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.
Alcohols and hydroxyl-containing compounds constitute a significant category of chemicals reported in hydraulic fracturing fluids. (See the group Alkoxylated Alcohols for other alcohols.) These substances are characterized by the presence of one or more hydroxyl (-OH) groups and serve a range of functions in fracking formulations. Reported data from FracFocus between 2014 and 2024 includes 530,000 records of alcohol-related compounds, representing a total mass of 1,620,000,000 pounds.1
This group includes multiple subcategories based on chemical structure and function, such as:
- Primary and secondary alcohols (24 reported compounds): Includes methanol, ethanol, isopropanol, and butanol derivatives, primarily used as solvents, friction reducers, or biocides.
- Polyols (16 reported compounds): Includes glycols (e.g., ethylene glycol, propylene glycol) and sugar alcohols, often used as scale inhibitors, hydrate inhibitors, or stabilizers.
- Ethers (18 reported compounds, including hydroxyl-functional ethers): Includes glycol ethers and similar compounds that act as surfactants or solvent modifiers.
- Phenols (13 reported compounds, including alkylphenols): Includes phenolic compounds, some of which function as antioxidants, stabilizers, or surfactant precursors.
- Unspecified/other alcohols (9 reported compounds): A broad category encompassing alcohol derivatives with varied functions.
Alcohols are incorporated into fracturing products for diverse applications, including corrosion inhibition, surfactant activity, emulsification control, biocidal action, scale inhibition, crosslinking, and iron control. Their specific function depends on molecular structure, concentration, and compatibility with other additives in the fluid formulation.
Subclass: primary and secondary alcohols¶
Number of reported materials: 24
Primary and secondary alcohols form a key subgroup within the alcohol classification of hydraulic fracturing chemicals. These compounds are characterized by a hydroxyl (-OH) functional group attached to a carbon atom, with primary alcohols having the hydroxyl carbon bonded to one other carbon (or none, as in methanol) and secondary alcohols bonded to two other carbons. These alcohols serve various roles in fracturing fluids, including as solvents, surfactants, defoamers, and corrosion inhibitors.
- Methanol (67-56-1) and ethanol (64-17-5) are widely used as solvents and co-solvents, facilitating the dissolution and stabilization of other chemical additives.
- Isopropanol (67-63-0) functions not only as a solvent but also as a surfactant or surfactant component, improving fluid performance by reducing interfacial tension.
- 2-Ethyl-1-hexanol (104-76-7), a branched primary alcohol, is commonly utilized as a defoamer or as a precursor for surfactant synthesis.
- Propargyl alcohol (107-19-7), while structurally a primary alcohol, contains a highly reactive alkyne (-C≡C-) group, making it useful as a corrosion inhibitor by forming protective films on metal surfaces and preventing oxidative degradation.
Most common primary and secondary alcohols:
| Material | Name | Records and mass |
|---|---|---|
67-56-1 | Methanol | 171,000 records — 832,000,000 pounds |
67-63-0 | Isopropanol | 84,700 records — 191,000,000 pounds |
64-17-5 | Ethanol | 59,800 records — 164,000,000 pounds |
107-19-7 | Propargyl alcohol | 42,500 records — 4,330,000 pounds |
104-76-7 | 2-Ethyl-1-hexanol | 7,490 records — 3,630,000 pounds |
Subclass: polyols¶
Number of reported materials: 16
Polyols, defined by the presence of multiple hydroxyl (-OH) groups, form an important subgroup within the alcohol classification of hydraulic fracturing chemicals. These compounds contribute diverse functionalities to fracturing fluids, including solvent properties, viscosity control, emulsification, and stabilization.
- Ethylene glycol (107-21-1) and 1,2-propylene glycol (57-55-6) serve as solvents, antifreeze agents, and hydration control additives, helping to regulate fluid performance in varying temperature conditions.
- Glycerol (56-81-5), a triol, functions as a humectant, viscosity modifier, and stabilizer in some fluid formulations. In certain cases, it may also contribute to crosslinking systems that enhance fluid gelation.
- 2-Mercaptoethanol (60-24-2), while technically a thiol rather than a true polyol, is sometimes included in this category due to its multiple functionalities. It is primarily used as a reducing agent or chain transfer agent in polymerization processes.
- Poly(propyleneoxy/ethyleneoxy)glycerol (9082-00-2) represents a class of polymeric polyols that can act as surfactants, emulsifiers, or rheology modifiers, depending on their molecular weight and ethylene-to-propylene ratio.
These polyols enhance the stability, flow behavior, and overall performance of fracturing fluids under diverse operational conditions.
Most common polyols:
| Material | Name | Records and mass |
|---|---|---|
107-21-1 | Ethylene glycol | 77,900 records — 296,000,000 pounds |
56-81-5 | Glycerol | 19,100 records — 47,600,000 pounds |
57-55-6 | 1,2-Propylene glycol | 8,460 records — 42,200,000 pounds |
60-24-2 | 2-Mercaptoethanol | 5,850 records — 4,560,000 pounds |
| 9082-00-2 | Poly(propyleneoxy / ethyleneoxy)glycerol | 871 records — 524 pounds |
Subclass: Ethers¶
Number of reported materials: 18
Ethers, characterized by an oxygen atom bonded to two alkyl or aryl groups, represent a notable subgroup within the broader classification of chemicals used in hydraulic fracturing. While they lack the hydroxyl (-OH) group that defines alcohols, some ethers are functionally related to alcohols and may originate from alcohol-based precursors. Their roles in fracturing fluids primarily include solvent action, surfactant properties, and chemical stabilization.
