Auxiliary energy-assisted biodiesel production data from solid food waste oil

A number of samples from solid food waste oil (SFWO) from different restaurants have been collected. Data regarding fatty acid profile, acid value, water content and kinematic viscosity were used for characterization purposes. Response surface methodology data has been used to carry out conventional transesterification optimization. The quality of the final product has been checked following the European biodiesel standard EN14214. To compare conventional and ultrasound-assisted transesterification results, energy consumption and reaction time data have been gathered. More information and result interpretation may be found in “Optimization of solid food waste oil biodiesel by ultrasound assisted transesterification” [1].

Renewable Energy, Sustainability and the Environment Specific subject area Solid food waste recycling to produce biodiesel through ultrasound-assisted low-cost transesterification  Type of data  Tables  Figures  Excel file  How data were acquired Gas chromatography, analytical analysis, Box-Behnken design, response surface methodology, mass spectrometry.

Value of the Data
• These data provide physico-chemical and energy properties of a variety of restaurant organic residues that may be used to provide a recycling model through the concept of a biorefinery. • Scientists working in biorefinery design and development may benefit from these data, besides biodiesel manufacturers. • These data may be part of a wider pool of data, including agrifood residues, that may be used to design a valorization strategy.

Data description
In the excel file SFWO brief.xlsx, sheet no. 1, raw data related to characterization of solid food waste oil (SFWO), belonging to solid residues from tested restaurants, is provided [1] . Information shows fatty acid content and distribution, besides length of chain (LC) and total unsaturation degree (TU). Characterization also includes raw data of some of the most relevant physico-chemical properties (considering the feasibility of the conversion of this oil into biodiesel), namely acid value, water content and kinematic viscosity ( Table 1 ).
For classification purposes, the comparison between a wide variety of oils and SFWO is provided by principal component analysis, shown in Table 2 . Principal component 1 (PC1) includes oils with a combination of C16:0 and C18:1 fatty acids, while PC2 includes only the presence of C18:2.
Transesterification was preceded by acid esterification, due to the high oil acid value. Raw data about evolution and reduction of the acid value during esterification is shown in Table 3 . Sheet no. 2 (excel file SFWO brief.xlsx) shows gas chromatography results (raw and analysed data) from the analysis carried out following a design of experiments (DOE) for SFWO transesterification. Fatty acid content was provided, besides ester yield, before and after cleaning process. Table 4 includes resulting fatty acid methyl ester (FAME) yield (measured by gas chromatography) under both conventional transesterification (CT) and ultrasound-assisted transesterification (UT), including standard deviation (SD). Table 5 exhibits the trend of glyceride (mono-, di-and triglycerides) concentration vs . time, during ultrasound-assisted transesterification. Calibration curves are also provided ( Table 6 and Figs. 1-4 ). Table 7 show energy analysis to compare energy consumption under both conditions, namely conventional and ultrasound-assisted transesterification. For this purpose, a new "energy use index" parameter has been defined ( Eq. (1) ).    Where, LHV is low calorific value (J/g) and CE is the amount of energy per mass unit required for its synthesis (J/g). Table 8 includes biodiesel properties, following European biodiesel standard EN 14,214. Finally, Table 9 includes a detailed quantitative analysis of metal content by inductivity coupled plasma mass spectrometry (ICP-MS).

Experimental design, materials, and methods
After collecting SFW samples from four restaurants during several weeks and seasonally (see [1] for more details) and once inorganic residues were discarded (plastics, etc.) they were mixed  together, homogenized, lyophilized and stored at 4 °C, oil was extracted using Soxhlet method. Lipids were winterized under centrifugation at 20 0 0 rpm, during 10 min, at 0 °C, as explained in [1] . For each analysis, three replicates were considered (samples 1-3), while four points were used to design each calibration curve. Oil was characterized as previously mentioned. Principal component analysis was used to classify the lipids considering most frequently used oils to provide biodiesel through transesterification. Acid value was measured to check whether a pre-treatment consisting in an acid esterification, prior to transesterification, was needed. Ex-   perimental design was performed with Statgraphics Centurion XVI software and Box-Behnken design [1] . Ultrasound-assisted transesterification was carried out with a sonicator probe Q700 QSonica LLC, under a frequency of 20 kHz, 100% duty cycle and 50% amplitude. The consumption of energy was analyzed using Eq. (1) and two Fluke power analyzers working at 10 0 0 V rms and     1250 V rms, respectively. More details are provided in reference [1] . Biodiesel characterization was carried out following European biodiesel standard EN 14,214. Metal content was analyzed using by ICP-MS.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.