I have questions regarding hydrocracking and hydrorefining
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I have a few questions for everyone: 1. Regarding hydrocracking, if I have feedstock in the C22-C40 range, which is mostly straight-chain alkanes, that is, waxes, and I want to convert it into diesel through hydrocracking, what carbon chain range within this feedstock would be most suitable as a raw material for producing diesel? For example, is C22-C30 better, or is C30-C40 more suitable? Why? Or my question is, in hydrocracking, carbon chains break, and it’s easier for them to break in the middle; for example, a C30 chain breaking in the middle to form two C15 chains? Or is it biased toward an open chain on one side? For example, can a C30 chain break into a C10 and a C20? 2. Generally speaking, when a saturated hydrocarbon breaks apart, it usually results in two unsaturated hydrocarbons. So, in hydrocracking, are the products obtained unsaturated or saturated? That is, is this process merely hydrocracking, or does it also possess the capability for both hydrocracking and olefin hydrogenation? 3. The issue of hydrorefining: If I have diesel fractionated oil that contains unsaturated hydrocarbons such as olefins, and I want to use hydrorefining to saturate these unsaturated hydrocarbons, then in this process, does only hydrogenation for saturation take place, or does both hydrogenation for saturation and cracking also occur? Please help everyone; it would be even better if the explanation could be more detailed! ! Thank you.
1. Hydrocracking products are diverse, including dry gas, light and heavy naphtha, liquefied gas, jet fuel, diesel, and residue oil. Hydrocracking involves numerous primary and secondary reactions, which are quite complex. Both of the types of chain-opening reactions you mentioned should be present, at least in terms of difficulty level. The products of 2-hydrocracking include both saturated and unsaturated hydrocarbons; for example, naphtha with carbon numbers C4–C6 is not entirely composed of saturated hydrocarbons, and the tail oil contains some polycyclic aromatic hydrocarbons, which are unsaturated. The 3 hydrogenation refining catalyst does not have a cracking function; if cracking reactions also occur during hydrogenation refining, it becomes more difficult to control the temperature.
Thank you for the reply from above; it was clearly explained that hydrocracking does not occur during hydrogenation refining. The products of cracking can be either saturated or unsaturated. So, is it possible to carry out both cracking and hydrogenation during the cracking process, thereby reducing the size of large molecules while also ensuring that the resulting products are saturated? By saturated, I mean chain hydrocarbons only. The feedstock I need for hydrocracking is just alkanes, and I believe this is relatively simpler than cracking in petroleum refining, after all, its elemental composition is relatively simple. If I remember correctly, it seems that the breaking of links can be done selectively, for example by prioritizing breaks at certain positions, or at the ends or in the middle. I’d also like to ask everyone for their opinions on this issue; if anyone knows anything, please share it.
1. Long straight-chain alkanes break at the middle, while alkanes with side chains generally break at the beta bond. 2. Hydrocracking products contain both saturated and unsaturated hydrocarbons; in some processes, the catalyst in the final bed layer serves a refining function. 3. The hydrorefining catalyst does not have a cracking function.
I’m still a beginner in oil refining, and I would like to ask the more experienced colleagues: is hydrocracking mainly used for producing diesel? It seems that naphtha also comes from the hydrorefining process, right?
From a chemical perspective, hydrocracking is a combination of catalytic cracking and hydrogenation reactions; it follows the mechanism of carbocation reactions as well as the principle of cleavage at the β-position of carbocations. Hydrogenation occurs throughout the hydrocracking process, and as long as hydrogenation active centers are present, the products are essentially saturated
This post was last edited by 660 on 2012-5-11 at 13:07. Hydrogenation processes result in products with low levels of sulfur, nitrogen, and unsaturated hydrocarbons, and they represent a technique for improving the quality of the products. The main purpose of hydrorefining is to remove heteroatoms, resulting in better product quality. In addition to achieving the same effects as refining, hydrocracking can also convert large molecules into smaller ones, that is, it transforms heavy and low-quality oils into light and high-quality oils.
The first issue is that the appropriate catalyst needs to be selected, with the carbon chain length falling within the range suitable for that catalyst’s design. As for the location of the bond breakage, it is related to the catalyst’s selectivity; there are types such as those involving tail oil, middle oil, and light oil, etc. It’s not necessarily the case that one large molecule yields two smaller molecules – it could be three or even five. The second issue is that, since the reaction takes place under hydrogen partial pressure, when the chains are broken to form unsaturated hydrocarbons, hydrogenation occurs, resulting in saturated hydrocarbons as the products. Thirdly, diesel hydrorefining involves some cracking, as the reaction takes place under high temperature and pressure, causing the molecules to undergo partial thermal decomposition; generally, this proportion is less than 10 percent
1. The choice of feedstock for cracking depends primarily on the intended use of the product, namely the application of the tail oil. The principle of cleavage is the principle of cleavage at the β-position of the positive carbocation, as well as the principle of homolysis. 2. Hydrocracking involves two types of reactions on the surface of the catalyst: a cracking reaction occurs on the surface of the support, while a hydrogenation reaction takes place on the metal surface; in essence, it is the combination of cracking and refining reactions. Moreover, cracking is an endothermic reaction, while refining is an exothermic reaction; ultimately, it is the exothermic reaction that manifests.