Main raw materials and reagents were showed in table 1.

Table 1

Table 1

Table 1 Main raw materials and reagents Sample Purity Manufacturer Catalyst A Industrial Products Lanzhou Petrochemical Company Ammonium phosphate Analysis pure Sinopharm Chemical Reagent Co., Ltd. Nickel nitrate Industrial grade Lanzhou Petrochemical Company

Table 1 Main raw materials and reagents

Phosphorus was introduced to catalyst A by impregnation^[4]. A certain amount of the catalyst was weighed, ammonium phosphate was used as the impregnating raw material, and mass fractions of impregnation solutions were 0.0%, 0.5%, 1.0%, and 1.5%, respectively. Modified catalysts A were labeled as A₀, A₁, A₂, and A₃. The sample was baked at 120 ℃ for 4 h and then calcined at 600 ℃ for 2 h.

The modified catalyst was subjected to a contamination test of heavy metal nickel.A certain amount of nickel nitrate solution was added to completely wet the catalyst. During the period, stirred regularly, then dried the contaminated catalyst sample at 120 ℃ for 4 h, stirred at regular intervals. After drying for 2 h at a certain temperature, the finished product was contaminated.

Specific surface area, pore volume and pore size distribution of the in-situ crystallization catalyst were determined by classical isothermal N₂ adsorption-desorption using Autochem-2920 temperature programmed desorber and Micromeritics ASAP-3000 automatic physical adsorption instrument.

Surface acidity of the in-situ crystallization catalyst was measured using Brook-TENSOR 27 type infrared spectrometer manufactured by Bruker, Germany.

Crystallinity of the catalyst was measured by XRD diffraction using D/max-2000PC type X-ray diffractometer manufactured by Rigaku Corporation of Japan. Operating voltage was 40 kV, working current was 20 mA, CuKα radiation, phase scanning angle was 5° -50° , scanning speed was 10° · min^-1. Crystallinity scanning angle was 22.5° -25.0° , scanning rate was 1° · min^-1 .

Activity of the catalyst was determined in a fixed bed catalytic cracking micro-reactor adopting MAT type micro-reaction activity evaluation device produced by Beijing Huier Sanji Green Chemical Technology Co., Ltd., and the raw material oil was Tianjin Dagang straight-run light diesel oil.

Catalyst selectivity evaluation was carried out using a fixed fluidized bed XGL-2 ×3. The device consisted injection system, reaction system, separation acquisition system and analysis system. The sample was hydrothermally aged before reaction at temperature of 800 ℃ for 6 h. Then it was charged into the fixed fluidized bed for reaction. The raw material oil was made from 3 million· a^-1 heavy-reactor of PetroChina Petrochemical, its properties were showed in Table 2. Reaction temperature was 500 ℃, and the ratio of solvent to oil was 5.5. The gas component and simulated distillation liquid product were analyzed by Agilent 6890 gas chromatograph.

Table 2

Table 2

Table 2 Properties of raw material oil item Numerical value Molecular weight/g· mol-1 > 500 density (70 ℃)/kg· m-3 890.6 Fe/μ g· g-1 6.44 Ca/μ g· g-1 17.88 Cu/μ g· g-1 0.17 V/μ g· g-1 14.39 P/μ g· g-1 < 0.1 ω(Carbon residue) / % 4.62 ω(Saturated hydrocarbon)/% 51.3 ω(Aromatic hydrocarbon)/% 42.2 ω(Colloid)/% 6.5

Table 2 Properties of raw material oil

Table 3 shows texture properties of catalyst with different phosphorus contents.

Table 3

Table 3

Table 3 Texture properties of catalysts with different P contents Samples Specific surface area/ m2· g-1 Pore volume/ mL· g-1 Average pore size/ nm Relative crystallinity/ % A0 305.5 0.41 5.39 base A1 287.5 0.40 5.63 -1 A2 278.2 0.42 6.01 0 A3 249.5 0.38 6.12 -1

Table 3 Texture properties of catalysts with different P contents

It can be seen from Table 3 that impregnation amount of phosphoric acid does not have a linear relationship with specific surface area, pore volume and pore size of the catalyst. Specific surface area of the catalyst gradually decreases as the amount of phosphorus increases. When phosphorus was not injected, specific surface area of the catalyst reached a maximum value of 305.5 m²· g^-1. When phosphorus is loaded, specific surface area of the catalyst is smaller. Further, as the amount of phosphorus increases, pore diameter of the catalyst gradually increases. This is because the change of specific surface area of the catalyst causes change of pore diameter. The larger the specific surface area of the catalyst is, the smaller the pore diameter is.

It also can be seen from Table 3 that after phosphorus is supported on the catalyst, crystallinity of the catalyst does not change much. When the phosphorus content is 2.0%(A₂), the change of relative crystallinity is 0, that is, there is no influence on crystallinity of the catalyst.

Surface acidity of the catalyst was determined by pyridine adsorption infrared spectroscopy. The results are shown in Figure 1 and Figure 2. Amount of B acid L acid obtained from Figure 1 and Figure 2 are shown in Table 4.

