This process occupies a somewhat special position compared to other dehydration reactions. In this case, the products of intra- and intermolecular dehydration are ketene and acetic anhydride:
These reactions are endothermic, and their equilibrium shifts to the right only at high temperatures: 500-600°C in the case of anhydride formation and 700°C in the case of ketene formation. Note that during the formation of ketene, reduced pressure also has a positive effect on the equilibrium transformation. Both reactions occur in the presence of heterogeneous acid-type catalysts (metal phosphates and borates) or phosphoric acid vapor, which can be introduced into the initial mixture in the form of esters that are easily hydrolyzed into free acid. The reaction mechanism is generally similar to other dehydration processes:
Keten- a gas with a pungent odor that condenses into liquid at -41°C. It is highly reactive, interacting with various substances to form acetic acid and its derivatives. In particular, with acetic acid it gives acetic anhydride:
Acetic anhydride is a liquid with a pungent odor (boiling point 141 °C). It is an important product of organic synthesis, widely used as an acetylating agent in the synthesis of esters of acetic acid, which are difficult to obtain in other ways - phenol acetates, tertiary alcohol acetates, and especially cellulose acetate and acetate fiber.
Acetic anhydride was previously obtained by the chlorine method - from sulfuryl chloride and sodium acetate:
Due to the high consumption of reagents and the formation of waste salts, this method was replaced by dehydration of acetic acid. The latter can be accomplished in two ways: intermolecular dehydration or through the intermediate formation of ketene. In both cases, the resulting gas mixture contains highly reactive acetic anhydride or ketene and water, which can easily be converted back to acetic acid upon cooling. Therefore, it is necessary to separate water from the reaction gases so that it does not have time to react with ketene or acetic anhydride. In the direct synthesis of acetic anhydride, this is achieved by rapidly cooling the reaction gas with the introduction of an azeotropic additive (ethyl acetate), which, together with water, is separated from the condensate, which is further separated into acetic anhydride and acetic acid. In the method with intermediate formation of ketene, the reaction gases are quickly cooled to 0°C, and unconverted acetic acid and water are condensed from them. The residual gas is passed through a column irrigated with acetic acid, where acetic anhydride is formed. By-products of these reactions produce acetone and methane
Classification
a) By basicity (i.e., the number of carboxyl groups in the molecule):
Monobasic (monocarbon) RCOOH; For example:
CH 3 CH 2 CH 2 COOH;
NOOS-CH 2 -COOH propanedioic (malonic) acid
Tribasic (tricarboxylic) R(COOH) 3, etc.
b) According to the structure of the hydrocarbon radical:
Aliphatic
limit; for example: CH 3 CH 2 COOH;
unsaturated; for example: CH 2 = CHCOOH propenoic (acrylic) acid
Alicyclics, for example:
Aromatic, for example:
Saturated monocarboxylic acids
(monobasic saturated carboxylic acids) - carboxylic acids in which a saturated hydrocarbon radical is connected to one carboxyl group -COOH. They all have the general formula C n H 2n+1 COOH (n ≥ 0); or CnH 2n O 2 (n≥1)
Nomenclature
The systematic names of monobasic saturated carboxylic acids are given by the name of the corresponding alkane with the addition of the suffix - ova and the word acid.
1. HCOOH methane (formic) acid
2. CH 3 COOH ethanoic (acetic) acid
3. CH 3 CH 2 COOH propanoic (propionic) acid
Isomerism
Skeletal isomerism in the hydrocarbon radical manifests itself, starting with butanoic acid, which has two isomers:
Interclass isomerism appears starting with acetic acid:
CH 3 -COOH acetic acid;
H-COO-CH 3 methyl formate (methyl ester of formic acid);
HO-CH 2 -COH hydroxyethanal (hydroxyacetic aldehyde);
HO-CHO-CH 2 hydroxyethylene oxide.
