Method for determining the amount of renewable fuel in a fuel blend.

Technical Field

The present invention relates to a method for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, and to the use of a system thereto.

Background Art

Combining bio-based liquid hydrocarbon fuel with fossil fuel has attracted increasing attention during the past years. National directives exist which vary considerable from one country to another, but many recommend biofuel to be present in the fuel. On the other hand, refining constraints exist which are imposed by commercial specifications limiting the degree of freedom in the integration of biofuel as a function of refining bases composing the fossil fuel. There is thus a need for analysing methods, which can provide accurate information on the content of biological components present in the fuel.

The state of the art and most accurate biogenic analysis method is the carbon-14- isotope analysis ( ¹⁴ C analysis) of the fuel. This analysis is based on knowledge of the ratio between the three naturally occurring isotopes of carbon, ¹² C, ¹³ C, and ¹⁴ C, combined with the decay time of the radioactive ¹⁴ C. Small amounts of ¹⁴ C isotopes are being formed in the upper atmosphere due to cosmic rays hitting atmospheric nitrogen atoms. The resulting ¹⁴ C/ ¹² C ratio in the atmosphere is rather constant and about 1 part-per-trillion (ppt;1 O ¹² ), that is, the amount of ¹⁴ C in the atmosphere is very very small, but yet it is still measurable. The ¹⁴ C atoms being formed in the atmosphere do not stay as isolated atoms in the atmosphere but instead they form molecules like carbon dioxide. All living organisms will subsequently take up the ¹⁴ C contained in the atmospheric carbon dioxide. The half-life time of ¹⁴ C is around 5700 years, which means that for fossil fuel, which is hundreds of millions of years old, all the ¹⁴ C has completely decayed. In contrast, the level of the residual ¹⁴ C left in biofuels, which are derived from young biomass (normally up to a few 1000 years old) can be measured with modern instrumentation. For determining if the liquid hydrocarbon fuel is fossil or bio-based, or what is the blending ratio between these two components, there are mainly two practically employed measurement techniques: Accelerator Mass Spectrometry (AMS) and Liquid Scintillation Counting (LSC).

The advantage of AMS is that it is the most accurate "scientific-grade" biogenic method. One disadvantage is that the instrument is large and presently costs 1 -2 MEUR. Further, it requires a dedicated laboratory and trained personnel for operation, where it typically takes about 2-14 days to get the analytical result of one analysis and the cost for analysis is therefore high. Thus, by no means can AMS be considered suitable for online analysis.

Also, the LSC can perform biogenic analysis, but is typically limited to visually clear gasoline and diesel fuels. It is more cost efficient (starting presently from 60 000 EUR) than AMS and ordinary lab technicians can perform the analysis, which takes typically 2-10 hours depending on the biogenic content of the fuel. However, LSC is only available as a laboratory off-line technique and hence is not suitable for online process analysis.

Consequently, there is a need for an online type fast analysis, which can provide knowledge on whether the liquid hydrocarbon fuel is fossil or bio-based, or if it is a mixture of the two, and what the blending ratio between these components might be.

Typically biofuel refers to a bio-based product manufactured through a transesterification reaction. For example vegetable oils and alcohols may be reacted into esters, and glycerol is formed as co-product. For example biodiesel may include mono-alkyl esters of vegetable oils or animal fats. Biodiesel is produced by transesterifying the oil or fat with an alcohol such as methanol under mild conditions in the presence of a base catalyst. Biodiesel can be used in any diesel engine when mixed with mineral diesel. However, the oxygenate containing bio-based fuels may only be used to a minor extent, such as 20 wt-% in a fuel blend for conventional diesel equipment designed for mineral diesel operation. Another type of product that may be obtained from lipid feedstocks is a fuel having a composition that simulates the composition of fossil diesel fuel, namely renewable diesel. Renewable diesel is produced from the fat or oil by a hydrodeoxygenation reaction at an elevated temperature and pressure in the presence of a catalyst. The renewable diesel has a considerably higher energy content compared to biodiesel containing oxygenates and is suitable for use as such, e.g. as 100 wt-%, in existing vehicles.

The applicant has disclosed production of renewable fuels based on vegetable oil or animal fat refining processes in several patent documents, e.g. FI100248, EP1396531 , EP1741768 and EP1741767. These depict detailed catalytic hydrotreatment and isomerization of plant oils and animal fats, which contain triglycerides, into the corresponding alkanes. The glycerol chain of the triglyceride is hydrogenated to the corresponding alkane without any glycerol sidestream. These processes remove oxygen from the oil or fat; the diesel produced is not an oxygenate like in e.g. traditional transesterified FAME biodiesel. Catalytic isomerization into branched alkanes is done to adjust the cloud properties in order to meet winter operability requirements. As the final product is chemically similar to conventional mineral diesel, it requires no modification or special precautions for conventional diesel engine use for example.

US2008162016 discloses a method for optimizing operation of an engine driven by an electronic or digital system. In the method, the fuel composition is analysed by at least one sensor located in a fuel circuit of an engine, wherein the fuel composition analysis comprises spectroscopic analysis of the molecular structure of the hydrocarbons, such as e.g. added alcohol, composing said fuel.

US2010168984 discloses a method for adjusting injection, combustion and/or post treatment parameters of an internal combustion engine with auto-ignition. The method includes a step of determining the content or type of ester-based biofuel present in the fuel feeding, the injection system, using a spectroscopic unit.

US2010305827 discloses a device for the centralized management of measurements and data relating to liquid and/or gas flows needed for the correct operation of a combustion engine controlled by an engine computer. This device comprises means for analyzing at least two liquid and/or gas flows including at least one light source, at least one optical signals detector and at least one system for analyzing the detected signals. The device is characterized in that at least one of said analysis means is arranged to be used for analyzing two of said flows. The description further discloses that in spite of the regulatory or internal provisions recommended by fuel distributors and vehicle manufacturers many users introduce a non-adapted fuel into the tanks of their vehicles. An increasing number of vehicles are used with products which are not certified by the manufacturers and the customs services like used frying oils, non-esterified vegetable oils, domestic fuel oils, causing serious damages to the power unit, the fuel supply system and the post treatment system. The damages may severely impact the engine injection and combustion phases and increase the regulated or not polluting emissions, which can lead to engine break. Similarly, some fuels such as water/gasoil or gasoline/alcohol or gasoil/bio-fuels emulsions can be instable and the quality thereof can deteriorate over time. Such deterioration of the nature of the fuel potentially entails an increase in the vehicle pollution, damages to the vehicle or at least important corrective operations. Thus, concepts and methods aim at providing preventive safety to the elements of the power unit of a vehicle equipped with a combustion engine, prior to or during the ignition phase further to deterioration of the nature of the fuel contained in the tank and the fuel supply system. Such concepts and systems involve the measurement of the fuel quality, ideally in the fuel supply system.

US20120226425 discloses that it aims at providing a method for optimising the operation of a thermal engine supplied with bio-fuel, wherein said bio-fuel is analysed with accuracy in order to provide adjustments of the engine to be best suited to the fuel. This is achieved by a method for optimizing the operation of a thermal engine having combustion parameters controlled by an electronic housing and at least one engine mapping. The method comprises the following steps: A step of carrying out a near-infrared spectroscopic analysis of a bio-fuel containing a mixture of alcohols and/or ethers and/or water in order to determine the proportion of water and of at least one other oxygenated compound of the alcohol and/or ether type contained in the bio-fuel; A step of selecting and/or modifying said mapping on the basis of the result of said step of analysis and determination in order to optimize the operation of the thermal engine. The description further discloses that thermal internal combustion engines must meet always stricter requirements as regards CO2, NOx, HC emission standards and this is the reason why the proportion of bio fuels in the commercial fuels, i.e. gasoline and gas-oil, such as bio-ethanol and bio diesel which are manufactured from multiple sources enabling the substitution of oxygen atoms for carbon atoms has been rising for a few decades.

