The main technological characteristics of water-fuel suspensions. Basic technological characteristics of polymeric materials Layout of the structural part of the foundation

The main task of the technologist is to create high-performance technological processes.

Structurally, the technological process consists of a set of technological operations (TO) necessary for the manufacture of products in accordance with the requirements of regulatory and technical documents.

The technological process is divided into technological operations. Establishing the content and sequence of operations is included in the task of developing a technological process.

In addition to technological operations, there are auxiliary operations... These include transportation, inspection, labeling, etc.

The organization of flexible production, like any other, is subject to such general principles:

• proportionality, that is, ensuring the same bandwidth of various GPS due to the possibility of partial redistribution of the load between them;
• specializations, that is, the distribution of work between various enterprises, workshops, sections, individual FPS and flexible production modules (FMP) according to the technological method of manufacturing;
• standardization, which is the main tool for reducing the range of manufactured products, which allows you to limit the range of products for one purpose, to increase the scale of production and facilitates the transition from multi-product FMS to more productive flexible automated production (HAP);
• rhythm, i.e. ensuring the production of products on schedule, which helps to reduce scrap;
• straightness- in this case, all material flows of production move by the shortest route;
• automaticity, i.e. automation of all technological operations, which contributes to an increase in labor productivity and the quality of products.

but basic principles the organization of production, fully disclosing all the capabilities of GAP, are:

• continuity of processes eliminating or significantly reducing various interruptions in the production of a particular product;
• parallelism of processes- provides for the simultaneous execution of various parts of the production process. In fact, there is an organic fusion of design and technological preparation of production, main and auxiliary processes. Parallelism is also ensured by centralization and integration of management processes.

The main parameters of the technological process are:

• accuracy (the degree of compliance of the parameters of the manufactured product with those parameters that are specified in the regulatory and technological documentation). It should be understood that the reason for the discrepancy is production errors (systematic or random), and be able to analyze the causes of their occurrence and the result of their impact on TP;
• stability - the property of the technological process (TP) to maintain the values ​​of product quality indicators within the specified limits for a certain time;
• productivity - the property of TP to ensure the release of a certain number of products over a specified period of time. Distinguish between hourly, shift, monthly, etc .;
• the cost of production, which is determined by the cost of its manufacture.

In addition, an important parameter is also the manufacturability of the design of products, which can be assessed both qualitatively and quantitatively, by calculating certain indicators.

The first reliably known technological processes were developed in ancient Sumer - the procedure for making beer was described in cuneiform on a clay tablet. Since then, the ways of describing technologies for the production of food, tools, household utensils, weapons and ornaments - everything that mankind has made - have become many times more sophisticated and improved. A modern technological process can consist of tens, hundreds or even thousands of separate operations; it can be multivariate and branch out depending on various conditions. The choice of one technology or another is not an easy choice of one or another machine, tool and equipment. It is also necessary to ensure compliance with the requirements of technical conditions, planned and financial indicators.

Definition and characterization

GOST gives a scientifically rigorous, but formulated in too dry and pseudoscientific language, a definition of a technological process. If we talk about the concept of a technological process in a more understandable language, then a technological process is a set of operations lined up in a certain order. It aims to transform raw materials and semi-finished products into finished products. To do this, certain actions are performed with them, usually performed by mechanisms. The technological process does not exist by itself, but is an important part of a more general one, which in general also includes the processes of contracting, purchasing and logistics, sales, financial management, administrative management and quality control.

Technologists at the enterprise occupy a very important position. They are a kind of intermediaries between the designers who create the idea of ​​the product and produce its drawings, and the production, which has to translate these ideas and drawings into metal, wood, plastic and other materials. When developing a technical process, technologists work in close contact not only with designers and production, but also with logistics, procurement, finance and quality control service. It is the technical process that is the point at which the requirements of all these divisions converge and the balance between them is found.

The description of the technological process should be contained in documents such as:

• The route map is a high-level description that lists the routes for moving a part or workpiece from one workplace to another or between workshops.
• Operational map - a description of the middle level, more detailed, it lists all operational transitions, set-up operations, tools used.
• The technological map is a document of the lowest level, contains the most detailed description of the processes of processing materials, blanks, assemblies and assemblies, the parameters of these processes, working drawings and the equipment used.

A technological map, even for a product that is simple at first glance, can be a rather thick volume.

