13th International Colloquium Fuels - September 2021 121 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users Dhanesh Goberdhan and Robin Hunt Infineum, UK Ltd Summary Hydrogenated vegetable oils (HVOs) are a sustainable alternative to diesel fuel. They are described as both fossil-free and Fatty Acid Methyl Ester (FAME) free fuels. HVOs are paraffinic renewable diesel fuels produced from sustainable raw materials. In addition to their green credits, they have superior cetane and oxidation stability properties over conventional diesel and FAME. These advantages with their green credentials have resulted in a growing market share as both a biofuel and biofuel component. HVOs are produced by isomerisation processes of a range of different vegetable oil sources, such as rapeseed, palm and soya oil, or even waste and residual fat fractions. In this paper we demonstrate how the appropriate use of cold flow additive technology can further enhance the opportunities for HVO by: - Increasing the flexibility of production sources. That is the range of raw materials, and processing to produce HVOs. - Reducing the production costs (and energy used) by reducing the required level of isomerisation to meet low temperature requirements. - Increasing flexibility for end users, by increasing the range of different types and sources of HVOs that meet specification requirements. This provides producers and users of HVOs with additional opportunities to optimise the value of their operations. 1. Introduction: There has been increasing interest in the production of chemicals and fuels from biomass, from renewable sources, driven by the desire to decarbonise the transport sector due to global concerns towards greenhouse gas emission. This is supported by Governmental and European Union policy. For example, in the Renewable Energy Directive, RED [1] and RED II [2] directives on the promotion of the use of energy from renewable sources. Hydrogenated Vegetable Oil (HVO) is a fast-growing next second-generation fuel with production plants being built globally. HVO is created through the hydrogen treatment of a renewable oil, which can be from a vegetable source. For example, Rapeseed, Soya and Palm Oil. Despite it being referred to as a “hydrogenated vegetable oil” it can also be produced from common non-vegetable sources, e.g., Tallow or used kitchen oil [3] It is referred to as a next generation biofuel as it is believed to be an advancement on first generation biofuels based on Fatty Acid Methyl Esters (FAME) [4]. The advantage of HVOs over FAME is that first-generation biofuels are derived from crops that potentially compete with food production. In addition, HVOs have better cetane number than fossil fuel derived diesel and better oxidative stability properties than FAME [5]. 2. Chemistry of HVOs HVOs can be produced by one or more step catalytic hydrotreating of different triglycerides containing vegetable oils. This causes the complicated hydrocarbons to be broken down into simpler straight chain alkanes. with typical production of a mixture of n-alkanes, namely C 15 H 32 , C 16 H 34 , C 17 H 36 and C 18 H 38 [6]. A further step is then carried out to isomerise the fuel and convert more of the straight chain alkanes into branched iso-alkanes. This is called isomerisation. The relative ratio of the n-alkanes will depend on the source of the vegetable oils. 122 13th International Colloquium Fuels - September 2021 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users Fig.1: Gas chromatogram (GC) of 4 HVO fuels with differing Cloud Points (CP) showing the n-alkane distribution. Fuel characteristics are shown in Appendix 1. Figure 1 shows the n-alkane distribution of how the nalkane distribution varies for four different HVO samples. The Cloud Point (CP) of the fuel is determined by the level of isomerisation of the samples. The CP is the temperature where the precipitating wax can be visibly observed [10]. From the n-alkane analysis in Figure 1, the lower levels of isomerisation, Fuel 2 and Fuel 3, correspond to higher level of C16/ C18 n-alkanes. Whereas high levels of isomerisation, Fuel 1 and Fuel 4, have lower levels C16/ C18 n-alkanes. 3. Cold flow issues Diesel fuel derived from fossil fuels also contain n-alkanes. At low temperatures the n-alkanes precipitates as thin rhombohedral plates (Figure 2a). These crystals can block fuel filters designed to protect diesel injectors and pumps. This would result in fuel starvation to the engine, leading to a loss of power and/ or stalling, and even potential failure of the engine to start. [7] Fig 2a: Photomicrograph of wax crystal precipitated from untreated diesel fuel. Fig 2b: Photomicrograph of wax crystal precipitated from untreated HVO. In contrast, the wax that precipitates from HVO, Figure 2b, shows uncontrolled crystal growth. In the case of this HVO, the wax precipitates too rapidly to allow the formation of the flat planar crystal arising from the slower wax crystal growth seen in Figure 2a. 4. Low temperature Properties of HVOs The low temperature properties of hydrocarbon fuels such as diesel, FAME and HVOs can be undesirable if wax precipitates at too high a temperature. This is governed by the distribution of the long-chain n-alkanes within the fuel. The high molecular weight n-alkanes become supersaturated during cooling, which results in their precipitation. These straight chain alkanes form the waxes that will crystallise out of solution and cause the filter blocking issues. [8] HVO can be produced from a variety of different feedstocks. HVOs from different sources will have different distributions of n-alkanes. The most prominent change is that the finished HVO will have different ratios of C16 and C18 carbon chains. Fig. 3: GC trace showing the n-alkane distribution of HVOs produced from different sources. 