None of the discussed prior art documents, however, addresses the issue of providing a reliable, cost efficient and fast analysis method for online analysis of fuel blends when the bio-based fuel component is renewable fuel component.

Consequently, there is a need for a reliable method and system, which can provide knowledge on the amount of renewable fuel components in a liquid fuel blend comprising mineral or fossil fuel and renewable fuel components.

Summary of the Invention

The object of the present invention is to provide online knowledge of the amount of a renewable fuel component in a fuel blend.

A further object of the present invention is to provide a method for adjusting the amount of renewable fuel component to the amount of fossil fuel in a fuel blend.

A yet further object of the present invention is to provide use of a system for determining the amount of the renewable fuel in a fuel blend.

To solve the problem, the present invention provides in a first aspect of the invention the use of a near infrared spectroscopic system for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, the near infrared spectroscopic system comprising:

• means for carrying out near infrared spectroscopic analysis of the fuel blend, and • means for determining the amount of the renewable fuel component in the fuel blend based on comparing results from the near infrared spectroscopic analysis of the fuel blend to one or more values obtained from predefined near infrared spectrum calibration curves thereby providing the amount of the renewable fuel component in the fuel blend.

By a renewable fuel component is meant a blend of constituents of renewable fuel. By a fossil fuel component is meant a blend of constituents of fossil fuel.

When determining the amount of a renewable fuel component in a fuel blend comprising a renewable fuel component and a fossil fuel component according to the above, one needs to be aware that the renewable fuel composition and fossil fuel composition have a very similar chemical composition in view of e.g. the use of these blends in vehicles. One clear difference can naturally be seen in the comparison between the carbons originating from fossil fuel and the carbons originating from renewable fuel, where the chemical compounds present containing those carbons may individually be structurally the same. Besides the difference in ¹⁴ C analysis, determination of one component from the other is quite difficult and not a straightforward process.

As shown in the present invention, the difference when comparing fossil fuel and renewable fuel is to be found in the amount of each of the individual components in relation to each other. The separation of fossil fuel components and renewable fuel components must be made based on the molecular distribution of the chemical constituents in the two fuel blends, as both components have essentially the same constituents but in different amounts. Consequently, near infrared (NIR) spectroscopy cannot differentiate between the individual carbons originating from renewable fuel and the individual carbons originating from fossil fuel, i.e. NIR spectroscopy cannot determine whether the individual carbons originating from the renewable fuel or from the fossil fuel. Instead, NIR spectroscopy can distinguish between vibrations from different chemical bonds between the molecules and differences in amounts of the different components can also be distinguished with NIR spectroscopy. Therefore, NIR spectroscopy can surprisingly be used for accurately determining the amount of the renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component. This provides the user with an advantageously fast manner of determining the renewable component in a fuel blend comprising the renewable fuel component and a fossil fuel component using NIR spectroscopy.

That is, the inventor of the present invention found that a number of advantages are obtainable for the first aspect of the invention including the obtainability of composition data in less than a few minutes compared to hours as is the case for other methods. Preferably the composition information is obtained in two minutes, more preferably within a minute, or even less, such as in 50 s or even in 30 s. The precision of the method is about 1 % which is accurate enough for the intended use. The composition analysis time is thereby greatly reduced compared to especially the conventional off-line ¹⁴ C analysis used for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component. The first aspect of the invention consequently provides revenue for being able to measure in real time and with good accuracy.

Additionally, the first aspect of the invention enables the manufacturing of precise quality blend products in situ or online, further enabling accurate determination of the cost for the renewable fuel blend. Presently, the blend composition quality is monitored ex situ with a possible delay of even 24 h while using the ¹⁴ C isotope measuring method.

The amount of the renewable fuel component in the fuel blend tends to drift from the desired or predetermined value during production of the fuel blend causing a too low anticipated amount or a too high actual amount of the renewable fuel component in a fuel blend. This blend quality fluctuation may in both cases imply cost related issues for the blender. The use of the system and the method of the present invention enable an accurate real time determination of the amount of the renewable fuel component, reducing the production cost notably and simplifying the quality monitoring. Furthermore, by having exact and real time knowledge of the amount of a renewable fuel component in a fuel blend, the amount of CO2 and particle emissions when using the blend in vehicle applications can be minimized by optimization of the engine performance to the known renewable fuel component in the fuel blend.

A second aspect of the invention disclosed herein is a method for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, wherein the method comprises the steps of:

• providing a sample of the fuel blend to a device comprising a near infrared spectrometer;

• measuring one or more infrared spectra of the fuel blend using the near infrared spectrometer;

• determining the amount of renewable fuel component in the fuel blend by analysing the one or more infrared spectra of the fuel blend and comparing the analysis result to one or more predefined near infrared spectrum calibration curves linking a known amount of the renewable fuel component in a fuel blend to the one or more measured near infrared spectra of the fuel blend.

Detailed Description of the Invention

In describing the embodiments of the invention specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

When describing the embodiments of the present invention, the combinations and permutations of all possible embodiments have not been explicitly described. Nevertheless, the mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage. The present invention envisages all possible combinations and permutations of the described embodiments. The terms“comprising”, “comprise” and “comprises” herein are intended by the inventors to be optionally substitutable with the terms“consisting of”,“consist of” and“consists of”, respectively, in every instance.

The present invention was made in view of the prior art described above, and the object of the present invention is to provide online knowledge of the amount of a renewable fuel component in a fuel blend.

In the first aspect of the invention is disclosed the use of a near infrared spectroscopic system for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, the near infrared spectroscopic system comprising:

• means for carrying out near infrared spectroscopic analysis of the fuel blend, and

• means for determining the amount of the renewable fuel component in the fuel blend based on comparing results from the near infrared spectroscopic analysis of the fuel blend to one or more values obtained from predefined near infrared spectrum calibration curves thereby providing the amount of the renewable fuel component in the fuel blend.

In some embodiments of the present invention, the means for carrying out near infrared spectroscopic analysis comprises means for measuring one or more near infrared spectra of the fuel blend, and means for analysing the measured one or more near infrared spectra. The means for measuring the one or more near infrared spectra may include infrared sensors operating in a narrow spectral band range spanning a few 100 nm up to larger spectral band ranges covering e.g. the near infrared spectral range from 700-3000 nm. Different types of sensors are commercially available.

Near infrared (NIR) spectroscopy is based on molecular overtone and combination vibrations. Combinational spectral region is e.g. observable around 1200-1700 nm. The combinations observable in the spectral range from 1200-1700 nm are normally combinations of three vibrations. Overtone regions originating from the strong fundamental vibrations observed at higher IR wavelength ranges are normally observed in the NIR spectral region. The 1 ^st , 2 ^nd and 3 ^rd overtone regions are normally observable in the spectral ranges from approximately 1500-2150 nm, 1325-1650 nm, and 825-1 100 nm, respectively. The combination region from 1200- 1700 nm may thus overlap with the overtone regions. Multivariant calibration technologies may be employed to extract the desired chemical information from the recorded spectra.

