Power to X, Food from Air
Next: Flow Chemistry
Power to Gas
Power-to-gas (P2G) is a technology that converts electrical power to a gas fuel. There are several methods for this. For example, polymer electrolyte membrane electrolysis (PEMEC) using plastics or photovoltaic electrolysis.
In electrolysis water is split to hydrogen and oxygen. The process also generates a lot of heat.
Hydrogen from the electrolysis phase can be directly used as a fuel and there is a trend to develop infrastructure for generating and storing it but today there are limited facilities for storing and moving it around. Same is true for deployment of fuel cells that turn hydrogen into electricity. Also, hydrogen needs special care for safety reasons (it leaks out of normal steel pipes and containers) adding to costs and risks.
First option for using the hydrogen to general fuel gases, is to convert it in a two-phase process to syngas (mixture of CO2 and Hydrogen and often some CO2). This is done in reverse gas shift reactor (RWGSR) that outputs hydrogen, carbon monoxide, and water. Syngas was earlier called town gas and used as a fuel for lighting and cooking in the early 19th century.
The name ‘syngas’ is because it can be used as intermediate for creating methanol, diesel fuel, synthetic natural gas or ammonia. (Syngas can also be produced with gasification of biomass or captured from landfills). The production of diesel from syngas relies on Fischer-Tropsch process that converts CO and H2 into into liquid
hydrocarbons (more in next post).
Syngas can and has directly been used as fuel but it has low energy per volume. If it needs to be pumped longer distances, it is best first be transformed to methane.
Second option to use the hydrogen from electrolysis, is to turn it into methane. In methanisation carbon dioxide is filtered from air with direct air capture and combined with hydrogen using using a methanation reaction such as the Sabatier reaction in high temperature and with a little help from nickel catalytic to produce methane (natural gas). Synthesised methane can directly be fed into existing gas transporting pipelines and used as a drop-in replacement for natural gas.
Methane is a fuel that can be used to store energy and to generate power and heat.
Methane is also used to produce fertilisers and other chemical products. First to make ammonia by combining it with molecular nitrogen in Haber-Bosch process and then converted into nitric acid in Ostwald process. Nitric acid in turn used to produce ammonium nitrate for making fertilisers, plastics and dyes.
Carbon capture from air can be improved if the incoming air has unusually high concentration of CO2, for example by scrubbing power flue gases from a power plant. Cement industries are another good source as they create about 5% of global CO2 emissions so collocating at cement manufacturing site increases yields. (In the process of making cement out of calcium carbonate, carbon is driven out of the mineral and released into air).
On the other hand, direct air capture (DAC) technologies that capture carbon dioxide directly from air instead of colocation with e.g., cement factory can be operated anywhere and there are already mobile DAC products.
Power-To-Liquid
Generating synthetic liquid fuels starts again with electrolysis where water is split into hydrogen and oxygen. Then hydrogen is combined with carbon dioxide that is captured from the air producing water, hydrogen and carbon monoxide as described earlier.
The last part is Fischer–Tropsch process - a set of chemical reactions that convert carbon monoxide and hydrogen into a mixture paraffinic and olefinic hydrocarbons, ranging from simple methane to high molecular weight waxes (a mixture of gases, liquids and flexible solids, mostly liquids). These reactions require a metal catalyst, high temperature (150–300 °C) and pressures of one to several tens of atmospheres. Cobalt and iron are possible catalysts. The generated methane can be directly used as fuel and source of chemical production.
The liquid part - synthetic crude - is comparable to fossil crude oil and can then be refined on site to create different products like petrol, diesel, waxes, kerosene etc. Refining on site means there is no need to build infrastructure for crude transportation. Liquid fuels have high energy contents and are easy to store (compared to hydrogen and batteries for example). They are also quite safe compared to hydrogen.
One usually thinks of refineries as huge installation for economics of scale but there is a market also for small scale refinery products typically targeting today a different market – refining cooking oils or sunflower oil and similar plant or animal oils.
Capturing energy from sun and using it to capture carbon from air to ultimately produce fuels is a method where we could create a closed loop for carbon. Carbon atoms get captured from air, turned to fuel, fuel is used to power vehicles releasing the carbon to be again captured. This would allow moving to a carbon neutral future without changing the world’s infrastructure.
Further links:
http://fortune.com/2015/04/28/audi-just-invented-fuel-made-from-co2-and-water/
https://www.eurofuel.eu/library/publications/item/267-what-future-liquid-fuels-to-heat-our-homes-3 *
Food from air
The methane generated can be used to cultivate Methylococcus capsulatus bacteria to produce protein rich feed for cattle, poultry and fish.
Different microbes can be used to grow protein rich food also for human consumption. For example, solarfoods is developing a solution where hydrogen from electrolysis and CO2 with direct air capture is fed to microbes that produces a mixture with more than 50 per cent protein and 25 percent carbohydrates. The rest is fats and nucleic acids.
Other nutrients needed for cell growth like nitrogen, phosphorus, potassium, salts and micronutrient are used in their process well. Before consumption the grown mass is first filtered, treated in ultra-high temperature and dried. The resulting mixture resembles dry protein powder. Intent is that this mixture could be used in cooking as such with no further processing steps.
The end result is estimated to be about 10 times as energy efficient as common photosynthesis used in cultivation of for example soy. One of the alternatives being considered is a home reactor, a type of domestic appliance that the consumers can use to produce the needed protein themselves.
One benefit is also that growing food and fodder these ways is continuous process having no seasonality.
As a summary all ingredients are taken directly from air and food production can be taken anywhere on the planet.
Next: Flow Chemistry