Green diesel production by hydrorefining renewable feedstocks
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Green diesel production by hydrorefining
renewable feedstocks
Life cycle analysis of green diesel produced from renewable feedstocks indicates
relatively high energy efficiency and low greenhouse gas emissions
Tom N Kalnes and Terry Marker UOP David R Shonnard and Ken P Koers Michigan Technological University
A
pproximately 50% of globally
produced crude petroleum is refined Water, CO 2
into transportation fuels, the fastest
growing component of the energy sector.
This sharply rising use of a non-renewable Hydrogen
feedstock has a significant impact on Oil, fat
grease Light
greenhouse gas emissions. Biomass is the R1 Separation fuels
only renewable energy source that can be
converted into liquid transportation fuels. Product Green diesel
R2 recovery
Therefore, increasing biofuel usage in the
transportation sector can significantly
reduce greenhouse gas emissions as well as
diversify energy sources, enhance energy Figure 1 Simplified Ecofining process diagram
security and stimulate the rural agricultural
economy. Worldwide production of biofuels and the volumetric yield of deoxygenated operates in mild conditions and integrates
has experienced rapid growth and increased hydrocarbon products is greater than 100%. well within existing petroleum refineries. If
international market demand. Projected Selectivity to diesel boiling-range paraffin required, a portion of the light fuel co-product
future shortages of crude oil coupled is very high. The primary deoxygenation can be steam reformed to generate all of the
with the growing worldwide demand for reaction by-products are propane, water hydrogen consumed in the process.
transportation fuels has also raised interest and carbon dioxide. The effluent from R1 is
in synthetic diesels (syndiesels) produced by immediately separated at reactor pressure Feedstocks
Fischer-Tropsch (FT) synthesis of a syngas to remove carbon dioxide, water and low Feedstocks that are suitable for the process
stream derived from coal (CTL), stranded molecular weight hydrocarbons. The include plant-derived oils such as soybean,
natural gas (GTL) or biomass (BTL). resultant diesel is mixed with additional rapeseed and palm. However, in the future,
This article describes the UOP/Eni hydrogen gas and then routed to an non-edible oils such as jatropha and algal oils
Ecofining process for green diesel production, integrated catalytic hydro-isomerisation will become increasingly important sources
and compares the energy efficiency and reactor (R2), where a branched paraffin- of Ecofining feedstock. Unlike base-catalysed
green house gas (GHG) emissions associated rich diesel fuel is produced. In this manner, transesterification, the Ecofining process is
with green diesel to those of petroleum the cold flow properties of the diesel are robust to high concentrations of free fatty
diesel, biodiesel and syndiesel derived from adjusted to meet required specifications. The acids, enabling other, lower-cost materials
coal and natural gas. isomerisation reaction is also selective and, such as tallow oil and waste greases to be used
as a result, consumes very little hydrogen. as feedstocks. Feedstocks rich in saturated
Two-stage hydrorefining Isomerised product is separated from fats, such as palm and tallow oils, require
The Ecofining process is an integrated two- excess hydrogen in a conventional gas/ substantially less hydrogen than feedstocks
stage hydrorefining process. A simplified liquid separator. After purification, the excess with a higher olefin content, such as soybean
block flow diagram of the process is shown hydrogen is recycled back to R1 and R2 to and rapeseed oils. However, depending on
in Figure 1. In the process, feedstock is maintain the minimum required hydrogen the concentration of specific contaminants,
pumped to process pressure, mixed with partial pressure. Make-up hydrogen is added a pretreatment of these materials to remove
recycle hydrogen, then sent to a multi-stage to the process to balance both chemical solids and salts may be required.
adiabatic, catalytic hydrodeoxygenation consumption and solution losses. The liquid
reactor (R1), where the renewable oil is product is sent to the product recovery Product range
saturated and completely deoxygenated. section of the process, where conventional While the primary product of the Ecofining
Gas recycle to R1 is set to achieve a minimum distillation steps are employed to separate process is green diesel, smaller amounts of
hydrogen partial pressure at the reactor co-products such as propane and naphtha. other renewable fuels are also produced.
outlet. Conversion of feed is complete The process for producing green diesel Table 1 contrasts Ecofining inputs and
www.biofuels-tech.com BIOFUELS TECHNOLOGY 7produced in the refinery’s fluid catalytic
Comparison of process feeds and main products
cracking (FCC) unit.