Examples of more narrow spectral ranges includes the near infrared wavelength range from 800 nm to 900 nm. In this spectral range signals are often weak. In this spectral range where the 3 ^rd overtones are normally found, near infrared signals are often weak. However, the different absorption features may possibly be better spectrally separated from each other in this spectral wavelength range although the signal is weak. More easily spectrally separable features may provide an improved accuracy and performance to the measurements. For example, silicon based detector technology may be used at these short NIR wavelengths, which lowers the costs due to the low price of silicon based detectors.

In the spectral range 800 nm to 900 nm, 3 ^rd overtone absorption signals originating from CH3, CH2 and CH groups are seen. The CH3 group will normally absorb at a lower wavelength than the CH2 group, which in turn will absorb at a lower wavelength than the CH group. The absorption will be in the form of bands having absorption maxima centred at 900 nm ± 25 nm, 910 nm ± 25 nm, and 920 nm ± 25 nm for the CH3, CH2 and CH groups, respectively.

Alternatively, the spectral wavelength range from 1000 nm to 1600 nm, such as from 1 100-1300 nm, or from 1 150-1250 nm may be used. In this spectral range, where the 2 ^nd overtone bands are observable, absorption signals are normally stronger, which increases the sensitivity of the measurements. In these spectral ranges, absorption signals are normally stronger, which increases the sensitivity of the measurements. The detectors suitable for measuring NIR spectra in the spectral wavelength range from 1000-1600 nm are, however, normally slightly more expensive compared to e.g. silicon based detectors In the spectral range between 1 100-1300 nm, absorption signals originating from the 2 ^nd overtones from CH3, CH2 and CH groups are also seen. The CH3 group will normally absorb at a lower wavelength than the CH2 group, which in turn will absorb at a lower wavelength than the CH group. The absorption will be in the form of bands having absorption maxima centred at 1 160 nm ± 50 nm, 1 175 nm ± 50 nm, and 1200 nm ± 50 nm for the CH3, CH2 and CH groups, respectively. Around 1 150 nm, absorption signals from aromatic CH are often seen if there is an aromatic content in the sample.

Also, in the spectral range between 1300-1600 nm, absorption signals originating from the 2 ^nd overtones from CH3, CH2 and CH groups are also seen. Absorption bands from CH3, CH2 and CH groups are seen both in the form of bands having absorption maxima centred at 1375 nm ± 50 nm, 1400 nm ± 50 nm, and 1435 nm ± 50 nm for the CH3, CH2 and CH groups, respectively for primarily 2 ^nd overtone bands.

Yet alternatively, the spectral wavelength range from 1600 nm to 1800 nm, or even more narrow spectral range from 1700 nm to 1775 nm, also provides NIR spectra, where signals from renewable fuel components may be separable from those from fossil fuel components.

In the spectral range between 1600-1800 nm, absorption signals originating from the 1 ^st and 2 ^nd overtone regions overlap. Absorption bands from CH3, CH2 and CH groups are seen in the form of bands having absorption maxima centred at 1670 nm ± 50 nm, 1715 nm ± 50 nm, and 1740 nm ± 50 nm for the CH3, CH2 and CH groups, respectively, for primarily 1 ^st overtone bands. Absorption signals from aromatic CH are also observable in the form of bands having absorption maxima centred at 1635 nm ± 25 nm if there is an aromatic content in the sample.

Thus, the near infrared spectral range, which is chosen for measuring the one or more near infrared spectra of the fuel blend, may vary depending on the requirements to cost, sensitivity and selectivity in the spectral data. In some embodiments of the present invention, the near infrared spectroscopic analysis of the fuel blend are based on measuring one or more near infrared spectra of the fuel blend in the spectral range between 700-1000 nm, such as between 700 nm to 900 nm, such as between 800 nm to 1000 nm, or such as between 800 nm to 900 nm.

In some embodiments of the present invention, the near infrared spectroscopic analysis of the fuel blend are based on measuring one or more near infrared spectra of the fuel blend in the spectral range between 1000-1400 nm, such as between 1000 nm to 1300 nm, such as between 1 100 nm to 1400 nm, such as between 1 100 nm to 1300 nm, or such as between 1 150 nm to 1250 nm.

In some embodiments of the present invention, the near infrared spectroscopic analysis of the fuel blend are based on measuring one or more near infrared spectra of the fuel blend in the spectral range between 1400-2000 nm, such as between 1500 nm to 1900 nm, such as between 1600 nm to 1800 nm, such as between 1600 nm to 1750 nm, or such as between 1550 nm to 1750 nm.

In some embodiments of the present invention, multiple bands are analysed, such as at least four bands. Different contents in the sample may give rise to absorption bands having a slightly different absorption maxima. If the concentration of the different content in the sample varies, if may be seen as a shift in the combined absorption spectra.

The means for analysing the one or more near infrared spectra may include chemometric models, which are able to produce one or more near infrared calibration curves from one or more near infrared spectra of fuel blends with known amounts of the renewable fuel component and/or compare near infrared spectra of fuel blends with unknown amounts of the renewable fuel component to the calibration curve(s), thereby determining the amount of the renewable fuel component in the fuel blend with the unknown amount of renewable fuel component.

In some embodiments of the present invention, the means for analysing the measured one or more near infrared spectra further comprises means for obtaining derivative spectra of the one or more measured near infrared spectra. By forming the derivative spectra of the measured near infrared spectra, background variation observed between measurements performed on different days or different times during the day may be vastly reduced if not completely avoided. A more robust system is thereby obtained.

In some embodiments of the present invention, the one or more predefined near infrared calibration curves are comprised in the near infrared spectroscopic system. Thus, the near infrared spectroscopic system may be set up to include a multiple of predefined near infrared calibration curves representing fuel blends with known amounts of renewable fuel components. Each of the near infrared calibration curves may be a representative of a known type of renewable fuel and its spectral characteristic in a fuel blend comprising known amounts of this known type of renewable fuel.

In some embodiments of the present invention, the amount of renewable fuel component in the fuel blend is determined within 2 minutes or less, preferably within 1 minute or less, such as within 50 s or less, even in 30 s. The operation time of 2 minutes or less renders the near infrared spectroscopic system very attractive for online measurements. The short operation time is a vast improvement compared to the ¹⁴ C detection method, which cannot be operated online and which typically takes days for providing the needed result.

In some embodiments of the present invention, the one or more predefined near infrared calibration curves are obtained by 1 ) forming fuel blends comprising different known amounts of the renewable fuel component in the fuel blends, and 2) recording multiple near infrared spectra of the fuel blends, 3) forming derivative spectra from the obtained multiple near infrared spectra, 4) obtaining absorbance values from each of the derivative spectra at a first wavelength, and 5) relating each of the absorbance values to the known amounts of the renewable fuel component in the fuel blends. It has been shown that reliable calibration curves focusing on the value of the derivative spectra at a favourably chosen wavelength are sufficient to obtain reliable calibration curves allowing for determination of the amount of renewable fuel component in a fuel blend. By obtaining the derivative spectra instead of the directly measured infrared spectra, the background signals are diminished to a reasonable extent.

