Preparation of Hierarchically Trimodal-Porous ZSM-5 Composites through Steam-assisted Conversion of Macroporous Aluminosilica Gel with Two Different Quaternary Ammonium Hydroxides

Zhao Tianbo; Wang Jia; Xu Xin; Wang Guijie

(1. School of Chemistry, Beijing Institute of Technology, Beijing 100081; 2. China Coal Information Institute, Beijing 100029)

Preparation of Hierarchically Trimodal-Porous ZSM-5 Composites through Steam-assisted Conversion of Macroporous Aluminosilica Gel with Two Different Quaternary Ammonium Hydroxides

Zhao Tianbo1; Wang Jia1; Xu Xin2; Wang Guijie1

(1. School of Chemistry, Beijing Institute of Technology, Beijing 100081; 2. China Coal Information Institute, Beijing 100029)

The hierarchically structured ZSM-5 composites (HZC) with trimodal pores (macropores/mesopores/micropore) were synthesized by transforming the skeleton of the macroporous aluminosilica gel into ZSM-5 pure phase crystals through steam-assisted conversion method. The monolithic aluminosilica gel was used not only as the silicon and aluminum sources, but also as a structural support. The synthesis parameters, such as the composition of the precursor solution, the Si/ Al feed ratios of the support gel, the time for impregnation of the support with the synthesis mixture and the structure-directing agents (SDAs) with different crystallization temperatures, were investigated. The textural properties of the resulting samples were characterized by means of the Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry (XRD), scanning electron microscopy (SEM) and N2adsorption-desorption isotherms. The experimental results indicated that the HZC could be manufactured with quaternary ammonium hydroxide as SDA without seeding and additional sources of silicon or aluminum, the Si/Al feed ratio of the support and pretreatment time had a significant effect on the morphology of the products using tetrapropyl ammonium hydroxide (TPAOH) as SDA. Furthermore, the textural properties varied from the macroporous aluminosilica gel when different SDAs at different crystallization temperatures were also discussed.

ZSM-5 composites; hierarchically trimodal-porous; steam-assisted conversion method; macroporous aluminosilica gel; quaternary ammonium hydroxide

1 Introduction

Zeolites are a series of porous crystalline materials which have been widely used in heterogeneous catalysis, adsorption, separation and ion-exchange owing to their high hydrothermal stability, strong acidity, unique shape selectivity, intrinsic chemical activity, and regular microporosity[1-5]. However, the zeolitic materials with sole pores are limited in their applications involving bulky molecules, which can generate diffusion limitations and coke deposition to have a negative influence on catalytic activity, selectivity and catalyst lifetime[6-9]. One of the strategies to solve these problems is to construct the hierarchically porous zeolites with at least two levels of pore sizes[10-13]. In recent years, considerable efforts have been devoted towards the preparation of the hierarchical zeolites, such as removal of framework atoms (including dealumination, desilication and irradiation)[5-8,10,11,14], dual templating with surfactants (soft-templating methods)[5-7,10-11,15-16], hard-templating methods (with carbonaceous, polymeric or other solids serving as templates)[5-7,10-11,17-21], assembling of nanosized zeolites[22-23], zeolitization of preformed solids[5,9,12-13,24-32](including vapour phase transport (VPT)[25-26,30,33]and steam-assisted conversion (SAC)[9,29,32,34-37]). Additionally, mixed approaches can also be used to synthesize the composites. However, there is still a big challenge to introduce both mesopores and macropores into zeolitic materials nowadays[6,10]. Zeolitization of preformed solids not only produce mesopores, but also macropores. The hierarchically porous scaffolds canbe categorized into four distinctly different types, namely, silica[12,33-40], silicoaluminophosphate[25], α-AlO[41]23and metal-silicate. When metal-silicate acted as scaffold, zeolite composites such as beta-[24,26,28], TS-1[24], MFI-[27,29,30], and zeolite A bars or tubes[31]had been produced by transforming the pre-formed amorphous aluminosilicate/titania-silica extrudates with the addition of seed gel[27,29-30], porous precursor diatomaceous earth[30], or aluminosilica monoliths prepared by a double-template technique[42]. Most of the above macropores are not interconnected but solely distributed in the monoliths or are parallel to each other[9,24,28,30]. The mesopores can be generated from the intercrystalline framework[24,29]or the effect of surfactant[13,28], furthermore, some of the composites[9,30-31]have no mesopores. The hierarchically structured beta zeolite[26]with trimodal pores manufactured by steam treatment of macro-mesoporous aluminasilica monolith has better activity and stability than the conventional beta zeolite for the transalkylation reaction, nevertheless, the synthesis of the support monolith needs the triblock copolymer to regulate the still worm-like orderless mesostructure. Various types of porous zeolite composites, such as FAU, SOD and GIS were obtained through the partial recrystallization of the amorphous mesoporous/macroporous aluminosilicates using NaOH as a templating agent, the porous aluminosilicates were synthesized by co-precipitation, however, the synthesis conditions were difficult to control and the impurity crystalline substances could readily form[43].

