Fundamentals of the theory of catalytic petrochemical productions: educational manual 9786010437135

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Fundamentals of the theory of catalytic petrochemical productions: educational manual
 9786010437135

Table of contents :
UDC LBC Tashmukhambetova
PREFACE
Chapter 1
C h a p t e r 2
C h a p t e r 3
C h a p t e r 4
C h a p t e r 5
C h a p t e r 6
C h a p t e r 7
C h a p t e r 8
C h a p t e r 9
GLOSSARY
LITERATURE
CONTENTS

Citation preview

AL-FARABI KAZAKH NATIONAL UNIVERSITY

Zh.Kh. Tashmukhambetova Y.A. Aubakirov L.R. Sassykova

FUNDAMENTALS OF THE THEORY OF CATALYTIC PETROCHEMICAL PRODUCTIONS Educational manual

Almaty «Qazaq University» 2018

UDC 665.6/7 LBC 35.514 T 22 Recommended for publication by the decision of the Academic Council of the Faculty of Chemistry and Chemical Technology, Editorial and Publishing Council of Al-Farabi Kazakh National University (Protocol №1 dated 11.10.2018) Reviewer Doctor of Chemistry, Professor S.M. Tazhibayeva

T 22

Tashmukhambetova Zh.Kh. Fundamentals of the theory of catalytic petrochemical productions: educational manual / Zh.Kh. Tashmukhambetova, Y.A. Aubakirov, L.R. Sassykova. – Almaty: Qazaq University, 2018. – 174 p. ISBN 978-601-04-3713-5 The educational manual contains questions of theory and practice of processing of oil and oil raw materials, requirements for raw materials and catalysts of secondary processes of oil processing: hydrocracking, reforming, hydrotreating, alkylation, isomerization, dehydrogenation. Particular attention is paid to the study of the properties of catalysts and processes occurring at the interface between the phases ‒ the reacting substance-catalyst, on the basis of existing theoretical approaches of representatives of different scientific schools. The educational manual has a glossary that can help in mastering the basic terms of catalytic petrochemical industries. The questions to selfchecking were added to each chapter. The educational manual is intended for students, bachelors, masters and doctoral students specializing in the field of chemical technology of organic substances and chemicals, petrochemicals, catalysis and oil and gas business. Published in authorial release.

UDC 665.6/7 LBC 35.514 ISBN 978-601-04-3713-5

© Tashmukhambetova Zh.Kh., Aubakirov Y.A., Sassykova L.R., 2018 © Al-Farabi KazNU, 2018

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Fundamentals of the theory of catalytic petrochemical productions

At present, catalytic processes have become most widespread in the technology of oil and oil products processing. The share of catalytic processes in petrochemicals and oil refining accounts for about 90% of all petroleum-based production processes. At the same time, it should be noted that the deepening of the processing of oil and waste products of petroleum production for the purpose of increase in the yield of the target products is mainly based on the use of catalysts. The main catalytic processes of oil refining are catalytic cracking, catalytic reforming, hydrotreatment, hydrocracking, alkylation, isomerization, dehydrogenation, etc. If the processes of catalytic cracking, reforming, hydrocracking and hydrotreating apply for the purpose of obtaining products on the basis of oil and to preparation of raw materials for processing, then processes of catalytic isomerization, alkylations and dehydrogenation apply to giving the products and intermediats on the basis of hydrocarbons of oil of specific properties for the purpose of expansion of the sphere of their consumption. Knowledge of the fundamentals of the theory and practice of catalytic processing of petroleum and petroleum raw materials, mechanisms for implementing these processes is particularly relevant and requires special study. In this educational manual the bases of the theory of heterogeneous and catalytic processes and modern technologies of catalytic petrochemical productions, such as hydrocracking, reforming, hydrotreating, alkylation, isomerization, dehydrogenation are presented to attention of students.

