Methylation Of 2-methylnaphthalene Research Articles

HBEA/MTW composite molecular sieves with shape-selectively catalyzed alkylation of 2-methylnaphthalene with methanol for the synthesis of 2,6-dimethylnaphthalene

The methylation of 2-methylnaphthalene (2-MN) and methanol is a highly promising approach to synthesize 2,6-dimethylnaphthalene (2,6-DMN). However, it is difficult to control the target product selectivity. Herein, a series of HBEA/MTW composite molecular sieves by secondary crystallization were produced by hydrothermal method and further applied for the alkylation of 2-MN. The results showed that composite molecular sieves had higher specific surface area and porosity than mechanically mixed molecular sieves, and the secondary crystallization reduced acid amount and acid density. The composite molecular sieve performed better in the alkylation of 2-MN with methanol, improving reaction conversion and selectivity of 2,6-DMN. To further improve the catalytic performance, we used Mg to modify the pure molecular sieve. The selectivity of 2,6-DMN over 1%Mg-BEA/MTW catalyst can be further increased with the 2,6-/2,7-DMN ratio of 1.5. Therefore, the composite molecular sieves have a high potential for application in the methylnaphthalene alkylation reaction.

Methylation of 2-methylnaphthalene over metal-impregnated mesoporous MCM-41 for the synthesis of 2,6-triad dimethylnaphthalene isomers

2,6-Dimethylnaphthalene (2,6-DMN) is one of the key intermediates for the production of polyethylene naphthalate (PEN), which demonstrates superior properties compared with the polyethylene terephthalate. However, the complex synthesis procedure of 2,6-DMN increases the production cost and decreases the commercialisation of PEN. In this study, selective synthesis of 2,6-triad DMN isomers (1,5-DMN, 1,6-DMN and 2,6-DMN) has been investigated by the methylation of 2-methylnaphthalene (2-MN) over mesoporous Cu/MCM-41 and Zr/MCM-41 zeolite catalysts. On the contrary of other DMN isomers, 2.6-triad isomers can effectively be converted to be profitable 2,6-DMN with an additional isomerisation reaction, which is a new approach to reach higher 2,6-DMN yield. The methylation reactions of 2-MN were investigated in a fixed-bed reactor at 400 °C and weight hourly space velocity of 1–3 h−1. The results showed that the activity of MCM-41 on the methylation of 2-MN has been enhanced with the impregnation of Cu. The conversion increased from about 17% to 35 wt% with the impregnation of Cu. Similarly, the 2,6-triad DMN selectivity and 2,6-/2,7-DMN ratio reached the maximum level (48 wt% and 1.95, respectively) over Cu-impregnated MCM-41 zeolite catalyst.

Catalytic performance of Cu- and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene

2,6-Dimethylnaphthalene (2,6-DMN) is a commercially important chemical for the production of polyethylenenaphthalate and polybutylene naphthalate. However, its complex synthesis procedure and high production cost significantly reduce the use of 2,6-DMN. In this study, the synthesis of 2,6-DMN was investigated with methylation of 2-methylnaphthalene (2-MN) over metal-loaded beta zeolite catalysts including beta zeolite, Cu-impregnated beta zeolite and Zr-impregnated beta zeolite. The experiments were performed in a fixed-bed reactor at atmospheric pressure under a nitrogen atmosphere. The reactor was operated at a temperature range of 400–500 °C and varying weight hourly space velocity between 1 and 3 h−1. The results demonstrated that 2,6-DMN can be synthesized by methylation of 2-MN over beta type zeolite catalysts. Besides 2,6-DMN, the product stream also contained other DMN isomers such as 2,7-DMN, 1,3-DMN, 1,2-DMN and 2,3-DMN. The activity and selectivity of beta zeolite catalyst were remarkably enhanced by Zr impregnation, whereas Cu modification of beta zeolite catalyst had an insignificant effect on its selectivity. The highest conversion of 2-MN reached 81%, the highest ratio of 2,6-DMN/2,7-DMN reached 2.6 and the highest selectivity of 2,6-DMN was found to be 20% by using Zr-modified beta zeolite catalyst.