Homologous series
Trivial name |
IUPAC name |
|
Formic acid |
Methane acid |
|
Acetic acid |
Ethanoic acid |
|
Propionic acid |
Propanic acid |
|
Butyric acid |
Butanoic acid |
|
Valeric acid |
Pentanoic acid |
|
Caproic acid |
Hexanoic acid |
|
Enanthic acid |
Heptanoic acid |
|
Caprylic acid |
Octanoic acid |
|
Pelargonic acid |
Nonanoic acid |
|
Capric acid |
Decanoic acid |
|
Undecylic acid |
Undecanoic acid |
|
Palmitic acid |
Hexadecanoic acid |
|
Stearic acid |
Octadecanoic acid |
Acidic residues and acid radicals
Acid residue |
Acid radical (acyl) |
|
UNDC |
NSOO- |
|
CH 3 COOH |
CH 3 COO- |
|
CH 3 CH 2 COOH |
CH 3 CH 2 COO- |
|
CH 3 (CH 2) 2 COOH |
CH 3 (CH 2) 2 COO- |
|
CH 3 (CH 2) 3 COOH |
CH 3 (CH 2) 3 COO- |
|
CH 3 (CH 2) 4 COOH |
CH 3 (CH 2) 4 COO- |
Electronic structure of carboxylic acid molecules
The shift in electron density towards the carbonyl oxygen atom shown in the formula causes a strong polarization of the O-H bond, as a result of which the abstraction of a hydrogen atom in the form of a proton is facilitated - in aqueous solutions the process of acid dissociation occurs:
RCOOH ↔ RCOO - + H +
In the carboxylate ion (RCOO -) there is p, π-conjugation of the lone pair of electrons of the oxygen atom of the hydroxyl group with p-clouds forming a π-bond, resulting in delocalization of the π-bond and a uniform distribution of negative charge between the two oxygen atoms:
In this regard, carboxylic acids, unlike aldehydes, are not characterized by addition reactions.
Physical properties
The boiling points of acids are significantly higher than the boiling points of alcohols and aldehydes with the same number of carbon atoms, which is explained by the formation of cyclic and linear associates between acid molecules due to hydrogen bonds:
Chemical properties
I. Acid properties
The strength of acids decreases in the following order:
HCOOH → CH 3 COOH → C 2 H 6 COOH → ...
1. Neutralization reactions
CH 3 COOH + KOH → CH 3 COOC + n 2 O
2. Reactions with basic oxides
2HCOOH + CaO → (HCOO) 2 Ca + H 2 O
3. Reactions with metals
2CH 3 CH 2 COOH + 2Na → 2CH 3 CH 2 COONa + H 2
4. Reactions with salts of weaker acids (including carbonates and bicarbonates)
2CH 3 COOH + Na 2 CO 3 → 2CH 3 COONa + CO 2 + H 2 O
2HCOOH + Mg(HCO 3) 2 → (HCOO) 2 Mg + 2СO 2 + 2H 2 O
(HCOOH + HCO 3 - → HCOO - + CO2 +H2O)
5. Reactions with ammonia
CH 3 COOH + NH 3 → CH 3 COONH 4
II. Substitution of -OH group
1. Interaction with alcohols (esterification reactions)
2. Interaction with NH 3 upon heating (acid amides are formed)
Acid amides 
hydrolyze to form acids:
or their salts:
3. Formation of acid halides
Acid chlorides are of greatest importance. Chlorinating reagents - PCl 3, PCl 5, thionyl chloride SOCl 2.
4. Formation of acid anhydrides (intermolecular dehydration)
Acid anhydrides are also formed by the reaction of acid chlorides with anhydrous salts of carboxylic acids; in this case it is possible to obtain mixed anhydrides of various acids; For example:
III. Reactions of substitution of hydrogen atoms at the α-carbon atom
Features of the structure and properties of formic acid
Molecule structure
The formic acid molecule, unlike other carboxylic acids, contains an aldehyde group in its structure.
