Comprehensive Utilization of Filter Residue from the Preparation Process of Zeolite-Based Catalysts

A novel utilization method of filter residue from the preparation process of zeolite-based catalysts was investigated. Y zeolite and a fluid catalytic cracking (FCC) catalyst were synthesized from filter residue. Compared to the Y zeolite synthesized by the conventional method, the Y zeolite synthesized from filter residue exhibited better thermal stability. The catalyst possessed wide-pore distribution. In addition, the pore volume, specific surface area, attrition resistance were superior to those of the reference catalyst. The yields of gasoline and light oil increased by 1.93 and 1.48 %, respectively. At the same time, the coke yield decreased by 0.41 %. The catalyst exhibited better gasoline and coke selectivity. The quality of the cracked gasoline had been improved.


Introduction
The main raw materials for the production of molecular sieve FCC catalyst include water glass, sodium hydroxide, aluminium hydroxide, kaolin, sulphuric acid, hydrochloric acid, liquid ammonia, ammonium chloride, and chlorinated rare earth, alkali, salt, etc.The molecular sieve FCC catalyst is prepared through three processes that involve synthesis of molecular sieve, modification of molecular sieve, and preparation of catalyst.During the above processes, a large amount of filter residue is produced.The filter residue is a mixture of amorphous silica-aluminas, zeolites Y and ZSM-5, composed mainly of silica, alumina, Re 2 O 3 , Na 2 O, Fe 2 O 3 .The moisture content in the filter residue is above 70 %.Compared to kaolin, the filter residue has larger pore volume, specific surface area.
Zeolite-based catalysts manufacturers generate tens of thousands tons of catalyst filter residue each year during production, causing environmental problems that are difficult to handle.2][3][4] Application of the filter residue was limited to extracting useful components, such as extracting active SiO 2 and Al 2 O 3 .The filter residue is predominantly used in the field of construction materials, such as filler for asphalt, and production of bricks and cement.NaX and 4A zeolite were also synthesized using these solid wastes.
9][10] The in situ synthesised zeolites have an ideal hydrothermal stability.In situ synthesizing of zeolite can surmount the difficulty of filtration in industrial production and reduce production costs.Because the filter residue has active useful components, these components can be used for the synthesis of zeolite.We envision synthesizing zeolite Y via in situ crystallization technology that enlarges utilization catalogues and quantities of industrial filter residue.
Herein, Y zeolite and an FCC catalyst were synthesized from filter residue.The physicochemical properties of synthesized zeolite and the cracking activity of the catalyst were investigated.The reference NaY zeolite synthesized by the conventional method involved the following steps: A reaction mixture was prepared by mixing the zeolite initiator with sodium silicate, and adding sodium aluminate solution.The mixture was stirred vigorously, and an aluminium sulphate solution was added to the mixture.The mixture was then heated at a temperature of 95 °C.After 28 hours, the product was filtered and washed.The X-ray diffraction analysis showed an excellent pattern characteristic of zeolite Y.

Catalyst preparation
Deionized water, kaolin, pseudo-boehmite were mixed with a hydrochloric acid solution and stirred at a rate sufficient to form a uniform slurry.The mixture was stirred for 2 h.Alumina sol and modified YZ were subsequently added, the mixture was stirred at room temperature for 1 -2 h.The mass ratio of deionized water, kaolin, pseudo-boehmite, alumina sol and modified YZ was 200 : 40 : 13 : 12 : 35.The catalyst (CAT) with a particle size of 0 -150 μm was produced by spray drying, then calcined at 500 °C for 0.5 h, washed with warm water, and dried.
The reference catalyst (RCAT) was a residue FCC catalyst obtained from a domestic refinery with a specific surface area of 283 m 2 g −1 and a specific pore volume of 0.22 cm 3 g −1 . 11

Sample characterization
Relative crystallinity, silica/alumina, crystalline unit cell size and phase of samples were recorded on a Rigaku Ultimi IV diffractometer using Cu-Kα radiation (λ = 1.54056Å) at an operating voltage and current of 40 kV and 30 mA, respectively.The samples were scanned at 0.2 ° min −1 .
The IR spectra were recorded on an AVATAR 370 FT-IR spectrometer in the range from 400 to 2000 cm −1 .The acidity properties of samples were determined using pyridine adsorption method.The FTIR spectra exhibited peaks at 1540 and 1450 cm −1 , suggesting the existence of Brønsted acid sites, and Lewis acid sites, respectively.The acid strength distributions were quantitatively calculated from the pyridine adsorbed IR spectra at 200 and 400 °C (representing total acid amount and strong acid amount, respectively). 8The morphology and size of the samples were determined using scanning electron microscopy (SEM) (JEOL JSM-6360) after coating with an Au-evaporated film.The specific surface areas, specific pore volumes, and pore size distributions were measured on an ASAP 2020 sorptometer using adsorption and desorption isotherm plots at 77 K.A Malvern Micro-P particle-size distribution analyser was used for determining the size distribution in the samples.The attrition index of the catalyst was determined using an attrition index analyser by the air injection method.

