Downstream seperation of new green fuel fractions

By Hochschule Bremerhaven

In the framework of the FLEXI-GREEN FUELS project the activities of BHV focused on two closely related fields of application. Therefore, promising separation sequences were conceptualized based upon the topological analysis of the feed stream compositions produced in WP5 (the upstream work package). In a second step, attractive schemes were rigorously modelled and simulated by use of computer aided process engineering (CAPE) tools, in particular the software packages of the Aspen One Engineering Suite (ASPEN), to quantify the performances of the individual set-ups. Finally, experimental fractionation of promising crude bio-oil mixtures was performed to create new fuel candidates for aviation and shipping applications.

A number of samples have been produced and analysed. A promising fuel candidate was an optimised hydrodeoxygenation (HDO) product (sample code FGF0069) from black soldier fly larvae lipid wax. The respective sample FGF0069 contained only very small amounts of components like sulfur (Thiols, thiophenes) and oxygen (Ketones, FAME’s) containing species and unsaturated species e.g. alkenes which are considered undesirable in jet fuel blending components.

The major group of components present in the stream were N-alkanes. Further, there was a small percentage of Iso-alkanes as well as cyclo-alkanes present. The amount of alkenes present was almost negligible. The mass flow rate was calculated assuming a basis of 1000 kg/hr mass flow rate for simulation purposes.

The simulations were performed in AspenPlus. A sketch of the fractionation sequence used is shown below.

The stream of interest in this case, was the stream coming out from the top of the distillation column, which is TOPPROD1 (see table below). The sequence was designed in such a way that the targeted final product had components in the boiling range of approximately 190°C to 300°C. A comparison with a typical Jet A-1 fuel composition is shown in the figure below (on the right side).

The figure above (on the right side) shows plots of the simulated mass fractions of stream TOPPROD1 and also mass fractions of a conventional JET-A1 fuel are shown. The mass fractions of undesired components (right from dotted line) are at a low level and mass fractions of desired components are comparable to those of a JET A1 fuel except the peak for ALKANC11 – Undecane. It can be concluded that undesired components can be “separated” by distillative fractionation into two streams the top product (light mass fraction) and the bottom product (heavy mass fraction). While the top product is suited for aviation fuel purposes, the bottom product can be used for shipping fuel applications.

In a next step an experimental fractionation by distillation of the large HDO-oil sample FGF0092 (based on FGF0069) produced by the upstream partner from University of Thessaloniki was performed. Therefore, a vacuum distillation apparatus (Rotational Evaporator) was used and the experimental set-up is depicted below (on the left side).

The HDO-oil sample has been fractionated into a light fraction and a heavy fraction which are depicted in the figure above (on the right). The targeted thermal “cut” was 275°C at 1,013 bar.

The resulting mass fractions have been determined to 55,95 mass-% of the light fraction and 42 mass-% of the heavy fraction. The data is visualized below.

Finally, samples of the new fractions were shipped for further analyses and upgrading to the respective project partners from German Aerospace Center (DLR), University of Rostock (UROS) and Hulteberg Chemistry and Engineering AB (HUL).