In some embodiments of the present invention, the amount of renewable fuel component in the fuel blend is from 1 to 100 wt-%, preferably from 20 to 80 wt-%, more preferably from 30 to 60 wt-%. The blend composition depends on the blend properties and its use, which again depend on the qualities of the blend components. The method of the present invention is capable of measuring virtually any ratios of renewable fuel component and mineral/fossil fuel components in a fuel blend comprising these components. But typically the desired contents of renewable fuel components are around 1 -70 wt-%. The contents of renewable fuel components vary depending on country, and time of year, etc. for example summer diesel aims at around 30 wt-% blend whereas winter diesel aims at around 50-60 wt-%. Another factor, which may also influence the chosen contents of renewable fuel components in fuel blends, is the national taxes imposed on the fuel blends. The method disclosed herein is able to provide a reliable result independently of the content of renewable fuel components in fuel blends.

In some embodiments of the present invention, a feedstock for the renewable fuel component originates from plant oils or fats, or animal oils or fats, or fish oils or fats. The feedstock originating from a biological raw material containing fatty acids and/or fatty acid esters that originate from plants, animals or fish may be used. The biomaterial being selected from the group consisting of vegetable oils/fats, animal fats, fish oils and mixtures thereof is also suitable for use as feedstock. Examples of suitable biomaterials are any kind of fats, and any kind of waxes such as e.g. :

• any kind of plant fats, plant oils, and plant waxes;

• any kind of animal fats, animal oils, animal waxes, animal-based fats, fish fats, fish oils, and fish waxes;

• fatty acids or free fatty acids obtained from plant fats, plant oils, plant waxes; animal fats, animal oils, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof by hydrolysis, transesterification or pyrolysis;

• fats contained in milk; • metal salts of fatty acids obtained from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof by saponification;

• anhydrides of fatty acids from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof;

• esters obtained by esterification of free fatty acids of plant, animal and fish origin with alcohols;

• fatty alcohols or aldehydes obtained as reduction products of fatty acids from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof;

• recycled fats of the food industry;

• fats contained in plants bred by means of gene manipulation or genetic engineering;

• dicarboxylic acids or polyols including diols, hydroxyketones, hydroxyaldehydes, hydroxycarboxylic acids, and corresponding di- or multifunctional sulphur compounds, corresponding di- or multifunctional nitrogen compounds, and

• compounds derived from algae, molds, yeasts, fungi and/or other microorganisms capable of producing compounds mentioned above or compounds similar to those.

Examples of fish oils include Baltic herring oil, salmon oil, herring oil, tuna oil, anchovy oil, sardine oil, and mackerel oil.

Examples of plant oils and/or wood-based oils include rapeseed oil, colza oil, canola oil, tall oil, crude tall oil, sunflower seed oil, soybean oil, corn oil, hemp oil, hempseed oil, olive oil, linen seed oil, cotton seed oil, mustard oil, palm oil, peanut oil, castor oil, Jatropha seed oil, Pongamia pinnata seed oil, palm kernel oil, and, coconut oil.

Examples of animal fats include lard, tallow, rendered lard and rendered tallow.

Examples of animal waxes include bee wax, Chinese wax (insect wax), shellac wax, and lanoline (woll wax). Examples of plant waxes include carnauba palm wax, Ouricouri palm wax, jojoba seed oil, candelilla wax, esparto wax, Japan wax, rice bran oil, terpenes, terpineols and triglycerides or mixtures thereof.

The basic structural unit of a typical vegetable or animal fat useful as the feedstock is a triglyceride, that is a triester of glycerol with three fatty acid molecules, having the structure presented in the following formula I :

wherein R-i , R2 and R3 are hydrocarbon chains, and R-i, R2 and R3 may be saturated or unsaturated C6-C24alkyl groups. The fatty acid composition may vary considerably in feedstocks of different origin.

Mixtures of a biological raw material and hydrocarbon may also serve as the feed, and further, the hydrocarbon component obtained as the product may, if desired, be recycled back to the feed to control the exothermal character of the reactions.

The renewable fuel component may be produced in a number of different manners. One process for producing renewable fuel components from a material of biological origin comprises the steps of:

a) evaporating the material of biological origin in order to remove impurities from the material of biological origin thereby producing purified biological material; b) hydroprocessing the purified biological material in the presence of hydrogen gas and at least one catalyst to form a mixture of hydrocarbon compounds; c) separating gaseous compounds from the mixture of hydrocarbon compounds to obtain liquid hydrocarbon compounds, and

d) fractionating the liquid hydrocarbon compounds to obtain fuel components. A further step of recycling a portion of the liquid hydrocarbon compounds obtained from the separation or fractionation back to the hydroprocessing may also be included in the process.

The material of biological origin may be selected from any material of biological origin or the above disclosed preferred options.

In some embodiments of the invention, the feedstock is subject at least to a hydrodeoxygenation reaction in the presence of hydrogen and a hydrodeoxygenation catalyst and optionally to an isomerisation reaction in the presence of an isomerisation catalyst, for obtaining the renewable fuel component.

If a hydrodeoxygenation step and an isomerisation step are applied, these may be done either simultaneously or in sequence. The hydrodeoxygenation reaction may be done in the presence of hydrogen gas and may be performed in the presence of a hydrodeoxygenation catalyst, such as CoMo, NiMo, NiW, CoNiMo on a support, for example an alumina support, zeolite support, or a mixed support. The hydrodeoxygenation reaction may for example be conducted at a temperature in the range from 250 to 400 °C, and at a pressure in the range from 20 to 80 barg, a WHSV (Weight Hourly Space Velocity i.e. mass flow/catalyst mass) in the range from 0.5 to 3 h-1 , and a H2/0N ratio of 350-900 nl/l, using a catalyst, such as NiMo, optionally on a alumina support.

The product of the hydrodeoxygenation step may be subjected to an isomerization step in the presence of hydrogen and an isomerization catalyst. The isomerisation catalyst may be a noble metal bifunctional catalyst such as for example Pt-SAPO or Pt-ZSM-catalyst or NiW. The isomerization reaction may for example be conducted at a temperature of 250-400 °C and at a pressure of 10-60 barg. The isomerisation reaction may for example be conducted at a temperature of 250-400 °C, at a pressure of between 10 and 60 barg, a WHSV of 0.5 - 3 h-1 , and a H2/0N ratio of 100-800 nl/l. The hydrodeoxygenation and hydroisomerisation steps may be done in a single step on the same catalyst bed using a single catalyst for this combined step, e.g. NiW, or a Pt catalyst, such as Pt/SAPO in mixture with a Mo catalyst on a support, e.g. NiMo on alumina.

In some embodiments of the present invention, the renewable fuel component has an iso-paraffin content of more than 70 wt-%, preferably more than 80 wt-%, more preferably more than 90 wt-%. Thus, the iso-paraffin content may be dominating in of renewable fuel.

In some embodiments of the present invention, the renewable fuel component comprises C15 to C18 paraffins in an amount of more than about 70 wt-%, preferably more than about 85 wt-%, and more preferably more than about 90 wt- %. By C15 and C18 paraffins are meant paraffins containing 15 carbons and 18 carbons, respectively. By C15 to C18 paraffins is meant paraffins containing either 15, 16, 17 or 18 carbons in each paraffin.

Alternatively or complementary, in some embodiments of the present invention, the renewable fuel component comprises paraffins smaller than C15 paraffins in an amount of less than about 20 wt-% of, preferably less than about 10 wt-%, more preferably less than about 7 wt-%.

Yet alternatively or complementary, in some embodiments of the present invention, the renewable fuel component comprises paraffins larger than C18 paraffins in an amount of less than about 10 wt-%, preferably less than about 5 wt-%, more preferably less than about 3 wt-%.

