Cleaning with Solvents: Science and Technology

John Durkee

• Publisher: William Andrew
• Year: 2013
• Print ISBN:
  9781455731312
• eBook ISBN:
  9781455731619
• Topic: Physical Sciences
• Subtopic: Toxicology

High-precision cleaning is required across a wide range of sectors, including aerospace, defense, medical device manufacturing, pharmaceutical processing, semiconductor/electronics, etc. Cleaning parts and surfaces with solvents is simple, effective and low-cost. Although health and safety and environmental concerns come into play with the use of solvents, this book explores how safe and compliant solvent-based cleaning techniques can be implemented. A key to this is the selection of the right solvent. The author also examines a range of newer "green" solvent cleaning options. This book supplies scientific fundamentals and practical guidance supported by real-world examples. Durkee explains the three principal methods of solvent selection: matching of solubility parameters, reduction of potential for smog formation, and matching of physical properties. He also provides guidance on the safe use of aerosols, wipe-cleaning techniques, solvent stabilization, economics, and many other topics. A compendium of blend rules is included, covering the physical, chemical, and environmental properties of solvents. - Three methods explained in detail for substitution of suitable solvents for those unsuitable for any reason: toxic solvents don't have to be tolerated; this volume explains how to do better - Enables users to make informed judgments about their selection of cleaning solvents for specific applications, including solvent replacement decisions - Explains how to plan and implement solvent cleaning systems that are effective, economical and compliant with regulations

Chapter 1

Relationship of Solvent Properties to Structure

Abstract

Many clients have asked consultants to select a solvent for an application e and then wondered why the list of proposed solvents was not only short but similar to other lists. A popular handbook of chemical information lists names of 455 organic (i.e. carbon-containing) chemicals whose first letter starts with “T.” Also listed are the names of 279 others whose first letter starts with “E” and 315 other whose first letter starts with “A.” Yet the list of available chemicals for solvent cleaning is surprisingly short.

This chapter is about why that is so, and how to design select solvents for cleaning applications.

Keywords

Global Warming Potential; dendrimers; nanotechnology; Ozone Depletion Potential; volume manufacture; physical and safety properties; molecular structure

1.1 Background

Many clients have asked consultants to select a solvent for an application—and then wondered why the list of proposed solvents was not only short but similar to other lists.

One such list is the solvents named on the horizontal axis of Figure 1.1. The vertical axis in this figure is a measure of solvency: the Kauri Butanol parameter (Kb).

Figure 1.1

A popular handbook of chemical information lists names of 455 organic (i.e. carbon-containing) chemicals whose first letter starts with “T.” Also listed are the names of 279 others whose first letter starts with “E” and 315 other whose first letter starts with “A.” Yet the list of available chemicals for solvent cleaning is surprisingly short.

This chapter is about why that is so, and how to design or select solvents for cleaning applications.

1.2 The Elements of Cleaning Solvents

Cleaning work is generally done by immersion of parts into a solvent, which:

• Is a liquid at ambient temperature, doesn’t freeze in normal storage, and boils at a temperature at which persons aren’t threatened or articles damaged¹.
This constraint eliminates metallic elements, those of substantial molecular weight, and those of low atomic weight. With some exceptions, the compounds of which these elements are constituents can’t have a molecular weight outside of the range 50 to 200.

• Has an affinity, through similar intermolecular forces, for the soiling material.
In other words, the solvent must be similar to the soil. Since most soils are oils or greases based on carbon and hydrogen, the solvents used to clean them are too. This also means that elements normally considered inert, such as argon and helium, are not useful as components of cleaning solvents.

• Doesn’t react chemically with the articles being cleaned, the soil material upon them, or the persons doing the cleaning work.
This constraint eliminates radioactive elements, thermally or chemically unstable elements, those of high reactivity with other elements, and those capable of producing harm to humans or the environment through their action or mere presence².

• Can be safely disposed in drum quantities.
Elemental reactivity and radioactivity again limit solvent composition. Furthermore, the solvent and its potential products of decomposition can’t be restricted by being specifically listed in environmental codes.

• Is economical to be produced and used in drum quantities.
Since the volume of solvents used for industrial cleaning is dwarfed by the volume of solvents used as reactants, refrigerants, diluents, or inert ingredients, there must be several additional and substantial non-cleaning uses for any proposed cleaning solvent. No manufacturer will produce a solvent for use only in cleaning operations. Furthermore, net cost-in-use, from purchase to disposal, must not exceed a few dollars per pound, which mitigates against the use of elements rarely in use.

• Already exists as a chemical in commerce.
This author believes that the cost of developing new chemicals as solvents will act as a brake on the development of new solvents³. A significant part of that development cost is toxicological and environmental testing.

In summary, there are probably no chemical elements which can be used by a chemist to create cleaning solvents! This is why it is sometimes argued that cleaning operations should be either avoided by design or by modification of downstream operations, done by contact with plasma or ionic solvents (Ref. 3, Chapter 9), or done by biological treatment.

