The new bio-based surfactant feedstock January 2022

By Rebecca Guenard

In This Section

January 2022

  • Conventional soybean oil is not common for making laundry surfactants since the long chain length of its fatty acids leads to molecules that lack the physical properties necessary for stain removal. Epoxides of conventional soybean oil can further lead to rapid side reactions causing undesirable by-products.
  • Epoxidized high-oleic soybean oil (HOSO), however, offers the flexible chemistry necessary to adjust functional groups, bio-based content, and hydrophilic-lipophilic balance.
  • Researchers claim they have developed 49 HOSO surfactant candidates, including cationic, anionic, nonionic, and amphoteric, with up to 100% biobased content that are stable over a range of pHs.
  • New HOSO surfactants are poised to launch in a range of business areas.

Scaling and commercializing sustainable surfactants has been an arduous challenge manufacturers attempted to surmount starting in the early 2000s. Researchers continue to pursue a solution since the ubiquity of surfactants for both home and industrial use implores sustainable sourcing. For example, analysts predict continued growth in the global cleaning products market alone will reach $58.3 billion by 2024 (https://tinyurl.com/6jb5hjvy). Low-toxicity, natural alternatives to petroleum-based surfactants would guarantee the sustainable use of these compounds in household cleaning, as well as agriculture, bioremediation, and personal care applications, for decades to come.

Pursuit of naturally sourced surfactants has taken many routes. One way to get environmentally friendly products is to take advantage of the surfactants present in the roots, seeds or leaves of plants. Although a small number of compounds, like lecithin and saponins, have achieved some level of commercial success, most remain too expensive to process at a high enough yield to commercialize for a large market. Biosurfactants, excreted from a microorganism, do not require as much chemical processing, but do undergo extensive purification to isolate the desired compound from a stew of biochemical products. Rhamnolipid biosurfactants have creeped into more household and personal care items, but so far cost of production has limited their wide-spread use.

Bio-based surfactants, made by replacing petroleum-sourced hydrophobic carbon chains with fatty acids from vegetable oils or animal fats, have proved to be the most economical way to produce a more sustainable ingredient. Coconut and palm kernel oils, containing up to 60% lauric acid (12:0), are currently the major feedstocks for the surfactant industry. Battelle Memorial Institute, a non-profit, technology development company in Columbus, Ohio, filed a patent last year introducing a new feedstock to compete against them.

“Since soybeans can be grown more sustainably than current feedstocks, we were interested in figuring out a way to make surfactants from C18 instead of C12,” says Dan Garbark, lead materials scientist at Battelle (http://www.battelle.org/). Instead of lauric acid, he says they focused on oleic acid as the building block for their natural surfactants.

The development groups of two different ingredient companies have also recently announced their efforts to take advantage of the more plentiful feedstock. Are soybeans likely to become a prominent bio-based feedstock?

Why soybean?

According to industry groups like the United States Soybean Export Council, soybean oil is one of the most economical and sustainable bio-based feedstocks. Almost 100% of US farmers participate in the Soy Sustainable Assurance Protocol (SSAP) following a set of guidelines to ensure responsible farming. The US Department of Agriculture conducts audits on participating farms as an independent third party. In addition, they are held to the standards of the European Feed Association. While adhering to current benchmarks for protecting environmental resources, SSAP members commit to continuously improve their sustainability performance.

The reputation of soybean oil and meal as a petroleum replacement has grown in the past decade. Chemical and materials manufacturers are achieving the high-performance requirements for applications like asphalt and tires from soybean feedstocks in markets where petroleum-based products have been a holdout. In particular, high-oleic soybeans gained the attention of researchers interested in the development and commercialization of sustainable versions of performance-demanding products since its fatty acids remain stable in extreme conditions.

High-oleic oils contain concentrations of between 60 and 90% oleic acid content, with a corresponding reduction in the amounts of linoleic and linolenic acids compared to conventional oils (Fig. 1). Varieties of high-oleic sunflower, safflower, and canola have been available for some time. By comparison, soybean is new to the high-oleic scene, but its unique chemistry makes it well-suited for surfactant development compared to other high-oleic crops.

FIG 1. Comparison of fatty acid profile for commodity versus high-oleic soybean oil. Source: soynewuses.org/benefits/
FIG 1. Comparison of fatty acid profile for commodity versus high-oleic soybean oil. Source: soynewuses.org/benefits/

Garbark says his group used an epoxidation ring-opening reaction to produce surfactants with different hydrophilic-lipophilic balances. This versatile industrial reaction involves forming ether groups by adding alcohols onto epoxides at the site of unsaturation. The chain length and functionality of the hydrophilic portion of the resulting surface-active molecule can be modified for specific performance needs.