In some embodiments of the present invention, the renewable fuel component comprises at least 95 wt-% saturated paraffinic hydrocarbons.

In some embodiments of the present invention, the renewable fuel component contains less than 5 wt-%, preferably less than 3 wt-%, more preferably less than 1 wt-%, of aromatic hydrocarbons, esters, oxygen containing hydrocarbons, and/or unsaturated hydrocarbons. In some embodiments of the present invention, the renewable fuel component contains less than 0.5 wt-% of the oxygen containing hydrocarbons, such as less than 0.3 wt-% of the oxygen containing hydrocarbons, such as less than 0.1 wt-% of the oxygen containing hydrocarbons. Often, only trace impurities of oxygen containing hydrocarbons are present. The lack of oxygen containing hydrocarbons results in absence of spectroscopic signals in the infrared spectra originating from oxygen containing hydrocarbons.

In some embodiments of the present invention, the renewable fuel component contains less than 0.5 wt-% of aromatic hydrocarbons, such as less than 0.3 wt-% of aromatic hydrocarbons, such as less than 0.1 wt-% of aromatic hydrocarbons. In some embodiments of the present invention, the renewable fuel component is free of aromatic hydrocarbons.

In some embodiments of the present invention, the renewable fuel component comprises:

- 10-40 wt-% of Cs-3o linear alkanes;

- 10-40 wt-% of Cs-3o cycloalkanes;

- up to 20 wt-% of C7-20 aromatic hydrocarbons, at least 90 wt-% of which are monoaromatic, and

- no more than 1 wt-% in total of oxygen-containing compounds,

wherein the total amount of Cs-3o alkanes in the fuel blend is 50-90 wt-%, and wherein the total amount of Cs-3o alkenes, C7-20 aromatic hydrocarbons and Cs-3o cycloalkenes is at least 95 wt-%.

In some embodiments of the present invention, the feedstock of renewable fuel is selected from plant oils and/or fats, animal fats and/or oils, fish fats and/or oils, fats contained in plants bred by means of gene manipulation, recycled fats of food industry and combinations thereof.

In some embodiments of the present invention, determining the amount of the renewable fuel component is carried out online while producing the fuel blend by mixing the renewable fuel component with the fossil fuel component. By online determination of the renewable fuel component in the fuel blend during the fuel blend mixing process, a constant feedback is obtainable allowing the producers of the fuel blend to interactively adjust the content of the renewable fuel added to the fuel blend. Thereby the amount of renewable fuel, which is to be added to a fuel blend in order to obtain a pre-determined ratio between renewable fuel and fossil fuel component (often defined by industry standards), does not need to be determined with a very high accuracy prior to starting the fuel blend mixing process, as the ratio between the different components may be adjusted during the mixing process based on the results of the infrared spectral analysis. This possibility does not exist if online measurements are not an option, making the use of the near infrared spectroscopic system according to the invention highly advantageous when producing large quantities of fuel blend comprising a mixture of renewable fuel and fossil fuel components.

In some embodiments of the present invention, it is the same renewable fuel, which is added to the fuel blend, when adjusting the content of the renewable fuel added to the fuel blend. Different renewable fuels blend are not used, thus it is merely the amount of the chosen renewable fuel added to the fuel blend, which is altered.

In some embodiments of the present invention, the fuel blend is produced at an oil refinery. At oil refineries, large quantities of fuels and fuel blends are produced. The high volumes make the use of the near infrared spectroscopic system according to the invention advantageous.

In some embodiments of the present invention, the near infrared spectroscopic system is used for adjusting the amount of the renewable fuel component to be added to the fuel blend at the oil refinery based on the amount of renewable fuel component in the fuel blend determined by the near infrared spectroscopic system. This may be done in order to meet the varying targets of fuel blend quality and economy and functionality. This use may be in the form of an iterative process. By adjusting the amount of the renewable fuel component to be added to the fuel blend, the ratio between the renewable fuel component and the fossil fuel component is varied. Another aspect of the present invention discloses the use of a near infrared spectroscopic system for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, the system comprising 1 ) means for carrying out near infrared spectroscopic analysis of the fuel blend, and 2) means for determining the amount of the renewable fuel component in the fuel blend based on comparing the near infrared spectroscopic analysis results of the fuel blend to one or more values obtained from predefined near infrared spectrum calibration curves thus providing the amount of the renewable fuel component in the fuel blend, wherein the system is used for decreasing CO2 and/or particle emissions from an engine in a vehicle, wherein the engine is being fuelled by said fuel blend, wherein the system further comprises means for adjusting the engine operating parameters regulating the amount of CO2 and particle emissions to match the amount of renewable fuel component in the fuel blend.

In one aspect of the invention, an engine may be equipped with a system for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, where the system comprises means for carrying out near infrared spectroscopic analysis of the fuel blend, and means for determining the amount of the renewable fuel component in the fuel blend based on comparing results from the near infrared spectroscopic analysis of the fuel blend to one or more values obtained from predefined near infrared spectrum calibration curves thereby providing the amount of the renewable fuel component in the fuel blend, wherein the calculated amount of renewable fuel in the fuel blend is used for optimization of the engine. The engine operation may be optimised based on the composition of the injected fuel composition. Software regulating the engine performance may be adjusted e.g. in terms of optimising power losses, injection, exhaust gas recycling, etc.

In the second aspect of the invention is disclosed a method for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component, wherein the method comprises the steps of: • providing a sample of the fuel blend to a device comprising a near infrared spectrometer;

• measuring one or more infrared spectra of the fuel blend using the near infrared spectrometer;

• determining the amount of renewable fuel component in the fuel blend by analysing the one or more infrared spectra of the fuel blend and comparing the analysis result to one or more predefined near infrared spectrum calibration curves linking a known amount of the renewable fuel component in a fuel blend to the one or more measured near infrared spectra in the fuel blend.

In some embodiments of the invention, the amount of renewable fuel component in the fuel blend is determined within 2 minutes or less, preferably within 1 minute or less, such as within 50 s or less. The precision of the method is about 1 % which is accurate enough for the intended use. The composition analysis time is thereby greatly reduced compared to especially the conventional off-line ¹⁴ C analysis used for determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component. The short operation time is a vast improvement compared to the ¹⁴ C detection method, which cannot be operated online and which takes days for providing the needed result. Presently, the blend composition quality is monitored ex situ with a possible delay of even 24 h while using ¹⁴ C isotope measuring method. Thus, the operation time of 2 minutes or less renders the near infrared spectroscopic system according to the present invention very attractive for online measurements.

Additionally, the second aspect of the invention enables the manufacturing of precise quality blend products in situ or online, further enabling accurate determination of the cost for the renewable fuel blend. The amount of the renewable fuel component in the fuel blend tends to drift from the desired or predetermined value during production of the fuel blend causing a too low anticipated amount or a too high actual amount of renewable fuel component in a fuel blend. This blend quality fluctuation may in both cases imply cost related issues for the blender. The use of the method of the present invention enables an accurate real time determination of the amount of the renewable fuel component, reducing the production cost notably and simplifying the quality monitoring.

Further, by having exact and real time knowledge of the amount of a renewable fuel component in a fuel blend, the amount of CO2 and particle emissions when using the blend in vehicle applications can be minimized by optimization of the engine performance to the known renewable fuel component in the fuel blend.

