Chinese Journal of Catalysis ›› 2024, Vol. 59: 97-117.DOI: 10.1016/S1872-2067(23)64626-1
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Vinoth Kumar Ponnumsamya,b, Hussein E. Al-Hazmic, Sutha Shobanad, Jeyaprakash Dharmarajae, Dipak Ashok Jadhavf, Rajesh Banu Jg, Grzegorz Piechotah, Bartłomiej Iglińskii, Vinod Kumarj, Amit Bhatnagark, Kyu-Jung Chaef,l, Gopalakrishnan Kumarm,n,*(
)
Received:2024-01-05
Accepted:2024-01-22
Online:2024-04-18
Published:2024-04-15
Contact:
*E-mail: About author:Dr. Gopalakrishnan Kumar serves as Associate Professor in Institute of Chemistry, Bioscience and Environmental Engineering, Faculty of Science and Technology, University of Stavanger, Stavanger, Norway. Additionally, he plays the role as “specially appointed Associate professor” concentrating on research in School of Civil and Environmental Engineering, Yonsei University, Republic of Korea. He has received his Ph.D. from Feng Chia University, China. He was the recipient of prestigious JSPS post-doctoral fellowships (JSPS, Japan) and Emilio Rosenblueth Fellowship (Mexico) for his post-doctoral studies. He is also visiting faculty in many universities around Europe (Hungary, Czech, Poland), India, Vietnam, China and Turkey. He has extensively published more than 375 SCI papers in highly prestigious Journals (including 4 cover image articles, 13 high cited/hot articles and 1 key scientific article), with total citations of > 26000 & h-index of 86. His major research interests include biofuel/biochemical production from lignocellulose/food-waste/wastewater and algal biomass via biorefinery and valorization schemes and Microbial fuel/electrolysis cell (MFC& MEC) technologies. Additionally, he is working on the application of green synthesized activated carbon and Nano particles for various environmental remediation applications.
Vinoth Kumar Ponnumsamy, Hussein E. Al-Hazmi, Sutha Shobana, Jeyaprakash Dharmaraja, Dipak Ashok Jadhav, Rajesh Banu J, Grzegorz Piechota, Bartłomiej Igliński, Vinod Kumar, Amit Bhatnagar, Kyu-Jung Chae, Gopalakrishnan Kumar. A review on homogeneous and heterogeneous catalytic microalgal lipid extraction and transesterification for biofuel production[J]. Chinese Journal of Catalysis, 2024, 59: 97-117.
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| Extraction technique | Solvent | Microalgal specie | Efficiency/yield (wt%) | Time (min) | Temp. (°C) | Pressure (MPa) |
|---|---|---|---|---|---|---|
| Bead beater + solvent | chloroform/methanol | botryococcus braunii | 28.60 | 50.00 | — | — |
| botryococcus sp. | 28.10 | — | ||||
| CO2 | chlorella vulgaris | 13.30 a | — | |||
| Bligh and Dyer's method | — | chlorella vulgaris | 10.60 a | — | ||
| Cold pressing | ethanol | scenedesmus obliquus | 62.04±72.42 | — | 73-75 | |
| Ionic liquids | [Bmim] [CF3SO3]d or [Emim] [MeSO4]e | chlorella vulgaris | 12.50 a or 11.90 a | — | — | |
| Organic solvent | 1-butanol | chaetoceros muelleri | 94.00 | 60.00 | 70 | |
| isopropanol/hexane | chlorococcum sp. | 06.80 | 450.0 | 25 | ||
| hexane | 01.50 | — | — | |||
| ethanol, 5 mL g-1 dried microalgae | phaeodactylum tricornutum | 29.00 | 1440 | |||
| Soxhlet | DBU b/Octanol | botryococcus braunii | 81.00 | 240.0 | 60 | |
| hexane | chlorococcum sp. | 03.20 | 330.0 | — | ||
| chlorella vulgaris | 01.77 | 140.0 | 70 | |||
| CO2, 2.0 mL min-1 | isochrysis galbana | 04.00-10.00 | — | 40 | 69.0 | |
| CO2/ethanol | 05.00-11.00 a | 50 | 6.89 | |||
| hexane | scenedesmus obliquus | 40.71±74.46 | — | 63-65 | — | |
| Supercritical fluid | CO2, 10 g min-1 | crypthecodinium cohnii | 09.00 | 180.0 | 50 | 30.0 |
| CO2 | chlorococcum sp. | 05.80 | 80.00 | 60 | 10.0-50.0 | |
| nannochloropsis sp. | 25.00 | — | 40 | 55.0 | ||
| ethanol | 90.21 | — | — | — | ||
| CO2 | spirulina maxima | 03.10 | — | 35 | 60.0 | |
| spirulina platensis | 08.60 | 60.00 | 40 | 40.0 | ||
| 90.00 a | 15.00 | 55 | 70.0 | |||
| DCM c/methanol (9:1) | tetraselmischui | 15.00 | — | 99 | 10.3 |
Table 1 Extraction methods for microalgal lipids (Adapted from Refs.[1,47]).
