Ionic liquid is a green solvent and catalyst. A new approach of using dimethyl carbonate (DMC) catalyzed by sulfonated imidazolium ionic liquid (SIIL) producing glycerol-free biodiesel was developed. Together with the fatty acid methyl ester (FAME), the other two products fatty acid 1,3-dimethoxypropyl ester and 1,3-dimethoxypropan-2-ol were also generated, which could be used as an oxygenate additive without separation from biodiesel. The overall reaction pathway was resolved upon the product analysis, which could well explain the whole process and product distributions. In this paper, the effects of the molar ratio of DMC/rapeseed oil, catalyst dosage, reaction temperature, and reaction time were explored. The highest yield of FAME with the SIIL catalyst 1-propylsulfonate-3-methylimidazolium hydrogen sulfate ([PrSO3HMIM][HSO4]) reached 95.77% under optimum conditions.

•Pore-broadened Al-SBA-15 was synthesized by tuning the hydrophobic core size.•Template micelle was sensitive to changes of temperature and TMB contents.•40–60 °C assembling temperature got high structure regularity, otherwise order lost.•18 nm highly-ordered pores were obtained at a TMB/P123 ratio of 0.25.•Catalytic acid sites were well reserved when broadened by TMB.A series of pore-broadened Al-SBA-15 samples were synthesized using a direct hydrothermal method. The effects of aluminum incorporation, assembling temperature, and co-solvent (1,3,5-trimethylbenzene (TMB)) content were investigated by low-angle XRD, N2 adsorption and desorption isotherm analysis, SEM, TEM, NH3-TPD, FTIR, pyridine-IR, and 27Al NMR. The results indicated that aluminum incorporation (Si/Al ratio = 10) increased the pore size of SBA-15 from 5.66 to 10.13 nm. A small pore size of 6.55 nm was observed at a low assembling temperature of 30 °C, attributing to the inadequate stretching of the molecular template. An increased pore size of 8.45 nm was obtained at an assembling temperature of 60 °C because of the partial hydrophobization of the hydrophilic groups, whereas a high temperature of 70 °C resulted in the generation of least ordered pores. The hydrophobic co-solvent TMB showed a significant broadening level as a result of its effective fusion into the hydrophobic micelle cores. A highly ordered pore framework with a pore size of 18 nm was obtained at a TMB/P123 ratio of 0.25, which was found to be optimum. More or less TMB led to the generation of mesocellular silica-aluminum foams with a complete loss of regularity. The 27Al NMR results showed that aluminum was mostly tetrahedrally coordinated. The NH3-TPD and pyridine-IR detection results indicated that a number of weak and medium acid sites (as Bronsted and Lewis acid sites) existed in Al-SBA-15 pore-broadened by TMB.

Four kinds of imidazolium ionic liquids (ILs) were employed to catalyze the transesterification reaction of rapeseed oil. The effects of molar ratio of methanol to rapeseed oil, catalyst dosage, reaction temperature, and reaction time, and the deactivation of water on catalytic activity were explored. The results showed that imidazolium ILs with long alkyl chains and sulfonated groups exhibited the best catalytic activities due to their strong Brønsted acidity. The catalytic activity was depend on the SO3H group in the cation, not the anion HSO4−. Water molecules competed with the anion to bind with the protons of the imidazolium cation. This results in the disruption of the structure of ILs, leading to deactivation; increasing the reaction temperature could alleviate this negative effect of water. The yield of fatty acid methyl ester (FAME) remained constant (∼85%) at 130 °C, when the water content increased from 1 wt% to 5 wt%. The highest yield of FAME for the catalyst 1-butylsulfonate-3-methyl imidazolium hydrogen sulfate ([BSO3HMIM][HSO4]) could reach 100% under optimum conditions.

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8–25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6–C8 olefins over the catalysts' Brønsted acid sites; these underwent Diels–Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6–C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Brønsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.

