NExBTL Renewable Synthetic Diesel

To be able to blend a year-round renewable fuel for the diesel pool requires an improved synthetic diesel over FAME. Neste Oil Corporation has proposed a different renewable diesel and has developed the corresponding biofuel technology, called Next generation Biomass To Liquid diesel technology. The novel NExBTL diesel component (GTL-like) utilises a proprietary conversion process for vegetable oils and animal fats [15, 74, 75]. NExBTL Renewable Synthetic Diesel is a biofuel of superior quality.

The feedstock for the traditional biodiesel esters and Neste Oil’s NExBTL product is the same, namely natural organic esters contained in vegetable oils and animal fats. The difference is in the processing and chemical nature of the end products. Whereas FAMEs are chemically methyl esters of long-chain fatty acids carrying oxygen in their ester group, NExBTL is a hydrocarbon diesel (linear and/or branched C10-C22 alkanes) containing no oxygen (see Fig. 15.19).

V egetable oils and animal fats may be processed to decompose the ester and/or fatty acid structure and to saturate the double bonds of the hydrocarbon chains, thus yielding about 80-85% of n-paraffin product relative to the mass of the starting material. This product, admixed with a diesel fuel, shows poor

rcooch2 R’—CH3 + CO + h2o

Triglyceride, NExBTL biodiesel,

R = nC R’ = (n-1)C

CH3CH2CH3 Propane (fuel gas)

15.20 Simplified Neste Oil’s NExBTL process scheme.

performance at low temperatures. In addition, и-paraffins having a carbon number of fatty acids are waxy with a high solidification point, typically above 283 K, thus limiting the use of these compounds in diesel fuels at least at low temperatures. PCT Int. Publ. No. WO 2004/022674 A1 to Jakkula et al. (to Fortum Oyj) [76] discloses a diesel fuel composition obtained by hydrotreating of vegetable oils, animal fats and/or fish oil, and optionally by isomerising the hydrocarbon, typically waxy и-paraffins, to give branched hydrocarbon chains, thus improving the low-temperature properties of the paraffin. In the NExBTL Renewable Synthetic Diesel process technology, the fatty acid feedstock is ‘hydrotreated’, that is, it is reacted with hydrogen (produced at a refinery), as shown in Fig. 15.20. Side products include propane and gasoline-premium fuels which are also produced from the renewable, biological feedstock. While NExBTL technology is not afflicted by the glycerol by-product problem, the process produces considerable amounts of

CO and CO2 (see Fig. 15.19). The NExBTL process generates only products for the fuel market, shows good energy efficiency and is fully integrated with a refinery. The NExBTL process allows conversion of vegetable oils to GTL-like biodiesel by:

• mild pre-treatment for removal of insaturations;

• hydrogenolysis of the fatty acid ester bond with production of paraffins and formation of CO2 and H2O; and

• hydro-isomerisation of linear paraffins for improvement of cold properties without loss of cetane number.

Table 15.17 compares NExBTL synthetic diesel and FAME manu­facturing.

NExBTL is made from renewable biomass sources, namely fatty acids from vegetable oils and animal fats. With only 2-3 wt% addition of hydrogen, NExBTL is 97-98% renewable (‘green’ product). NExBTL contains no sulphur, oxygen, nitrogen or aromatics and has a very high cetane number compared to FAME-based compositions (see Table 15.18). Renewable diesel satisfies ASTM D 975 diesel standards either as a neat component or when blended with other typical diesel-fuel components. The absence of sulphur, aromatics and oxygenates allows NExBTL to be used in the world’s most stringent diesel fuel formulations like California’s CARB diesel, Swedish MK1 diesel and the ultra-clean burning World Wide Fuel Charter (WWFC) Category 4 diesel. The high cetane value of between 84 and 99 means that NExBTL can be used to improve the quality of conventional diesel or to upgrade off-spec diesel fuel.

Advantages of this diesel fuel composition are superior performance at low temperature. Cold properties are flexible by modulation of the hydro-

Table 15.17 Comparison between NExBTL synthetic diesel and FAME manufacturing (after ref. [77])

Feature

NExBTL diesel

FAME

Raw material

Flexibility in use of several

More restricted to specific

origin

vegetable oils and animal fats

feedstock

Additional feeds

Hydrogen

Methanol

Product quality

Excellent blending properties; no real restriction

Limitations with blending, stability and cold properties

By-products

Handled in refinery

Glycerol

NOx emission

Reduced

Increased

CO2 balancea

0.5-1.5

1.4-2.0

Logistics

Refinery logistics

Separate logistics

Plant size

Large units integrated with oil refinery

Small to large independent units

kg CO2/kgoe fuel.