The basis of the study was as follows:
Feeds
Ecofining green diesel
Weight, % Volume, % Feeds
Biodiesel
Weight, % Volume, %
• Northern European location
Vegetable oil 100 100 Vegetable oil 100 100 • 150 000 barrels per day (bpd) capacity
Hydrogen 1.5–3.8 – Methanol 10 11 • Crude mix: 50% Brent/44% Arab
Chemicals 4 – Light/6% Arab Heavy
Products
Propane
Weight, % Volume, %
5 9
Products
FAME
Weight, % Volume, %
96 100
• Crude price: $491/MT Brent, $458/MT
Butane 0–2 0-3 Glycerol 10 7 Arab Light, $423/MT Arab Heavy
Naphtharapeseed oil, palm oil and inedible tallow. forms of that energy (fossil, biomass and so are transported to a processing facility,
Four inventory data sources were included on). Of further interest is the Fossil Energy where they are crushed to extract oil. The
in the scope of the expanded study, with Demand (FED), which accounts for all of conversion of plant oil to biodiesel was
the aim of adding confidence to the study’s the fossil energy sources used throughout modelled using data from a 2003 Nexant
conclusions. The study’s major assumptions the life cycle, including the fossil energy report,1 and conversion to green diesel
and references are shown in Table 4. Even contained in the fuel. This is particularly was modelled using data from UOP and
though the LCAs reported in the sources in important, because biofuels often require Eni. Tallow, unlike energy crops, is
Table 4 used different allocation methods, larger amounts of biomass-derived energy, considered a waste from the meat
their inventory data enabled us to calculate which is a renewable source of energy. processing industry, and thus carries no
and apply energy allocation factors to the Greenhouse gas emissions were calculated environmental burdens. However, tallow
LCAs reported here based on product and co- using the Eco-indicator 95 method in units must still be transported and rendered to
product lower heating values. These studies of CO2 equivalents for all GHGs. Primary become a usable feedstock. Once tallow
highlight important differences in LCA input GHGs of concern were CO2, N2O and CH4 has been rendered, it can be processed
data for many raw material choices. Other (IPCC, 2007). GHG emissions were derived into biofuel in accordance with input data
important study assumptions for green from all combustion processes consuming supplied by a 2002 literature source,5 or
diesel and biodiesel are the inclusion of N2O fuels containing fossil carbon (diesel for converted into green diesel in accordance
emissions, which contribute significantly to transportation, electricity consumption with data supplied by UOP.
the greenhouse gas inventories of biofuels and so on). The combustion of bio-based Unlike the cases based on rapeseed
from agricultural activities, and the effects fuels in vehicle engines was not included and tallow oils, the palm oil case can vary
of land use. Although N2O emissions are in the GHG assessment. For example, green greatly, depending on the process.7 As
included in this study, the effects of N2O diesel contains carbon derived only from standard practice, palm meal from the oil
variation are not. This factor and land use renewable oils, and therefore CO2 emissions extraction step is burned on-site for power
change, although important, are not within following combustion do not count towards generation, so displacing fossil fuels. Palm
the scope of this study, but will be included GHG totals. For biodiesel, only methanol- oil mill effluent (POME), a nutrient-rich
in future work. derived CO2 (assumed to be of fossil liquid, is anaerobically digested on-site to
The system boundaries include the origin) was included in GHG totals from produce a solid that can be used as fertiliser
following life cycle stages: raw material combustion emissions. on the palm plantation, a measure that
extraction, raw material transportation, raw displaces imported fertiliser. A methane-
material processing to final product, product Comparisons of diesel life cycles rich biogas is produced as a digestion by-
transportation and end use (combustion in a LCA inputs for low sulphur petroleum diesel product. This is a factor in establishing
direct injection-internal combustion engine). were taken from the ecoinvent database in GHG emissions, because the biogas can
For end use, biodiesel is often mixed with SimaPro 7.0, assuming average European contain as much as 70% methane by mass.