Figure 1

	Figure Option ViewDownloadNew Window
	Figure 1 IR spectra of pyridine adsorbed on catalysts with different P content

Figure 2

	Figure Option ViewDownloadNew Window
	Figure 2 IR spectra of pyridine adsorbed on catalysts with different P contents

Table 4

Table 4

Table 4 Acid quantity of catalyst with different P content Samples 200 ℃/μ mol· g-1 350℃/μ mol· g-1 L acid B acid B/L L acid B acid B/L A0 342.553 236.196 0.690 159.091 185.989 1.169 A1 313.577 202.631 0.647 94.503 73.921 0.782 A2 226.453 146.419 0.646 88.955 65.179 0.732 A3 200.986 119.133 0.593 83.477 52.161 0.625

Table 4 Acid quantity of catalyst with different P content

B acid center is generally characterized by 1 540 cm^-1 absorption band, and L acid center is characterized by 1 450 cm^-1 absorption band. The total amount of B acid and L acid can be calculated from Lambert Beer’ s law. It is generally believed that the acid amount at 200 ℃ is the total acid amount, the acid amount at 350 ℃ is the strong acid amount and medium strong acid amount. The strong acid and medium strong acid center are cracking active center of the catalyst^[4]. For the catalytic cracking catalyst, B acid is mainly provided by molecular sieve, L acid is mainly provided by matrix and binder. B acid guides positive carbon ion reaction, and strong B acid center helps to enhance the cracking ability of the catalyst for heavy oil. L acid mainly guides the reaction of positive carbon ions, and can also guide free radical reaction. Strong L acid is more likely to generate coke and dry gas. Weak L acid helps cracking of heavy oil macromolecules. Therefore, it is required that the catalyst has a proper amount of weak L acid center and tries to reduce the strong L acid center.

It can be seen from Table 4 that when phosphorus content is A₀, the total acid amount, strong acid amount, medium strong acid amount and B/L value reach the maximum value. With the increase of phosphorus content, L acid amount decreases rapidly, amount of B acid reduced slowly, so that the B/L value is continuously reduced. This indicates that the addition of phosphorus does not enhance acidic active sites on surface of the in-situ crystallization FCC catalyst.

Whenphosphorus is loaded, total acid amount and strong acid amount decrease, which maybe due to the interaction of phosphorus with substance in the internal of the catalyst, thereby reducing the number of active centers on the catalyst surface. The amount of acid is reduced.

Using 0.5% nickel solution as the pollution source, samples A₀ (0%), A₁ (0.5%), A₂ (1.0%) and A₃ (1.5%) were contaminated, and the obtained products were respectively labeled as B₀ (0%), B₁ (0.5%), B₂ (1.0%), B₃ (1.5%). The micro-reaction activity values of B₀, B₁, B₂, and B₃ were experimentally determined and showed in Figure 3.

Figure 3

	Figure Option ViewDownloadNew Window
	Figure 3 Effect of phosphorus content on micro-reaction activity

It can be seen from Figure 3 that the micro-reaction activity is the highest when phosphorus is not loaded, reaching 80%, and the micro-reaction activity decreases as phosphorus contents increases. When phosphorus content is B₃(1.5%), the micro-reaction activity of the catalyst is reduced by 36% compared to B₀. This indicates that when large amount of phosphorus is supported and the catalyst is contaminated with a certain amount of nickel, the micro-reaction activity of the catalyst is seriously lowered, which is disadvantageous for the catalytic cracking reaction.

The catalytic reaction performance of B₀, B₁, B₂, and B₃ catalysts was evaluated by fixed fluidized bed, and the results are showed in Table 5.

Table 5

Table 5

Table 5 Catalytic performance of B0, B1, B2, and B3catalysts Catalyst Conversion/% Yield/% Dry gas Liquefied Gas C5 gasoline Diesel Heavy oil Coke Total B0 79.87 3.20 18.12 48.47 14.57 4.85 10.09 99.29 B1 75.87 2.61 16.85 45.29 17.89 6.26 11.07 99.97 B2 73.90 2.06 15.31 44.46 19.25 6.38 11.73 98.19 B3 57.90 1.75 11.53 40.82 23.11 7.42 11.90 97.33

Table 5 Catalytic performance of B0, B1, B2, and B3catalysts

It can be seen from Table 5 that under the condition of nickel pollution, over B₀ (0%) catalyst, conversion of heavy oil, yield of C₅ gasoline, dry gas yield and liquefied gas are highest, yield of diesel, heavy oil yield and coke are lowest. This indicates that the cracking depth and cracking activity of the catalyst are strongest.

Under nickel polluted conditions, with the increase of phosphorus, heavy oil conversion and C₅ gasoline yield decrease, yield of diesel and heavy oil increase. Products distribution is poor. This indicates that under the same nickel pollution conditions, loading of phosphorus on the catalyst can not improve conversion of heavy oil and yield of C₅ gasoline, but the cracking depth is reduced, cracking activity and selectivity are weakened. At the same time, this also indicates that supporting phosphorus on the in-situ crystallization catalyst by impregnation method fails to improve nickel resistance of the catalyst. When phosphorus loading is B₃ (1.5%), heavy oil conversion is greatly reduced, only 57.90%. This may be due to the excessive phosphorus blocking the catalyst pores, surface contact surface for heavy oil molecules and catalyst active is small, making the cracking reaction difficult