ME505 Report: Diesel Hydrodesulfurization and Sulfur Removal

This report provides a detailed analysis of diesel hydrodesulfurization, a critical process in petroleum refining aimed at removing sulfur from diesel fuel to meet environmental regulations. The report begins with an executive summary highlighting the importance of sulfur elimination in the context of industrial growth and environmental concerns. It covers the chemical synthesis involved, the reactions, and the mechanisms behind hydrodesulfurization. The literature review explores chemical synthesis and the diesel hydrodesulfurization process, including the reactions involved, such as hydrogenation and refining reactions like desulfurization and denitrification. The report further delves into the design aspects of the process, including the workings, implementation, challenges, and recommendations. The report also explores the main purpose of this process which is to perform desulfurization of the diesel fuels in the reactor feed to obtain the desired specification and use a catalyst to determine hydrogenation of eventual olefin structure. The conclusion summarizes the key findings and the importance of hydrodesulfurization in producing cleaner fuels. References are included to support the information provided.

Running head: DIESEL HYDRO DESULFURIZATION
Sulfur Elimination Through Hydrodesulfurization
Name of Student
Institution Affiliation

DIESEL HYDRO DESULFURIZATION 2
Executive summary
Growth of industries is the basis of trend in most countries in the world, industrialization
contributes to the development of the state in terms of infrastructure and raising the living
standards of the natives through employment opportunities that come with the development of
industries. Development of industries leads to an equivalent increase in power production to run
heavy machines in plant operations. This result in growing hydroprocessing, to achieve this
combustion of petroleum fuels to provide the driving energy for the industries. Combustion of
petroleum fuels if not properly regulated and monitored can lead to detrimental effects on the
environment [1].
In line with this aspect, Ministry of Petroleum and natural gas allowed a maximum of
0.25 wt. % of sulfur from 1 wt % can be present in petroleum fuels [2]. This regulation demands
that all the refineries construct desulfurization facilities for diesel with the principal aim of
eliminating sulfur content and other petroleum fuels to ensure that their use is environmentally
friendly. This process involves hydro sulfurization, hydro nitrification and olefins, and aromatic
saturation, where these reactions are conducted in bi-functional catalysts. Reactor effluents are
divided into liquid and gas in a chamber known as a separator.
Table of Contents
Executive summary.........................................................................................................................2
Introduction......................................................................................................................................5

DIESEL HYDRO DESULFURIZATION 3
Literature Review............................................................................................................................7
Chemical Synthesis......................................................................................................................7
DIESEL HYDRO DESULFURIZATION..................................................................................7
Hydro Desulfurization.............................................................................................................8
The main purpose of this process is to:..................................................................................9
Chemical reaction mechanism.................................................................................................9
Hydrogenation reactions..........................................................................................................9
Refining reactions..................................................................................................................10
Catalytic hydrotreating..............................................................................................................12
The process....................................................................................................................................13
Reactions and chemical equations.............................................................................................13
DESIGN.........................................................................................................................................17
Workings....................................................................................................................................17
Implementation..........................................................................................................................18
Results............................................................................................................................................22
Challenges..................................................................................................................................25
Recommendations/Future Work)...................................................................................................25
Conclusion.....................................................................................................................................25
References......................................................................................................................................27

