Oil content
The average oil content of different families and the distribution of species number are shown in Supplementray Fig.S1. The families with an average oil content higher than 20% are: Cephalotaxaceae (1 species, 56.14%), Styracaceae (1 species, 48.30%), Lauraceae (5 species, 41.85%), and Simaroubaceae (1 species, 36.24) %), Magnoliaceae (8 species, 35.11%), Thymelaeaceae (1 species, 33.20%), Taxaceae (1 species, 31.79%), Linaceae (1 species, 31.71%), Celastraceae(10 species, 31.39%), Schisandraceae (1 species, 30.80%), Papaveraceae (3 species, 29.96%), Cruciferae (19 species, 29.79%), Acanthaceae (2 species, 29.67%), Eucommiaceae ( 1 species, 27.60%), Camellia (2 species, 27.19%), Sterculiaceae (2 species, 25.30%), Lamiaceae (15 species, 25.23%), Alangiaceae (2 species, 24.31%), Pinaceae (8 species, 24.14%), Sapindaceae (6 species, 22.53%), (8 species, 22.36%), Paeoniaceae (3 species, 22.20%), Flacourtiaceae (1 species, 21.53%), Primulaceae (2 species, 20.81%). Among them, Lauraceae, Magnoliaceae, Euonymaceae, Cruciferae, Lamiaceae, Sapindaceae, and Euphorbiaceae are the dominant families with high oil content.
Oil content distribution among different species. Whether a plant is suitable as a raw material for biodiesel depends firstly on its oil production per unit area, and the oil production depends on the unit organs production (mainly seeds or fruits) and the oil content. Therefore, oil content is one of the most important characteristics of diesel energy plants. The oil content distribution of 587 specices plant seeds (fruits) are shown in Supplementray Fig.S1. Overall, 54.1% of the species have an oil content of less than 10%; the oil-rich plant species with an oil content of more than 30% account for 12.3% (in 72 species), and in 6 species (1.0%), the seed oil content is more than 50%, Corylus ferox Wall. (59.72%) of the Betulaceae, Cephalotaxus sinensis (Rehder & E. H. Wilson) H. L. Li (56.14%) of the Cephalotaxaceae, and Lindera erythrocarpa Makino (55.31%) and Litsea mollis Hemsl. (51.42%) of the Lauraceae, Amygdalus pedunculata Pall. (53.09%) of the Rosaceae, Salvia umbratica Hance (51.70%) of the Lamiaceae.
The 72 species of plants with oil content greater than 30% is shown in Table 1, Supplementary Fig. S2 and Supplementary Fig. S3. They mainly distributed in the families of Cruciferae (12 species), Rosaceae (10 species), Celastraceae (6 species), Magnoliaceae (6 species), Lauraceae (5 species), Lamiaceae (4 species), Euphorbiaceae (4 species), Pinaceae (4 species), Betulaceae (2 species) and one species in each family of Styracaceae, Taxaceae, Juglandaceae, Campanulaceae, Compositae, Simaroubaceae, Ranunculaceae, Actinidiaceae, Lardizabalaceae, Aceraceae, Thymelaeaceae, Cephalotaxaceae, Theaceae, Rhamnaceae, Sapindaceae, Schisandraceae, Linaceae,Papaveraceae and Ulmaceae (Fig. 1).
Iodine value
Iodine value is a measure used to measure the degree of unsaturation of fatty acids, equal to the number of grams of iodine taken by 100 g of fatty acids. The iodine value indicates the average number of double bonds of fatty acids. If the average number of double bonds is high, the combustion performance of biodiesel will decrease, and it will easily become rancid and deteriorate, but the low temperature properties will increase due to the iodine value of biodiesel and the iodine of raw oil The values are basically the same, so the iodine value of the prepared biodiesel can be estimated by analyzing the iodine value of oil. The EU biodiesel standard stipulates that the iodine value is less than 120 g/100 g.
Except for 20 species whose iodine value could not be measured due to low oil content or insufficient seed collection, among the remaining 567 species, 422 species with an iodine value of less than 120g/100g, accounting for 74.4%, meet the requirements of biodiesel (Fig. 2A).
