Membrane methods for separating mixtures. Membrane technology Membrane separation technology

Membrane separation methods include:

1. Dialysis and electrodialysis.

2. Reverse osmosis.

3. Microfiltration.

4. Ultrafiltration.

These methods are based on the phenomenon of osmosis - the diffusion of dissolved substances through a semi-permeable partition, which is a membrane with a large number (up to 10 10 -10 11 per 1 m 2) of small holes - pores, the diameter of which does not exceed 0.5 microns.

A membrane is usually understood as a highly porous or nonporous flat or tubular partition made of polymeric or inorganic materials and capable of effectively separating particles of various types (ions, molecules, macromolecules and colloidal particles) found in a mixture or solution. The use of membranes makes it possible to create economically highly efficient and low-waste technologies.

Among membrane processes, baromembrane processes develop especially intensively. While reverse osmosis has been studied quite fully, this concerns microfiltration and, even more so, ultrafiltration, to a much lesser extent, despite its obvious promise. The boundaries of baromembrane separation methods are not clearly defined, which is apparently fundamentally impossible, since micro- and ultrafiltration and reverse osmosis overlap widely both in terms of their physicochemical description and the problems they solve. Consequently, the above classification of barometric separation methods is largely arbitrary. However, each of these methods has its own characteristic features, on the basis of which several classifications have been proposed.

Microfiltration is basically a hydrodynamic process similar to conventional filtration. A specific feature of microfiltration is the use of membranes with a pore diameter of 0.1 to 10 microns to separate small particles of the solid phase, including microorganisms, in this case it is called sterilizing filtration. Therefore, in contrast to the filtration process, in microfiltration, diffusion phenomena (especially with small pore sizes from 0.1 to 0.5 μm) also play a role.

Ultrafiltration is based on the use of membranes with a pore diameter of 0.001 to 0.1 microns. Ultrafiltration is used to separate cells and molecules.

Membrane separation methods, when applied to biological suspensions, have a number of advantages.

1. Concentration and purification are carried out without changing the state of aggregation and phase transformations.

2. The processed product is not exposed to thermal and chemical influences.

3. The mechanical and aerodynamic impact on biological material is insignificant.

4. Sealing and aseptic conditions are easily ensured.

5. The hardware design is compact in design, there are no moving parts.

6. The process does not have high energy intensity; in most cases, energy is spent only on pumping solutions.

The mechanism of transfer of atoms, molecules or ions of various substances through semi-permeable membranes can be explained by one of the following theories.

Sieving theory suggests that a semipermeable membrane contains pores that are large enough to allow solvent to pass through, but too small to allow solute molecules or ions to pass through.

The theory of molecular diffusion is based on unequal solubility and the difference in the diffusion coefficient of separated components in polymer membranes. The theory of capillary filtration permeability is based on the difference in the physicochemical properties of the boundary layer of liquid on the surface of the membrane and the solution in the bulk.

Of the proposed theories, the capillary-filtration model has become widespread.

The main working body of membrane devices are semi-permeable membranes. Membranes must have high separation ability or selectivity, high specific productivity or permeability, consistency of their characteristics during operation, chemical resistance in the separating medium, mechanical strength, and low cost. Selectivity and permeability are the most important technological characteristics of membranes and the apparatus as a whole.

The selectivity of the membrane depends on the size and shape of the solute molecules. It should be borne in mind that in almost all cases there are molecules that are only partially retained by the membrane. Membranes are made from various materials: polymer films, glass, ceramics, metal foil, etc. Membranes made of polymer films have become widespread.

Semi-permeable membranes are either porous or non-porous. Through non-porous membranes the process is carried out due to molecular diffusion. Such membranes are called diffusion membranes and are used to separate components with similar properties. Porous membranes are made mainly from polymeric materials and can be anisotropic or isotropic.

Porous membranes are usually obtained by removing solvents or washing out pre-introduced additives from polymer solutions during their formation. The membranes obtained in this way have a thin 0.25-0.5 micron surface layer on a microporous substrate with a thickness of 100-250 microns. The membrane separation process is carried out in the surface active layer, and the substrate provides the mechanical strength of the membrane.

Nuclear membranes, or nucleopores, have become widespread. These membranes are formed by irradiating thin polymer films charged with alpha particles, followed by etching the pores with chemical reagents.

The main advantages of nuclear membranes include:

Regular round pore shape;

The ability to obtain membranes with predetermined sizes and number of pores;

Same pore size;

Chemical resistance.

Nuclear membranes are made on the basis of carbonate films with a pore diameter of 0.1 to 8 microns.

Along with polymer membranes, membranes with a rigid structure are known:

metal, porous glass, ceramics.

Metal membranes are made by leaching or sublimating one of the foil alloy components. In this case, highly porous membranes with pores of the same size are obtained - in the range of 5-0.1 microns.

Another way to produce metal membranes is to sinter metal powder at high temperatures using powder metallurgy.

Disadvantages of membrane separation methods:

1. Some materials from which membranes are made wear out quickly.

2. Certain difficulties arise when processing solutions containing a solid phase.

Nevertheless, it should be noted that the use of membrane separation methods in microbiological synthesis technology is promising.

BASIC REGULARITIES OF SELECTIVE SEPARATION OF BIOLOGICAL SOLUTIONS AND SUSPENSIONS ON POROUS MEMBRANES

The main membrane methods for separating liquid systems include reverse osmosis, ultra- and microfiltration. These methods are characterized by such common features as the use of semi-permeable, i.e. membranes that transmit different components of solutions and suspensions differently, the use of excess pressure as the driving force of the process, methods of combating concentration polarization.

The division of these methods is largely arbitrary and is based, as a rule, on the size of the filtered objects and the pore sizes of the corresponding semi-permeable membranes.

It is necessary to distinguish more clearly between the methods of ultra- and microfiltration according to the phase states of the separated systems (solutions and suspensions, respectively), and the methods of ultrafiltration and reverse osmosis according to the mechanism of permeability (viscous flow and activated diffusion).

It can be approximately determined that reverse osmosis membranes can retain particles larger than 1-10 -4 microns, i.e. hydrated inorganic ions, and ultrafiltration is most effective for particles larger than 1-10 -3 microns, i.e. ultrafiltration membranes can retain organic molecules and ions. Accordingly, microfiltration allows you to effectively retain particles from 5-10 -2 to 10 microns, those that do not precipitate from solutions in the field of gravitational forces.

However, it is not possible to clearly define the boundaries of application of various membrane methods, both because of the commonality of the physical phenomena underlying these methods and because of the wide range of properties and nature of the substances separated by pressure membrane processes.

