Page 434 - Fundamentals of Enhanced Oil and Gas Recovery

422 Afshin Tatar

Table 10.2 (Continued)
Surfactant type Producing Microorganisms References
Biodispersan Acinetobacter calcoaceticus [464,514,515]
Liposan Candida lipolytica [516 518]
Carbohydrate lipid protein Pseudomonas fluorescens, Yarrowia lipolytica, [441,519,520]
Pseudomonas nautica
Mannan lipid protein Candida tropicalis [521 524]
Particulate surfactant
Vesicles Acinetobacter calcoaceticus [441,468,525]
Cells Various bacteria [441,510]
Source: Data are gathered from different sources [441,464,468,470 525].

3. Fatty acids, neutral lipids and phospholipids;
4. Polymeric surfactants; and
5. Particulate surfactant.
Several different microorganisms produce different types of biosurfactants, a list of
which is presented in Table 10.2 [441,464,468,470 525].
Regarding the molecular weight, surfactants can be categorized as the low and
high molecular weight categories [19,524]. The former, are generally glycolipids or
lipopeptides, while the latter include amphipathic polysaccharides, proteins, lipopoly-
saccharides, lipoproteins or complex mixtures of these biopolymers. The main func-
tions of low and high molecular weight biosurfactant in MEOR applications are
lowering of surface and IFTs and stabilizing oil-in-water emulsions, respectively,
therefore called emulsifiers [404,457,524,535 537]. Many microorganisms including
yeasts, bacteria, and some filamentous fungi are capable of producing biosurfactants
with different surface activities and molecular structures [538].
Van Hamme et al. [19] listed the major biosurfactants produced by microorganisms
classified as low and high molecular weight microorganisms.
Youssef et al. [6] mentioned the most common low molecular weight biosurfac-
tants used in MEOR as [427,457,541 546]
1. Lipopeptides produced by Bacillus and some Pseudomonas spp.;
2. Glycolipids (rhamnolipids) produced by Pseudomonas sp.; and
3. Trehalose lipids produced by Rhodococcus sp.
And high molecular weight ones as the bioemulsifiers as [182,524,547 549]:
1. Emulsan produced by genus Acinetobacter;
2. Heteropolysaccharides produced by Halomonas eurihalina and Pseudomonas tralucida;
3. Protein complexes produced by Methanobacterium thermoautotrophicus;
4. Protein polysaccharide lipid complex produced by Bacillus stearothermophilus;
5. Carbohydrate protein complex as liposan produced by Candida lipolytica; and
6. Mannan protein produce by Saccharomyces cerevisiae.