Chemical properties
Formic acid undergoes reactions characteristic of both acids and aldehydes. Displaying the properties of an aldehyde, it is easily oxidized to carbonic acid:
In particular, HCOOH is oxidized by an ammonia solution of Ag 2 O and copper (II) hydroxide Cu(OH) 2, i.e. it gives qualitative reactions to the aldehyde group:
When heated with concentrated H 2 SO 4, formic acid decomposes into carbon monoxide (II) and water:
Formic acid is noticeably stronger than other aliphatic acids because the carboxyl group in it is bonded to a hydrogen atom rather than to an electron-donating alkyl radical.
Methods for obtaining saturated monocarboxylic acids
1. Oxidation of alcohols and aldehydes
General scheme of oxidation of alcohols and aldehydes:
KMnO 4, K 2 Cr 2 O 7, HNO 3 and other reagents are used as oxidizing agents.
For example:
5C 2 H 5 OH + 4KMnO 4 + 6H 2 S0 4 → 5CH 3 COOH + 2K 2 SO 4 + 4MnSO 4 + 11H 2 O
2. Hydrolysis of esters
3. Oxidative cleavage of double and triple bonds in alkenes and alkynes
Methods for obtaining HCOOH (specific)
1. Reaction of carbon monoxide (II) with sodium hydroxide
CO + NaOH → HCOONa sodium formate
2HCOONa + H 2 SO 4 → 2HCOON + Na 2 SO 4
2. Decarboxylation of oxalic acid
Methods for producing CH 3 COOH (specific)
1. Catalytic oxidation of butane
2. Synthesis from acetylene
3. Catalytic carbonylation of methanol
4. Acetic acid fermentation of ethanol
This is how edible acetic acid is obtained.
Preparation of higher carboxylic acids
Hydrolysis of natural fats
Unsaturated monocarboxylic acids
The most important representatives
General formula of alkene acids: C n H 2n-1 COOH (n ≥ 2)
CH 2 =CH-COOH propenoic (acrylic) acid
Higher unsaturated acids
Radicals of these acids are part of vegetable oils.
C 17 H 33 COOH - oleic acid, or cis-octadiene-9-oic acid
Trance The -isomer of oleic acid is called elaidic acid.
C 17 H 31 COOH - linoleic acid, or cis, cis-octadiene-9,12-oic acid
C 17 H 29 COOH - linolenic acid, or cis, cis, cis-octadecatriene-9,12,15-oic acid
In addition to the general properties of carboxylic acids, unsaturated acids are characterized by addition reactions at multiple bonds in the hydrocarbon radical. Thus, unsaturated acids, like alkenes, are hydrogenated and decolorize bromine water, for example:
Selected representatives of dicarboxylic acids
Saturated dicarboxylic acids HOOC-R-COOH
HOOC-CH 2 -COOH propanedioic (malonic) acid, (salts and esters - malonates)
HOOC-(CH 2) 2 -COOH butadioic (succinic) acid, (salts and esters - succinates)
HOOC-(CH 2) 3 -COOH pentadioic (glutaric) acid, (salts and esters - glutorates)
HOOC-(CH 2) 4 -COOH hexadioic (adipic) acid, (salts and esters - adipates)
Features of chemical properties
Dicarboxylic acids are in many ways similar to monocarboxylic acids, but are stronger. For example, oxalic acid is almost 200 times stronger than acetic acid.
Dicarboxylic acids behave as dibasic acids and form two series of salts - acidic and neutral:
HOOC-COOH + NaOH → HOOC-COONa + H 2 O
HOOC-COOH + 2NaOH → NaOOC-COONa + 2H 2 O
When heated, oxalic and malonic acids are easily decarboxylated:
Alkenes and alkadienes are obtained. Dehydration of alcohols can occur in two directions: intramolecular and intermolecular.