The average iodine value of each family is different, and the distribution is shown in Fig. 2B and Supplementary Fig. S4. The average iodine value of 81.4% of the family is less than 120 g/100 g, which shows that this indicator is easy to meet the standard. The remaining 18 families with a higher iodine value of more than 120 g/100 g are mainly Leguminosae and Polygonaceae.
Acid value
The acid value is the number of milligrams of potassium hydroxide required to neutralize the free fatty acids in 1 g of oil. It is often used to indicate the degree of rancidity due to slow oxidation. The value reflects the amount of free fatty acids in the measured oil and is used to evaluate the oil. The quality priority is also the basis for calculating the amount of alkali added during deacidification. Biodiesel is a fatty acid monoester, which is produced by the esterification reaction of fatty acids. If the acid value of the oil is too high, the amount of alkali used for deacidification must be increased, which will increase the cost and reduce the efficiency of the subsequent transesterification reaction affecting the production of biodiesel. Therefore, vegetable oils with relatively small acid values (generally less than 10) should be selected as the raw materials for biodiesel production.
As shown in Fig. 3, families, and species with acid value less than 10% accounted for 19.6% and 31.9%, respectively. Families with an acid value of less than 10 are mainly distributed in the families of Rosaceae (20 species), Leguminosae (18 species), Cruciferae (17 species), Labiatae (9 species), Compositae (7 species), Liliaceae ( 6 species), Aceraceae (6 species), Rhamnaceae (6 species), Solanaceae (5 species), Cannabaceae (4 species), Malvaceae (4 species), Oleaceae (4 species), Cornaceae (4 species) Sapindaceae (4 species), Chenopodiaceae (3 species), Polygonaceae (3 species), Loniceraceae (3 species), Euonymaceae (3 species), Celastraceae (3 species), Corylaceae (3 species), Tiliaceae (2 species), Zygophyllaceae (2 species), Ranunculaceae (2 species), Aesculus (2 species), Umbelliferae (2 species), Paeoniaceae (2 species) , Pinaceae (2 species), Amaranthaceae (2 species), Convolvulaceae (2 species), etc.
Saponification value
The saponification value is the number of milligrams of potassium hydroxide required to completely saponify 1g of oil. It is the sum of the acid value and the ester value. It can reflect the molecular weight of fatty acids in the oil. The higher free fatty acids content in the oil, the greater the saponification value of the oil. The higher the saponification value, the smaller the molecular weight of the fatty acid, that is, the shorter the carbon chain length, the lower the viscosity; on the contrary, the lower the saponification value, the longer the fatty acid carbon chain length. With the saponification value, we can also calculate the alkali consumption of fat to prepare fatty acid methyl ester.
The analysis results show that the saponification value of plant oil tested is concentrated between 140 and 220 mg/g (Fig. 4) in 344 species (62.66%). In 116 plant species (21.13% of the total species tested) the saponification value exceeds 220 mg/g. In 89 plant species(16.21%), the saponification value is less than 140 mg/g. Species with saponification value higher than 400 mg/g are Ligustrum japonicum Thunb. (403.02 mg/g) of the Oleaceae, Corydalis pallida (Thunb.) Pers. (424.73 mg/g) of the Papaveraceae, Paulownia tomentosa Steud. (428.36mg/g) and Rehmannia glutinosa (Gaertn.) DC. (470.17mg/g) of the Scrophulariaceae, Indigofera amblyantha Craib (438.84mg/g) and Kummerowia stipulacea (Maxim.) Makino (545.47mg/g) of the Leguminosae, Carpinus turczaninowii Hance (441.54mg/g) of the Corylaceae, Euptelea pleiosperma Hook. f. & Thomson (448.57mg/g) of the Eupteleaceae, Saussurea nivea Turcz. (477.15mg/g) of the Compositae, Angelica dahurica (Fisch. ex Hoffmann) Benth. et Hook. f. ex Franch. et Sav. (503.39mg/g) of the Umbelliferae, Isatis tinctoria L. (576.16mg/g) of the Cruciferae, Atriplex centralasiatica Iljin (641.10mg/g) of the Chenopodiaceae.
