BIOFUEL
REVIEW PROJECT
Hydrotreating of Vegetable Oil to Produce Renewable Diesel Fuel
IBUKUN OLUWOYE
NICOSIA 2012
i
ABSTRACT
In search for an alternative to the non-sustainable fossil fuel, scientist had come out with many options. Production
of renewable fuels from biomass source being one of the major point of consideration.
Biofuels are produced from a renewable source of biomass, depending on the source and the method apply it yields
bioethanol, biodiesel, renewable diesel fuel and others.
In this review paper, process of producing renewable diesel fuel will be discussed focusing majorly of Hydrotreating
of vegetable oil to produce renewable diesel fuel.
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TABLE OF CONTENTS
Abstract ……………………………………………………………………………………i
Table of Content ……………………………………………………………………………………………..ii
1. INTRODUCTION ………………………………………………………………..1
2. RENEWABLE DIESEL FUEL …………………………………………………. 2 2.1 Definition of Renewable Diesel Fuel 2.2 Difference between renewable diesel fuel and Biodiesel 2.3 Methods of Producing Renewable Diesel Fuel 2.4 Remarks
3. HYDROTREATING OF VEGETABLE OIL ……………………………………6
3.1 Hydrotreating process 3.2 Types of HP 3.3 HP of vegetable oil 3.4 Remarks
4. CONCLUSIONS………………………………………………………………….10
5. REFERENCES …………………………………………………………………...11
1
1. INTRODUCTION
In search for an alternative to the non-sustainable fossil fuel, scientist had come
out with many options. Production of renewable fuels from biomass source being one of
the major point of consideration.
Climate change consciousness has served as an important additional driver to the
embrace of biofuel because it assists climate change mitigation effort by displacing fossil
fuel consumption [1].
Biofuels are produced from a renewable source of biomass, depending on the
source and the method apply it yields bioethanol, biodiesel, renewable diesel fuel and
others [2].
Figure 1: Type of Biofuel [3].
Diesel fuel (the second arrow from ‘oil’ in figure 1) can be produced from
biomass via several types of technologies. Some use specific biomass components, while
others can convert many forms of biomass into fuel. It must be noted that at present,
federal tax initiatives apply only to certain biomass-derived diesel fuels; others do not
qualify. Understanding the technologies used and resulting products helps to identify
eligible fuels [4].
In the next chapter, process of producing renewable diesel fuel will be discussed
focusing majorly of Hydrotreating of vegetable oil to produce renewable diesel fuel.
Differences between biodiesel and renewable diesel fuel will also be shown together with
its advantages and disadvantage if any.
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2. RENEWABLE DIESEL FUEL
2.1 Definition of Renewable Diesel Fuel
Renewable diesel is also refers to as “green diesel” or “second generation diesel”.
It is a petro-like fuel derived from biological sources that are chemically not esters
and thus distinct from biodiesel. Renewable diesel is chemically the same as
petroldiesel, but it is made of recently living biomass.
The definition or renewable diesel is not as straight forward as that of biodiesel.
The term “renewable diesel” has been defined separately by the Department of
Energy ( DOE, USA) with the Internal Revenue Service (IRS) and the environmental
protection agency (EPA) [5].
According to EPA Act 2005, renewable diesel is diesel fuel derived from
biomass, as defined in Section 45K (c)(3), using the process of thermal
depolymerization that meets the following:
o Registration requirements for fuels and chemicals established by the
Environmental Protection Agency under Section 211 of the Clean Air Act
(42 U.S.C. 7545)
o Requirements of the American Society of Testing and Materials (ASTM)
D975 or D396. [4]
Since there are other methods involved. Hydrotreating or hydroprocessing does
not fall under the chemical engineer’s definition of thermal depolymerization. The
term “green diesel” has been used for hydrotreated fuels, which is hydrogenation
conducted on molybdenum-or tungstensulfide-based catalysts supported on alumina
and promoted with cobalt or nickel.
2.2 Difference between Renewable Diesel Fuel and Biodiesel
While renewable diesel are exactly like petro-diesel produced form methods
mentioned earlier and to be discussed later.
Biodiesel, on the other hand, is defined as methyl and ethyl esters of fatty acids
meeting the requirements of ASTM specification D6751. Biodiesel is also referred to
as FAME (fatty acid methyl ester) or, in Europe, as RME (rape seed methyl ester).