petroleum diesel at a concentration of 20% technology. Biodiesel and green diesel For this study, the composition is assumed
(B20). Green diesel can be used as a straight inventory data were input into SimaPro 7.0 to be 70% methane, 20% carbon dioxide, 7%
diesel substitute. However, this study only using values from the studies cited in Table nitrogen, 1% hydrogen and 2% hydrogen
accounts for the combustion of petroleum 4. Inputs for biofuel production include sulphide. This biogas is often simply vented
diesel, syndiesel and biofuels. the farming of an energy crop, in this case to the atmosphere, but can be captured and
The functional unit for this LCA is rapeseed or palm oil, or the production of burned on-site for energy production.8 Thus,
one megajoule (MJ) of petroleum fuel, tallow. Energy crop production requires there are two likely scenarios: one in
FT syndiesel, biodiesel or green diesel. four major inputs: seeds, fertilisers, which the biogas is vented, and another in
Inventories of inputs of materials and energy chemicals such as pesticides, and fuel used which the biogas is combusted to produce
over the life cycle for each fuel product were for harvesting and sowing, among other electricity for the oil extraction/biofuel
accumulated based on this functional unit. farm uses. After harvesting, the seeds processing stage.
The software used for this LCA was SimaPro
7.0, and for processes not already in the
SimaPro library (such as biodiesel and green Study assumptions and sources
diesel conversion process steps) the data
were obtained either from the sources cited Diesel source Transportation Study allocation method Data source
Coal gasification Estimated Energy Marano, 20016
in Table 1 or supplied by UOP for certain
FT synthesis
processes such as green diesel production Wax refining
via the Ecofining process.
NG gasification Estimated Energy Marano, 20016
For this study, the impact assessment
FT synthesis
methods used in SimaPro were Cumulative Wax refining
Energy Demand (CED) and total GHGs
Rapeseed Not included Displacement Concawe, 2006
from Eco-indicator 95. The Cumulative
Palm oil Estimated Not allocated Yusoff, 20077
Energy Demand is all of the energy that is Tallow Estimated Energy/economic Judd, 20025
consumed throughout the entire life cycle, FT = Fischer-Tropsch, NG = Natural gas
including the energy that is contained within
the product of interest, as well as primary Table 4
www.biofuels-tech.com BIOFUELS TECHNOLOGY 9energy inputs compared to those for coal
syndiesel. Rapeseed oil biodiesel and green
diesel both have a slightly lower CED than
3.5
FT syndiesel, with green diesel requiring
Renewable, water
3.0 Renewable, biomass slightly lower inputs than biodiesel. When
M J (inp ut )/ M J (o ut p ut )
Non-renewable, nuclear palm oil is used as a feedstock, the CED is
2.5 Non-renewable, fossil
substantially higher than for petroleum
2.0 diesel. This reflects the reuse of biomass
waste from palm oil production as a fertiliser
1.5
or a thermal energy source.
1.0 Since all of the by-products of palm oil
0.5
production are used in the oil extraction
process, the biomass energy inputs are
0.0 higher. Furthermore, all of the environmental
el al G el D el C D C el D
i es co m N i es O G ies w / B O G w / B i es w G burdens are carried by the oil because no
d m o o d S o d l P o d o
o fr bi bi e D bi ll
um T f r R
es G Ta by-products leave the process. Rapeseed as
le F FT SO O di O o w
rto P o P l l feedstock, for example, shares 39% of the
R bi Ta
Pe
PO burdens with rapeseed cake. So although
the inputs for palm oil are much lower, the
Figure 2 Cumulative energy demand for petroleum diesel, FT syndiesel, biodiesel and green diesel lack of an allocation somewhat distorts the
results. As with rapeseed oil, green diesel
from palm oil shows slight benefits over
palm oil biodiesel. And for the palm oil
2.5
Use
case, fewer energy inputs are needed when
Transportation biogas is used as a fuel.
2.0 Fuel production Tallow looks promising as a feedstock.
M J (inp ut )/ M J (o ut p ut )
Oil production
Cultivation Tallow biodiesel has a slightly higher CED
1.5 than petroleum diesel, while tallow-derived
green diesel is the only fuel to have a lower
CED than petroleum diesel.
