Alkylation

Alkylation Unit process

1. Alkylation Introduction Definition Agent Technologies Applications. 1

2. Alkylation Introduction Types of Alkylated Compounds Alkylation may be defined as the introduction of an alkyl radical by substitution or addition into an organic compound. We also include under this procedure the introduction of an aralkyl radical, such as benzyl, and those alkylations presented in discussions of the Friedel -Crafts reaction. Alkylation is of six general types, depending on the linkage effected. 2

3. Substitution for hydrogen in carbon compounds This is nuclear alkylation when aromatic hydrogen is substituted. The carbon of the alkyl is bound to carbon of either aliphatic or aromatic compounds. This is carbon-to-carbon alkylation and includes the alkylations hereto classified under the Friedel -Crafts reaction, e.g., 3

4. Substitution for hydrogen in the hydroxyl group of an alcohol or a phenol Here the alkyl is bound to oxygen, e.g., 4 Substitution for hydrogen attached to nitrogen Here the alkyl is bound to trivalent nitrogen, e.g .

5. Addition of an alkyl halide or an alkyl ester to a tertiary nitrogen compound Here the binding of the alkyl is to the nitrogen, and the trivalent nitrogen is often assumed to be converted to a pentavalent linkage. In reality, the nitrogen possesses four ordinary covalencies and one electrostatic bond, e.g ., 5 Alkyl-metallic compounds Here the alkyl is bound to the metal, e.g., Pb (C 2 H 5 ) 4 and C 6 H 4 ( COONa )S.Hg-C 2 H 5

6. Miscellaneous alkylations In mercaptans , the alkyl group is bound to sulfur ; in the alkyl silanes , it is bound to silicon: n-C 12 H 25 -SH and C 2 H 5 -SiCl 3 While the number of possible different alkyl radicals is very large, the following are the principal ones of technical importance: methyl, ethyl, propyl, butyl, amyl, and hexyl. The introduction of the aralkyl or benzyl radical, as well as the unsaturated allyl group, also is included here, for they are technically important. There are many other miscellaneous alkylations , e.g., involving bonding to lithium, boron, phosphorus, germanium, thallium, selenium, etc. 6

7. Types of alkylation C-alkylation It consists of substitution of alkyl group for hydrogen atom attacked to carbon atom. Paraffinic hydrocarbon and aromatic compound undergo this type of alkylation : 7 O- and S-alkylation By this reaction alkyl group can attached to oxygen or sulfur atom:

8. N-alkylation Replacement of hydrogen atom present in ammonia by alkyl group: R—OH + NH 3 →R-NH 2 + H 2 O N-alkylation is also known as ammonolysis or aminolysis . > Si and Pb alkylation By this reaction organometalic compound is produced. 2 R—Cl + Si → R 2 SiCI 2 8

9. Alkylating agent Olefins The alkylating agents employed most extensively for carbon-carbon alkylations are ethylene, propylene, butylenes , and amylenes ( 2M2B ). Ethylene and propylene are obtained from petroleum-cracking operations. These olefins as well as butylenes and amylenes are also obtained by dehydrogenating ethane, propane, butanes, and pentanes, respectively. In general, the olefins of higher molecular weight, e.g., amylene , and most branched chains, e.g., tert /-butyl derivatives, react more readily than do propylene and ethylene . 9

10. The, olefins tend to polymerize and are, therefore, often employed in the presence of an excess of the other reactant , which may be benzene or isobutane . During the course of the reaction, there is a transfer of hydrogen from the carbon of an aliphatic, aromatic, or hydroaromatic compound to the carbon of the olefin, thereby forming an alkyl radical. In most cases, olefins are used to only a relatively limited extent for alkylations other than the carbon-carbon type, although they are employed to make other alkylating agents such as ethyl chloride and isopropyl hydrogen sulfate. 10