PHYSICAL BASICS OF MICROFILTRATION

The separation of solutions and suspensions by microfiltration is based on the difference and effective hydrodynamic sizes of the separated molecules and particles. The separation process is described within the framework of various theories and mechanisms of semi-permeability, which take into account the influence of physicochemical, hydrodynamic and intermolecular factors on the passage of particles through membranes.

As a rule, the analysis and calculation of ultra- and microfiltration processes is carried out from a unified position. This approach is justified if we take into account that the occurrence of these processes is usually accompanied by the formation of a layer of sediment on the membrane, which provides the main resistance to mass transfer. The formation of this precipitate and its properties can be described by uniform dependencies.

Surface phenomena at the membrane-solution interface, the properties of the solution and the dissolved substance (for microfiltration - the properties of dispersed particles) have a significant impact on the process of ultra- and microfiltration.

The object of application of microfiltration is, as a rule, colloidal (dispersed) systems having a dispersed medium (“solvent”) and a dispersed phase (particles suspended in the solvent). The separation of these phases is often the task of microfiltration of liquids.

The most important role in all membrane separation processes is played by adhesive and electrostatic interactions of particles with the membrane surface.

Biological cellular objects are typical lyophilic systems. They, unlike lyophobic systems, are characterized by strong intermolecular interaction of the dispersed phase substance with the dispersed medium. This interaction leads to the formation of solvate hydration (if the dispersion medium is water) shells of molecules of the dispersion medium around particles of the dispersed phase. In addition, the cells of microorganisms have a charge (electrokinetic potential - EKP), the magnitude of which varies among different microorganisms. For the same type of microorganism, the amount of charge varies depending on environmental conditions and processes occurring in the cell itself. The presence of a charge in cells allows us to consider biological suspensions as solutions of electrolytes.

CONCENTRATION POLARIZATION

When separating solutions and suspensions using semipermeable membranes, the solvent preferentially passes through the membrane. In this case, the concentration of the dissolved substance in the boundary layer at the membrane surface increases. The concentration increases until, under the influence of the emerging concentration gradient of the solute, a dynamic equilibrium is established between the membrane surface and the volume of the solution.

The phenomenon of formation of a boundary layer at the surface of the membrane, in which the concentration of the dissolved substance is greater than in the main volume of the solution, is called concentration polarization. The effect of concentration polarization on filtration is always negative for the following reasons:

The effective pressure decreases due to an increase in the osmotic pressure of the solution, which is determined by the concentration in the boundary layer. This leads to a decrease in both process speed and selectivity, and the service life of the membranes, which largely depends on the concentration of the dissolved substance, is reduced.

Concentration polarization is associated with the formation of a boundary layer separating the membrane surface from the solution in the bulk. The thickness of this layer is generally determined by the hydrodynamic conditions in the installation - the intensity of mixing and the speed of flow. The concentration profile of this layer depends on the mode of movement of the solution.

There are two modes of concentration polarization:

Pre-gel, when the concentration at the membrane surface Cw is lower than the gelation concentration Cg;

Gel polarization mode, when Cw = Cg, and a gel layer is formed on the membrane.

The formation of a gel on the surface of the membrane leads to a sharp drop in permeability and an increase in the retention capacity of microfiltration membranes. However, there is an assumption that a decrease in permeability during concentration polarization of a membrane is achieved not by completely blocking its pores with a gel layer, but by modifying them with a gel in such a way that the effective sizes of all pores decrease by a certain constant value R. A so-called dynamic gel membrane is formed. In this case, the classic capillary filtration separation mechanism is implemented in the reduced pores of the membrane.

It is also believed that for concentration polarization to occur, the sizes of filtered particles must provide a “critical” ratio of particle to pore sizes, which characterizes the transition from the pre-gel to the gel mode of concentration polarization due to an increase in the retention coefficient.

To reduce the harmful effect of concentration polarization on the microfiltration process, various methods are used: increasing the temperature (as a result of which the viscosity decreases and the gelation concentration increases), using an electric field, using high tangential flow rates and pulsating filtration modes.

INFLUENCE OF EXTERNAL FACTORS ON SEPARATION CHARACTERISTICS

The choice of operating pressure depends on the type of process, the nature and concentration of the solution being separated, the type of membrane used, the design of the apparatus, hydraulic resistance, etc. For microfiltration, the operating pressure is 0.03-0.1 MPa, and is determined experimentally for each solution.

An increase in operating pressure leads to an increase in the filtration rate to certain limits, due to the fact that an increase in pressure also leads to an increase and compaction of the gel layer on the membrane surface.

As a result of exposure to high pressure on membranes, significant residual deformations can be observed: when the pressure is removed, the membrane structure does not return to its original state. Shrinkage of the membrane structure reduces permeability and increases selectivity.

Analysis of data on the effect of temperature on the selectivity and permeability of membranes during microfiltration shows that an increase in temperature leads to an increase in both permeability and selectivity. This is explained by the fact that the viscosity of the permeate decreases, and the influence of concentration polarization of membranes is significantly reduced.

With an increase in the concentration of dissolved substances in the separated solution, the performance characteristics of the membranes - specific productivity and selectivity - deteriorate. When concentrating, the osmotic pressure of the solution increases, and therefore the effective driving force of the separation process decreases.

LECTURE 4. VACCINES.

Vaccination helps the recipient develop immunity to pathogenic microorganisms and thereby protects him from infection. In response to oral or parenteral administration of the vaccine, the host's body produces antibodies to the pathogenic microorganism, which during subsequent infection lead to its inactivation (neutralization or death), block its proliferation and prevent the development of the disease.

The effect of vaccination was discovered more than 200 years ago - in 1796 - by the doctor Edward Jenner. He proved experimentally that a person who has had cowpox, a not very serious disease of cattle, becomes immune to smallpox. Smallpox is a highly contagious disease with a high mortality rate: even if the patient does not die, he often develops various deformities, mental disorders and blindness. Jenner publicly inoculated an 8-year-old boy, James Phipps, with cowpox using exudate from a pustule of a cowpox patient, and then after a certain time twice infected the child with pus from a pustule of a smallpox patient. All manifestations of the disease were limited to redness at the injection site, which disappeared after a few days.

Previously, infectious diseases such as tuberculosis, smallpox, cholera, typhoid fever, bubonic plague and polio were a real scourge for humanity. With the advent of vaccines, antibiotics and the introduction of preventive measures, these epidemic diseases were brought under control. However, protective measures became ineffective over time, and new outbreaks of diseases emerged. In 1991, a cholera epidemic struck Peru; Over the next three years, approximately 1 million cases were identified, and several thousand of them died. Unfortunately, there are no vaccines against many human and animal diseases. Today, more than 2 billion people worldwide suffer from diseases that could be prevented by vaccination. Vaccines can also be useful in preventing “new” diseases that are constantly emerging (for example, AIDS).