A new vision of using carbon dioxide (CO2) catalytic processing of oleic acid into C8–C15 alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO2 atmosphere. The yield of C8–C15 ingredients reaches 73.10 mol% in a CO2 atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H2) atmosphere. In the absence of an external H2 source, products which are similar to aviation fuel are generated where aromatization of propene (C3H6) oxidative dehydrogenation (ODH) involving CO2 and propane (C3H8) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO2 atmosphere is significantly different from that in the H2 atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H2 spillover is observed in the H2 atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H2. The CO2 processing of oleic acid described in this paper will significantly contribute to future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel.

•A preparation-free gasified-straw slag as solid base catalyst for biodiesel production.•The catalyst shows superior stability and activity in 33-run test.•Three crystallites, quartz, åkermanite, and leucite are included in the catalyst.•Fixed-crystal-structure was responsible for the excellent stability.•Basic sites include low-coordination oxygen anions, OH groups, and metal-oxygen pairs.A novel solid base catalyst derived from gasified straw slag for producing biodiesel was prepared by simple pulverization and sieving. This catalyst exhibited high stability, low leaching of the catalytic species, and good catalytic activity, caused by high-temperature melting in the biomass gasifier. SiO2, CaO, K2O, MgO, FeO, and Al2O3 were the common constituents (calculated as oxides) as per XRF analysis and EA. XRD and TEM-EDS analysis indicated that the catalyst comprises three crystallites: quartz, leucite, and åkermanite. The catalyst was strongly basic with a basic site concentration of 0.3974 mmol⋅g−1, including strongly basic low-coordination oxygen anions, moderately basic OH groups, and metal–oxygen pairs, as identified by CO2-TPD and IR. TGA results indicated that the catalyst is thermally stable up to 400 °C, which is greater than the typical reaction temperature. BET analysis results indicated that the slag exhibits a broad pore distribution with pore diameters of 5–15 and 45–75 nm. The catalyst exhibited high catalytic activity and stability, exhibiting a fatty acid methyl ester (FAME) conversion of 95% for transesterification conducted at 200 °C for 8 h with a catalyst dose of 20% and a methanol–oil molar ratio of 12:1. The FAME conversion remained greater than 85% even after reusing the catalyst for 33 reactions without any appreciable loss of catalytic activity. Small amounts of K and Mg (<10 ppm) leached into the product from the catalyst. These results indicated that the gasified straw slag catalyst demonstrates promise for producing biodiesel.Download high-res image (145KB)Download full-size image

•A new membrane-blot assay was developed for screening in directed evolution.•The membrane-blot assay balance colony growth and enzyme absorption and increase the clarity of coloration so as to increase the success rate of screening.•Thermostability and methanol tolerance of the developed RML mutants was improved.•Our assay may also be used for screening in the directed evolution of other lipases.Directed evolution has been proved an effective way to improve the stability of proteins, but high throughput screening assays for directed evolution with simultaneous improvement of two or more properties are still rare. In this study, we aimed to establish a membrane-blot assay for use in the high-throughput screening of Rhizomucor miehei lipases (RMLs). With the assistance of the membrane-blot screening assay, a mutant E47K named G10 that showed improved thermal stability was detected in the first round of error-prone PCR. Using G10 as the parent, two variants G10-11 and G10-20 that showed improved thermal stability and methanol tolerance without loss of activity compared to the wild type RML were obtained. The T5060-value of G10-11 and G10-20 increased by 12 °C and 6.5 °C, respectively. After incubation for 1 h, the remaining residual activity of G10-11 and G10-20 was 63.45% and 74.33%, respectively, in 50% methanol, and 15.98% and 30.22%, respectively, in 80% methanol. Thus, we successfully developed a membrane-blot assay that could be used for the high-throughput screening of RMLs with improved thermostability and methanol tolerance. Based on our findings, we believe that our newly developed membrane-blot assay will have potential applications in directed evolution in the future.

