Neste, currently largest producer of renewable drop-in fuels (primarily diesel) with its NEXBTL platform (earlier post), has filed a patent (US20150144087) on a gasoline composition (and the method for making it) comprising up to 20 vol% (preferably from about 10-15 vol.%), of paraffinic bio-hydrocarbons originating from the NEXBTL process.
In addition, the fuel can incorporate oxygenates such as ethanol (5 to 15 vol%); iso-butanol (5 to 20 vol%, preferably about 10 to 17 vol%); or ETBE (7 to 25 vol%, preferably about 15 to 22 vol%). The resulting fuels with high bioenergy content can be used in conventional gasoline-fueled automotive engines. In a related paper published in the ACS journal Environmental Science & Technology, a team (Aakko-Saksa et al.) from VTT Technical Research Centre in Finland and Neste showed that a combination of ethanol or isobutanol with bio-hydrocarbon components offers an option to reach high gasoline bioenergy content for E10-compatible cars.
The NEXBTL process hydrotreats, deoxygenates and isomerizes vegetable oils or waste fats to produce drop-in renewable diesel and jet fuels; renewable isoalkane; renewable propane; and renewable naphtha.
Naphtha is a generic term applied to the liquid fraction produced in petroleum refining with an approximate boiling range between 122–400 °F, and comprises C5 to C10 paraffinic hydrocarbons. Naphta is classified as light or heavy, and has numerous applications—including gasoline blending—depending upon, among other things, paraffin content (lean or rich), volatility, solvent properties, purity and odor. Neste began sales of NEXBTL Naphtha in 2012. (Earlier post.)
The patent. The use of ethanol in conventional gasoline cars is generally limited to 10-15 v/v % (vol%, approx. 7-10 as an energy equivalent percentage) due to technical restrictions, Neste notes. Higher ethanol blending ratios are currently possible only by using Flexible Fuel Vehicle (FFV) technology designed to use any proportion of, for example, ethanol and gasoline in the blend.
Neste found that a gasoline fuel containing increased proportion of components derived from renewable sources can be formulated by incorporating paraffinic hydrocarbons originating from biological sources—i.e., the NEXBTL naphtha stream—optionally together with oxygenates, into a hydrocarbon fuel composition.
As part of the patent application, Neste submitted emissions test results from a range of 13 biofuels and one fossil fuel. The test fuels represented different bioenergy contents, oxygen contents and fuel chemistries. The fuels, except for the E85 fuel on the market, were match-blended using fossil gasoline refinery components and gasoline biocomponents.
Biocomponents were ethanol, isobutanol, n-butanol, ETBE and a paraffinic and oxygen-, aromatic- and sulphur-free Neste Oil renewable gasoline component represented liquid bio-hydrocarbons from different processes.
Neste divided the test fuel matrix into two sets: high-oxygen containing fuels (oxygen content 6 to 30 m/m %) and low-oxygen containing fuels (oxygen content 0 to 4 m/m %).
The five high-oxygen containing fuels were tested only with a flex-fuel vehicle. The nine low-oxygen fuels were tested using both conventional cars and the FFV car. Oxygen-free fossil hydrocarbon gasoline was used as a reference fuel.
Neste used three bioenergy substitution levels (7, 14 and 21 Eeqv%) were used. The 7 Eeqv% bioenergy level represented currently used biocomponents, ethanol (10 v/v %) and ETBE (22 v/v %), whereas the Eeqv% level represented either butanol or bio-hydrocarbon alternatives in concentrations of 15-17 v/v %.
The highest bioenergy level, 21 Eeqv%, was designed to represent both oxygenated and non-oxygenated biocomponent alternatives. The 21 Eeqv% bioenergy level was achieved either by adding 15 v/v % non-oxygenated bio-hydrocarbon (14 Eeqv%) to the oxygenated component or purely by increasing the fuel’s oxygenate content. Market fuel E85 represented the highest bioenergy substitution value, 56 Eeqv%.
Aromatic contents, densities, sulfur contents and vapor pressures of the fuels were kept as constant as possible. The aromatic content of the high-oxygen content fuels was 16-21 v/v %, whereas the low-oxygen containing fuel aromatics were 27-35 v/v %. The benzene content was below 0.5 m/m % in all fuels. The density of all blended fuels was 740 to 756 kg/m.sup.3. The sulphur contents of all fuels were below 10 mg/km.