Zeolite ZSM-5 has been found extensive applications in the field of oil refining, petrochemistry, and organic synthesis as a solid acid catalyst[2,44]. So the preparation of the hierarchical porous ZSM-5 zeolite commanded much interest due to the improved mass transport and tunable catalytically active sites in comparison with conventional catalysts. The porous composites of pure Mfiphase were synthesized using TPAOH as the template, the pre-shaped meso-/macroporous silica-alumina monoliths, which were prepared by the sol-gel method using cetyltrimethyl ammonium bromide (CTABr) as the surfactant, which functioned as the scaffold, but the resulting composites might have no mesopores and the zeolite crystals were formed exclusively on the outer surface of the isolated macropores, which might block the material transport[45]. Moreover, the amorphous silica-alumina was partially transferred to ZSM-5 zeolite perhaps because of the insufficient quantity of the template impregnation solution[46]. In our previous work, we prepared the Mficomposites with different types of morphology by transforming the Nakanishi type silica-alumina monolith[47]via the seed-induced insitu and layer-by-layer (LBL) synthetic methods[33]. In this study, we manufactured the HZC via dry gel conversion with the steam-assisted method, the structural support was synthesized without the surfactant, which could exhibit trimodal pores. Besides, we tested various precursor solutions, different Si/ Al feed ratios of the support gel, various impregnation times of the support into the synthesis mixture and different SDAs with different crystallization temperatures to synthesize HZC. The zeolite composites structure and porosity were investigated by FT-IR, XRD, SEM and N2adsorption-desorption analyses. The degree of pore retainment, the morphology and the crystallinity could be systematically controlled by choosing the abovementioned conditions. The method for synthesis of zeolite composites is presented in this paper because this result may provide valuable chemistry for generating macro-/ meso-/ microporous zeolite composites that might be useful in some applications involving bulky molecules.

2 Experimental

2.1 Chemicals and reagents

The macroporous aluminosilica monoliths were prepared through the sol-gel process as previously reported by Ryoji Takahashi, et al.[47-48]albeit with a little change, since the average molecular weight of the phase separation agent polyethylene oxide (PEG, Xilong Chemical Co., Ltd, China) used in experiments was 10 000 instead of 100 000. Tetraethyl orthosilicate (TEOS, Beijing Chemical Plant, China) and aluminum nitrate nonahydrate (Al(NO3)3·9H2O, Tianjin Jinke Fine Chemical Research Institute, China) were used as sources of silicon and aluminum, respectively. Nitric acid (HNO3, 65 wt%, Beijing Chemical Plant, China) was used as the catalyst for the hydrolysis and polycondensation of TEOS. Deionized (DI) water was used throughout the study.

The synthesis of ZSM-5 zeolite applied the organic templates directing method. The reactants used in thissection are shown below. Tetraethyl ammonium hydroxide (TEAOH) and tetrapropyl ammonium hydroxide (TPAOH) were used as SDA, both of which were provided by the Sinopec Research Institute of Petroleum Processing. Sodium hydroxide pellets (NaOH, 96% pure) were manufactured by the Xilong Chemical Co., Ltd., and sodium aluminate (NaAlO2, Al2O3content≥41%) was manufactured by the Sinopharm Chemical Reagent Co., Ltd. All reagents were used without further purification.

2.2 Synthesis

2.2.1 Preparation of macroporous aluminosilica gel

The mixed oxides of hierarchically porous alumina-silica monoliths with different Si/Al feed ratios were prepared by adding different amounts of aluminum source, labeled as SA-40, SA-30, SA-20 and SA-10, respectively. A typical procedure for synthesis of SA-20 was as follows. Firstly, 1.2 g of PEG was dissolved in a mixture containing 1.8 mL of HNO3, 1.62 g of Al(NO3)3·9H2O and 20 g of DI water. Subsequently, 18 g of TEOS was added under vigorous stirring for 30 minutes. The resulting homogeneous and transparent solution was moved into a plastic container with its top tightly sealed, and was aged at 323 K for 24 h. After gelation, the wet gel obtained thereby was then dried at the same temperature for 7 days. Finally, the dried sample was subjected to calcination with its temperature raising from room temperature to 973 K for 2 h.