•Macroporous resin solid acid (ST-DVB) was synthesized to convert FFAs to biodiesel.•ST-DVB shows higher FFAs conversion with high FFAs oil than commercial resin.•Original water and generated water deactivate the resin catalysts differently.•A linear relationship between original water and esterified FFAs was found.•ST-DVB exhibits a FFAs conversion up to 97.8% and can be reused over 10 times.Using high free fatty acids (FFAs) contents oil as the raw material for biodiesel production can reduce the production cost and make fully use of the bio-oil resources. Macroporous cation exchange resins contain numerous acid sites to catalyze heterogeneous esterification reactions to reduce the FFAs contents and prevent the saponification reaction. This study focuses on the synthesis and performance tests of the macroporous resin catalysts and its water deactivation mechanism. Self-synthesized macroporous cation exchange resins have a surface area of 185 m2 g−1 with an average pore diameter of 9.7 nm and the ion exchange capacity is 3.37 ± 0.11 mmol g−1. Owing to their pore structure, macroporous resin performs better than gel-type resin in low methanol concentration or high FFAs contents, but they show physical instability in reusability tests. The FFAs conversion reaches 97.8% (substrate oil with acid value of 64.9 mg KOH/g) under 100 °C and a methanol/FFAs molar ratio of 15:1 with 10 wt% catalyst loading. Water that originally exists in oil or that is produced in the reaction deactivates differently on the activity of the resin, but this deactivation can be decreased by increasing the reaction temperature. In this study, a linear relationship between original water content and esterified FFAs was identified and differences in deactivation models were investigated.

Rhizomucor miehei lipase (RML) is an industrially important enzyme, but its application is limited due to its high cost. In this study, a series of measures such as codon optimization, propeptide addition, combined use of GAP and AOX1 promoters, and optimization of culture conditions were employed to increase the expression of RML. Three transformants of the constitutive-inducible combined Pichia pastoris strains were generated by transforming the pGAPZαA-rml vector into the pPIC9K-rml/GS115 strain, which resulted in high-expression yields of RML. Using the shake flask method, highest enzyme activity corresponding to 140 U/mL was observed in the strain 3-17, which was about sixfold higher than that of pPIC9K-rml/GS115 or pGAPZαA-rml/GS115. After optimization of culture conditions by response surface methodology, the lipolytic activity of strain 3-17 reached 175 U/mL in shake flasks. An increase in the copy number simultaneously with the synergistic effect provided by two promoters led to enhanced degree of protein expression.

A kind of Fe(II)-Zn double-metal cyanide (DMC) complexes solid catalyst was prepared through coreaction of potassium ferrocyanide, zinc chloride, and complexing agent of tert-BuOH. The catalyst has highly catalytic activity on the simultaneous transesterification of triglycerides and esterification of free fatty acids (FFA) reactions. The effect of various factors on the reaction was studied, including different cocomplexing agents, DMC catalyst amount, reaction temperature, methanol/oil molar ratio, reaction time, and water and fatty acid content in raw materials. High catalytic activity was observed for DMC under relatively higher content of water or FFA. Under the optimum condition, the methyl ester yield can reach 98%. The 93.45% catalyst can be recovered after 6 cycles.

Ca2MgSi2O7 has been investigated in the transesterification of rapeseed oil with a view to determining its viability as a solid base catalyst for use in biodiesel synthesis. This catalyst exhibited both high catalytic activity and reusability, giving a fatty acid methyl ester (FAME) conversion of 99% when the reaction was conducted with 20 wt% catalyst and a methanol/oil molar ratio of 10:1 at 190 °C over 6 h. The FAME conversion remained >85% after 16 cycles without catalyst compensation. BET test illustrates that Ca2MgSi2O7 has a narrow pore size distribution centred at 5.0 nm. Transesterification takes place on the catalyst surface, the basic characteristics or basicity of the catalyst decide greatly catalytic activity. CO2-TPD analysis showed that the total number of basic sites of åkermanite is 0.8822 mmol·g−1. This includes three different oxygen anions exhibiting different chemical environments on the catalyst surface. The basic strength of oxygen anions increased in the order O2 < O3 < O1, which were identified by XPS. In addition, the excellent reusability of the catalyst was associated with the presence of stable [MgO4] and [CaO8] structures. These results suggest that Ca2MgSi2O7 is a promising catalyst for biodiesel synthesis.

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8–25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6–C8 olefins over the catalysts' Brønsted acid sites; these underwent Diels–Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6–C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Brønsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.