In some embodiments of the present invention, the method further comprises the step of mixing the renewable fuel component and the fossil fuel component to obtain the fuel blend prior to providing the sample of the fuel blend to the near infrared spectrometer.

In some embodiments of the present invention, an iterative method may be used in which the method further comprises the step of adjusting the amount of renewable fuel component to be mixed with the fossil fuel component in the fuel blend based on the determination of the amount of renewable fuel component in the fuel blend. The iterative process provides a robust and cost efficient method, as it allows the producers to account for drift from the desired/predetermined value during production of the fuel blend, thereby avoiding a too low anticipated amount or a too high actual amount of renewable fuel component in a fuel blend. The use of the method of the present invention instead enables an accurate real time determination of the amount of renewable fuel component in the fuel blend, thereby reducing the production cost notably.

Thus, in some embodiments of the present invention, the adjustment of renewable fuel component and the determination of the amount of renewable fuel component in the fuel blend is done in an iterative process until a predefined target value is reached.

The method may further comprise the step of stopping the adjustment of the amount of renewable fuel in the fuel mixture when a desired pre-defined amount of renewable fuel in the fuel mixture is obtained. As the amount of renewable fuel can be determined within a minute or less, the mixing can be stopped at the exact correct time in the process. With exact correct time may be meant before the determined amount of renewable fuel content deviates too much from the pre-defined amount or when the renewable fuel content is at a pre-defined value.

The adjustment of the amount of renewable fuel component may be performed by decreasing or increasing the amount of renewable fuel component mixed with the fossil fuel component. The iterative process can thus be controlled by adjusting the amount of renewable fuel component added to the fuel blend. Alternatively, the method may be set up to adjust the amount of fossil fuel added to the fuel blend.

The fuel blend may be obtained and/or mixed in an oil fuel refinery.

The one or more near infrared calibration curves may be obtained by 1 ) obtaining a multiple of infrared spectra of fuel blends comprising a known amount of the renewable fuel component in the fuel blend, 2) calculating derivative spectra curves of the multiple of infrared spectra, 3) obtaining a derivative value from each of the derivative spectra curves at a first wavelength, and 4) relating each of the derivative values to the known amount of the renewable fuel component in the fuel blend.

Description of the Drawings

The invention is here described in the following figures and examples, wherein:

Figure 1 shows an overview of the different groups of hydrocarbons normally present in fuel components.

Figure 2 shows NIR spectra of fuel blends with known amounts of renewable fuel components.

Figure 3 shows derivative of the NIR spectra of fuel blends with known amounts of renewable fuel components of figure 2.

Vegetable oils have extremely varying origins like rapeseed, palm oil, soya, soybean oil and other vegetables, which may all be used as possible raw materials for the production of renewable fuel components. By renewable fuel component is therefore normally meant fuel component produced from renewable resources such as vegetable oil or fats and/or animal fats. Other examples include waste fats and residues from the food industry, biogas, algae oil, jatropha oil, and/or microbial oil. Examples of possible waste fats from the food industry include cooking oil, animal fat, and/or fish fat.

The applicant has disclosed production of renewable fuels based on vegetable oil or animal fat refining processes in several patent documents, e.g. FI100248, EP1396531 , EP1741768 and EP1741767. Examples of suitable biomaterials are any kind of fats, and any kind of waxes such as e.g.:

• any kind of plant fats, plant oils, and plant waxes;

• any kind of animal fats, animal oils, animal waxes, animal-based fats, fish fats, fish oils, and fish waxes;

• fatty acids or free fatty acids obtained from plant fats, plant oils, plant waxes; animal fats, animal oils, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof by hydrolysis, transesterification or pyrolysis;

• fats contained in milk;

• metal salts of fatty acids obtained from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof by saponification;

• anhydrides of fatty acids from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof;

• esters obtained by esterification of free fatty acids of plant, animal and fish origin with alcohols;

• fatty alcohols or aldehydes obtained as reduction products of fatty acids from plant fats, plant oils, plant waxes; animal fats, animal waxes; fish fats, fish oils, fish waxes, and mixtures thereof;

• recycled fats of the food industry;

• fats contained in plants bred by means of gene manipulation or genetic engineering;

• dicarboxylic acids or polyols including diols, hydroxyketones, hydroxyaldehydes, hydroxycarboxylic acids, and corresponding di- or multifunctional sulphur compounds, corresponding di- or multifunctional nitrogen compounds, and

• compounds derived from algae, molds, yeasts, fungi and/or other microorganisms capable of producing compounds mentioned above or compounds similar to those.

Examples of fish oils include Baltic herring oil, salmon oil, herring oil, tuna oil, anchovy oil, sardine oil, and mackerel oil.

Examples of plant oils and/or wood-based oils include rapeseed oil, colza oil, canola oil, tall oil, crude tall oil, sunflower seed oil, soybean oil, corn oil, hemp oil, hempseed oil, olive oil, linen seed oil, cotton seed oil, mustard oil, palm oil, peanut oil, castor oil, Jatropha seed oil, Pongamia pinnata seed oil, palm kernel oil, and, coconut oil.

Examples of animal fats include lard, tallow, rendered lard and rendered tallow.

Examples of animal waxes include bee wax, Chinese wax (insect wax), shellac wax, and lanoline (woll wax).

Examples of plant waxes include carnauba palm wax, Ouricouri palm wax, jojoba seed oil, candelilla wax, esparto wax, Japan wax, rice bran oil, terpenes, terpineols and triglycerides or mixtures thereof.

Future methods may also make it possible to increase the diversity of renewable fuels using biomass and grease of animal origin, for example.

The diversity of the sources and the production methods entails significant differences in the chemical structures such as the number of carbon atoms composing the hydrocarbon chains on the one hand, and the ester chemical group on the other hand. These significant chemical specificities entail significant differences as regards the emissions of nitrogen oxide and particles upon their combustion. The amount of renewable fuel component in the fuel blend will naturally vary from 1 to 100 wt-%. The variation may depend on a number of factors including the country in which the fuel blend is to be sold, the time of year and naturally, the composition and properties of the renewable fuel components.

Renewable fuel components typically comprise iso-paraffins and n-paraffins and only a minor amount of other compounds. In the renewable fuel component, the amount of iso-paraffins is typically more than about 50 wt-%, more than about 60 wt-%, more than about 70 wt-%, more than about 80 wt-%, or more than about 90 wt-%. The saturated paraffin content is thus most often the dominating one. In some examples, less than 5 wt-% of the renewable fuel component contains aromatic hydrocarbons, esters, oxygen containing hydrocarbons, and/or unsaturated hydrocarbons. Thus, the renewable fuel component preferably contains less than 3 wt-%, more preferably less than 1 wt-%, of aromatic hydrocarbons, esters, oxygen containing hydrocarbons, and/or unsaturated hydrocarbons.

In some embodiments of the present invention, the renewable fuel component contains less than 0.5 wt-% of the oxygen containing hydrocarbons and esters, such as less than 0.3 wt-% of the oxygen containing hydrocarbons and esters, such as less than 0.1 wt-% of the oxygen containing hydrocarbons and esters. Often, only trace impurities of oxygen containing hydrocarbons and esters are present. The lack of oxygen containing hydrocarbons results in absence of spectroscopic signals in the infrared spectra originating from oxygen containing hydrocarbons or esters.

In some embodiments of the present invention, the renewable fuel component contains less than 0.5 wt-% of aromatic hydrocarbons, such as less than 0.3 wt-% of aromatic hydrocarbons, such as less than 0.1 wt-% of aromatic hydrocarbons. In some embodiments of the present invention, the renewable fuel component is free of aromatic hydrocarbons.