2.2.2 Preparation of monolithic zeolite

Herein, The HZC were synthesized by transforming the skeletons of silica-alumina monolith into zeolite through the SAC method. The starting aluminosilica monolith was firstly immersed in the precursor solution under ultrasonic conditions until no bubbles were observed, and then the solution was left to stand for different time intervals. The molar compositions of different precursor solutions are listed in Table 1. The precursor solution containing TPASi-Al was prepared by mixing sodium hydroxide pellets, sodium aluminate, TEOS, TPAOH (30.39% solution) and DI water according to a molar composition of Na2O: Al2O3: 25SiO2: 1 200 H2O: 4 TPA.

Subsequently, the monolith was transferred into shelves built via handwork inside the autoclave, which was filled with 10 mL of pre-added 1% TPAOH solution at the bottom, and then was subjected to SAC at 423 K for 48 h. Finally, the obtained materials were washed with DI water, dried at 373 K for more than 24 h and calcined at 823 K for 6 h to remove the SDA.

Table 1 Conditions for the synthesis of HZC

2.3 Characterization

The XRD patterns were recorded on a Shimadzu 7000 diffractometer using Cu Kα radiation (at a tube voltage of 40 kV and a tube current of 30 mA) at a scan rate of 5(°)/min through each step of 0.02°, and at 2θ angles ranging from 5° to 90°.

The microstructures of the fractured surfaces of the samples were observed by SEM micrographs taken by a Hitachi S-4800 scanning electron microscope (25 kV).

The IR spectra were recorded on a Thermo Scientific FTIR spectrometer with samples pressed in KBr pellets.

The nitrogen adsorption-desorption experiments were carried out at 77 K on a Micrometrics QUADRASORB SIsurface area analyzer and pore size analyzer. All samples were degassed at 573 K prior to each measurement. The micropore volume and micropore surface area were determined by the t-plot method. The mesopore size distribution, the mesopore volume and the mesopore surface area were calculated from the desorption branch using the Barrett- Joyner- Halenda (BJH) method, and the surface area was determined using the Brunauer- Emmett- Teller (BET) method. The total pore volume was evaluated at p/p0=0.99.

3 Results and Discussion

3.1 Effect of the compositions of the precursor solution on the zeolite loading

The original silica-alumina monoliths were immersed in the precursor solution having different compositions under ultrasonic conditions until no bubble was observed, then were left to stand for 30 min. Figure 1 shows the XRD patterns of the HZC samples treated with different precursor solutions. When the solution, which was synthesized to form high crystallinity zeolite ZSM-5, was used as precursor solution, the XRD pattern of the resultant composite labelled as TPA-Si-Al (Figure 1a) showed a broad band in the 2θ range of 17°—27°[49], which was characteristic of the amorphous hierarchically porous alumina-silica mixed oxides monoliths. The broad reflections were also observed for TPA-Si (Figure 1b) corresponding to the amorphous support. The sample collected from TPA-Al (Figure 1c), which showed no additional silicon source added to the precursor solution, exhibited diffraction peaks at 7.99°, 8.88°, and 23.20° that were assigned to the MFI-type zeolite. The existence of the halo of the amorphous monolith and the lower ZSM-5 crystallinity suggested that amorphous aluminosilicate macroporous walls were partly converted into the Mfistructure. Nevertheless, without silicon and aluminum source in the precursor solution, TPA (Figure 1d) exhibited higher Mfipeaks as compared to TPA-Al and the halo of amorphous aluminosilicate gel disappeared, indicating that the amorphous phase was almost completely consumed, which had been further verified by the IR spectra. As shown in Figure 2c and 2d, the bands at 550 cm-1and 1 220 cm-1were characteristic of ZSM-5 zeolite; moreover, the higher intensity of the band of TPA (Figure 2d) indicated that the ZSM-5 obtained from the porous aluminosilicate monoliths was highly crystalline. Additionally, the diffraction peaks corresponding to ZSM-5 of TPA-Al showed a small shift to higher degree from the peaks of TPA. This difference could be attributed to the unique unit cell parameters of the two samples. It is known that the interplanar crystal spacing reduced[50]and the unit cell shrank[51-52]with the increase of SiO2/Al2O3ratio in the zeolite, which was caused by the shorter bond length of Si—O (0.161 nm) than that of Al—O (0.175 nm). The different precursor compositions between TPA-Al and TPA resulted in the difference of the eventual SiO2/Al2O3ratios in the zeolite. With regard to TPA, the silicon and aluminum sources used to synthesize zeolite ZSM-5 all came from the macroporous silica-alumina monoliths. Because of the different dissolution rates between silicon and aluminum, silicon was more abundant than aluminum. On the other hand, at the beginning of the reaction, aluminum usually was adsorbed or would form complex onto the surface of the porous aluminosilicate monolith[49], the aluminumsource was more needed for the growth of zeolite. Thus, in the current synthesis system, the SiO2/Al2O3ratio of the TPA was suitable for supporting the ZSM-5 zeolite, otherwise other Si/Al ratios were not in the appropriate range.

