阅读说明：本技术 用仲酰胺/磷酸三烷酯复合溶剂从含镁卤水中分离镁提取锂的萃取体系、萃取方法和其应用 (Extraction system for separating magnesium from magnesium-containing brine by using secondary amide/trialkyl phosphate composite solvent, extraction method and application thereof ) 是由 杨立新 李聪 刘长 周钦耀 李海博 于 2019-11-08 设计创作，主要内容包括：本发明公开了用仲酰胺/磷酸三烷酯复合溶剂从含镁卤水中分离镁提取锂的萃取体系、萃取方法和其应用。萃取体系中含有仲酰胺和磷酸三烷酯分别由其单一化合物或两种以上的混合物组成,分子中碳原子总数分别为12～18和12～36,萃取体系的凝固点小于0℃。在有机相与卤水相体积比1～10:1、卤水密度为1.25～1.38g/cm<Sup>3</Sup>和温度0～50℃下进行单级或多级逆流萃取,反萃取得到低镁锂比水相,经过浓缩、除杂与制备,分别得到氯化锂、碳酸锂和氢氧化锂。本发明的优异效果：仲酰胺萃取剂分子结构简单,容易生产,磷酸三烷酯改进复合溶剂的粘度等性质；Li<Sup>+</Sup>多级萃取率高,锂镁分离系数大,用水反萃取,酸碱消耗大大减少；萃取分离流程缩短,萃取体系溶损小,具有工业应用价值。(The invention discloses an extraction system, an extraction method and application for separating magnesium from magnesium-containing brine and extracting lithium by using a secondary amide/trialkyl phosphate composite solvent. The extraction system contains secondary amide and trialkyl phosphate respectively composed of single compound or mixture of more than two compounds, and the total number of carbon atoms in molecule12-18 and 12-36 respectively, and the freezing point of an extraction system is less than 0 ℃. The volume ratio of the organic phase to the brine phase is 1-10: 1, and the brine density is 1.25-1.38 g/cm 3 And performing single-stage or multi-stage countercurrent extraction at the temperature of 0-50 ℃, performing back extraction to obtain a low magnesium-lithium ratio water phase, and performing concentration, impurity removal and preparation to respectively obtain lithium chloride, lithium carbonate and lithium hydroxide. The excellent effects of the present invention: the secondary amide extractant has simple molecular structure and easy production, and the trialkyl phosphate improves the properties of the composite solvent such as viscosity and the like; li + The multi-stage extraction rate is high, the lithium-magnesium separation coefficient is large, and the acid-base consumption is greatly reduced by using water for back extraction; the extraction separation process is shortened, the dissolution loss of an extraction system is small, and the method has industrial application value.)

1. An extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent is characterized in that the extraction system contains A and B substances; wherein the A-type substance is a secondary amide and consists of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (I):

wherein R is ₁Selected from C2-C12 alkyl or C3-C12 cycloalkyl containing single ring structure, R ₂Selected from C1-C11 alkyl or C3-C11 cycloalkyl containing single ring structure, and R ₁And R ₂The sum of the numbers of carbon atoms contained in the two groups is 11 to 17, wherein the alkyl or cycloalkyl group includes various isomers;

wherein the B-type substance is trialkyl phosphate which is composed of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (II):

wherein R is ₃、R ₄And R ₅Are respectively selected from alkyl of C4-C12, and R ₃、R ₄And R ₅The sum of the number of carbon atoms contained in the trialkyl is 12-36, wherein the alkyl comprises various linear chain isomers or branched chain isomers;

the freezing point of the extraction system containing the substances A and B is less than 0 ℃.

2. The extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using the secondary amide/trialkyl phosphate composite solvent as claimed in claim 1, wherein the volume percentage of the A-type substance for extraction in the whole organic phase is 50-100%, and the end value is not 100%; the B-type substance has a synergistic effect, and accounts for 0-50% of the whole organic phase by volume, excluding 0% of the end point.

3. An extraction system for extracting lithium from magnesium-containing brine by using secondary amide/trialkyl phosphate composite solvent as claimed in claim 1, wherein in said class B material, 3 alkyl groups R in the molecular structure of trialkyl phosphate are ₃、R ₄And R ₅The same alkyl groups as each other.

