This blog post provides a review of the different molecules and biomolecules in energy and green energy processes.  I describe two opportunities that use novel autotrophic microbes for BioPropane Production from biogas.

Growing Interest in BioPropane Production

The growing trend of energy sustainability for reducing climate change increases the interest in novel processes for generating Green Energy including BioPropane.  Current interests focus on wind and solar energy.  However, there is potential in both renewable natural gas (RNG) and biofuels, such as BioPropane.  Renewable Identification Numbers (RINs) can be valuable for green energy.  The Inflation Reduction Act of 2022 includes substantial funding ($369B) for developing technologies for reducing carbon emissions by 40% by 2030.

Autotrophic microbiology may be the last major area of untapped potential for green energy.  Difficulty in culturing autotrophs, such as methanogens, have set back commercialization by decades.  Carbon dioxide (CO2), the source of carbon for autotrophic cell biosynthesis, inhibits growth at elevated concentrations.

Known Versus Predicted Autotrophic Microbes

Most readers with an interest in green energy are familiar with autotrophic methanogens, which are responsible for the production of methane derived from biomass.  Are there other autotrophic microbes of interest for green energy production?

Autotrophic microbes use CO2 as their carbon source for cell growth.  Some also use CO2 as reactant for energy production.  Other autotrophic microbes of general interest include: sulfate reducing bacteria (SRB), homoacetogens, nitrifying bacteria, and anammox.  The SRB and homoacetogens can impact biogas quality (hydrogen sulfide or H2S) and anaerobic digesters (elevated acetic acid).

Key Insight #1

All autotrophic microbes share an unusual growth sensitivity to CO2.  Elevated CO2 concentration inhibits the growth of autotrophic microbes.  A tight band of low CO2 concentration provides optimal growth conditions for autotrophic microbes.

Key Insight #2

Thermodynamic analysis predicts multiple groups of novel autotrophs including Alkanogens and Alcohologens.  This thermodynamic analysis predicted Anammox. It took microbiologists about 10 years to isolate the first Anammox strain, but inhibitory concentration of CO2 was to blame. Isolation of these novel autotrophic microbes will be much faster with the ideal CO2 concentration.

Known Autotrophic Microbes for Green Energy

The methanogens are the only known autotrophic microbe used for Green Energy.  Methanogens use two types of metabolism: CO2 reducing or aceticlastic.  CO2 reducing methanogens use hydrogen (H2) to generate methane, while aceticlastic methanogens split acetic acid into methane and CO2.

Predicted Autotrophic Microbes for BioPropane Production

For BioPropane production, two novel autotrophs convert methane to BioPropane using hydrogen and carbon dioxide, as shown in the table below.

BioPropane Production Opportunities

The addition of bioreactors for Ethanogens and Propanogens could be deployed to convert biogas to BioPropane.  Supplemental hydrogen and carbon dioxide would be required for these bioreactors.

BioPropane Production Using Biogas

There are two opportunities for biopropane production from biogas generated by anaerobic digesters and landfills.

BioPropane and RNG Production Using Biogas and Hydrogen

A two step process converts biogas and hydrogen into bioethane and biopropane.  In this example, I assumed biogas with 50% methane and carbon dioxide.  Biogas processing of the biopropane reactor headspace recovers both BioPropane and RNG.  The green dashed arrows from the bioreactors represent possible recycle of the wasted biomass to the anaerobic digester or landfill.  Recycle of this biomass into the anaerobic digester may cause downstream problems with biosolids.  Aerobic, high temperature, or pH inactivation of these anaerobes may be required to prevent their application to land.

BioPropane using Hydrogen and Carbon Dioxide

The same two step process is used to convert biogas, hydrogen, and carbon dioxide into bioethane and biopropane.  Cryogenic biogas processing of the biopropane reactor headspace recovers Biopropane.  The carrier gas in this system is methane.

Revenue Comparison for BioPropane Using Biogas

The table below compares the revenue potential of BioPropane production using biogas.  I used costs of $0.10/kg CO2 and $1.80/kg H2 and $2.76 D3 RIN credit (December 2022) for both RNG and BioPropane.  I used the City Gate price of $1.00/gallon of BioPropane (May 2023).  The revenue potential for BioPropane production from biogas is very attractive.  This may be an attractive option for biogas producers that are not located near a natural gas pipeline.  Improve the evaluation by including bioreactor and biogas processing costs.

Commercialization Pathway

A three-step commercialization plan exploits these opportunities.  First, isolate and characterize the Ethanogen and Propanogen.  Characterization optimizes the bioreactor size and operating conditions.  Second, a pilot-scale demonstration of the bioreactors using a small anaerobic digester system.  Finally, full-scale demonstration of the bioreactor system.

Additional Information Regarding Novel Autotrophic Microorganisms

I provided a video that describes multiple business opportunities that could impact Agriculture, Environmental Remediation, Water and Wastewater Treatment, Metals Recovery, BioEnergy, and Health markets.

Send Me Your Questions About BioPropane Production

Send me your questions about generating BioPropane from biogas to pete@glixin.com.