As a rule, modern vaccines are created on the basis of killed (inactivated) pathogenic microorganisms or live, but non-virulent (attenuated) strains. To do this, the wild-type strain is grown in culture, purified, and then inactivated or modified so that it produces an immune response that is sufficiently effective against the virulent strain. Despite significant advances in the creation of vaccines against diseases such as rubella, diphtheria, whooping cough, tetanus, smallpox and polio, the production of modern vaccines faces a number of limitations:

Not all pathogenic microorganisms can be cultured, so vaccines have not been created for many diseases.

To obtain animal and human viruses, an expensive animal cell culture is required.

The titer of animal and human viruses in culture and the rate of their reproduction are often very low, which increases the cost of vaccine production.

Precautions must be strictly observed to prevent infection of personnel.

If the manufacturing process is disrupted, some vaccine batches may contain live or insufficiently weakened virulent microorganisms, which can lead to the unintentional spread of infection.

Attenuated strains can revert to the original strain, so virulence must be constantly monitored.

Some diseases (such as AIDS) cannot be prevented by traditional vaccines.

Most current vaccines have a limited shelf life and remain active only at low temperatures, making their use in developing countries difficult.

In the last decade, with the development of recombinant DNA technology, it has become possible to create a new generation of vaccines that do not have the disadvantages of traditional vaccines. Genetic engineering methods are used to develop them.

The pathogenic microorganism is modified by deleting the genes responsible for virulence. The ability to induce an immune response is retained. Such a microorganism can be safely used as a live vaccine, since growing in a pure culture eliminates the possibility of spontaneous restoration of the entire gene.

They create living non-pathogenic systems for the transfer of individual antigenic determinants of an unrelated pathogenic organism. This transport system contributes to the development of a pronounced immune response to the pathogenic microorganism.

If pathogens do not grow in culture, they can be isolated, cloned, and expressed in an alternative host (e.g. E. coli or mammalian cell lines) genes for those proteins that contain the major antigenic determinants, and use these proteins as “subunit” vaccines (see next section).

Some pathogenic microorganisms act indirectly, causing the development of an autoimmune reaction to infected cells of the host body. For such diseases, it is possible to create a system for the specific destruction of target cells by constructing a gene encoding a chimeric protein, one part of which will bind to the infected cell, and the other will destroy it. This system is not a true vaccine, although it acts only on infected cells, eliminating the very cause of the development of an autoimmune reaction.

Vaccines for animals have less stringent requirements, so the first vaccines obtained using recombinant DNA technology were vaccines against foot-and-mouth disease, rabies, dysentery and piglet diarrhea. Other vaccines for animals are being created, and recombinant vaccines intended for humans will soon appear.

GOST R ISO 15859-7-2010

Group L21

NATIONAL STANDARD OF THE RUSSIAN FEDERATION

SPACE SYSTEMS

Characteristics, sampling and analytical methods of fluids

Part 7

HYDRAZINE-BASED ROCKET FUEL

Space systems. Fluid characteristics, sampling and methods of analysis. Part 7. Hydrazine propellant

OKS 71.080.30*
OKP 24 7640
________________
* In IUS 10-2011 it is given with OKS 49.140. -
Database manufacturer's note.

Date of introduction 2012-01-01

Preface

The goals and principles of standardization in the Russian Federation are established by Federal Law of December 27, 2002 N 184-FZ "On Technical Regulation", and the rules for applying national standards of the Russian Federation are GOST R 1.0-2004 "Standardization in the Russian Federation. Basic Provisions"

Standard information

1 PREPARED BY FSUE "VNITSSMV" on the basis of its own authentic translation into Russian of the standard specified in paragraph 4

2 INTRODUCED by the Technical Committee for Standardization TC 339 “Safety of raw materials, materials and substances”

3 APPROVED AND ENTERED INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated December 21, 2010 N 930-st

4 This standard is identical to the international standard ISO 15859-7:2004* "Space systems - Characteristics, sampling and methods of analysis of fluids - Part 7: Hydrazine-based propellants" (ISO 15859-7:2004 "Space systems - Fluid characteristics, sampling and test methods - Part 7: Hydrazine propellant").
________________
* Access to international and foreign documents mentioned in the text can be obtained by contacting Customer Support. - Database manufacturer's note.

When applying this standard, it is recommended to use instead of reference international standards the corresponding national standards of the Russian Federation and interstate standards, information about which is given in the additional appendix DA

5 INTRODUCED FOR THE FIRST TIME


Information about changes to this standard is published in the annually published information index "National Standards", and the text of changes and amendments is published in the monthly published information index "National Standards". In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the monthly published information index "National Standards". Relevant information, notifications and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet

Introduction

Introduction

Hydrazine propellant operations at a spaceport or spacecraft launch site may involve multiple operators and supplier-consumer interfaces from the manufacturing plant to delivery to the launch vehicle or spacecraft. The purpose of this standard is to establish uniform requirements for components, sampling methods, and analytical methods for hydrazine-based propellant used in servicing spacecraft and ground-based equipment. The established limits on the composition of hydrazine-based rocket fuel are intended to determine the purity and impurity limits of hydrazine-based rocket fuel for fueling into spacecraft and ships. Sampling methods and analysis methods for hydrazine propellants are adapted for use by any operator. Sampling methods and methods of analysis for hydrazine propellant are acceptable for monitoring hydrazine propellant limits.

1 area of ​​use

This standard applies to anhydrous hydrazine used as a rocket fuel in space systems, as well as in aircraft equipment and ground-based facilities, systems and equipment, of the following grades:

- standard fuel: normal production and quality control (suitable for most purposes);

- single-component fuel: conventional fuel with strictly controlled impurity content (intended only for rocket engines operating on single-component catalytic fuels in cases where it is desirable to extend the shelf life of the catalyst);

- high purity fuel: special production with strict control of the amount of impurities.

This standard covers the sampling necessary to ensure that hydrazine-based propellant, when introduced into a launch vehicle or spacecraft, meets the compositional limits specified in this standard or the technical documentation agreed upon for the particular application.

This standard specifies limits for the constituents and physical properties of anhydrous hydrazine (NH) and requirements for sampling methods and analytical methods for monitoring the composition of anhydrous hydrazine.

2 Normative references

This standard uses normative reference to the following International Standard*:
_______________
* For dated references, only the edition of the standard cited applies. For undated references, the latest edition of the standard including all amendments and amendments.
For a table of correspondence between national standards and international ones, see the link. - Database manufacturer's note.


ISO 9000 Quality management systems. Fundamentals and vocabulary (ISO 9000, Quality management systems - Fundamentals and vocabulary)

3 Terms and definitions

This standard uses terms from ISO 9000, as well as the following terms with their corresponding definitions:

3.1 particulate matter(particulate) (standard fuel grade): Insoluble particles retained on filter paper, nominal sizes 10 and 40 microns.