| Extraction technique | Solvent | Microalgal specie | Efficiency/yield (wt%) | Time (min) | Temp. (°C) | Pressure (MPa) |
|---|---|---|---|---|---|---|
| Bead beater + solvent | chloroform/methanol | botryococcus braunii | 28.60 | 50.00 | — | — |
| botryococcus sp. | 28.10 | — | ||||
| CO2 | chlorella vulgaris | 13.30 a | — | |||
| Bligh and Dyer's method | — | chlorella vulgaris | 10.60 a | — | ||
| Cold pressing | ethanol | scenedesmus obliquus | 62.04±72.42 | — | 73-75 | |
| Ionic liquids | [Bmim] [CF3SO3]d or [Emim] [MeSO4]e | chlorella vulgaris | 12.50 a or 11.90 a | — | — | |
| Organic solvent | 1-butanol | chaetoceros muelleri | 94.00 | 60.00 | 70 | |
| isopropanol/hexane | chlorococcum sp. | 06.80 | 450.0 | 25 | ||
| hexane | 01.50 | — | — | |||
| ethanol, 5 mL g-1 dried microalgae | phaeodactylum tricornutum | 29.00 | 1440 | |||
| Soxhlet | DBU b/Octanol | botryococcus braunii | 81.00 | 240.0 | 60 | |
| hexane | chlorococcum sp. | 03.20 | 330.0 | — | ||
| chlorella vulgaris | 01.77 | 140.0 | 70 | |||
| CO2, 2.0 mL min-1 | isochrysis galbana | 04.00-10.00 | — | 40 | 69.0 | |
| CO2/ethanol | 05.00-11.00 a | 50 | 6.89 | |||
| hexane | scenedesmus obliquus | 40.71±74.46 | — | 63-65 | — | |
| Supercritical fluid | CO2, 10 g min-1 | crypthecodinium cohnii | 09.00 | 180.0 | 50 | 30.0 |
| CO2 | chlorococcum sp. | 05.80 | 80.00 | 60 | 10.0-50.0 | |
| nannochloropsis sp. | 25.00 | — | 40 | 55.0 | ||
| ethanol | 90.21 | — | — | — | ||
| CO2 | spirulina maxima | 03.10 | — | 35 | 60.0 | |
| spirulina platensis | 08.60 | 60.00 | 40 | 40.0 | ||
| 90.00 a | 15.00 | 55 | 70.0 | |||
| DCM c/methanol (9:1) | tetraselmischui | 15.00 | — | 99 | 10.3 |
Fig. 1. Dry and wet route involved in microalgal lipid extraction and energy production process.
Scheme 1. Dissolution of cellular components in ionic liquids (ILs).
| Method | Efficiency rating | Cost concerned | Energy necessity | Remarks |
|---|---|---|---|---|
| Bead beating | moderate | cost-effective | energy intensive | difficult to scale up |
| Electroporation | very high | cost-intensive; comparatively cost-effective operation | less energy | appears promising but comprehensive pilot-scale studies have to be conducted |
| Expeller press | low-moderate | high | energy intensive | heat generation and possible damage of the compounds |
| Isotonic extraction | moderate-high | — | — | less hazardous |
| Microwave | very high | — | — | easy to scale up |
| organic solvent extraction | — | — | — | intensive fire, health and environmental hazards; regulatory issues |
| Osmotic shock method | moderate-high | very high | less energy | appears promising but comprehensive pilot-scale studies have to be conducted |
| Pressurized solvent extraction | high | high because of cumulative costs incurred by use of solvent as well as use of pressurized nitrogen | energy intensive | environmental hazards; regulatory issues |
| Sonication method | — | high | — | poor product quality due to the damage during the process |
| Supercritical CO2 | moderate | — | — | environmental and safety issues |
Table 2 Comparison of the cost and energy efficiency of different lipid extraction methods (adapted from modified Ref. [61]).
| Method | Efficiency rating | Cost concerned | Energy necessity | Remarks |
|---|---|---|---|---|
| Bead beating | moderate | cost-effective | energy intensive | difficult to scale up |
| Electroporation | very high | cost-intensive; comparatively cost-effective operation | less energy | appears promising but comprehensive pilot-scale studies have to be conducted |
| Expeller press | low-moderate | high | energy intensive | heat generation and possible damage of the compounds |
| Isotonic extraction | moderate-high | — | — | less hazardous |
| Microwave | very high | — | — | easy to scale up |
| organic solvent extraction | — | — | — | intensive fire, health and environmental hazards; regulatory issues |
| Osmotic shock method | moderate-high | very high | less energy | appears promising but comprehensive pilot-scale studies have to be conducted |
| Pressurized solvent extraction | high | high because of cumulative costs incurred by use of solvent as well as use of pressurized nitrogen | energy intensive | environmental hazards; regulatory issues |
| Sonication method | — | high | — | poor product quality due to the damage during the process |
| Supercritical CO2 | moderate | — | — | environmental and safety issues |
| Microalgal species | Stress | |
|---|---|---|
| Physical stress: irradiation | ||
| Chaetoceros muelleri | increase in monounsaturated FAs with UV-A radiation | |
| Chaetoceros simplex | increase in saturated fatty acid with high UV-B irradiation | |
| Nannochloropsis sp. | increase in the total lipid content, about > 31.3% with 100 μmol L-1 m-2 s-1/18 h light intensity: 6 h, dark cycle | |
| Nannochloropsis sp. | increase in saturated FAs:PUFAs ratio via UV-A irradiation | |
| Neochloris oleoabundans | about 19%-25% increase in the TAG content with 50-200 μmol L-1 m-2 s-1 of light intensity | |
| Neochloris oleoabundans | increase in the biomass concentration from 1.2-1.7 g L-1 with increase in light intensity from 50-200 μmol L-1 m-2 s-1 | |
| Pavlova lutheri | increase in total lipid content with high light intensities stress | |
| Pavlova lutheri | about 23%-78% increase in the TAG content with 9-19 W m-2 increase in light intensity | |
| Scenedesmus sp. | lipid and TAG content increased from 26%-41% and 16%-32%, respectively, with increase in light intensity from 50-250 μmol L-1 m-2 s-1 | |
| Selenastrum capricornutum | increase in linoleate FAs (18:02) with dark treatment stress; increase in biomass concentration 2.5-3.6 g L-1 with 50-250 μmol L-1 m-2 s-1 increase in light intensity | |
