Fertilizers and Explosives
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Let’s see how fertilisers can be made in decentralised manner. We’ll find nitrogen containing fertilizers to be not too hard for decentralised manufacture and others more or less so.
Fertilizers
Growing plants need water, air and energy from sun to capture carbon, hydrogen and oxygen. These three elements make 90-95% of their dry mass. In addition, they need nutrients that are divided into primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulfur) and micronutrients (boron, chlorine, copper, iron, manganese, molybdenum and zinc).
Nitrogen helps leaf growth and protein production (plants adapt leaf growth on nitrogen limitation and therefore photosynthetic capacity), phosphorus help root and seedling growth (root supply nutrients, water, and physical support for the plant), and potassium regulates the transport of other nutrients and water in the plant.
Sulfur is essential in protein synthesis and magnesium for the formation of chlorophyll.
The primary nutrients for plants can be locally sourced with relative ease: nitrogen captured from air, potassium generally available through the world or recycled (phosphorous).
Fertilizers are materials that contain at least one of the plant nutrients in a format that is soluble in soil and can be easily taken up by plant roots. Chemical fertilizer production started in 1840 when Liebig recommended to treat pulverized animal bones with sulfuric acid to make phosphates easily available to plants.
When plants are nitrogen deficient, they are marked by reduced growth and yellowing of leaves.
79% of atmosphere is made of nitrogen, but very few plants species – mainly legumes – can utilize it directly. Small amounts of it are converted in lightning to nitrogen oxides that through rain water enter the soil and can be taken up by plants. But the amounts are very small. Continuous cropping will soon deplete soil.
All nitrogen-containing fertilizers are made via ammonia. About half of nitrogen applied worldwide as fertilizers is in the form of urea (carbamide). Other nitrogen containing fertilizers are ammonium nitrate and calcium ammonium nitrate (80% ammonium nitrate and 20% calcium carbonate).
To make fertilizers nitrogen needs to be captured from air and made into a suitable format, normally via ammonium synthesis. Ammonium today is made with Haber-Bosch process that was invented already 1909. It converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2). A metal catalyst is used and the reaction is done under high temperatures and pressures.
Hydrogen can be made via electrolysis from water (today due to cost issues it is in large facilities made from natural gas (methane) through stream reforming).
The hydrogen is then catalytically reacted with nitrogen to form anhydrous liquid ammonia. This is difficult and expensive, as lower temperatures result in slower reaction rate and high pressure requires high-strength pressure vessels
Development is still ongoing to improve the Haber-Bosch especially on the choice of catalyst. Recent developments for example by Hideo Hosono's group on Ru-loaded calcium-aluminum oxide, a novel perovskite oxynitride-hydride. Aim for new catalysts is to work under lower temperature and/or pressure.
Ammonia itself can also be used as a fertilizer, but is normally converted to other substances for ease of handling. Nitric acid is produced by first mixing ammonia and air in a tank and in the presence of a catalyst a reaction occurs which converts the ammonia to nitric oxide. The nitric oxide is further reacted in the presence of water to produce nitric acid.
Nitric acid and ammonia materials are finally mixed together in a tank and a neutralization reaction occurs, producing ammonium nitrate. This material can then be stored until it is ready to be granulated and blended with the other fertilizer components.
As an alternate older nitrogen source can be considered. Earlier people used manure or crop rotation to supply needed nitrogen to plants. In crop rotation nitrogen fixing legumes such as peas, clover or alfalfa are first grown. These are plowed into the soil before other crops are grown on next season. Some American Indian tribes had a practice of burying dead fish in corn fields to increase production.
Plants also need phosphorus, a component of nucleic acids, phospholipids, and several proteins. Phosphorous can be extracted from black waters creating a closed loop for it. Phosphorous then needs to be made into suitable format for plants – either into triple superphosphate or ammonium phosphate.
Today phosphorous fertilizers are created from phosphate rock, that is treated with sulfuric acid, producing phosphoric acid. Some of this material is reacted further with sulfuric acid and nitric acid to produce a triple superphosphate. Phosphoric acid can also be reacted with ammonia in a separate tank. This reaction results in ammonium phosphate, another primary fertilizer.
This is the hardest to achieve in decentralized manner. Options include incarcerating toilets and reclaiming it from black waters. We’ll return to this topic when discussing sanitation.
Potassium is another major substance that plants need from the soil. It is used in protein synthesis and other key plant processes. Yellowing, spots of dead tissue, and weak stems and roots are all indicative of plants that lack enough potassium.
the main source of potassium – potash – is mined around the world in places like Canada, Russia, Belorus, Germany, Israel, Kazakhstan, Jordan and the US.