1.3 The Incredible Shrinking Periodic Table

In industrial enterprise, as in life, compromise is necessary. The above constraints on the identity and number of elements which can be found in cleaning solvents shrinks the list of candidate compounds from many many thousands to a few hundred, and the list of candidate elements to about a half-dozen.

The periodic table for elements currently used in cleaning solvents is shown in Table 1.1. Most of the atoms in it can’t be used in the synthesis of solvents because their products with carbon and hydrogen are metals and not solvents. In addition to carbon or hydrogen, there are basically only eight other atoms (elements) which can be components of cleaning solvents: silicon, nitrogen, oxygen, sulfur, and the four halogens (fluorine, chlorine, bromine, and iodine). Sulfur is not a popular component in solvent molecules because of its odor, and because it adds potential for toxicity and corrosion. Iodine is quite reactive, so stable solvents containing it are difficult to commercialize.

Table 1.1

The Periodic Table of Elements for Cleaning Solvents

That basically leaves only six atoms besides carbon and hydrogen from which to synthesize solvents: three halogens, silicon, nitrogen, and oxygen. That’s it—a total of eight different atoms (elements) from which useful cleaning solvents can be and are synthesized!

1.4 A Solvent can be Elements Arranged in a Structure

The list of chemical solvents proposed for applications by consultants is often short because there aren’t enough degrees of freedom (variability) from which to create them. The variability in solvent design comes from the elements from which the structure is populated (probably only carbon and hydrogen), the nature of the structure in which atoms (elements) are arranged, and the additional elements inserted into the basic structure (the other six elements). The major types are shown in Table 1.2.

Table 1.2

Solvent Structures

Some useful cleaning solvents contain no atoms other than carbon and hydrogen. In Table 1.2 from top to bottom, they are: hexane; 2-methyl,4-methyl-butane; benzene⁴; cyclohexane; and 1-octene. Other commercial cleaning solvents are blends of the above or similar structures. Examples are mineral spirits and VM&P⁵ naphtha (Ref. 3, Chapter 5). Cyclic structures containing nine and more carbon atoms are underused solvents for oils and greases.

1.5 A Solvent can also be a Structure Populated with Additional Elements...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Acknowledgments
• Disclaimer
• What You Can Do with This Book
• A Note on Organization
• Units Used in This Book
• External References Cited in This Book
• Chapter 1. Relationship of Solvent Properties to Structure
• Chapter 2. Solubility Scales (Parameters)
• Chapter 3. Solvent Selection for Specific Tasks
• Chapter 4. SHE Management (Solvent Substitution)
• Chapter 5. Toxicology of Cleaning Solvents
• Chapter 6. The VOC Exemption Game
• Chapter 7. Economics of Solvent Use
• Chapter 8. Solvent Azeotropes
• Chapter 9. Wipe Cleaning with Solvents
• Chapter 10. Cleaning with Solvent Aerosols
• Chapter 11. Stabilization of Solvents
• Chapter 12. Solvent Cleaning: Questions and Answers
• Group A. Basic Information
• Appendix A1. Basic Data about Cleaning Solvents
• Appendix A2. Estimation of Properties of Solvent Blends
• Appendix A3. Derivation of Blend Rule for Solubility Parameters
• Appendix A4. Compatibility of Wipe Cleaning Solvents with Surface Materials and Protective Gloves (With Database)
• Appendix A5. Management of Flow of Cleaning Solvents to Wet Surfaces (The Wettability Index and the Dimensionless Ohnesorge Number)
• Group B. Reduction of Ozone Formation by VOCs
• Appendix B1. Chemistry of Atmospheric Reactions of VOCs Leading to Smog
• Appendix B2. Calculation of MIR through Group Contribution Methods
• Group C. Solubility Parameters
• Appendix C1. Optimization Method for Determination of Solubility Parameters
• Appendix C2. Estimation of Hansen Solubility Parameters (HSP) from Binary Data—PES
• Appendix C3. Estimation of HSP from Multilevel Data—Bitumen
• Appendix C4. Estimation of HSP from Solvent Mixtures
• Appendix C5. Estimation of HSP from Correlations
• Appendix C6. Estimation of HSP using the “Pythagorean Theorem”
• Appendix C7. Estimation of HSP from an Equation of State
• Appendix C8. Estimation of HSP from Group Contribution Methods
• Appendix C9. Estimation of HSP for Soil Mixtures
• Appendix C10. Hoy Solubility Parameters
• Appendix C11. Values of Hansen Solubility Parameters for Solvents, Soils, and Polymers
• Appendix C12. The Teas Graph
• Group D. Solvent Substitution
• Appendix D1. Examples and Methodology of Solvent Substitution
• Appendix D2. Examples of Solvent Substitution to Achieve VOC Reduction
• Index