Traditionally, hydrocarbons present in fuel components can be classified in different groups including aromatic (ARO), linear (LIN), isomerised (ISO), naphthenic (NAPH), and olefinic (OLE) hydrocarbons. Further, fatty acid methyl ester (FAME) type components may also be present in fuel components. The FAME type components are, however, normally not observed in renewable fuels, as renewable fuels are essentially oxygen free due to the manufacturing method i.e. hydrodeoxygenation (and isomerisation) processing.

Figure 1 illustrates different groups of hydrocarbons normally present in fuel components and which can be classified in different groups including aromatic 10, linear 12, naphthenic 14, isomerised 16, and olefinic 18 hydrocarbons. Further, fatty acid methyl ester 20 type components may also be present in fuel components.

When the renewable fuel component is produced from feed, comprising plant oils or fats, or animal oils or fats, or fish oils or fats, the resulting renewable fuel component may often have an iso-paraffin content of more than 70 wt-%. In some examples, the iso-paraffin content may constitute more than 80 wt-% or even more than 90 wt- % of the renewable fuel component. This makes the iso-paraffin content in the renewable fuel the dominating type of component.

Often, the renewable fuel component comprises C15 to C18 paraffins as the dominant paraffin type. The paraffins smaller than C15 paraffins and the paraffins larger than C18 paraffins will normally be present in an amount of less than about 20 wt-% and 10 wt-%, respectively.

The renewable fuel component may be produced by means of a hydrotreatment process. Hydrotreatment involves various reactions where molecular hydrogen reacts with other components, or the components undergo molecular conversions in the presence of molecular hydrogen and a solid catalyst. The reactions include, but are not limited to, hydrogenation, hydrodeoxygenation, hydrodesulfurization, hydrodenitrification, hydrodemetallization, hydrocracking, and isomerization. The renewable fuel component may have different distillation ranges which provide the desired properties to the component, depending on the intended use.

When choosing an analysis method for determining the amount of a renewable fuel component in a fuel blend, spectroscopic analysis in the near infrared region has proven to be a promising method. By the term near infrared (NIR) is meant light in the wavelength range between 700-3000 nm, preferably in the wavelength range from 700-2500 nm.

In the longer mid infrared (MIR) wavelength range between 3.000-10.000 nm, the fundamental strong vibrational absorption bands are normally observed. However, in this spectral range the liquid may absorb so strongly that the absorption length needs to be much less than 1 mm in order to get any light through the sample. Additionally, the detection instrumentation is normally expensive and difficult to use due to the requirement of cooled detectors etc. Thus, the NIR spectral region is favoured compared to the MIR spectral range, since instrumentation is more affordable and robust and the absorption path length can be on the order of millimetres or even more without observation of signal saturation.

The NIR spectral range can be divided into a number of different sub-ranges all being regions where specific molecular vibrations may be observed. When choosing an adequate operational spectral range, the sensitivity of the obtainable signal always needs to be balanced with the obtainable selectivity, i.e. how well one can spectrally separate the different absorption bands originating from different substances and/or hydrocarbons in the solution.

In the spectral NIR region from approximately 1950-3000 nm bordering to the MIR spectral region, absorption signals origination from the combinations of e.g. a stretch and a bending mode, are normally observed. An additional combinational spectral region is observable around 1200-1700 nm. The combinations observable in the spectral range from 1200-1700 nm are normally combinations of three vibrations.

Overtone regions originating from the strong fundamental vibrations observed at higher IR wavelength ranges are normally observed in the NIR spectral region. The 1 ^st , 2 ^nd and 3 ^rd overtone regions are normally observable in the spectral ranges from approximately 1500-2150 nm, 1325-1650 nm, and 825-1 100 nm, respectively. The combination region from 1200-1700 nm may thus overlap with the overtone regions. Depending on the chemical structure of a specific hydrocarbon compound, the NIR spectrum observed will vary, as small differences in the hydrocarbon structure often result in differences in the NIR spectrum.

Using an adequate chemometric model employing NIR data, hydrocarbons and fatty acid components or the combinations thereof can be identified and quantified. Overall, the NIR spectra of renewable fuel has been found to differ from the NIR spectra of fossil fuel in such a way which allows the determination of the composition of fuel blends by utilizing knowledge obtained from NIR spectra of known amounts of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component. In this manor, the specific origin of spectral absorbance peaks is not in itself a known requirement as the difference in spectral signatures may be used for determining the ratio of the fuel blend mixture.

Different NIR spectral ranges may be used for identifying spectral differences allowing for determination of the renewable fuel component in a fuel blend also comprising fossil fuel.

An example of a narrow spectral range includes the near infrared wavelength range from 800 nm to 900 nm. In this spectral range where the 3 ^rd overtones are normally found, near infrared signals are often weak. However, the different absorption features may possibly be better spectrally separated from each other in this spectral wavelength range although the signal is weak. More easily spectrally separable features may provide an improved accuracy and performance of the measurements. Silicon based detector technology may be used at these short NIR wavelengths, which lowers the costs due to the low price of silicon based detectors.

Alternatively, the spectral wavelength range from 1000 nm to 1600 nm, such as from 1 100-1300 nm, or from 1 150-1250, nm may be used for determining the amount of renewable fuel in a fuel blend also comprising fossil fuel components. In this spectral range, where the 2 ^nd overtone bands are observable, absorption signals are normally stronger, which increases the sensitivity of the measurements. The detectors suitable for measuring NIR spectra in the spectral wavelength range from 1000-1600 nm are however normally slightly more expensive compared to e.g. silicon based detectors.

Yet alternatively, the spectral wavelength range from 1600 nm to 1800 nm, or even more narrow from 1700 nm to 1775 nm, also provides NIR spectra, where signals from renewable fuel components may be separable from those from fossil fuel components. Thus, which spectral range within the NIR spectral range to use may vary depending on the requirements to cost, sensitivity and selectivity in the spectral data.

Figure 2 shows infrared spectra of fuel blends measured in the spectral range from 1550-1950 nm, where the composition of the different mixtures of renewable fuel and fossil fuel components are known for each blend. As seen in figure 2, the absorbance signals in the bands centred at approximately 1665 nm, 1750 nm, and 1880 nm (indicated with arrows) increases as the amount of renewable fuel decreases, whereas an opposite trend is seen in the band centred at approximately 1820 nm. By band is to be understood the band and/or combination of bands, which originate from the vibrations mainly relating to 1 ^st overtones from CH3, CH2 and CH groups, possible with contributions from vibrations relating to 2 ^nd overtones from CH3, CH2 and CH groups. If the majority of the renewable fuel component is saturated paraffinic, a larger contribution from CH3 and CH2 groups are expected - in particular from the CH2 groups if the saturated paraffinic contribution are the long chained C15-C18 paraffins.

When analysing the infrared spectra as the ones e.g. shown in figure 2, chemometric models employing the NIR data may be utilized. From the NIR spectra as exemplified in figure 2, one or more calibration curves may be obtained e.g. relating the known amounts of the renewable fuel component to an absorption value at one or more wavelength. The calibration curves may subsequently be used when comparing infrared spectra of fuel blends with unknown amounts of the renewable fuel component for determining the amount of the renewable fuel component in the fuel blend with the unknown amount of renewable fuel component on basis of the calibration curve(s). When looking at figure 2, the absorption value at the band centred around 1750 nm may be applied for creating a calibration curve plotting the absorption value as a function of the known wt-% of renewable fuel component in the fuel blend.