If there is a supply shock, it can also be gained from pot ash (giving also potassium its name) referring to plant ashes soaked in a pot with water. This was the earlier method of manufacturing it before industrial age.
The manufactured fertilizers need also granulation at the end. Each compound like ammonium nitrate and potassium chloride is granulated and then blended together before bagging.
Additional item to improve soil quality is quicklime that is primarily used to correct acidity. It also provides calcium and magnesium to soild It can be manufactures quite easily by burning sea shells or by calcining limestone in kilns at high temperatures. Calcium and magnesium oxides are then formed. Hydrated lime is produced by adding water to quicklime. It is less reactive than quicklime and is as an ingredient in mortars to improve workability, water resistance and durability. You make mortar with quicklime, water and an aggregate such as sand.
To probe further:
https://www.essentialchemicalindustry.org/materials-and-applications/fertilizers.html
Precision Agriculture
The trend in agriculture is towards precision agriculture where nutrients are applied at varied amounts at different locations based on what the plants need. The need can be analysed either from soil samples or just taking hyperspectral images of plants and using machine learning models to detect what is causing problems in growth.
To implement precision agriculture, single nutrient fertilisers are used rather than compounds popular nowadays. This allows using just the missing nutrient and nothing is wasted.
Ammonia as a Power Source
Ammonia can be burned in a combustion engine to generate power or used in fuel cells for electricity instead of current fossil fuels. NH3 contains no carbon, so it emits no carbon dioxide when burned. Unlike hydrogen, it does not need to be stored in high-pressure tanks or in cryogenic format in vacuum flasks (dewards). It has 10 times the energy density of lithium-ion batteries. Both fuel cells and internal combustion engines can use it.
So, ammonia can be used to store excess energy during peak times like summer and release it during winter for example to generate electricity or to power up machines. In the maritime industry there are a number of ongoing projects to use it to power ships with ammonia fuel cells.
Solar farm concept
Solar farm is a concept where a farm has renewable energy resources like sun, wind and water for generating its own electricity. During times of excess (summer for example) part of it is stored into ammonia using the Haber-Bosch process mentioned above.
The ammonia can be used to generate electricity (and heat in combined heat and power – CHP – power plant) when renewables are not available like during rainy season or winter.
Ammonia is also used to create fertilizers. The farm generates its own fertilizers and power.
On a larger area the energy could be generated in a small modular reactor (SMR) or geothermal. SMR can also be used to generate heat for a small town or settlement in cold climates.
This model can be extended for example by having adding small modular water purification systems, local mobile networks that are connected via satellite to the external world, local cheap servers and you start moving towards a self-sufficient unit concept – cellular or decentralized world with self-sufficient communities and towns interacting with each other via the Internet.
We’ll return to this concept later.
Explosives
Last major chemical product category to consider is explosives. It is another one that does not use carbon captured from air, but can be made with captured nitrogen.
To make an explosive, you need an oxidizer and fuel. The big difference between normal burning of matter and explosion is the speed of oxidation, in an explosion it is very rapid.
Explosives where the fuel and oxidizer are in the same molecule, are called molecular explosives. Example are for example TNT (2,4,6 trinitrotoluene), PETN (pentaerythritol tetranitrate) and nitroglycerin. TNT is commonly used for military, industrial, and mining applications. It is insensitive to shock and friction, which reduces risk for accidental detonation when compared to more sensitive explosives like nitroglycerin. Manufacturing does not need to be complex, for example TNT is made by direct trinitration of toluene with nitric acid. In these molecules the fuel part comes from carbon and hydrogen. Oxygen is supplied from nitro (-NO) or nitrate (-NO2) groups.
Explosives where the oxidizer and fuel are different, are called composite explosives. ANFO is an example of such as it is a mixture of solid ammonium nitrate (AN 94%) and liquid fuel oil (FO 6%). It is used in mining and civil constructions as an easy to use and low-cost alternative when there are no big demands (like water resistance or high detonation velocity or performance in small diameters).
ANFO is an example compound that could be produced locally from nitrogen (,oxygen) from air and hydrogen and oxygen via electrolysis.
Ammonium nitrate (the main ingredient) is made with the following formula:
HNO₃ + NH₃ → NH4NO3
Very shortly: The ammonia required for this process is made with the Haber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidised to nitric acid by the Ostwald process.
Ammonium nitrate is also an important fertiliser. It is has smaller concentration of nitrogen than urea. Which means there is small advantage for urea in transportation costs. But ammonium nitrateis more stable and does not rapidly lose nitrogen to the atmosphere.
To probe further:
https://en.wikipedia.org/wiki/TNT
https://en.wikipedia.org/wiki/Ammonium_nitrate
https://ammoniaindustry.com/the-capital-intensity-of-small-scale-ammonia-plants/