Group: 22-16. Name: vohidov farrux to’lqinjon o’G’LI

TASHKENT

CHEMICAL-TECHNOLOGICAL

INSTITUTE

GROUP:22-16.

NAME:VOHIDOV FARRUX TO’LQINJON O’G’LI.

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The HDT process

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Introduction

Fundamentals of HDT

Hydrotreating of

oil fractions

Introduction

Catalytic hydrotreating (HDT) is a mature technology used in the petroleum refining industry for the upgrading of hydrocarbon streams for the last 60 years. For conventional distillate HDT, the main purpose of the process is to remove impurities such as heteroatoms (sulfur, nitrogen, and oxygen) and saturate aromatic compounds, whereas in the case of heavy oils and residues, it also comprises the elimination of metals (nickel and vanadium) and conversion of asphaltene molecules. Its major applications in current refinery operations can be grouped in the following categories: (i) feed pretreatment for conversion processes such as catalytic reforming, catalytic cracking, and hydrocracking (HCR) and (ii) post-HDT of distillates. In the first case, generally the objective is to reduce the amount of sulfur, basic nitrogen compounds, metals, and polynuclear aromatics (PNA), which act as deactivation agents in acid-catalyzed processes. The second group is mainly the finishing step to produce transportation fuels that meet ecological standards (e.g., ultralow sulfur gasoline and diesel).

Abstract

Abstract

Catalytic hydrotreating represents a fundamental process in modern petroleum refining operations. It allows removing hydrocarbon contaminants, such as sulfur, nitrogen, oxygen, and metals, saturating aromatic rings and olefins, and breaking high molecular weight molecules into lighter compounds. Due to its flexibility, the process can be employed to upgrade a variety of petroleum streams, ranging from naphtha to vacuum residues, or even full-range crude oils. Conventional hydrotreating is typically used as a pretreatment step to provide suitable quality feeds for conversion processes, such as reforming, catalytic cracking, and hydrocracking, and also as a finishing step to produce transportation fuels that meet ecological standards. Over the years, hydrotreating has also been gaining acceptance in the primary upgrading of heavy and extra-heavy crude oils to produce the so-called synthetic crudes. Among all the available hydrotreating reactor technologies, fixed-bed reactors are the most frequently used in the petroleum industry. In such systems, both gas and liquid flow cocurrently down through a catalyst bed in trickle-flow regime. Modeling and simulation of hydrotreating becomes a challenging task due to the complex interaction of numerous physical and chemical processes: vapor–liquid equilibrium, gas–liquid and liquid–solid mass transfer of reactants and products, diffusion inside the catalyst particle, vast reaction networks, and catalyst deactivation.

The HDT process

• Overview

Catalytic HDT is a fundamental refininwide variety of streams, ranging from straight-run naphtha to vacuum residue (VR) or even heavy and extra-heavy crude oils. The HDT process is commonly employed for reducing the contents of hydrocarbon impurities such as sulfur, nitrogen, oxygen, and aromatics by the so-called hydrogen addition route. When it is applied to the processing of heavy feeds, it also has the virtue of bringing down the concentration of metals (Ni and V) and simultaneouslyincreasing distillate yield at the expense of the heaviest fractions such as VR and asphaltenes [5]. The process has gained significant relevance in the industry due to the growing demand for transportation fuels and the strict environmental legislations.

The reactions that take place during the HDT process are hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodearomatization (HDA), hydrodeoxygenation(HDO),hydrodemetallization (HDM). Another type of reaction in which high molecular weight compounds are broken down into lighter molecules is HCR. In the case of HCR of asphaltenes, the process is often referred to as hydrodeasphaltenization (HDAs). The chemistry of these reactions can be visualized as a hydrogen exchange process where hydrogenolysis and hydrogenation mechanisms consume the externally supplied hydrogen in order to replace heteroatoms and stabilize unsaturated products. However, in reality, HDT chemistry is far more complicated due to the intrinsic complexity of oil composition

The reactions that take place during the HDT process are hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodearomatization (HDA), hydrodeoxygenation(HDO),hydrodemetallization (HDM). Another type of reaction in which high molecular weight compounds are broken down into lighter molecules is HCR. In the case of HCR of asphaltenes, the process is often referred to as hydrodeasphaltenization (HDAs). The chemistry of these reactions can be visualized as a hydrogen exchange process where hydrogenolysis and hydrogenation mechanisms consume the externally supplied hydrogen in order to replace heteroatoms and stabilize unsaturated products. However, in reality, HDT chemistry is far more complicated due to the intrinsic complexity of oil composition

In the first step of petroleum refining, crude oil is fed to the atmospheric fractionation tower to obtain straight-run distillates such as naphtha, kerosene, and gas oil. Such raw products cannot be used directly as transportation fuels due to several technical limitations such as high amounts of impurities (sulfur, nitrogen, and aromatics) and low octane and cetane numbers in the cases of gasoline and diesel fuels, respectively. These streams are converted into valuable products through a variety of refining processes. In this context, HDT operations play a major role at several stages in a refinery. According to a recent worldwide refining survey [10], HDT has in fact the largest processing capacity among all refining operations (45 431 300 bpcd).

In the first step of petroleum refining, crude oil is fed to the atmospheric fractionation tower to obtain straight-run distillates such as naphtha, kerosene, and gas oil. Such raw products cannot be used directly as transportation fuels due to several technical limitations such as high amounts of impurities (sulfur, nitrogen, and aromatics) and low octane and cetane numbers in the cases of gasoline and diesel fuels, respectively. These streams are converted into valuable products through a variety of refining processes. In this context, HDT operations play a major role at several stages in a refinery. According to a recent worldwide refining survey [10], HDT has in fact the largest processing capacity among all refining operations (45 431 300 bpcd).

FBR (trickle-bed)	MBR (cocurrent)	MBR (countercurrent)	EBR (fluidized bed)	SFR
Oil/H2	Oil/H2	Products/H2	Products/H2	Products/H2/cat

Fundamentals of HDT

• Chemistry

HDT chemistry is the basis for understanding the transformations that the hydrocarbon goes through at process conditions and offers the basic guidelines for process modeling. The chemistry of HDT reactions can be simply visualized as a hydrogen transfer process [22]. In this generalization, hydrogen is supplied from an external source to replace heteroatoms and reduce the molecular weight of the original hydrocarbon mixture by means of various hydrogenation and hydrogenolysis mechanisms. Nevertheless, the events that take place at the molecular level are far more intricate.

The main problem in elucidating the details of HDT reactions arises from the complex composition of commercial feedstocks. Depending on the boiling range, oil fractions may contain from a few hundred to several thousands of different components.

HDS

During HDS, sulfur is extracted from hydrocarbons and released as hydrogen sulfide (H2S). Reactivity of S-components can vary greatly depending on the structure of the molecule. In general, HDS reactivity increases according to the hydrocarbon type: paraffins > naphthenes > aromatics. Mercaptans and sulfides are the most reactive species, followed by naphthenic and six-membered aromatic structures [25]. Five-membered aromatic compounds such as thiophenes are more refractory, whereas benzothiophenes, dibenzothiophenes, and alkylsubstituted dibenzothiophenes are the least reactive species.

Sulfur removal is accomplished directly by a hydrogenolysis mechanism or indirectly by prior hydrogenation. Figure 13.6 shows the two possiblepathways for dibenzothiophene HDS. In the direct route, the S-atom is eliminated and replaced by hydrogen. The other mechanism requires saturation of one aromatic ring before sulfur removal. The sulfur-free products may undergo further hydrogenation until the molecule is completely saturated.