| Tetraselmis sp. | increase in saturated and monounsaturated FAs and decrease in PUFAs with UV-B irradiation | |
| Thalassiosira pseudonana | increase in polar lipids (79%-89% of total lipid) with 100 μmol L-1 m-2 s-1/12:12 h, 100 μmol L-1 m-2 s-1/24 h and 50 mol L-1 m-2 s-1/24 h light: dark, harvested at the logarithmic phase | |
| Thalassiosira pseudonana | increase in TAGs (22-45% of total lipid) with 100 μmol L-1 m-2 s-1/12:12 h, 100 μmol L-1 m-2 s-1/24:0 h and 50 μmol L-1 m-2 s-1/24:0 h light: dark, harvested at the stationary phase | |
| Temperature | ||
| Chlamydomonas reinhardtii | about 56-76% of TAG content with 17-32 °C increased temperature | |
| Chlorella ellipsoidea | increase in unsaturated FAs with decreased temperature (chilling sensitivity) | |
| Cryptomonas sp. | increase in lipid productivity by 12.70% at 27-30 °C | |
| Isochrysis sp. | increase in lipid production by 21.70% within 27-30 °C | |
| Monoraphidium sp. | lipid content decreased from 33%-39% with increase in temperature from 25-35 °C. | |
| Monoraphidium sp. | increased biomass concentration with increase in temperature from 25-30 °C but then decreased with further increase in temperature up to 35 °C | |
| Nannochloropsis oculata | increase in lipid production by 14.92% with temperature range of 20-25 °C | |
| Nannochloropsis oculata | decreased lipid content from 15% to 8% with increase in temperature from 15 to 20 °C but then raised up to 14% with further increase of temperature to 25 °C | |
| Nannochloropsis oculata | increased specific growth rate with raise in temperature from 15-20 °C but then decreased with further raise in temperature to 25 °C | |
| Rhodomonas sp. | increase in lipid production by 15.50% with temp. range of 27-30 °C | |
| Scenedesmus sp. | decreased lipid content from 35% to 22% with increase in temperature from 20 to 30 °C | |
| Selenastrum capricornutum | increase in oleate FAs (18:1) with temperature range of 10-25 °C | |
| Salinity | ||
| Botryococcus braunii | increased TAG content from 5%-31% with an increased concentration of NaCl from 0-0.7 mol L-1 | |
| Botryococcus braunii | decreased growth rate, significantly with an increase in NaCl concentration from 0-0.7 mol L-1 | |
| Chlorococcum sp. | increased lipid content from 10% to 30% with an increased concentration in NaCl from 0% to 2% | |
| Chlorococcum sp. | concentration of biomass significantly decreased, around 4-fold with an increased concentration of NaCl from 0-2% | |
| Dunaliella salina | increased concentration of C18 FAs with culture, transferred from 029.2-204.5 g L-1 NaCl (from 0.5-3.5 mol L-1 NaCl) | |
| Dunaliella tertiolecta | increased TAG contents from 40%-57%, with an increased concentration in NaCl from 0.5-1.0 mol L-1 | |
| Dunaliella tertiolecta | similar growth rate over 0.5-1.0 mol L-1 range of salinity | |
| Hindakia sp. | 3-fold higher lipid production, compared to N starvation by 8.8 g L-1 NaCl (0.15 mol L-1 NaCl) | |
| Nannochloropsis salina | increased lipid contents, highest at 34 g L-1 | |
| Nitzschia laevis | increased neutral and polar unsaturated FAs with 10-20 g L-1 increase in NaCl (from 0.17-0.34 mol L-1 NaCl) | |
| Schizochytrium limacinum | increased greatly in saturated FAs (C15:0 and C17:0) with 9-36 g L-1 salinity at 16-30 °C temperature range. | |
| pH | ||
| Coelastrella sp. | TAG content increased with increase in pH | |
| Neochloris oleoabundans | increased TAG content, from 13%-35% with increased pH from 8.10-10.0 | |
| Scenedesmus obliquus | TAG content increased with increase in pH | |
| Scenedesmus sp. | increase in TAG accumulation | |
| Chemical stress: nitrogen stress | ||
| Chlorococcum infusionum | lipid productivity: 15-40% | |
| Chlorococcum oleofaciens | lipid productivity: 127 (mg L-1 d) | |
| Chlorella sorokiniana | lipid production: 85% | |
| Chlorella sp. | lipid productivity: 54% | |
| Chlorella vulgaris | lipid productivity: 146%-178% | |
| Dunaliella tertiolecta | 5-fold increase in lipid fluorescence | |
| Dunaliella tertiolecta | increased lipid content from 10% to 48%, after 4 d nitrogen depletion | |
| Neochloris oleoabundans | productivity of lipids: 131 (mg L-1 d) | |
| Neochloris oleoabundans | accumulation of TAGs, increased from 1.50 wt% to 12.4 wt% | |
| Neochloris oleoabundans | increased TAG contents from 8% to 26%, after 3-d nitrogen depletion | |
| Neochloris oleoabundans | production of biomass decreased from 220-297 mg L-1 d-1, after 3 d nitrogen depletion | |
| Nannochloropsis sp. | increased lipid contents from 39% to 69%, after nitrogen depletion | |
| Nannochloropsis sp. | decreased production of biomass, after nitrogen depletion | |
| Parachlorella kessleri | lipid productivity: 0-29% | |
| Scenedesmus dimorphus | lipid production: 111 (mg L-1 d) | |
| Scenedesmus naegleii | lipid productivity: 83% | |
| Scenedesmus naegleii | nitrogen and phosphorus stress | |
| Scenedesmus sp. | lipid contents increased to 30% and 53%, respectively | |
| Chaetoceros sp. | phosphorus limitation | |
| Isochrysis galbana | increase in total lipids | |
| Phaeodactylum tricornutum | increase in total lipid contents | |
| Monodus subterraneus | increase in TAG accumulation | |
| Chlorella kessleri | increase in unsaturated fatty acids | |
| Sulphur stress | ||
| Chlamydomonas reinhardtii | 2-fold increase in the phosphatidylglycerol or Increase in TAGs | |
| Silicon stress | ||
| Cyclotella cryptica | increase in total lipids from 27.6% to 54.1% | |
Table 3. Impact of physicochemical stress on microalgal lipid accumulation (adapted from modified Refs. [68,70,71]).