13th International Colloquium Fuels - September 2021 123 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users The different base oils produce a different ratio of C16 and C18 n-alkanes depending on the distribution of fatty acids in the original oil. However, this seems to have little effect on the base fuel characteristics, CP and CFPP (See Appendix 1). The CP seemingly dominated by the total level of the n-alkane rather than the distribution of n-alkanes (Figure 4). 5. Potential solutions low temperature issues 5.1 Isomerisation In the production of HVOs the isomerisation step has a significant effect on the low temperature properties of the HVO [9]. The isomerisation step converts the long n-alkanes into more branched structures which have better solubility and would precipitate as wax at lower temperatures. Fig 4: Graph showing a variety of HVO samples, comparing the base cloud with the total n-alkanes, derived from GC analysis. The CP of the HVO decreases with increasing levels of isomerisation of the total n-alkane content, increasing levels of isomerisation lowers the base cold flow properties of the finished HVO. From the data in Figure 3 and 4, the level of isomerisation is more significant than the source of the HVO. Whilst isomerisation can reduce low temperature issues by reducing the amount of n-alkane wax, it is an energy intensive process and alternative solutions may offer more value to refiners. 5.2 Dilution BX/ Co-processing Use of HVOs as a blend component is also an alternative route to improve the sustainability credits fossil diesel. HVO can be combined with diesel and acts as a bio component. This can be done in two ways. One, by blending with the distillate diesel, allowing close control over the level of HVO being added. Two, by co-processing. Coprocessing involves the addition of the renewable oil to the diesel stream in the refinery prior to the standard hydrotreating required to reduce sulphur fuel levels. The blend of the renewable oil and gas oil components are then hydrotreated together, resulting in a similar product to a fossil diesel blended with an HVO. This results in less control over the HVO created, but removes some blending and hydrogenation complexity. The high variation of characteristics from blending HVO into diesel can results in a fuel with a range of low temperature properties. The differences in the finished fuel will be due to both the variation in the HVO, from the level of isomerisation and the variation in the source oils, as well as due to the variation in the fossil diesel characteristics. The differences in the final fuel characteristics will influence the low temperature properties for the finished blend. 5.3 Use of additive technology to achieve low temperature targets in HVOs and HVO blends Cold flow additives can be used to treat both pure HVOs and blends of HVOs in fossil fuel. 5.3.1 Cold flow additives for pure HVO: As we have seen, the cold flow attributes of an HVO sample depend heavily on the level of isomerisation applied. An alternative methodology to achieving the required low temperature performance targets is to use cold flow additives. This would enable the use of a less isomerised HVO in the blend. Cold flow additives can have a significant effect, allowing refiners to achieve an improvement to CFPP performance of more than 5 o C when the correct additive is used. In a pure HVO, because the fuel is highly paraffinic the fuels will be difficult to treat due to the high level of wax precipitation. However, additive treatability improves with higher levels of isomerisation (see Figure 5). Fig 5: Bar chart representing depression of CFPP when treated with 5000 ppm of cold flow additive for HVOs of different CP. Fuel 2 CP is 17 o C; Fuel 8 CP is-6 o C; Fuel 10 CP is -19 o C and Fuel 11 CP is -31 o C Even though the source of the raw material has little effect on base characteristics it can have an impact on how the 124 13th International Colloquium Fuels - September 2021 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users fuel responds to additives. This can result in differing additives needs for HVOs produced with different base oils. This adds an extra layer of complexity to additive formulation (see Figure 6). Fig.6: CFPP treat curve for an additive technology in two HVOs with similar CPs but different vegetable oil sources Figure 6 shows how the same additive technology gives different levels of additive response in HVOs with similar CP and untreated CFPPs. Fuel 6 which shows a greater level of response than Fuel 5. 2000 ppm of additive is required to get a 5 degree improvement in CFPP in Fuel 6. However, Fuel 5 requires 10,000 ppm of the same cold flow additive. In this case, the source of the base oil can have a significant impact on additive response of the finished HVO. 5.3.2 Cold flow additives for BX/ Blended/ co-processed HVO Additive selection is highly dependent on the overall nalkane content of the finished fuel. This can act as a limiting factor when deciding how much and which kind of HVO can be added into a blend. When the original diesel already has a high n-alkane content, this can limit the level of HVO quantity and quality that can be added. Fig 7: Graph showing the GC n-alkane plots of different HVOs blended into a gasoil sample, Fuel 12, at 10%. Details of Fuel blends is shown in Appendix 1. Figure 7, shows that the addition of different HVOs with different CPs, blended at 10% into diesel impact the nalkane distribution. The different HVOs have a range of CPs due to