Comparison of Fuel Properties of Alternative Fuels from Insect Lipids and Their Blending with Diesel Fuel

Abstract

Drop-in fuels are renewable alternatives that can be integrated into an existing fuel infrastructure without modification. Among these, fuels synthesized from hydroprocessed renewable lipids have garnered significant attention owing to their compatibility with petroleum-based diesel. In this study, we investigated the feasibility of hydrodeoxygenated insect oil (HIO), derived from black soldier fly larvae (Hermetia illucens; BSFL), as a renewable drop-in fuel for a diesel blend. The optimal growth conditions for BSFL were studied to maximize lipid production, and the extracted insect oil was subjected to hydrodeoxygenation (HDO) via catalytic reaction. The HIO was blended with commercial diesel at ratios of 5–30%, and its fuel properties were compared with commercial diesel. A detailed fuel property analysis was conducted for the 5% blend to evaluate its suitability as a diesel fuel. Characterization of the blended fuels’ physicochemical properties was carried out to assess the potential of insect-derived fuels for diesel applications.

1. Introduction

Renewable fuels have been demonstrated to play a crucial role in reducing greenhouse gas emissions when compared with fossil fuels [1,2,3]. Among them, drop-in fuels have recently gained attention due to their ability to seamlessly integrate with an existing fuel infrastructure without requiring modifications to storage, transportation, or engine systems [4,5]. This advantage renders drop-in fuels a promising solution for accelerating the transition to sustainable energy sources. Among the various drop-in fuel candidates, hydrotreated vegetable oil (HVO) is particularly promising due to its notable physical and chemical properties. HVO demonstrates a higher cetane number, enhanced cold flow properties, and broader applicability across various transportation sectors, including aviation [6,7]. However, HVO faces several challenges, including high production costs, competition with food resources, and environmental concerns related to land use [8,9]. To address these limitations, increasing attention has been given to non-edible feedstocks for biofuel production.

Insect-derived lipids, particularly those from black soldier fly larvae (Hermetia illucens; BSFL), have garnered attention as a non-edible feedstock for renewable fuel production. BSFL can efficiently convert organic waste into biomass with a high lipid content (approximately 15–49%), presenting an economically viable and sustainable alternative energy source [10,11,12]. This process simultaneously addresses waste management and energy production challenges, potentially overcoming limitations associated with crop-based biofuels. The composition of BSFL lipids is particularly suitable for bio-diesel production, with a high content of medium-chain fatty acids (MCFAs), especially lauric acid (C12:0). This composition contributes to improved cold flow properties and fuel quality when the lipids are converted to biodiesel [13,14]. While most research has focused on converting insect lipids into fatty acid methyl ester (FAME) bio-diesel, the potential for producing hydrotreated oil from insect lipids remains largely unexplored.

In this study, we investigated the potential of hydrodeoxygenated insect oil (HIO) as a drop-in fuel for commercial diesel. We evaluated the fuel properties of the produced HIO and its compatibility as a drop-in fuel by blending it with commercial diesel. To achieve this, we analyzed the rearing conditions of BSFL and the lipid extraction efficiency, followed by the hydrodeoxygenation (HDO) process to convert the extracted lipids into HIO. Furthermore, the fuel properties of HIO, commercial diesel, and their blends were compared to confirm compatibility with existing fuel standards. The results suggest that HIO is a sustainable alternative drop-in fuel.

2. Materials and Methods

2.1. Preparation of Black Soldier Fly Larvae (BSFL) Oil

BSFL were reared at the Korea Beneficial Insects Laboratory Co., Ltd. in Gokseong-gun, Jeollanam-do, Republic of Korea, following the protocol from our previous study [15]. The rearing conditions were maintained as before, with larvae cultivated in experimental boxes (400 × 600 × 150 mm) under controlled conditions (27 ± 2 °C, 65 ± 5% relative humidity, 16:8 L:D cycle). Building upon our previous research, we have expanded the range of dietary treatments. The new diet formulations are detailed in

Table 1. Proportions of different feeding mixtures.