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Fundamentals of the theory of catalytic petrochemical productions

Chapter 1

BASIC CONCEPTS AND DEFINITIONS OF CATALYSIS. PECULIARITIES OF CATALYSIS IN PETROCHEMICAL PRODUCTION

The oil-processing industry allows to produce more than 500 names of solid, liquid and gaseous oil products. Among them besides different types of fuel and lubricant products a specific place is held by polymeric materials, synthetic fibers, solvents, varnishes and dyes, medical supplies, synthetic detergents, construction materials and many other things. The main products of oil refining are various types of fuels and only about 5% is spent on the production of individual olefinic hydrocarbons (ethylene, propylene, butylene, isobutylene), butadiene, aromatic hydrocarbons (benzene, toluene, xylene). Products of oil refining are used practically in all branches of industry, transport, construction, energy, agriculture, for domestic needs, etc. Refinery products

Motor fuels

Petroleum oils

Energy Fuels

Petrochemical raw materials

Carbon and astringent materials

Petroleum products for special purposes

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Chapter 1. Basic concepts and definitions of catalysis. ...




Fundamentals of the theory of catalytic petrochemical productions

In general, the current definition corresponds to the following: catalysis is a change in the rate of a chemical reaction in the presence of substances (catalysts) that repeatedly enter into an intermediate chemical reaction with the participants in the reaction, but restore their chemical composition after each cycle of intermediate interactions. Catalytic processes are subdivided by the nature of the intermediate interaction of the catalyst with the reactant and by the type of the formed intermediate products. Distinguish a direct and reverse catalysis, depending on the direction of acceleration of reversible reaction of type: А  В . Acceleration of the catalytic reaction by the resulting intermediate products is called autocatalysis.

The main properties, which must have a catalyst are: ‒ high activity; ‒ selectivity; ‒ thermal stability; ‒ resistance to abrasion; ‒ developed specific surface area; ‒ resistance to hydrodynamic factors; ‒ resistance to poisoning by catalytic poisons; ‒ ability to regenerate and etc. 1. When the difference of the catalysts common to them is to increase the rate of the catalyzed reaction. The same reaction may occur in the presence of catalysts different in nature and without them. The difference lies in the speed of the process. For example, the rate of hydrogenation of ethylene on a chromium catalyst is 1, on a nickel catalyst – 13, on platinum – 100, on palladium – 1,000, on rhodium – 1,800. It follows that rhodium has the greatest activity. Namely, the nature of the catalyst determines its activity in the reaction.

Chapter 1. Basic concepts and definitions of catalysis. ...




Fundamentals of the theory of catalytic petrochemical productions

Where А, В are the initial substances; R is a target product; D is by-product. Selectivity is equal to:

S

mR , mR  mD

where mR and mD are the mass of the target and by-products, respectively. Thus, the catalysis process can be regarded as a selective acceleration of one of the thermodynamically possible directions of the reaction. 3. The most important property of the catalyst is its ability to maintain activity in time, which is called stability. At a homogeneous catalysis the catalyst can be deactivated owing to accumulation in a zone of reaction of the products reducing concentration of the active centers. At a heterogeneous catalysis decrease in stability is caused by both physical, and chemical changes. Long temperature influence leads to recrystallization of the catalyst that is followed by decrease in its specific surface and number of the active centers. To prevent the recrystallization process, special substances-promoters are added to the catalyst, which promote the strengthening of the crystal lattice of the catalyst, being built into its structure. Promoters can also create additional activation sites in the catalyst. The structure of the catalyst can also be violated due to mechanical and thermal effects. Chemical changes are associated with chemisorption on the catalyst surface of impurities and reaction products, which are called catalytic poisons. Over time, coking of the catalyst may occur, as a result of which its active surface is blocked by coke deposits, and the overall activity of the catalyst is accordingly reduced. The activity of the coked catalyst can be restored by treating it with air oxygen or steam at elevated temperatures.

Chapter 1. Basic concepts and definitions of catalysis. ...




Fundamentals of the theory of catalytic petrochemical productions

Values of standard heat of formation of some, of the most characterristic carbocations are given in tab. 1. Analysis of the data of Table. 1 shows that the most reactive ability is possessed by phenyl carbocation +C6H5, therefore, it has the least stability. Another conclusion is that the tertiary carbocation is more stable than the secondary ones, and those in turn are more stable than the primary carbocation. The main reactions of carbocations, as well as radicals – monomolecular disintegration by the β-rule and bimolecular reactions of substitution and addition. Difference of carbocations from radicals are their ability to reactions of an isomerization that is connected with decrease in free energy upon transition from primary to secondary and tertiary carbocations. Table 1 The standard heat of formation of carbocation Carbocation

