BIOFUEL

REVIEW PROJECT

Hydrotreating of Vegetable Oil to Produce Renewable Diesel Fuel

IBUKUN OLUWOYE

NICOSIA 2012

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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

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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).

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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].

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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

.pdf

[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