Green Surfactants (Biosurfactants): A Petroleum-Free Substitute for Sustainability-Comparison, Applications, Market, and Future Prospects

Abstract

Surfactants are a group of amphiphilic molecules (i.e., having both hydrophobic and hydrophilic domains) that are a vital part of nearly every contemporary industrial process such as in agriculture, medicine, personal care, food, and petroleum. In general surfactants can be derived from (i) petroleum-based sources or (ii) microbial/plant origins. Petroleum-based surfactants are obvious results from petroleum products, which lead to petroleum pollution and thus pose severe problems to the environment leading to various ecological damages. Thus, newer techniques have been suggested for deriving surfactant molecules and maintaining environmental sustainability. Biosurfactants are surfactants of microbial or plant origins and offer much added advantages such as high biodegradability, lesser toxicity, ease of raw material availability, and easy applicability. Thus, they are also termed "green surfactants". In this regard, this review focused on the advantages of biosurfactants over the synthetic surfactants produced from petroleum-based products along with their potential applications in different industries. We also provided their market aspects and future directions that can be considered with selections of biosurfactants. This would open up new avenues for surfactant research by overcoming the existing bottlenecks in this field.

Figure 1

Possible systematic modifications of sugar-based surfactants centered on octyl-β-d-glucoside. Adapted with permission from ref (70). Copyright 2019 Elsevier.

Scheme 1. Synthesis of Sorbitan Esters by Intramolecular Dehydration of Sorbitol in the Presence of Acid

RCOOH: fatty acids. Adapted with permission from ref (68). Copyright 1999 John Wiley and Sons.

Scheme 2. Synthesis of Sucrose Esters by Base Catalyzed Transesterification with Fatty Acid Methyl Esters (R′COOMe)

Adapted with permission from ref (68). Copyright 1999 John Wiley and Sons.

Scheme 3. Reaction of Glucose and Fatty Alcohol to Form Alkyl Polyglycosides (APGs) Carrying Units of Glucose

Adapted with permission from ref (68). Copyright 1999 John Wiley and Sons.

Scheme 4. Formation of Fatty Acid N-Methylglucamide with Two-Step Process

Adapted with permission from ref (68). Copyright 1999 John Wiley and Sons.

Figure 2

Types of microbial surfactants: (a) mannosylerythritol lipid; (b) surfactin; (c) trehalose lipid; (d) sophorolipid; (e) rhamnolipid.

Figure 3

Types of amino acid based surfactant: (I) linear or single chain; (II) dimeric or gemini; (III) glycerolipid-like/glycolipid-like.

Figure 4

Flowchart representing formation of petro-based surfactants from nonrenewable sources.

Scheme 5. Reaction Forming Alkylbenzene Sulfonic Acid from Alkylbenzene

Scheme 6. Reaction Forming α-Olefin Sulfonates

Scheme 7. Reaction Forming Alkane Sulfonates

Scheme 8. Reaction Forming Monoester Sulfosuccinate

Figure 5

Classification of biosurfactants based on molecular weight.

Figure 6

Manufacturing process for rhamnolipids.

Figure 7

Manufacturing process for sophorolipids.

Figure 8

Manufacturing process for surfactin.

Scheme 9. Different Routes to Form Fatty Alcohol Sulfates

Scheme 10. Reaction to Form Fatty Acid Methylesters

Scheme 11. Reaction to Form Sucroesters

Figure 9

General properties of biosurfactants.

Figure 10

Methods used to test biosurfactant efficiencies.

Figure 11

Comparison between synthetic surfactants and biosurfactants.