Feeding Mixtures	Meat Byproduct (wt%)	Wet Food Waste (wt%)	Dried Food Waste (wt%)	Processed Food Waste (wt%)
M1	0	100	0	0
M2	20	80	0	0
M3	0	80	20	0
M4	0	50	50	0
M5	30	40	30	0
M6	0	0	0	100
M7	0	20	0	80
M8	0	50	0	50

. BSFL were reared for 6 to 14 days, then harvested and dried. The drying process for the harvested larvae was uniformly carried out using a microwave drying method. Following the drying process, insect oil (IO) was extracted using a screw press (National engineering, Goyang-si, Republic of Korea). To increase the productivity of the BSFL oil, the larvae were subjected to a drying process at temperatures ranging from 100 to 120 °C. The moisture content was determined using the drying method, while the lipid yield was calculated using the following equation:

$$Lipidyield\left(\mathrm{w}\mathrm{t}\mathrm{\%}\right)={\displaystyle \frac{weightofcrudelipid}{weightofdrymatterandcrudelipid}}\times 100$$

2.2. Preparation of the Blends

Commercial diesel was obtained from the Sambo gas station (Anseong, Gyeonggi, Republic of Korea), supplied by GS Caltex. The fuel met the specifications for ultra-low sulfur diesel with a sulfur content below 10 ppm, as reported by the manufacturer, and complies with the Korean diesel fuel standard (KS M 2610:2023) [16].

The HIO was prepared by subjecting the extracted IO to an HDO process. The HDO reaction was carried out in a fixed-bed reactor using a 1 wt% Pt/Al₂O₃ catalyst. The reaction conditions were set at 40 bar hydrogen pressure and temperatures ranging from 340 °C to 440 °C, with a weight hourly space velocity (WHSV) of 1 h⁻¹ [17].

The prepared IO and HIO were blended with commercial diesel fuel at volume ratios of 5%, 10%, 15%, and 30%. The resulting blends were designated as IO 5, IO 10, IO 15, and IO 30 for the insect oil blends and HIO 5, HIO 10, HIO 15, and HIO 30 for the hydrodeoxygenated insect oil blends.

2.3. Analytical Methods

2.3.1. Fourier Transform-Infrared (FT-IR) Spectroscopy

FT-IR spectra were obtained using a Nicolet iS50 FT-IR spectrometer from Thermo Fisher Scientific (Waltham, MA, USA). Measurements were conducted using the attenuated total reflectance (ATR) method with a diamond ATR sample plate. Liquid samples were directly placed on the ATR plate, and infrared light was applied from below for measurement. Each spectrum was recorded from 4000 cm⁻¹ to 400 cm⁻¹ at a resolution of 0.5 cm⁻¹, averaging 32 scans.

2.3.2. Proton Nuclear Magnetic Resonance (¹H NMR)

¹H NMR spectra were recorded using a Bruker AVANCE III 600 spectrometer equipped with a 14.1 Tesla Ascend™ magnet from Bruker (Billerica, MA, USA). The instrument operated at a proton resonance frequency of 600 MHz. Deuterated chloroform (CDCl₃) was used as the solvent for sample preparation. Measurements were performed with the number of scans set to 16. Data acquisition and processing were conducted using Bruker TopSpin 3.1 software. Automated sample handling was performed using SampleXpress Lite.

2.3.3. ¹³C Nuclear Magnetic Resonance (¹³C NMR)

¹³C NMR spectra were obtained using the same Bruker (Billerica, MA, USA) AVANCE III 600 spectrometer. The instrument operated at a carbon-13 resonance frequency of 150 MHz. Samples were prepared in CDCl₃, and the number of scans was set to 1024. Data acquisition and analysis were performed using Bruker TopSpin 3.1 software.

2.3.4. GC Analysis

The prepared blends were analyzed using a gas chromatograph (iGC7200A, DS Science, Gwangju-si, Republic of Korea) equipped with a flame ionization detector for quantification. The column was an Rtx-5MS (30 m, 0.25 mm ID, 0.25 μm) from Restek (Bellefonte, PA, USA). The temperature of the inlet and the detector was 300 °C, and the oven was analyzed under the condition of raising the temperature at a rate of 15 °C/min from 45 °C to 300 °C.