| Microalgal species | Stress | |
|---|---|---|
| Physical stress: irradiation | ||
| Chaetoceros muelleri | increase in monounsaturated FAs with UV-A radiation | |
| Chaetoceros simplex | increase in saturated fatty acid with high UV-B irradiation | |
| Nannochloropsis sp. | increase in the total lipid content, about > 31.3% with 100 μmol L-1 m-2 s-1/18 h light intensity: 6 h, dark cycle | |
| Nannochloropsis sp. | increase in saturated FAs:PUFAs ratio via UV-A irradiation | |
| Neochloris oleoabundans | about 19%-25% increase in the TAG content with 50-200 μmol L-1 m-2 s-1 of light intensity | |
| Neochloris oleoabundans | increase in the biomass concentration from 1.2-1.7 g L-1 with increase in light intensity from 50-200 μmol L-1 m-2 s-1 | |
| Pavlova lutheri | increase in total lipid content with high light intensities stress | |
| Pavlova lutheri | about 23%-78% increase in the TAG content with 9-19 W m-2 increase in light intensity | |
| Scenedesmus sp. | lipid and TAG content increased from 26%-41% and 16%-32%, respectively, with increase in light intensity from 50-250 μmol L-1 m-2 s-1 | |
| Selenastrum capricornutum | increase in linoleate FAs (18:02) with dark treatment stress; increase in biomass concentration 2.5-3.6 g L-1 with 50-250 μmol L-1 m-2 s-1 increase in light intensity | |
| Tetraselmis sp. | increase in saturated and monounsaturated FAs and decrease in PUFAs with UV-B irradiation | |
| Thalassiosira pseudonana | increase in polar lipids (79%-89% of total lipid) with 100 μmol L-1 m-2 s-1/12:12 h, 100 μmol L-1 m-2 s-1/24 h and 50 mol L-1 m-2 s-1/24 h light: dark, harvested at the logarithmic phase | |
| Thalassiosira pseudonana | increase in TAGs (22-45% of total lipid) with 100 μmol L-1 m-2 s-1/12:12 h, 100 μmol L-1 m-2 s-1/24:0 h and 50 μmol L-1 m-2 s-1/24:0 h light: dark, harvested at the stationary phase | |
| Temperature | ||
| Chlamydomonas reinhardtii | about 56-76% of TAG content with 17-32 °C increased temperature | |
| Chlorella ellipsoidea | increase in unsaturated FAs with decreased temperature (chilling sensitivity) | |
| Cryptomonas sp. | increase in lipid productivity by 12.70% at 27-30 °C | |
| Isochrysis sp. | increase in lipid production by 21.70% within 27-30 °C | |
| Monoraphidium sp. | lipid content decreased from 33%-39% with increase in temperature from 25-35 °C. | |
| Monoraphidium sp. | increased biomass concentration with increase in temperature from 25-30 °C but then decreased with further increase in temperature up to 35 °C | |
| Nannochloropsis oculata | increase in lipid production by 14.92% with temperature range of 20-25 °C | |
| Nannochloropsis oculata | decreased lipid content from 15% to 8% with increase in temperature from 15 to 20 °C but then raised up to 14% with further increase of temperature to 25 °C | |
| Nannochloropsis oculata | increased specific growth rate with raise in temperature from 15-20 °C but then decreased with further raise in temperature to 25 °C | |
| Rhodomonas sp. | increase in lipid production by 15.50% with temp. range of 27-30 °C | |
| Scenedesmus sp. | decreased lipid content from 35% to 22% with increase in temperature from 20 to 30 °C | |
| Selenastrum capricornutum | increase in oleate FAs (18:1) with temperature range of 10-25 °C | |
| Salinity | ||
| Botryococcus braunii | increased TAG content from 5%-31% with an increased concentration of NaCl from 0-0.7 mol L-1 | |
| Botryococcus braunii | decreased growth rate, significantly with an increase in NaCl concentration from 0-0.7 mol L-1 | |
| Chlorococcum sp. | increased lipid content from 10% to 30% with an increased concentration in NaCl from 0% to 2% | |
| Chlorococcum sp. | concentration of biomass significantly decreased, around 4-fold with an increased concentration of NaCl from 0-2% | |
| Dunaliella salina | increased concentration of C18 FAs with culture, transferred from 029.2-204.5 g L-1 NaCl (from 0.5-3.5 mol L-1 NaCl) | |
| Dunaliella tertiolecta | increased TAG contents from 40%-57%, with an increased concentration in NaCl from 0.5-1.0 mol L-1 | |
| Dunaliella tertiolecta | similar growth rate over 0.5-1.0 mol L-1 range of salinity | |
| Hindakia sp. | 3-fold higher lipid production, compared to N starvation by 8.8 g L-1 NaCl (0.15 mol L-1 NaCl) | |
