Some processes do not produce CO2 because they don't emit carbon dioxide whenever they are generating energy. For Instance, most renewable energy sources do not produce carbon dioxide, usually because of the reason stated above. Examples of renewable energy sources that are carbon-free are wind, hydroelectric, and solar.
Unlike other sources of energy, some of these renewable energy sources do not burn. Also, most of them do not create any pollution or emissions. This is in contrast to most non-renewable energy sources such as oil, coal, natural gas, and other fossil fuels. This is because when they burn, they produce greenhouse gas emissions.
In biology, there are different biological reactions that do not produce carbon dioxide. A perfect example is Lactate fermentation, a type of anaerobic respiration. This reaction only produces lactic acid. Unlike other types of anaerobic respiration, lactate fermentation does not produce carbon dioxide.