Heat of formation, kJ/mol

Carbocation

Heat of formation, kJ/mol

+СН 3

1,092

СН3СН2СН+-СН3

765

+С Н 2 5

916

(СН3)3С+

706

СН3СН2СН2+

869

+С Н 6 5

1,105

СН3(СН2)2СН2+

844

+С Н СН 6 5 2

897

The most common acid catalysts are crystalline and amorphous aluminosilicates, modified with additives, halides, Al, B, Sb; Al2O3, sulphides of some transition metals, as well as a number of protonic acids, for example, H2SO4, H3PO4, etc. These acids are used in the processes of reforming, catalytic cracking, alkylation, isomerization, etc. Classification of oxidation-reduction processes and catalysts The following processes of oil and oil products processing are related to oxidation-reduction processes: ‒ oxidation; ‒ hydrogenation (hydrotreatment, hydrodesulphurization);

Chapter 1. Basic concepts and definitions of catalysis. ...


1, and the parameters n and c usually decrease with increasing temperature). The thermodynamic conclusion allows us to interpret n as the interaction constant between adsorbed particles. Usually, n exceeds one, and this means that adsorbed molecules repel each other. The equation of the Freundlich adsorption isotherm satisfactorily describes the data over a wide range of values for systems that do not obey the Langmuir adsorption isotherm. Even for systems described by the Langmuir isotherm, in the medium-filled region this isotherm is almost equivalent to proportionality to the fractional power of P. This equation is satisfied only when the average surface area of the catalyst is filled with reactants in the middle range of the change in equilibrium pressure (6-7 orders of magnitude) and characterizes uniformly inhomogeneous surfaces. The Freundlich isotherm equation can be derived theoretically using a statistical approach and applying the Langmuir equation to a

Chapter 3. Adsorption. Features of adsorption on energetically ...




Fundamentals of the theory of catalytic petrochemical productions

depend on each other. The entry of the active atom into the same migration region is random. Carriers of catalytic activity are ensembles composed of a small number of atoms (2-4 atoms). For different reactions, depending on the type of the bond being converted and the mechanism of the process, different ensembles exhibit activity. S

a

b

U

Figure 2. Geometric and energy barriers (a) separating migration areas (b): S – geometric barrier (protruding areas of the carrier surface); U – energy barrier (potential well); • – active atom (ensemble of 1-2-3 atoms); U is the specular reflection of S.

Thus, in the decomposition of hydrogen peroxide and oxidation, 1-atom ensembles are active, hydrogen atoms and dehydrogenations of hydrocarbons are active in two atomic ensembles, and in the ammonia synthesis reaction there are 3 atomic ensembles. The supported catalyst achieves the maximum specific activity, when, according to the law of the case, the largest number of ensembles of the desired structure is formed on its surface. There are two types of dependence of aspec and Atot of α (fig. 3): a) with a single maximum on the curves Atot and aspec of α (for small dilutions); b) with two maxima on the curves of the Atot and aspec of α (with strong dilutions of 10-3-10-2). N.I. Kobozev proposed a quantitative calculation of the migration area (p), the number of atoms in the ensemble (n), the total number of migration cells (z0), the activity of a single ensemble (rn). The area of the migration region, expressed in the atomic areas of the catalyst, is:

Chapter 4. Catalysis theories

43




Fundamentals of the theory of catalytic petrochemical productions

Insofar as   c   , so  

wn 

    p   ; this implies: 

p n   n  e  p n!

The total number of ensembles ( z n ) is:

z n  z 0  wn  z 0

 p   n  e  p n!

The overall catalytic activity of an ensemble is defined through the equality:  p   n  e  p , A  z n  rn  z 0  rn n! where rn is a catalytic activity of one active center with n atoms. The specific catalytic activity is:

a

A



 rn  z 0  p n

 n 1 n!

 e  p

Accordingly, the total and specific activities reach a maximum at the following values α: A  max  n / p;

a  max  n  1 / p

Thus, by the degree of filling of the catalyst surface with active centers at maximum activity, it is possible to determine the migration area and the number of atoms in the ensemble. For a monoatomic ensemble (n = 1), the equation of specific activity is: a r

s  p e , 

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

4.3. Theory of an active surface of S.Z. Roginsky. Promotion and poisoning of catalysts. Modification of catalysts According to the theory of S.Z. Roginsky, the basis of heterogeneity of the surface of the catalyst are physical and chemical factors. This is a deformation of the structure of the catalyst, as well as heterogeneity in chemical composition, due to the presence of impurities – promoting additives, the use of mixed catalysts, etc. The physical inhomogeneity is unstable under catalysis, it is reversible and can change with time depending on temperature. The chemical heterogeneity is temperature resistant. The study of pure (one-component) and mixed (multicomponent) catalysts showed that the mixed ones are more effective. This is due to the presence in the catalysts of a mixed type of solid phases of different chemical composition. The catalyst is heterogeneous in its chemical composition and the introduction of impurities at the phase interface leads to an increase in its activity. Basic provisions of the theory of an active surface of S.Z. Roginsky: 1. During the synthesis of the catalyst, various technological impurities can both activate it and serve as poisons. The effect of activation will be the same as with the artificial promotion of the catalyst by various additives or promoters. 2. Thus, in catalysis only those sites of a surface where the content of impurity will correspond to optimum will be active. Weakening of effect of additive will also lead to activation of the catalyst. 3. The source of the promoting or poisoning impurities can be the catalytic reaction itself. The proof of provisions is studying of a gas promotion of the metals used as ethylene hydrogenation reaction catalysts. The pure plates of metals Ni, Cu, Fe, Pt, Pd, W were inactive for this reaction. However the same plates of metals in the presence of the dosed amounts of gas impurity (N2, O2, H2, etc.) were active. The effects gained by method of a gas promotion considerably exceed on reaction speed on various planes of one-component catalysts. The activity of other one-component catalysts in reaction of hydrogenation of ethy-

Chapter 4. Catalysis theories



Fundamentals of the theory of catalytic petrochemical productions

in the absolute value of the catalyst surface or the amount of catalyst. At the same time, a number of factors characterizing the process do not change: 1) the mechanism of the process, the ratio of the rates of the parallel and the sequential stages of the total catalytic process, the composition of the reaction products; 2) basic kinetic characteristics of the process; 3) the activation energy of the process in the absence of poison and when the surface of the catalyst is constantly filled with a poison must coincide. When poisoning, the overall activity of the catalyst (A) and the reaction rate constant (k) change А = А0 (1- ·С), where А is a total activity, А0 is activity of the poisoned catalyst, C – poison concentration,  is a poisoning coefficient (the surface poisoned with poison). Poisoning of an inhomogeneous (non-uniform) surface with blocking For an inhomogeneous (a non-uniform) surface there is essential a dependence of activity on the nature of placement of poison on the surface of the catalyst. We consider three cases of blocking by the example of the dependence of the distribution function of the active regions on the activation energy (Е) on E: 1) the poison is located on the surface irrespective of the activetion energy of the surface sections (E); 2) microscopic blocking during poisoning begins with the least active sites, while the reaction occurs in areas with Еmin; 3) if the blockage starts from the most active parts of the catalyst surface, then the first portions of the poison act most strongly and the activation energy changes smoothly. Let us consider examples of the blocking of a catalyst by a poison propagating along its surface in directions indicated by the a-b boundary. The distribution of the poison is possible both from the most active sites of the catalyst with the minimum activation energy, and

Chapter 4. Catalysis theories

49




Fundamentals of the theory of catalytic petrochemical productions

1. When poisoning inhomogeneous surfaces, the activation energy changes sharply and depends on the nature of the distribution of the poison on the surface. 2. The change in the activity of the catalyst from the amount of the absorbed poison is expressed by exponential and other kinds of functions. Compensation effect. Theory of supersaturation of S.Z. Roginsky Follows from the theory of an active surface of S.Z. Roginsky that the same impurity can play at certain values a role of either promotors, or poisons. An investigation of the influence of the process temperature on the activity in the presence of impurities in hydrocarbon oxidation reactions showed that the curve of the dependence of the velocity on the impurity concentration passes through a maximum. Also, the curve of the dependence of the velocity on the activation energy for a given process passes through a maximum at the same values of the impurity concentration. This fact contradicts the usual ideas, since the most active catalyst has a high activation energy, and not low, as is customary. Therefore, to highest Ea there corresponds the high speed and k0. This regularity is called compensation effect. Change of energy of activation and k0 of a symbasis in the presence of additives and process goes without change of a specific surface of the catalyst. According to Arrhenius’s equation: k=k0·е–Еа/RT, where k0 is the pre-exponential factor characterizing the number of active collisions. Thus, increase in Ea leads to reduction of е–Еа/RT. Characteristic is the symbasis of Ea and k0 to various effect of the entered additive with change of temperature. The same catalyst, depending on the temperature, becomes either promoted or poisoned. Therefore S.Z. Roginsky offered another terminology for poisoning and promotion.