Fatty acid composition
The fatty acid composition directly affects the properties of biodiesel (Knothe 2005). Therefore, the fatty acid composition of all speices is analyzed. The analysis shows that the fatty acid composition and mass fraction of various vegetable oils are very different, showing the characteristics of different families, genera, and species (Fig. 5 and 6). For example, erucic acid was mainly found in the Cruciferae;pinolenic acid and taxoleic acid was mainly found in the Pinaceae; oleic acid was mainly found in the Euphorbiaceae. The decadecanoic acid is the main fatty acid in Zelkova serrata (Thunb.) Makino of the Ulmaceae with the content over 70%. Fatty acids are mainly composed of C12:0~C20:0. In 30.6% of plant species their seeds contain dodecanoic acid, which is the dominant component in the families of Lauraceae and Palmaceae, with a content of 22.3%-75.0%. In 68.75% of plant species, the seeds contain myristic acid (tetradecanoic acid), which is the dominant component of Pyrus pyrifolia (Burm. f.) Nakai seeds of th Rosaceae, with a content of 71.3%. In 99.1% of the tested species, their oil contains palmitic acid (C16:0), it is the main oil component of most species. In 81.4% of species, their oil contains hexadecenoic acid (C16:1). Almost all plant species contain stearic acid, oleic acid, and linoleic acid.
Lauric acid (C12:0):C12:0 was not detected in 53.2% of species, 16.3% of species had C12:0 content less than 1%, in 27.1% of species had C12:0 content of 1-5%, only in 3.3% of species had C12:0 content greater than 5%, of which 5 species had content of greater than 20%, i.e., Lindera glauca (Sieb. et Zucc.) Bl. (22.33%) of the Lauraceae, Lindera erythrocarpa Makino (28.08%), Cinnamomum camphora (L.) Presl (29.10), Litsea mollis Hemsl. (74.97%) of the Lauraceae, Archontophoenix alexandrae (F. Muell.) H. Wendl. et Drude (44.10%) of the Arecaceae (Supplementary Fig. S5). Litsea mollis Hemsl. is the representive species highly rich in C12:0.
Myristic acid (C14:0): Myristic acid is a non-main oil component in most plant species, with the average content of 0.43%. This component is not detected in 20.2% of the species, and in most (75.5%) species the C14:0 content is less than 1%. Only in 9 species the C14:0 content is greater than 5%. They are Lindera erythrocarpa Makino (6.02%) of the Lauraceae, Bischofia polycarpa (Lévl.) Airy Shaw (6.67%) of the Euphorbiaceae), Trachycarpus fortunei (Hook.) H. Wendl. (6.76%) and Archontophoenix alexandrae (F. Muell.) H. Wendl. et Drude (8.95%) of the Arecaceae, Iris tectorum Maxim. (7.23%) of the Iridaceae, Sophora davidii (Franch.) Skeels (7.26) of the Leguminosae, Ulmus parvifolia Jacq. (8.83%), Jasminum lanceolaria Roxb. (10.01%) of the Oleaceae, Pyrus pyrifolia (Burm. f.) Nakai (71.30%) of the Rosaceae (Supplementary Fig. S6). Pyrus pyrifolia (Burm. f.) Nakai is the special one with the remarkable highest C14:0 content.
Palmitic acid (C16:0):The average stearic acid C16:0 content of the tested plant species is 9.42%, which is one of the main components of oil in most species. The C16:0 content in 85.7% species was 1-15%. The C16:0 content in 47.1% of species is 5%-10%. There are 26 species with C16:0 content exceeding 20% (Supplementary Table S2), among them, 4 species with content exceeding 40%, namely Bidens alba (L.) DC (42.07%) and Cosmos sulphureus Cav. (46.74%) of the Asteraceae, Toxicodendron vernicifluum F. A. Barkl. (46.40%) and Sapium sebiferum (L.) Roxb. (47.90%) of the Euphorbiaceae (Supplementary Fig. S7A).