The following characteristics are used to compare and measure batch production processes:

The production program of the enterprise consists of the production programs of its workshops and sections. It contains:

• List of manufactured products with details of types, sizes, quantities.
• Production schedules with reference to each key date of a certain volume of manufactured products.
• The number of spare parts for each item as part of the product lifecycle support process.
• Detailed design and technological documentation, three-dimensional models, drawings, detailing and specifications.
• Manufacturing specifications and quality management techniques, including test and measurement programs and procedures.

The production program is a section of the general business plan of the enterprise for each planning period.

Types of technical processes

The classification of technical processes is carried out according to several parameters.

According to the criterion of repetition rate in the manufacture of products, technological processes are divided into:

• a single technological process, created for the production of a part or product that is unique in terms of design and technological parameters;
• a typical technical process is created for a number of products of the same type, similar in their design and technological characteristics. A single technical process, in turn, can consist of a set of typical technical processes. The more typical technical processes are used at the enterprise, the lower the costs of preparation of production and the higher the economic efficiency of the enterprise;
• the group technical process is prepared for parts that are structurally different, but technologically similar.

According to the criterion of novelty and innovativeness, such types of technological processes are distinguished as:

• Typical. The main technological processes use traditional, proven designs, technologies and operations for processing materials, tools and equipment.
• Promising. Such processes use the most advanced technologies, materials, tools typical for enterprises - industry leaders.

According to the criterion of the degree of detail, the following types of technological processes are distinguished:

• The route technical process is executed in the form of a route map containing information of the top level: a list of operations, their sequence, class or group of equipment used, technological equipment and the general standard of time.
• The step-by-step technical process contains a detailed processing sequence down to the level of transitions, modes and their parameters. Executed in the form of an operating card.

The step-by-step technical process was developed during the Second World War in the United States in the face of a shortage of skilled labor. Detailed and detailed descriptions of each stage of the technological process made it possible to attract people who did not have production experience to work and to fulfill large military orders on time. In peacetime conditions and the availability of well-trained and sufficiently experienced production personnel, the use of this type of technological process leads to unproductive costs. Sometimes a situation arises in which technologists diligently publish thick volumes of operational maps, the technical documentation service replicates them in the prescribed number of copies, and the production does not open these talmuds. In the workshop, workers and foremen for many years of work have accumulated sufficient experience and acquired a sufficiently high qualification in order to independently perform a sequence of operations and select the operating modes of the equipment. It makes sense for such enterprises to think about abandoning operational maps and replacing them with route maps.

There are other classifications of types of technological processes.

TP stages

In the course of design and technological preparation of production, such stages of writing a technological process are distinguished as:

• Collection, processing and study of initial data.
• Determination of the main technological solutions.
• Preparation of a feasibility study (or feasibility study).
• Documenting the technical process.

It is difficult the first time to find technological solutions that ensure the planned time, and the required quality, and the planned cost of the product. Therefore, the technology development process is a multivariate and iterative process.

If the results of economic calculations are unsatisfactory, then the technologists repeat the main stages of the technological process development until they reach the parameters required by the plan.

The essence of the technological process

A process is called a change in the state of an object under the influence of internal or external conditions in relation to the object.

External factors will be mechanical, chemical, temperature, radiation effects, internal - the ability of a material, part, product to resist these influences and maintain its original shape and phase state.

During the development of the technical process, the technologist selects those external factors under the influence of which the material of the workpiece or raw material will change its shape, size or properties in such a way as to satisfy:

• technical specifications for the final product;
• planned indicators for the timing and volumes of product release;

For a long time, the basic principles of building technological processes have been developed.

The principle of enlargement of operations

In this case, a larger number of transitions are collected within one operation. From a practical point of view, this approach allows you to improve the accuracy of the relative position of the axes and the processed surfaces. This effect is achieved due to the execution of all combined in the operation of the transitions in one stop on the machine or multi-axis machining center.

The approach also simplifies internal logistics and reduces shop floor costs by reducing the number of installations and equipment setups.

This is especially important for large and complex parts, the installation of which is time-consuming.

The principle is applied when working on turret and multi-cutter lathes, multi-axis machining centers.

The principle of dismemberment of operations

The operation is divided into a series of simplest transitions, the adjustment of the operating modes of the processing equipment is performed once, for the first part of the series, then the remaining parts are processed in the same modes.

This approach is effective for large batch sizes and relatively uncomplicated spatial configuration of products.

The principle gives a significant effect of reducing the relative labor intensity due to improved organization of workplaces, improving the skills of workers in monotonous movements for setting and removing workpieces, manipulating tools and equipment.

At the same time, the absolute number of installations grows, but the time for setting up the equipment modes is reduced, due to which a positive result is achieved.

To obtain this positive effect, the technologist will have to take care of the use of specialized equipment and devices that allow quickly and, most importantly, accurately to set and remove the workpiece. The batch size should also be significant.

Wood and metal processing

In practice, one and the same part, of the same size and weight, from the same material can be made by different, sometimes very different methods.

At the stage of design and technological preparation of production, designers and technologists jointly work out several options for describing the technological process, manufacturing and processing the product. These options are compared in terms of key indicators, how well they satisfy:

• technical specifications for the final product;
• the requirements of the production plan, the timing and volume of shipment;
• financial and economic indicators laid down in the business plan of the enterprise.

At the next stage, these options are compared, the optimal one is selected from them. The type of production has a great influence on the choice of option.

In the case of one-off or discrete production, the likelihood of repetition of the release of the same part is small. In this case, an option is chosen with minimal costs for the development and creation of special equipment, tools and fixtures, with the maximum use of universal machines and customizable equipment. However, exceptional requirements for dimensional accuracy or operating conditions, such as radiation or highly corrosive environments, may necessitate the use of both specially made tooling and unique tools.

With serial production, the production process is divided into the release of repeated batches of products. The technological process is optimized taking into account the existing equipment at the enterprise, machine tools and machining centers. At the same time, the equipment is supplied with specially designed equipment and devices that allow to reduce non-productive loss of time by at least a few seconds. On a batch-wide scale, these seconds will add up and give a sufficient economic effect. Machine tools and machining centers are subject to specialization; certain groups of operations are assigned to the machine.

In mass production, the sizes of the series are very high, and the manufactured parts do not undergo design changes for a fairly long time. Equipment specialization goes even further. In this case, it is technologically and economically justified to assign the same operation to each machine for the entire production time of the series, as well as to manufacture special equipment and use a separate cutting tool and measuring and control instruments.

In this case, the equipment is physically moved in the workshop, placing it in the order of the operations in the technological process.

Technological process execution tools

The technological process exists first in the heads of technologists, then it is recorded on paper, and in modern enterprises - in the database of programs that provide the product lifecycle management (PLM) process. The transition to automated means of storing, writing, replicating and checking the relevance of technological processes is not a matter of time; it is a matter of the enterprise's survival in the competition. At the same time, enterprises have to overcome the strong resistance of highly qualified technologists of the school system, who, over the years, are accustomed to writing technical processes by hand, and then giving them for reprinting.

Modern software tools allow you to automatically check the tools, materials and equipment mentioned in the technical process for applicability and relevance, to reuse previously written technical processes in whole or in part. They increase the productivity of the technologist and significantly reduce the risk of human error when writing a technical process.

In order for a technological process to turn from ideas and calculations into reality, physical means of its implementation are needed.

Technological equipment is designed for installation, fixing, orientation in space and supply of raw materials, blanks, parts, units and assemblies to the processing zone.

Depending on the industry, this includes machine tools, machining centers, reactors, smelting furnaces, forging presses, plants and entire complexes.

The equipment has a long service life and can change its functions depending on the use of one or another technological equipment.

Technological equipment includes tools, molds, dies, devices for installing and removing parts, to facilitate workers' access to the area of ​​operations. The accessories complement the basic equipment, expanding its functionality. It has a shorter life span and is sometimes specially made for a specific batch of products or even for one unique product. When developing a technology, it is necessary to make wider use of universal accessories that are applicable for several standard sizes of the product. This is especially important in discrete industries, where the cost of tooling is not distributed over the entire series, but is entirely borne by the cost of one product.

The tool is designed to exert a direct physical effect on the material of the workpiece in order to bring its shape, dimensions, physical, chemical and other parameters to those specified in the technical conditions.

When choosing a tool, a technologist should take into account not only the purchase price, but also resource and versatility. It often happens that a more expensive tool makes it possible, without replacing it, to release several times more products than a cheaper analogue. In addition, modern versatile and high-speed tools will also reduce machining times, which also directly leads to cost savings. Every year, technologists acquire more and more economic knowledge and skills, and writing a technical process from a purely technological matter turns into a serious tool for increasing the competitiveness of an enterprise.

A number of techniques carried out to obtain a product with predetermined properties from a feedstock are called technological process.

To describe a single technological process or compare it with other processes, various indicators are used or options technological process.

Material characteristics of the technological process yavl. technological parameters. Parameters can be mechanical, electrical, thermal, temporary or other quantities.