- Ethylene oxide (75-21-8) and propylene oxide (75-56-9) are highly reactive cyclic ethers used in the production of surfactants, polymers, and other functional additives through alkoxylation reactions.
- 1,4-Dioxane (123-91-1), a cyclic diether, is used as a solvent and stabilizer in certain formulations.
- Alkylene glycol ethers, such as 2-(2-butoxyethoxy)ethanol (112-34-5), function as co-solvents, surfactants, or emulsifiers, improving the solubility of other additives within fracturing fluids.
- Prop-2-yn-1-ol–2-methyloxirane (38172-91-7) is a specialized ether that may serve as a stabilizer or as a reactive intermediate in chemical modifications.
These ethers enhance the performance and stability of hydraulic fracturing fluids, facilitating the effective delivery of other chemical components.
Most common Ethers:
| Material | Name | Records and mass |
|---|---|---|
75-21-8 | Ethylene oxide | 8,620 records — 75,700 pounds |
123-91-1 | 1,4-Dioxane | 3,290 records — 33,500 pounds |
112-34-5 | 2-(2-Butoxyethoxy)ethanol | 1,950 records — 887,000 pounds |
75-56-9 | (+/-)-1,2-Propylene oxide | 1,780 records — 3,790 pounds |
38172-91-7 | Prop-2-yn-1-ol–2-methyloxirane (1/1) | 1,270 records — 1,940,000 pounds |
Subclass: phenols¶
Number of reported materials: 13
Phenols, a distinct class of aromatic compounds characterized by a hydroxyl (-OH) group directly attached to a benzene ring, play various roles in hydraulic fracturing formulations. While structurally different from alcohols, they are sometimes grouped together due to their hydroxyl functionality. Phenols serve as biocides, surfactants, antioxidants, and stabilizers within fracturing fluid compositions.
- Phenol (108-95-2) is used as a biocide, disinfectant, and chemical intermediate in the production of resins and other industrial materials.
- Nonylphenol (25154-52-3 and branched isomers like 104-40-5) and its ethoxylated derivatives function as surfactants, emulsifiers, and wetting agents, although their use is declining due to environmental persistence and regulatory restrictions.
- Butylated hydroxytoluene (BHT, 128-37-0) is a hindered phenol that acts as an antioxidant, preventing oxidation and degradation of other chemical additives in the fracturing fluid.
- (Z)-Nerol (106-25-2), an acyclic monoterpene alcohol, is sometimes included in this category due to its stabilizing properties and potential use as a biocidal agent, though it is not a true phenol.
Phenols contribute to the stability, effectiveness, and longevity of hydraulic fracturing fluids by enhancing oxidative resistance, improving emulsification, and reducing microbial contamination.
Most common phenols
| Material | Name | Records and mass |
|---|---|---|
104-40-5 | 4-Nonylphenol, branched | 403 records — 638,000 pounds |
108-95-2 | Phenol | 310 records — 156,000 pounds |
25154-52-3 | n-Nonylphenol | 145 records — 1,960 pounds |
106-25-2 | (Z)-Nerol | 46 records — 51,800 pounds |
128-37-0 | Butylated hydroxytoluene | 36 records — 2,490 pounds |
Subclass: unspecified/other¶
Number of reported materials: 9
The “unspecified/other” alcohols subgroup in hydraulic fracturing encompasses a range of alcohol-related compounds that don’t neatly fit into other categories. This often includes mixtures of alcohols with varying carbon chain lengths, such as Alcohols, C7-9-iso-, C8-rich (68526-83-0) and Alcohols, C6-12 (68603-15-6), which may be used as solvents or co-solvents. Also included are complex mixtures like Alcohols, C2-33, manuf. of, by-products from, overheads (876065-86-0), suggesting a mixture derived from industrial processes. 2-Hydroxyethyl disulfide (1892-29-1), while not strictly an alcohol but containing a hydroxyethyl group, may be present as a reaction byproduct or serve a specialized function. Solketal (100-79-8), a cyclic ketal derived from glycerol and acetone, may function as a solvent or additive. The precise composition and function of these “other” alcohols can vary significantly.
Most common unspecified/other:
| Material | Name | Records and mass |
|---|---|---|
| 68526-83-0 | Alcohols, C7-9-iso-, C8-rich | 1,580 records — 703,000 pounds |
| 876065-86-0 | Alcohols, C2-33, manuf. of, by-products from, overheads | 1,550 records — 7,060,000 pounds |
1892-29-1 | 2-Hydroxyethyl disulfide | 620 records — 25,400 pounds |
| 68603-15-6 | Alcohols, C6-12 | 535 records — 47,200 pounds |
100-79-8 | Solketal | 269 records — 682,000 pounds |
- All molecular structure images courtesy of the US EPA, except where noted. ↩︎