CO2 Capture Improvement

If I have this right, CO2 can be absorbed and converted to sodium carbonate and separated easily as crystals for shipping to a convenient separation system. This is a convenient procedure were it can be engineered into the industrial process.

I am skeptical regarding the economic viability of the process if one is to haul solids from producer to sequestration facility. However, this is the beginning and we will want to track results to see if it has a chance. It certainly can be used to separate the CO2 itself from a waste stream.

Thus a smokestack that is using say chlorine stoichemistry to separate SOx and NOx and also heavy metals (search this site for acid rain) can now look to converting the end product into a shippable solid to better dispose of the CO2. Imagine the nastiest metal smelter available becoming completely nonpolluting while producing a range of useful acids and salts. The value is unlikely to fund the exercise, but will still be significant.
I was involved in causing a proper bench test of chlorine stoichemistry at a UBC lab some years ago and have an appreciation of the capabilities of this methodology. The remaining issue was CO2 disposal.

Boosting carbon dioxide capture from the air

Researchers at the University of Calgary in Canada have developed a new process for recovering the alkaline solution that enables wet scrubbing systems to capture carbon dioxide from air. The technique appears to be better than conventional chemical recovery processes because it requires much less energy, so it's more economical.

Atmospheric concentrations of greenhouse gases like carbon dioxide must be lowered if we are to avoid dangerous climate change. The concentration of carbon dioxide, one of the most important greenhouse gases, has increased from 280 ppm in pre-industrial times to more than 380 ppm today. And global emissions of carbon dioxide are increasing by more than 3% per year, which means that the concentration of the gas is increasing by more than 2 ppm a year.

Most carbon capture and storage technologies aim to remove carbon dioxide at its source – for example, in power plants. The problem is that only around half of worldwide emissions of carbon dioxide come from such stationary sources. The rest comes from causes such as transport, so capturing carbon dioxide directly from the air could be crucial.

Scientists have known how to remove carbon dioxide from the air using alkaline solutions for more than half a century. Large-scale scrubbing of carbon dioxide was first put forward at the end of the last decade. In wet scrubbing, the gas is absorbed into a solution of sodium hydroxide (which is alkaline), leaving behind an aqueous solution of sodium hydroxide and sodium carbonate.

Maryman Mahmoudkhani and David Keith have now developed a new technique based on an R&D level process borrowed from the pulp and paper industry. In general, once sodium carbonate is formed, it needs to be decarbonised to separate the absorbed carbon dioxide and recover fresh sodium hydroxide. This step needs an oxidising material. Conventional processes use lime but Mahmoudkhani and Keith's process uses titanate instead.

"A titanate cycle appears to be more energy efficient because roughly half the amount of energy is required to perform the decarbonisation reaction (135 kJ/mol CO 2 compared to 250 kJ/mol CO 2)," Mahmoudkhani told environmentalresearchweb.

Keith says the process is low-tech because it exploits readily available industrial components that are cheap to make and easy to operate. "What makes the process so novel is that we propose to separate crystals of sodium carbonate from a solution of sodium carbonate-sodium hydroxide," he explains. "This approach is based on fundamental solubility chemistry and might be useful for any other process in which sodium carbonate needs to be separated as a pure solid stream from an aqueous solution."

Once carbon dioxide is liberated from the sodium carbonate in the kiln, it can then be compressed and transported by pipeline to geological sequestration sites for storage.

Mahmoudkhani and Keith are now performing actual laboratory tests and pilot experimental studies. "The next stage is to do detailed engineering calculations, including cost estimations of the whole process," said Mahmoudkhani.

The results were published in Int. J. Greenhouse Gas Control.

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