The vapor pressure of the gasolines was 69±2 kPa, except for the market E85 fuel (35 kPa). Research Octane Numbers (RON) were within the measuring range of the ASTM D2699 method with low-oxygen containing fuels, whereas the RON value of the high-oxygen containing fuels must be considered only indicative. Motor Octane Numbers (MON) in both fuel sets were from 86 to 92 and within the ASTM D2700 method measuring range. The E85(56) was commercial grade fuel, and its octane numbers were not measured. Typically, commercial grade E85 fulfills the Swedish standard SS 155480, with the RON around 104 and the MON around 88.
|Bioenergy Eeqv%||Volume v/v%||Oxygen m/m%||LHV MJ/kg|
|High oxygen content|
|Ethanol + ETBE||19||39||10.3||38.4|
|Isobutanol + ETBE||20||36||7.3||40.1|
|Low oxygen content|
|Renewable + ethanol||22||26||4.0||41.4|
|Renewable + ETBE||21||35||3.4||41.6|
|Renewable + isobutanol||28||32||3.8||41.5|
The results show that there are many options for increasing the bioenergy content of gasoline by up to 30% without increasing the gasoline oxygen content to a higher level than can be tolerated by conventional gasoline cars. This means that various fuels with a high bioenergy content and different chemistries can be used with conventional gasoline-fueled cars. In most cases, using ethanol, isobutanol, n-butanol, ETBE or blends of these together with renewable hydrocarbon components in gasoline does not significantly or harmfully impact emissions from conventional cars. In particularly preferred embodiments, the combination of a renewable component with oxygenates indicated a reduced exhaust toxicity when compared with fossil fuel.—“Gasoline Compositions And Method Of Producing The Same”
Aakko-Saksa et al. In their study, Aakko-Saksa et al. examined the exhaust emissions of three cars using different biofuels at a temperature of −7 °C. The biofuels studied contained both low- and high-concentration ethanol blends, isobutanol, and biohydrocarbons. A multipoint fuel injection car (MPFI), direct-injection spark-ignition car (DISI), and flex-fuel car (FFV) represented three different spark-ignition-car technologies.
The Neste Oil renewable gasoline component represented liquid biohydrocarbons. The batch used was a C5−C9 paraffinic component (oxygen-, aromatic-, and sulfur- free; density, 672 g/L; dry vapor pressure equivalent (DVPE), 45 kPa), which is a side product of producing renewable diesel from vegetable oil and animal fat by using Neste Oil’s NExBTL hydroprocessing technology.
They found differences among ethanol, isobutanol, and biohydrocarbons as fuel components. For example, E85 resulted in high acetaldehyde, formaldehyde, ethanol, ethene, and acetylene emissions when compared to E30 or lower ethanol concentrations. Isobutanol-containing fuel showed elevated butyraldehyde, methacrolein, and isobutanol emissions. The highest particulate matter (PM) emissions, associated polyaromatic hydrocarbon (PAH) and indirect mutagenicity emissions were detected with the DISI car.
Oxygenated fuels reduced PM emissions and associated priority PAH emissions in the DISI car. PM and PAH emissions from the MPFI and FFV cars were generally low. A combination of 10% ethanol and biohydrocarbon components did not change emissions significantly when compared to ethanol-only-containing E10 gasoline.
In this study, emissions from the spark-ignition gasoline cars proved to be elevated at low test temperature. The impact of fuels on exhaust emissions was substantial in many cases, but in this respect there were differences between cars representing different engine technologies. Direct-injection engine technology (DISI car) showed elevated PM emissions and associated PAH and mutagenicity emissions compared to the indirect-injection engine technology (MPFI and FFV cars). The PM emissions and associated PAH emissions of the DISI car could be reduced by oxygenated fuels. This applies to ethanol and isobutanol as well as to a combination of ethanol and biohydrocarbons. In the FFV car, the use of high ethanol concentrations at low temperatures deserves further research.
… Spark-ignition gasoline car emissions are concentrated close to living areas and parking places, where cold-start emissions play a significant role. In particular, PAH and mutagenicity emissions from gasoline cars at moderate and cold temper- atures warrant further attention. In-depth research on health and environmental perspectives, including the secondary atmospheric reactions, should be considered in parallel with climate change issues when new fuels and technologies are considered.—Aakko-Saksa et al.
Päivi T. Aakko-Saksa, Leena Rantanen-Kolehmainen, and Eija Skyttä (2014) “Ethanol, Isobutanol, and Biohydrocarbons as Gasoline Components in Relation to Gaseous Emissions and Particulate Matter” Environmental Science & Technology 48 (17), 10489-10496 doi: 10.1021/es501381h