The single unsaturated bond in oleic acid simplifies the ring-opening epoxide reaction. Multiple unsaturated bonds, as in linoleic and linolenic acid, can lead to cross-linking during the ring-opening reactions. These reactions decrease water miscibility and cause sporadic gelation of the surfactant when attempting to formulate for laundry applications. By contrast, functional groups can be added to the epoxidized oleic acid without interference from nearby epoxides leading to undesirable properties.

Finally, surfactants made from high-oleic soybean oil cost less to produce at commercial scale than other plant-based materials since epoxidizes can be formed at low temperatures using enzymes. Also, since there are fewer reaction products, minimal purification is needed to isolate the desired surfactant.

Formulating for detergents

Currently, only about one percent of conventional soybean oil is used for surfactant production. Garbark says a highly reactive hydroxyl can be used effectively to functionalize the fatty acids in epoxidized conventional soybean oil for surfactant synthesis. However, new high-oleic varieties of soybeans, predicted to increase production to 600 billion pounds in the next two years, will bring a welcome expansion to current bio-based options.

According to Garbark, the detergents market in the United States will require an estimated 14.3 billion pounds of surfactants in 2022. Currently, only a third of the surfactants in cleaning applications are made from bio-based sources. Therefore, his organization chose to first target this growing market when developing high-oleic soybean surfactants. He says his research group synthesized molecules with a range of functionalities using plant-sourced chemicals, and then evaluated their effectiveness on stain removal.

Of the 49 surfactants Battelle developed, they created more HOSO equivalents for nonionic surfactant than for anionic surfactants. However, they synthesized HOSO replacements for cationic, anionic, nonionic, and amphoteric surfactants, typically using 60% soybean oil by weight; although, they could go as high as 100% bio-based.

In developing their product range, Garbark says they started by making ethoxylates and propoxylates of hydroxy-acids, such as citric, lactic, and malic (Fig. 2). The alkoxylates of those acids create a more reactive hydroxyl group which could lead to future production benefits. In addition to these initial structures, they created dozens of other soy-based surfactants with functionalities corresponding to popular surfactants currently on the market. Then the researchers tested those surfactants.

FIG 2. An example of a structure created by reacting a lactate with epoxidized oleic acid. After saponification the molecule becomes a bio-based surfactant. Source: Battelle
FIG 2. An example of a structure created by reacting a lactate with epoxidized oleic acid. After saponification the molecule becomes a bio-based surfactant. Source: Battelle

Performance and price

In early testing, the soy-based structure formed by a reaction with citric acid resulted in a surfactant with improved stain removal when replacing the nonionic surfactant in a standard laundry formulation. The standard formulations contained sodium dodecylbenzene sulfonate, sodium lauryl sulfate, cocamidopropylbetaine, and other surfactants that are common in name brands. Successful stain removal compared to the standards encouraged the researchers to test against off-the-shelf detergents (Table 1).

TABLE 1. Comparing stain lifting ability of surfactants synthesized from high-oleic (soy mix 1, candidate 43) and conventional (candidate 48) soybean oil with name brand products currently on the market. Source:Battelle
TABLE 1. Comparing stain lifting ability of surfactants synthesized from high-oleic (soy mix 1, candidate 43) and conventional (candidate 48) soybean oil with name brand products currently on the market. Source:Battelle

“A mix of all soy surfactants, with a small amount of sodium xylene sulfonate to maintain solubility, surprisingly resulted in equivalent cleaning to off-the-shelf detergents,” said Garbark.

The formulation, composed of nearly 90% bio-based content, achieved soil removal for common stains even when scaled up to 30 gallons. In addition, other newly developed surfactants showed potential for applications in oil recovery and hard surface cleaning. However, he says his group has not yet considered personal care surfactants.

Garbark said his group evaluated the costs of producing the surfactant candidates that performed stain removal best. Taking into consideration both capital expenditures and operating expenses, they found that several of their soy-based products were cost equivalent to surfactants currently on the market.

HOSO in personal care

Rob Comber, vice president of research and development at Colonial Chemical, in South Pittsburg, Tennessee (https://colonialchem.com/), also says that for certain products high-oleic soybean surfactants can bring down cost. For several years, his specialty chemical company has been evaluating where the longer fatty acid chains in soybean oil could be advantageous as personal care ingredients.

“The shorter chain lengths you get from palm and coconut oils are traditionally more popular in a surfactant company because they provide more detergency and foaming,” Comber says. “But soy-based products provide different benefits, like thickening and shine, that are important in the personal care space.”