3
Figure 2 and figure 3& 4 shows the difference based on production process and
properties
Figure 2: Renewable fuel creation process [6].
Figure 3: Comparison of FAME and HVO properties [7].
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Figure 4: Procedure of HVO and FAME production [7].
2.3 Methods of producing renewable diesel
There are basically three methods in producing renewable diesel fuel. This also define
the basic two classifications that we have. The production methods are as follows:
o Thermal Depolymerization (renewable diesel process): It is also known as
hydrothermal processing, thermal conversion, cracking, pyrolysis, rapid
thermal processing.
o Indirect Liquefaction (green diesel process): It is also called biomass-to-
Liquid (BTL) and Fischer Tropsche for using Fischer- tropsch (FT) synthesis
as applied to coal, natural gas and heavy oils.
o Hydrotreating (green diesel process): also known as hydroprocessing or
hydrodeoxygeneration. Details is given in the next chapter [4][5].
2.4 Remarks
It must be noted that renewable diesel fuel are similar to petroleum diesel fuel.
They have better energy value compared to biodiesel and also lower green house gas
emission as referred to figure 5, 6 and 7.
Figure 5: Percentage of GHG saving for FAME and HVO [7].
5
Figure 6: GHG emission by stage for HVO and FAME (g CO2 eq/MJ) [7].
Figure 7: Diesel fuel properties.
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3. HYDROTREATING OF VEGETABLE OIL
It must be noted that Hydrotreating or any other process is necessary because straight
vegetable oil cannot be use in diesel engine. There are many limitations in doing so.
3.1 Hydrotreating Process
In convectional diesel plant, Hydrotreating is use to remove contaminants (sulfur,
nitrogen, metals) and saturate olefins and aromatics to produce a clean product for
further processing or finished product sales.
Basically, Hydrogenation occurs in a fixed catalyst bed to improve H/C ratios and to
remove sulfur, nitrogen, and metals [10].
Figure 8 refers to basic steps involved in hydrotreating process
o Feed is preheated using the reactor effluent
o Hydrogen is combined with the feed and heated to the desired hydrotreating
temperature using a fired heater
o Feed and hydrogen pass downward in a hydrogenation reactor packed with
various types of catalyst depending upon reactions desired
o Reactor effluent is cooled and enter the high pressure separator which
separates the liquid hydrocarbon from the hydrogen/hydrogen
sulfide/ammonia gas
o Acid gases are absorbed from the hydrogen in the amine absorber
o Hydrogen, minus purges, is recycled with make-up hydrogen
o Further separation of LPG gases occurs in the low pressure separator prior to
sending the hydrocarbon liquids to fractionation
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Figure 8: Hydrotreating process schematic [10].
3.2 Type of Hydrotreating Process
o Naphtha Hydrotreating– Primary objective is to remove sulfur contaminant
for downstream processes; typically < 1wppm
o Gasoline Hydrotreating– Sulfur removal from gasoline blending components
to meet recent clean fuels specifications
o Mid-Distillate Hydrotreating– Sulfur removal from kerosene for home
heating
– Convert kerosene to jet via mild aromatic saturation
– Remove sulfur from diesel for clean fuels
o Ultra-low sulfur diesel requirements are leading to major unit revamps
o FCC Feed Pretreating– Nitrogen removal for better FCC catalyst activity
– Sulfur removal for Sox reduction in the flue gas and easier post-FCC
treatment
– Aromatic saturation improves FCC feed “crackability”
– Improved H/C ratios increase FCC capacity and conversion
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3.3 Hydrotreating process of vegetable oil
Also, the renewable diesel referred to as “green diesel” can be produced from
fatty acids by traditional hydroprocessing technology. The starting biomass-derived
oils can be the same as for biodiesel or renewable diesel. The triglyceride-containing
oils can be hydroprocessed either as a co-feed with petroleum or as a dedicated feed.