Selective synthesis of 2,6-triad dimethylnaphthalene isomers by disproportionation of 2-methylnaphthalene over mesoporous MCM-41

2,6-Dimethylnaphthalene (2,6-DMN) is one of the crucial intermediates for the synthesis of polybutylenenaphthalate and polyethylene naphthalate (PEN). The complex synthesis procedure and the high cost of 2,6-DMN production significantly reduce the commercialisation of PEN even though PEN demonstrates superior properties compared with polyethylene terephthalate. 2,6-DMN can be produced by methylation of 2-methylnaphthalene (2-MN) and/or naphthalene, disproportionation of 2-MN, and/or isomerisation of dimethylnaphthalenes (DMNs). In this study, synthesis of 2,6-triad DMN isomers consisting of 2,6-DMN, 1,6-DMN, and 1,5-DMN have been investigated with the disproportionation of 2-MN over unmodified and Zr-modified mesoporous MCM-41 zeolite catalysts. In contrast to other DMN isomers, both 1,5-DMN and 1,6-DMN can be effectively isomerised to be profitable 2,6-DMN. The disproportionation of 2-MN experiments were carried out in a catalytic fixed-bed reactor in the presence of 1 g of catalyst at a temperature range of 350–500 °C and weight hourly space velocity between 1 to 3 h−1. The results demonstrated that mesoporous MCM-41 zeolite catalyst has a selective pore shape for 2,6-triad DMN isomers, which may allow a decrease in the production cost of 2,6-DMN. Additionally, 2,6-DMN was successfully synthesised by the disproportionation of 2-MN over MCM-41 zeolite catalyst. Furthermore, both the conversion of 2-MN and the selectivity of 2,6-DMN were considerably enhanced by the Zr impregnation on MCM-41.

Development of mesoporous ZSM-12 zeolite and its application in alkylation of 2-methylnaphthalene

Desilicated MTW zeolite was evaluated in methylation of 2-methylnaphthalene (2-MN) in a fixed-bed flow reactor at 450 °C. Mesoporous MTW was fabricated via a microwave-assisted desilication process using a harsh alkaline solution to improve the pore volume and the surface area. H-ZSM-12 zeolite was treated with 0.3 M of NaOH solution with different treatment times. Due to the harsh alkaline treatment, micropores were blocked by the deposition of the removed atoms. Due to the importance of methylnaphthalenes intermediates, modified MTW zeolites were evaluated in methylation of 2-MN. Methanol (MeOH), 2-MN and 1,3,5-trimethylbenzene (TMB) were fed to the reactor with a molar ratio of 15:15:70. Higher selectivity to 1-methylnaphthalene (1-MN) was observed rather than dimethylnaphthalene and trimethylnaphthalene with a yield of 13.6, 8 and 2.5 mol%, respectively. Moderate conversion up to 24.1 mol% was reached for 30 min reaction.

Synthesis of hierarchical ZSM-5 by cetyltrimethylammonium bromide assisted self-assembly of zeolite seeds and its catalytic performances

Hierarchical ZSM-5 zeolites with controllable structure were hydrothermally synthesized through self-assembly of zeolite seeds by the assistance of cetyltrimethylammonium bromide (CTAB) without other organic co-solvent or additive, and characterized by XRD, FT-IR, SEM, TEM and N2 adsorption. The results show that the synthesized samples are of pure MFI structure with high crystallization, and the crystal sizes of hierarchical ZSM-5 are primary nanoparticles. The addition of CTAB can decrease the primary nanoparticle sizes to 10 nm and hinder further aggregation of nanoparticles into zeolite crystal. The BET surface area, total pore volume and external surface area of hierarchical ZSM-5 samples can be tuned by the amount of CTAB. It is thought that the addition of NaOH and CTAB plays an important role in crystallization and self-assembly of zeolite seeds. Compared with ZSM-5 prepared without CTAB, the hierarchical ZSM-5 shows better stability and 2,6-dimethylnaphthalene yield in the methylation of 2-methylnaphthalene with methanol.

Synthesis of 2,6-dimethylnaphthalene by methylation of 2-methylnaphthalene on mesoporous ZSM-5 by desilication

Abstract Mesoporous ZSM-5 was prepared by NaOH-treatment of ZSM-5 and examined for selective synthesis of 2,6-dimethylnaphthalene (2,6-DMN). The results showed that mesopores were formed owing to desilication. The catalytic activities and lifetime were significantly enhanced with increasing treatment time. About 37% 2-methylnaphthalene(MN) conversion, compared to 5.3% on parent ZSM-5, was obtained at 10.25 h on mesoporous ZSM-5 by 8 h NaOH-treatment. It is thought that mesopores in alkaline-treated ZSM-5 result in higher catalytic activities and longer lifetime. Higher 2,6-/2,7-DMN ratio, selectivity and yield of 2,6-DMN were obtained on modified mesoporous ZSM-5 with Zr.

Methylation of 2-methylnaphthalene with methanol to 2,6-dimethylnaphthalene over HZSM-5 modified by NH 4F and SrO

The methylation of 2-methylnaphthalene (2-MN) into 2,6-dimethylnaphthalene (2,6-DMN) was investigated over the solid acid catalysts. The results show that HZSM-5 modified by NH 4F has better catalytic performance than parent HZSM-5 due to the decrease in the acidity. When NH 4F/HZSM-5 is further modified by SrO, its catalytic activity decreases due to the decrease in the total acid amount and acidic strength. As a result, the comprehensive modification of NH 4F and SrO leads to the increase in the 2,6-DMN selectivity (2,6-DMN to DMN), up to 64.8% when 2-MN conversion is 10%. We calculated the ESP charge by density functional theory and the results show that the 6-position in 2-MN has higher ESP charge value than 7-position. The formation of 2,6-DMN is favored energetically as compared to that for 2,7-DMN. This suggests during the alkylation of 2-MN inside the ZSM-5 channel, the formation of 2,6-DMN is favored electronically than that of 2,7-DMN. Hence, lowering the acidity of catalyst is a key factor to obtain high selectivity of 2,6-DMN.

Methylation of 2-Methylnaphthalene with Methanol to 2,6-Dimethylnaphthalene over ZSM-5 Modified by Zr and Si

ZSM-5 samples modified by isomorphic substitution of Si, Zr, or a combination thereof were characterized by FT-IR and UV spectroscopies, XRD, XRF spectroscopy, and NH 3 -TPD and used in the methylation of 2-methylnaphthalene (MN) to produce 2,6-dimethylnaphthalene (2,6-DMN). The results indicated that Si or Zr is inserted in the framework of ZSM-5 after modification and Zr is unstable and preferentially substituted by Si in the simultaneous presence of Zr and Al. Siliconization of ZSM-5 mainly improves its stability and is slightly preferable to enhancement of selectivity to DMNs, 2,6-DMN, and β,β-DMNs. A Zr-substituted sample can obviously improve the 2,6-DMN selectivity, yield, and ratio of 2,6- to 2,7-DMN. Co-modified ZSM-5 embodies the advantages of stable activity on Si-modified ZSM-5 and high selectivity on Zr-modified ZSM-5. The preferable catalyst was prepared by incorporation of Zr in silicated ZSM-5. About 52% 2,6-DMN and 85% β,β-DMNs selectivity, over a 2.0 ratio of 2,6- to 2,7-DMN, and a 9% 2,6-DMN yield can be obtained. The superior methylation performance can be ascribed to the weakening of the acid strength and change in pore dimensions for different modifications.

Selective synthesis of 2,6-dimethylnaphthalene by methylation of 2-methylnaphthalene with methanol on Zr/(Al)ZSM-5

A new catalyst, Zr/(Al)ZSM-5, prepared by partly isomorphic substitution of Al in ZSM-5 framework by Zr, was used to synthesize 2,6-dimethylnaphthalene (DMN) by methylation of 2-methylnaphthalene (MN) with methanol. The catalyst exhibits higher selectivity of DMNs, 2,6-DMN and β,β-DMNs, 2,6- to 2,7-DMN ratio and lower isomerization than unmodified ZSM-5. About 10% of 2-MN conversion, 56% of 2,6-DMN selectivity, ratio of 2,6- to 2,7-DMN being 3.0 are obtained on Zr/(Al)ZSM-5. The improvement in catalytic performance is mainly attributed to the weakening of acid strength and the expansion of pore dimension from partial incorporation of Zr in ZSM-5 framework.