All parameters of the technological process are conventionally divided into three groups:

- private parameters, allowing to compare technological processes that produce the same products and use the same technology. The particular parameters include: the composition and concentration of the feedstock, the features of the equipment and tools used, the modes of the process (temperature, pressure), etc .;

- single parameters, allowing you to compare technological processes that produce the same products, but use different technologies. The unit parameters include resource parameters (material intensity, labor intensity, energy intensity, capital intensity), as well as such an integral indicator as cost, which expresses the actual cost of resources in monetary terms for the production and sale of products;

- generalized parameters, which allow you to compare a variety of technological processes. These include, first of all, specific ones, i.e. per unit of output, calculated in monetary terms, the costs of living (human) labor and past (material) machine labor.

Tools, subject of labor for rare excl. not found. in post. contact, therefore it is necessary. spatial movement is provided. this contact and interaction. Thus, the main part of the elementary act of transformations. subject of labor into products yavl. process of direct. the impact of the tool on the subject of labor. This elementary part of tech. process naming. working stroke. The working move leads to betrayal. properties of the object of labor towards the finished product. The auxiliary part of the converter. subject of labor into a product yavl. the spatiality of combination with the subject of labor. This part is auxiliary. process naming. auxiliary progress.

The set of working and auxiliary moves forms a technological transition.

To perform. technological transition, as a rule, it is necessary to carry out your group of auxiliary. actions, but a higher Lv. It includes actions to close tools and parts, change equipment, etc. These actions are called. auxiliary transition.

Technological and auxiliary. the transition form a technological operation. To do it. also need auxiliary. actions. Technological. the operation precedes the transportation of the object of labor from one equipment to another, loading and releasing, moving. one, securing and removing parts.This group is auxiliary. action name. auxiliary operation.

After going through a number of technological. and auxiliary. operations subject of labor transform. into the product, i.e.

the set of operations leads to production. product that yavl. direct. aim

Apparatus and machines are used to carry out technological processes. Apparatus is a device or device designed to carry out a particular technological process (digester, boiler, etc.). Under the term "a car" understand a mechanism (or a combination of mechanisms and accessories) designed to convert mechanical energy into useful work.

Technological processes can be divided into general (basic) and specific. With all the variety of technological processes in food or chemical industries, many of them are common for various industries. In any production, for example, there is mixing, which is necessary to ensure contact between the reactants. In sugar, alcoholic beverages, alcoholic beverages and many other industries, evaporation is used to increase the concentration of dry substances in solutions. The drying process is the final stage in the production of rusks, pasta, sugar, many confectionery products, dry dairy products, vegetables and fruits, vitamins, wet grains, etc. All food production uses cooling and heating processes.

The position of an element in the Periodic Table, i.e. the structure of the electron shells of atoms and ions, ultimately determines all the basic chemical and a number of physical properties of matter. Therefore, a comparison of the catalytic activity of solids with the position of the elements that form them in the Periodic Table led to the identification of a number of regularities in the selection of catalysts.

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Classification of technological indicators of catalysts. Basic technological characteristics of heterogeneous catalysts. Laboratory methods for their determination.

3.1 Classification of technological indicators of catalysts.

In catalysis, the most fruitful concepts are those that take into account the chemical correspondence of the catalyst and the catalyzed reaction.

The position of an element in the Periodic Table, i.e. the structure of the electron shells of atoms and ions, ultimately determines all the basic chemical and a number of physical properties of matter. Therefore, a comparison of the catalytic activity of solids with the position of the elements that form them in the Periodic Table led to the identification of a number of regularities in the selection of catalysts.

For a general orientation in the selection of catalysts, it is useful to classify catalytic processes according to the mechanism of catalyst action.

When creating a new solid catalyst or upgrading an existing catalyst, the following basic parameters for catalysts should be considered:

Physical and mechanical;

Chemical;

Operational and economic.

The physicomechanical properties or parameters of the catalyst include porosity, bulk density, true density, specific surface area, average pore volume and pore radial distribution, fractional composition, particle size, amorphousness or crystallinity, particle shape, heat capacity, heat resistance or water-vapor heat resistance. , the ability to poison and regenerate.

The chemical parameters of catalysts include the chemical composition, the content of impurities, the ability to activate (promote, modify) and poison with poisons, the formation of alloys, modifications and phases, and the grafting of activators to the surface of solid catalysts.

Operational and economic indicators or properties of catalysts are activity and selectivity, easy regeneration from various deposits and inclusions (coke, oxides, reversible poisons), the possibility of creating simple methods for catalyst synthesis on an industrial scale, increased heat capacity, bulk density, low sensitivity to poisons, long-term operating time in the reactor without regeneration, ease of transportation and storage, ease of separation from the reaction mixture, availability of raw materials for catalyst production and environmental friendliness.

Technological characteristics of solid catalysts.

The selection of catalysts for industrial processes is an extremely difficult task. Catalysts are very specific with respect to various chemical reactions. Existing theories of catalysis explain this specificity by a number of energetic and geometric factors, as a result of which a given catalyst affects the rate of only one reaction or a very narrow group of reactions. A strictly scientific choice of a specific catalyst for a given chemical-technological process is not always possible, although the theory of catalytic processes has been significantly developed in recent decades and is characterized by many new achievements.

Solid catalysts are, as a rule, highly porous substances with a developed inner surface, characterized by a certain porous and crystalline structure, activity, selectivity, and a number of other technological characteristics.

3.2 The main characteristics of solid catalysts.

3.2.1 Activity.

When comparing different catalysts, the more active one is usually chosen if it meets the basic technological requirements.

Catalyst activity is a measure of the accelerating effect in relation to a given reaction.

To quantify activity in an industrial environment, determine:

- general conversion of the feedstock;

- the yield of the target product;

- the rate of transformation of a certain amount of raw materials per unit of time;

- per unit mass of the catalyst;

- per unit volume of catalyst;

- per unit surface area of ​​the catalyst;

- for a single active center, which is of scientific interest as an objective criterion for comparing the activity of identical or different catalysts.

Due to the wide variety of catalytic processes, there is no single quantitative criterion for activity. This is due to the fact that the use of different catalysts, even for the same chemical reaction, can change its mechanism in different ways. As a rule, the use of a catalyst leads to a change in the order of the reaction, and the activation energy, and the preexponential factor.

A quantitative criterion for the activity of a catalyst for a given reaction can be, for example, the rate constant measured for different catalysts under comparable conditions (standard). This approach is applicable if the reaction order remains the same for all compared catalysts of a given group.

If the catalytic reaction is of the same order as the non-catalytic, i.e., their rate constants k kt and k - have the same units of measurement, then the activity of catalyst A can be determined as the ratio of the constants

where E ° and E are the activation energies of catalytic and non-catalytic reactions, exp is an exponential factor.

From the equation of exponential dependence it follows that the activity is the higher, the more the activation energy decreases in the presence of a catalyst. In this case, however, it should be borne in mind that in the presence of a catalyst, not only the activation energy changes, but also the preexponential factor. The increase in activity due to a decrease in the activation energy is inhibited by a decrease in

K about km compared to K O (the so-called compensation effect takes place).

Sometimes catalysts are compared according to the reaction rate or the degree of conversion of the reactants under standard conditions, according to the amount of reactants interacting per unit time per unit surface area of ​​the catalyst (productivity, or tension, catalyst), etc.

The activity of a catalyst for a process proceeding in the kinetic region is determined, first of all, by the nature of the reactants and the specificity of the catalysts, i.e. the activity of the catalyst corresponds to its activity in a chemical reaction.

However, in cases where the rates of the chemical and diffuse stages of catalysis are comparable, the activity of the catalyst does not coincide with its activity in the chemical reaction.

To compare the activity of a catalyst in any reaction under different conditions, the intensity of the process on a given catalyst is used as a measure of the activity. It is expressed by the amount of product obtained per unit of time from one volume of catalyst.

A = G pr. / (V cat.t) 3.2

Or per unit of weight

A beats = G pr / (G cat t) 3.3

Comparison of the activity of different catalysts in this process under these standard conditions is carried out according to the degree of conversion of the basic substance, and the determination of the activity according to the degree of conversion.

The main factors affecting the activity of catalysts.

Catalyst concentration - there is almost always an excess of catalyst in the reaction system, because part of the mass of the catalyst either does not participate at all in the reaction, or participates insignificantly.

Concentration of the activator or promoter - if the amount of the activator or promoter is large, then some of the active sites of the catalyst are screened out, and the overall activity decreases.

The concentration of the starting substances - if they differ greatly from the required substances in the reaction, then the limiting stages of the process can be replaced, i.e. for example, the transition from the external diffusion region to the kinetic region or vice versa.

Concentration of the resulting products - usually an increase in concentration slows down the overall reaction rate, because in this case, the adsorption equilibrium is shifted and the catalyst surface occupied by the product increases. This surface is either turned off from the further operation of the catalyst, or, even worse, secondary side reactions begin to occur on it.

A strong increase in the concentration of products sometimes leads to complete poisoning of the catalyst. Sometimes these phenomena occur so quickly that after 5 - 15 minutes the catalyst becomes inactive and requires regeneration.