different levels of isomerisation. As seen in Section 5.1, the greater the level of isomerisation, the lower the CP and the lower the level of n-alkanes. Thus, the n-alkane distribution of the fuel blends is most perturbed by the addition of the higher CP HVOs. That is, Fuel 13, which is a blend of HVO with a CP 17 o C and Fuel 14, with a HVO with a CP of -6 o C, show the greatest difference compared to those fuels with lower CPs. That is, Fuel 16 with a HVO with CP of -19 o C and Fuel 17 with a HVO of -31 o C. Fig 8: Bar chart of CFPP decrease from base CFPP, for a variety of different HVO/ diesel blends, treated with cold flow at 500 ppm. The fuel characteristics are shown in Appendix 1. As seen in Figure 8, increasing the levels of HVO isomerisation can improve CFPP response within a blend, but CFPP of low level isomerised HVO can still be improved by specialist additives. The correct additive selection is crucial for optimum low temperature performance. Different additive technologies providing optimum performance depending on the different levels of n-alkane in the final fuel blend. With high levels of isomerised HVOs performing in a similar fashion to a standard diesel. As the level of isomerisation, and hence n-alkane levels from the HVO increase, more advanced chemistries are needed to achieve an adequate level of performance. Fig 9: Chart showing the CFPP decrease from base CFPP, for a variety of different additives at the same treat rate. 13th International Colloquium Fuels - September 2021 125 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users Figure 9 shows the sensitivity of the fuel blend to different cold flow additive technologies. Additive 4 gives the greatest CFPP depression. Dependant on the HVO characteristics the choice of cold flow additive selection is crucial 6. Discussion A key property in the utilisation of HVOs is their low temperature properties. As HVOs are produced by isomerisation, you can choose to use a high level of isomerisation to be generate a HVO with the required low temperature properties by isomerising the waxes in the HVO to give the required low temperature properties. However, HVO manufacturing units may only be set up to produce one level of isomerisation, and thus this solution could lack flexibility when supplying markets with a range of different low temperature requirements. This can result in an over specified product for a particular market. An alternative methodology to overcoming the low temperature issue and also an alternative way of deploying HVOs would be to use the HVO as a blend component. That is, to produce a BX fuel by blending with an appropriate middle distillate and at an appropriate level of HVO to produce a fuel of the required low temperature properties. However, the properties of distillate fuels and their low temperature properties can be highly varied themselves. So that it is not always possible to both predict and obtain the desired cold flow properties by simply blending the two together. This is also even more of a potential issue when producing a co-processed HVO, where there is potentially even more issues in being able to tailor the production to specific cold flow properties consistently. The use of cold flow additives allows the use of HVOs which have lower levels of isomerisation to be used more flexibly in different markets. This has the additional benefit of reducing the isomerisation costs. In addition, it can more flexibly deal with HVOs produced from a variety of different sources. 7. Conclusion Hydrogenated vegetable oils (HVOs) are a sustainable alternative to diesel fuel. They are paraffinic renewable diesel fuels produced from sustainable raw materials. Their green credentials have resulted in a growing market share as both a biofuel and biofuel component. A key property in the utilisation of HVOs is their low temperature properties. These low temperature properties are governed by the balance of iso and n-alkanes that are present in the HVO. These levels are governed by the level of isomerisation in production and also the source of the material used to produce the HVO. Different methodologies are available to improve low temperature properties of HVOs and HVO containing distillate fuels. This paper identifies how the appropriate use of cold flow additive technology can further enhance the opportunities and value of using HVOs by 1. Increasing the flexibility of production sources. That is the range of raw materials, and processing to produce HVOs. 2. Reducing the production costs (and be greener by using less energy) by reducing the required level of isomerisation and still meet low temperature requirements. 3. Increasing flexibility for end users, by increasing the range of different types and sources of HVOs that meet specification requirements. This provides producers and users of HVOs with additional opportunities to optimise the value of their operations. 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Cloud and pour pheno- 126 13th International Colloquium Fuels - September 2021 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users mena exhibited by solutions of binary n-paraffin mixtures”, Journal of the institute of petroleum, 51(499) 1965, 228-252 Definitions, acronyms and abbreviations BX Fossil fuel with X% biofuel component CFPP Cold filter Plugging Point test CP Cloud Point FAME Fatty acid methyl ester GC Gas Chromatogram HVO Hydrogenated Vegetable Oil Appendix 1 HVO and fuel blend characteristics 1a HVO characteristics 13th International Colloquium Fuels - September 2021 127 Improving Hydrogenated Vegetable Oils Green Credentials and Value to Producers and End Users 1b Fuel blend characteristics