3.2 particulate matter(particulate) (single-component and high-purity fuel grades): Insoluble particles retained on filter paper, nominal sizes 2 and 10 microns.

3.3 proof test verification test: An analysis performed on a fluid in a container or on a sample from a container that is representative of the supply to verify the chemical composition limits of hydrazine-based propellant.

4 Chemical composition and physical properties

4.1 Chemical composition

Unless otherwise specified in the applicable technical documentation, the chemical composition of hydrazine propellant supplied to the aircraft must comply with the limits set forth in Table 1 when tested in accordance with the applicable methods of analysis.


Table 1 - Limits on the chemical composition of hydrazine-based rocket fuel

Index	Limit value
	Standard fuel	Single-component fuel	High purity fuel
Mass fraction of hydrazine, %, not less
Mass fraction of water, %, no more
Mass fraction of ammonia, %, no more
Solid particles, %, no more
Mass fraction of chlorides, %, no more
Mass fraction of aniline, %, no more
Mass fraction of iron, %, no more
Mass fraction of non-volatile sediment, %, no more
Mass fraction of carbon dioxide, %, no more
Mass fraction of other volatile components containing carbon, %, no more
Total content in terms of monomethylhydrazine (MMH), unsymmetrical dimethylhydrazine (UDMH) and alcohol.

4.2 Physical properties

When visually examined in transmitted light, rocket fuel should be a colorless, homogeneous liquid.

5 Delivery

Hydrazine of the grades specified in Section 1 shall be supplied in accordance with this standard.

6 Sampling

Warning- Hydrazine in liquid and gaseous states is a flammable, toxic, volatile fuel and is highly reactive when in contact with an oxidizing agent. Care should be taken when handling and storing hydrazine, use protective equipment, and avoid contact with materials incompatible with hydrazine.

6.1 Sampling plan

To ensure that the chemical composition of hydrazine-based propellant meets the limits set by this standard, a hydrazine sampling plan from production to spacecraft loading must be established by all involved operators and approved by the end user. Sampling and analytical methods must comply with all safety regulations and rules. This plan should establish:

- sampling points;

- sampling techniques;

- frequency of sampling;

- volume of samples;

- number of samples;

- methods of analysis;

- responsibility for sampling of each operator.

6.2 Responsibility for sampling

Unless otherwise specified in the applicable technical documentation, the supplier responsible for providing the aircraft with hydrazine-based fuel shall sample and test the quality of the hydrazine supplied to the aircraft by the supplier. The supplier may use its own or other resources suitable to perform the control tests specified in this International Standard unless otherwise directed by the customer.

6.3 Sampling points

Unless otherwise specified, it is recommended that sampling be carried out at the location where hydrazine-based propellant is stored or before refueling into the aircraft.

6.4 Sampling frequency

Sampling should be carried out annually or according to a schedule agreed between supplier and customer.

6.5 Sample volume

The amount of hydrazine-based fuel in one sample container must be sufficient to perform the limit analysis. If one individual sample does not contain enough hydrazine fuel to perform all the analyzes required to confirm quality, additional samples should be collected under similar conditions.

6.6 Number of samples

The number of samples must correspond to the following:

a) one sample - from a storage container;

b) any number of samples - as agreed between the supplier and the consumer.

6.7 Storage container

Unless otherwise specified in the applicable sampling plan, the storage container should not be refilled after the sample has been collected.

6.8 Liquid samples

Liquid samples should be representative samples from a supply of liquid hydrazine. Samples must be collected using one of the following methods:

a) by filling the sample container and storage containers simultaneously from the same manifold and under the same conditions using the same procedure;

b) by removing the sample from the supplied container through a convenient connection to the sample container. No pressure regulator is permitted between the supplied container and the sample containers (suitable purge and drain valves are permitted). To ensure safety, the sample container and sampling system must have a design operating pressure equal to or greater than the pressure in the container supplied.

6.9 Rejection

If any sample of hydrazine propellant tested in accordance with Section 7 does not meet the requirements specified in this standard, the hydrazine propellant represented by that sample shall be discarded. The procedure for disposal of rejected hydrazine-based rocket fuel is determined by the consumer.

7 Methods of analysis

7.1 General provisions

The supplier must ensure the quality level of hydrazine. Alternative methods of analysis are described in 7.3-7.12. Other methods of analysis not specified in this standard are acceptable if agreed upon between supplier and user.

These tests are a single analysis or series of analyzes performed on hydrazine-based propellant to confirm the ability of storage facilities to provide the required level of quality. This can be monitored by analyzing representative samples of hydrazine-based propellant, taken from warehouses at specified intervals as agreed between supplier and customer. The tests may be performed by the supplier or by a laboratory selected by agreement between the supplier and the customer.

Requirements for analyzes should include the determination of all indicators of hydrazine that have limitations.

7.2 Analysis parameters

The parameters of the analytical methods presented in sections 7.3-7.12 are as follows:

- purity and impurity content must be expressed as a percentage by weight (% wt.), unless otherwise provided;

- gas calibration standards containing the liquid components used may be required for the calibration of analytical measuring instruments used to determine the limits of hydrazine-based rocket fuel;

- at the request of the consumer, the accuracy of the measuring equipment used in the preparation of these reference materials must be confirmed by an official standards institute;

- analytical equipment must be used in accordance with the manufacturer's instructions.

7.3 Hydrazine purity

The purity of hydrazine is determined by gas chromatography. This method can be used to determine not only the purity of hydrazine, but also to determine the content of water, ammonia, aniline and other volatile carbon-containing components (Appendix A). The analyzer must be capable of separating and detecting a component with a sensitivity of 10% of the specified maximum content of that component . The analyzer must be calibrated in the appropriate ranges using calibration standards.

The solids content is determined by gravimetric measurement. A known volume of fuel is filtered through a pre-weighed test membrane filter and the increased mass of the membrane filter after washing and drying is determined. The change in mass of the control membrane filter located under the test membrane filter is also determined. The amount of particulate matter is determined by the increase in mass of the test membrane filter relative to the control membrane filter.

a) by ion chromatography method;

b) colorimetric method with mercury thiocyanate;

c) potentiometric method using a chloride-selective electrode;

d) potentiometric method using titration with silver nitrate.

The chloride content cannot be determined directly in a sample of liquid hydrazine, but can be determined in the non-volatile residue after dissolving it in an aqueous acid solution.

a) by gas chromatography according to 7.3;

b) by ultraviolet spectroscopy for hydrazine grade single-component fuel.

a) by atomic absorption method;

b) colorimetric method;

c) by inductively coupled argon plasma emission spectrometry.

The iron content cannot be determined directly in a sample of liquid hydrazine, but can be determined in the non-volatile residue after dissolving it in an aqueous acid solution.

The sample must be introduced into a strong acid to absorb the hydrazine and ammonia components and release carbon dioxide. The carbon dioxide content is then determined by one of the following methods:

a) gas chromatography method. The technique must be selective for the separation and analysis of carbon dioxide;

b) by infrared analysis;

c) CO-selective colorimetric method.

7.12 Content of other volatile components containing carbon

Appendix A (for reference). Applications of Gas Chromatography (GC)

Appendix A
(informative)

Gas chromatography (GC) is recommended as a reference or preferred method for the analysis of hydrazine impurities, such as ammonia and water, aniline (for high purity fuel grades), other volatile material containing carbon, and carbon dioxide to control the purity of hydrazine.

Table A.1 indicates the application of these methods to the analysis of hydrazine.


Table A.1 - GC applications

Index	GC with TCD detector on Tenax GC column or PEG (or similar)	GC with FID detector on Tenax GC or Apiezon L/AT200 column or wide bore capillary column (Carbowax 20M) (or equivalent)	GC with on-column FID detector with Tenax GC or PEG1540 or PEG 400 (or similar)	GC with TCD detector and cryogenic trap and activated carbon column or Porapak (or similar)
Hydrazine Purity
Ammonia
Aniline (high purity)
Other volatile carbonaceous components
Carbon dioxide
Column packing Tenax GC®, Apiezon® L/AT200, Carbowax® 20M and Porapak® are examples of suitable commercially available materials. This information is provided for the convenience of users of this standard. Note - The following symbols are used in this table: TCD - thermal conductivity detector; PEG - polyethylene glycol; FID - flame ionization detector; "X" - the method can be used; "-" - the method is not used.

Appendix YES (for reference). Information on the compliance of reference international standards with reference national standards of the Russian Federation (and interstate standards acting as such)

Application YES
(informative)

Table DA.1

Designation of the reference international standard	Degree of compliance	Designation and name of the corresponding national standard
Note - This table uses the following symbol for the degree of compliance with standards: IDT - identical standards.

Electronic document text
prepared by Kodeks JSC and verified against:
official publication
M.: Standartinform, 2011

Tokar A.Yu.

St. Petersburg State Technological Institute (Technical University)

MEMBRANE SEPARATION PROCESSES

annotation

The article examines the essence of membrane separation processes through familiarization with the main publications in periodical scientific publications, familiarization with educational and methodological literature on this topic.

Keywords: membrane processes, separation of liquid and gas mixtures, membranes.

Tokar A.J.

St. Petersburg State Technological Institute (technical university)

MEMBRANE SEPARATION PROCESS

Abstract

The article discusses the essence of membrane separation processes through familiarity with basic publications in scientific periodicals, familiarization with instructional literature on the subject.

Keywords: membrane processes, the separation of liquid and gas mixtures, the membrane.

The processes of separation of liquid and gaseous systems play an important role in many sectors of the national economy. Thus, to carry out processes for separating liquid mixtures, for example, methods such as distillation, rectification, extraction, adsorption, etc. are used. However, the most universal separation method is separation using semi-permeable membranes (membrane methods).

The importance of membrane technology has increased dramatically in recent years, primarily as a technology that can bridge the gap between industry and ecology.

The global nature of the impact and influence of membrane technology on the implementation of other Russian and world scientific and technological priorities has recently received further confirmation. Critical technology at the federal level “Membranes” was included in 17 priority areas for Russian science, in which Russian scientists are ahead of the world level, and without the use of membrane processes it is impossible to ensure the maintenance of the required scientific and technical level in 12 priorities. To this it is necessary to add the serious capabilities of membrane processes in solving the most important task of the current stage of development of our society - the technological renewal of domestic industry.

The vital need for large-scale implementation of membrane processes is determined by many factors and, above all, their direct influence on national economic problems and the prospects for their practical use.

Over the past decades, membrane separation methods have been intensively developed and implemented in a wide variety of areas of human activity. These methods are especially widely used for desalination of salt water. Thus, in 1980, more than half of all desalinated water on earth was obtained using membrane methods, and the productivity of some membrane plants reached several tens of thousands of m3 of desalinated water per day.

In the chemical and petrochemical industries, membrane methods are used to separate mixtures of high and low molecular weight compounds, azeotropic mixtures, to separate helium and hydrogen from natural gases, oxygen from air, etc. .

In the food industry - for the production of high-quality sugar, pasteurization of beer, stabilization of grape wines, processing and canning of milk in order to obtain basic dairy products; canning fruit and vegetable juices, etc. .

In biotechnology and the medical industry - for the isolation and purification of biologically active substances, vaccines, enzymes, etc.; in the food industry - for concentrating fruit and vegetable juices, milk, producing high-quality sugar, etc.

Membrane processes are most widely used in the treatment of water and aqueous solutions, and wastewater treatment.

The use of semi-permeable membranes for environmental monitoring, control and forecasting of the state of the environment during the exploration of space and the waters of the world's oceans is very promising.

Work is underway to create synthetic membranes that facilitate the reproduction of some of the photochemical reactions. Occurring in green plants. In this case, the main task is not so much to obtain carbohydrates, proteins, fats, nucleic acids produced with the participation of natural membranes, but to obtain hydrogen and other “energy” substances. These membranes are capable of using the energy of sunlight to split water and produce hydrogen, which can be stored and used as fuel.

Further widespread implementation of membrane processes is associated with the need to develop analytical and graphic-analytical methods for calculating equipment for their implementation, developing normals, nomograms, standards, references and systems for solving specific technological problems, as well as creating methods for optimizing membrane equipment using electronic computing technology.

Of course, a short list of the main areas of use of membrane methods does not exhaust all possible areas of their application.

Calculations and accumulated large amount of factual material show that the use of semi-permeable membranes can provide a significant economic effect in existing traditional industries, opens up wide opportunities for creating fundamentally new, simple, low-energy and environmentally friendly technological schemes (especially when combined with such widespread separation methods as rectification, adsorption, extraction, etc.).

However, all problems in the study of membranes and membrane processes have not yet been solved. An urgent task now remains the development of the theory of targeted production of membranes with predetermined properties and technological calculation of membrane processes and devices.

Purpose This work was a comprehensive study of the essence of membrane separation processes through familiarization with the main publications in periodical scientific publications, familiarization with educational and methodological literature on this topic.

Membrane technology is one of the new directions in the development of chemical technological processes, the purpose of which is to separate liquid and gas mixtures using semi-permeable membranes.