4. The extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using secondary amide/trialkyl phosphate composite solvent as claimed in claim 1, further comprising diluent 260# solvent oil, 300# solvent oil or sulfonated kerosene for dilution.

5. The extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium is characterized by comprising the following steps of:

s1, taking magnesium-containing brine as a brine phase before extraction; wherein, in the magnesium-containing brine, the concentration of lithium ions is 0.1-21 g/L, the concentration of magnesium ions is 80-125 g/L, the concentration of chloride ions is 200-400 g/L, the mass ratio of magnesium to lithium is 4.8-1100: 1, and the density of the brine at 20 ℃ is 1.25-1.38 g/cm ³The pH value of the brine is 1-7;

s2, using the extraction system of any one of claims 1 to 4 as a pre-extraction organic phase;

s3, mixing the organic phase before extraction and the brine phase before extraction according to the volume ratio of 1-10: 1, performing single-stage extraction or multi-stage countercurrent extraction, and separating the two phases to obtain a loaded organic phase and an extracted brine phase.

6. The extraction method of claim 5, wherein the magnesium-containing brine further comprises one or more of sodium ions, potassium ions, iron ions, ferrous ions, sulfate ions, boric acid, and borate ions.

7. The extraction process of claim 5, wherein the magnesium-containing brine comprises but is not limited to lithium-containing salt lake brine.

8. The extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using the secondary amide/trialkyl phosphate composite solvent as claimed in claim 5, wherein in the step S3, the extraction temperature is 0-50 ℃; the mixing of the two phases is carried out by stirring, and the separation of the two phases after extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

9. The extraction process for separating magnesium and extracting lithium from magnesium-containing brine by using secondary amide/trialkyl phosphate composite solvent as claimed in claim 5, further comprising the step of, after said step S3:

s4, taking water as a back extraction agent, carrying out single-stage back extraction or multi-stage counter-current back extraction on the loaded organic phase, wherein the volume ratio of the back extraction agent to the loaded organic phase is 1: 1-20, and carrying out two-phase separation to obtain a back-extracted organic phase and a back-extracted aqueous phase;

s5, returning the organic phase after back extraction to the step S2, and realizing the recycling of the extraction system.

10. The extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using the secondary amide/trialkyl phosphate composite solvent as claimed in claim 9, wherein in the step S4, the back extraction temperature is 0-50 ℃; the two-phase mixing is carried out by a stirring mode, and the two-phase separation after back extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

11. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium in the preparation of a lithium product, which is characterized by further comprising the following steps after the step S4:

s6, further removing oil, purifying and concentrating the back-extracted water phase, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

s7, concentrating, crystallizing, separating and drying the refined lithium chloride solution to obtain the lithium chloride product.

12. The application of the extraction method for separating magnesium from magnesium-containing brine and extracting lithium by using a secondary amide/trialkyl phosphate composite solvent in obtaining lithium carbonate serving as a lithium product is characterized by further comprising the following steps after the step S4:

s6, further removing oil, purifying and concentrating the back-extracted water phase, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

and S8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product.

13. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium in the preparation of a lithium product, which is lithium hydroxide, is characterized by further comprising the following steps after the step S4:

s6, further removing oil, purifying and concentrating the back-extracted water phase, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

s9, electrolyzing the refined lithium chloride solution to obtain a lithium hydroxide product, and simultaneously by-producing hydrogen and chlorine, wherein the hydrogen and chlorine can be used for producing hydrochloric acid;

or after the step S6, the method further includes the steps of:

s8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product;

and S10, adding calcium hydroxide emulsion into the prepared lithium carbonate, carrying out solid-liquid reaction, separating to obtain a lithium hydroxide solution, and concentrating, crystallizing and drying the lithium hydroxide solution to obtain a lithium hydroxide product.

Technical Field

The invention relates to a method for extracting lithium from magnesium-containing brine, in particular to an extraction system for separating magnesium from magnesium-containing brine by using a composite solvent to extract lithium, an extraction method and application thereof.

