1. The effect of the amount of magnesium oxide added on the content of magnesium oxide in the FCC catalyst
It is the comparison between the amount of magnesium oxide added and the content of magnesium oxide in the FCC catalyst. Magnesium oxide addition does not have a linear relationship with the magnesium oxide content in the catalyst, and when the magnesium oxide addition is less, the magnesium oxide content in the catalyst increases faster: when the magnesium oxide addition is more, the magnesium oxide content in the catalyst increases slowly. This may be because the surface of the catalyst contains a certain number of acidic centers that can react with magnesium oxide to produce acid-base reactions. When the acidic active centers on the catalyst surface react with magnesium oxide to reach saturation, it is difficult for magnesium oxide to enter the pores and react with the internal acidic active centers. The magnesium oxide content in the catalyst increases slowly.
2. Effect of magnesium oxide content on acid type and acid amount of FCC catalyst
The acid type and acid content of magnesium oxide modified FCC catalyst were determined by infrared spectroscopy, and the acid content was obtained by integrating the peak area. The FCC catalyst modified by magnesia contained L acid and B acid, and the acid content first increased and then decreased with the increase of magnesia content, and reached the maximum when the magnesia content was about 1.50% (D). The overall acid strength of magnesia modified FCC catalysts is dominated by weak acids (peak around 150°C). The acid strength at around 150°C increases first and then decreases. When the MgO content reaches 1.50%, the acid strength on the surface of the catalyst reaches the maximum value, indicating that adding an appropriate amount of magnesium to the FCC catalyst can increase the acid strength on the surface of the FCC catalyst.
Since the main forms of magnesium are MgO, Mg2+Mg(OH)*Mg(OH)2, etc., its existing forms will directly affect the acid content and micro-reaction activity of the molecular sieve surface. Introduction of magnesium element into FCC catalyst Magnesium element may interact with the active center on the surface of the catalyst to form a new compound. The acidity of the hydroxyl group in this compound may be stronger than that of the silicon-aluminum hydroxyl group, thereby increasing the acidity of the FCC catalyst. Due to the limited number of acid centers on the surface of the FCC catalyst, the amount of acid on the surface of the catalyst will not increase when the MgO content reaches a certain value.
3. The effect of magnesium oxide content on the micro-reaction activity of FCC catalyst
The microreaction activity of FCC catalyst increases firstly and then decreases with the increase of MgO content. When the MgO content is 1.50%, the microreaction activity of FCC catalyst reaches the maximum value. This is because, on the one hand, the addition of an appropriate amount of alkaline earth metal magnesium to the catalyst improves the interaction between the matrix and the active center, and this strong interaction may improve the dispersion and anti-sintering ability of the metal element magnesium on the surface of the FCC catalyst, reducing the Reducing the amount of carbon deposited on the surface of the catalyst increases the activity of the catalyst: on the other hand, adding an appropriate amount of magnesia to the catalyst may interact with free aluminum in the catalyst to form a magnesium-aluminum compound, which can improve the microreactivity of the catalyst. When the content of magnesium oxide exceeds 1.5%, the microreactive activity decreases with the increase of magnesium oxide content. This may be due to the excessive deposition of magnesium oxide in the pores of the catalyst, which reduces the pore volume and surface area of the catalyst, thereby reducing the microreaction activity of the catalyst.
4. Effect of magnesium oxide modification on the reaction performance of FCC catalyst
Compared with the unmodified FCC catalyst, the light oil yield and total liquid yield of the magnesium oxide modified catalyst were significantly increased. With the increase of magnesium oxide content, the conversion first increased and then decreased, and the conversion rate reached the maximum when the Mg content was about 1.50%. The coke selectivity (coke factor) showed a trend of first decrease and then increase with the increase of magnesium oxide content. Its change law basically corresponds to the activity, and the coke selectivity reaches the best value when the activity is high.
in conclusion:
Magnesium was introduced into the catalytic cracking (FCC) catalyst by impregnation method, and the acid content and concentration of the sample were determined by infrared spectroscopy (FT-IR), ammonia temperature-programmed adsorption-desorption (NH3-TPD) and micro-reaction activity (MAT). The micro-reaction activity was characterized and evaluated with a catalytic cracking riser pilot plant. The results showed that the FCC catalyst was modified with magnesia, and with the increase of magnesia content, the amount of L acid and B acid on the surface of the catalyst first increased and then decreased, the acid strength of the catalyst at about 150 °C increased first and then decreased, and the catalyst’s micro The reaction activity, conversion rate and coke selectivity first became better and then became worse. When the magnesium oxide content was about 1.50% (mass fraction), the total acid content, acid strength and activity of the catalyst were the highest, and the conversion rate and coke selectivity of the catalyst also decreased. reach the optimum value.