Background for this classification summary
- Visit the Classification Index to see other groups.
- The summary on this page follows the classification scheme of Elsner and Hoelzer, 2016. Quantitative Survey and Structural Classification of Hydraulic Fracturing Chemicals Reported in Unconventional Gas Production. Environmental Science and Technology. 3290-3314. DOI: 10.1021/acs.est.5b02818.
- Elsner and Hoelzer’s thorough and influential article provides a wealth of chemical context about fracking materials including health and environmental implications and suggestions for deeper analysis. However, the work was based partially on a early set of FracFocus (through 2013). Subsequent years have added new materials and millions more records. To extend their analysis to the rest of the FracFocus materials, we used Google’s Gemini to assist us in assigning classifications in line with EH’s methodology.
- Analysis from a FracFocus download, Jan 2025.
- Masses are not available for all records, so reported masses below are sums of only the available masses. See documentation.
- To provide useful technical information about these chemical groups, we use generative AI tools to assist with summaries (Google’s Gemini). These tools are prompted with details of the classification scheme (by Elsner and Hoelzer, 2016) and information about reported chemicals in the group. To limit inaccuracies, we feed the resulting output to competing models (OpenAI’s ChatGPT) to check for accuracy and ambiguity. In addition, we consulted Fink, Johannes, “Petroleum Engineer’s Guide to Oil Field Chemicals and Fluids” Third Edition. (2021) Gulf Professional Publishing. 1028pp.
- Functions reported here are summarized from the FracFocus field “Purpose.” There are limitations to this data: not all chemical records have a reported purpose (the “systems approach” explicitly excludes “Purpose” values from chemical records). Furthermore, “Purpose” typically describes the product, not individual chemicals within the product. The individual ingredient may serve a chemical role in the product that is different from the reported “purpose” (for example, synthetic polymers might be labeled “proppant”, but they are not primary proppants, but rather coatings for sand grains to enhance their performance.) In general, consider these “functions” as the larger purpose played by the product that contains the ingredient.
Alkoxylated alcohols are a class of organic compounds frequently used in hydraulic fracturing fluids. These chemicals are characterized by the addition of alkoxy groups (RO-, where R is an alkyl group) to an alcohol molecule. (See other alcohols here.) This modification alters the properties of the original alcohol, often enhancing its solubility in water and its surface activity. Alkoxylated alcohols can function as surfactants, emulsifiers, and wetting agents. Between 2014 and 2024, 344,000 records referencing alkoxylated alcohols were published on FracFocus. The total mass of these chemicals reported during this period was 726,000,000 pounds.1
Several subgroups of alkoxylated alcohols are used in fracking. These include ethoxylated alcohols (56 reported chemicals), propoxylated alcohols (9 reported chemicals), alkoxylated phenols (9 reported chemicals), and a category designated as unspecified/other (12 reported chemicals). Further details on the specific chemical structures and properties of these subgroups will be provided separately.
While the specific function of an alkoxylated alcohol within a fracturing fluid formulation is not always disclosed in FracFocus records, these chemicals are typically incorporated into products reported to serve various purposes. The most commonly reported purposes for products containing alkoxylated alcohols include friction reducers, surfactants, corrosion inhibitors, emulsifier control agents, gelling agents, biocides, and activators. It is important to note that these reported purposes describe the function of the product containing the alkoxylated alcohol, and not necessarily the direct function of the alkoxylated alcohol itself.
Subclass: ethoxylated alcohols
Number of reported materials: 56
Ethoxylated alcohols are a subgroup of alkoxylated alcohols characterized by the addition of multiple ethylene oxide (Câ‚‚Hâ‚„O) units to an alcohol molecule. This ethoxylation process creates a polyether chain, increasing the hydrophilicity of the molecule. The degree of ethoxylation, or the number of ethylene oxide units added, can be varied to tailor the solubility, surfactant properties, and emulsifying behavior of the resulting compound. At higher degrees of ethoxylation, the structure resembles polyethylene glycol (PEG), though lower ethoxylation levels retain more hydrophobic character.
This modification typically enhances the water solubility and surface activity of the alcohol. Common ethoxylated alcohols used in hydraulic fracturing include ethoxylated C10-16 alcohols and ethoxylated C12-16 alcohols, which function as surfactants and emulsifiers in fracturing fluids. 2-Butoxyethanol, while structurally related, is an ethylene glycol ether rather than a true ethoxylated alcohol, though it is sometimes used for similar purposes in hydraulic fracturing.
Most common ethoxylated alcohols:
| Material | Name | Records and mass |
|---|---|---|
| 68551-12-2 | Alcohols, C12-16, ethoxylated | 44,100 records — 99,000,000 pounds |
111-76-2 | 2-Butoxyethanol | 35,000 records — 49,100,000 pounds |
| 68002-97-1 | Ethoxylated C10-16 alcohols | 21,800 records — 50,500,000 pounds |
| 78330-21-9 | Alcohols, C11-14-isoalcohols, C13-rich, ethoxylated | 21,400 records — 70,700,000 pounds |
| 68439-50-9 | Alcohols, C12-14, ethoxylated | 16,100 records — 25,300,000 pounds |
Subclass: propoxylated alcohols¶
Number of reported materials: 9
Propoxylated alcohols are a subgroup of alkoxylated alcohols formed by the addition of propylene oxide (C₃H₆O) units to an alcohol molecule. This process creates poly(propylene oxide) chains, which can resemble polypropylene glycol (PPG) at higher molecular weights. The degree of propoxylation can be controlled to adjust the properties of the resulting compound.
