biogas and landfill gas have similar composition and primarily consist of 50%+ methane and 30%+ carbon dioxide in addition to ubiquitous species such as water vapor and hydrogen sulfide. If not properly managed, the decomposition of organic waste on farms and in municipal landfills generate uncontrolled emissions of hydrogen sulfide, methane, and carbon dioxide, the last two being potent greenhouse gases. In addition to hydrogen sulfide being a well-known air pollutant with adverse human health impacts, it causes severe odor issues in the communities adjacent to landfills and farms. To minimize such adverse environmental and societal impacts, biogas and landfill gas can be collected and purified to produce biomethane, also known as renewable natural gas, which can be injected into natural gas pipelines for use as a carbon-neutral fuel. Although landfill gas and biogas are among the most rapidly growing biofuels in the United States, their upgrading is lagging their collection/production because commercialized purification technologies are costly and often require multiple separate units for desulfurization, drying, and compression or cooling of the feed gas before carbon dioxide removal. In “Phase 1”, a cyclic adsorption-desorption process was proposed to integrate and intensify the upgrading process. This process consists of an adsorption step in which all impurities, namely carbon dioxide, water vapor, and hydrogen sulfide, are simultaneously removed from biogas and landfill gas to produce high-purity biomethane. Once saturated with the impurities, the adsorbents are regenerated at elevated temperatures in the presence of air to recover their adsorption affinity for the subsequent cycle. The overarching objective of “Phase 1” was to develop made-to-order adsorbent materials that fulfil the cost, performance, and stability requirements of this process. Explicitly, the adsorbents should be (i) capable of simultaneous and reversible removal of carbon dioxide, water vapor, and hydrogen sulfide, while letting methane through; (ii) compatible with ultra-rapid adsorption-desorption cycling to maximize biomethane production; (iii) stable in the presence of hot air; and (iv) inexpensive. In “Phase 1”, it was theorized that amine-functionalized silicas, also known as aminosilicas, can be specifically engineered for use in the described application. To meet the cost, performance, and stability attributes, the following aminosilica synthesis conditions were considered: (i) using a commercial mesoporous silica as support to minimize materials development cost; (ii) completing amine functionalization of silica via covalent bonding instead of physical mixing to improve adsorption performance and long-term stability; and (iii) amine functionalization was limited to isolated primary amines, which demonstrate the highest air oxidation resistance along with the highest affinity toward the target impurities. “Phase 1” initially consisted of eight tasks, namely: (i) synthesizing aminosilicas with varying chemical properties; (ii) evaluating the adsorptive properties of all aminosilicas in terms of carbon dioxide uptake and adsorption kinetics to develop a shortlist of best-performing materials; (iii) assessing the thermal and oxidative stability of the shortlisted aminosilicas to determine a final aminosilica candidate with best adsorption performance and stability attributes; (iv) investigating the performance of the final aminosilica through column-breakthrough experiment in the presence of different dry and humid gas streams containing carbon dioxide and hydrogen sulfide; (v) converting the final candidate to pellets for easier testing at larger scale; (vi) arranging the field campaign logistics with the partnering landfill facilities in West Palm Beach, FL, and Orlando, FL; (vii) field testing of the best-performing aminosilica using real landfill gas; and (viii) compiling and submittal of a final report and “Phase 2” application. Tasks (vi) and (vii) must be adapted owing to the travel restrictions associated with COVID-19 pandemic. Thus, the field testing of the final candidate will be completed in lab instead of field, using real landfill gas samples provided by the partners.

Progress Summary:

Over 100 aminosilicas with different properties were prepared via manipulation of synthesis conditions, namely particle size of the silica support, and the amounts of water and amine added during synthesis. All aminosilicas were analyzed in terms of amine content. Overall, higher amine loadings were observed on aminosilicas prepared in the presence of higher water and amine amounts. All aminosilicas were also screened in terms of adsorption capacity in the presence of dry carbon dioxide. Initially, carbon dioxide uptakes increased as amine contents increased. However, at high amine loadings, carbon dioxide uptakes either plateaued or dropped owing to amine accessibility issues in the structure of aminosilica. Upon conclusion of performance screening, 16 aminosilicas with equilibrium carbon dioxide uptakes greater than 6 wt.% were identified. These samples were further evaluated in terms of carbon dioxide adsorption kinetics in the first five minutes of the adsorption step. It should be noted that adsorption kinetics is an important industrial measure to demonstrate how fast the carbon dioxide uptake occurs. A faster kinetics is beneficial since it shortens the duration of the adsorption cycle, purifying higher volumes of landfill gas and biogas over a given period. Three best-performing aminosilicas with the fastest adsorption kinetics were selected for further evaluation in terms of thermal and oxidation stability in the presence of nitrogen and air, respectively. Two cyclic adsorption-desorption experiments (100 cycles each) were completed for each aminosilica. All three aminosilicas were thermally stable throughout the cycling, as demonstrated by negligible changes in their carbon dioxide uptakes (less than 2%). This is consistent with previous reports that covalently bonded amines are stable in the presence of inert gases at temperatures below 150 °C. Similar results were observed for oxidative stability and all three aminosilicas experienced negligible carbon dioxide uptake deterioration (less than 1%). This finding is consistent with previous findings that identified isolated primary amines as the most stable amine species in the presence of air at elevated temperatures. Nonetheless, this finding is significant because all previous reports on the oxidative stability of amines used air for cooling and/or drying aminosilicas, not as purge gas in a cyclic adsorption-desorption process. Moreover, the finding indicates that the aminosilicas can be used for biogas and landfill gas purification in remote areas (e.g. farms) where access to other purge gases such as steam or nitrogen is expensive and/or impractical. Finally, the use of air as purge gas would drastically reduce the operational costs of the proposed process, increasing its long-term viability. Based on the above results, one aminosilica with the best overall performance in terms of amine content, carbon dioxide uptake and adsorption kinetics, thermal stability, and oxidative stability, was chosen as the final candidate for all subsequent experiments. Whereas carbon dioxide uptake screening is a useful tool to study equilibrium adsorption capacity and adsorption kinetics, it provides little information about the real-world performance of adsorbent materials. Industrial gas purification applications involve larger amounts of adsorbent materials placed in an adsorption column through which the feed gas passes. The adsorption step is typically stopped as soon as traces of target impurities appear at the effluent of the column (i.e., breaking through the bed), not allowing the complete saturation of the adsorbent material. To investigate the performance of the final aminosilica under more realistic conditions, column-breakthrough experiments were completed after designing and building the required experimental setup. The setup consisted of mass flow controllers, three-way valves, stainless steel tubes and fittings, high-purity and specialty gas cylinders, gas bubbler, heating tape, and thermocouple. A solid-state relay was used to control the power application to the heating tape. A data acquisition and control system, consisted of LabVIEW software and a data logger equipped with analog input and output modules, was interfaced to the thermocouple and the solid-state relay. Temperature was measured using the thermocouple and a proportional-integral-derivative algorithm was used to control the power applied to achieve desired temperatures. Different gas analyzers, including relative humidity meter, carbon dioxide sensor, and photo-ionization detector, were used to monitor and record the concentrations of the target compounds. Overall, the results indicated that the final aminosilica candidate can effectively and simultaneously remove carbon dioxide, water vapor, and hydrogen sulfide, integrating the biogas and landfill gas purification process into one single stage. Going forward, the focus will be on the remaining “Phase 1” activities, particularly the testing of the final aminosilica candidate with real landfill gas samples provided by the partnering landfill facilities.

Future Activities:

The objective of “Phase 1” research was to purify biogas and landfill gas in one single step using FAU’s made-to-order amine-functionalized silica materials. The results discussed above indicated that aminosilicas can effectively and concurrently remove all target impurities, namely water vapor, carbon dioxide, and hydrogen sulfide. The environmental benefits from this research are five-fold. If not properly managed, landfill gas and decomposed waste on farms generate uncontrolled emissions of hydrogen sulfide, carbon dioxide, and methane, the last two being potent greenhouse gases. Also, hydrogen sulfide is a well-known air pollutant with adverse human health impacts. Moreover, hydrogen sulfide can cause severe odor issues in nearby communities. Once biomethane is produced, it replaces coal and oil, both of which not only emit more carbon dioxide per unit of power produced, but also generate such air pollutants as sulfur oxides, mercury, particulates, and hydrocarbons. Global biogas market was estimated at $25.5 billion in 2019 and is projected to exceed $31 billion by 2027, necessitating more active participation from the United States in this emerging market. Based on March 2021 data from the EPA, there were 550 operational landfill gas energy projects in the United States, with an additional 480 “candidate” landfills where landfill gas can be turned to energy in a cost-effective manner. This indicates an immense potential for the proposed research theme to make lasting impacts across the United States, namely creating well-paying jobs, improving air quality, reducing carbon footprint and greenhouse gas emissions, and providing the green energy we all aspire to. On a broader front, this research provided valuable training opportunities for female, Black and Hispanic students at Florida Atlantic University, which is a Hispanic-Serving Institution. Over the course of “Phase 1”, nine students were trained through this multidisciplinary research program, which crosses the boundaries of materials science, physical chemistry, chemical engineering, and environmental engineering. Such broad, multifaceted training opportunities foster creativity and build bridges between disciplines that can prove invaluable in innovation-driven job markets. Moreover, the Principal Investigator has incorporated this project into multiple educational activities, namely (i) an undergraduate course, entitled Introduction to Pollution Prevention and Sustainability; (ii) a pollution prevention lecture series geared towards adult learners who are curious and passionate about learning but do not want to deal with the stress of grades/tests; and (iii) the informal STEM learning initiative for the public, which is a virtual forum at Florida Atlantic University’s College of Engineering and Computer Science. 

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this project

Supplemental Keywords:

green chemistry; treatment and emission control technologies; waste to energy; chemicals; toxics; clean technologies; sustainable development; global climate; southeast; Florida; FL; Atlantic coast; EPA Region 4 

Progress and Final Reports:

Original Abstract

Final Report

P3 Phase II:

Single-Stage Process for Biogas Purification  | 2023 Progress Report  | 2024 Progress Report