| Nannochloropsis salina | increased lipid contents, highest at 34 g L-1 | |
| Nitzschia laevis | increased neutral and polar unsaturated FAs with 10-20 g L-1 increase in NaCl (from 0.17-0.34 mol L-1 NaCl) | |
| Schizochytrium limacinum | increased greatly in saturated FAs (C15:0 and C17:0) with 9-36 g L-1 salinity at 16-30 °C temperature range. | |
| pH | ||
| Coelastrella sp. | TAG content increased with increase in pH | |
| Neochloris oleoabundans | increased TAG content, from 13%-35% with increased pH from 8.10-10.0 | |
| Scenedesmus obliquus | TAG content increased with increase in pH | |
| Scenedesmus sp. | increase in TAG accumulation | |
| Chemical stress: nitrogen stress | ||
| Chlorococcum infusionum | lipid productivity: 15-40% | |
| Chlorococcum oleofaciens | lipid productivity: 127 (mg L-1 d) | |
| Chlorella sorokiniana | lipid production: 85% | |
| Chlorella sp. | lipid productivity: 54% | |
| Chlorella vulgaris | lipid productivity: 146%-178% | |
| Dunaliella tertiolecta | 5-fold increase in lipid fluorescence | |
| Dunaliella tertiolecta | increased lipid content from 10% to 48%, after 4 d nitrogen depletion | |
| Neochloris oleoabundans | productivity of lipids: 131 (mg L-1 d) | |
| Neochloris oleoabundans | accumulation of TAGs, increased from 1.50 wt% to 12.4 wt% | |
| Neochloris oleoabundans | increased TAG contents from 8% to 26%, after 3-d nitrogen depletion | |
| Neochloris oleoabundans | production of biomass decreased from 220-297 mg L-1 d-1, after 3 d nitrogen depletion | |
| Nannochloropsis sp. | increased lipid contents from 39% to 69%, after nitrogen depletion | |
| Nannochloropsis sp. | decreased production of biomass, after nitrogen depletion | |
| Parachlorella kessleri | lipid productivity: 0-29% | |
| Scenedesmus dimorphus | lipid production: 111 (mg L-1 d) | |
| Scenedesmus naegleii | lipid productivity: 83% | |
| Scenedesmus naegleii | nitrogen and phosphorus stress | |
| Scenedesmus sp. | lipid contents increased to 30% and 53%, respectively | |
| Chaetoceros sp. | phosphorus limitation | |
| Isochrysis galbana | increase in total lipids | |
| Phaeodactylum tricornutum | increase in total lipid contents | |
| Monodus subterraneus | increase in TAG accumulation | |
| Chlorella kessleri | increase in unsaturated fatty acids | |
| Sulphur stress | ||
| Chlamydomonas reinhardtii | 2-fold increase in the phosphatidylglycerol or Increase in TAGs | |
| Silicon stress | ||
| Cyclotella cryptica | increase in total lipids from 27.6% to 54.1% | |
| Property | Unit | Microalgal biodiesel | Petrodiesel | ASTM standard method | Limit |
|---|---|---|---|---|---|
| Acid number | mg KOH/g | 0.022-0.003 | 0.5 | D 664 | 0.80 max |
| Boiling point | °C | 182-338 | 188-343 | — | — |
| Calorific (heating) value | MJ kg-1 | 41 | 40-45 | — | — |
| Carbon residue | wt% | — | 0.05 max %mass | D 4530 | 0.050 max |
| Cetane number | — | 48-65 | 40-55 | D 613 | 47 min |
| Cloud point | °C | -5.2 to 3.9 | -35 to 5 | D 2500 | Report to customer |
| Cold filter plugging point | °C | — | -7 to -2 | -3 (max.-6) | 0 to -15 |
| Copper(Cu) | wt% | 0.042 | — | — | — |
| Copper strip corrosion | (3 h at 50 °C) | 1 ppm | No. 3 max | D 130 | No. 3 max |
| Density | Kg L-1 | 0.864 | 0.838 | — | 0.86-0.9 |
| Flash point, closed cup | °C | > 160 | 75 | D 93 | 130 min |
| Free glycerin | wt% | 0.009-0.014% (m/m) | — | D 6584 | 0.02 |
| Fuel composition | — | C12-C22 FAME | C10-C21 HC | — | — |
| H:C ratio | — | 1.81 | 1.81 | — | — |
| Nickel (Ni) | wt% | 0.074 | — | — | — |
| Phosphorus (P) | wt% | < 0.1 ppm | — | D 4951 | 0.0010 |
| Pour point | °C | -16 | -17 | — | — |
| Solidifying point | — | -12 | -50 to 10 | — | — |
| Specific gravity | Kg L-1 | 0.88 | 0.85 | — | 0.88 |
| Stoichiometric air/fuel ratio (AFR) | — | 13.8 | 15 | — | — |
| Sulfated ash | wt% | <0.005 | 0.0015 max | D 874 | 0.020 max |
| Total glycerin | wt% | 0.091%-0.102% (m/m) | — | D 6584 | 0.240 |
| Total sulfur | wt% | 0.6-5.1 ppm | — | D 5453 | 0.05 max |
| Vacuum distillation end point | % distilled | — | — | D 1160 | 360 °C max, at T-90 |
| Viscosity (mm2 s-1) at 40 °C | mm2 s-1 | 4.519-4.624 | 1.9-4.1 | D 445 | 1.9-6.0 |
Table 4 Comparison of the properties of microalgal biodiesel and petrodiesel to the ASTM Standard (D6751-02) (adapted from modified Refs. [70?-72]).