Example: Catalytic cracking, residence time 15 - 30 minutes.

Impurity Concentration - Impurities will always slow down the reaction rate. If the impurities are inert, then this decrease is not significant, if these are "contact poisons", then their influence is very strong, preliminary purification of the raw material is necessary.

Medium temperature and pressure - this influence is ambiguous for each reaction in its own way.

T - has a significant effect on the rate of the process proceeding both in the kinetic and in the diffusion regions.

A number of catalytic processes are carried out at elevated pressure in order to mix the equilibrium towards the product.

Structural characteristics of catalysts - general trend - fine pore catalysts are preferred.

The molecular weight of the initial substances - this factor has almost no effect when flowing in the kinetic region, insignificantly - in the external diffusion region, and strongly - in the intra-diffusion region.

3.2.2 Selectivity (selectivity) of catalysts.

Selectivity is especially important for multi-path parallel reactions, as well as for reactions of a number of sequential transformations.

Complex catalytic reactions can proceed along several thermodynamically possible directions with the formation of a large number of different products. The predominant course of the reaction depends on the catalyst used, and the process is not always accelerated, thermodynamically the most advantageous of several possible.

Of a number of thermodynamically possible reactions, a selective catalyst should only accelerate the reaction for obtaining the target product. Typically, as a result of the selective catalyst, the target conversion temperature is lowered and side reactions are thereby suppressed.

Selectivity or selectivity of a catalyst is its ability to selectively accelerate the target reaction in the presence of several side effects.

Quantitatively, the selectivity of the catalyst can be estimated as the selectivity of the process - integral or differential. If several parallel reactions occur simultaneously, then different selective catalysts can be selected for each of these reactions.

For example: in the presence of aluminum oxide or thorium oxide, ethanol decomposes mainly into ethylene and water:

C 2 H 5 OH ---> C 2 H 4 + H 2 O

In the presence of silver, copper and other metals, practically only the reaction of alcohol dehydrogenation with the formation of acetaldehyde takes place:

C 2 H 5 OH ---> CH 3 CHO + H 2

In the presence of a mixed catalyst (A1 2 Oz + ZnO ) with a sufficiently high selectivity, dehydration and dehydrogenation reactions take place with the formation of butadiene:

2 C 2 H 5 OH ---> C 4 H 6 + 2H 2 O + H 2,

Selectivity depends not only on the chosen catalyst, but also on the process conditions, on the region of the heterogeneous catalytic process (kinetic, external or internal diffusion), etc.

An example of the selective action of catalysts is the oxidation of ammonia during the production of nitric acid.

Several parallel and sequential reactions are possible:

1. 4 NH 3 + 3 O 2 = 2 N 2 + 6 H 2 O + 1300 KJ;
2. 4 NH 3 + 4 O 2 = 2 N 2 O + 6 H 2 O + 1100 KJ;
3. 4 NH 3 + 5 O 2 = 4 N O + 6 H 2 O + 300 KJ;

3rd reaction is more active on Pt catalyst; oxide catalyst 1 and 2 are the same.

Selectivity is assessed using the following formula:

A -> B + C,

Where B is the target, C is the secondary.

S =,

The overall selectivity of the catalyst can be expressed by the ratio of the amount of the target product (B) to the total amount of the target and by-products (C).

The selectivity is affected by the same parameters as the activity, but the nature of the influence of the parameters is somewhat different:

Selectivity, as a rule, decreases with an increase in the contact time of the reactants with the catalyst, i.e. with a decrease in the volumetric feed rate of raw materials, especially for those reactions in which the target product is an intermediate: A --- B --- C.

The volumetric velocity determines the achievement of equilibrium in the system, the direction of reactions and the yield of products.

It is the ratio of the volume of the gas mixture, reduced to normal conditions (NU), passing per unit time to the bulk volume of the catalyst.

V = V g.c. / V cat. 3.4

Example:

Consider systems for the conversion of n-paraffins.

At high temperatures and low speeds of n-paraffins C 6 - C 8 turn into Pt - catalysts, the main reaction is the reaction of aromatization or dehydrocyclization of n-paraffins.

At high temperatures and medium speeds, Pt - catalysts, the main reaction is the isomerization reaction, n-paraffins are converted to olefins and isomerized. Since the speed is higher in the 1st case, the cyclization does not have time to occur.

At high temperatures and high speeds, the hydrocracking process - paraffins are split, olefin radicals are saturated with hydrogen and converted into other paraffins, but since the speeds are high, the formed paraffins do not have time to isomerize and cyclize.

