How big is the pressure on carbon emissions in the chemical industry?

3. Carbon emission calculation of typical chemical products

In this chapter, we will calculate the unit carbon emissions of several important types of chemical products in more detail to sort out the main sources of carbon emissions in major chemical production processes and chemical products with high environmental costs. The three paths are mainly competitive in the fields of C1 and C2. C3 is mainly propylene, similar to C2 ethylene is no longer a single column. For the two core sources of carbon emissions, energy-related emissions can be significantly reduced or even reduced to zero through power substitution in the future, but process emissions are different due to the reaction mechanism and conversion efficiency. The carbon emission caused by hydrocarbon conversion is the most important process emission in the production process of chemical products.

3.1 How to understand the process emissions of energy chemical industry

Because coal is mainly composed of carbon elements, the hydrogen-carbon molar ratio is only about 0.2 to 1, and a part of C needs to be sacrificed to replace hydrogen from other raw materials, and the carbon conversion rate is not as good as oil and gas. From the point of view of the specific reaction process, coal is converted into gas through the coal gasification process and then the subsequent preparation task. In an ideal water-gas preparation reaction, one part of C and water becomes one part of CO and hydrogen. However, this reaction process is a strong endothermic reaction, which does not exist alone in the actual coal gasification process, but must be combined with another carbon oxidation exothermic reaction to heat this process. These exothermic reactions consume C, but do not displace an equal proportion of hydrogen from the water molecules, resulting in a final product with a hydrogen ratio greater than 1, and even some CO2. In addition, taking methanol, an important chemical intermediate product, as an example, the ratio of hydrocarbon in its raw material is as low as 0.5, and the consumption of hydrogen is significantly greater than that of CO. Therefore, a conversion reaction is often added after the coal gasification process to adjust the ratio of CO and hydrogen. In this process, one part of CO and water molecules are consumed, and one part of hydrogen and CO2 are produced. These are the main sources of CO2 process emissions in coal chemical routes. On the other hand, the hydrogen-carbon ratio of oil is 1.6-2, the hydrogen-carbon ratio of natural gas is above 2, and the hydrogen content is significantly higher than that of coal. Taking the C1 chemical industry of natural gas as an example, because the hydrogen carbon ratio of methane itself reaches 4, from the core reaction equation, the ratio of H2 and CO generated by the first step of steam reforming to synthesis gas is as high as 3 times, which is far greater