| Property | Unit | Microalgal biodiesel | Petrodiesel | ASTM standard method | Limit |
|---|---|---|---|---|---|
| Acid number | mg KOH/g | 0.022-0.003 | 0.5 | D 664 | 0.80 max |
| Boiling point | °C | 182-338 | 188-343 | — | — |
| Calorific (heating) value | MJ kg-1 | 41 | 40-45 | — | — |
| Carbon residue | wt% | — | 0.05 max %mass | D 4530 | 0.050 max |
| Cetane number | — | 48-65 | 40-55 | D 613 | 47 min |
| Cloud point | °C | -5.2 to 3.9 | -35 to 5 | D 2500 | Report to customer |
| Cold filter plugging point | °C | — | -7 to -2 | -3 (max.-6) | 0 to -15 |
| Copper(Cu) | wt% | 0.042 | — | — | — |
| Copper strip corrosion | (3 h at 50 °C) | 1 ppm | No. 3 max | D 130 | No. 3 max |
| Density | Kg L-1 | 0.864 | 0.838 | — | 0.86-0.9 |
| Flash point, closed cup | °C | > 160 | 75 | D 93 | 130 min |
| Free glycerin | wt% | 0.009-0.014% (m/m) | — | D 6584 | 0.02 |
| Fuel composition | — | C12-C22 FAME | C10-C21 HC | — | — |
| H:C ratio | — | 1.81 | 1.81 | — | — |
| Nickel (Ni) | wt% | 0.074 | — | — | — |
| Phosphorus (P) | wt% | < 0.1 ppm | — | D 4951 | 0.0010 |
| Pour point | °C | -16 | -17 | — | — |
| Solidifying point | — | -12 | -50 to 10 | — | — |
| Specific gravity | Kg L-1 | 0.88 | 0.85 | — | 0.88 |
| Stoichiometric air/fuel ratio (AFR) | — | 13.8 | 15 | — | — |
| Sulfated ash | wt% | <0.005 | 0.0015 max | D 874 | 0.020 max |
| Total glycerin | wt% | 0.091%-0.102% (m/m) | — | D 6584 | 0.240 |
| Total sulfur | wt% | 0.6-5.1 ppm | — | D 5453 | 0.05 max |
| Vacuum distillation end point | % distilled | — | — | D 1160 | 360 °C max, at T-90 |
| Viscosity (mm2 s-1) at 40 °C | mm2 s-1 | 4.519-4.624 | 1.9-4.1 | D 445 | 1.9-6.0 |
| Advantage | Disadvantage |
|---|---|
| More cost-effective | difficult to harvest due to microscopic size of most planktonic microalgae |
| Less water demand than land crops. Algae can grow on brackish water from saline aquifers or in seawater,y solve some of the water availability problems | salt precipitation on the bioreactor walls; precipitates on pump sand valves; presence of salts in the final biomass |
| High growth rate; no sulfur content | low biomass concentration |
| High-efficiency CO2 mitigation | there is a need to develop techniques for growing a single species. evaporation losses are reduced and CO2 utilization is increased |
| Growing algae do not require the use of herbicides/pesticides. | drying and extraction is difficult. In dry extraction (drying the algae by sun or artificially), a much lower yield is obtained. when using artificial dryers (using electricity) it takes more energy to extract than the energy obtained from the yield |
| Capability of performing the photobiological production of biohydrogen | not cost-effective |
| Non-toxic and highly biodegradable biofuels | natural algal strands are not favored, possibly due to their low productivity for target organisms. Most microalgae species are not adapted to local climates and outdoor cultivation |
| Easy to provide optimal nutrient levels due to the well-mixed aqueous environment as compared to soil | limited genomic data for algal species |
| Ability to adjust harvest rates to keep culture densities at optimal levels at all times; especially with the continuous culture systems, such as raceway ponds and bioreactors, harvesting efforts can be controlled to match productivity | microalgae grown in open pond systems are prone to contamination |
| High levels of polyunsaturated fatty acids in algae biodiesel suitable for cold weather | biodiesel performs poorly compared to its mainstream alternative. |
| Continuous production avoids establishment periods of conventional plants. | large-scale extraction procedures for microalgal lipids are complex and still in the developmental stage |
| A high per-acre yield (7-31 times greater than the next best crop-palm oil) | sun-stable biodiesel with many polyunsaturates are produced |
| Algae oil extracts can be used as livestock feed and even processed into ethanol | limited data on large-scale cultivation |
| Algae-based fuel properties allow use in jet fuels | large-scale production could present many other drawbacks |
Table 5 Advantages and disadvantages of microalgae-based biofuels (adapted from modified Ref. [1]).