Background

Since this century, the application of lithium in the field of new energy has reached an unprecedented and alarming level both in depth and breadth, and people have made thousands of batteries as power sources for electric vehicles and tens of thousands of batteries as combined structures for energy storage devices, so that the use of lithium materials in 3C products has become increasingly widespread and widespread, and the demand for lithium has increased day by day. Lithium is taken as a key anode and cathode material and an electrolyte raw material in the battery and is obtained from natural resources, and Australia, Chilean, China and Argentina are major countries for producing and storing lithium ores in the world according to the annual book statistics of American mineral products in 2019. China has two types of brine type and hard rock type lithium reserves simultaneously, wherein the amount of salt lake lithium resources accounts for about 80% of the domestic reserves, and the proven lithium salt resource storage amount of the Qinghai firewood Da Mu basin is up to 1982 ten thousand tons (calculated by LiCl) [ beautiful Wu, Liu xi Fang, Zheng xi Ping, etc.. modern chemical engineering, 2017,37(5), 1-5 ].

However, the lithium resources of brine in China are obviously different from those of salt lake brine in the lithium triangle region in south America, besides Tibet Zaubeya carbonate type brine, a large amount of magnesium sulfate subtype brine and magnesium chloride type brine are distributed, lithium is very difficult to extract from the brine, a large amount of magnesium salt needs to be removed from the brine due to coexistence of lithium and magnesium, and a particularly effective lithium and magnesium separation method is lacked for a long time.The existing production technology for developing the lithium resource in the Qinghai salt lake mainly comprises 4 technologies of an ion adsorption method, a calcination leaching method, a membrane separation method and a solvent extraction method, and all the technologies have defects to different degrees. The extraction method is a method for separating lithium and magnesium by utilizing the special extraction performance of an organic solvent on lithium, and is considered to be the most promising lithium extraction method for brine with high magnesium-lithium ratio [ Song J.F., Nghem L.D., LiX.M., He T.Environ.Sci.: Water Res.Technol.,2017,3(4), 593-]The quality of the extracting agent is a key factor of the technical process. Taking tributyl phosphate (TBP) as an extracting agent and FeCl ₃The system of co-extractant is continuously and widely researched, and the Jilianmin et al in the patent of invention granted by CN105039743B use TBP and surfactant to form composite extractant to reduce equipment corrosion, extractant dissolution loss and degradation in acidic environment. In the Yuanyuan industry and the like, neutral phosphorus-oxygen compounds and different tertiary amides are selected to be combined or only the tertiary amides are used as an extracting agent in multiple Chinese patent applications such as application numbers 201610383061, X and 201610560041.5, the extraction rate of lithium in brine is improved under the co-extraction effect of iron salts, but the loaded organic phase still needs to be back-extracted by concentrated hydrochloric acid. In addition, the bengqingfen and the like use a composite system (CN107502741B) formed by a neutral phosphine compound and an acid phosphine compound as an extracting agent to extract lithium from salt lake brine, wherein the composite system is a pyrrole hexafluorophosphate ionic liquid (CN106498184B), a phosphate ionic liquid (CN108866352A), Zhumegawu and the like.

However, the extraction method has not completed the scale test verification and screening of the extracting agent all the time, and the most suitable extraction system has not been found so far. The contradiction of extraction and back extraction and the contradiction of acid and alkali consumption always exist in the lithium extraction technology of the solvent extraction method, the contradiction is not solved fundamentally, the solvent extraction method cannot be a competitive method, and the reason lies in the development of an extraction system and an extraction technology. The trialkyl phosphate is used as a neutral solvent with wide application and stable property, is beneficial to two-phase separation, and can form a new extraction system by combining with other effective components. After the salt lake high magnesium-lithium ratio brine is converted into low magnesium-lithium ratio brine by lithium-magnesium separation, basic chemical products such as lithium chloride, lithium carbonate and lithium hydroxide required in the market can be prepared.

Disclosure of Invention

The invention aims to provide an extraction system, an extraction method and application for economically and effectively separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium, aiming at the defects in the prior art.