Palmitoleic acid (C16:1) :In Supplementary Fig. S7B, the average content of palmitoleic acid is 0.46%, in 15.1% of species C16:1 was not detected, 77.2% of species have a content of less than 1%, 7% of species have a content of 1-5%, and only in 4 specie C16:1 content was higher than s(5%), namely Raphanus sativus L.(5.33%) of the Cruciferae, Cynanchum hancockianum (Maxim.) Iljinski (8.48%) of the Asclepiadaceae, Toxicodendron vernicifluum F. A. Barkl. (8.63%) of the Anacardiaceae, and Decaisnea insignis (Griff.) Hook. f. et Thoms. (52.17%) of the Lardizabalaceae. Especially in Decaisnea insignis (Griff.) Hook. f. et Thoms., the content of C16:1 was very high, which was the only one with outstanding content among the tested species.
Stearic acid (C18:0):Stearic acid is one of the main components of vegetable oils in most species (82.5%), with the content ranged 1%-5% (averaged 3.02%). Only in 3 species, was stearic acid content found higher than 20%, i.e., Momordica cochinchinensis (Lour.) Spreng. (24.65%) of the Cucurbitaceae, Kolkwitzia amabilis Graebn. (28.15%) of the Loniceraceae, and Litsea pungens Hemsl. (39.19%) of the Lauraceae (Supplementary Fig. S8A).
Oleic acid (C18:1):In Supplementary Fig. S8, except for 2 species in which oleic acid was not detected, and 98.61% of the tested species have a content greater than 5%, with an average content of 24.71%, and highest proportion of species (22.09% of all tested spieces has a content of 15-20%. The highest Oleic acid (83.35%) was found in Amygdalus davidiana (Carrière) de Vos ex Henry. There are 45 species (7.83%) with an oleic acid content of more than 50% (Supplementary Table S3), which are mainly distributed in the families of Rosaceae (13 species), Umbelliferae (7 species), Betulaceae (3 species), Oleaceae (3 species), Lamiaceae (2 species), Fagaceae (2 species), Verbenaceae (2 species), Loniceraceae (2 species), Araliaceae (2 species), etc (Supplementary Fig. S8B).
Linoleic acid (C18:2):Linoleic acid is the most important component in vegetable oils. The analysis results (Supplementary Table S4 and Supplementary Fig. S8C) showed only in one species was linoleic acid not detected and 98.83% of species have a content greater than 5%, 30.3% of species have linoleic acid content higher than 50%. Linoleic acid content basically showed a normal distribution with an average content of 39.42% and the median 40%-45%. The species with linoleic acid content lower than 30% accounted for 34.4%. Since the cetane number of linoleic acid is relatively low, only 38.2, which is less than the standard (49), it is better to have a relatively low content of this component.
Linolenic acid (C18:3):The cetane number of linolenic acid is 20.6 (Bamgboye and Hansens 2008), which is the lowest among the tested components, so the lower the content, the better. Supplementary Fig. S8D shows that the average content of linolenic acid in all tested species is 8.83%, and there are 132 species (22.95% of all speices) with a linolenic acid content greater than 12%. The linolenic acid content are higher than 30% in 57 species, mainly distributed in Labiatae (7 species), Cruciferae (7 species), Leguminosae (6 species), Rosaceae (5 species), Berberidaceae (5 species), Euphorbiaceae (4 species), Ranunculaceae (4 species), Paeoniaceae (3 species), Rhamnaceae (3 species), Rutaceae (2 species), as well as Eucommiaceae, Fangsiaceae, Impatiaceae, Juglandaceae, Zygophyllaceae, Nyssaceae, Eupteleaceae, Actinidiaceae, Taxodiaceae and Celastraceae.