Membrane separation processes for mixtures are carried out using semi-permeable membranes. The driving force of the membrane process can be: a gradient of chemical (for uncharged particles of the flow) or electrochemical (for charged particles of the flow) potential, as well as a gradient of the factor that determines the rate of this process (pressure, temperature, etc.). Membrane separation processes are characterized by the following parameters: permeability and selectivity. Basic membrane separation methods: reverse osmosis, ultrafiltration, pervoparation, dialysis, electrodialysis, diffusion separation of gases.

The mechanism of transfer of atoms, molecules or ions of various substances through semi-permeable membranes can be explained by the following theories.

Sifting theory suggests that a semipermeable membrane contains pores that are large enough to allow solvent to pass through, but too small to allow solute molecules or ions to pass through.

Theory of molecular diffusion based on unequal solubility and differences in diffusion coefficients of separated components in polymer membranes.

Theory of capillary filtration permeability is based on the difference in physicochemical properties of the boundary layer of liquid on the surface of the membrane and the solution in the bulk.

The main factors that significantly influence the speed and selectivity of membrane separation processes are: concentration polarization, operating pressure and temperature, hydrodynamic conditions inside the membrane apparatus, the nature and concentration of the mixture being separated.

Membranes must satisfy the following basic requirements, namely, have: high separating ability (selectivity); high specific productivity (permeability); chemical resistance to the environment of the separated system; mechanical strength sufficient for their safety during installation, transportation and storage. In addition, the properties of the membrane should not change significantly during operation. Various polymers are used to make membranes ( cellulose acetates, polyamides, polysulfone and etc.), ceramics, glass, metal foil etc. Depending on the mechanical strength of the materials used, membranes are divided into: liquid, compacting(polymer), with rigid structure, porous, non-porous(diffusion) .

When studying and analyzing any membrane process, it is necessary to take into account three main factors and their relationship: 1) membrane structure by thickness(porous, non-porous, isotropic); 2) physical and chemical properties of the separated system(for solutions it is very important to take into account their basic thermodynamic properties); 3) interaction of the mixture being separated with the membrane material. If at least one of the listed factors is not taken into account, a fundamental mistake can be made when developing a model of the mechanism of a particular membrane process.

Depending on the type of the main driving force of the process, the following are distinguished: typesmembrane processes: baromembrane processes, diffusion-membrane processes, electric membrane processes, thermomembrane processes.

Baromembrane processes are caused by a pressure gradient across the thickness of membranes, mainly polymer ones, and are used to separate solutions and colloidal systems at 5-30 °C. The following processes are classified as baromembrane processes: reverse osmosis, ultrafiltration, microfiltration.

Diffusion membrane processes are caused by a concentration or pressure gradient across the thickness of porous or non-porous membranes based on polymers or materials with a rigid structure. They are used to separate gas and liquid mixtures.

Electromembrane processes are caused by the gradient of electrical potential across the thickness of the membranes. Among electromembrane methods, electrodialysis has found the greatest practical application - the separation of solutions under the action of an electromotive force created in the solution on both sides of the membrane partition separating it.

Thermal membrane processes– temperature gradient across the thickness of a porous membrane based on polymers or materials with a rigid structure. Currently, the most fully developed membrane distillation process . It is advisable to use membrane distillation to solve the following main problems: concentration and desalting of aqueous solutions of electrolytes; desalination of sea water; obtaining water to feed steam boilers, etc.; obtaining especially pure water and pyrogen-free water for medical purposes. The membrane distillation process is carried out at almost atmospheric pressure, so apparatus for this process can be made from cheap polymer materials. Membranes in membrane distillation devices operate for a long time without noticeable contamination.

To successfully solve specific technological problems associated with the use of membrane processes, it is necessary to carry out calculations of membrane installations and equipment. A complete calculation includes technological, hydraulic and mechanical reports using modern electronic software.

Modern devices for membrane processes are divided into four main types, differing in the way membranes are laid: devices with flat membrane elements; with tubular membrane elements; with roll-type membrane elements; with membranes in the form of hollow fibers. But it must be taken into account that for each specific separation process, an apparatus of such a design should be selected that would provide the most favorable conditions for the process.

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Membrane technologies (membranology, membranes) are an avant-garde direction in the development of science and modern technologies. Membrane methods for separating gas and liquid media have already taken a strong place among industrial technological processes, although the full development and impact of membrane science and technology are expected later.

The essence of the membrane separation process is as follows. The initial (gas or liquid, binary or multicomponent) mixture of substances separated in the apparatus comes into contact with a semi-permeable membrane on one side, and due to the special properties of the membrane, the filtrate (permeate) passing through it is enriched with one of the components of the initial mixture. The separation can be so complete that the filtrate contains virtually no impurities of those components of the initial mixture that are retained by the membrane and removed from the apparatus on the other side of the membrane in the form of a concentrate stream (retentate). Membrane separation is characterized primarily by the following main parameters of all membranes: permeability, selectivity and stability over time. Permeability is the specific performance of the membrane, equal to the amount of filtrate (kg/h), through a unit of membrane surface (m2), or it is the speed of the membrane separation process (kg/(m2-h)). Membrane selectivity (separation factor) characterizes the efficiency (completeness) of the membrane separation process in relation to the target (key) component. Among the existing hypotheses, diffusion, capillary, sorption theories, etc. are used to describe mass transfer in membranes.

A membrane is a film, a flat body, the extent of which along two coordinates significantly exceeds the extent along the third coordinate. The membrane acts as a kind of partition that, under the influence of a driving force, ensures the physical process of selective separation of mixtures of substances. Currently, there are many artificially prepared membranes, which can be represented by a variety of structures - from coarse sieve-type membranes to extremely thin polymer films and fibers. They are made from a variety of both porous and non-porous organic (polymer films, tubes, capillaries, hollow fibers, flat thin sheets) and inorganic (zeolite, carbon, glass, ceramic, metal) materials. This is due to the fact that there are no universal membranes.

Various materials are used for the manufacture of semi-permeable membranes: polymer films (polyethylene, polypropylene, polycarbonate, fluoroplastic, etc.); metal foil (from alloys of platinum, palladium, silver, molybdenum, etc.); porous glasses (sodium borosilicate), etc. Porous polymer membranes are usually obtained by removing solvents or washing out pre-introduced additives from polymer solutions during their molding. The membranes obtained in this way have a thin (0.25-0.50 µm) surface layer on a microporous substrate 100-200 µm thick. The membrane separation process is carried out in the surface active layer, and the substrate provides the mechanical strength of such a composite membrane.

Metal porous membranes are made by leaching or sublimating one of the foil alloy components. In this case, highly porous membranes with pores of the same diameter in the range of 0.1-5.0 microns are obtained. Another method for producing porous metal membranes is sintering fine metal powder at high temperature. Porous polymer and metal membranes are used for reverse osmosis and ultrafiltration processes. Membranes are assembled into membrane modules (systems); they can be semi-permeable to gases and liquids or impermeable.

