Synthesis, Acidity and Catalytic of the Rare Earth Ce Loaded on the Composite Pore Zeolite Catalyst for Hydrogenation Cracking

Reagents and apparatus

The heavy oil is daqing-mixing oil, while the main properties of it are shown in Table 1.

Sodium aluminate, sodium hydroxide, sodium silicate, cerium nitrate, heptane, toluene, and tetraethyl orthosilicate (TEOS) were all analytical pure reagents and purchased from Sinopharm Group Co. Ltd. Triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic P123) was purchased from Sigma Aldrich, America. Y-type microporous materials are provided by Fushun Petrochemical Research Institute.

The catalyst was synthesized with XH-MC-1 laboratory microwave reactor, and was characterized by GC7890II gas chromatograph, WYS-2S digital thermogravimetric analyzer, and WAY-IS abbe refractometer. Strengthen the catalyst cracking performance is completed by strengthening cracking transpose (made by ourselves).

Synthetic experiments

A 4.0-g triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) P123 was dissolved in 30.0 g of deionized water and stirred until fully dissolved. To the above solution was added 9.5 g of TEOS and stirred magnetically and powerfully, followed by the addition of 2.0 g prepared Y-type microporous materials and 120 ml certain concentration of hydrochloric acid, resulting a mixture solution with pH of 2 by a powerful magnetic stirring. After reacting in microwave reaction apparatus at 100 °C for 2 h, the crystallized product was washed with fresh deionized water and transferred again in an autoclave dried at 110 °C. Finally, the solid was calcined at 550 °C to afford a powder micro–mesoporous Y/SBA-15 composite material.

Certain amount of cerium nitrate was dissolved in concentrated sulfuric acid to afford a saturated Ce(NO₃)₂–H₂SO₄ solution, followed by the addition of the activated Y/SBA-15. One gram of the calcined Y/SBA-15 composite material was impregnated with 15 ml saturated Ce(NO₃)₂–H₂SO₄ solution and stirred at room temperature for 24 h. The resulting mixture was filtrated several times and the resultant solid was transferred again in an autoclave dried at 100 °C for 24 h. Finally, the solid was calcined at 550 °C for 3 h to afford the desired catalyst.

First, we take a certain quality of molecular sieve (conditions: Ce-Y/SBA-15, Y/SBA-15, Y), Al₂O₃, field of well-known powder and deionized water, then mix them, at last, turn them into the dough by rolling method. We put the dough in a squeeze of the extruding machine, next get mitsubishi article carrier, and then cut them into small pieces. The pieces were dried at 100 ℃ for 6 h and calcinated at 823 K for 5 h. Catalyst samples are named respectively as: C-X, C-Y, and C-Z.

Catalyst characterization

FT-IR was conducted to analyze the components change during the catalyst preparation; KBr (IR grade) was used to prepare the pellet (1:200). Thus, the raw powder of the molecular sieve was grinded with KBr (IR) with a ratio of 1:200 to afford the KBr pellets, with a testing range of wace number of 4,000–400 cm⁻¹.

X-ray fluorescence spectrometry (XRF) images were recorded on a JEOL X’Pert ProI-type X-ray fluorescence spectrum instrument.

Pyridine adsorption in spectrometry (Py-FTIR) was taken on a Fourier spectrometer Bio-Rad FTS15/C-type instrument.

Thermal analysis (TG-DTG) was conducted by NETZSCH STA449F3C 951-type instrument.

Hydrocracking reaction

Design parameters of hydro cracking unit are in Table 2.

The evaluation conditions of hydrocracking reaction

Heavy oil is Daqing-mixed VGO. Heavy oil is plunger into the vaporizing chamber by double-trace pump, which occurs gasification and mixed with hydrogen at high temperature, and then mixed gas went into the preheating chamber and the reactor. The material of the reactor is stainless steel, the length of 540 mm, inner diameter of 10 mm. Filling length is 10 cm of catalyst in the reactor, the rest of the ceramic is filled by bead with 30 purposes.

Evaluation criteria of the hydrocracking reaction

Miniature hydrocracking reactor increased its temperature to 180 °C by the rate of about 2 °C/min, when the temperature reaches 330 °C temperature for 6 h, and then we empty the separator. Continue reflecting for 4 h, the record into the fluid volume and the amount of produced liquid, and gas chromatography analysis. In the hole reaction process, the total reaction pressure is 3 mPa, space velocity is 3 h⁻¹, and hydrogen oil volume is 700:1.

