Today’s cleaner has a number of available options when choosing a new dry cleaning system, or in some cases, for operating the system one has. New solvent choices continue to become available, and there are upgrades to traditional solvents to choose from as well. IFI frequently receives inquiries concerning petroleum solvent options from both newcomers and experienced operators alike. This bulletin has been designed to help you understand what’s new in the petroleum and hydrocarbon solvents arena by explaining the changes and the differences in petroleum solvents and equipment.
New, processed petroleum solvents typically referred to as hydrocarbon solvent have stimulated the most fundamental changes. New equipment technologies have been developed to take advantage of improvements in the new solvents’ flash point and odor characteristics, and employ new methods to minimize the fire hazard. In addition, new hydrocarbon cleaning units offer improvements for easier vacuum distillation, efficient solvent consumption and safer operation.
Is it Petroleum or Hydrocarbon?
In recent years, there has been some confusion over the terms “petroleum” and “hydrocarbon” solvent. The formal definition of hydrocarbon is “one of a very large group of chemical compounds composed only of carbon and hydrogen; the largest source of hydrocarbons is from petroleum crude oil” (Dictionary of Scientific and Technical Terms, McGraw Hill, Publisher). The word petroleum can be used to describe most of the traditional solvents developed from crude oil, but lately some new petroleum-based solvents have emerged, namely, DF-2000TM Fluid and EcoSolv, manufactured by ExxonMobil Chemical Company and Chevron Phillips Chemical Company, respectively. Both manufacturers and their distributors prefer to call them “Hydrocarbon Solvents.” The term hydrocarbon in this context refers to a high-flash, essentially odorless solvent derived from or processed from petroleum.
The difference between the traditional petroleum solvents and the new hydrocarbon solvents derives from their composition. Generally, the quality of traditional petroleum solvent depends on its mixture of three types of hydrocarbons: paraffinic, naphthenic, and aromatic. Most petroleum solvents contain all three, but the ratio of each depends on the source of crude oil from which the solvent was derived and the degree of refining employed. The new hydrocarbon solvents are made via a process that does not depend on the crude oil source to determine quality and consistency and is able to produce predominantly paraffinic hydrocarbons.
Paraffinic hydrocarbons have the lowest solvent power of these three classes. On the other hand, they have fewer environmental and personal exposure concerns and very little odor. Naphthenic hydrocarbons occur in all petroleum. They typically make up the largest portion of petroleum solvents. They have stronger solvent power and stronger odors than paraffinic hydrocarbons.
Aromatic hydrocarbons have the strongest solvent power. Usually, the KB value of a petroleum solvent is reflected in its aromatic content. The more aromatic hydrocarbons in the solvent, the higher its KB value. Depending on the relative amounts of each hydrocarbon, a solvent’s physical properties can vary greatly. As a result, there are many different types of petroleum solvent.
For a variety of reasons, it is desirable to limit the aromatic content of petroleum solvents. One important reason is that aromatic hydrocarbons (as the name indicates) have fairly strong odors. Another is that aromatic hydrocarbons contribute more strongly to smog formation. Several states have adopted legislation that limit aromatic hydrocarbon concentrations in cleaning solvents – e.g., California’s South Coast Air Quality Management District Rule 102.
The newer “hydrocarbon” solvents contain predominantly paraffins and have higher flash points (over 140°F) and lower toxicity. They are virtually odorless and safer to handle.
The American Society for Testing and Materials (ASTM) Specification D235 classifies petroleum-based solvents into four distinctive groups based on their flash points, boiling range, and KB value.
- Type I Stoddard Type III Odorless
- Type II 140°F Solvent
- Type III Odorless
- Type IV Low Dry Point
Most petroleum solvents fall under one of these four categories, however some odorless solvents may meet the KB value requirements of Type III and the flash point and volatility requirements of Type II or IV.
Petroleum/Hydrocarbon Solvent Properties
- The flash point is the temperature at which solvent vapors above a pool of liquid solvent will ignite in the presence of a spark or flame.
- Petroleum and hydrocarbon solvents do not have a specific boiling point but instead have a boiling range. This is because they contain a multitude of components, each with its own boiling point.
- The Kauri-Butanol Value (KBV) indicates the solvent’s ability to dissolve oils and greases. The higher the KBV, the more oils and greases are dissolved. The KBV of a petroleum/hydrocarbon solvent depends on its composition with aromatics, naphthenics, and paraffins.
- The odor of the traditional petroleum solvent will also vary with the solvent’s composition. Aromatics, and to a lesser extent naphthenics, have a fuel-like scent while paraffins may possess a sweet type of smell.