11. Alcohols Methanol and ethanol have long been important alkylating agents , especially for nitrogen bonding . In practically every case, a catalyst is necessary to cause the alkylation to proceed smoothly, and in many instances, this is a mineral acid. Alcohols are used in the manufacture of ethers, such as ordinary ethyl ether, isopropyl ether, carbitol ( 2-(2-Ethoxyethoxy)ethanol ), cellosolve ( 2-Ethoxyethanol ), and naphthyl methyl ether. It should be noted that, although naphthols react with alcohol in the presence of a mineral acid, the aryl alkyl ethers cannot be formed by this reaction in the case of phenols . 11

12. Dimethylaniline is made from aniline and methanol in the presence of a small amount of sulfuric acid , Diethylaniline is prepared from aniline and ethyl alcohol using hydrochloric acid . The ethylation does not proceed so completely as the methylation . The alcohols are employed to effect the replacement of aromatically bound halogen atoms by heating in the presence of an alkali . p- nitrophenetole is synthesized by treating p-nitro chlorobenzene with ethanol o- nitroanisole is synthesized by treating o- nitrochlorobenzene with methanol. The lower alcohols have also been employed extensively for the catalytic vapor phase synthesis of alkylamines and for the alkylation of phenols . 12

13. Alkyl halides The alkyl halides are probably the most commonly used laboratory alkylating agents. and are also employed for certain manufacturing processes whore the alkyl halide is available economically, as in making tetraethyllead . Most of the lower alkyl halides are now abundant and cheap because of recent developments relating to: Addition of HCl to olefins Chlorination of paraffins 13

14. Certain of the lower alkyl halides are so volatile that they must be used in autoclaves. While the chlorides are frequently employed because of their cheapness, other alkyl halides have occasionally given sufficiently higher yields to justify their increased cost. This has been true of alkyl bromides in certain carbon-to-carbon alkylations for the preparation of barbiturates. The tertiary alkyl halides react vigorously and, in the case of tert -amyl chloride, can alkylate phenols without the intervention of a catalyst. Methyl iodide is used in the preparation of such methylated products as Pinaverdol and other sensitizing dyes, which possess pentavalent nitrogen . 14

15. Phenols , such as o- nitrophenol (cf. Acetophenetidine ), are alkylated by heating with alkyl chlorides in the presence of aqueous alkali. Methyl and ethyl bromides or iodides react very smoothly and, in spite of their cost, find application in the field of dyes and medicinal products, e.g., pyramidone and antipyrine , for the preparation of simple and mixed ethers and for the alkylation of phenols and amines. Allyl bromide is employed for making diallylbarbituric acid (Dial ). 15

16. Alkyl Sulfates The alkyl sulfates used most frequently are dimethyl sulfate, methyl hydrogen sulfate, and diethyl sulfate. Sulfates with longer alkyl groups are employed, however, in some cases. Dimethyl sulfate is very toxic and should be handled with care. The alkyl sulfates often give higher yields than the alkyl halides but except for methyl and ethyl sulfates are more expensive . 16

17. The alkyl sulfates are frequently employed for carbon-oxygen type alkylations to obtain compounds such as dialkyl ethers, alkyl aryl ethers, ethyl cellulose, cellosolve , and polyvinyl ethers. Alkyl sulfates have also been employed to alkylate nitrogen atoms for such compounds as caffeine, acriflavine , and diethylaniline . Both alkyl groups of dialkyl sulfates react if the reaction system is practically anhydrous. In the presence of a substantial amount of water, however, only one group reacts. In certain instances, monoalkyl sulfate may be regarded as the active Alkylating reagent as, for example, in the formation of ether from ethyl alcohol and sulfuric acid . 17

18. Aralkyl Halides Benzyl chloride is almost universally used for the introduction of the benzyl group, for instance, in the preparation of benzyl ethylaniline from ethylaniline . In actual practice, the benzyl ethylaniline is usually obtained by treating a mixture of ethylaniline and diethylaniline and fractionating . Benzyl chloride is also used in the preparation of benzyl cellulose. 18

