## 4 Solketal Synthesis
### Recent Advances on the Continuous Process
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Author** & **Catalyst** & **Catalyst** & **Reaction Conditions** & **Results** & **Observations** & **Ref** \\ \hline \multicolumn{5}{c}{Microwave Reactor} \\ \hline \multirow{5}{*}{Cablewski, 1994} & \multirow{5}{*}{pTSA} & 0.05 & G:A = 1:13.5 & \multirow{5}{*}{Y\({}_{\text{solk}}\) = 84\%} & \multirow{5}{*}{Continuous process.} & [68] \\  & & \(\text{gcat}/\text{ggly}\) & T = 1 bar & & \\  & & & Space time = 1.2 h & & \\ \hline \multirow{5}{*}{Priya, 2017} & Copper metal & \multirow{5}{*}{0.43} & G:A = 1:3 & \multirow{5}{*}{X\({}_{\text{gly}}\) = 95\%} & Three cycles without & \multirow{5}{*}{[116]} \\  & supported on & \(\text{gcat}/\text{ggly}\) & T = 373 K & & \\  & & \(\text{gcat}/\text{ggly}\) & P = 1 bar & & \\  & & & Space time = 0.25 h & & \\ \hline \multicolumn{5}{c}{Reactive Distillation} \\ \hline \multirow{5}{*}{Clarkson, 2001} & \multirow{5}{*}{Amberlyst DPT-1} & 0.05 & G:A = 1:23.6 & \multirow{5}{*}{X\({}_{\text{gly}}\) = 70\%} & “Only a slight loss of & \\  & & \(\text{gcat}/\text{ggly}\) & T = 343 K & & \\  & & \(\text{gcat}/\text{ggly}\) & Reactive Stages = 10 & & \\  & & & Space time = 0.5 & & \\  & & & h/stage & & \\ \hline \multirow{5}{*}{Li, 2020} & Seepage packing & \multirow{5}{*}{NA} & G:A = 1:3 & \multirow{5}{*}{X\({}_{\text{gly}}\) = 85.9\%} & \multirow{5}{*}{[104]} \\  & internals filled & & T = 323 K & & \\  & with cation & & P \(\approx\) 1 bar & & \\  & Exchange & & Reactive Stages = 20 1 & & \\  & ResinNKC-9 & & & Space time = 20 s & \\  & & & Reflux ratio = 2.5 & & \\ \hline \multicolumn{5}{c}{Membrane Reactor} \\ \hline \multirow{5}{*}{Roldán, 2009} & \multirow{5}{*}{K10} & \multirow{5}{*}{0.1} & G:A = 1:2 & \multirow{5}{*}{X\({}_{\text{gly}}\) = 90\%} & \multirow{5}{*}{Vapor permeation.} & [54] \\  & & & T = 333 K & & \\  & montmorillonite & \(\text{gcat}/\text{ggly}\) & P = 1 bar & & \\  & & & Vaccum = 2 mbar & & \\ \hline \multicolumn{5}{c}{Adsorptive Reactor} \\ \hline \multirow{5}{*}{Moreira, 2020} & \multirow{5}{*}{Amberlyst-35} & \multirow{5}{*}{25 g} & G:A = 1:2 & \multirow{5}{*}{X\({}_{\text{gly}}\) = 81\%} & \multirow{5}{*}{[11]} \\  & & & T = 313 K & & \\ \cline{1-1}  & & & P = N.A. & \\ \cline{1-1}  & & & Solv. = Ethanol & & \\ \cline{1-1}  & & & Space time = 0.25 h & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Process intensification strategies for the synthesis of solketal. Microwave irradiation has been explored as a heating intensification strategy in continuous and batch processes. According to the authors, heat transfer is more efficient because the microwave energy is transferred directly to the reaction molecules; moreover, since there is a faster response in comparison to conventional heating, the process is safer. Cablewski et al. produced solketal with pTSA and high excess of acetone in an apparatus that comprises a reaction coil inside a microwave cavity. The reactants were preheated and fed together with the catalyst continuously. Years later, Priya et al. tested a more environmentally friendly process in batch with several transition metals supported over Mordenite and stated that Cu-Mor performed better, which they attributed to the greater acidity of this catalyst [68, 116]. Reactive distillation is an appealing PI strategy because it tackles the thermodynamic limitation by removing water from the reaction medium at the same time it integrates reaction and separation by distillation, eliminating the need for post-treatment processes. Clarkson et al. proposed to carry the reaction on a multiray reactive distillation column with deep stages containing Amberlyst-DPT in suspension. They proposed a 15 stages column, with 10 reactive stages. Pre-heated glycerol would be fed at the top of the column so it could flow down through all the stages and acetone would be fed at the bottom so it could pass up the column agitating the resin and stripping out the water generated. Solketal would be purified in the bottom three stages and collected with a purity of more than 99% [67].