Comber says, for customers interested in developing sustainable, palm-free surfactants, his group at Colonial has expanded their soy-based product line to include HOSO surfactants. Among other compounds, they have a hair conditioning ingredient proven to lower combing forces and a deodorizer that enhances odor removal. He says his group also developed a high-oleic soybean oil equivalent to replace olive oil in product formulations. The HOSO surfactant significantly reduces the price to manufacture personal care products that contain olive oil.

“So far, the personal care side of the business has been more involved with finding uses for what we have developed,” Comber says. “With time, I think other business areas will find applications for some of these candidates.” He says the utility of soy should not be considered for personal care alone, it can be used for a broad range of industries.

Enhancing biosurfactant processing

In addition to the synthesis of new bio-based surfactants from HOSO, biotech manufacturer Jeneil, based in Saukville, Wisconsin, is evaluating HOSO’s potential as a substrate for rhamnolipid production (https://www.jeneilbiotech.com/). Researchers compared the fermentation of different oils to see how they affected rhamnolipid yields. They found that more of the biosurfactant formed in the presence of high-oleic oils than those containing a greater proportion of linoleic acid.

Tom Overbeck, research scientist at Jeneil, says the company hopes to optimize its established soybean oil fermentation processes using high-oleic varieties. If the switch successfully increases rhamnolipid yields, the cost of producing the biosurfactants would decrease, lowering a barrier for bringing more of these surfactants to the marketplace.

The GMO hurdle

While high-oleic soybean oil has great potential to revolutionize the plant-based surfactants industry, opposition to genetically modified (GM) organisms could limit its potential. In 2018, the Court of Justice of the European Union in Luxembourg ruled that gene-edited crops mimicked conventional genetically modified organisms enough that they should be regulated according to the same strict standards. While the law is meant to impose restrictions for developing GM crops for food, business developers generally avoid any GM application to sidestep regulatory procedures and negative consumer perceptions.

The most efficient way to produce high-oleic soybean oil is through genetic mutation. By altering the genes that produce the enzyme responsible for removing hydrogen atoms and creating double bonds (known as fatty acid desaturase), scientists restrict how much linoleic and linolenic acids a soybean plant produces. Food-grade high-oleic soybean oil is gaining popularity in the United States as the product proves its value through longer frying times in restaurants and greater stability of baked goods. As industrial uses also gain success, the acreage of gene-edited soybean in the United States is likely to increase (https://tinyurl.com/eawptxb7).

Growers will have to wait and see if EU companies adopt high-oleic soybean oil for industrial use. So far, they remain hesitant. Garbark noted that Battelle has developed a handful of surfactants using commodity soybean oil for customers interested in ingredients that have not come from gene-edited plants. Comber says his company has also developed products from conventional soy. Regardless of the soybean oil’s source, these plant-based surfactants have proven their potential for manufacturing new products.

“You would not normally think of getting a detergent or surfactant from a molecule with a C18 chain length,” Comber says. “Battelle found a clever way to get into laundry by doing that. In the next ten years, we are going to see soy-based products like this in a lot more business areas.”

To find out more about HOSO surfactants, view two recent presentations outlining their development. During the 2021 AOCS Annual Meeting, Dwight Rust, commercialization manager for the consulting group Omni Tech International, introduced the new technology. A few months later, the consulting group hosted a webinar in which Dan Garbark described the bio-based chemistry in detail and Rob Comber discussed some of the soy-based surfactants Colonial Chemical has developed for personal care ingredients. Both innovations rely on high-oleic soybean oil as a platform for developing natural surfactants (https://tinyurl.com/3y7b8x4j).

This research was partially funded by the United Soybean Board in support of industrial uses for HOSO.
This research was partially funded by the United Soybean Board in support of industrial uses for HOSO.

About the Author

Rebecca Guenard is the associate editor of Inform at AOCS. She can be contacted at rebecca.guenard@aocs.org

Information

Production of green surfactants: Market prospects, Farias, C. B. B., et al., electronic Journal of Biotechnology, 51, 28-39, 2021.

Laundry builders and surfactants derived from bio-based hydroxyacids and epoxides, Garbark, D.B., Cafmeyer, J.T., and Lalgudi, R.S., Patent no. US 2019/0177655 A1, June 13, 2019.

Enzymatic epoxidation of high oleic soybean oil, Zhang, X., Burchell, J., and Mosier, N. S., ASC Sustainable Chem Eng, 6, 7, 8578-8583, 2018.

Direct stacking of sequence-specific nuclease-induced mutations to produce high oleic and low linolenic soybean oil, Demorest, Z., L., et al., BMC Plant Biol, 16, 1, 225, 2016.

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