The product is a premium diesel fuel containing no sulfur and having a cetane number
of 90 to 100. An analysis by B. Arena and others indicates that capital and operating
costs are substantially lower than those for transesterification. NESTE in Finland is
constructing a $100 million green diesel plant, and Petrobras in Brazil already
produces a renewable diesel called H-Bio. Petroleum refiners use hydroprocessing to
remove impurities by treating feeds with hydrogen. Hydroprocessing conversion
temperatures are typically 600° to 700°F, pressures are typically 40 to 100 atm, and
the reaction times are on the order of 10 to 60 minutes. Solid catalysts are employed
to increase certain reaction rates, improve selectivity for certain products, and
optimize hydrogen consumption. Refiners normally do not refer to hydroprocessing
as a thermal depolymerization process. Yet all hydroprocessing requires heat and
pressure, and all ultimately lead to a reduction in the molecular weight of the feed
(except for olefin saturation). In the case of triglyceride-containing oils, the
triglyceride molecule is reduced to four hydrocarbon molecules under
hydroprocessing conditions: a propane molecule and three hydrocarbon molecules in
the C12 to C18 range [4].
The Hydrotreating process is a process utilized by petroleum refineries today to
remove contaminants such as sulfur, nitrogen, condensed ring aromatics, or metals.
In this process, feedstock is reacted with hydrogen under elevated temperature and
pressure to change the chemical composition of the feedstock. In the case of
renewable diesel, hydrogen is introduced to the feedstock in the presence of a catalyst
to remove other atoms such as sulfur, oxygen and nitrogen to convert the triglyceride
molecules into paraffinic hydrocarbons. In addition to creating a fuel that is very
similar to petro-diesel, this process creates propane as a byproduct. Because this
process requires fossil fuel-derived hydrogen, this process is not 100% renewable and
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this must be considered when calculating the energy return, greenhouse gas emissions
(GHG) and carbon life cycle [5]
Figure 9: Hydrotreating process.
3.4 Remarks
It must be noted that the main advantage of hydrotreating of vegetable oil in the
production of renewable diesel is that it make use of a well defined procedure that is
already in use in the production of convection fossil diesel.
4. CONCLUSIONS
Hydrotreating/Hydroprocessing of renewable diesel offers a unique opportunity to
produce a sustainable hydrocarbon diesel fuel completely compatible with existing fuel
infrastructure and engine technology. The process is very versatile in terms of feed type
and thus offers great potential for future operation on e.g. algae oils or other high-yield
feedstock that cannot be used for human nutrition [11].
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REFERENCES [1] Govinda R. Timilsina, Ashish Shresttha, “How much hope should we have for
biofuel”, Energy 36, 2055-2060 (2011).
[2] Jane Earley, Alice McKeown, “Smart choice for biofuels”, World Institute & Sierra
club, USA (2009).
[3]http://mediawiki.middlebury.edu/wikis/OpenSourceLearning/images/archive/3/3d/200
81029210647%21Pathways_of_different_biofuels.jpg, 2012
[4] Richard Bain, “ Biodiesel and other renewable diesel fuels”, innovation for our
energy future, National renewable energy laboratory, USA (2006).
[5] Jesse Jin Yoon, “What’s the difference between Biodiesel and Renewable (Green)
Diesel, Advance Biofuels, USA.
[6] Renewable diesel fuels, diesel technology forum,
http://www.dieselforum.org/files/dmfile/RenewableFuelsFactSheet.pdf, 2012.
[7] Daniel Garrain, Israel Herrera, Carmen Lago, Yolanda Lechon, Rosa Saez,
“Renewable diesel fuel processing of vegetable oil in Hydrotreating units: theoretical
compliance with european directive 2009/28/EC and ongoing projects in Spain”, Smart
Grid and Renewable Energy, 2010, 1, 70-73.
[8] Kalnes, Tom. Marker, Terry. Shonnard, Dr. David. Koers, Kenneth. “Green Diesel
and
Biodiesel, A Technoeconomic and Life Cycle Comparions.” 1st Alternative Fuels
Technology Conference 18 Feb. 2008. Web-page.
a. http://www.uop.com/renewables/Presentations/Green_Diesel_AFTC_Kalnes%20rev2
[9] “Properties of Fuel”
a. http://www.afdc.energy.gov/afdc/pdfs/fueltable.pdf
[10] Ronald (Ron) F. Colwell, P.E., “Oil refinery Processes: A brief overview”, Process
engineering associates, LLC (2009)
[11] Turning over a new leaf in renewable diesel hydroheating:
http://www.topsoe.com/business_areas/refining/~/media/PDF%20files/Refining/topsoe_n
pra_2010_turning_over_a_new_leaf.ashx
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