Grantee Research Project Results

Final Report: Single-Stage Process for Biogas Purification

EPA Grant Number: SV840418
Title: Single-Stage Process for Biogas Purification
Investigators:
Institution:
EPA Project Officer:
Phase: II
Project Period: November 1, 2022 through May 9, 2025
Project Amount: $100,000
RFA: 17th Annual P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2022) Recipients Lists
Research Category: P3 Awards

Objective:

The overarching goal of this research is to develop an alternative upgrading technique capable of integrating (i.e., reducing the number of treatment units) and intensifying (i.e., decreasing power consumption) the purification process.

Summary/Accomplishments (Outputs/Outcomes):

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 compositions and primarily consist of 50%+ methane and 30%+ carbon dioxide in addition to ubiquitous species such as water vapor, hydrogen sulfide, and siloxanes. If not properly managed, the decomposition of organic waste on farms and in municipal landfills generates 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 health 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 as a carbon-neutral fuel.

In “Phase I”, a cyclic adsorption-desorption process was proposed to integrate and intensify the upgrading process. The overarching objective of “Phase I” was to develop made-to-order amine-modified silica materials (i.e., aminosilicas) that fulfill the cost, performance, and stability requirements of this process. In “Phase I”, over 100 aminosilicas with different properties were prepared via manipulation of synthesis conditions. All aminosilicas were analyzed in terms of amine content and adsorption capacity based on which 16 aminosilicas were selected for further analysis in terms of adsorption kinetics. Three performant aminosilicas with the fastest adsorption kinetics were selected for further evaluation in terms of thermal and oxidation stability throughout 100 successive adsorption-desorption experiments, based on which one aminosilica with the best overall performance was chosen as the final candidate. This material was assessed through column-breakthrough experiments, achieving effective and simultaneous removal of carbon dioxide, water vapor, and hydrogen sulfide.

The “Phase II” project pursued further improvements in the adsorption performance and long-term stability of the final aminosilica candidate. The “Phase II” project consisted of the following activities: (i) improving the oxidation stability of aminosilica (Task 1), (ii) studying the removal of other biogas and landfill gas impurities such as siloxanes (Task 2), and (iii) assessing the long-term stability of aminosilica during cycling (Task 3). In Task 1 of “Phase II”, the final candidate from “Phase I” underwent further modifications in the support material including acid etching to remove metal impurities and addition of aluminum to improve its oxidation stability. The results showed a mix of improvement and deterioration in the oxidative stability of the materials. Whereas the former alteration caused marginal deterioration, the latter one slightly improved oxidation stability. In Task 2, the aminosilica successfully captured different siloxanes such as trimethylsilanol, octamethyl cyclotetrasiloxane, and decamethyl cyclopentasiloxane, from air. Whereas regeneration at 150 °C in nitrogen gas achieved complete removal of the adsorbed trimethylsilanol and octamethyl cyclotetrasiloxane, it failed to fully remove the adsorbed decamethyl cyclopentasiloxane due to its relatively high boiling point of 210 °C. It should be noted that using a higher regeneration temperature was not investigated due to potential degradation of the aminosilica. In Task 3, the final candidate material underwent 100 successive ultra-rapid adsorption-desorption cycles, maintaining 100% of its carbon dioxide adsorption capacity. Overall, the results suggested that aminosilicas can integrate landfill gas upgrading by separating multiple impurities in one step. Moreover, the aminosilica maintained its performance over many successive adsorption-desorption cycles, potentially reducing the purification cost. Finally, aminosilicas achieved effective removal of siloxanes; however, incomplete regeneration indicated that pre-filtration of siloxanes is needed to preserve the aminosilica cyclic performance in terms of carbon dioxide, water vapor, and hydrogen sulfide capture.

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

Relevant Websites:

Air Emissions Characterization and Control Lab Exit

Progress and Final Reports:

Original Abstract

2023 Progress Report

2024 Progress Report

P3 Phase I:

Single-Stage Process for Biogas Purification  | 2021 Progress Report  | Final Report