1.0
Fossil Energy Demand (FED) values are
shown in Figure 3. The FED of petroleum
0.5 diesel is very close to the CED value, at
1.25 MJ per MJ of fuel. Coal and natural
0.0 gas syndiesel have significantly higher FED
el al G se
l D
G i es e
l C D C el D values compared with petroleum diesel,
es co N ie /B G / B i es G
di m o m o d SO
o d l w PO w
o d l o w requiring about 60% more fossil energy for
o r i i e D i l
um T f r f b R b es G b Ta
le F FT SO O di O lo w the same energy content of fuel. All of the
rto R P i o P l
Pe
b Ta biofuels have very similar FED values. For
PO all feedstocks, green diesel has a slightly
lower energy requirement than biodiesel
Figure 3 Fossil energy demand for petroleum diesel, FT syndiesel, biodiesel and green diesel (with a more significant reduction for tallow),
and palm oil has a slightly lower FED than
The production of FT syndiesel varies Energy.6 The impact of carbon sequestration rapeseed oil. In palm oil production, the FED
slightly from biofuel production. The coal technologies was not included in this study. is reduced when biogas is combusted. An
pathway includes inventory data for the assessment of the processes that contribute
current European Union (EU) hard coal Summary of LCA results to the FED shows that fuel use (the
mix, as well as gasification using steam Figure 2 indicates Cumulative Energy embodied energy of the fuel itself) is a major
reforming and partial oxidation followed by Demand (CED) for petroleum diesel, contributor for FT syndiesel and petroleum
FT synthesis. The life cycle for the conversion FT syndiesel, biodiesel and green diesel diesel, but has a negligible effect for biofuels.
of natural gas to syndiesel is assumed to derived from various feedstocks. Table 5 For rapeseed oil, cultivation is the largest
represent average conditions in Europe, contains a legend for the abbreviations used contributor, with oil processing taking about
which includes long-distance transport from in Figure 2. Petroleum diesel, which is used as much energy as fuel production. The
Russia and the Middle East. As with the coal as the baseline for comparison, requires cultivation of oil palms requires less energy
pathway, steam reforming of natural gas 1.27 MJ of input energy to yield 1 MJ of compared with the cultivation of rapeseed,
followed by FT synthesis is included. For diesel fuel. FT syndiesel requires higher as well as fewer oil processing requirements,
the syndiesel life cycles, inventory data was energy inputs throughout the life cycle, but more energy is used for processing the
input into SimaPro 7.0 from data supplied regardless of feedstock, although natural fuel. Almost all of tallow’s energy demands
by a 2001 study for the US Department of gas FT syndiesel requires slightly lower are from fuel production.
10 BIOFUELS TECHNOLOGY www.biofuels-tech.comGHG emissions associated with fuel life
cycles are shown in Figure 4. FT syndiesel
250
produced from a feedstock of coal produces
Use
more than twice as much greenhouse gas (in Transportation
CO2 equivalents) over its life cycle compared 200 Fuel production
Oil production
with petroleum diesel. Syndiesel from Cultivation
g CO2 eq ./ M J
natural gas generates fewer emissions than 150
syndiesel from coal, but still produces higher
emissions than petroleum diesel. Neither of
100
the syndiesel cases considered the potential
impact of emerging carbon sequestration
technologies to capture process emissions. 50
All of the biofuels considered produce
lower GHG emissions than petroleum diesel. 0
Overall, green diesel emits less GHG than el al G el D el C D C el D
i es co N i es O
G i es w / B O G w / B i es w G
d m o m o d S o d l P o d o
biodiesel for all feedstocks. For rapeseed fr D l
um T f r
o bi R bi es
e G bi Ta
l
oil-based biofuels, cultivation accounts for a le F FT SO O di O o w
rto P o P l l
R bi Ta
significant portion of life cycle GHG, due in Pe
PO
part to emissions of N2O from the field. Oil
palms are responsible for fewer emissions
in cultivation compared with rapeseed. Figure 4 Greenhouse gas emissions for petroleum diesel, FT syndiesel, biodiesel and green diesel
However, depending on whether or not
biogas is burned, palm oil processing can diesel produced via the Ecofining process California Alternative Diesel Symposium, August
have a significant effect on GHG production. has environmental benefits over petroleum 2003.