The technical scheme and the technical process provided by the invention are as follows:

1. an extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent, wherein the extraction system contains A and B substances; wherein the A-type substance is a secondary amide and consists of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (I):

wherein R is ₁Selected from C1-C12 alkyl or C3-C12 cycloalkyl containing single ring structure, R ₂Selected from C1-C11 alkyl or C3-C11 cycloalkyl containing single ring structure, and R ₁And R ₂The sum of the number of carbon atoms contained in the two groups being 11 to 17, wherein the alkyl or cycloalkyl group includes various isomers (due to R) ₁、R ₂Is variable when R ₁、R ₂When uniquely identified, class A is a single compound, and mixtures thereof refer to compounds that follow R ₁、R ₂A mixture of two or more compounds produced by the change of (1);

wherein the B-type substance is trialkyl phosphate which is composed of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (II):

wherein R is ₃、R ₄And R ₅Are respectively selected from alkyl of C4-C12, and R ₃、R ₄And R ₅Carbon atom contained in trialkylThe sum of the number of the subgroups is 12 to 36, wherein the alkyl group comprises various isomers (due to R) which are linear or branched ₃、R ₄、R ₅Is variable when R ₃、R ₄、R ₅When uniquely identified, class B is a single compound, and mixtures thereof refer to compounds that follow R ₃、R ₄、R ₅A mixture of two or more compounds produced by the change of (1);

the freezing point of the extraction system containing the substances A and B is less than 0 deg.C (the freezing point of a single component constituting the extraction system may be less than, equal to or greater than 0 deg.C, the conditions for the extraction system of the present invention can be satisfied when the freezing point of the single component is less than 0 deg.C, and when the freezing point of the single component is greater than or equal to 0 deg.C, the single component may be mixed with other components having freezing points less than 0 deg.C, and dissolved to finally form a mixture having a freezing point less than 0 deg.C).

In the extraction system, the volume percentage of the A-type substances in the whole organic phase for extraction is 50-100%, and the end value is not 100%; the volume percentage of the B-type substance in the whole organic phase is 0-50% by taking the synergistic effect, and the end value is not 0%.

In the B-type substance, 3 alkyl groups R in the molecular structure of the trialkyl phosphate ₃、R ₄And R ₅The same alkyl groups as each other.

The extraction system consisting of the substances A and B also comprises diluent No. 260 solvent oil, No. 300 solvent oil or sulfonated kerosene for dilution.

2. The extraction method for separating magnesium from magnesium-containing brine by using secondary amide/trialkyl phosphate composite solvent to extract lithium comprises the following steps:

s1, taking magnesium-containing brine as a brine phase before extraction; wherein, in the magnesium-containing brine, the concentration of lithium ions is 0.1-21 g/L, the concentration of magnesium ions is 80-125 g/L, the concentration of chloride ions is 200-400 g/L, the mass ratio of magnesium to lithium is 4.8-1100: 1, and the density of the brine at 20 ℃ is 1.25-1.38 g/cm ³The pH value of the brine is 1-7;

s2, taking the extraction system in the step 1 as an organic phase before extraction;

s3, mixing the organic phase before extraction and the brine phase before extraction according to the volume ratio of 1-10: 1, and performing single-stage extraction or multi-stage countercurrent extraction to obtain a loaded organic phase and an extracted brine phase.

The magnesium-containing brine also contains one or more of sodium ions, potassium ions, iron ions, ferrous ions, sulfate radicals, boric acid, or borate ions.

The magnesium-containing brine comprises lithium-containing salt lake brine, but is not limited to the brine.

Further, in the step S3, the extraction temperature is 0-50 ℃; the mixing of the two phases is carried out by stirring, and the separation of the two phases after extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

Further, after the step S3, the method further includes the steps of:

s4, taking water as a back extraction agent, and carrying out single-stage back extraction or multi-stage counter-current back extraction on the loaded organic phase, wherein the volume ratio of the back extraction agent to the loaded organic phase is 1: 1-20, so as to obtain a back-extracted organic phase and a back-extracted aqueous phase;

s5, returning the organic phase after back extraction to the step S2, and realizing the recycling of the extraction system.

Further, in the step S4, the back extraction temperature is 0-50 ℃; the two-phase mixing is carried out by a stirring mode, and the two-phase separation after back extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

3. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium in obtaining a lithium product, namely lithium chloride, further comprises the following steps after the step S4:

s6, further removing oil and purifying the back-extracted water phase, concentrating, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

s7, concentrating, crystallizing, separating and drying the refined lithium chloride solution to obtain the lithium chloride product.

4. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium in obtaining lithium product lithium carbonate further comprises the following steps after the step S4:

s6, further removing oil and purifying the back-extracted water phase, concentrating, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

and S8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product.

5. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent to extract lithium in obtaining a lithium product, namely lithium hydroxide, further comprises the following steps after the step S4:

s6, further removing oil and purifying the back-extracted water phase, concentrating, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

s9, electrolyzing the refined lithium chloride solution to obtain a lithium hydroxide product, and simultaneously by-producing hydrogen and chlorine, wherein the hydrogen and chlorine can be used for producing hydrochloric acid;

or after the step S6, the method further includes the steps of:

s8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product;

and S10, adding calcium hydroxide emulsion into the prepared lithium carbonate, carrying out solid-liquid reaction, separating to obtain a lithium hydroxide solution, and concentrating, crystallizing and drying the lithium hydroxide solution to obtain a lithium hydroxide product.

The secondary amide type compound used in the examples of the present invention was synthesized by reacting an organic acid chloride or acid anhydride with a primary amine in a stoichiometric ratio, purified by washing with water and distillation under reduced pressure, and evaluated by detection using a gas chromatograph-mass spectrometer model 7890A/5975C of agilent usa. Part of the sources of the trialkyl phosphate compounds used in the embodiment of the invention are synthesized by reacting phosphorus oxychloride with alkyl alcohol according to a stoichiometric ratio, purified by water washing and reduced pressure distillation, and obtained by detection and evaluation by an American Agilent 7890A/5975C gas chromatography-mass spectrometer; and another part is purchased from chemical products companies.

Compared with the prior art, the invention has the advantages that a secondary amide/trialkyl phosphate composite solvent composed of the compounds shown in the formula (I) and the formula (II) is used as a new extraction system, so that a new extraction method for separating magnesium from magnesium-containing brine and extracting lithium and application thereof are obtained, unexpected effects are achieved, no literature report that a solvent composed of secondary amide and trialkyl phosphate is used as a brine lithium extraction system is found, and a new technology is provided for the development of the current high magnesium-lithium ratio salt lake brine lithium resource. The invention has the following advantages:

1) the secondary amide as the A substance in the extraction system has simple molecular structure, easily obtained source, easy production and extraction effect, is a novel special-effect component for separating magnesium and extracting lithium from magnesium-containing brine, wherein the secondary amide functional group is a key part for separating lithium and magnesium and extracting lithium, and hydrogen atoms on N-H are arranged before and after extraction ¹Shift of H NMR spectrum to low field, for Li ⁺Plays a key role in the extraction. The trialkyl phosphate used as a B substance in an extraction system is easy to synthesize, can effectively improve the properties of the composite solvent such as viscosity, freezing point and the like, increases the mixed entropy of the system and generates a synergistic effect through a phosphorus-oxygen functional group.

2) In ensuring Li ⁺On the premise of single-stage extraction capacity with a certain size, the loaded organic phase is compatible and easy to be directly back-extracted by water, and acid does not need to be used for strengthening Li ⁺Without the use of alkaliAnd the acid recovers the extraction capability of the organic phase and the acid-base property of the water phase, greatly reduces the acid-base consumption in the process of separating lithium and magnesium from brine, realizes the bidirectional balance of the extraction and back extraction processes, and extracts Li ⁺While also facilitating Li ⁺Back extraction of (4). After the magnesium-containing brine is subjected to multi-stage countercurrent extraction, the lithium-magnesium separation coefficient is large, and the mass ratio of magnesium to lithium in the water phase after back extraction is remarkably reduced.

3) The whole extraction and separation process is greatly simplified, the organic phase is directly recycled, the corrosion degree of equipment is low, and the production process is easy to control. The low density of the organic phase is suitable for the two-phase separation when the loaded organic phase is back-extracted with water. By adjusting the molecular structure and composition of the extraction system, the solubility of the preferred extraction system in water is significantly reduced compared to the solubility of TBP.

Description of the figures

FIG. 1 is a block diagram of an extraction system, an extraction method and a process flow of the application of the extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using a secondary amide/trialkyl phosphate composite solvent.

Table 33 shows the common names, corresponding canonical names and code numbers of the secondary amides of substance A referred to in the examples of the present invention.

Table 34 shows the common names, corresponding specification names and code numbers of the trialkyl phosphates of the substance B mentioned in the examples of the present invention.

Detailed Description

The invention is further illustrated by the following examples: