bài giảng quá trình chưng cất

Hydrotreating processes aim at the removal of impurities such as sulfur and nitrogen from distillate fuels—naphtha, kerosene, and diesel—by treating the feed with hydrogen at elevated t

1

Chapter

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Hydrotreating processes aim at the removal of impurities such

as sulfur and nitrogen from distillate fuels—naphtha, kerosene, and diesel—by treating the feed with hydrogen at elevated temperature and pressure in the presence of a catalyst

Hydrotreating has been extended in recent years to atmospheric resids to reduce the sulfur and metal content of resids for producing low-sulfur fuel oils

The operating conditions of treatment are a function of type

of feed and the desulfur- ization levels desired in the treated product

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Introduction

oils, Atmospheric resids or reduced crudes

The principal impurities to be removed are: Sulfur, Nitrogen, Oxygen, Olefins, Metals

Basic Reactions in Hydrotreating

HC - CH

CH3 - HC CH

S

+ 4H2 C5H12 + H2S

Methyl thiophene n-pentane

Desulfurization

C5H12 + H2S

Amyl mercaptan n-pentane

CH3 - CH2 - CH2 - CH2 - CH2 - SH + H2

CH3 - CH2 - CH2 -S - S - CH2 - CH2 - CH3 + 3H2 2C3 H8 + 2H2S

Dipropyl disulfide

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Basic Reactions in Hydrotreating

Denitrification

HC - CH

CH3 - HC CH

NH

+ 4H2 C5H12 + NH3

N

+ 5H2 + C3H8 + NH3 Methyl pyrrol

Quinoline

Basic Reactions in Hydrotreating

R - OH + H2 OH

RH + H2O

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Basic Reactions in Hydrotreating

Metals

The metals contained in the naphtha feed are arsenic, lead, and to a lesser degree copper and nickel, which damage the reforming catalyst permanently

Vacuum gas oils and resid feeds can contain a significant amount of vanadium and nickel

During the hydrotreating process, the compounds that contain these metals are destroyed and the metals get deposited on the hydrotreating catalyst

Cobalt (molybdenum on alumina support) This is the general catalyst for HDS service

Nickel (molybdenum on alumina support) This is used especially for denitrification

Cobalt (molybdenum and other metals on neutral support) The neutral support prevents the polymerization of the olefins This catalyst is employed in conjunction with other catalysts for olefinic feeds

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Operating Variables

Temperature

The HDS reactions are favored by an increase in temperature, but at the same time, high temperature causes coking reactions, diminishing the activity of the catalyst

Pressure

The increase in partial pressure of hydrogen increases the HDS rate and diminishes the coke deposits on the catalyst, thereby reducing the catalyst fouling rate and increasing the catalyst

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Space Velocity

The liquid hourly space velocity (LHSV) is defined as

HDS reactions are favored by a reduction in VVH The rate of desulfurization is a function of (PPH2 /VVH) or the ratio of

partial pressure of hydrogen in the reactor to liquid hourly

space velocity

Operating Variables

Recycle rate

In an HDS process, the hydrogen separated in a high-pressure (HP) separator drum is recycled to the reactor via a recycle

compressor and furnace This stream joins the incoming fresh feed, which has been heated in the feed furnace

Operating Variables