DIESEL HYDRO DESULFURIZATION 4
Introduction
Petroleum has been essential to humans as it is used in one way or another to aid daily
operations. Petroleum contains hydrocarbons as the main component with some considerable
amount of nitrogen, sulfur, trace metals and oxygen [5]. From petroleum, fuels are derived such
as diesel among many which are comprised of approximately 0.25 aromatic hydrocarbons and
0.75 saturated hydrocarbons[5]. In diesel sulfur makes the main contaminant ranging between
0.1% and 0.5%, this is undesirable to the environment since it increases the polarity of the fuel,
poison catalysts enhance emulsion stability and confer color [7]. During combustion of diesel
fuel, sulfur oxides may be released into the environment either as gaseous or particulate solid
matter. Gaseous discharge of burning sulfur include Sulfur oxide (SO2) and (SO3), these causes
great damage to the atmosphere and environment [11]
The target of international and domestic environment agencies has always been to control
and lessen the use of sulfur fuels to a level of environment-friendly. In situations where sulfur
related fuels are commonly used, the concentration of sulfur is also high to about 300ppm. The
objective of these agencies is to reduce this concentration level to about 100ppm. [6]
For effective and efficient removal of this sulfur from diesel fuels desulfurization process is most
ideal. With the current fast-growing of the automobile industry and industrialization leads tom
high demand for crude oil and diesel fuel as the operating fuel [4]. These lead to a corresponding
increase in the amount of sulfur released to the environment. Thanks to the endless efforts geared
towards achieving the lowering of sulfur content in these fuels through various processes.
Desulfurization is used by refiners in the context of eliminating production onboard
transportation fuels due to high compliance expenses to the set regulations [8]. Advanced
technologies have been established to obtain the most viable and economical methods of sulfur

DIESEL HYDRO DESULFURIZATION 5
removal from petroleum fuels. Through the major source of sulfur pollution, petroleum refining
industries, both direct and indirect motor fumes, are in the front line for the struggle to achieve
environment-friendly and sustainable operation.
Problem statement
The increased concerns in the petroleum refining industry concerning the quality of air
has resulted in the urge to eliminate the heteroatoms which contain molecules from the products
of gasoline, diesel and their major products. Despite various efforts aimed at reducing the
contents of sulfur in the diesel oil, the quality of fuel, as well as the regulations, is deemed to be
affected. Various options have also indicated improvements in one sector while giving rise to
environmental and sustainability concerns. It is for this note that this design will be of great
significance in attempting to create a balance for both the factors.

DIESEL HYDRO DESULFURIZATION 6
Literature Review
Chemical Synthesis.
Chemical synthesis is the process that involves the disorientation of the already existing
chemical bonds that both hold molecules or compounds together and form new bonds in
molecule or compounds that are more valuable than the existing ones. Synthesis of more
complex molecules at times involve quite a number of individual reactions that eventually
undergo sequential reaction from available initial materials to the desired final product with each
step involving reaction at the only single chemical bond in the molecule [2]. This process
requires planning and analysis of the route of chemical reactions, this demands that the chemists
have to visualize the end product and develop a backward work formula towards increasingly
simpler compounds. These are often used depending on many other factors such as availability
of starting material together with their costs [5], amount of energy required to start and sustain
these reactions and separating costs and purification of the end product.
DIESEL HYDRO DESULFURIZATION
The issue of desulfurization is gaining a lot of focus since crude oil is getting higher in
sulfur content. In order to control the level of sulfur in hydrocarbon fuels for fuel use and
protection of the environment, diesel hydrodesulfurization of the model duel and real fuel are
studied by Selective absorption for removing Sulfur (SARS) process using appropriate adsorbent
[6], examining the temperature during the desulfurization process. In regard to technology
availability, the current hydrodesulfurization is hard to control the sulfur concentration in diesel
fuels below 50 ppm since the remaining sulfur concentration in commercial diesel fuels are 4-