2.3.5. Thermogravimetric Analysis (TGA)

TGA (TGA N-100, Seoul, Republic of Korea) was used to determine the similarity of volatile components in the material. Approximately 50 mg of the sample was loaded into a platinum crucible and heated from 30 °C to 600 °C at a rate of 10 °C/min under a nitrogen (N₂) carrier gas with a flow rate of 15 mL/min.

2.3.6. Physicochemical Fuel Properties

Fuel properties were characterized according to standard test methods [18,19]. The American Society for Testing and Materials (ASTM) standards are committed to international testing (ASTM D4052-22 [20], ASTM D5453-19a [21], and D4737-21 [22]). The Korean Industrial Standards (KS) are the national standards of Korea (KS M ISO 3104:2020 [23] and KS M ISO 2719:2016 [24]).

Density at 15 °C was determined using a digital density meter following ASTM D4052-22. Kinematic viscosity at 40 °C was measured using a calibrated glass capillary viscometer according to KS M ISO 3104:2020. Total sulfur content was analyzed using the ultraviolet fluorescence method following ASTM D5453-19a, which is applicable for liquid hydrocarbons with boiling points between 25 °C and 400 °C. The flash point was measured using a Pensky–Martens closed-cup tester according to KS M ISO 2719:2016. The cetane index was calculated using the four-variable equation method following ASTM D4737-21, which provides a means for estimating the cetane number from density and distillation recovery temperature measurements.

3. Results and Discussion

3.1. Effect of Feeding Mixtures on BSFL Growth

According to previous studies, it was confirmed that food waste feed is economically superior, and insects were grown by changing feeding conditions [25,26]. Therefore, in this study, we further investigated the effect of food waste feed on insect growth performance. The nutrient composition for each substrate is shown in

Table 2. Nutritional analysis of substrates used in the trial.

	Crude Protein (% w/w)	Crude Lipid (% w/w)	Crude Ash (% w/w)	Crude Fiber (% w/w)	Moisture (% w/w)	Salt Content (% w/w)
Meat byproduct	28.3	3.4	2.5	0.2	65.0	trace
Wet food waste	3.0	1.2	3.0	3.0	87.0	1.5
Dried food waste	23.1	9.4	16.6	16.2	3.8	1.2
Processed food waste	4.5	4.6	2.6	2.7	80.7	0.7

. The BSFL were fed with meat byproduct, wet food waste feed, dried food waste feed, and processed food waste.

Table 3. Effects of different feeding mixtures on larval growth performance.

Feeding Mixture	Mean ± SE
	Moisture (%)	Lipid Yield (%)	Feeding Mixture Price (USD/kg)
M1	6.65 ± 0.2	30.21 ± 3.3	0.014
M2	5.71 ± 0.5	25.27 ± 1.0	0.014
M3	6.33 ± 0.1	31.57 ± 2.6	0.008
M4	4.71 ± 0.2	33.2 ± 1.6	0.001
M5	3.89 ± 0.1	26.08 ± 0.5	0.006
M6	4.68 ± 0.5	49.54 ± 1.1	0.210
M7	3.63 ± 0.4	48.71 ± 1.3	0.171
M8	4.02 ± 0.2	45.21 ± 0.5	0.112

shows the lipid yield of BSFL fed with different feed compositions. Among the tested feed conditions, M6 exhibited the highest lipid yield, which was 49.54 ± 1.1%. This indicates that the specific composition of M6 was more effective in promoting lipid accumulation in BSFL compared to other feed types. Although M6 resulted in the highest crude lipid yield, the price of processed food waste as a substrate is high, so it is not economically feasible. In contrast, wet food waste and dried food waste demonstrated relatively high lipid accumulation while being more cost-effective as insect feed sources.

3.2. Fuel Properties Analysis

3.2.1. Properties of Commercial Diesel, IO, and HIO

FT-IR

The extracted IO was converted into HIO through an HDO reaction after a catalytic reaction. In order to identify the various characteristic functional groups and chemical structures present in commercial diesel, IO, and HIO, FT-IR spectroscopy was used. In Figure 1a, the FT-IR spectrum of commercial diesel reveals prominent peaks corresponding to functional groups [27]. Strong absorption bands at 2921.90 cm⁻¹ and 2853.38 cm⁻¹ indicate the presence of C-H stretching in alkanes, thus confirming the dominance of aliphatic hydrocarbons [28]. The peaks observed at 1457.90 cm⁻¹ and 1377.03 cm⁻¹ are attributed to -CH₃ bending vibrations [29,30].