Figure 1 XRD patterns of the HZC samples treated with different precursor solutionsa—TPA-Si-Al; b—TPA-Si; c—TPA-Al; d—TPA

Figure 2 IR spectra of the HZC samples treated with different precursor solutionsa—TPA-Si-Al; b—TPA-Si; c—TPA-Al; d—TPA

3.2 Effect of Si/Al feed ratio of the support on the zeolite loading

To study the effect of alumina of the support on the zeolite loading, the support samples were prepared by varying the TEOS to Al(NO3)3·9H2O molar ratios in the initial gel mixture in the range from 10 to 40 followed by immersion of the gel in the TPAOH solution for 30 min after no further bubble was delivered. The HZC samples obtained during the synthesis process were denoted as SAZ-40, SAZ-30, SAZ-20 and SAZ-10, respectively, where the suffix indicates the molar ratio of silica source to aluminum source added to the reaction mixture. The crystallinity of the resulting HZC shows its dependence on the Si/Al feed ratios. As shown in Figure 3, SAZ-30 (Figure 3b) exhibits the highest crystallinity, followed by SAZ-40 (Figure 3a) and SAZ-20 (Figure 3c). However, SAZ-10 (Figure 3d) with the addition of a largest amount of aluminum source displayed a broad halo centered at around 21°, suggesting that the lower Si/Al ratio in the feed was not readily susceptible to form ZSM-5 zeolite, which agreed well with the earlier report issued by Gao, et al.[53]This phenomenon might be caused by the higher amount of adsorbed aluminum, which was not conducive to the formation of nuclei when the silicon skeleton of the Mfistructure was gradually depolymerized to release the adsorbed aluminum species to form the lattice by a certain arrangement during the crystallization process. The morphology of the resulting HZC also showed its dependence on the Si/Al feed ratio. The image of SAZ-20 (Figure 4c) displayed three-dimensionally interconnected macroporeswith a diameter of ca. 3 μm, which were aggregated with small particles, about 200 nm in diameter, on the inner surface of the macroporous aluminosilicate monolith. The macropore size of SAZ-20 was similar to the original gel named SA-20 (inset of Figure 4c), whereas the samples named SAZ-40 (Figure 4a) and SAZ-30 (Figure 4b) exhibited larger particles with their diameter in the range of 500—600 nm, which could reduce the porosity of the support’s macropores, while SAZ-30 (Figure 4b) showed large amount of bulk ZSM-5 crystals and the destroyed support skeleton, which agreed well to the result of the highest crystallinity of the XRD analysis. In contrast, SAZ-10 (Figure 4d) with no zeolite loaded wherein showed the uncrosslinked skeleton as the original aluminosilicate monolith formed at a Si/Al feed ratio of 10.

Figure 3 XRD patterns of the HZC with different feeding Si/Al ratios of the supporta—SAZ-40; b—SAZ-30; c—SAZ-20; d—SAZ-10

Figure 4 SEM images of the HZC with different Si/Al feed ratios of the supporta—SAZ-40; b—SAZ-30; c—SAZ-20; d—SAZ-10