19. Arylsulfonic Alkyl Esters The methyl or ethyl esters of p-toluene-sulfonic acid are used to alkylate certain amines for which alcohols give unsatisfactory yields. Under Codeine (q.v.) is described the use of methyl benzenesulfonate and of methyl toluene sulfonate in the preparation of tetra- alkylammonium compounds. The higher alkyl (C10 and above) esters of p-toluene sulfonic acid have been used as alkylating agents for amines, mercaptans , and thiophenols and for phenolic groups. These higher alkyl esters of p-toluene sulfonic acid are more satisfactory than the sluggish higher alkyl halides and are more easily obtained than the higher alkyl sulfates . 19

20. Alkyl Quaternary Ammonium Compounds These have long been applied in certain special fields, and their further use may well be warranted in many instances. A detailed specific example of this application s given under Codeine, where the preparation and use of phenyltrimethyl ammonium chloride, C 6 H 5 N(CH 3 ) 3 Cl, is described. These quaternary alkyl substances have also been recommended for alkylations leading to phenetole , antipyrine , pyramidone , acriflavine , and caffeine. 20

21. Metallic Alkyl Derivatives The alkyl magnesium halides are frequently expensive for commercial application, but they can be used to make alkyl phenols, to prepare other metal alkyls and silicon alkyls from the corresponding halides, and in many laboratory syntheses. The Grignard synthesis is particularly applicable for making mixed ethers: 21

22. Effect of alkylation Although the effect of alkylation on the properties of organic compounds is sometimes contradictory, there are some general observations that are of value, particularly in the field of motor fuels, medicinals , dyes and solvents . High-octane motor fuels are manufactured in large amounts by alkylation because the desired branched chains are thus economically obtained. 22

23. Schmiedeberg formulated a series of rules regarding the effect of alkyl groups on physiological activity, which May summarizes as follows. In the first place, a close connection exists between "medical" action and the ordinary physical properties of volatility and solubility. In the aliphatic paraffin series, the lower members, which are more volatile, exhibit a narcotic effect that is absent in the insoluble, nonvolatile higher members . 23

24. Alkylation often causes very poisonous compounds to lose this effect; e.g., the nitriles (RCN) and isonitriles are poisonous only when HCN is split off. The action of alkyl radicals can be masked or inhibited by the presence of other radicals; this is illustrated by the behavior of methyl-, dimethyl-, and trimethylamine, which react like ammonia but have no narcotic effect. In this conduct, these amines follow Schmiedeberg's preceding rule and are less toxic than ammonia. The physiological action of alcohols and ethers is ascribed to the nature of the alkyl groups. For the ethers, single or mixed, the effect is due to the presence of the alkyls, each of which acts independently of the other . 24

25. One of the most interesting studies of the effect of various alkyl groups on physiological activity is illustrated by the alkyl derivatives of resorcinol, which are discussed under Hexylresorcinol. The bactericidal action at first increases with the length of the side chain and then diminishes because of decreased solubility of the alkyl resorcinol. Coincident with this increase is found a decrease in toxicity . 25

26. Phenol was the first antiseptic used, and a thorough study of its derivatives has been made. The substitution of a methyl group for the hydrogen in the ring of phenol, forming the cresols, increases the antiseptic action. In the case of the dihydroxy benzenes, the alkyl derivatives of resorcinol have been carefully investigated, and it is found that the entrance of the methyl group into the ring, forming orcinol , depresses the bactericidal power. The influence of higher alkyl groups on the nucleus of the resorcinol molecule is considered under Hexylresorcinol (q.v.). 26

27. Reactors used in alkylation > Tubular reactor 27 After completion of reaction, mass is entered in to separator and alkylated product can be separated from catalyst mixture from upper side of the separator . It is made up of vertical tube containing stirrer for the mixing purpose. Benzene , olefins are introduced from the bottom of the reactor. Reactor contains number of pipes for water circulation which removes the heat, produced during the reaction. Figure: Tubular reactor

28. Cascade of stirred reactor It consist series of reactors which are joined with each other. Proper mixing can be done by stirrer installed in it. Water jacket is also provided through which reaction heat is removed. Benzene , alkylating agents and catalyst mixture are entered from the top of the reactor. Through overflow pipe extra reaction mixture is transferred to second reactor. Followed by separator alkylated product can be separated from catalyst mixture. Catalyst is recycled. 28

