Kevin N Wilkins of trepwise On How To Take Your Company From Good To Great

As part of my series about the “How To Take Your Company From Good To Great”, I had the pleasure of interviewing Kevin N. Wilkins, Founder and CEO of trepwise. Kevin N. Wilkins is the Founder and CEO…

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Switchable Polarity Solvents

In our efforts to enhance daily products, medicines or crop production, we caused unintended damage to our environment and ourselves. It's not unusual, that certain processes or chemicals were declared as safe, although long term effects haven’t been studied. This dilemma produced severe damage to our planet, like ozone holes produced due to the release of chlorinated fluorocarbons to the atmosphere. To prevent any further issues from happening, governments ask companies to redesign chemical processes to fit environmental regulations. Green chemistry is a new approach to think about chemistry. It was developed to set principles to how we design chemical processes. These principals enable scientists to find innovative ways to reduce waste, displace hazardous substances and conserve energy. Beyond, green chemistry tries to feature a green life cycle — like the use of renewable resources and recycling of the final disposition. In short — green chemistry is the future of chemistry.

Solvents play an incredibly important role in the large-scale chemical industry. They are used in several applications like extractions, precipitations or just as a reaction medium for chemical reactions. Solvents have a fixed polarity which leads to a layer separation with certain other solvents (e.g. hexane and water). Non-polar solvents are often needed to extract oils or fats and as their trivia “hydrophobic solvents” suggest — they are mostly water-insoluble at room temperature.

Switchable Polarity Solvents (SPS) have a low polarity until exposed to a trigger, which changes them to a high polarity solvent. This trigger is often CO2. It reacts with the molecule to produce a water-miscible form. This is pretty useful because it can separate dissolved products from the solvent. At regular extraction processes, the solvent has to be evaporated, which yields in high energy needs. SPS can be converted by bubbling CO2 through the solution at 1atm pressure. This requires very little energy and carbon dioxide is also cheap and safe to handle.

Even though water and hydrophobic substances are poorly miscible, there will always be a small amount dissolving in the water according to the solubility. If CO2 is passed through the solution it dissolves forming hydrated carbon dioxide, which forms an equilibrium with carbonic acid (H2CO3). If the hydrophobic substance is basic relative to water it can be protonated by the carbonic acid to form a bicarbonate salt. A salt is much more soluble in water, due to its ionic/polar bonds. This reaction does only work with few functional groups though, amines being the following example.

Amine groups are separated into three types: primary, secondary or tertiary. This depends on how many alkyl or aromatic groups (-R) are bonded to the nitrogen atom. This is important because it affects the reaction behavior in the SPS-system. Primary and Secondary amines can undergo a second reaction pathway, while tertiary can only form the bicarbonate salt. The second reaction pathway forms a carbamate salt. It's much more stable than the bicarbonate salt and therefore the preferred reaction, leading to faster conversion of the initial biphasic mixture of solvent and water. The problem is, that stable bonds need more energy to be broken, so in turn, more heat is required to turn the mixture back to the biphasic form. Carbamate salts are therefore avoided by using tertiary amines.

When the salt form of the amine is obtained it readily dissolves in the water, leaving the desired product behind. It's then easily separated and the solvent-salt/ water solution is ready to be converted. This can be achieved by heating, which forces the CO2 out of solution or by displacing the CO2 by another gas. Most of the time an inert gas, like nitrogen or argon, is used to avoid any side reactions.

Switchable polarity solvents align indeed with many of the green principles of green chemistry. They already have been tested in multiple industrial applications. Oil from oil sand, as well as soybean oil, have been extracted and it was used in several recovery processes. There seems to be a decent commercial interest because patents are being submitted by researchers but also industrial collaborators. Standard solvents have the huge advantage of being cheap and widely available. Still, it has been shown that SPS technology can be both energy and material efficient. But most importantly they are green and of considerable environmental advantage.

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