3.3 Effect of the impregnation time of the support on the zeolite loading

The hierarchically porous alumina-silica mixed oxides monoliths obtained at a Si/Al feed ratio of 20, namely: SA-20, was immersed in the TPAOH solution for various periods of time to investigate their influence on the zeolite loading, the sample formed thereby was designated as SA-20-x, where x represented the impregnation time (in hours). Figure 5 shows that the relative crystallinity of the HZC at first increased and then decreased with an increasing impregnation time. The inset of Figure 5 reveals that the major characteristic peaks of ZSM-5 were obvious during impregnation of samples within 0.5—12 h, however, after extending the immersion time to 24 h, the peak at 23.2° corresponding to the crystal plane (200) was significant, while the other peaks of planes (101), (501), (422) and (313) were small. After further extending the immersion time to 36 h, only a much weaker peak corresponding to the plane (200) was identified, and other peaks disappeared, indicating that the immersion time was too long to load ZSM-5 zeolite. When the soaking time was less than 2 h, the increased formation of crystal nuclei resulted in the increase in the total amount of deposited ZSM-5 as well as its crystallinity. Because of the different dissolution rates between silicon and aluminum, the longer soaking time caused the mismatching of silicate and aluminate, which could lead to a decrease of crystallinity. It can be seen from Figure 6 that SEM observations of the samples revealed that longer immersion time could lead to a large number of ZSM-5 particles with smaller crystal size, and when the immersion time was less than 2 h, an outcome in the reverse direction was obtained. After having been immersed in the TPAOH solution for 2 h (Figure 6a), the ZSM-5 particles with crystal size in the range of about 200—300 nm were deposited on the inner surface of the support. Furthermore, the size and the morphology of the ZSM-5 particles were homogeneous compared to the sample that had been immersed in the solution for 0.5 h (Figure 4c). However, the macropores size of SA-20-2 was smaller than SAZ-20, viz. SA-20-0.5 (Figure 4c). It can be seen that a majority of the ZSM-5 crystals were spherical with a diameter of about 1—2 μm in the sample SA-20-4 (Figure 6b) and were composed of prismatically shaped hexagons with a size of about 1 μm in the sample SA-20-8 (Figure 6c). Besides these crystals, there were still macropores with a pore size of about 1—2 μm. The sample SA-20-12 (Figure 6d) exhibited irregular ZSM-5 particles with a size of about 2 μm on the skeleton, which showed more fine framework caused by the excessive dissolution.

3.4 Effect of different crystallization temperatures using TEAOH as SDA on the zeolite loading

Figure 5 Relative crystallinity curve of the HZC obtained at different impregnation times (The inset is the XRD patterns of the HZC)a—SA-20-0.5; b—SA-20-1; c—SA-20-2; d—SA-20-4; e—SA-20-6; f—SA-20-8, g—SA-20-12;h—SA-20-24; i—SA-20-36

Figure 6 SEM images of the HZC with different impregnation timea—SA-20-2; b—SA-20-4; c—SA-20-8; d—SA-20-12

Figure 7 XRD patterns of the HZC prepared at different crystallization temperatures using TEAOH as SDAa—TEA-423; b—TEA-443

Figure 8 SEM images of the HZC sample prepared at different crystallization temperatures using TEAOH as SDAa—TEA-423; b—TEA-443 (Inset of b is the SEM image enlarged at high magnification.)

Figure 7 presents the effect of crystallization temperature using TEAOH as SDA on the zeolite loading. Crystallization of ZSM-5 occurred both in the TEA-423 sample (Figure 7a) and the TEA-443 sample (Figure 7b). It can be seen that the ZSM-5 peaks of the TEA-423 sample were superimposed on the highly scattering background from the amorphous aluminosilicate gel, while no amorphous phase was observed in the XRD pattern of the TEA-443 sample, indicating that the higher crystallization temperature obviously promoted the crystallization of ZSM-5 zeolite. The morphology of the resulting HZC also varied at different crystallization temperatures. The image of TEA-423 sample (Figure 8a) exhibited a rough surface compared with the smooth inner surface of the macroporous aluminosilicate gel. Besides, the interconnected skeleton was aggregated with small particles, ca. 0.5 μm in diameter. However, the morphology of the TEA-443sample (Figure 8b) displayed a thinner and more uniform skeleton. The magnification of the TEA-443 sample (inset of Figure 8b) showed that the inner surface of the gel was obviously smooth and there was no zeolite crystal deposited on the skeleton. Compared to the image of SA-20-2 (Figure 6a), which was impregnated for 2 h by using TPAOH as SDA, the TEA-443 sample exhibited slightly larger macropores and better permeability than SA-20-2. Figure 9 shows the isotherms of N2adsorption for the original macroporous aluminosilicate gel and the HZC obtained with different SDAs. All samples exhibited similar type IV isotherms with H4-type hysteresis loop, indicating that the materials possessed the uniform slit-like mesopores. The steep uptakes at the relative pressure p/p0<0.02 represented the existence of micropores[20,22,25-26,28], and the little increase in adsorption occurred when the p/p0>0.9, indicating to the presence of macropores[6,18-19,35,39,50]. The capillary condensation occurred at lower pressure corresponding to the smaller mesopores. As revealed by the BJH pore size distribution curves, mesopores were distributed in a broad range. Moreover, the textural properties of the samples summarized in Table 2 indicated that the samples exhibited a trimodal macro-/ meso-/ microporous structure and had similar mesopores, whereas, the BET specific surface area and the volume of total pores, mesopores and micropores of the original macroporous aluminosilicate gel were larger than those of the HZC after the steam-assisted conversion because of the structural change of the aluminosilica skeleton during the crystallization. The micropores of the hierarchically porous aluminosilica gel came from the interstices of the primary aluminosilica particles, and the mesopores were formed by the secondary particles, which was constructed from the aggregates of primary particles[54]. Meanwhile, the different mesoporous and microporous volume between two samples indicated to the different effect of different SDAs on the textural properties.