Intramolecular dehydration of alcohols belongs to elimination reactions ($E$). Depending on the structure of the alcohol, elimination can occur via the $E1$ and $E2$ mechanisms. In this case, primary alcohols react predominantly according to the $E2$ mechanism, and secondary and tertiary alcohols - according to the $E1$ mechanism. As in the case of nucleoprofile substitution, the elimination of alcohols occurs with the formation of an oxonium cation.
Like haloalkanes, primary alcohols react with intermolecular dehydration usually by the $S_N2$ mechanism, tertiary alcohols - by the $S_N1$ mechanism, secondary alcohols can react both with the $S_N2$ and $S_N1$ mechanisms.
Intramolecular dehydration
Tertiary alcohols dehydrate more easily, then secondary and then primary, according to the $E1$ or $E2$ mechanism, similar to dehydrohalogenation reactions. The process of dehydration of alcohols obeys A. Zaitsev’s rule with the formation of the most branched alkenes. Thus, the dehydration of a tertiary alcohol occurs via the $E1$ mechanism and is often accompanied by a nucleophilic substitution reaction via the $Sn1$ mechanism:
Picture 1.
The slowest stage of this mechanism is the conversion of alkoxonium cations to carbocations:
Figure 2.
The production of a particular alkene during dehydration is determined by the lability of intermediate carbocations and the thermodynamic stability of branched alkenes. For example, for isoamyl alcohol, in accordance with Zaitsev’s rule, only 3-methyl-1-butene should be formed, but in reality three alkenes $C_5H_(10)$ are obtained:
Figure 3.
The formed primary carbocation is the least stable and, in addition to proton abstraction, is also prone, due to 1,2-hydride movements, to isomerize into a stable secondary carbocation, from which alkenes are obtained:
Figure 4.
The secondary carbocation, in turn, can also isomerize into a tertiary one, which is maximally stable:
Figure 5.
Thus, during the dehydration of isoamyl alcohol, a mixture of 3-methyl-1-butene, 2-methyl-2-butene and 2-methyl-1-butene is formed, and most of the reaction products will contain 2-methyl-2-butene as branched product.
For alcohols in elimination reactions, the $E1$ mechanism is more typical than the $E2$ mechanism. This is also due to the acidity of the reaction medium, in which the strong base - alkoxide anion $RO-$ does not exist, since it quickly interacts with the proton.
Figure 6.
Intermolecular dehydration
The reactions considered are examples of intramolecular dehydration, next to which there is also intermolecular dehydration, an example of which, as mentioned above, is the formation of an ether:
Figure 7.
Intermolecular dehydration of alcohols in the presence of concentrated acids, depending on temperature and the ratio of the volumes of alcohol and acid, can occur with the formation of various products. For example, ethyl alcohol at 105$^\circ$C forms an acid ester with sulfuric acid - ethylsulfuric acid (reaction 1). With an excess of alcohol and high temperature (130-140$^\circ$C), intermolecular dehydration occurs, the main product of which is diethyl ether (ether; reaction 3). At temperatures above 160$^\circ$С, ethyl sulfuric acid decomposes to form ethylene (reaction 2):
Figure 8.
Substitutes for acids in the process of acid dehydration
For processes (both intra- and intermolecular) dehydration of alcohols, especially on an industrial scale, instead of conventional acids, it is more convenient to use anhydrous Lewis acids or other oxidizing agents, such as aluminum oxide, as dehydrating agents. The process of heterogeneous catalytic dehydration of alcohols over $Al_2O_3$ at 350-450$^\circ$C leads to alkenes:
Figure 9.
Essay
Dehydration processes
Introduction 3
1. Dehydration processes 4
2. Technology of dehydrogenation processes 9
References 11
Introduction
The processes of hydrolysis, hydration, dehydration, esterification and amidation are very important in the basic organic and petrochemical synthesis industry. Hydrolysis of fats, cellulose and carbohydrates has long produced soap, glycerin, ethanol and other valuable products. In the field of organic synthesis, the processes in question are used mainly for the production of C 2 -C 5 alcohols, phenols, ethers, -oxides, many unsaturated compounds, carboxylic acids and their derivatives (esters, anhydrides, nitriles, amides) and other compounds.
