TURI’s Hansen Solubility Parameters in Practice (HSPiP) October Challenge: Safely Dissolving PET

TURI has been using the Hansen Solubility Parameters (HSP) theory for various solvent replacement projects such replacing methylene chloride for paint stripping, but we are hoping to replace other hazardous cleaning solvents. Senior students who have used the Hansen Solubility Parameters in Practice Program (HSPiP) are leaving next year, so we have started training the next generation of TURI students to learn how to use the program to solve real problems in solvent cleaning. Our students, ranging in major from plastics engineering to public health, engaged in the training and wanted more hands-on approach to solving problems. As a learning exercise, the students were given a case study and had to find a safe replacement using the HSPiP Solvent Optimizer.

A Brief Overview of the Hansen Solubility Parameters (HSP) Theory

HSP theory is a theory of solubility rooted in thermodynamics that predicts if a solvent will dissolve a solute. Essentially, the theory boils down to “like dissolves like”. The Hansen Solubility Parameters are based on the strength of a chemical’s intermolecular forces:

London dispersion forces, ẟD
Dipole-dipole forces, ẟP
Hydrogen bonding, ẟH

Each force is quantified by its strength. The three parameters are then mapped in 3D space (Hansen Space), with the solvents represented as points, and the solute represented as a large sphere with an experimentally determined radius (as seen in the photo to the left). If a solvent falls within the sphere, it will dissolve the solute, and if it falls outside the sphere, it will not dissolve the solute. The closer the solvent is to the center of the sphere, the better the dissolution. This is called the Relative Energy Distance (RED) which is calculated in the HSPiP analytical software. The RED is the distance from a solvent to the center of the sphere divided by the radius of the sphere. A RED less than 1 indicates that the solvent is within the sphere and the lower the RED, the more effective the dissolution will be.

HSPiP contains the very useful Solvent Optimizer function. With this theory, there is proportional mixing of the solvents, meaning that if you mix two solvents together in a 1:1 ratio, the new HSP value will be an average of the two HSP values. This gives potential for two solvents outside of the sphere to be mixed together to have a new HSP within the sphere and work as a replacement solvent. The goal is to mix solvents together in a ratio that obtains the lowest RED, which the program does based on the solvents you input. This means that if a hazardous chemical cleans a soil from a surface, we can blend together safer solvents to achieve the same level cleanliness.

Case Study

Students were given the following scenario to try and find a safer substitution using HSPiP:
A company is manufacturing parts by using a polyethylene terephthalate (PET) mold that needs to be dissolved. The company is using methylene chloride at room temperature to dissolve the PET mold. The workers are using proper gloves and eye protection, but no masks. Find a solvent or create a solvent blend using HSPiP that can optimally dissolve the PET mold and is safer for the workers to use.

Details
PET: (18.2, 6.4, 6.6) Radius: 4

· Methylene chloride’s RED to PET is 0.65

· Make sure your solvents are liquid at room temperature

· Make sure the solvents are safe for the workers

· You do not need to worry about cost of the solvents for this challenge

The submitted replacements were ranked based on their effectiveness, smallest distance to PET, and their safety scores, using TURI’s P2OASys (https://p2oasys.turi.org/).

Submissions

Blend	D	P	H	RED	P2OASys Score
Benzyl Acetoacetate (100%)	18.04	6.47	6.21	0.13	4.300
Butyl Benzoate (50%) Dimethyl Isosorbide (50%)	18	6.4	6.5	0.1	4.200
Butyl Benzoate (50%) Glycerol Triactetate (50%)	17.4	5.1	7.3	0.54	3.950
Benzyl Benzoate (18%) Butyl Benzoate (24%) Dimethyl Isosorbide (58%)	18.2	6.4	6.6	0	4.184
Butyl Benzoate (83%) Caprolactone (8%) 2-Propanol (9%)	18.1	6.4	6.6	0.05	4.314
Butyl Benzoate (82%) γ-Butyrolactone (7%) 2-Phenoxy Ethanol (11%)	18.2	6.4	6.6	0	4.254

Solvents Proposed:

Benzyl Acetoacetate (CAS: 5396-89-4)

Hazards: SDS indicates none, through a deeper search we found it was a skin irritant, eye irritant, and hazardous to aquatic life.

Butyl Benzoate (CAS: 136-60-7)

Hazards: Acute toxicity, Oral (Category 4), Skin irritation (Category 2), Eye irritation (Category 2A)

Dimethyl Isosorbide (CAS: 5306-85-4)

Hazards: None

Benzyl Benzoate (CAS: 120-51-4)

Hazards: Acute toxicity, Oral (Category 4), Acute aquatic toxicity (Category 1), Chronic aquatic toxicity (Category 1)

Glycerol Triactetate (CAS: 102-76-1)

Hazards: None

Caprolactone (CAS: 502-44-3)

Hazards: Eye irritation (Category 2A)

2-Propanol (CAS: 67-63-0)

Hazards: Flammable liquids (Category 2), Eye irritation (Category 2A), Specific target organ toxicity - single exposure (Category 3), Central nervous system

γ-Butyrolactone (CAS: 96-48-0)

Hazards: Acute toxicity, Oral (Category 4), Serious eye damage (Category 1), Specific target organ toxicity - single exposure (Category 3), Central nervous system

2-Phenoxy Ethanol (CAS: 122-99-6)

Hazards: Acute toxicity, Oral (Category 4), Eye irritation (Category 2A)

Winners

Dan Anspach and Lily Green 2/3 of the winning team!

1^st Place: Dan, Lily, and Justin
Benzyl Benzoate (18%) Butyl Benzoate (24%) Dimethyl Isosorbide (58%)

2^nd Place: Aaron
Butyl Benzoate (50%) Dimethyl Isosorbide (50%)

3^rd Place: Diana and Sabrina
Benzyl Acetoacetate (100%)

All teams participating created safer blends that had and RED less than 0.65; congrats to everyone for learning! Students cited that the hardest part of the challenge was finding solvents within the program that were safe and spent most of their time looking at SDS sheets and toxicology databases. Our first place winners received a $50 Visa gift card and trophies. They will be presenting on their blends at a presentation to the whole TURI staff.

Our November/December HSPiP Challenge will be focusing on a real solvent replacement for TCE for electroplating. The winners of the next challenge will then purchase their solvents and test to see if their solution will work in a realistic setting. They will also receive a $50 Visa gift card and trophies. Stay tuned!