Currently, synthetic polymer membranes are the basis of technological processes using the principles of membrane separation. The transfer of substances (mass transfer) through membranes often (but not always) occurs under the influence of the driving force of the process - the pressure difference on both sides of the membrane - these are the so-called Baromembrane Separation Processes: microfiltration, ultrafiltration, nanofiltration and reverse osmosis. If the driving force is the difference in concentrations of a substance (component) at the boundaries before and after the membrane, then the membrane method is called dialysis. The membrane method, which uses the difference in electrical potential on both sides of the membrane as the driving force of the process, is called electrodialysis. Dialysis is widely used today in medicine to introduce into the body medicinal substances placed in a capsule made of a selective membrane. In this case, the diffusion transition of the drug from the capsule into the body becomes long-lasting and, most importantly, with a constant concentration of the active component. Hemodialysis is also widespread today - the use of membranes in medicine as an artificial kidney, when toxins are removed from the body through the membrane. Dialysis is also used in industry to remove acids and bases from wastewater. Membrane dialysis processes make it possible to purify waste and industrial solutions (streams, mixtures) from mercury, lead, zinc, copper, silver, nickel, cadmium, and chromium. The world leaders in the production of membranes and membrane elements are Dow Chemical, Filmtec, Hydranautics, Osmonics (USA).

Filtration is a hydromechanical process of separating solid particles from gases and liquids. Conventional filtration can separate suspended particles larger than 10 microns (0.01 mm) from a gas or liquid. To carry out this process, a pressure difference before and after the filter of up to 0.2 MPa is used, while the process pressure is limited by the strength of the filter - a porous material (fabric, fiber, woven metal mesh made of thin wire, etc.). Filtration is used in technologies in almost all industries.

With microfiltration, membrane filters for liquid solutions have smaller pore sizes than with conventional filtration, and therefore a larger pressure difference is required (up to 0.5 MPa). In this case, it is possible to separate particles from the solution ranging in size from 0.1 to 10 microns with a pore size of 0.05-10 microns. Membranes based on synthetic polycarbonate films with equal pore radii (isopority) are effectively used as filter materials. Microfiltration is successfully used to obtain sterile water (in this case, dispersed particles are retained by the membrane), to clarify and stabilize wines, to replace pasteurization, etc.

Ultrafiltration allows you to separate particles ranging in size from 0.001 to 0.02 microns (1-20 nm) with a pore size of 1-100 nm at an excess pressure of 0.3-1.0 MPa. It can separate colloidal solutions and solutions of high molecular weight compounds (for which membranes are impermeable) from electrolytes, etc. Ultrafiltration is also used to concentrate milk into cream, fruit juices, coffee and other extracts, etc. Ultrafiltration modules are capable of separating not only bacteria, but also viruses from solutions. Water passed through membrane ultrafilters can be drunk even when the source water was biologically contaminated. A composite ultrafiltration membrane can have a separating layer with a thickness of 0.05-3.00 microns and one or two layers of supporting substrates with a thickness of 100-110 microns.

With nanofiltration, membranes can retain particles of the order of 1 nm in size at fairly high pressures - 0.8-3.0 MPa. Nanofiltration is used to purify aqueous solutions from organic substances and mineral impurities.

Selective diffusion of, for example, water through membranes is called osmosis. The particles present in the water are captured by the membrane, and the water, being purified, penetrates through the membrane surface. Due to osmosis, the penetration of water through a specially selected membrane occurs even when the pressure on both sides of the membrane is equal. The driving force by which water passes through the membrane is called osmotic pressure, which depends on the nature of the solute and its concentration. The phenomenon of osmosis underlies the metabolism of all living organisms; thanks to it, nutrients are supplied to every living cell and, conversely, waste products are removed from it.

The process of reverse osmosis (Reverse Osmosis) consists of filtering liquid solutions through selectively permeable membranes under pressure exceeding osmotic pressure, while predominantly water passes through the membranes, and dissolved substances remain in solution. The driving force of this process is the difference between applied and osmotic pressure. Membrane reverse osmosis methods make it possible to separate particles ranging in size from 0.0001 to 0.001 microns (0.1-1.0 nm) from a liquid solution at an excess pressure of 3-10 MPa. This process requires the creation of excess pressure on the side of the solution or contaminated (salty) water: usually 0.2-1.7 MPa for drinking and brackish water and 4-7 MPa for sea and ocean water with its own osmotic pressure of about 2.4 MPa, which needs to be overcome. With reverse osmosis, separation occurs at the level of molecules and ions.

The first industrial reverse osmosis systems appeared in the early 1970s of the 20th century, and currently reverse osmosis has become one of the most economical, universal and reliable methods of water purification, which allows reducing the concentration of colloidal and dissolved components by 96-99% and practically 100% get rid of microorganisms and viruses. Synthetic polyamide, polysulfone, and polyimide membranes are used as reverse osmosis composite thin-layer membranes. For compactness, membranes are made into roll membrane modules; membranes are also formed from hollow fibers, which significantly increases the productivity of membrane installations.

Membrane gas separation is successfully used, for example, in the separation of air components. Fractions enriched with oxygen up to 60% have found use in oxygen blasting in the steel industry, in medicine, for oxygenation (temporary shutdown of the human heart and lungs during complex surgical operations), and fractions enriched with nitrogen - in the synthesis of ammonia. Membrane methods for separating gas mixtures are used in the synthesis of ammonia, separation of hydrogen isotopes, and separation of helium from natural and petroleum gases. A membrane method is being introduced for separating sulfur dioxide (sulfur dioxide) S02 from emissions from thermal power plants, purifying gases from carbon dioxide C02 and hydrogen sulfide H2S. Membranes for gas separation are made from polymeric organic and inorganic materials. Isotopes of uranium were first separated using an iron membrane; hydrogen was selectively passed through a palladium membrane; helium was selectively passed through by a fused silica membrane. To separate gases, membranes made of silicones, tetrafluoroethylene, polyetherimides, cellulose acetate, ceramics, and glass are used.

The pervaporation method (Pervaporatiori) is based on the evaporation of liquid through a membrane. Pervaporation occurs as an irreversible process under the combined action of several driving forces that cause mass transfer: differences in pressure, concentration and temperature on both sides of the membrane. Multi-stage pervaporation in the form of many membrane stages in one vertical apparatus is sometimes called membrane distillation. Pervaporation has found application in concentrating milk and coffee extract; for the separation of hydrocarbons in oil refining processes (mixtures of xylene isomers, benzene-cyclohexane mixtures); to isolate fractions with different octane numbers; for dehydration of ethanol, etc. In the future, pervaporation may partially replace rectification, but currently it complements it in cases where the resulting azeotropic mixtures (for example, ethanol-water mixtures), boiling at the same temperature, cannot be separated by rectification of spiral rolls , between which drainage layers-spacers are placed, “wound” on a perforated central drainage pipe. All elements of the membrane layers are sealed to create a certain direction of movement of the initial liquid solution through the surface of the membrane, to collect and drain the filtrate and concentrate. The durable body of the device allows you to create increased process pressures.