Temperature influences in much the same way as the space velocity on these processes. At high temperatures - monocyclic A r hydrocarbons, when the temperature rises to 500 O C - bicyclic A r hydrocarbons.

The interaction between the catalyst and the medium is not limited to the influence of the catalyst on the reactants, but there is also a feedback between the medium and the catalyst. We can talk about the catalytic activity of the entire system, including the contact mass and the reaction mixture.

In a catalyst, under the influence of the environment, the following can change: the state of the surface; structural characteristics of the contact mass; chemical composition and properties of the entire volume of the catalyst without the formation of new phases; chemical composition with the formation of new phases.

3.2.3 Ignition temperature.

Along with the activity and selectivity, an important technological characteristic is the catalyst ignition temperature Tzag.

The concept of "ignition" means that when the temperature rises above the limit equal to Tcg, there is a sharp, abrupt increase in the reaction rate. Ignition can also take place in non-catalytic reactions.

The ignition temperature is the minimum temperature at which the technological process begins to move at a speed sufficient for practical purposes.

The catalyst ignition temperature is the minimum temperature at which the catalyst has sufficient activity to carry out an autothermal process in an industrial environment.

This factor is primarily taken into account when carrying out high-temperature reversible reactions in adiabatic fixed bed reactors.

An adiabatic reactor is a system that is deprived of the possibility of supplying it from the outside or removing it into the environment.

When graphically solving the system of equations of material and heat balances of a flow-through reactor when carrying out an exothermic reaction in it. Suppose that the relative position of the lines describing the equations of material and heat balances corresponds to that shown in the drawing, i.e. line 2 of the heat balance equation is tangent at point A to line 1 of the material balance equation. Then a small change in the initial temperature at the inlet to the reactor from T 1 - T to T 1 - T will lead to an abrupt change in the degree of conversion achieved in the reactor from X A; 1 to X A, 2 ... This means that at the same values ​​of the reactor volume and the volumetric flow rate of the reagents through it, a sharp increase in the reaction rate (and simultaneously the rate of heat release) occurred.

Therefore, the temperature T 1 and is the ignition temperature. Numerical value of T 1 in the drawing (and, accordingly, the position of point A) is determined primarily by the kinetic features of the reaction that affect the position of line 1 of the material balance equation. Since each catalyst is characterized by its own kinetic parameters, the ignition temperatures will be different for different catalysts.

Drawing. Joint solution of the equations of material and heat balances of a flow-through reactor:

1 - the line of the material balance equation; 2 — line of the heat balance equation

From a technological point of view, it is better to use catalysts with a low ignition temperature, which makes it possible to reduce the energy consumption for preheating the reaction mixture.

For exothermic reactions, the concept of "ignition temperature" can be specified quantitatively. The lower the temperature of the process, the lower the reaction rate and the less heat is released. At a certain minimum temperature (ignition temperature), the rate of heat release becomes equal to the rate of heat removal (heat consumption for heating the initial reaction mixture and heat removal with the reaction products). Thus, the ignition temperature for exothermic reactions is the minimum temperature at which the process can be carried out in an autothermal mode, without the supply of heat from the outside.

It is especially important to have a low catalyst ignition temperature when carrying out reversible exothermic reactions, then low temperatures during the process make it possible to shift the equilibrium of the reaction towards its products.

3.2.4 Service life of the catalyst.

Catalyst life is extremely difficult to estimate in a laboratory setting because catalytic activity is characterized by many factors that are difficult to take into account in the laboratory, for example: coking; chemical poisoning; recrystallization, in the case of using a support having a crystalline structure.

Catalyst life can be expressed as:

1. In units of time (for example: for catalytic cracking - several seconds, and ammonia synthesis - several years);
2. In the intermediate time between regeneration or total duration until complete loss of activity.

Resistance to oxidative regeneration: total catalyst life divided by regeneration period.

1. The mass of the product obtained during the entire operation of the catalyst.

Sometimes it is more advantageous to replace a catalyst with residual activity than to keep it in the reactor until it is completely deactivated.

Catalyst Reload Cost

Duration of work

The more the catalyst has worked, the lower the cost of replacing it, but this should be correlated with the activity of the catalyst, it decreases with the duration of operation.

When replacing a catalyst with a new one or looking for intensification, the following factors should be considered:

1. Simple when replacing the catalyst;
2. Dimensions of industrial reactors;
3. The cost of replacing catalysts;
4. Losses associated with a decrease in the total power of the catalysts;
5. The complexity of the preparation of new active catalysts.

