3 ms·

> This article is discussing the CO2 emissions related to some integral processes within the smelter In slightly more (but still high school level!) detail, th

by twic 6y ago

> This article is discussing the CO2 emissions related to some integral processes within the smelter In slightly more (but still high school level!) detail, the raw material for aluminum refining is Al2O3. That is dissolved in a bath of molten salt, where the ions dissociate. The 2 Al3+ is electroplated out by adding electrons at the cathode. The 3 O2- comes out by withdrawing electrons at the anode; usually, the anode is carbon [1], and the reaction is: 2 O2- + C -> CO2 + 4 e- The innovation here is to use an inert anode, so the reaction is: 2 O2- -> O2 + 4 e- The fundamental chemistry of this is pretty obvious, so presumably there are good practical reasons why everyone was using carbon anode before. EDIT It seems [2] that the process is using the carbon to do some of the energetic work of reducing the oxygen (carbon loves to reduce oxygen even when it doesn't have two extra electrons, a fact exploited in an earlier industrial process [3]), therefore requiring less electrical energy. This is sort of a way to stealthily burn some carbon to produce energy. [1] https://en.wikipedia.org/wiki/Prebaked_Consumable_Carbon_Anodes https://en.wikipedia.org/wiki/Prebaked_Consumable_Carbon_Ano... [2] https://chemistry.stackexchange.com/questions/6774/why-do-they-use-graphite-anodes-in-the-hall-heroult-process https://chemistry.stackexchange.com/questions/6774/why-do-th... [3] https://en.wikipedia.org/wiki/Fire https://en.wikipedia.org/wiki/Fire

catalogia 6y ago
Do you know how they might be dealing with the oxygen? I assume it comes out very hot and ready to oxidize stuff. I suppose there are stainless alloys that can cope with it?
twic 6y ago
Re-reading this, I realise I've got the bit about carbon reducing oxide ions wrong. The oxide ions are being oxidised here, not reduced. But ending up at CO2 rather than O2 means they don't need to be oxidised as hard - oxygen in CO2 is a bit more reduced than in O2. I think. I probably wouldn't pass A level chemistry if I sat the exams today. When neutral carbon and oxygen react, the carbon reduces the oxygen because it gives it a fractional share of its electrons when they form a bond. But when oxygen is charged, it already has lots of electrons. In this reaction the carbon is helping oxidise the oxide ions.

by twic 6y ago

catalogia 6y ago

Do you know how they might be dealing with the oxygen? I assume it comes out very hot and ready to oxidize stuff. I suppose there are stainless alloys that can cope with it?

twic 6y ago

Re-reading this, I realise I've got the bit about carbon reducing oxide ions wrong. The oxide ions are being oxidised here, not reduced. But ending up at CO2 rather than O2 means they don't need to be oxidised as hard - oxygen in CO2 is a bit more reduced than in O2. I think. I probably wouldn't pass A level chemistry if I sat the exams today. When neutral carbon and oxygen react, the carbon reduces the oxygen because it gives it a fractional share of its electrons when they form a bond. But when oxygen is charged, it already has lots of electrons. In this reaction the carbon is helping oxidise the oxide ions.