DIESEL HYDRO DESULFURIZATION 7
methyldibenzothiophene, 4, 6-dimethyl dibenzothiophene and other alkyl dibenzothiophenes
which are quite difficult to eliminate.
In recent research, the process of sulfur removal from transportation fuels has become of
great importance to every organization and nations worldwide due to heightened interest to have
clean air in the atmosphere hence increasingly stringent laws and regulations for sulfur fuels to
the environment [8]. The high demand for ultra-low sulfur fuels for fuel cells with modern
automobiles that are much more efficient and friendly to the environment [11]. Liquid
hydrocarbon fuels are on the rise due to the fact that they are a promising ingredient because of
their high energy density, storage, and transportation safe [7]. Automotive fuel cells, for
example, the developing PEFC and SOFC auxiliary power units in vehicles diesel and gasoline
are the most preferred fuels since they are easily available and ease in their production, storage,
and delivery. However, gasoline and diesel fuels contain a significant amount of sulfur ranging
from 300 to 450 ppm [9]. The sulfur content in fuel and hydrogen sulfide H2S produced by these
fuels are very poisonous to catalysts both electrode catalysts and in hydrocarbon fuel processor
catalysts. Thus for fuel cell application in industries and in automobiles, the sulfur content in the
fuels needs to be maintained at the lowest level possible [5]
Hydro Desulfurization
This is referred to a catalytic chemical reaction process where sulfur is eliminated or
removed from petroleum fuels such as petrol, diesel fuels, jet fuels, kerosene and natural gas [2].
The process is usually used in advancing the rating of octane in naphtha streams. Fuels obtained
through this process reduce sulfur and its oxide emission in vehicles, train, power plant, aircraft,
residential furnace, and industrial furnaces and other fuel combustion forms. [8]

DIESEL HYDRO DESULFURIZATION 8
The main purpose of this process is to:
1. To perform desulfurization of the diesel fuels in the reactor feed to obtain the desired
specification
2. To use a catalyst to determine hydrogenation of eventual olefin structure.
Chemical reaction mechanism
1. Hydrogenation reactions
2. Refining reactions
Hydrogenation reactions.
These are processed reactions that affect directly aromatics, diolefins, and olefins and are
associated with high temperatures where olefins and diolefins are transformed into saturated
compounds with a restriction on the reaction rate of aromatics.
The feed to the diesel hydrodesulfurization unit is a merger of cracked gas oils and straight run.
These feed fuels are then filtered through a filter package to surge drum where the pressure is
maintained at a constant level through fuel gas blanketing [10].
The liquid phase feed pump is pumped underflow control by feed pump, combined with
hydrogen recycle compressor delivery stream and let in the heat exchanger train. The injection of
inhibitors that prevents polymerization at the inlet of the reactor facilitates the combining the
recycle hydrogen with feed to ensure sufficient hydrogen partial pressure. [9]
Hydrogenation of olefin compounds
RCH=CH2 + H2 RCH2 –CH3
Hydrogenation of aromatic compounds
C6H6 + 3H2 C6H12

DIESEL HYDRO DESULFURIZATION 9
The incoming hydrogen make up gas is directed via chlorine adsorbent before it is
compressed. Some portion of this gas is channeled into the reactor as quench gas. In the heat
exchanger, the combined stream is intensified before passed to the second exchanger and lastly
to the reactor heater where it's heated to the desired input temperature [8]. The temperature of the
reactor is regulated by regulating the fuel oil to fuel gas into the heater and then the stream is
then introduced to the reactor with catalysts. This is done in three beds and the temperature of
each bed is controlled by introducing cold quench hydrogen from the recycling compressor [11].
Water is let at the effluent inlet to prevent deposition of ammonium salts that might cause
corrosion of the reactor. The sour water is partly recycled since it contains ammonium salt and
can be used in washing.
Refining reactions
Denitrification- this reaction only occurs in cases of heterocyclic compounds with an
aromatic structure such as pyridine and the rate of reaction of denitrification is lower compared
to the rate of desulfurization. Denitrification leads to the establishment of ammonia gas and the
elimination of hydrogen gas[7]
Denitrification
C2H2N + 5H2 C2H2 + NH 3
Desulfurization is the reaction that involves saturated sulfides, disulfide, and aromatic
compounds. Sulfur combine in the cycle of the aromatic structure is not easy to eliminate like in
case of thiophene. This reaction leads to the formation of hydrogen sulfide and hydrogen
consumption. [5]
Desulfurization
RSH + H2 R-H + H2S