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

Questions for self-control 1. What are the basic provisions of the theory of supersaturation of S.Z. Roginsky? 2. What is meant by the active center in the theory of the active surface of Roginsky? 3. What features of poisoning of a uniform (homogeneous) surface with blocking? 4. Describe the main types of poisoning of a non-uniform (heterogeneous) surface of the catalyst with blocking. 5. How do metal additions introduced into the catalyst affect the activity of the catalyst during gas promotion? 6. What does “compensation effect” mean in catalysis? 7. What are poisoning, promotion, modification of catalysts? On what do these factors depend? 8. How does the activity of the catalyst depend on supersaturation? 9. Define the main types of supersaturation of catalysts in the processes of their preparation.

4.4. Theory of foresight of catalytic action of G.K. Boreskov Basic provisions of the theory of G.K. Boreskov (1953) 1. The change in the rate of chemical reactions in heterogeneous catalysis is caused by the intermediate surface chemical interaction of the reactants with the catalyst. Accordingly, the activity of the solid catalyst with respect to this reaction is determined, first of all, by its chemical properties. 2. The catalytic activity is inherent in the normal surface of crystalline solids and isn't connected with a special condition or singular structural elements of their surface. 3. The specific catalytic activity (unit surface activity) of the constant-composition catalysts is approximately the same. The main factor determining the specific catalytic activity is the chemical composition and chemical structure of the catalyst. 4. For catalysts of a certain specific catalytic activity, a powerful factor of increasing the activity of a unit of volume, characterizing the industrial value of the catalyst, is an increase in the operating surface. An increase in the working surface can be achieved by increasing the internal surface and creating an optimal porous catalyst structure

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

catalyst is essentially considered only as a geometric place of reaction, characterized by a certain potential; the effect of reactants on the catalyst, leading to a change in its properties, is ignored. Meanwhile, the construction of a theory of catalysis capable of explaining and foreseeing catalytic action is possible only on the basis of the concepts of catalysis as a chemical phenomenon in its essence, by studying the specific features of the intermediate chemical interaction. Catalytic activity of crystalline substances The vast majority of catalysts used in engineering are crystalline substances. The surface of solid crystalline catalysts is large enough to explain their catalytic effect. Adsorption studies indicate that the surface of catalytic metals, oxides and other compounds has significant chemical activity; it binds molecules of many gases with great speed and considerable heat release. High chemical activity of the surface of crystalline substances is also confirmed by data on the rate of isotope exchange of surface atoms with different gases. Crystalline substances have sufficient chemical activity for intermediate interaction with reacting substances, and there is no need to postulate specific non-crystalline states or structures to explain the catalytic action. From here doesn’t follow that only crystals can have catalytic activity. In a heterogeneous catalysis also amorphous (or in any case X-ray amorphous) catalysts, for example aluminosilicates, silica gel, etc. are used. Working surface of solid catalysts Acceleration of reaction at a heterogeneous catalysis is in most cases caused by the fact that energy of activation of all stages of the new reactionary way resulting from superficial interaction with the catalyst below energy of activation of reaction in the absence of the catalyst. Only in rare cases, the acceleration of the process is associated with the emergence of a chain reaction that goes over into the volume. Therefore, in the overwhelming majority of cases, the catalytic activity of solid catalysts is proportional to the value of their

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

The amount of the working surface is defined not only the nature of porous structure of the catalyst. It depends also on its specific activity, and on reaction implementation conditions. Specific catalytic activity is the value specific to catalyst substance. The specific activity of the catalyst with respect to a definite reaction must depend on the chemical composition and chemical nature of the catalyst. For the development of the theory of preparation of catalysts, it is very important to know to what extent the specific catalytic activity of a constant composition catalyst can change, i.e. to what extent it depends on the state of the substance. Most catalysis guidelines and original studies indicate that, depending on the conditions of preparation, heat treatment and other factors, the specific catalytic activity of the catalysts of a constant composition can vary within very wide limits. It is noted that a high specific activity is inherent in a substance in a finely dispersed state, with a broken, deformed crystal lattice, while well-formed large crystals are inactive or a little active. The notion that catalytic activity manifests itself in a particular state of matter has largely determined the direction of theoretical work on heterogeneous catalysis in the direction of searching for the specific structures of the substance that determine the catalytic activity and the methods for creating these structures (for example, the theory of supersaturation). It has been suggested that catalytic activity is inherent only in certain elements of the crystal lattice of catalysts, pre-crystalline amorphous ensembles (N.I. Kobozev), all sorts of disturbances in the normal crystal lattice, which have excess free energy (S.Z. Roginsky), and others. In the majority of researches of catalytic activity the surface of the catalyst wasn't known and the complications connected with slowness of course of processes of transfer of the reacting substances to the internal surface of grains weren't always considered. With the help of adsorption methods for measuring the internal surface of porous catalysts and for separately measuring the surface of individual components for some complex systems, the specific catalytic activity of some catalysts was measured.

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

For the metals of period IV, 9 orbitals are suitable for the formation of a bond: 1-s; 3-p; 5-d. Consequently, in the Ni crystal there are two structures of Ni-A and Ni-B in different ratios: 3d

4s

4p

Ni-A; v=6

d2sp3

Ni-B; v=6

d3sp2

On the orbitals of Ni-A there are 2-d and 1-s electrons, on Ni-B – 3-d and 1-s electrons. The magnetic saturation moment of Ni is equal to 0.6 μB and determines the statistical weights with which the Ni-A and Ni-B structures are represented in the crystal: 30% Ni-A and 70% Ni-B. Thus, for every 100 Ni atoms 30 Ni-A atoms give 10 electrons with unpaired spin, and 70 Ni-B atoms do not have any electrons with unpaired spin. In the sum of 100 Ni atoms, there are 10 electrons with unpaired spin, respectively, 1 atom of 0.6 electrons or a magnetic moment equal to 0.6 μB. These representations developed by Pauling allowed us to introduce yet another characteristic of the electronic state of metals – the percentage or weight of the d-nature of the metal bond per metal atom. For example: for Ni-A, there are 2 d electrons in 6 connecting orbits; in Ni-B, there are 3-d electrons in 7 electron orbitals. Consequently, the % of d-nature of Ni is: 30·2/6 + 70·3/7=39.5% For elements I-III of large periods, Pauling developed a table of data on the weights of d-states. The more binding electrons enter the d-orbital, the greater the weight of d-states in the metal bond. The most catalytically active Me VIII groups have 0.5-0.6 holes in atomic d-orbitals.

Chapter 4. Catalysis theories




Fundamentals of the theory of catalytic petrochemical productions

Petroleum (crude oil) is a naturally occurring mixture of gaseous, liquid, and solid hydrocarbon compounds usually found trapped deep underground beneath impermeable cap rock and above a lower dome of sedimentary rock such as shale; most petroleum reservoirs occur in sedimentary rocks of marine, deltaic, or estuarine origin. Petroleum coke is a black solid by-product, obtained mainly by cracking and carbonising petroleum-derived feedstock, vacuum bottoms, tar and pitches in processes such as delayed coking or fluid coking. It consists mainly of carbon (90% to 95%) and has a low ash content. It is used as a feedstock in coke ovens for the steel industry, for heating purposes, for electrode manufacture and for production of chemicals. Petroleum natural gases are gases consisting of a mixture of gaseous hydrocarbons of the paraffin series (СnН2n+2): methane CH4 (sometimes up to 99%), ethane C2H6, propane C3H8, butane C4H10, with an admixture of nitrogen, carbon dioxide, hydrogen sulfide and gasoline vapors. Distinguish dry gas – with a predominance of methane – and fatty gas – with a high content of heavy hydrocarbons. The phase transfer catalyst is a substance that facilitates the acceleration of reactions in heterophase systems by accelerating the transport of molecules between different phases in heterophase systems. For example, ammonium and phosphonium salts (or their organic analogues), as well as crown ethers, aliphatic ethers and other compounds serve as phase transfer catalysts for the most common systems of the type of water-organic solutions. The mechanism of action of the phase transfer catalysts depends on the phase in which the reaction takes place. Example: the process of nucleophilic substitution in alkyl halides proceeding in the organic phase is accelerated in the presence of ammonium cations NH4+, which are capable of transferring the inorganic anion from the aqueous phase to the organic phase. In some cases, the interfacial catalyst increases the solubility of the organic matter in the aqueous phase due to the effect of salting, for example, such an action has NH4+X- salts during benzoin condensation. Phosphoric acid polymerization is a process using a phosphoric acid catalyst to convert propene, butene, or both, to gasoline or petrochemical polymers. Photoadsorption is adsorption, usually chemisorption initiated by ultraviolet, visible or infrared radiation absorbed by adsorbate or adsorbent. Photoadsorption often is considered as primary stage of heterogeneous photocatalytic reaction. However in some cases photocatalytic reaction is initiated not by adsorption on the surface of the photocatalyst. Example: photocatalytic oxidation of the chlorinated hydrocarbons. Photodesorption is a desorption caused by absorption of ultraviolet, visible or infrared radiation by an adsorbate or adsorbent. Photodesorption can be a step in the general mechanism of heterogeneous photocatalysis. Photodesorption is the reverse process of photoadsorption. For a specific system, both processes (or reactions) are caused by ultraviolet, visible or infrared radiation of the same wavelength range.

