Parallel circuits of Direct Ocean Capture of CO2 for Methanol and microalgae production

Another oil refinery in Australia? What about this one...

 

Perplexity.ai prompt:

what fossil fuels can methanol replace

 

I have enough to give a comprehensive, well-cited answer without a formal report given this is a direct factual question.

Methanol can substitute for gasoline, diesel, marine bunker fuel (heavy fuel oil), and to a lesser extent kerosene/jet fuel and natural gas, across transport, shipping, aviation, and industrial heat/power applications.

Road Transport Fuels

Methanol can directly replace or blend with gasoline in spark-ignition engines, since its high octane rating (87-110) and combustion properties are similar enough that both blended fuels (like M15 or M85) and dedicated high-concentration M100 engines have been developed and commercialized, particularly in China for passenger cars and heavy-duty trucks. Studies comparing methanol, ethanol, and butanol blends with gasoline confirm methanol's viability as a gasoline extender or substitute in modern engine designs. Methanol is also used as a feedstock to produce dimethyl ether (DME), which itself functions as a diesel substitute with a high cetane number (>55), efficient combustion, and low particulate emissions, making it a viable pathway for methanol to indirectly displace diesel.pubs.rsc+4

Marine Bunker Fuel (Heavy Fuel Oil)

Shipping is one of the strongest use cases for methanol as a fossil fuel replacement, since it's a liquid at ambient conditions and can be handled with only modest retrofits to existing fuel oil infrastructure — much simpler than switching to LNG, ammonia, or hydrogen. Analyses of the "methanol economy" find shipping to be among the most cost-effective sectors for methanol adoption, and methanol engines exhibit substantially lower greenhouse gas slippage than ammonia or liquefied methane alternatives.iopscience.iop+5

Aviation Fuel (Kerosene/Jet Fuel)

Via the methanol-to-kerosene (MtK) process, methanol can be converted into sustainable aviation fuel (SAF) as a drop-in replacement for petroleum-based jet fuel, without requiring major changes to existing aircraft or airport infrastructure. This pathway is technologically mature (TRL 7+) and the first commercial MtK plant investment has already occurred in the Netherlands, though aviation is projected to be one of the later sectors to convert due to cost and scale constraints.pubs.rsc+1

Natural Gas (for Heat, Power, and Industrial Processes)

Methanol serves as an easier "drop-in" substitute for natural gas/methane in burners, boilers, kilns, cookstoves, and gas turbines than hydrogen, since it doesn't require the specialized storage and pipeline modifications hydrogen does. It can be used for backup power generation and process heat (e.g., in flat glass manufacturing) where direct electrification isn't feasible, filling gaps left by fossil natural gas in hard-to-electrify industrial heat applications.methanol+1

Petrochemical Feedstocks (Naphtha and Crude-Derived Chemicals)

Beyond direct fuel use, methanol can replace fossil-derived naphtha as the feedstock for producing building-block chemicals like olefins and aromatics via methanol-to-olefins (MtO) and methanol-to-aromatics (MtA) processes, which then flow into plastics (polyethylene, polypropylene), solvents, and pharmaceuticals — sectors otherwise dependent on petroleum and natural gas.pubs.rsc+1

Summary Comparison

Given your background in biomass conversion, it's worth noting that the carbon source matters enormously for climate impact: methanol produced from natural gas is currently the cheapest and most common route, but methanol from biomass gasification, biogas upgrading, or captured CO2 combined with green hydrogen ("e-methanol") is what actually displaces net fossil carbon rather than just fossil fuel use. Analysis suggests biomass and biogas routes alone could only cover about 45% of a fully renewable methanol economy's demand, meaning captured-CO2 pathways will likely be needed to scale beyond that ceiling.link.springer+2

 

 

Perplexity.ai prompt:

overview of Direct Ocean Capture for methanol using a parallel circuit with seawater for microalgae cultivation without using flue gases

 

This is a coherent design — running DOC's own seawater intake/outfall as one circuit, and a fully separate seawater circuit feeding the algae ponds, with neither flue gas nor DOC-captured CO2 used for the algae. The tradeoff is that the ponds must then rely on relying on their own natural carbon supply, either atmospheric CO2 exchange or alkaline/bicarbonate chemistry, since no external gas stream is being injected.