3.2.5 Thermal conductivity of catalyst grains.

Thermal conductivity of catalyst grains - helps to equalize the temperature in the catalyst bed and reduces the temperature difference in the adiabatic reactor.

If the thermal effect is very high, then the thermal conductivity of the catalyst, in addition to the activity, is the most significant factor, because such a catalyst is able to eliminate local overheating, which lead to a decrease in the product yield, due to the fact that coke formation occurs in the section (in isothermal).

And in exothermic processes, low thermal conductivity leads to the following: adsorption of raw materials on catalyst grains is disturbed and capillary condensation of raw material vapors, reagents in the pores of the catalyst begins - everything is essential in a fixed bed.

3.2.6 Strength and durability.

Strength and durability - must ensure the normal operation of the catalyst for several years.

In a fixed catalyst bed, strength losses occur for the following reasons:

1.due to temperature changes;

2. due to the erosion of the catalyst grain by a gas or liquid stream of reagents;

3. due to the pressure of the layer of overlying catalyst grains.

The crushing strength of the fixed bed catalysts should be 0.7 - 11 MPa.

In a moving catalyst bed, strength is understood as the wear resistance of the catalyst grain during friction and impact of them against each other, against the walls of the reactor, regenerator, elevator or pipeline.

Abrasion resistance is characterized by two reasons: abrasion resistance and splitting resistance.

The relationship between strength and splitting determines the fluidized bed strength of the catalyst.

Introduce the concept of "Catalyst consumption per ton of raw material" or catalyst consumption per ton of freshly loaded catalyst.

3.2.7 Catalyst cost.

The cost of the catalyst is a small percentage of the cost of the resulting product.

The reforming catalyst costs 300,000 - 0.01% of all reforming costs.

Catalyst components are very expensive - Pt.

Cost reduction ways:

1. Application of an expensive component of the catalyst to the carrier;

2. Rational technology of its production.

All these consumer characteristics are determined by two factors:

1. The composition of the contact masses;
2. Porous structure.

The possibility of using this or that material for the production of various products is determined by a whole list of qualities and properties. The main role in the choice of the processing method is played by the technological properties of metals and alloys, it is they that determine the possibility of their use for the manufacture of a particular product.

Basic properties of metals

All the basic qualities of metals and their alloys can be classified according to a number of indicators, each of which has a significant impact on determining the scope of the material.

• The physical properties of metals include their weight, heat capacity, ability to conduct electric current and other similar indicators. Everyone understands that the use of, for example, cast iron is impossible in aircraft construction, and any metal that perfectly conducts electricity is not applicable in the production of insulators.
• Mechanical properties are determined by the ability to withstand various loads, including hardness, ductility, elasticity and many other qualities.
• Performance characterizes the possibility of using metal for operation in various conditions - resistance to abrasion, high and low temperatures, and so on.
• The chemical properties of metals and alloys are determined by the ability of their constituent elements to react with other substances. So, for example, everyone knows that gold does not lend itself to the action of acids, which cannot be said about other types of metal.
• The technological properties of the material determine the list of production processes that are applicable to the metal in subsequent processing.

Metals - technological properties

The main technological properties include the following characteristics:

• Liquid fluidity (casting) - the ability of a material in a molten state to fill a casting mold, without leaving voids.
• Weldability - the ability to perform permanent joints of parts under the influence of various types of welding (gas, electric, pressure).
• Malleability (deformability) - the ability to change the shape of a product in a hot state or at normal temperature under the influence of pressure.
• Hardenability - the ability to improve various properties of a metal by quenching to different depths.
• The ability to perform metal processing using cutting equipment shows the ability to perform turning and milling operations.

All these technological properties of metals and alloys in combination determine the further scope of application.

Technological properties of steel

Steel is considered one of the most common metals, its technological properties depend on the chemical composition, various impurities included in it can improve or worsen these characteristics.

The negative impurities that significantly affect the technological characteristics include sulfur and phosphorus. An excess of these substances can lead to red brittleness and cold brittleness, respectively. That is, steel with an excess of sulfur becomes brittle when heated, and if there is a large amount of phosphorus in it, then it will break at low temperatures. That is why, when smelting steel, many efforts are aimed at reducing these impurities in the metal, but, unfortunately, it is impossible to get rid of them completely.

As you can see, the chemical constituents of steel have a great importance on its technological properties, therefore, when choosing a processing method, a thorough analysis of the alloy composition must be carried out, otherwise problems may arise, both in production and during the operation of the product.