Glossary




Fundamentals of the theory of catalytic petrochemical productions

Polydisperse – this term is applied to dispersed systems, if in a dispersed phase there are particles of unequal size. The polymerization catalyst is a substance which excites ionic or coordination and ion polymerization. The role of the catalyst of polymerization consists in creation of the active centers on which growth of molecules of polymer is carried out. The nature of active centers determines the mechanism of the process, the kinetics of the elementary stages of the process, the molecular weight distribution of polymer molecules, and the spatial structure of the polymer formed. Thus, the polymerization catalyst, in contrast to the polymerization initiator, takes part not only in the polymerization excitation stage but also in all subsequent polymer chain growth stages. Polymolecular adsorption is adsorption, in which several adsorbate molecules can be adsorbed on a single adsorption center. For example, the theory of BET adsorption is based on the assumption of polymolecular adsorption. Polynuclear hydroxocomplexes (PGA) are polymer multinucleated complex metal compounds containing bridging bonds of OH-hydroxide-ions. Polynuclear hydroxocomplexes are formed from amorphous and difficult-to-crystallize hydroxides in the process of hydrolysis of metal salts. Pores are cavities (emptiness) or channels in solid particles. It is commonly believed that the depth of the pores exceeds their width. There are open pores and closed pores. Pore size distribution is the statistical distribution of pore volume, depending on their size in the material under study. It is determined experimentally by the results of porosimetry or by calculation methods (by the adsorption isotherm). The pore size distribution affects the diffusion of the reactants and products in the solidphase catalyst particles. The pore volume is the total volume of all pores present in the solid material. Porometry is the determination of the pore size in a solid. Porometry provides information on the minimum and maximum pore size, the distribution of pores by size, and the average pore size in the sample. The main porometry methods are the adsorption method (pore size from 0.35 to 100 nm) and mercury porosimetry (pore size from 3 nm to 400 μm). Porosity is a share of the free volume which isn't occupied with catalyst granules in a layer from such granules. Porosity is the presence of pores or cavities in the material. Numerically, the porosity is expressed as the ratio of the pore volume in the particle of the substance to the total volume of this particle. Thus, the porosity can vary from 0 (total absence of pores) to ~ 1, and a strict value of 1 is unattainable. In industrial catalysts, the porosity is 0.2-0.8. Porous structure of substance is structure of porous space, i.e. a spatial arrangement and the sizes of pores in substance particles. Post-adsorption is adsorption after preliminary irradiation of the photocatalyst in a vacuum. Precipitation is the process of formation of a solid precipitate in a solution. The precipitation of the solution can be caused by evaporation of the solution, a decrease in the solubility of the substance when the solvent is replaced, a

Glossary




Fundamentals of the theory of catalytic petrochemical productions

The pulse reactor is a flow reactor operating in a pulsed mode. It is used in laboratory studies to study fast processes. In a pulsed reactor, a carrier gas stream is continuously fed through the catalyst, into which a stream of reagents is periodically added in the form of a short pulse. After each pulse, the reaction products can be analyzed, or the changes that have occurred to the catalyst are studied. Pyrolysis is a thermal process of decomposition of hydrocarbon feedstock to produce ethylene, propylene, benzene, butadiene, hydrogen and a number of other products. Pyrolysis gasoline is a by-product from the manufacture of ethylene by steam cracking of hydrocarbon fractions such as naphtha or gas oil.

