(307b) Vegetable Oil Process Intensification with Sterically Hindered Alcohols to Biofuels and Biochemicals

Vegetable oils, refined to different degrees, are the raw material to manufacture biodiesel. Commercial batch times can exceed 8 h due to poor mass transfer and miscibility between oil and methanol. Moreover, free fatty acids methyl esters (FAME) have a cloud point (CP) and pour point (PP) ranging from −3 °C to 12 °C and −15 °C to 10 °C, respectively [1], i.e. poor cold flow properties unsuitable for most climates unless blended with petro-diesel. Substituting methanol with branched alcohols to transesterify or esterify vegetable oil matrices improves the cold flow properties of the fatty alkyl esters. For example, the CP and PP of isopropyl esters range from −14 °C to 0 °C and −20 °C to −5 °C, respectively [1]. We propose a fluidized catalytic bed and ultrasound-based processes to either transesterify vegetable oils with alcohols other than methanol or esterify free fatty acids with a trimethylolppropane to produce biolubricants.

A fluidized catalytic bed concurrently transesterified and cracked canola oil with iso-propanol (iPrOH) to fatty acid isopropyl esters in the vapour phase. We alternated the injection of vegetable oil + iPrOH (reaction stage) and air (regeneration stage) to remove the coke from the CaO/Al₂O₃ catalyst. The reaction stages and regeneration stages lasted 2 min. We varied the iPrOH:oil ratio from 35 to 51 (mol:mol) and the air flow for during the regeneration step. The coke yield ranged from 3.5% to 34% and the isopropyl esters yield from 2% to 31%. The highest hydrocarbons yield was 42% (GC analysis). Fluidized beds are excellent candidates for biodiesel process intensification because as little as 10 t of catalyst may produce 80 kt/y of biodiesel, which corresponds to a reactor size at least 10X lower than the current commercial processes [2-4].

We propose a new ultrasonic-assisted mixing device to transesterify vegetable and waste cooking oil with ethanol and iso-propanol in a continuous process. We adapted a 13 mm diameter tip ultrasound probe to a media mill, where a rotating basket circulated the oil: alcohol mixture at 1200 rpm in the vicinity of the tip [5]. The alcohol:oil ratio was stoichiometric and we adopted KOH as basic catalyst. Ultrasound operated at 20 KHz and 500 W nominal power and with pulses 1 s on and 1 s off. After 1 min reaction, 40 %, 55 % and 90 % oil converted to isopropyl, ethyl and methyl esters, respectively. In absence of ultrasound, the same conversions were reached after 2 hours. Ultrasound creates a very fine oil: alcohol emulsion that increases the contact among the reagents and the catalyst.

Vegetable oils as biolubricants suffer from poor oxidative stability because of the hydrogen in b position to the ester groups, which have the tendency to give b-elimination [6]. Trimethylolpropane (TMP) esterify free fatty acids to biodegradable and stable tri-esters whose application is as biolubricants. We apply ultrasound to esterify oleic acid with TMP with heterogeneous catalysts including Al₂O₃-supported H₃PW₁₂O₄₀ and sulphated ZrO₂ systems. We vary the power amplitude (20 to 60 % of 500 W) and adopt different ultrasound pulses lengths. Sulphated zirconia systems convert over 80 % of substrate in 2 hours, while Al₂O₃-supported H₃PW₁₂O₄₀ is mostly inactive.

References

[1] Joshi R.M., Pegg M.J., Flow properties of biodiesel fuel blends at low temperatures, Fuel, 2007, 86:143–151

[2] Boffito D.C., Galli F., Pirola C., Patience G.S., CaO and isopropanol transesterify and crack triglycerides to isopropyl esters and green diesel, Energ. Conv. Mangement., 2017, 139, 71-78

[3] Boffito D.C., Neagoe C., Edake M., Pastor-Ramirez B., Patience G.S., Biofuel synthesis in a capillary fluidized bed, Cat. Today, 2014, 237, 13–17

[4] Boffito D.C., Blanco-Manrique G., Patience G.S., One step cracking/transesterification of vegetable oil: Reaction–regeneration cycles in a capillary fluidized bed, Energ. Conv. Manage., 2015, 103, 958–96

[5] Boffito D.C., Galli F., Martinez P.R., Pirola C., Bianchi C.L., Patience G.S., Transesterification of triglycerides in a new ultrasonic-assisted mixing device, Chem. Eng. Trans., 2015, 43, 427-432.

[6] Zaccheria F., Mariani M., Psaro R., Bondioli P., Ravasio N., Environmentally friendly lubricants through a zero waste process, Appl. Catal. B., 2016, 181, 581–586