IR specrum

Figure 1 illustrates the IR-spectra patterns of C-X, C-Y, and C-Z. C-X’s characteristic peak is 792 cm⁻¹ and SBA-15’s characteristic peak 1,096 cm⁻¹. OH-group (1,632 cm⁻¹) and Si–OH–group (3,500 cm⁻¹) of the C-Y is not the same as the single C-Z or SBA-15, respectively. The absorption peaks (488 cm⁻¹, 1,096 cm⁻¹) of C-X is more obvious than C-Y [21]. There are still C-Y’s skeleton characteristic absorption peaks in C-X, which shows that there is no distinction between C-X and C-Y at the endemic skeletal structures.

Figure 1:

IR-spectra patterns of C-X, C-Y, and C-Z.

XPS specrum

Table 3 listed out silica alumina ratio of the three kinds of molecular sieve catalyst. Silica alumina ratio of C-X is the highest of the three kinds of molecular sieve catalyst. It indicated that the acid center density of molecular sieve loaded on Ce decreased and the acid strength increased.

The higher the silica alumina ratio is, the better thermal stability and hydrothermal stability of molecular sieve have. Because C-X’s silica alumina ratio is higher than C-Y’s, C-X has better thermal stability and hydrothermal stability than C-Y. Therefore, based on the XRF data, the order of acid strength, thermal stability, and hydrothermal stability from big to small is: C-X, C-Y, and C-Z. The type of acid and acid strength is needed to prove by virtue of further characterization methods such as Py-FTIR spectra.

Py-FTIR spectra

Figure 2 shows Py-FTIR spectra of pyridine desorbed on C-X, C-Y, and C-Z. The IR spectra of pyridine desorption at 473 and 673 K are shown in Figure 2. A characteristic absorption peak (1,442 cm⁻¹) belongs to weak acid L of C-Z shows that the Na⁺ and non-framework aluminum species of C-Z are in weak acid L. The concentration of pyridinium ions (1,545 cm⁻¹, the signature of Brǿnsted acid sites) is higher with Ce loaded at 473 and 673 K than without Ce [22, 23], whereas the coordinated pyridine (1,455 cm⁻¹, the signature of Lewis acid sites) is of the basic quite with C-X and C-Y [24]. The value of L acid center strength from big to small is C-Y, C-X, and C-Z.

The addition of rare earth can improve the activity of the catalyst. In molecular sieve cage, rare earth ions increased the probability of electronic migration to the cage on the skeleton and hydroxyl silicon aluminum hydroxy through function and induced polarization effect. Due to the increased density of electron cloud of molecular sieve’s cage, hydroxy has the stronger B acid strength than without Ce, while accordingly improve the activity of C-X. The value of B acid center strength from big to small is C-X, C-Y, and C-Z.

Figure 2:

Py-FTIR spectra of pyridine desorbed on C-X, C-Y, and C-Z.

TG-DTG specrum

The thermal decomposition curves of two kinds of catalysts were shown in Figure 3. Two kinds of catalyst’s decomposition temperature are both at 700 K, whereas they have good stability. It suggested that the two kinds of catalysts have no volatile under the condition of catalytic reaction’s temperature.

Figure 3:

The thermal decomposition curves of two kinds of catalysts.

Catalytic of the catalyst

Table 4 shows the evaluation results of catalyst with homemade on the hydrocracking device. Hydrocracking catalysts for enhancing middle distillates yield were prepared by such composite supports [25, 26]. Composite molecular sieves’ selective of middle oil is higher and the product performance is better than microporous molecular sieves’, respectively. They have fantastic smoke point of aviation kerosene and tail oil of BMCI value. Under the same reaction temperature, as compared with C-Z, the selectivity and yield of middle distillates over C-X was 4.0 % and 4.7 % higher, respectively; besides, it is 0.7 % higher in contrast C-Y. It adequately embodies the advantages of Ce doped on composite molecular sieves which applied to the hydrocracking of heavy oil.

Reusability of the catalyst

The ability to be recycled and reused is an important criteria for catalysts, so the reusability of the three catalysts, C-X, C-Y, and C-Z, was investigated under the optimized esterification reaction conditions. The results are shown in Table 5.

From Table 5, it can be seen that there was an increase in the recycling times, and an obvious decrease in the yield of middle oil after reusing the catalyst for three cycles. This can be attributed to the loss of amount and surface activity of the catalyst caused by washing and filtration steps during the recycling process. In order to maintain the yield of middle oil, the quality of the catalyst should be increased and the catalysts should be activated.

Overall, the yield of middle oil by using C-X is higher than that by using C-Y or C-Z. This result is consistent with our expectations, as the value of B acid center strength from big to small is C-X, C-Y, and C-Z.