When measuring NIR spectra on different days, a difference in offset in the data may be observable even when measuring the same sample. This difference is normally a result of NIR sensor drifts and day-to-day variations. For a reliable determination of the amount of renewable fuel in a fuel blend, a new calibration curve often needs to be determined before starting to analyse the amount of renewable fuel in a fuel blend with an unknown amount of renewable fuel component.

Alternatively, background subtraction from the measured NIR spectra may be performed before identifying a usable value of the absorption at a pre-determined wavelength.

As an alternative to subtracting background signals from the measured NIR absorption spectra, means for analysing the one or more infrared spectra may obtain the derivative spectrum of the one or more infrared spectra. By determining the derivative spectra of the measured infrared spectra, background variation observed between measurements performed on different days/different times during the day may be vastly reduced, if not completely avoided. A more robust system is thereby obtained.

Figure 3 shows the first derivative of the infrared spectra shown in figure 2. From figure 3, the spectral difference when varying the content of renewable fuel and fossil fuel is detectable at different wavelengths compared to the absorbance spectra shown in figure 2. The advantage of comparing the first derivative of the spectra instead of the raw spectra is that equipment-induced background variations are not observable. Calibration curves can therefore be obtained directly from the first derivative spectra without correcting for background signals in the original spectra first. One way of obtaining background free calibration curves is to first calculate derivative spectra curves of a multiple of infrared spectra of fuel blends comprising a known amount of the renewable fuel component in the fuel blend. An example of such derivative spectra is shown in figure 3. After obtaining the derivative spectra, a derivative value from each of the derivative spectra curves at a first wavelength is obtained. In figure 3, a suitable wavelength choice for a calibration wavelength could be e.g. somewhere between 1705-1710 nm, around 1730 nm or around 1755 nm, where a large change in the derivative absorption value is observed depending on the amount of renewable fuel in the fuel blend. The derivative values at the chosen wavelength are afterwards matched to the known amount of the renewable fuel component in the fuel blend. Normally, one will obtain a set of NIR spectra and corresponding first derivative spectra to ensure that the correct calibration wavelength is chosen.

It has surprisingly been shown that very reliable calibration curves focusing on the value of the derivative spectra at a favourably chosen wavelength are sufficient to obtain a very reliable calibration curve allowing for determination of the amount of renewable fuel in a fuel blend. By obtaining the derivative spectra instead of the directly measured infrared spectra, the background signals are greatly diminished.

The other spectral regions/sub-regions in the NIR spectrum may also be used for analysing and determining the amount of a renewable fuel component in a fuel blend comprising said renewable fuel component and a fossil fuel component in a similar manner as exemplified with the examples shown in figures 2 and 3.

The NIR calibration curve may be comprised in the system. Thus, the system may be setup to include a multiple of calibration curves representing fuel blends with known amounts of renewable fuel components.

Each of the measured calibration curves may be a representative of a known type of renewable fuel and its spectral characteristic in a fuel blend comprising known amounts of this known type of renewable fuel. The renewable fuel component may change as a function of the season of the year and the source of the renewable fuel, resulting in that the NIR absorption spectra of the fuel blend may change over the year. Regular measurements of calibration curves based on known blend mixtures may thus be required. The amount of renewable fuel in the fuel blend is normally determined within 1 -2 minutes or less. The operation time of 1 -2 minutes or less makes the system and the method very suitable for online measurements, e.g. at an oil refinery. The short time for obtaining reliable information on the amount of renewable fuel component in the fuel blend is a vast improvement compared to the ¹⁴ C detection method, which is not online and which takes a day or more before providing a result.

Determining the amount of the renewable fuel component may be carried out online while producing the fuel blend, i.e. during the process of mixing a renewable fuel component and a fossil fuel component. By online determination of the renewable fuel component in the fuel blend during the fuel blend mixing process, a constant feedback is obtainable allowing the producers of the fuel blend to interactively adjust the content of the renewable fuel added to the fuel blend. Thereby the amount of renewable fuel, which is to be added to a fuel blend in order to obtain a pre determined ratio between renewable fuel and fossil fuel component (often defined by industry standards), does not need to be determined with a very high accuracy prior to starting the fuel blend mixing process, as the ratio between the different component may be adjusted during the mixing process based on the results of the infrared spectral analysis. This possibility does not exist if online measurements are not an option, making the use of the system according to the invention highly advantageous when producing large quantities of fuel blend comprising a mixture of renewable fuel and fossil fuel components.

The fuel blend may be produced at an oil refinery. After the amount of renewable fuel has been determined in a fuel blend with an unknown amount of renewable fuel using the method described herein, the amount of renewable fuel may subsequently be regulated on site in the refinery. At oil refineries, large quantities of fuel blends are normally produced making the use of the system according to the invention highly advantageous, as the amount of renewable fuel component mixed with the fossil fuel component during the production process may be adjusted up and down at least once a minute based on the measurement of the exact renewable fuel component online. The iterative process provides a robust and cost efficient method, as it allows the producers to account for drift from the desired/predetermined value during production of the fuel blend, thereby avoiding a too low anticipated amount or a too high actual amount of renewable fuel component in a fuel blend. The use of the method of the present invention instead enables an accurate real time determination of the renewable fuel component in the fuel blend, thereby reducing the production cost notably.

The process of regulating the amount of renewable fuel added to a fuel blend in a refinery may thus advantageously be performed iteratively by determining the amount of renewable fuel in the fuel blend, regulating the amount of renewable fuel added to the fuel mixture, measuring the amount of renewable fuel component in the fuel blend as so forth iteratively until a desired pre-defined amount of renewable fuel component in the fuel blend is obtained.

Stopping the adjustment of the amount of renewable fuel in the fuel mixture when a desired pre-defined amount of renewable fuel in the fuel mixture is obtained is also possible based on the online measurements and the updates of the result online. As the amount of renewable fuel can be determined within a minute or less, the mixing can be stopped at the exact correct time in the process, where the pre determined amount of renewable fuel component in the fuel blend is obtained.

Examples

Example 1

12 samples of fuel blends all with known amounts of summer grade renewable fuel and summer grade fossil fuel were provided and the near infrared spectra of the samples were measured in the NIR spectral range from 1550 to 1950 nm. The fuel blends varied in composition, with mixtures from one fuel blend having no renewable fuel component to another fuel blend comprising only renewable fuel components. Six samples were chosen for obtaining a calibration curve. Before calculating the calibration curve, the measured NIR spectra were corrected for off-set variation by calculating the derivative of the NIR spectra. A representative wavelength was chosen and the absorbance value of the obtained derivative spectrum was plotted as a function of the known content of the renewable fuel component in the fuel blend. A calibration curve line was obtained from the plots. Derivative spectra were obtained from the NIR spectra of the remaining six samples. A wavelength was chosen and the absorbance value of the obtained derivative spectrum at this chosen wavelength was obtained. By comparing the absorbance values from the remaining six samples with the calibration curve, values representing the estimated content of renewable fuel component in the fuel blend in the six remaining samples were obtained. By comparing the obtained estimated values for the renewable fuel component with the known values of the same in the six samples, it could be determined that the precision of the method when using only six samples as basis for obtaining the calibration curve, was more than 2%. Using a larger set, such as double amount, for obtaining the calibration curve improves this accuracy to about 1 %.