System Architecture

DOC extracts CO2 by acidifying an intake seawater stream via electrodialysis, then hydrogenates the concentrated CO2 with green hydrogen to synthesize methanol, a process already demonstrated at pilot scale and modeled in multiple techno-economic studies. Running the algae ponds on a fully independent seawater circuit avoids any competition for dissolved carbon between the two systems, but means the ponds cannot rely on gas sparging (flue gas or purified CO2) for productivity, since that was explicitly excluded.sciencedirect+3

How the Ponds Would Get Carbon Without Flue Gas

Two viable pathways exist for supplying algae carbon requirements purely from seawater/atmosphere, without any injected gas stream:

• Direct air-CO2 diffusion at high pond pH: raising pond pH (to around 10-12) chemically enhances the rate at which atmospheric CO2 dissolves into the water by reacting with hydroxide ions, and DOE-funded studies measured air-CO2 uptake rates up to 10 g C/m²/day at pH 12 in brackish water, supporting biomass productivity near 20 g AFDW/m²/day — though this requires specialized alkaliphilic strains tolerant of pH 11+.osti+1

• Bicarbonate-rich alkaline cultivation: research on an alkaliphilic Chlorella sorokiniana strain grown in high-pH, high-carbonate/bicarbonate medium (pH>10, alkalinity>100 mequiv/L) achieved productivities above 16 g/m²/day using atmospheric CO2 alone, with measured air-CO2 uptake rates matching or exceeding the algae's photosynthetic carbon demand, avoiding any need for concentrated CO2 input entirely.pubs.acs

Performance Tradeoff vs. Gas-Fed Systems

Without concentrated CO2 supplementation, productivity is meaningfully lower: DOE research found ponds relying solely on air-CO2 exchange achieved about half the biomass productivity of otherwise-identical ponds fertilized with supplemental CO2. This matches broader literature showing CO2 represents over 50% of microalgae cultivation's feedstock cost specifically because open ponds are inherently CO2-limited without supplementation, and low ambient CO2 concentrations (under 0.5% in air) constrain growth due to weak substrate affinity of the Rubisco carbon-fixing enzyme. So this two-circuit, no-flue-gas design trades lower biomass yield for operational simplicity, avoidance of flue-gas contaminant management (NOx/SOx/pH sensitivity), and full decoupling from any nearby industrial CO2 source, which may be attractive if you don't have a co-located flue-gas emitter or want to keep the algae side purely marine/atmospheric-carbon-based.pmc.ncbi.nlm.nih+3

Practical Recommendation

If yield matters most, choose alkaliphilic or bicarbonate-tolerant strains (e.g., Chlorella sorokiniana SLA-04, Dunaliella salina, or Arthrospira/Spirulina) and operate the pond at elevated pH, since these are the only validated approach demonstrating commercially relevant productivity without any injected CO2 source. Given your South Australian coastal siting, this pairs naturally with the earlier "two parallel circuits" concept — DOC draws its own intake water for methanol feedstock, while the algae circuit draws seawater independently and manages its own carbon economy via pH control rather than any interaction with DOC's gas or water streams.pubs.acs+1

 

Sorry about the bad references. A couple of comments:

• though flue gases are appealing for microalgae cultivation, which I'm not against, available real estate for DOC and raceway ponds could be a problem
• in a linear circuit, if wastewater from DOC is used, the water may need to be held for 6 months or longer for atmospheric CO2 to be reabsorbed to an acceptable level for the microalgae (strain dependent), which grows with CO2, nutrients and sunlight
• shared seawater infrastructure can be used for both the DOC and microalgae parallel circuits which is cost saving
• China's going crazy on Methanol
• Brackish water, methanol, microalgae, biodiesel...
• National Highway hubs?
• the microalgae biorefinery, as discussed in recent prior blogs, can extract both lipids for Ultra Low Sulfur biodiesel and produce battery and supercap grade Carbon for electrodes and electrolytes, using pyrolysis with 'Variable Frequency Microwave Assisted Pyrolysis' (VFMAP)
• methanol or biodiesel/Carbon-based EV golf buggy expedition (with solar 'Flower Power' trailer) from ADL-ADL via the National Highway - count me in!
• a custom alert tone for the AusAlert - hang on, is that democratic? Why not a 'Shakuhachi' catchy Zen melody? Prepares the mind. Fines for inappropriate AusAlert alarms in public places? Where is all this going? Climate change emergencies aka unnatural disasters, natural disasters, police emergencies eg. a cat is trapped on a tree? Where does it end? Aeroplane mode?