The Solvay Process was invented in 1861, and is still used everywhere today. It bubbles CO2 up through ammonia-based brine in a four-step chemical engineering process that produces and uses CO2 at various points in the process.
By Michael Barnard
This is the third in a series of articles I’m writing about flow battery technology, with a couple of articles devoted to Agora Energy Technologies’ specific technology. The first article dealt with flow batteries in general, and why they are a strongly promising component for grid storage. The second dealt with Agora’s unique diff
erentiators. This article is devoted to a compelling alternative use case for their technology, one that’s immediate and high value.
The past three years have been a deeper dive into industrial processes and chemical engineering for me, and the implications for global warming. The CleanTechnica report on Carbon Engineering was a major effort, as were the many articles on industrial processes for carbon sequestration. The assessment of cement manufackturing, with and without the nonsensical use of concentrating solar power was another.
This has led me to a deeper interest in the edge cases of climate solutions. My assessments and research over the past few years has led me to understand the major solution sets for energy, transportation, and biological carbon sequestration, but there’s still a lot of carbon and pollution emitted in industrial processes that needs to be addressed. As one example, there is the $44 billion global carbonates market.
Potassium carbonate is in a lot of things we use daily. It’s used in soaps, glass, and china dishes. It’s used as a drying agent in chemical processes. It’s in both Asian noodles and Dutch cocoa powder. Wine makers use it. It’s a water softener and a fire extinguisher. It’s used in welding and animal feed.
Sodium carbonate is equally widely used. It’s in glass, paper, rayon, soaps, and detergents. It’s used for water softening. It’s a food additive that controls acidity. As a weak, safe to handle base, it’s used in a lot of chemical processes. Over 40 million metric tons are produced each year, amounting to several kilograms for every person on Earth.
Between them, they represent a roughly $44 billion global annual market. And the current processes that make them are pretty nasty in a lot of ways.
Let’s take sodium carbonate as an example. About 75% of all the sodium carbonate used in the world is made by the Solvay Process. The US gets most of its sodium carbonate from a massive trona deposit in Wyoming.
Syracuse Solvay process works circa 1900 courtesy US Library of Congress
The Solvay Process was invented in 1861, and is still used everywhere today. It bubbles CO2 up through ammonia-based brine in a four-step chemical engineering process that produces and uses CO2 at various points in the process. And of course there’s the ammonia, which is highly toxic, with 15-minute exposure limits to levels of 35 ppm of gaseous ammonia per the US Occupational Safety and Health Administration.
Ammonia is a manufactured substance in and of itself, using hydrogen created from fossil fuels today with 8-35 times the mass of CO2 as hydrogen. Prolonged exposure to small amounts of ammonia cause irreversible health effects. The ammonia is mostly recycled with only small amounts being lost, but eliminating it entirely would be beneficial.
The Solvay process actually captures some CO2 produced in one step to use in a later stage, but overall, the deployed process is a net emitter of 2.74 times the mass of CO2 as the mass of carbonates produced.
The source of heat in the first step interested me. That step in the process is the same as for cement, incidentally. It requires substantial heat, in the 600 to 1000 degree Celsius range to calcinate limestone to make quicklime and CO2. Some of the CO2 and all of the quicklime are used in later steps in the process, unlike cement making where all the CO2 is just emitted into the atmosphere.
As a side note, a Lafarge cement expert told me when I was exploring cement that they had no good process for capturing limestone kiln CO2 emissions, which clearly isn’t the case as it has been done as an industrial process for 160 years. Capturing flue CO2 isn’t hard, it’s just expensive, so it isn’t done unless there’s a very good economic reason.
Then there’s another temperature challenge, which is that the third step in the process is strongly exothermic, which means it gives off a lot of heat, just not usefully. One of the key challenges in the process is keeping the temperature low enough.
That’s typically done with cooling water from ground sources, a challenged source in many parts of the world today, with thermal generation plants shutting down or running on diminished capacity as ground water heats up past the point where it works well with the designed equipment.
The Solvay company shut down four of its 22 Sao Paulo, Brazil units due to the river they take water from drying up in 2014, a taste of the future for many heavy water consuming industrial plants located on water sources at risk from global warming.
The second instance of the application of heat in step 4 is also interesting. That requires another kiln with a temperature of about 300 degrees Celsius. Any time I see heat these days in industrial processes, I assume it’s coming from fossil fuels, and I was unsurprised to find that the preferred energy source for the Solvay Process was coke, a processed coal derivative.
That’s not all of course. The Solvay Process is much less polluting than the Leblanc Process it replaced, but inland sites end up with 50% more waste deposits of by-products than the sodium carbonates of value.
Solvay, New York, which was renamed when the Solvay company built a plant there, has massive waste beds that have polluted the local area and contributed to the nearby Onondaga Lake being declared a Superfund Site.
Long wall trona mine image courtesy Government of Wyoming
I haven’t done the same assessment of the environmental impacts of the US trona mining and processing sodium carbonate stream, but at first glance it looks like a high CO2 emitter with a fair amount of use of toxic chemicals and a challenging waste stream as well.
Why is this digression interesting? Well, the Agora technology can create sodium carbonate in two steps without any heat and with barely any temperature management required.
Wait. What? It’s a battery, not a chemical plant, isn’t it?
Well, yes. The closed-loop model cycles the chemicals between their base form and their charged form and back. But the open-loop model, which changes in some of the details, produces sodium carbonate after the second cycle instead of turning it back into CO2, in a up to 35% by weight solution with water. And both act as batteries, taking in electricity in the charging stage and producing electricity in the discharge phase.
So the ammonia-based, high-heat, high-cooling, five-step process turns into a shorter process with much less harmful outcomes. It takes electricity when it’s cheap at night or other times, from renewables wherever possible of course, to ‘charge’ the battery.
Then during the daytime, instead of reversing the process as in the open-flow approach, it sends it through Agora’s cells with a different chemistry and produces carbonates in solution and electricity. The entire daytime process from lights to pumps to drying the carbonate solution and the like can be run by a portion of the electricity that’s produced.
The output sodium carbonate is pure as well. It’s a pure compound in pure water. Heat the water to evaporate it off, and the purity should be well over the 98% purity typically guaranteed for food additives for the most expensive variants.
There’s enough electricity in the battery to power the evaporation directly per my calculations with the CEO Dr Christina Gyenge, but there’s far more than enough to use heat pump technology with a COP of 4 to do that, or to pump it over a source of waste industrial heat elsewhere, and leave a lot of electricity left over for other uses in the industrial facility or to sell to the grid.
So, this technology can take a cheap feedstock we have too much of in the world, CO2, regardless of where it comes from and using renewable electricity produce very high quality industrial chemicals that are used globally in a market worth tens of billions of dollars.
Originally published at Clean technica