Arachidic acid(C20:0)and arachidic acid (C20: 1):The distributions of the arachidic acid and arachidic acid contents among tested species are similar (Supplementary Fig. S9) The contents of C20:0 and C20:1 in most species is lower than 1%, with the average content of arachidic acid 0.73%, the average content of arachidic acid 1.31%, and the content of arachidic acid is slightly greater than that of arachidic acid. The highest arachidic aicd content (17.98%) was detected in Daucus carota L. of the Umbelliferae. Other species with an arachidic aicd content greater than 10% included: Rubia cordifolia L. (10.38%) of the Rubiaceae and Cryptomeria fortunei Hooibr. (10.78%) of the Taxodiaceae, Clematis grandidentata (Rehder et E. H. Wilson) W. T. Wang (11.41%) of the Ranunculaceae, and Amygdalus mongolica (Maxim.) Ricker (12.89%) of the Rosaceae. The species with arachidic acid content higher than 5% accounted for 6.8% and the highest content was found to reach more than 40% in Koelreuteria bipinnata (42.97%) and Koelreuteria paniculata Franch. (42.69%) of the Sapindaceae. Other species with a content higher than 20% included Pittosporum truncatum Pritz. (35.44%) of the Pittosporaceae, Rhododendron micranthum Turcz. (25.07%) of the Ericaceae, and Sapindus saponaria L. (21.64%) of the Sapindaceae.
Predicted cetane number value
The predicted cetane number of tested vegetable oils and fats is shown in Fig. 7. The cetane number in most plant species (74.0%) is among 44-58, and among them, 41 species (account for 7.1% of the tested plant species) meet the national biodiesel standard, mainly distributed in the families of Rosaceae, Anacardiaceae, Betulaceae, Fagaceae, Oleaceae, Umbelliferae, Theaceae, Celastraceae, etc. Taking into account the error of the predicted value, plants with a cetane number greater than 44 can also be used as candidates. In this case, suitable species can be expanded to 143 (24.9%).
Recommend promising plant species based on oil content, iodine value, linolenic acid content and predicted cetane number
The results showed that 60.87% of species with oil content greater than 20% have a cetane number greater than 49 (Table 2). According to the oil content greater than 30%, iodine value ≤120 g/100 g, cetane number ≥49, only 51 plants meet the standard, namely Rosaceae: Amygdalus mongolica (Maxim.) Ricker, Amygdalus davidiana (Carrière) de Vos ex Henry, Amygdalus triloba f. multiplex, Amygdalus triloba (Lindl.) Ricker; Celastraceae: Euonymus japonicus Thunb. and Euonymus maackii Rupr.; Euphorbiaceae: Sapium sebiferum (L.) Roxb.; Betulaceae: Corylus heterophylla Fisch. ex Trautv.; Theaceae: Camellia oleifera Abel. Based on the above analysis, and combined with the field investigation, the following promising non-grain diesel energy plants are initially recommended:
(1) Rosaceae plants: Amygdalus davidiana (Carrière) de Vos ex Henry and Armeniaca sibirica (L.) Lam, are characterized by strong adaptability, high yield and high oil content. Their oil could be used to produce qualified biodiesel. They may be used for food and biodiesel feedstock and showed a good development prospect for comprehensive use.
(2) Magnoliaceae plants: Yulania denudata (Desr.) D. L. Fu, Yulania biondii (Pamp.) D. L. Fu, Magnolia grandiflora L., Magnolia officinalis Rehd. et Wils. and Magnolia sieboldii K. Koch, etc. It is a popular ornamental plant with a high oil content in its seeds. It can be used to produce qualified biodiesel, which can also be used for afforesting or as ornamental plant.
(3) Celastraceae plants: Euonymus japonicus Thunb., Euonymus maackii Rupr. and Euonymus macropterus Rupr., etc. They are greening tree species with high oil content, can be used for afforesting and biodiesel.
(4) Theaceae plant: Camellia oleifera Abel, has a high yield, suitable for both energy and food, and suitable for development in the southern part of Henan provinve.
(5) Euphorbiaceae plant: Sapium sebiferum (L.) Roxb., the fruit yield and the oil content are high.
(6) Sapindaceae plant: Koelreuteria paniculata Laxm., a greening tree species, although the oil content is not very high, only 20%, the seed yield is high. After the leaves are dry, the seeds are left on the tree, shake the tree body, the seeds can fall, which is convenient for seed collection.
(7) Anacardiaceae plant: Rhus typhina L. and Toxicodendron vernicifluum F. A. Barkl.. They ae green ornamental plants with medium oil content in seeds but high seed yield.