Catalytic properties evaluation
The catalytic performance of the catalyst was evaluated on an advanced catalyst evaluation bench unit (ACE, Kayser Corp.).The evaluation conditions were as follows: reactor temperature of 520 °C, catalyst-to-oil mass ratio of 6.0 and WHSV of 19 h −1 .Prior to evaluation, the catalyst was steam-deactivated at 800 °C for 17 h with 100 % steam.The feedstock oil consisted of a mixture of 70 % vacuum gas oil (VGO) and 30 % vacuum tower bottom (VTB), and its properties are listed in Table 2.

Structure of zeolite
The chemical composition of CFR was mainly composed of SiO 2 and Al 2 O 3 , and had higher specific surface area and specific pore volume (Table 1).Using this CFR as raw material, the typical zeolite Y can be obtained.The intensity and shape of the peaks in Fig. 1 indicated that the sample was pure zeolite Y.Under the optimum conditions, the synthesized Y zeolite (YZ) had a relative crystallinity of 71.5 %, and a silica/alumina amount ratio of 5.7, respectively.Fig. 2 displayed that the sizes of the Y zeolite particles were 0.2 -0.5 μm, which indicated that smaller crystals had agglomerated with the larger particles.Fig. 3 shows the nitrogen adsorption-desorption isotherms and pore-size distribution of YZ.Typical type IV isotherms of YZ confirmed the presence of mesopores and macropores.YZ possessed a wide pore distribution, the distribution was concentrated on approximately 3.0, 4.0, and 5 -10 nm, respectively.The total specific surface area of YZ reached a maximum of 640 m 2 g −1 and its external specific surface area was 76 m 2 g −1 (Table 3).The fraction of the external surface area in total surface area was 11.9 % (Table 3), which was much larger than that of Y zeolite synthesized by the conventional method, its fraction of external surface area in total surface area was only 4.4 %.Fig. 4 shows TG-DTA spectra of YZ.When calcination temperature was up to 920 °C, the skeleton of YZ collapsed, while skeleton collapse occurred at about 850 °C for zeolite synthesized by the common route. 12YZ exhibited high thermal stability.The main reason is that the YZ zeolite led to wide distribution of particles, which reduced the instability due to low coordination of zeolite synthesized by the common route. 13g. 4 -TG-DTA spectra of YZ Slika 4 -TG-DTA-spektar zeolita YZ

Characterization of catalyst
The properties of the catalyst and the reference catalyst are summarized in Table 4. Comparably, the catalyst has a much larger BET surface area, micropore surface area, total pore volume, and average pore diameter.There were more surface active atoms on the surface compared to the reference catalyst.Therefore, reactant molecules easily get close to the active sites, and thus improve the utilization rate of active sites, leading to higher conversion by the catalysts.total pore volume ⁄ ml g −1 specifični ukupni obujam pora ⁄ ml g −1 0.35 0.22 micropore pore volume ⁄ ml g −1 specifični obujam mikropora ⁄ ml g −1 0.18 0.10 BJH pore volume ⁄ ml g −1 obujam pora po BJH-u ⁄ ml g −1 0.20 0.14 average pore diameter ⁄ nm prosječni promjer pora ⁄ nm 5.30 4.20 unit cell size ⁄ nm veličina jedinične ćelije ⁄ nm 2.460 2.456 Fig. 5 shows the nitrogen adsorption-desorption isotherms and pore-size distribution of CAT and RCAT.In Fig. 5 (1), the isotherms of CAT had a steeper drop and a larger hysteresis loop than RCAT, indicating that larger pores existed in CAT.In Fig. 5 (2), the distribution of CAT appeared from approximately 4.0 to 100 nm, a broad distribution was observed in the pore diameter range > 60 nm, signifying the existence of macropores, and RCAT was observed at approximately 4.0 nm.These results confirmed the hierarchical pore structure of CAT.The catalysts with hierarchical pore structure have the advantages of microporous materials and meso-macroporous materials.Hierarchical materials possessing at least two levels of porosity can reduce diffusion limitations in reactions catalysed by microporous zeolites, which have good selectivity and mass transfer capability. 14The determined acidities of CAT and RCAT are listed in Table 4 and Fig. 6.Comparably, the strong Brønsted acid and the weak Lewis acid amounts of CAT were higher.The more Brønsted acid sites are ascribed to the better crystal structure of Y zeolite synthesized from filter residue.

Catalytic properties evaluation
The results of catalytic performance for CAT and RCAT are shown in Table 6.It can be seen that compared with the RCAT, the CAT can increase gasoline yield, conversion and liquid yields (LPG + gasoline + LCO) by 1.93, 2.27 and 2.29 %, respectively.At the same time, coke yield is decreased by 0.41 %.Table 7 shows the cracked gasoline compositions over the two catalyst.Comparably, the olefin content of CAT reduced by 2.98 % with the research octane number, and motor octane number of gasoline increased by 0.7 and 0.5.These excellent catalytic performances can be attributed to the novel utilization technology of industrial filter residue.
2.1 MaterialsCatalyst filter residue (CFR) was obtained from the Catalyst Factory of Sinopec in China.The filter residue was white gel.Moisture content was 77.8 %.The properties of CFR