Compared to ethoxylation, propoxylation tends to increase hydrophobicity, though it still modifies the solubility and surface activity of the parent alcohol. The balance between hydrophilic (ethylene oxide) and hydrophobic (propylene oxide) segments in these molecules determines their function in hydraulic fracturing fluids.
Examples of propoxylated compounds used in hydraulic fracturing include propoxylated C10-16 alcohols, polymers of propylene oxide combined with ethylene oxide (e.g., poloxalene), and co-polymers incorporating polypropylene glycol segments. Dipropylene glycol monomethyl ether (DPGME), though an ether rather than an alcohol, is sometimes used in similar applications. These materials can act as surfactants, emulsifiers, or contribute to other functional roles within fracturing fluid formulations.
Most common propoxylated alcohols:
| Material | Name | Records and mass |
|---|---|---|
34590-94-8 | Dipropylene glycol monomethyl ether | 12,900 records — 15,700,000 pounds |
| 9003-11-6 | Poloxalene | 9,590 records — 23,200,000 pounds |
25322-69-4 | Polypropylene glycol | 1,580 records — 459,000 pounds |
| 37251-67-5 | Oxirane, 2-methyl-, polymer with oxirane, monodecyl ether | 614 records — 592,000 pounds |
68015-67-8 | Poly(oxy-1,2-ethanediyl), alpha-(2,3,4,5-tetramethylnonyl)-omega-hydroxy- | 335 records — 211,000 pounds |
Subclass: alkoxylated phenols¶
Number of reported materials: 9
Alkoxylated phenols are a distinct class of alkoxylated compounds in which the base molecule is a phenol rather than a simple alcohol. These compounds are synthesized by reacting a phenol with an alkylene oxide (such as ethylene oxide or propylene oxide), leading to the formation of polyether chains attached to the phenolic hydroxyl group. Due to the electron-donating effects of the aromatic ring, phenols are more reactive toward alkoxylation than simple alcohols, which can influence their surfactant properties.
This structural modification significantly alters the solubility and surface activity of the phenol, making alkoxylated phenols valuable surfactants and emulsifiers in hydraulic fracturing fluids. A notable example is nonylphenol ethoxylates (NPE) (CASRN: 9016-45-9 and 68412-54-5), which were widely used but have declined recently. Other examples include polyoxyethylene branched-C9-alkylphenols, which serve similar functions.
These materials are commonly employed as surfactants and emulsifiers in fracturing fluids, where their ability to reduce surface tension and stabilize emulsions plays a critical role.
Most common alkoxylated phenols:
| Material | Name | Records and mass |
|---|---|---|
| 127087-87-0 | Poly(oxy-1,2-ethanediyl),alpha-(4-nonylphenyl)-omega-hydroxy-,branched | 26,000 records — 27,400,000 pounds |
9016-45-9 | Nonylphenoxypolyethoxyethanol | 8,470 records — 10,500,000 pounds |
| 68412-54-4 | Polyoxyethylene branched-C9-alkylphenol | 4,540 records — 410,000 pounds |
26027-38-3 | 26-(4-Nonylphenoxy)-3,6,9,12,15,18,21,24-octaoxahexacosan-1-ol | 1,020 records — 167,000 pounds |
Subclass: unspecified/other¶
Number of reported materials: 12
The “unspecified/other” subgroup of alkoxylated alcohols includes materials that do not fit neatly into the primary categories of ethoxylated, propoxylated, or alkoxylated phenols. These compounds are often complex mixtures, branched structures, or polymers that incorporate both ethoxylation and propoxylation, creating molecules with polyethylene glycol (PEG) and polypropylene glycol (PPG) segments. The combination of these segments allows for precise tuning of hydrophilic-lipophilic balance (HLB), making them highly versatile in fracturing fluid applications.
Common examples include ethoxylated-propoxylated alcohols derived from C10-12, C12-15, and C9-11 iso-alcohols. These materials, like other alkoxylated alcohols, primarily function as surfactants and emulsifiers, with their mixed ethoxylation-propoxylation profile allowing for optimized performance in water- or oil-based fracturing fluids.
Another example is ethoxylated-propoxylated trimethylolpropane (TMP), a branched polyol with three hydroxyl groups that can undergo extensive alkoxylation. This structural complexity makes it difficult to classify under traditional alkoxylated alcohol categories, placing it within this “unspecified/other” group.
Most common unspecified/other:
| Material | Name | Records and mass |
|---|---|---|
| 120313-48-6 | Alcohols, C12-15-branched and linear, ethoxylated propoxylated | 5,450 records — 15,100,000 pounds |
| 154518-36-2 | Alcohols, C9-11-iso-, C10-rich, ethoxylated propoxylated | 2,580 records — 3,180,000 pounds |
| 68154-97-2 | Alcohols, C10-12, ethoxylated propoxylated | 2,440 records — 1,880,000 pounds |
| 52624-57-4 | Ethoxylated, propoxylated trimethylolpropane | 1,710 records — 264,000 pounds |
| 68551-13-3 | C12-15 ethoxylated propoxylated alcohols | 1,140 records — 3,330,000 pounds |
- All molecular structure images courtesy of the US EPA, except where noted. ↩︎