Table 15.18 Characteristics of Neste Oil’s NExBTL Renewable Synthetic Diesel

• Very high cetane value (84-99)

• Flexible cold properties (CP as low as 239 K)

• Excellent storage stability

• No sulphur, no aromatics, well-balanced distillation curve

• Less emissions than ultra-low sulphur diesel fuel

• Renewable content exceeding 97% (‘green’ product)

• Exploits existing fuel infrastructure

• Superior fuel properties that can be used to upgrade the diesel pool

• Blending with diesel in high ratios (up to 60%)

• Rather low density

• No need for engine modifications

• Registered product (conforms with European norm 2003/30/EC)

isomerising capacity of the process. Cloud point of NExBTL can be adjusted in production from 268 K to 239 K to meet the needs of various climatic conditions. Heating value is similar to the EN 590 hydrocarbon fuel. NExBTL is a stable hydrocarbon without unsaturated components and can be stored for extended periods. The hydrocarbon molecular structure makes solubility of the synthetic diesel product into water very low. NExBTL synthetic diesel is compatible with the existing vehicle fleet as well as with the diesel fuel logistic system and is technically easy to blend in petrodiesels in all ratios. NExBTL in diesel blends decreases both regulated and unregulated (e. g. aldehydes) exhaust emission components. Decrease in emissions is dependent on the proportion of NExBTL. When compared with emissions from the ‘ clean’ European sulphur-free EN 590 diesel, NExBTL Renewable Synthetic Diesel shows positive environmental benefits with considerable reductions in tailpipe emissions: life cycle GHG, >60%; NOx, 7-14%; PM, 28-46%; HC, >20%; and CO, >5%. An assessment of energy and GHG of NExBTL from rapeseed oil and palm oil is available [78].

The non-oxygenated NExBTL synthetic, produced in a conventional hydrogenation process using vegetable oils and animal fats as a raw material, has similar chemistry and fuel properties as the present GTL and BTL diesel fuels, but higher raw material costs (closer to conventional biodiesel). NExBTL and most GTL-type hydrocarbon fuels have different chemistry compared to conventional biodiesels (FAMEs). Table 15.19 compares the properties of the isomerised biological NExBTL component, GTL diesel, RME and a commercial diesel fuel. Properties of the high-quality NExBTL synthetic diesel, which is basically a mixture of n — and iso-paraffins, are comparable to the best existing premium hydrocarbon diesels available today, such as GTL distillate fuels. In theory, NExBTL can be used neat. NExBTL biofuel meets the requirements of both the European diesel fuel standard EN 590 and the automotive and engine manufacturers WWFC Category 4

Table 15.19 Comparison of some key fuel properties of diesel fuels (after refs [15, 74, 79])

Fuel property

NExBTL biofuel

GTL diesel

FAME (RME)

EN 590/2005

Density @ 288 K (kg/m3)

775-785

770-785

~ 885

820-845

Viscosity @ 313 K (mm2/s)

2.9-3.5

3.2-4.5

~ 4.5

~ 3.5

Cetane number

84-99a

73-81

~ 51

~ 53

Distillation 10 vol% (K)

533-543

~ 531

~ 613

~ 473

Distillation 90 vol% (K)

568-573

598-603

~ 608

~ 623

Cloud point (K)

268-239

273-248

~ 268

273-258

Energy density (MJ/kg)

~ 44

~ 43

~ 38

~ 43

Energy content (MJ/L)

~ 34

~ 34

~ 34

~ 36

Total aromatics (wt%)

0

0

0

~ 25

Polyaromatics (wt%)

0

0

0

~ 4

Oxygen content (wt%)

0

0

~ 11

0

Sulphur content (ppm)

~ 0

< 10

< 1

< 10

Lubricity

< 460b

< 460b

< 460

< 460b

Oxidative stability

Good

Good

Challenging11

Good

aMeasured as blending cetane number. bLubricity additive required. cAdditive requirement.

fuel specification, except for density, which is ~ 780 kg/m3 (EN 590: 835 kg/m3). The density value is the only blending constraint limiting blending of the synthetic diesel product to about 65 vol%, which of course is not a real restriction in refinery operations. NExBTL technology proves that no compromise is necessary with renewable fuel products and product quality for transportation fuels.

Although biomass-based renewable fuels are usually produced outside of refineries, the NExBTL technology shows profitable opportunities to incorporate biomass-based materials into the refining industry [77]. In fact, there exists a clear commercial driver to integrate synthetic diesel production within a refinery and use the existing utility and quality systems as well as diesel oil logistics systems.

The first 170 kt/yr NExBTL production plant at Porvoo refinery in Finland, which started operating in the first half of 2007, runs on a mixture of PMO (80%), RSO and animal fat and is producing a product that meets ASTM D 975 standards with a 253 K cloud point. A second, similar plant, again in Porvoo, is scheduled for 2009. Albemarle Corp. supplies the catalysts for Neste Oil’s renewable diesel. Neste Oil has recently started construction of the world’s largest (800 000 MT/yr, 271 MMgy) renewable diesel production facility in Tuas, Singapore (scheduled late 2010; 7550 million), based on NExBTL technology, using primarily RSPO certified palm oil from Malaysia and Indonesia (when available in sufficient volumes) and animal fats. Similary, in May 2009 Neste Oil also broke ground for a 7670 million, 800 kt/yr capacity hydrodiesel plant in Rotterdam, The Netherlands, to be run on a variety of feedstocks. Investment costs per installed gallon (72.85) are higher than for biodiesel plants. On the other hand, hydrogen production requires far less energy than methanol. Another NExBTL unit (200 kt/yr) is expected in Austria. Also a large-scale NExBTL plant adjacent to one of Total’s oil refineries has been designed for a wide range of VOs and animal greases. The technology could also find application for the conversion of algal oil [80] and jatropha oil (both not yet available in commercial quantities), although saturated oils are better feedstocks in terms of hydrogen consumption. The NExBTL Renewable Diesel process was honoured with the Cleantech Finland award (Sitra Innovation Fund).

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