R Raffinate is the product resulting from a solvent extraction process and consisting mainly of those components that are least soluble in the solvents. The product recovered from an extraction process is relatively free of aromatics, naphthenes, and other constituents that adversely affect physical parameters. Radiation catalysis is a change in the rate of a chemical reaction under the action of ionizing radiation in the presence of a radiation catalyst. When using ionizing radiation, from vacuum ultraviolet to higher energies, the phenomenon of photocatalysis does not differ from the phenomenon of radiation catalysis. In connection with non-selective absorption of ionizing radiation, it is possible to excite all participants in the reaction (both reagents and catalysts). Thus, the phenomenon designated as "radiation catalysis" includes both direct radiation and catalytic processes. Reaction speed is the number of acts of chemical transformation for a unit of time carried to unit of volume of reactionary mixture (in case of homogeneous reaction) or to surface unit of area (in case of heterogeneous reaction). Reactive adsorption is dissociative adsorption, in which one molecule fragment is attached to the adsorbent, and the second – to another adsorbed molecule. Reactive desorption is an associative desorption, the reverse process to reactive adsorption. Reactor is the vessel in which chemical reactions take place during a chemical conversion type of process, usually defined by the nature of the catalyst bed, e.g., fixed-bed reactor, fluid-bed reactor and by the direction of the flow of feedstock, e.g., upflow, downflow. The reactor of periodic action is a hermetically closed capacity where reactionary mixture and the catalyst are placed. After certain time process is stopped for extraction of products. As during process the reactor remains hermetically closed, partial pressure of substances in the reactor can change considerably at course of reactions. The reactor productivity is the quantity of the obtained product in unit of time referred to volume (sometimes to weight) of the reactor.

Glossary




Fundamentals of the theory of catalytic petrochemical productions

In the process of reforming, alkane molecules undergo rearrangement without changing the number of carbon atoms in the molecule (isomerization, dehydrogenation and dehydrocyclization reactions). Bifunctional catalysts containing active centers of acidic and dehydrogenating type, for example, Pt/Al 2O3, are used. Reformulated gasoline (RFG) is gasoline designed to mitigate smog production and to improve air quality by limiting the emission levels of certain chemical compounds such as benzene and other aromatic derivatives; often contains oxygennates. Regeneration is the treatment of the deactivated catalyst under conditions other than the reaction one. Regeneration is carried out in order to completely or partially restore the catalytic activity. A regular surface is the perfect surface of a solid without inhomogeneities and defects. In practice, this term is used to denote local areas of the space of real relaxed and reconstructed surfaces, if it is possible to neglect the indignations caused by the nearby (surface) defects. Relative catalytic activity is a value determined to compare the activity of several catalysts when they interact with a reaction mixture of the same composition. Usually compare time demanded for achievement of the same degree of transformation of reactionary mixture on different catalysts. An alternative way is comparison of temperature at which various catalysts give identical conversion at the same time of reaction. The method of relative catalytic activity is applicable for a number of similar catalysts when the mechanism of catalytic reaction doesn't change. Reserves are well-identified resources that can be profitably extracted and utilized with existing technology. Residuum (resid; pl. residua) is the residue obtained from petroleum after nondestructive distillation has removed all the volatile materials from crude oil, e.g., an atmospheric (345 °C, 650 °F) residuum. Resins are that portion of the maltenes that is adsorbed by a surface-active material such as clay or alumina; the fraction of deasphaltened oil that is insoluble in liquid propane but soluble in n-heptane. Resource is the total amount of a commodity (usually a mineral but can include nonminerals such as water and petroleum) that has been estimated to be ultimately available. The reverse spillover is the transfer of adsorbed particles from the carrier to the active component in the supported (deposited) catalyst as a result of surface diffusion. A rock is a mineral mass of more or less constant composition and structure, usually consisting of several minerals, sometimes from one mineral (for example, gypsum), and is involved in the structure of the earth's crust. The rocks are divided into three large groups according to their origin: magmatic, sedimentary and metamorphic.

Glossary