(93d) Design of Synthetic Fuels and Value-Added Chemicals Derived from Natural Gas via Combined Experimental and Statistical Methodology

Gas-To-Liquids (GTL) technology is increasingly becoming an attractive source of ultra-synthetic clean fuels, such as jet fuel. However, synthetic fuels still face challenges in acquiring certification based on their properties. The focus of our work is to conduct systematic experimental campaigns to determine the physical properties of synthetic fuel blends, along with statistical and visualization campaigns to find optimum blend compositions that meet industry standards. Through a series of distinct phases and with local funding from the Qatar National Research Fund (QNRF) and Qatar Science and Technology Park (QSTP) our research team has built an extensive Fuel Characterization Laboratory at Texas A&M at Qatar (TAMUQ).

Our methodology involved generating series of surrogate synthetic jet fuel blends, using base components designed to represent the main hydrocarbon groups present in GTL fuels (i.e. normal-, iso- and cyclo-paraffins) besides other hydrocarbon groups (e.g. aromatics). The blends were tested for certain key physical properties such as density, heat content, freezing point, flash point and viscosity following the standard testing procedures as defined by the ASTM. The subsequent data analysis, using linear regression and Artificial Neural Networks (ANN) to correlate the data, allowed us to map composition-property relationships for the given fuel blends. This will enable the identification of areas within the sample space where the fuel blend has optimum properties for use as aviation jet fuel.

In our latest experimental campaign we studied the influence of aromatic additives (e.g. toluene) on the fuel blend properties [1]. Aromatics improve the fuel density, which one of the major challenges to certify these synthetic fuels. It also enhances its elastomer compatibility and lubricity. The percentage of aromatics added was limited based on ASTM specification to a maximum of 25% in order to comply with environmental regulations. The results from this campaign were used to build a 3D visualization model which will be a used as a predictive tool to help optimize the new generation of synthetic Jet fuels. In this campaign the blends were limited in carbon number range in order to focus on the effect of hydrocarbon groups in determining the blend properties; however, to improve on the model we are currently expanding on our study to include a wider range of carbon numbers (e.g. C9-13, the conventional jet fuel range), by using boiling-range cuts of real GTL fuels mixed with pure solvents, where applicable. In addition we are looking at the effect of different aromatic additives (e.g. mono- and bi-aromatics) on fuel properties.

Our future efforts will be directed towards finding alternatives to replace aromatics with heavy paraffinic hydrocarbons to minimize their composition in jet fuels, and our multidimensional visualization techniques will significantly improve our understanding of the experimental data and minimize the experimental data needed to identify the optimum compositions of synthetic fuel blends.

References:

[1] Elmalik, Elfatih; Raza, Bilal; Warrag, Samah; Ramadhan, Haider; Alborzi, Ehsan; Elbashir, Nimir  (2013) "Role of Hydrocarbon Building Blocks on GTL Derived Synthetic Jet Fuel Characteristics"  Ind. Eng. Chem. Res. (in press). Available online at: http://dx.doi.org/10.1021/ie402486c.