| Advantage | Disadvantage |
|---|---|
| More cost-effective | difficult to harvest due to microscopic size of most planktonic microalgae |
| Less water demand than land crops. Algae can grow on brackish water from saline aquifers or in seawater,y solve some of the water availability problems | salt precipitation on the bioreactor walls; precipitates on pump sand valves; presence of salts in the final biomass |
| High growth rate; no sulfur content | low biomass concentration |
| High-efficiency CO2 mitigation | there is a need to develop techniques for growing a single species. evaporation losses are reduced and CO2 utilization is increased |
| Growing algae do not require the use of herbicides/pesticides. | drying and extraction is difficult. In dry extraction (drying the algae by sun or artificially), a much lower yield is obtained. when using artificial dryers (using electricity) it takes more energy to extract than the energy obtained from the yield |
| Capability of performing the photobiological production of biohydrogen | not cost-effective |
| Non-toxic and highly biodegradable biofuels | natural algal strands are not favored, possibly due to their low productivity for target organisms. Most microalgae species are not adapted to local climates and outdoor cultivation |
| Easy to provide optimal nutrient levels due to the well-mixed aqueous environment as compared to soil | limited genomic data for algal species |
| Ability to adjust harvest rates to keep culture densities at optimal levels at all times; especially with the continuous culture systems, such as raceway ponds and bioreactors, harvesting efforts can be controlled to match productivity | microalgae grown in open pond systems are prone to contamination |
| High levels of polyunsaturated fatty acids in algae biodiesel suitable for cold weather | biodiesel performs poorly compared to its mainstream alternative. |
| Continuous production avoids establishment periods of conventional plants. | large-scale extraction procedures for microalgal lipids are complex and still in the developmental stage |
| A high per-acre yield (7-31 times greater than the next best crop-palm oil) | sun-stable biodiesel with many polyunsaturates are produced |
| Algae oil extracts can be used as livestock feed and even processed into ethanol | limited data on large-scale cultivation |
| Algae-based fuel properties allow use in jet fuels | large-scale production could present many other drawbacks |
Scheme 2. Transesterification of viscous microalgal lipids.
Fig. 2. Proposed mechanism of esterification and transesterification of algal feedstocks (a) and pathways of the transesterification process (b).
Fig. 3. (a) Proposed acid-and (b) base-catalyzed transesterification pathways
Scheme 3. Hydrolysis of esters and soap formation
Fig. 4. (a) Predicted Bronsted and Lewis active sites in sulphonated zirconia solid acid catalyst and (b) influence of the surface hydrophobicity in the solid acid catalytic activity respectively (Adapted from Ref. [47]).
Fig. 5. Proposed heterogeneous base catalysis using mesoporous silica Fe-MSN for the production of biodiesel from algal feedstock. (a) Conversion of oleic oil to nonadecanol and (b) conversion of nonadecanol to n-nonadecane (adapted from Ref. [84]).
Fig. 6. Langmuir-Hinshelwood model of oleic acid hydrotreatment with Fe-MSN (adapted from modified Ref. [84]).
Fig. 7. Proposed mechanism for the formation of algal bio-oil from algal feedstock (adapted from a modified version of Ref. [70]).
Fig. 8. Proposed mechanism for the formation of algal bio-oil from algal feed stock and mechanism involved in algal oil production by tri/diglycerides (adapted from Ref. [70]).
| Solid acid | Solid base |
|---|---|
| Zinc acetate supported over silica: Zn(Ac O)2-SiO2 & Copper supported over silica: Cu-SiO2 | oxides of group IIA elements: CaO, MgO, SrO & BaO; Carbonates of group IA elements: K2CO3 |
| Free sulphated tin oxide supported over alumina: SO42--SnO2/Al2O3 & Free sulphated tin oxide supported over silica: SO42--SnO2/SiO2 | carbonates of group IIA elements:CaCO3, MgCO3, SrCO3, BaCO3 & Li-promoted oxides of group IIA elements |
| Heteropoly acids and their derivatives: H3PW12O40-phosphotungstic acid & H4SiW12O40-silicotungstic acid | metal complexes: Schiff base metal complexes |
| Organosulphonic acids supported over mesoporous silica/alumina: R-SO3H-SiO2/Al2O3 | free and mixed transition metal oxides: ZnO, CuO, CaLaO3,CaCeO3, CaZrO3, CaMnO3&CaTiO3 |
| Nafion (sulfonated tetrafluoroethylene based fluoro polymer-copolymer): C7HF13O5S·C2F4 | basic zeolites, Mg-Zr & Aluminates of Zinc (Spinel):ZnAl2O4 |
| Sulfated zirconia mixed with other transition metal (M) Oxides : SO42--ZrO2/WO3 & SO42--ZrO2/MO3 | Cs-exchanged sepiolite: Mg4Si6O15(OH)& Iron supported on mesoporous silica nanoparticles (Fe-MSN) |
| Sulfated zirconia supported over silica: SO42--ZrO2/SiO2/Al2O3 | hydrotalcites: (Mg-Al)& bimetallic Sn-Ni |
| Microporous aluminosilicates (Zeolitic materials): HeY, HBeta, ZSM-5, H-MOR, ETS-10, and ETS-4 | quanidine-anchored cellulose or other polymers, metal-generated salts of primary amino acids: organometallic compounds: P(RNCH2CH2)3N |
Table 6 List of significant heterogeneous solid acid/base catalysts.