Figure 9 N2physisorption isotherms (left) and BJH pore size distribution (right) of samples■—SA-20;●—TPA-423;▲—TEA-443

Table 2 Pore structural parameter of macroporous aluminosilicate gel and the macroporous ZSM-5 composites with different SDAs

4 Conclusions

In summary, a synthetic method has been established for the preparation of ZSM-5 zeolite composites with a hierarchical pore system by steam-assisted transformation of the micro-/ meso-/ macroporous silica-alumina monolith without seeding. The support can provide silicon and aluminum species which join in the skeleton zeolitization in the presence of different quaternary ammonium hydroxides as SDAs. Based on the consideration of the different dissolution rates between silicon and aluminum, coupled with the support skeletal retention, characterization of samples by XRD and SEM analyses showed that higher Si/Al ratio and shorter immersion time favored the ZSM-5 zeolite loaded on the support with higher relativeintensity and better morphology. When crystallization was conducted at lower temperature using TPAOH or TEAOH as SDA, the ZSM-5 zeolite preferentially grew on the external surface of the support skeleton, and when TEAOH was used as SDA, the crystallization at higher temperature could produce smoother and larger macropores. The resulted hierarchically trimodal-porous ZSM-5 composites partially retained the macropores of the parent aluminosilicate support, and exhibited textural properties that were different from the original support. The interconnected macropores facilitated the transport of large reactants to mesopores or micropores in which reactions could take place. It is believed that the hierarchically porous ZSM-5 composite will be extensively used as catalysts, ion exchange agents and adsorbents in industries.

Acknowledgements:The authors are pleased to acknowledge the financial support by the National Natural Science Foundation of China (No. 20973022 and No. 11472048).

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Commissioning of First in the World DMTO-II Demonstration Unit in Pucheng City

On December 21, 2014 the first in the world coal-based second-generation methanol-to-olefin (DMTO-II) commercial demonstration unit was successfully started up at the Clean Energy Chemical Company Limited in Pucheng city, Shaanxi province, which has symbolized the major achievements of this phase associated with the dissemination and application of the new generation technology for manufacture of olefins from methanol, the independent intellectual property rights of which are in the hands of this Chinese enterprise.

This unit is one of the core production units comprising an 1.8 Mt/a methanol project and a 700 kt/a coal-based olefins project, and is the first commercial demonstration DMTO-II unit, which was constructed using the technology jointly developed by the CAS Dalian Institute of Chemical Physics, the Shaanxi Xinxing Coal Chemicals Company Limited and the SINOPEC Luoyang Petrochemical Engineering Company. It is learned that the DMTO-II technology includes the MTO reaction and regeneration (the 1st generation technology) system and the C4reaction and regeneration system, while the newly added C4+ recycle system can increase the ethylene and propylene yield by 10%. In comparison with the 1st generation DMTO technology, the DMTO-II technology is characteristic of low energy consumption and significant reduction of production cost to assume an international leading position.

Furthermore, the downstream polypropylene unit of this project had been precommissioned on December 30, 2014, while the PE unit was also started up on January 4, 2015.

date: 2014-11-04; Accepted date: 2015-01-09.

Professor Zhao Tianbo, Telephone: +86-10-88583326; E-mail: zhaotb@bit.edu.cn.