Sulfonated mesoporous Y zeolite with nickel to catalyze hydrocracking of microalgae biodiesel into jet fuel range hydrocarbons

https://doi.org/10.1016/j.ijhydene.2018.11.110Get rights and content

Highlights

  • Ni/sulfonated meso-Y zeolite catalyst was applied to microalgae biodiesel conversion.

  • Sulfonic acid groups (-SO3H) were successfully grafted to meso-Y zeolite framework.

  • The strong acid density significantly increased when meso-Y zeolite was sulfonated.

  • Biodiesel conversion rate and jet fuel range hydrocarbon selectivity were improved.

Abstract

To promote catalytic performances of Ni-based mesoporous Y (meso-Y) zeolite in the hydrocracking conversion of microalgae biodiesel to jet fuel range hydrocarbons, 3-mercaptopropyltrimethoxysilane was utilized as sulfonating agent to improve the acid density of meso-Y zeolite. The physiochemical properties of sulfonated meso-Y zeolite were characterized via temperature-programmed desorption of ammonia, X-ray diffraction, Fourier-transform infrared spectroscopy, energy dispersive spectroscopy, scanning electron microscopy, and N2 physisorption. It was detected that sulfonic acid groups (-SO3H) composed of Ssingle bondO and Sdouble bondO bonds were successfully grafted onto meso-Y zeolite framework. The strong acid density significantly increased from 0.31 mmol/g to 1.21 mmol/g when meso-Y zeolite was treated with 0.38 mL/g sulfonating agent. The crystalline interplanar spacing of meso-Y zeolite expanded with a shifted position (2θ) of X-ray diffraction peak from 15.72° to 15.70°. The enhanced hydrocracking capacity of 10% Ni/sulfonated meso-Y zeolite catalyst resulted in improvements in microalgae biodiesel conversion (from 82.1% to 99.7%) and jet fuel range alkane selectivity (from 31.2% to 52.3%).

Introduction

As the third generation of biofuels, microalgae biofuel is regarded as a promising approach to sustainably meet the global energy demands, because the cultivation of microalgae does not compete for farmland with food crop growing. Some microalgae species can yield up to 60% of their weight in the form of oil [1]. However, Song et al. produced crude bio-oil from microalgae (Cyanophyta) biomass by hydrothermal liquefaction and the maximum yield reached only 29.24% [2]. Therefore, to obtain high quality biofuel products, lipids are supposed to be extracted from microalgae cell before further processing. The approach of in-cell lipid transesterification proposed by our laboratory solved the problem of lipid extraction and produced fatty acid methyl esters (FAMEs), i.e., microalgae biodiesel, in one step [3]. Comparing to traditional crops, microalgae has the potential to produce biodiesel 200 times more efficiently [4]. Nevertheless, biodiesel contains a notable proportion of oxygen, which restricts its heating value. By further hydroprocessing to deoxygenation and cracking, jet fuel range hydrocarbons could be produced. According to the life cycle assessment carried out by Bicer and Dincer, the cost of jet fuel during aircraft operation was much lower than other alternative fuels such as methanol and hydrogen [5]. Developing sustainable jet biofuel is hence of significance on carbon emission reduction in aircraft industry.

Zeolites were widely applied as catalysts in the conversion of bio-oil such as soy bean oil, jatropha oil, and palm oil to hydrocarbons [6], [7], [8]. However, mesoporous zeolites have attracted more and more attention recently owing to the better accessibility to active sites and longer lifespan [9]. In our previous study, a maximum jet fuel range alkane selectivity of 53% was obtained from waste cooking oil over nickel based mesoporous Y (meso-Y) zeolite catalyst [10]. The decentralized sources of waste cooking oil limit its industrial application prospect. Since microalgae can be cultivated intensively, it is regarded as an ideal feedstock for carbon-neutral biofuel production with the advantage of high biomass productivity [11]. Nevertheless, the hydroprocessing of FAMEs over Ni/HZSM-5 zeolite catalyst carried out by Chen et al. exhibited high selectivity of diesel (C17 single bond C18) alkane (47.7%) other than jet (C8 single bond C16) alkane (32.5%) [12], which was attributed to the insufficiency of hydrocracking activity. In order to increase product value, the upgrading conversion of microalgae biodiesel to jet fuel range hydrocarbons was of significance to study. We screened several kinds of mesoporous zeolite catalysts for microalgae biodiesel conversion, finding that meso-Y zeolite catalyst achieved a relative high jet fuel range alkane selectivity (44.5%) [13]. However, considering the compositions of microalgae biodiesel (C16 single bond C22) were with longer carbon chains than waste cooking oil (C16 single bond C18), the hydrocracking capacity of the catalyst was supposed to be further enhanced to exhibit better catalytic performances.

Hydrocracking was principally related to the acidity of the metal/acid bifunctional catalysts [14]. The incorporation of sulfonic acid groups was an organic surface modification approach widely adopted in polymer electrolyte membrane fuel cells to promote proton conductivity [15], [16], which provided highly reactive acid sites. Hence it had also been applied to microporous or mesoporous materials, enhancing the activity of solid acid catalysts such as graphene oxide [17]. Sulfonic acid group-functionalized mesoporous organosilica synthesized by Wu et al. achieved significant acid capacity improvement (from 2.00 to 5.59 mmol H+/g) at the expanse of acceptable BET surface area loss (from 589 to 214 m2/g) [18]. González et al. reported a one-step post-synthesis grafting method to prepare sulfonated zeolite beta for the first time and it showed effective catalytic performances in the etherification of glycerol [19], demonstrating that sulfonic acid groups could be introduced to zeolite framework. Felice et al. found that the proton conductivity of faujasite-type (typical structure of Y) zeolite was improved by sulfonation, especially for that with lower Si/Al ratio [20], indicating the synergy of sulfonic acid groups and acid bridges on zeolite framework. The research of Zhou et al. revealed that sulfonation treatment could remarkably improve both acid strength and acid density of mesoporous USY (meso-USY) zeolite without destroying its mesoporous structure [21]. When applied to the hydrolysis of hemicellulose, the sulfonated meso-USY increased the yield of total reducing sugars to 78% from 35%, showing enhanced cracking activity. Estevez et al. compared zeolites functionalized with two different organosilica precursors, i.e. 3-mercaptopropyltrimethoxysilane (MPTS) and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane [22]. The smaller molecule size and more flexible structure of MPTS made it easier to graft onto zeolite framework, so that the zeolite treated by MPTS showed the highest acidity and the best substituted ether yield (13%). The study of Jin et al. showed that sulfonated mesoporous ZSM-5 (meso-ZSM-5) exhibited best catalytic activity in liquid-phase reaction of 2′-hydroxyacetophenone and benzaldehyde comparing with non-functionalized meso-ZSM-5 and sulfonated microporous ZSM-5 [23], which demonstrated mutual promotion on catalysis of sulfonation and mesoporousity.

There have been no such studies, however, investigating the impact on acidity and structure properties of meso-Y zeolite functionalized with MPTS. How the enhanced characteristics function in the hydrocracking process of microalgae biodiesel is of interest to study. Therefore, nickel based sulfonated meso-Y zeolite catalyst was prepared and applied to the production of microalgae based jet fuel range (C8 single bond C16) hydrocarbons for the first time in this paper. The physiochemical properties and surface features of sulfonated meso-Y zeolite were characterized and evaluated via temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction of hydrogen (H2-TPR), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherms. Eventually, high microalgae biodiesel conversion and jet fuel range hydrocarbon selectivity were obtained in the experiment carried out on the fixed bed continuous flow reaction system.

Section snippets

Preparation of Ni-based sulfonated meso-Y zeolite catalyst

Meso-Y zeolite was purchased from Hangzhou Huacai Xinrui Technology Co. Ltd. China. Ni(NO3)2·6H2O (≥98.0% analytical standard), toluene (≥99.5% analytical standard), hydrogen peroxide (H2O2) aqueous solution (≥30.0% analytical standard) were purchased from Sinopharm Chemical Reagent Co. Ltd. China. 3-mercaptopropyltrimethoxysilane (MPTS) (≥97.0% analytical standard) was purchased from Shanghai Macklin Biochemical Co. Ltd. China.

The meso-Y zeolite was sulfonated as reported [21]. 6 g meso-Y

Acid properties of sulfonated meso-Y zeolite catalyst

To verify the amount of sulfonic acid groups grafted onto zeolite framework, elemental analysis of sulfonated meso-Y zeolite was carried out through EDS (Table 1). The conventional meso-Y zeolite framework was mainly composed of O, Si and Al. The emerging C and S after sulfonation indicated that the structure of MPTS was successfully grafted onto meso-Y zeolite as demonstrated in Fig. 1. Considering some methoxyl groups (-OCH3) instead of main structure of MPTS were grafted onto zeolite

Conclusion

Nickel based sulfonated meso-Y zeolite catalyst efficiently promoted microalgae biodiesel conversion and jet fuel range hydrocarbon selectivity. Since Ssingle bondO and Sdouble bondO bonds were detected in FTIR and S content increased along with rising sulfonating agent dosage according to EDS, sulfonic acid groups (-SO3H) were successfully grafted onto meso-Y zeolite framework. The XRD and SEM results revealed the expansion of meso-Y zeolite crystal structure due to the graft. When meso-Y zeolite was treated with

Acknowledgements

This study was supported by the National Natural Science Foundation - China (51476141), National Key Research and Development Program - China (2016YFB0601003).

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