In Figure 1b, the spectrum of IO shows characteristic triglyceride peaks. The strong absorption band at 1742.62 cm⁻¹ corresponds to the C=O stretching of ester groups, confirming the presence of triglycerides [31,32]. Peaks at 2921.73 cm⁻¹ and 2852.52 cm⁻¹ represent the asymmetric and symmetric stretching vibrations of C-H bonds in long-chain fatty acids, and the band at 1112.41 cm⁻¹ indicates C-O stretching in ester linkages.

In Figure 1c, the HIO spectrum exhibits characteristic absorption bands of hydrocarbon compounds. Strong absorption peaks observed at 2920.64 cm⁻¹ and 2852.13 cm⁻¹ are attributed to the asymmetric and symmetric C-H stretching vibrations of alkyl chains, respectively. The presence of CH₂ bending vibrations is confirmed by the peak at 1466.27 cm⁻¹, while the distinctive peak at 720.83 cm⁻¹ corresponds to the CH₂ rocking vibration, which is characteristic of long-chain hydrocarbons [33]. Notably, the absence of the strong carbonyl (C=O) stretching band at 1742.62 cm⁻¹ in the HIO spectrum confirms the effective removal of oxygen-containing functional groups during the hydrodeoxygenation reaction. This indicates that ester linkages in IO were successfully broken down, resulting in the formation of hydrocarbon structures. Furthermore, the disappearance of the C-O stretching band at 1112.41 cm⁻¹ corroborates the removal of oxygenated compounds. The FT-IR spectrum of HIO closely resembles that of commercial diesel, with prominent absorption bands associated with aliphatic hydrocarbons. The strong C-H stretching vibrations indicate the presence of long-chain saturated hydrocarbons, characteristic of diesel fuel components.

¹H-NMR

The chemical compositions of commercial diesel, IO, and HIO were analyzed using ¹H-NMR spectroscopy, with the resulting spectra presented in Figure 2. In Figure 2a, the ¹H-NMR spectrum of commercial diesel exhibits strong signals in the 0.8–1.5 ppm region, corresponding to the methyl (-CH₃) and methylene (-CH₂-) protons of aliphatic hydrocarbons. Weak signals between 2.0 and 2.5 ppm are attributed to α-methylene protons (R-CH₂-C=), suggesting the presence of branched or partially unsaturated hydrocarbons. Additionally, a set of multiplet peaks between 6.5 and 7.2 ppm can be observed, which correspond to aromatic protons, confirming the presence of aromatic compounds in diesel [34].

The IO has been found to exhibit triglyceride characteristic peaks as revealed in Figure 2b. Two doublets of doublets with resonances centered at 4.14 and 4.30 ppm were assigned to the protons of the -CH₂-OCOR fragments of the glycerol portion. Notably, peaks in the 5.4 ppm region correspond to olefinic protons (-CH=CH-), and peaks in the 2.0 ppm region correspond to allylic protons (CH₂-CH=CH), suggesting the presence of unsaturated fatty acids in IO [35].

In Figure 2c, the ¹H-NMR spectrum of HIO shows significant changes compared to IO. The olefinic proton signal at 5.2–5.4 ppm is nearly absent, indicating that the hydrogenation process has effectively eliminated most unsaturated bonds. The peaks in the 0.8–1.5 ppm region, attributed to methyl and methylene protons, signify the increased content of saturated hydrocarbons. The observed spectral changes indicate that the HDO reaction has effectively converted IO into a saturated hydrocarbon mixture, which is chemically similar to commercial diesel.