The listed substances have very important applications as intermediate products of organic synthesis (alcohols, acids and their derivatives, aldehydes, -oxides), monomers and starting materials for the synthesis of polymeric materials (phenol, esters of acrylic and methacrylic acids, melamine, chloroolefins), plasticizers and lubricants (esters), solvents (alcohols, ethers and esters, chloroolefins), pesticides (esters of carbamic and thiocarbamic acids). Very often, the reactions under consideration are an intermediate step in multi-stage syntheses of other products for the intended purpose.
The production of these substances is on a large scale. Thus, in the USA they synthesize 500 thousand tons of ethanol and isopropanol, 900 thousand tons of propylene oxide, 200 thousand tons of epichlorohydrin, over 4 million tons of esters, about 300 thousand tons of isocyanates.
1. Dehydration processes
1. Dehydration with the formation of unsaturated compounds
The process is used to extract isobutene from C 4 fractions of cracking and pyrolysis gases, when one of the stages consists of dehydrogenation of tert-butanol catalyzed by sulfuric acid or a sulfonic cation. Or dehydration to produce isobutene is carried out with tert-butanol formed by the hydroxide method for producing propylene oxide:
(CH 3) 3 COH → (CH 3) 2 C=CH 2 + H 2 O
In this and other cases, dehydration to form unsaturated substances is most often one of the stages in the production of many monomers. Thus, in one of the new processes, styrene is produced by dehydration of methylphenylcarbinol:
C 6 H 5 -CHOH-CH 3 → C 6 H 5 -CH=CH 2 + H 2 O
The well-known method for the synthesis of isoprene from isobutene and formaldehyde also involves the final dehydration of a diol and an unsaturated alcohol:
(CH 3) 2 C(OH)-CH 2 CH 2 (OH) (CH 3) 2 =CHCH 2 OH
(CH 3) 2 =CHCH 2 OH CH 2 =C(CH 3)CH=CH 2
When the first molecule of water is separated from a diol, a mixture of unsaturated alcohols of different structures is obtained, but upon further dehydration they all give isoprene, and the reaction is accompanied by the movement of double bonds:
Another option for obtaining unsaturated compounds, consisting in the introduction of a vinyl group through reactions such as aldol condensation followed by dehydration, examples include the synthesis of nitroethylene, vinyl methyl ketone and 2-vinylpyridine:
CH 3 NO 2 + HCHO HOCH 2 -CH 2 NO 2 CH 2 =CHNO 2
CH 3 COCH 3 + HCHO CH 3 COCH 2 CH 2 OH CH 3 COCH=CH 2
Dehydration is also one of the stages in the production of methacrylic acid esters CH 2 =C(CH 3)COOR, some primary alcohols, for example n-butanol:
2CH 3 CHO → CH 3 CH(OH)CH 2 CHO CH 3 CH=CHCHO
CH 3 CH=CHCHO CH 3 (CH 2) 2 -CH 2 OH
2-ethylhexanol, methyl isobutyl ketone and many other substances.
