Coke Formation on Zeolite Catalysts in Naphtha Cracking

Abstract

Coke formation was investigated in the catalytic cracking of alkanes into light alkenes over ferrierite and ZSM-5 zeolites. H-ferrierite had the highest alkene selectivity in heptane cracking because of its smaller pore size. Ca 2 -exchange into H-ferrierite improved the selectivity and controlled coke formation. Ca 2 ions located at the center of the 8-membered ring converted ferrierite pores into one-dimensional channels of 10-membered rings, which suppressed the bimolecular hydride transfer to form alkanes and coke precursors. H-ZSM-5 zeolites having various extents of coke deposited in hexane cracking were characterized by adsorption measurements of various alkane molecules. Small amounts of coke did not affect the hexane conversion and micropore volume, whereas the adsorption rate of 2,3-dimethylbutane decreased significantly. These results suggest that coke is accumulated on the external surface of H-ZSM-5. Most coke would be formed via aromatic hydrocarbons. Selectivity for the transformation of aromatics into coke correlated with crystallite size of H-ZSM-5, indicating that aromatics formed in short channels can diffuse out of the crystallite immediately without coke precursor formation. H-ZSM-5 with smaller crystallite size is likely to be a stable catalyst for naphtha cracking into light alkenes with adequate catalyst life.

Assessment of acidity and the zeolite porous structure on hydrocracking of HDPE

“…This behavior is in accordance with other literature data, either for plastics 84,88–90 or other types of hydrocarbon. 91,92 For similar reasons, H-FER (10) also shows a low tendency for the formation of heavy hydrogen deficient molecules (11 wt%). In this case, the H-FER (10) 2D structure with small pores coupled to a low number of active acid sites suppresses the formation of large coke precursors.…”

Development of Pure Copper with Superior Electrical Conductivity at Cryogenic Temperatures

“…9,10) The effect of impurities was obtained from the analytical values for each element and increase in resistivity per 1 atomic ppm. [9][10][11] The resistivities of the Cu-17 atomic ppm Ca sample and the OFC sample at 4.2 K were calculated as above for heat treatment temperatures ranging from 473 K to 1073 K. Figure 5 presents a comparison of the calculated values with experimental values. The experimental µ 4K values were obtained by dividing µ(L) by RRR, assuming µ 293K of all experimental samples is mainly µ(L) and the effect of µ(D) and µ(I ) is extremely small in comparison.…”

“…Consequently, we obtained pure copper that did not require a special refining process and exhibited a high RRR over a wide range of heat treatment temperatures. Considering the standard Gibbs free energy of formation of sulfides 8) and the increase in resistivity with dissolution, [9][10][11] Ca, La, Mg, Sr, Ti, Y, and Zr were selected as additive elements to precipitate S from the matrix as a compound, as shown in Table 1.…”