| Solid acid | Solid base |
|---|---|
| Zinc acetate supported over silica: Zn(Ac O)2-SiO2 & Copper supported over silica: Cu-SiO2 | oxides of group IIA elements: CaO, MgO, SrO & BaO; Carbonates of group IA elements: K2CO3 |
| Free sulphated tin oxide supported over alumina: SO42--SnO2/Al2O3 & Free sulphated tin oxide supported over silica: SO42--SnO2/SiO2 | carbonates of group IIA elements:CaCO3, MgCO3, SrCO3, BaCO3 & Li-promoted oxides of group IIA elements |
| Heteropoly acids and their derivatives: H3PW12O40-phosphotungstic acid & H4SiW12O40-silicotungstic acid | metal complexes: Schiff base metal complexes |
| Organosulphonic acids supported over mesoporous silica/alumina: R-SO3H-SiO2/Al2O3 | free and mixed transition metal oxides: ZnO, CuO, CaLaO3,CaCeO3, CaZrO3, CaMnO3&CaTiO3 |
| Nafion (sulfonated tetrafluoroethylene based fluoro polymer-copolymer): C7HF13O5S·C2F4 | basic zeolites, Mg-Zr & Aluminates of Zinc (Spinel):ZnAl2O4 |
| Sulfated zirconia mixed with other transition metal (M) Oxides : SO42--ZrO2/WO3 & SO42--ZrO2/MO3 | Cs-exchanged sepiolite: Mg4Si6O15(OH)& Iron supported on mesoporous silica nanoparticles (Fe-MSN) |
| Sulfated zirconia supported over silica: SO42--ZrO2/SiO2/Al2O3 | hydrotalcites: (Mg-Al)& bimetallic Sn-Ni |
| Microporous aluminosilicates (Zeolitic materials): HeY, HBeta, ZSM-5, H-MOR, ETS-10, and ETS-4 | quanidine-anchored cellulose or other polymers, metal-generated salts of primary amino acids: organometallic compounds: P(RNCH2CH2)3N |
Scheme 4. Enzyme immobilization pathways.
Fig. 9. Steps involved in in-situ transesterification for biodiesel production (adapted from modified Ref. [93]).
| Extraction process | Technique | Circumstance | Lipid productivity (%) |
|---|---|---|---|
| Chemical method | n-hexane-soxhlet extractor | — | 95-99 |
| chloroform, ethanol, deionized water | 8 h | 49 ± 72.4 | |
| aqueous oil | 2 h | 38 | |
| ultrasound assisted aq. oil | 50 °C; pH = 9; 6 h | 67 | |
| acetone, n-hexane | — | — | |
| subcritical ethanol | 20:1 (v/w) ethanol:alga, 105 °C, 100 min | 73 | |
| Enzymatic method | aqueous enzymatic oil-cellulase/hemicellulose | 60 °C, pH = 4.5, 2 h | — |
| aqueous enzymatic oil-alk. protease | 60 °C, pH = 7.0, 2 h | 86 | |
| 50 °C, pH = 9.0, 6 h | 64 | ||
| ultrasound-alk. protease | — | 74 | |
| Mechanical methods | engine driven | — | 68 |
| screw press | — | 79-80 | |
| ram press | — | 63 | |
| Microwave method | B20 co-solvent a | 80 °C,1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 13 ± 0.8 |
| B20 co-solvent a | 100 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 17 ± 1.6 | |
| B20 co-solvent a | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 12 ± 2.0 | |
| B40 co-solvent b | 80 °C,1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 32 ± 6.0 | |
| B40 co-solvent b | 100 °C, 1.2kW, 2.45 GHz, 15 min hold, 30 min cool-down | 38 ± 8.0 | |
| B40 co-solvent b | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 57 ± 8.0 | |
| chloroform + ethanol | 80 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 16 ± 0.7 | |
| B40 co-solvent b | 100 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 46 ± 2.2 | |
| B40 co-solvent b | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 53 ± 3.0 | |
| Super critical method | Sc-CO2 c | 80 °C, 250 bar | 14 |
Table 7 Different oil extraction techniques and their lipid productivity (adapted from modified Ref. [47]).
| Extraction process | Technique | Circumstance | Lipid productivity (%) |
|---|---|---|---|
| Chemical method | n-hexane-soxhlet extractor | — | 95-99 |
| chloroform, ethanol, deionized water | 8 h | 49 ± 72.4 | |
| aqueous oil | 2 h | 38 | |
| ultrasound assisted aq. oil | 50 °C; pH = 9; 6 h | 67 | |
| acetone, n-hexane | — | — | |
| subcritical ethanol | 20:1 (v/w) ethanol:alga, 105 °C, 100 min | 73 | |
| Enzymatic method | aqueous enzymatic oil-cellulase/hemicellulose | 60 °C, pH = 4.5, 2 h | — |
| aqueous enzymatic oil-alk. protease | 60 °C, pH = 7.0, 2 h | 86 | |
| 50 °C, pH = 9.0, 6 h | 64 | ||
| ultrasound-alk. protease | — | 74 | |
| Mechanical methods | engine driven | — | 68 |
| screw press | — | 79-80 | |
| ram press | — | 63 | |
| Microwave method | B20 co-solvent a | 80 °C,1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 13 ± 0.8 |
| B20 co-solvent a | 100 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 17 ± 1.6 | |
| B20 co-solvent a | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 12 ± 2.0 | |
| B40 co-solvent b | 80 °C,1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 32 ± 6.0 | |
| B40 co-solvent b | 100 °C, 1.2kW, 2.45 GHz, 15 min hold, 30 min cool-down | 38 ± 8.0 | |
| B40 co-solvent b | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 57 ± 8.0 | |
| chloroform + ethanol | 80 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 16 ± 0.7 | |
| B40 co-solvent b | 100 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 46 ± 2.2 | |
| B40 co-solvent b | 120 °C, 1.2 kW, 2.45 GHz, 15 min hold, 30 min cool-down | 53 ± 3.0 | |
| Super critical method | Sc-CO2 c | 80 °C, 250 bar | 14 |
Fig. 10. SEM photographs of the morphology before the extraction process (BEP) and after the extraction process (AEP) for microalgal cells (adapted from modified Refs. [70,71]).
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