- The Permissible Exposure Level (PEL) is the maximum amount of vapor a worker may be exposed to under OSHA regulations. The PEL for solvent vapors is a time-weighted average concentration of the chemical in the air for a normal 8-hour work day and is usually expressed in parts per million (ppm).
- The National Fire Protection Association (NFPA) classifies solvents into four different types based on their flash points. Most manufacturers will specify a solvent class that can be used safely in their machines.
- Class I Solvents – Liquids having a flash point below 100°F (37.8°C).
- Class II Solvents – Liquids having a flash point at or above 100°F (37.8°C) and below 140°F (60°C).
- Class IIIA Solvents – Liquids having a flash point at or above 140°F (60°C) and below 200°F (93.4°C).
- Class IIIB Solvents – Liquids having a flash point at or above 200°F (93.4°C).
Machine Properties
In order for combustion to occur, there must be oxygen, an ignition source, and fuel. These three elements make up what is known as the “Fire Triangle.” Therefore, manufacturers of newer petroleum machines eliminate one or more legs of the triangle to control or reduce the possibility of explosion.
Nitrogen Blanketing
Combustion can only occur in the presence of oxygen. To minimize this risk, some petroleum machines inject nitrogen gas into the drum to replace most of the oxygen. Nitrogen can be used in both the wash and dry cycles. An oxygen monitor maintains the level of oxygen below 8%, which is the minimum level needed for combustion.
Vacuum
In a vacuum system, 90% of the air is removed from the machine. This deletion of air reduces the oxygen in the wheel below combustion levels. Typically, in dry-to-dry machines, the vacuum will start during extraction and be carried over into the drying cycle.
LEL Monitoring
These systems reduce the risk of explosion by maintaining the concentration of flammable solvent vapors below critical levels during the drying phase. The lower explosive limit (LEL) is the lowest concentration of vapor that will burn or explode if ignited. The upper explosive limit (UEL) is the highest concentration of vapor that will burn or explode if ignited. The concentration between the LEL and UEL is explosive. Below the LEL, the mixture is too lean (not enough fuel) to burn. Above the UEL, the mixture is too rich in fuel (not enough oxygen to burn). LEL monitoring is used in both dry-to-dry machines, as well as in separate petroleum-reclaiming dryers.
Distillation
As in the older petroleum machines, distillation is conducted under vacuum. The vacuum conditions are necessary to lower the boiling point of the solvent. High temperatures necessary to boil petroleum solvents risk causing decomposition of the solvent.
Stain Removal
Contrary to some sales claims, conventional stain removal agents can be used in conjunction with both traditional petroleum and the newer hydrocarbon dry cleaning systems. This will come as good news for some because stain removal agents containing more powerful solvents for the removal of stains such as nail polish, lipstick, or shoe polish are necessary for effective removal of those stain types. However, it is important to completely flush out all stain removal agents from the fabric before dry cleaning. After flushing, the stained area should be thoroughly dried before cleaning. Excessive moisture in a petroleum system can cause serious problems such as shrinkage, dye bleeding, redeposition, and foul odors. It is also important to flush stain removal agents before cleaning because the ingredients of some solvent-based chemicals can alter the physical properties of hydrocarbon solvents if they are allowed to build up.
Water Separator
All dry-to-dry hydrocarbon machines and recovery tumblers are equipped with water separators. Most machines have two or even three water separators to assure a more efficient separation of solvent from water. The solvent initially separates in the first water separator, then flows into a second, and if equipped, into a third. The water separator(s) should be cleaned at least once a week. Failure to routinely clean the separator(s) will lead to bacterial growth in the water phase of the apparatus and may, in turn, cause odor in the garments. Once bacteria have grown, they will be very difficult to remove. If the water is not separated sufficiently from the solvent, excess water can be transferred to the solvent tank(s) with the distilled solvent. This then creates an opportunity for bacterial growth in the solvent tank as well.
Cleaning Quality
Our experience and test results from various dry cleaning plants around the country show comparable test data between perc and petroleum solvent cleaning when all important parameters such as solvent condition, load factors, etc. are adhered to.
Cleaning in petroleum/hydrocarbon solvents is safer on some dyes, beads, sequins, and other types of trims because of the lower KBV of petroleum-based solvents; therefore, it is considered a gentler solvent as compared to perc with a KBV of 90. However, given the lower KBV and lower specific gravity, the length of the cleaning cycle with petroleum/hydrocarbon solvents is longer than perc solvents. A complete cycle will be in the range of about 50~70 minutes in most dry-to-dry machines, depending on the type and weight of the load.
Due to the various properties of petroleum-based solvents and machines, it is crucial that you use a solvent that is compatible with the machine type. Consult the manufacturer for a recommended solvent to use in your machine.
This article is from DLI’s TOI-698