2. Dehydration to form ethers
By the by-product formation of ethers during the hydrolysis of chlorinated derivatives and hydration of olefins, all the required quantities of esters such as diisopropyl are obtained. But diethyl ether has a fairly wide application, and it is specially produced by intermolecular dehydration of ethanol at 250 0 C on a heterogeneous catalyst AI 2 O 3:
2C 2 H 5 OH → (C 2 H 5) 2 O + H 2 O
The possibility of using the same method for the synthesis of ethers from isopropanol and higher alcohols is limited by the development of by-product formation of olefins. As a result, most esters are obtained in the liquid phase at a lower temperature using acid catalysts - sulfuric, phosphoric, and arylsulfonic acids. The method is suitable mainly for the synthesis of symmetrical esters having the same alkyl groups, since when dehydrating a mixture of two alcohols, the yield of the mixed ester is small:
3ROH + 3R"OH → R 2 O + R" 2 O + ROR" + 3H 2 O
Of the symmetrical ethers with a straight chain of carbon atoms, β-dichlorodiethyl ether (chlorex) is of interest, which is a valuable solvent and extractant, as well as a starting material for the production of polysulfide polymers. It is produced by dehydration of anhydrous ethylene chlorohydrin over an acid catalyst:
2CICH 2 -CH 2 OH → (CICH 2 -CH 2) 2 + H 2 O
Dihydric alcohols under acid catalysis are capable of closing stable five- or six-membered rings. In this way, dioxane (1) is obtained from diethylene glycol, morpholine (2) from diethanolamine, and tetrahydrofuran (3) from butanediol-1,4. All these substances are solvents:
3. Dehydration of carboxylic acids
The process of dehydration of carboxylic acids occupies a somewhat special position compared to other dehydration reactions. In this case, the products of intra- and intermolecular dehydration are ketene and acetic anhydride:
CH 3 -COOH CH 2 =C=O
2CH 3 COOH (CH 3 CO) 2 O
These reactions are endothermic, and their equilibrium shifts to the right only at high temperatures: 500 - 600 0 C in the case of anhydride formation and 700 0 C in the case of ketene formation. During the formation of ketene, reduced pressure also has a positive effect on the equilibrium transformation. Both reactions occur in the presence of heterogeneous acid-type catalysts (metal phosphates and borates) or phosphoric acid vapor, which can be introduced into the initial mixture in the form of esters that are easily hydrolyzed into free acid. The reaction mechanism is generally similar to other dehydration processes:
CH 3 -COOH CH 3 COOH 2 CH 3 -C=O
CH 2 =C=O CH 3 -C=O 
(CH 3 -CO) 2 O
Ketene is a gas with a pungent odor that condenses into liquid at – 41 0 C. It is highly reactive, interacting with various substances to form acetic acid and its derivatives. In particular, with acetic acid it gives acetic anhydride:
CH 2 =C=O + CH 3 COOH → (CH 3 CO) 2 O
Acetic anhydride is a liquid with a pungent odor (bp 141 0 C). It is an important product of organic synthesis, widely used as an acetylating agent in the synthesis of esters of acetic acid, difficult to obtain in other ways - phenol acetates, tertiary alcohol acetates and especially cellulose acetate and acetate fiber.
Acetic anhydride was previously obtained by the chlorine method - from sulfuryl chloride and sodium acetate:
SO 2 CI 2 + 4CH 3 COONa → 2(CH 3 CO) 2 O + Na 2 SO 4 + 2NaCI
Due to the high consumption of reagents and the formation of waste salts, this method was replaced by dehydration of acetic acid. The latter can be accomplished in two ways: intermolecular dehydration or through the intermediate formation of ketene. In both cases, the resulting gas mixture contains highly reactive acetic anhydride or ketene and water, which can easily be converted back to acetic acid upon cooling. Therefore, it is necessary to separate water from the reaction gases so that it does not have time to react with ketene or acetic anhydride. In the direct synthesis of acetic anhydride, this is achieved by rapidly cooling the reaction gas with the introduction of an azeotropic additive (ethyl acetate), which, together with water, is separated from the condensate, which is further separated into acetic anhydride and acetic acid. In the method with intermediate formation of ketene, the reaction gases are quickly cooled to 0 0 C, and unconverted acetic acid and water are condensed from them. The residual gas is passed through a column irrigated with acetic acid, where acetic anhydride is formed. As a side effect, these reactions produce acetone and methane:
2CH 3 COOH → CH 3 COCH 3 + CO 2 + H 2 O
CH 3 COOH → CH 4 + CO 2
But the yield of acetic anhydride is quite high and equal to 90%.
