## 2 Acetin (Glycerol Esters or Acetyl Glycerol)
### Influence of Reaction Parameters on the Acetylation of Glycerol  
#### 2.2.1 Catalyst and Catalyst Load  
The presence of a catalyst in the reaction medium is to lower the activation energy and to form the desired product. In acetylation, the nature of the catalyst plays an important role, just like other reactions. Glycerol acetylation is mostly catalysed with acid catalysts [80; 91]. These catalysts could be homogeneous or heterogeneous [92]. Although some studies have reported a high yield of acetylated products using homogeneous acid catalysts such as sulphuric, nitric, hydrofluoric, hydrochloric, p-toluenesulfonic acids, as well as phosphoric acids [19; 76; 93], they are bedevilled with many environmental and technical drawbacks. Some of these include difficulty in separating the homogeneous catalyst from the product, the corrosion of equipment, difficulty in waste disposal, and toxicity of the reagents [22; 58; 73]. With the above disadvantages, efforts have generally shifted to the use of heterogeneous catalysts that are less toxic, highly selective, more stable, easy to separate, greener, and more sustainable [78; 94; 95]. The major advantage of heterogeneous catalysts is that it affords scientists the ability to manipulate the surface area and the acid density to suit a particular reaction. The reusability of heterogeneous catalysts aids their industrial applications irrespective of the type of reactor used [96]. A lot of heterogeneous catalysts have been used in glycerol acetylation, some of which include ion-exchange and functionalized resins [82; 97; 98; 99], zeolites and functionalized zeolites [73; 100; 101], heteropoly acids and supported heteropoly acids [93; 102; 103; 104]], metal oxides including mixed oxides and supported mixed oxides [105; 106; 107; 108], montmorillonite (K-10 clay) and modified montmorillonite [87; 91; 109], mesoporous silica and functionalized silica [94; 110; 111], activated carbon and functionalized biomass-derived carbon [112; 113; 114]. However, it is important to indicate that the focus of most of the studies has been the effect of the type of catalyst, loading, and reusability. However, other salient features that also aid the efficiency of catalysts in the acetylation of glycerol include the pore size and volume, surface acidity, and preparation techniques [41; 87; 105; 115; 116]. The findings of various researchers in glycerol acetylation using different catalysts are hereby reviewed in a cluster of catalyst type. Montmorillonite (K-10 Clay) and Modified Montmorillonite  
Montmorillonite is an aluminohydroxysilicate (an octahedral AlO\({}_{6}\) layer sandwiched between two tetrahedral SiO\({}_{4}\) layers), which is the main constituent of most clay minerals. Most clay minerals are swellable (and also reversible) and have high ion-exchange capacity, and hence are widely used in catalysis generally [117]. The representative structure of montmorillonite clay is shown in Figure 4. Recent advances have shown various modifications of montmorillonite, thereby improving its Bronsted and Lewis acids and pore size distribution [118]. These modifications might have informed their deployment as a catalyst and catalyst support in glycerol acetylation. [PERSON] et al. [91] reported the synthesis of a series of sulphuric acid-modified Montmorillonite (K-10) catalysts (10, 20, and 30% (_w/w_) H\({}_{2}\)SO\({}_{4}\)/K10). They were used for the acetylation of bio-glycerol with acetic acid at reaction conditions of 120 \({}^{\circ}\)C, 0.4 g catalyst loading, the glycerol-to-acetic acid molar ratio of 1:12, and for 5 h. Furthermore, 20% (_w/w_) H\({}_{2}\)SO\({}_{4}\)/K10 performs better with 99% glycerol conversion and 23%, 59%, 15%, and 2% yield towards monoacetin, diacetin, triacetin, and diglycerol triacetate. The obtained results were found to correlate with the acidity and other textural properties of the catalysts.