Devices with a hollow fiber module (Hollow Fibers) for reverse osmosis and ultrafiltration processes are more advanced in terms of higher packing density of semi-permeable membranes up to (20,000-30,000 m2/m3). This is achieved by using membrane hollow fiber tubes with a length of 1.5-2.0 m, a diameter of 45-200 microns (0.045-0.200 mm) and a tube wall thickness of 10-50 microns (0.01-0.05 mm). Hollow fiber tubes can withstand operating pressures of tens of megapascals. There are different design solutions for assembling and sealing (usually with epoxy resin) the ends of the fiber tubes in a round flat partition, which is clamped between the flanges of the body and the cover of the apparatus. This design allows you to connect the ends of hollow fiber tubes into a U-shaped bundle and secure them in one tube sheet. The initial mixture can either pass inside the tubes or wash their outer surface. In other designs, the ends of the hollow tubes are attached to different tube sheets placed in the cylindrical body of the apparatus.

For membrane separation of industrial gases, such as, for example, “fast” gases, i.e. quickly penetrating membranes: water vapor H20, helium He, hydrogen H2, ammonia NH3, carbon dioxide CO2, oxygen 02, and “slow” gases, or slowly penetrating membranes: carbon monoxide CO, nitrogen N2, methane CH4, ethane C2H6, propane C3H8, synthetic polymer hollow fiber membranes are used, consisting of porous membrane tubes-fibers, with a gas separation layer applied to their outer surface with a thickness of no more than 0.1 microns ( 0.0001 mm). The use of porous substrates makes it possible to increase the process pressure to 6.5 MPa. The membrane module is made in the form of a replaceable gas separation cartridge with a membrane packing density of 500-700 m2/m3, mounted in a cylindrical housing into which a gas mixture enters and two streams of separated components are removed from it. Such membrane separation processes make it possible to obtain oxygen with a purity of up to 50% at a pressure of 0.003-0.1 MPa and nitrogen with a purity of up to 99.9% at a pressure of 0.5-4.0 MPa from air, from hydrogen-containing gases, for example, at a refinery to obtain hydrogen with a purity of 90 -99% pressure up to 5 MPa. To obtain oxygen, nitrogen and hydrogen of higher purity, adsorption and cryogenic technologies are used.

As an example, we provide brief information about those used since the 80s of the 20th century. some membrane processes "Separex" company "UOP", USA. Separex processes can be used to purify hydrogen, helium, as well as natural and associated gases from carbon dioxide C02, hydrogen sulfide H2S, water vapor and heavy hydrocarbons according to the requirements of pipeline transport. Separex membrane systems are simple, operate without the use of liquid absorbents and with minimal use of machinery. Therefore, they are successfully used both for land-based installations and on offshore platforms. These systems may have one or two stages of purification. The initial gas mixture with a CO2 content in the range of 3-75% at an excess pressure of 3-11 MPa is passed over a polymer membrane, while the initial gas mixture is divided into two streams. Carbon dioxide, hydrogen sulfide and water vapor are easily forced through the membrane and collected in the low-pressure space of the membrane apparatus (this flow is called permeate). Methane, ethane, other hydrocarbons and nitrogen accumulate in the higher pressure residual gas, which is thus enriched in these components. In a two-stage system, the low-pressure permeate is compressed for subsequent membrane separation in the second stage to extract hydrocarbons from it. Hydrocarbon recovery rates can reach 95% for a single-stage system and 99% for a two-stage system (depending on the composition of the feed gas and purification requirements). The productivity of the installations is from 28 thousand to 28 million m3/day. When upgrading natural gas before its pipeline transport, the costs of its membrane purification are lower or comparable to the costs of an amine gas purification plant.

UOP's Polysep process is designed to extract and purify hydrogen from gas streams from oil refining, petrochemical and chemical processes. Another area of ​​its application is matching the composition of synthesis gas and separating carbon monoxide CO. The feedstock gas can be refinery gas streams, including catalytic reforming, catalytic cracking off-gas, hydrotreating and hydrocracking purge gas, as well as gas streams from petrochemical and chemical processes: ethylene and methanol plant off-gas, ammonia purge gas, synthesis gas from processes steam reforming, partial oxidation or other gasification processes. Hydrogen purification is achieved with a recovery rate of 70 to 95% with a purity degree of 70-99% (by quantity) depending on the composition of the raw material, pressure and product requirements. Polysep membrane systems are also designed to produce high-purity carbon monoxide CO for the synthesis of polyurethanes and polycarbonates, to adjust the CO/H2 ratio in the synthesis gas for the production of methanol and oxyalcohols. A new area of ​​application for the Polysep process is the extraction of hydrogen from gas in gas and power co-production cycles (1GCC).

The Polysep system is based on modern composite polymer membranes in the form of hollow fibers. These fibers are collected in special bundles operating in countercurrent mode, which allows for maximum driving force of the separation process and minimizes the need for replacement parts and assemblies, materials, chemical reagents, etc.; huge energy costs; environmental hazards during the operation of installations; the need to build additional installations for expensive preliminary water treatment; huge operating costs. A serious problem for large desalination complexes is also the need to create powerful thermal boiler houses of thermal power plants and even the use of nuclear reactors, since the cost of heat is about 40-50% of the cost of all expenses of the desalination complex. Large amounts of money are spent on solving environmental problems and on the maintenance of such complexes.

The experience of operating membrane desalination plants around the world shows that there is no trend towards reducing their operating costs, since the most difficult problems remain in overcoming the consequences of contamination and scale formation of both filter and membrane equipment. Therefore, the level of pre-treatment of raw seawater becomes one of the dominant aspects of membrane methods of water desalination, and the cost of pre-treatment of water is sometimes significantly higher than the cost of membrane plants themselves. For example, before feeding seawater into membrane modules, it must be thoroughly cleaned of suspended matter, colloidal contaminants, hardness salts, metals, active chlorine, boron; it must be softened with inhibitors; it is necessary to disinfect, wash and sanitize the membranes, the service life of which is reduced to 0.5-1.0 years. Complete regeneration of membranes is usually impossible,” mechanical and chemical (acid, alkaline, etc.) flushing of membranes is often used when the installation productivity decreases by 10-15% or when the pressure drop across the membrane circuit increases by 0.20-0.25 MPa. Currently, capital and operating costs of membrane plants remain high, especially with high productivity of process plants.