Reusable gypsum based catalyst for synthesis of glycerol carbonate from glycerol and urea

doi:10.1016/j.apcata.2015.06.024

Applied Catalysis A: General

Volume 502, 5 August 2015, Pages 312-319

https://doi.org/10.1016/j.apcata.2015.06.024 Get rights and content

Highlights

•
First report on utilizing gypsum as catalyst for synthesis of organic carbonate.
•
Different pre-treatment produced different crystalline structure of catalyst.
•
The yield of glycerol carbonate depends on the specific phase of gypsum.
•
Accelerated formation of glycerol carbonate via glycerol carbamate intermediate.
•
The catalyst is reusable.

Abstract

In this study, the catalytic carbonylation of glycerol with urea in the presence of gypsum based heterogeneous catalyst is reported for the first time. Gypsum (CaSO₄·2H₂O) is one of the two calcium sulphate minerals found in nature and also one of the waste materials produced from advanced material industrial processing plant. The effect of physical and chemical pre-treatment procedures on gypsum was investigated. To obtain the catalyst structure-activity relationship, the treated catalysts were characterized by means of several characterization techniques (i.e. XRD, TGA, BET surface area, SEM, FTIR, CO₂–TPD, NH₃–TPD and Hammett test). Tuneable physico-chemical properties of gypsum based catalysts were successfully prepared by varying the pre-treatment techniques, which later on contributed to the variation of catalytic activity toward glycerol carbonate formation from glycerol. The highest catalytic activity obtained was for catalyst consisting β-CaSO₄ phase where it produced 92.8% conversion of glycerol, 90.1% selectivity and 83.6% yield of glycerol carbonate, respectively. The gypsum catalyst is easily recoverable and reusable for subsequent cycles of reaction. Similar physico-chemical properties of fresh and used catalyst were confirmed through XRD, FTIR and Hammett test analysis. Besides, the mechanistic pathway of glycerol carbonate was confirmed through the formation of glycerol carbamate as intermediate compound which was further established through time online analysis study using ¹³C NMR and ATR–FTIR, respectively. The study also clearly supports conversion of waste into wealth while promising proper disposal of waste to produce value added product.

Graphical abstract

Introduction

The development of new routes of chemical products from renewable feedstock is one of the critical importance for a sustainable future. Nowadays, the expanding production of biodiesel has generated glycerol in quantities exceeding the current demand. This leads a drop of the glycerol price and the risk of seeing a surplus of glycerol. By the year 2016, the world biodiesel market is estimated to be at 308 billion kg, which means more than 33 billion kg of crude glycerol will be produced every year [1]. The production cost of biodiesel increases by U.S. $0.0022/L for every U.S. $0.022/kg reduction in glycerol selling price [2]. The potential sale of this product could make biodiesel cheaper. Thus, it is important to find alternative uses for glycerol. Recently, the new opportunities for conversion of glycerol waste into high value-added product have increased due to the special structure, properties and the renewable feature of glycerol [3]. The glycerol waste can make a comfortable place in the global market by using it as a source of feedstock for value-added product such as glycerol carbonate [4].

Glycerol carbonate is one of the important building blocks for chemical industry and characterized by a low toxicity, good biodegradability and high boiling point, which are useful for solvents and chemical intermediate [5]. Due to the combination of wide reactivity and bio based origin, carbonates become a versatile and renewable building block for organic chemistry as well as possibility to become a major chemical intermediate, for instance, in the manufacturing of polymer, adhesives, foams, coatings and lubricants [6], [7], [8].

Glycerol carbonate is produced from glycerol in many different routes. Previously, it was synthesized in conventional method via phosgenation of methanol [9]. However, due to high toxicity, chemical and corrosive nature of phosgene, the alternative routes were suggested such as from ethylene carbonate and propylene [10]. Glycerol carbonate also synthesized from glycerol with dimethyl carbonate. This route has its disadvantages because the reaction required expensive catalyst and higher ratio of dimethyl carbonate to glycerol as well as a shift in chemical equilibrium [11]. Alternatively, an equally attractive route to prepare glycerol carbonate is the reaction of glycerol with urea. This phosgene-free process utilised low cost raw material with low toxicity [12]. Besides, there is a possibility to convert ammonia formed during reaction back into urea using carbon dioxide captured technology [9].

Gypsum is the most common naturally occurring sulphate minerals with the chemical formula of CaSO₄·2H₂O. Gypsum is also produced as a waste product from advanced material manufacturing industry, such as titanium dioxide (TiO₂) processing plant [13]. Titanium (IV) oxide is extracted from ilmenite ores by sulphuric acid digestion and the spent acid is neutralized by calcium carbonate thus produces the waste gypsum [14]. Hunstman Tioxide is one of the largest companies that produce TiO₂ in the world. The capacity of their plant in Malaysia alone is about 56,000 metric tons per year. This industry is estimated to produce ∼ 400,000 tonnes of waste gypsum annually [15], [16]. Therefore, for the first time this present research utilizes commercial gypsum material as a model catalyst for the synthesis of glycerol carbonate from glycerol and urea.

Section snippets

Chemicals

Glycerol (99.5%) and urea (AR grade) were purchased from Friendemann Schmidt Chemical. Standard glycerol carbonate, hydrogen peroxide (30% w/w H₂O₂ in water) and tetraethylene glycol (TEG) were purchased from Sigma–Aldrich while commercial gypsum (CaSO₄·H₂O) and calcium oxide (CaO) were purchased from R&M chemical. All other chemicals except gypsum and calcium oxide were used directly without further purification and pre-treatment.

Catalyst preparation

The commercial gypsum (denoted as GypF) is calcined in static air

Thermo-gravimetric analysis (TGA)

In order to determine the calcination temperature as well as the effect of temperature on GypF (CaSO₄·2H₂O), the GypF was subjected to thermogravimetric analysis. Fig. 1 illustrates the TGA curve for GypF catalyst. Single stage decomposition was clearly observed from the TGA thermogram. The decomposition of the precursor started at 80 °C and completed at 200 °C. The total weight loss was about 0.74 mg from 3.63 mg of sample placed at the beginning of the test equal to 20.5% of weight loss. The

Conclusion

It is clear from the work details in this study that gypsum based catalyst is efficient and reusable for the synthesis of glycerol carbonate from glycerol and urea. The reaction is environmental friendly and also introduces a proper and an alternative way for disposal of gypsum. Simple pre-treatment techniques were shown to successfully produce different physico-chemical properties of gypsum based catalysts. The β-CaSO₄ structure was identified as the most active phase where it produced 92.8%

Acknowledgements

The authors acknowledge Universiti Malaysia Pahang for UMP Internal grants scheme (RDU120363) and Graduate Research Scheme (GRS) as well as the Ministry of Education for Research Acculturation Collaborative Effort (RACE, RDU121301). We also would like to thank the Ministry of Education Malaysia for MyBrain15.

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Citation Excerpt :
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Reusable gypsum based catalyst for synthesis of glycerol carbonate from glycerol and urea

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Catalyst preparation

Thermo-gravimetric analysis (TGA)

Conclusion

Acknowledgements

Renew. Sust. Energ. Rev.

Renew. Sust. Energ. Rev.

Fluid Phase Equilib.

J. Catal.

J. Mol. Catal. B: Enzym.

J. Catal.

Sci. Total Environ.

Fuel Process. Technol.

J. Environ. Chem. Eng.

Mater. Charact.

Fluid Phase Equilibr.

Appl. Catal.

Chem. Eng. J.

Chin. J. Catal.

Appl. Catal.

Appl. Catal. A

Open Fuels Energ. Sci.