【Weekly Topic】What are the differences between wax oil catalytic cracking and heavy oil catalytic cracking catalysts?

The older catalysts used for wax oil catalysis included the A3 microsphere catalysts, followed by the Y-7, Y-9, and Y-15 molecular sieve catalysts； At the beginning of heavy oil catalysis, catalysts used for wax oil catalysis were also employed; later, with the development of heavy oil catalysis, super-stable Y catalysts and heavy oil catalysts suitable for processing large molecular weight compounds were developed.

Different raw materials, different catalysts, different operating conditions result in different products

This post was last edited by chengkang on 2010-11-30 20:24: Paraffin catalytic cracking catalyst: low activity ； Based mainly on superstable molecular sieves, with little rare earth content ； It has a higher distribution of small and medium pores, with fewer large pores ； The product has good selectivity and low amount of char formation. Heavy oil catalytic cracking catalysts: high activity; low content of ultra-stable molecular sieves and high content of rare earth elements; a smaller proportion of small and medium-sized pores with a larger proportion of large pores; strong resistance to heavy metal contamination and strong resistance to basic nitrogen compounds; poor selectivity of the products and higher amounts of coke formation.

Catalysts for heavy oil catalysis are required to have strong capacity for converting heavy oil, good thermal stability, selective carbon formation, and resistance to heavy metal contamination; examples include ultra-stable molecular sieve catalysts and REUSY molecular sieve catalysts. These catalysts feature large pore sizes, low specific surface areas, and moderate activity, which facilitate the entry of large molecules such as those in heavy oil (with molecular diameters typically ranging from 5 to 10 nm, while larger residues have molecular diameters of around 1 to 3 nm) into the matrix (amorphous aluminum silicate or clay, with pore sizes generally ranging from 0 to 50 nm), where they are cracked into smaller molecules. These smaller molecules then enter the micropores of the zeolite and are converted into the desired products. Catalysis for distillate oil processing generally employs REY or REHY-type catalysts, which result in high gasoline yields, low levels of coke and gases, as well as a gasoline composition with fewer olefins and more aromatics. This is due to the high activity of such catalysts, their strong hydrogen transfer capacity, and their ability to dehydrogenate naphthenes into aromatics.

The information on the 5th floor is quite comprehensive. As heavy oil catalysis results in a large amount of coking, a high main air flow rate and thus a high coking intensity are required; therefore, heavy oil catalysts need to possess properties such as wear resistance and resistance to hydrothermal deactivation.

The feedstock for wax oil catalytic cracking has good properties: it has a low residue content, a low coking rate, a low dry gas yield, and a high overall yield of products； If the properties of the wax oil are good, it’s still possible that there will not be enough heat regenerated ； The most prominent issue in heavy oil cracking is excessive heat in the regenerator; it is necessary to use internal and external heat exchangers to adjust the temperature of the regeneration bed, and the quality of the product is also inferior to that obtained from wax oil cracking.

I. Wax oil catalytic cracking catalysts mainly have the following characteristics: low activity； Based on superstable molecular sieves, rare earth elements are mostly distributed in medium and small pores, with fewer in large pores ； It has poor resistance to heavy metal pollution and poor resistance to alkaline nitrogen ； The product has good selectivity and low amount of char formation. II. Heavy oil catalytic cracking catalysts mainly have the following characteristics: high activity ； There are fewer superstable molecular sieves and more rare earths ； There are fewer small and medium pores, while there are more large pores ； Strong resistance to heavy metal pollution and strong resistance to alkaline nitrogen ； The product has poor selectivity and generates a large amount of coke. Generally speaking, compared to paraffin oil catalytic cracking catalysts, heavy oil catalysts have a stronger ability to crack heavy oil (due to larger molecular sieve pore sizes) ； Strong resistance to heavy metal pollution ； High stability. The development of catalytic cracking catalysts for heavy oil is based on the goal of maximizing the proportion of residue used in the feedstock, while also taking into account the specific requirements of different users regarding the properties of the raw materials, the operating conditions of the plants, and the desired distribution of the end products. Current heavy oil catalytic cracking catalysts mainly consist of two major product series: the MLC series and the DVR series. The MLC-500 series of catalysts can significantly improve the diesel-to-gasoline ratio even at high proportions of residue blending. The DVR series of catalysts features strong capability for cracking heavy oil macromolecules, high cracking activity, good coke selectivity, and excellent resistance to heavy metal contamination.

The wax oil hydrogenation catalyst has some cracking capabilities; the product quality remains relatively stable, it offers good adaptability, and it is easy to operate. Those produced by the Institute of Rock Mechanics perform relatively well in terms of usage. It is very difficult to remove the catalysts from residue hydrogenation units. Among all regions in the country, Jiangsu Tianpeng has the strongest and fastest capability for removing such catalysts. The residue hydrogenation catalysts produced in Fushun have good performance and a long service life, but they are relatively expensive; currently, many factories use those produced in Beijing.

Actually, I’m not that familiar with catalysts; when I saw this question, I asked a colleague who is doing a Ph.D. study. As for heavy oil: its molecules are relatively large, it has a high carbon residue content, as well as high levels of heavy metals, sulfur, and nitrogen. Therefore, in order to ensure the catalyst’s service life, catalysts with larger pore sizes are chosen. Heavy oil catalytic cracking is a decarburization process, and acidic catalysts are used for this purpose. Wax oil: Due to its low molecular weight, wax oil requires catalysts with small pore sizes. With the use of fluidized beds, catalysts in the form of small particles are generally employed; the reactions take place on their outer surfaces. These catalysts are highly active but also deactivate relatively quickly, which necessitates continuous regeneration. They belong to the category of acidic catalysts as well, but their acidity level differs from that of catalysts used in heavy oil catalytic cracking. Let’s discuss this further

Catalysis for wax oil is essentially the same as that for heavy oil; however, differences in the properties of the feedstocks lead to changes in operating conditions, such as the amount of coke formed, heat balance, product distribution and properties, as well as factors like the oil-to-catalyst ratio, linear velocity, and reaction time. Heavy oil catalysis simply involves more stringent reaction conditions, but it is used to obtain the desired product. The energy consumption of the device increases significantly, and the requirements for the equipment also become higher.