¹³C-NMR

As illustrated in Figure 3a, the ¹³C-NMR spectrum of commercial diesel is indicative of various hydrocarbon functional groups. The spectrum predominantly exhibits signals within the 10–40 ppm range, indicative of methyl (-CH₃) and methylene (-CH₂-) groups, which are characteristic of aliphatic hydrocarbons. Furthermore, the presence of weaker peaks at 120–140 ppm is indicative of olefinic or aromatic carbons, suggesting the presence of unsaturated or aromatic components in the diesel sample. These spectral features confirm that the diesel primarily consists of saturated and unsaturated aliphatic chains with minor aromatic contributions [36].

The ¹³C-NMR spectrum of IO in Figure 3b reveals peaks corresponding to hydrocarbon chains and functional groups associated with lipid-based feedstocks. Peaks between 120 and 140 ppm suggest the presence of unsaturated carbons, likely from residual olefinic structures. The signals detected at 170–180 ppm were related with ester or carboxyl carbonyl groups in the triglyceride [37].

In Figure 3c, the ¹³C-NMR spectrum of HIO exhibits characteristic signals corresponding to saturated hydrocarbons, thus confirming the effective removal of oxygenated compounds. The dominant peaks in the 10–40 ppm region correspond to methyl (-CH₃) and methylene (-CH₂-) groups, which are characteristic of paraffinic hydrocarbons. The absence of significant signals in the 170–180 ppm range, previously observed in the IO, indicates the complete removal of ester or carboxyl carbonyl groups through the hydrodeoxygenation reaction. Furthermore, the absence of significant peaks in the 120–140 ppm range suggests the elimination of unsaturated carbons.

3.2.2. Properties of Blends

IO Blends

In order to establish a comparison basis for assessing the impact of blending HIO with commercial diesel, initial trials were carried out using IO as the blending component for comparison. The blending ratio was expected to influence the physicochemical properties of the resulting fuel. Thus, it was essential to observe and confirm these property changes to assess the compatibility of the IO blend with commercial diesel. The blending of IO with diesel resulted in noticeable changes in the color of the fuel. While commercial diesel exhibited a pale-yellow color, the addition of IO progressively altered the blend’s color to shades of brown, as illustrated in Figure S1a.

TGA was performed on the IO and commercial diesel blends, and the results are shown in Figure S2a. As the blending ratio of insect lipids increased (5%, 10%, 15%, and 30%), the TGA profiles deviated significantly from that of pure commercial diesel. For diesel, most of its components volatilized below 300 °C. However, with increasing insect lipid content, a larger fraction of the fuel exhibited volatility above 300 °C.

Gas chromatography–flame ionization detection (GC-FID) analysis was conducted to examine the hydrocarbon distribution in the blends. In Figure S2b, the analysis of commercial diesel revealed a distinct n-paraffin distribution characteristic of diesel fuel. It was expected that blending with IO would introduce hydrocarbons outside the typical diesel range. As expected, IO cannot be vaporized during GC-FID analysis due to its high boiling point (above 350 °C), and thus the method used in this study could not effectively analyze the hydrocarbon composition of the blends.

HIO Blends

Following the evaluation of IO blends, HIO was blended with commercial diesel to assess its compatibility as an alternative drop-in fuel. To evaluate the physicochemical differences between the blends, HIO was mixed with commercial diesel at 5%, 10%, 15%, and 30% by volume. Unlike IO-commercial diesel blends, the HIO-commercial diesel blends showed minimal color variation, similar to that of the commercial diesel shown in Figure S1b. The TGA results in Figure 4a demonstrate similarity to those of commercial diesel, despite the blended content of HIO reaching 30%. The TGA results indicate that despite the increasing HIO content up to 30%, the thermal decomposition profile of the blended fuel closely resembled that of commercial diesel, suggesting similar volatility and thermal behavior.

The chemical composition of the HIO blends was further analyzed using GC-FID, as shown in Figure 4b. The HIO predominantly consists of normal alkanes ranging from C11 to C18, which are derived from the fatty acids present in insect lipids [15]. As the HIO content in the blend increased, the peak intensity of normal alkanes also increased, indicating a higher proportion of saturated hydrocarbons in the fuel.