If biogas is burned, emissions are low and life diesel, biodiesel and fossil-derived syndiesel 3 Blending Study: Comparative profitability of
cycle GHG emissions are very low. Inedible (without carbon sequestration). Although blending green diesel or FAME to meet B5 and
B10 Blending Targets, UOP confidential report,
tallow, because it carries no environmental green diesel consumes more total energy
November 2007.
burdens, has very low GHG emissions. to produce than petroleum-derived diesel,
4 Kalnes T, Marker T, Shonnard D, “Green Diesel: A
Processing tallow for biodiesel adds a small the majority of this energy is renewable.
Second Generation Biofuel”, International Journal
amount of GHGs.9 Green diesel produced Compared to biodiesel, green diesel shows of Chemical Reactor Engineering, Vol 5, Article A48,
from tallow has emissions that are greatly higher savings in fossil energy per tonne January 2007.
reduced, with life cycle GHG emissions as of biofuel, regardless of the source of input 5 Judd B, Biodiesel from Tallow, prepared for
low as 2% of petroleum diesel’s emissions. data or differences in study assumptions. Energy Efficiency and Conservation Authority,
Overall, green diesel can contribute to the November 2002.
Summary world’s growing need for clean diesel fuel. Its 6 Marano J, Life Cycle Greenhouse Gas Emissions
Growing worldwide demand for diesel fuel, environmental benefits alone are substantial, Inventory for Fischer-Tropsch Fuels, prepared for
coupled with concerns over global warming, but when its fuel properties compared to US DOE National Energy Technology Laboratory
by Energy and Environmental Solutions, June
has sparked interest in renewable alternatives those of biodiesel are taken into account it
2001.
that show the potential for reduced GHG is clear that green diesel technology merits
7 Yusoff S, “Feasibility Study of Performing a Life
emissions at a reasonable cost of production. further investigation towards large-scale
Cycle Assessment on Crude Palm Oil Production
LCA studies indicate that green diesel industrial production. in Malaysia”, International Journal of LCA, Vol 12,
produced via the UOP/Eni Ecofining process No 1, January 2007.
can be an attractive supplement to petroleum Ecofining is a mark of UOP LLC and Eni SpA. 8 Yusoff S, “Renewable Energy from Palm Oil
diesel, biodiesel and syndiesel. However, the — Innovation on Effective Utilization of Waste”,
amount of green diesel that can be produced References Journal of Cleaner Production, Vol 14, 2006.
will be limited ultimately by feedstock 1 Nexant Chem Systems, PERP Report Biodiesel 9 Zheng D, “Preparation and Properties of Methyl
02/03S2, December 2003. Esters of Beef Tallow”, Bioresource Technology, Vol
availability and price.
2 Rockwell J, Conoco Phillips Gas-to-Liquids, 57, No 2, August 1996.
Green diesel has quality attributes
comparable with those of syndiesel,
including complete compatibility with List of abbreviations used Tom N Kalnes is Senior R&D Associate, UOP, US.
petroleum diesel, high energy density (44 Email: Tom.Kalnes@uop.com
Terry Marker is Ecofining Team Leader, Renewables
MJ/kg), low specific gravity (0.78), excellent Acronym Meaning
FT Fischer-Tropsch R&D, UOP, US.
storage stability and very low combustion
NG Natural gas Ken P Koers is an MS candidate, Department of
emissions. Furthermore, the cold flow
GD Green diesel Chemical Engineering, Michigan Technological
properties of green diesel can be adjusted RSO Rapeseed oil University, Houghton, MI, US.
within the Ecofining process, enabling the PO Palm oil David R Shonnard is a Professor in the Department
producer to adapt to varying feedstock BC Biogas combustion of Chemical Engineering and Deputy Director
sources and seasonal product specifications. of the Sustainable Futures Institute, Michigan
As determined by LCA studies, green Table 5 Technological University, Houghton, MI, US.
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