Synthesis of dimethyl carbonate over waste eggshell catalyst
Graphical abstract
Highlights
► Eggshell waste as catalyst precursors. ► Catalyst for transesterification of propylene carbonate and methanol. ► Calcination temperature affected the structure and activity of eggshell catalysts. ► Highly active and reusable solid catalyst derived from eggshell waste.
Introduction
Eggs are consumed worldwide because they contain all essential amino acids, vitamins, and minerals. Eggshell weighs approximately 10% of the total mass (ca. 60 g) of hen egg, and eggshell is the significant solid waste produced from food processing and manufacturing plants [1]. In China, for example, it is estimated that annually about 4,000,000 tonnes is generated and this will continue to grow in future [2]. Most of the eggshell waste is commonly disposed in landfills without any pretreatment because it was traditionally useless. However, the waste management is not a desirable practice in view of the environmental odor from biodegradation [3], [4]. Eggshell has a little porosity and pure CaCO3 as an important constituent. The chemical composition (by weight) of eggshell has been reported as follows: calcium carbonate (94%), magnesium carbonate (1%), calcium phosphate (1%) and organic matter (4%) [1]. In recent years, a great deal of effort has been conducted for the application of eggshell as value-added products. These major applications included a possible bone substitute [5], the starting material for preparing calcium phosphate bioceramics (e.g. hydroxyapatite) [6], coating pigments for inkjet printing paper [7], and a low-cost adsorbent for removal of ionic pollutant and dyes from the aqueous solution [3], [8].
In our recent work, we found that waste eggshell could be used as an active heterogeneous catalyst for biodiesel synthesis [9]. It was proved that eggshell was an interesting unconventional heterogeneous basic catalyst for biodiesel synthesis [10], [11]. Except for the reaction of biodiesel synthesis, only one other reaction, lactose isomerization, was reported utilizing eggshell as a basic catalyst [12]. However, base catalysis is important in chemical industry where it is widely applied [13]. Investigation of eggshell as a catalyst for base-catalyzed reaction is not only helpful recycling this solid eggshell waste, but also could make the reaction process environmentally benign. Though it was already demonstrated that CaO is the active phase of the eggshell waste-derived catalysts [9], there is no report to date comparing of pure CaO and eggshell waste-derived materials.
Dimethyl carbonate (DMC) is considered as an environmentally benign chemical due to negligible ecotoxicity, low bioaccumulation and low persistence [14]. Therefore, the production and chemical application of DMC have attracted much attention in the view of so-called ‘sustainable society’ and ‘green chemistry’, mainly for replacing dimethylsulfate and methylhalides in methylation reactions and for replacing harmful phosgene in polycarbonate and isocyanate syntheses [15]. Generally, DMC has been mainly produced through two environmentally compatible routes: oxidative carbonylation of methanol and transesterification between methanol and propylene carbonate (PC) or ethylene carbonate (EC). Transesterification of cyclic carbonate and methanol is a green process, which uses naturally abundant CO2 as a starting material as shown in Scheme 1. In the first step, cyclic carbonate can be synthesized with conversion and selectivity close to 100% under moderate conditions. Therefore, much attention has been paid to the transesterification of cyclic carbonate and methanol. Both acid and base catalysts catalyzed the reaction, and base catalysis was reported to be more effective. However, homogeneous basic catalysts, such as alkali alcoholates or hydroxides and trialkyl amine, give rise to the problems of product separation and catalyst reuse, and consequently, solid base catalysts are of much interest [16], [17], [18], [19].
In this paper, we studied the catalytic properties of eggshell-derived catalyst for DMC synthesis from the transesterification of PC and methanol. One aim of this investigation was to examine the feasibility of using eggshell as a solid base catalyst for DMC synthesis. The other aim was to compare the catalytic activity of pure CaO and eggshell catalysts.
Section snippets
Materials
Eggshell was collected from local bakeries. The preparation method of eggshell catalyst was described elsewhere [9]. To remove impurity and interference material, the eggshell was rinsed several times with deionized water. Then, the eggshell was dried at 100 °C for 24 h in the dry oven. Calcination was performed in the muffle furnace at 1000 °C for 2 h under static air after crushing the dried eggshell.
Pure CaO (analytical reagent, 98.0%) used was a commercial sample (Sinopham Chemical Reagent Co.,
BET surface area and pore size
Table 1 presents the nitrogen physisorption data of natural eggshell, calcined eggshell and pure CaO (A.R.). The surface area and pore volume of natural eggshell were 0.84 m2 g−1 and 0.0049 cm3 g−1, respectively (Table 1, entry 1), which indicated that natural eggshell processed low porosity [20]. Both the surface area and pore volume of other samples (i.e. calcined eggshell and pure CaO) were similar to that of natural eggshell (Table 1, entries 2–4). They also processed low porosity.
Chemical composition of eggshell waste-derived catalysts
Element
Conclusion
This is the first report of the synthesis of DMC by transesterification through the use of eggshell-derived catalyst. The eggshell-derived catalyst was active and reusable for DMC synthesis. CaO was proved to be the active phase of eggshell catalysts. The experimental results showed that under the optimum conditions, a 10:1 molar ratio of methanol to PC, addition of 0.8 wt% eggshell catalysts, room temperatures and 1 atm pressure gave the best results, and conversion of PC and yield of DMC
Acknowledgments
This work was supported by the project funded by Natural Science Basic Research Plan in Shaanxi Province of China (Program No. 2010JM2003) and by the Fundamental Research Funds for the Central Universities (Program No. GK200902006).
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