A distinguishing feature of IO, compared to conventional vegetable oils, is its high lauric acid (C12:0) content [38]. Most plant-based feedstocks primarily consist of C16–C18 fatty acids [39,40], which, upon hydrodeoxygenation, predominantly yield hydrocarbons with carbon numbers of C15 and above [41]. Consequently, the composition of hydrodeoxygenated vegetable oils results in a higher proportion of long-chain paraffins, resulting in a distinct composition compared to commercial diesel.

In contrast, HIO contains both low- and high-boiling-point hydrocarbons, ranging from C11 to C18. This broader distribution more closely aligns with the carbon range of commercial diesel, resulting in improved blending compatibility compared to hydrodeoxygenated vegetable oils. The presence of shorter-chain hydrocarbons in HIO contributes to enhanced volatility and cold flow properties [42], making it a more suitable candidate for blending commercial diesel.

3.2.3. Comparison of Fuel Properties

A comparative evaluation of commercial diesel, HIO, and the 5% HIO blend (HIO 5) reveals key characteristics that influence their potential as alternative fuels. The results and analysis of their fuel properties are presented in

Table 4. Fuel properties of commercial diesel, HIO, and HIO 5 compared to diesel standard.

		Experimental Values			Standard Values
Property	Unit	Commercial Diesel	HIO	HIO 5	Diesel Standard No. 1-D S15 (ASTM D975)
Density at 15 °C	kg/m3	823.1	770.2	820.0	-
Kinematic viscosity at 40 °C	mm2/s	2.205	2.196	2.182	1.3–2.4
Sulfur	mg/kg	6.7	Max 1.0	5.6	Max 15
Flash point	°C	43	72.0	43	Min 38
Cetane index	NA	49.4	84.8	51.7	Min 40

. The density at 15 °C for commercial diesel measured 823.1 kg/m³, which is compatible with other studies [43,44], while HIO showed a lower density of 770.2 kg/m³. The blended HIO 5 exhibited an intermediate density of 820.0 kg/m³, indicating that the addition of HIO slightly reduces the density. The kinematic viscosity at 40 °C showed minimal variation across all samples, with values of 2.205, 2.196, and 2.182 mm²/s for diesel, HIO, and HIO 5, respectively. These viscosity values fall within the acceptable range specified by ASTM D975-24a [45], confirming that the blends retain appropriate flow properties for fuel injection and combustion. HIO has a significantly lower sulfur content, measuring below 1.0 mg/kg, compared to 6.7 mg/kg in commercial diesel. The blended HIO 5 exhibited an intermediate sulfur content of 5.6 mg/kg. This substantial reduction in sulfur content allows for reduced emissions and environmental impact [46]. The flash point of HIO was significantly higher at 72.0 °C, compared to the 43.0 °C flash point of commercial diesel. In the case of HIO 5, the flash point remained unchanged at 43.0 °C, indicating minimal impact at low blending ratios. The cetane index of HIO was measured at 84.8, substantially higher than the 49.4 of commercial diesel. HIO 5 also demonstrated an improved cetane index of 51.7, indicating enhanced ignition quality. The high cetane number of HIO is attributed to its paraffinic composition, which is expected to improve engine performance and fuel efficiency. Overall, the HIO 5 values in Table 4 meet the requirements specified by Diesel Standard No. 1-D S15 (ASTM D975-24a). The fuel properties of HIO 5 demonstrate a high degree of similarity to commercial diesel, thus confirming its potential as an alternative drop-in fuel. Furthermore, HIO 5 exhibits enhanced fuel characteristics, including a higher cetane index and a lower sulfur content. These characteristics contribute to improved combustion performance and environmental benefits.

4. Conclusions

The feasibility of producing HIO from BSFL as an alternative drop-in fuel was tested, and the optimal feed compositions for BSFL to maximize lipid accumulation were analyzed. Extracted IO was then converted into HIO via an HDO reaction, and characterization analyses, including FT-IR, ¹H-NMR, ¹³C-NMR, TGA, and GC, confirmed the effective removal of oxygenated groups in IO, resulting in a carbon number of hydrocarbons similar to that of commercial diesel. The physicochemical properties of HIO 5 blends met standard fuel specifications. The findings suggest that HIO from non-edible insect lipids is a sustainable alternative to petroleum diesel.