DIESEL HYDRO DESULFURIZATION 10
Diesel hydrodesulfurization is also referred as hydrotreating as it is widely used in
petroleum refineries and mining industries for the purpose of producing high-quality fuels as
well as upgrading crude oil by eliminating or lowering concentration of metal, sulfur or nitrogen.
For the design and installation of new plants [2], detailed research is of the essence to function at
optimal conditions. This involves steady-state reactor which becomes significant in the actual
process of refining. When considering light-medium reactors and because it involves probably
mixture hundreds of compounds, which not all of these compounds can be explicitly considered.
In such a case, hypothetical compounds are clearly defined to take the basis of feed. This is
followed by a characterization step of feed to obtain feed composition in reference to the
hypothetical components [8].
Some previous approach to tackle this process was by defining quasi compounds
generated as a result of true boiling. Another approach is to employ lumping of species where
various species are clustered by their chemical families with similarities in their structural and
chemical behavior [7]. Hydrotreating of diesel fuels is based in three phases that are varied
catalysis: where the model have proper consideration on how to formulate the starting points
stating all kinetics that defines the reactions, then estimate this kinetic essentials with data
obtained at pilot plant scale eventually scaling up [3]. Even though this aspect of hypothetical
considerations, it's associated by some setbacks that might arise in the refinery reactor modeling
and as new feeds which prevent the formulation of a fixed reaction set. The best way to manage
this, there should be a hydrocarbon mixture beginning with the feedstock properties where
configuration of molecular techniques have produced satisfactory outcomes. [10]

DIESEL HYDRO DESULFURIZATION 11
Catalytic hydrotreating
It refers to the hydrogenation process that is employed to eliminate environmental
pollutants such as nitrogen, metals, and sulfur from petroleum fractions such as diesel, petrol
kerosene and gasoline [4]. Elimination of these pollutants is very crucial since when they are
carelessly released to the atmosphere, they have harmful implications on the equipment's, end
products and even the catalysts. Hydrotreating is also efficient since it removes about 90% of
these contaminants from crude petroleum [9]. This process of hydrotreating is done prior to
catalytic reforming to avoid contamination of catalysts by untreated feedstock. It also comes
before catalytic cracking to boost product yield and upgrade middle distillate petroleum portions
into finished end products such as heating fuel oils, kerosene, and diesel fuels [3]. It also
enhances the conversion of aromatics and olefins to saturated compounds.
The process
Figure 1.1Schematic of hydrodesulfurization
Hydrodesulfurization is the hydrotreating that involves the removal of sulfur from diesel
fuels [8]. The process commences with the feedstock being deaerator then combined with
hydrogen which is preheated in the heater to a temperature of 8000F then charged at a pressure of

DIESEL HYDRO DESULFURIZATION 12
up to 1000 pascal via a catalytic reactor [10] [12]. The conversion of sulfur and nitrogen
compounds present in feedstock takes place to produce hydrogen sulfide H2S and ammonia NH3.
After cooling to considerably low temperature these products leaves the reactor and enters to the
gas-liquid separator. The gas rich of hydrogen is then recycled back to the feedstock while low-
pressure gas stream reaches in hydrogen sulfide H2S is directed to the gas treating unit for
removal. The clean gas is channeled to fuel refinery chamber [4], liquid stream product from
hydrotreating id sent to doffing tanks for extraction of H2S together with other unwanted
components.
Reactions and chemical equations
The removal of sulfur demands for special conditions in order to efficiently eliminate
sulfur from diesel fuels. In the case of organosulfur compounds involving reaction with hydrogen
gas producing hydrogen sulfide, this reaction requires high hydrogen pressure greater than 200
atm and temperature of 4500C [3] [11]
There are different types of catalysts that escalate various reactions depending on the
requirements for the reaction to occur. The selection is also pegged on the type of oil being
purified. The most commonly used catalysts are a combination of Mo and Co sulfides with
alumina, a mixture of Ni and Mo. There a number of models that gives a detailed clarification to
the manner thiophene moieties are oriented on the catalysts, generally, the Co-Mo-S model
developed by Topsoe. Under this catalysts are formed in a mono layer of Mos2 with Co or Ni at
the edges [6].
The coordination of thiophene Moieties occurs in a way that all the thiophene molecules,
present the sides with an increased electronic density forming the single pair of sulfur atoms and