2. Technology of dehydrogenation processes
Dehydrogenation processes are carried out by two main methods: in the liquid and gas phase.
Liquid-phase dehydration is used in cases where the product or starting reagents are not sufficiently stable at elevated temperatures of the gas-phase process. This applies to the synthesis of chlorex, dioxane and morpholine, but nitro alcohols, hydroxylaldehydes and hydroxyketones are also often dehydrated in the liquid phase, which can be converted into the corresponding unsaturated substances in the gas phase. Sulfuric acid (concentration up to 70%), phosphoric acid, acid phosphates of calcium or magnesium, and sulfonic cations (the latter at temperatures up to 150 0 C) are used as catalysts. The process is carried out at temperatures from 100 to 160 – 200 0 C and normal pressure.
Liquid-phase dehydration (Fig. 1) is most often carried out continuously in two main ways. In the first of them, the process is carried out by continuously distilling off more volatile products from the catalyst solution - the target unsaturated substance or ether and water, which often give low-boiling azeotropic mixtures. The reactor is heated with steam and the initial organic reagent is continuously fed into the apparatus. Above the reactor there is a return condenser (sometimes a reflux column), with which you can regulate the return of condensate, maintaining the catalyst concentration constant.
Rice. 1 Reaction unit for liquid-phase dehydration process
The second method is used to carry out practically irreversible and fairly fast reactions of elimination of H 2 O with the formation of nitroolefins, unsaturated aldehydes and ketones and other substances. It involves passing the acidified reagent through a coil or tube reactor at the desired temperature.
Gas-phase dehydration is used to produce styrene (from methylphenylcarbinol), isoprene (from tert-butanol), diethyl ether (from ethanol), tetrahydrofuran (from butanediol-1,4), acetic anhydride (directly from acetic acid or via ketene) and other products . The most commonly used catalysts are phosphoric acid on porous supports, aluminum oxide, acid and medium calcium or magnesium phosphates. The temperature ranges from 225 – 250 0 C (production of diethyl ether) to 700 – 720 0 C (dehydration of acetic acid into ketene). The pressure is most often normal, but when producing diethyl ether it can be 0.5 - 1.0 MPa, and when dehydrating into ketene 0.02 - 0.03 MPa.
Gas-phase dehydration is also carried out by two main methods. The first is used to carry out endothermic processes of intramolecular dehydration. The reactor is a tubular apparatus heated by a coolant (Fig. 2a), in the pipes of which a heterogeneous catalyst is located.
Rice. 2 Reaction units of the gas-phase dehydration process
Due to the high metal consumption of these devices, adiabatic reactors with a continuous layer of a heterogeneous catalyst (Fig. 2 b), which do not have heat exchange surfaces, are most widely used. They are especially suitable for carrying out weakly exothermic reactions of the formation of unsaturated compounds; in order to maintain the required temperature regime, they often dilute the initial mixture with superheated water vapor, which prevents the mixture from cooling excessively and at the same time contributes to an increase in the selectivity of the reaction. Finally, there are installations with two sequential adiabatic type reactors: the gas, cooled in the first apparatus, is heated to the desired temperature in a heat exchanger using a suitable coolant before being supplied to the second apparatus.
Bibliography
1. Gabrielyan O. S., Ostroumov I. G. Chemistry. M., Bustard, 2008;
2. Chichibabin A.E. Basic principles of organic chemistry. M., Goskhimizdat, 1963. – 922 p.;
3. Lebedev N. N. Chemistry and technology of basic organic and petrochemical synthesis. M., Chemistry. 1988. – 592 pp.;
4. Paushkin Ya. M., Adelson S. V., Vishnyakova T. P. Technology of petrochemical synthesis. M., 1973. – 448 pp.;
5. Yukelson I. I. Technology of basic organic synthesis. M., "Chemistry", 1968.
Loading...