Elsevier

Energy Conversion and Management

Volume 196, 15 September 2019, Pages 739-750
Energy Conversion and Management

Synthesis of Na+ trapped bentonite/zeolite-P composite as a novel catalyst for effective production of biodiesel from palm oil; Effect of ultrasonic irradiation and mechanism

https://doi.org/10.1016/j.enconman.2019.06.027Get rights and content

Highlights

  • Bentonite/zeolite-P catalyst was synthesized for effective transesterification of palm oil.

  • Its catalytic activity was studied by normal stirring and under ultrasonic irradiation.

  • The best biodiesel yields are 96.2% (normal stirring) and 98.8% (ultrasonic irradiation)

  • The ultrasonic irradiation reduced the operating values of the reaction parameters.

  • The catalyst is of high stability and the obtained biodiesel match the international standards.

Abstract

Bentonite/zeolite-P composite (B/ZP) was synthesized by simple alkaline hydrothermal treatment at 150 °C for 4 h and characterized by different analytical techniques. The composite was introduced as a low-cost catalyst of enhanced physiochemical properties and catalytic activity in the transesterification of palm oil into biodiesel. The catalytic activity of B/ZP catalyst was inspected by normal stirring mixing and under ultrasonic irradiation of different powers (20–60%). The best biodiesel yield by normal stirring (96.2%) was achieved at operating conditions of 210 min as conversion time, 20:1 as a methanol-to-oil molar ratio, 5 wt% as a catalyst loading, 90 °C as temperature and 900 rpm as stirring speed. The conversion reaction under the ultrasonic irradiation (power 60%) gives biodiesel yield of 98.8% after 120 min as reaction time using 5 wt% as catalyst loading, 20:1 as a methanol-to-oil ratio, and 90 °C as temperature. The ultrasonic irradiation is of positive impacts in reducing the conversion time interval, reaction temperature, catalyst loading, and methanol-to-oil molar ratio with biodiesel yield similar to that obtained by normal stirring at its best conditions. The catalyst is of higher activities than several homogenous and heterogeneous catalysts and can be reused several times with high catalytic activity especially using an organic solvent either by normal stirring or under the ultrasonic irradiation. The physicochemical specification of the obtained biodiesel by both methods matches the requirements of STM D-6571 and EN 14214 international standards.

Introduction

The renewable and clean energy resource attracted the considerations of the responsible energy and environmental organizations as a potential solution for the future energy shortage problems and the associated hazardous emissions of traditional fuels [1], [2], [3], [4]. In the later years, biodiesel and biofuels were suggested as an effective and eco-friendly alternative for traditional fuels [6], [7]. It was reported that the produced biodiesel from the transesterification of vegetable oil and animal fats is of biodegradable properties, no toxic emissions and excellent diesel technical properties [8], [9], [10]. This qualifies it to be used directly in the engines or integrated into a blend with petroleum diesel [11], [12], [13].

The transesterification reaction for oil into biodiesel performed mainly in the existence of a potential catalyst either homogenous catalyst or heterogeneous catalyst to accelerate the process [14], [15], [3]. The previous literature reported that the applying of homogenous catalysts is of high catalytic activities but they suffer from non-reusability, high separation costs, high corrosion properties, and of toxic residuals [5], [16]. However the heterogeneous catalysts are of lower catalytic activities than homogenous catalysts, they are environmental materials of low fabrication cost and can be reused several times with simple separation and recovery techniques [1], [14].

The recorded low catalytic activities of heterogeneous catalysts related to the weak interactions between them and the liquid phases of the transesterification system (oil and alcohol). This assigned mainly to the high immiscibility between such components which result in high mass transfer resistance and in turn low activity rates [11], [17]. The incorporation of an ultrasonic source as mixing technique during the transesterification reactions can provide high mixing properties and enhance the catalytic activities of heterogeneous catalysts by the associated activation energy and cavitation phenomenon [11], [18]. The cavitation phenomenon associated with continuous generation of fine emulsion droplets between the liquid phases and collapse of such droplets results in the generation of continuous micro-streams, microjets, and shockwaves in the system [17], [19]. This provides effective mixing properties between the immiscible liquids; reduce the mass transfer resistance, and enhance velocity gradients [2]. The previous effects cause an increase in the interaction area between the present phases which promotes the transformation rates at low temperature, short time intervals, and low alcohol-to-oil molar ratio [20]. Moreover, the ultrasonic waves are of impressive effect in reducing the particle size of the solid catalyst which can increase the exposed active catalytic sites and the surface area [2].

Fabrication of the heterogeneous catalysts from natural materials became the main interest of the researchers in the later periods to reduce the total production cost and for their environmental properties [3], [21]. From the known natural materials, clay and zeolite materials were applied widely as a heterogeneous catalyst in the biodiesel production after their functionalization by acidic and basic chemical groups or by supporting their structures with alkali elements (sodium and potassium) and metal oxide [1], [22], [23]. Zeolite either in synthetic or natural forms is of alkali aluminosilicate chemical composition, micro-porous properties, extraordinary ion-exchange capacities, and eco-friendly properties which are vital properties for superior catalytic activities [23], [24], [25], [26], [27]. This also was recorded for clay minerals as they exhibit flexible chemical structure, low cost, high ion replacement capacities [4], [28]. The commonly studied clay and zeolite based catalysts are natural zeolite, mordenite, Zeolite-A, zeolite-X, zeolite-Y, sodalite, bentonite, kaolinite and chrysotile [13], [23], [29], [30], [31], [32], [33], [34], [35], [36], [37]

Recently novel hybrid products between natural clays and synthetic zeolite were produced as composites and evaluated as promising materials of superior physicochemical properties [28], [37], [38]. Bentonite/zeolite-P composite was synthesized by Shaban et al., [28] as a hybrid product of enhanced surface area, ion exchange capacity, porous structures, and of good swelling properties. Unfortunately, the catalytic activities of such hybrid materials in the transesterification of oil into biodiesel have not been investigated. Thus, this study aims to synthesis a novel composite of bentonite/synthetic zeolite-P (B/ZP) as a catalyst in the transformation of palm oil into biodiesel by normal stirring mixing and under ultrasonic irradiation in a comparison study. The conversion reactions were accomplished based on the commonly studied factors as conversion time, temperature, catalyst loading, methanol-to-oil molar ratio, stirring speed and the reusability of the catalyst.

Section snippets

Materials

Raw bentonite (SiO2 (54.82%), Al2O3 (17.56%), Fe2O3 (9.5%), Na2O (2.6%), MgO (2.5%), CaO (2.4%), TiO2 (1.45%), and LOI (9.2%)) from Western desert bentonite quarry and NaOH (97%) was used in the preparation of Na+ trapped bentonite/zeolite-P catalyst. Commercial palm oil, pure methanol of chemical analytical grade (99.8%, Sigma Aldrich) was used in the transesterification system.

Preparation of the catalyst

The raw bentonite sample was ground extensively to be less than 70 µm and then was activated by thermal treatment in

Structural properties

The bentonite precursor showed the existence of montmorillonite clay mineral as the dominant type of smectite clay groups (Fig. 1A). The other crystalline phases as kaolinite, calcite, and quartz were identified as associated impurities. The characteristic XRD peaks of montmorillonite were recognized at 2θ angles of 6.55°, 19.85°, 25.1° and 28.35° which were assigned to (0 0 2), (0 2 0) and (1 0 5) lattice planes, respectively (card No: 00-003-0010 and No: 00-058-2010). The present

Conclusion

Bentonite/zeolite-P composite (B/ZP) was synthesized and characterized as a heterogeneous catalyst of basic properties. It was applied effectively in the transformation of palm oil into biodiesel by normal stirring and under ultrasonic irradiation. The conversion reaction by normal stirring resulted in biodiesel yield of 96.2% after 210 min using 5 wt% as catalyst loading, 20:1 as a methanol-to-oil ratio, 90 °C as temperature, and stirring speed of 900 rpm. The conversion reaction under the

Recommendation

Further studies will be conducted to investigate the catalytic activity of B/ZP catalyst at the pilot scale and using the chemicals at their commercial grades

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group No. RG-1440-043.

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