Evaluation of nopol production obtained from turpentine oil over Sn/MCM-41

What is it about?

A face-centered Central Composite Design (CCD) was used for nopol synthesis from turpentine oil over Sn/MCM-41 catalyst synthesized with sodium silicate as silicon source and incorporating Sn by wetness impregnation using SnCl2.2H2O as metal source. The catalyst was characterized by XRD, NH3-TPD and UV–vis-DRS. The catalyst was used four times without an apparent loss of catalytic activity and with no leaching of Sn. The CCD was constructed from 24 factorial points, eight axial points and seven central points, with time, paraformaldehyde to β-pinene molar ratio, catalyst concentration and solvent to β-pinene ratio as factors. Three response variables were selected (β-pinene conversion, nopol selectivity and nopol yield), and second order models were obtained taking into account all possible effects and identifying the non statistically significant effects. The optimal values found by response surface methodology were 71 %, 99 % and 61 % for conversion, selectivity and yield, respectively. The reactions were carried out under the established optimal conditions and the error varied between 2.14 and 2.63 %. Finally, the assumptions of independence, normality and homoscedasticity for each of the models were satisfactorily validated.

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Why is it important?

Nopol is a synthetic monoterpenic alcohol for household product applications that has been synthesized by Prins reaction of β-pinene and paraformaldehyde, which is an appropriate aldehyde source when anhydrous conditions are required. For the heterogeneous catalytic synthesis of nopol, Alarcón et al. reported a very detailed state of the art until 2012 where the most active materials were FePO4, Zn-montmorillonite, Zn-Al-MCM-41, Zn-anionic resin, Fe-Zn cyanide and Sn-SBA-15. The analysis of the design stages to obtain nopol in batch processes, showed that a large part of the annual processing costs correspond to raw materials, which come mainly from β-pinene. Therefore, a first step to improve the profitability of the process is to study the nopol synthesis using turpentine oil as a source of β-pinene instead of high purity β-pinene, which is one of the purposes of the present work. There are two alternatives for nopol synthesis regarding the source of the olefin. The first option is first to separate β-pinene from turpentine oil and subsequently carry out the Prins reaction to obtain nopol. The second option consists in nopol production by Prins reaction with turpentine and subsequently separate nopol from the reaction mixture. For the first alternative significant technical drawbacks are involved such as performing single rectification because turpentine components such as α-pinene, β-pinene, 3-carene and camphene have similar boiling points, which requires distillation columns with numerous stages, while the separation of nopol from the reaction mixture is more technically feasible due to its boiling point (230–239 ◦C) is much higher than the boiling points (around 156–169 ◦C) of the main monoterpenes present in turpentine oil.