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30. > Column type reactor It is made up of single vertical column. Benzene, olefin and catalyst mixture is reacted in the reactor. After completion of reaction alkylated product is separated via separator while catalyst mixture can be reused. 30

31. Sulfuric acid alkylation for petroleum Fresh acids Olefins Isobutane Manufacture 31

32. Despite some disadvantages, such as acid- recovery expense and refrigeration to minimize oxidation, about four fifths of the alkylate produced for motor fuels is based on sulfuric acid as a catalyst. As with HF alkylation, isobutane is alkylated with olefins (other than ethylene), and a flow diagram for such a process is given in Figure. The alkylation is exothermic, and means must be provided to control the temperature and to secure good contact with the reactants and the catalyst. 32

33. This is done by having the sulfuric acid saturated with the isobutane and by feeding the olefins into the system in such a manner to provide the isobutane in excess. This procedure and keeping the temperature down minimize any polymerization of the olefins used. As practically employed, an emulsion of the acid and the isobutane is circulated in large volume past the point of olefin injection . 33

34. Isobutane is charged and is also returned from the deisobutanizer tower. The olefins are injected in small amounts in each of the five successive zones of the reactor, thus maintaining a high ratio of isobutane olefin in the reaction zones with a low isobutane concentration in the effluent. The settling zone of this cascade reactor serves to separate isobutane vapors going to the refrigeration system from the spent and recycle acid, and the effluent. 34

35. The effluent is fractionated in the series of four towers shown in the flow diagram. “ The higher the isobutane concentration, isobutane to olefin ratio, acid to olefin ratio and acid strength, and the lower the reaction temperature, the higher the octane rating of the 338 F end-point material and the lower the acid consumption and the quantity of heavy polymer formed." As the sulfuric acid is contaminated, a portion is withdrawn and replaced by fresh acid. The effluent treater is to remove acidic material . 35

36. Alkyl aryl detergents Raw materials Benzene Dodecene Reaction 36

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38. Figure represents a continuous-flow diagram for manufacturing alkyl aryl detergents. The benzene is alkylated with dodecene catalyzed by AlCb continuously introduced. The temperature is kept at 460C as a maximum, this being controlled by cooling coils or by circulating a part of the benzene alkylate through an external cooler and back to the agitated alkylator . The alkylator is followed by a continuous settler. The benzene is in excess to suppress the formation of isomers ("heavy" alkyl aryl hydrocarbons). 38

39. After separation of the AlCl 3 sludge, the charge goes to a benzene fractionator where the excess benzene is distilled overhead and recycled. The bottoms from the benzene fractionator as shown in Figure are passed the intermediate fractionator, furnishing as overhead a small quantity of a light alkyl aryl hydrocarbon, then to the dodecylbenzene vacuum fractionator. The dodecylbenzene has a boiling range of 275-315 o C and is a blend predominantly of monoalkyl benzenes with a saturated side chain averaging 12 carbons . 39

40. The solubilities of sodium alkyl benzene sulfonates were found to decrease considerably with the length of the alkyl group. The surface tension showed a minimum value for the dodecyl group, however . Naphthalene and phenol and its homologues are also alkylated to produce synthetic detergents which have excellent properties but are more expensive than detergents produced from benzene. 40

41. Ethyl benzene Ethyl benzene has been made in a very large quantity in recent years as a step in the manufacture of styrene for GR-S synthetic rubber and for plastics. The reactions involved are essentially Raw materials Benzene Ethylene Reaction: 41

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43. Gaseous ethylene is passed into the liquid benzene in the presence of a metal chloride catalyst, such as aluminum chloride, at moderate temperatures (40-100 C). The reaction is promoted by hydrogen chloride. A continuous process for ethylbenzene is shown in figure. Anhydrous conditions must prevail; hence the 99+ percent purity benzene is pumped through an azeotropic drying column from which benzene with less than 30ppm water is withdrawn. This benzene is mixed with recirculated "catalyst complex" and fresh catalyst (anhydrous AlCl3 ). The hydrogen chloride which serves as a promoter is furnished indirectly from the ethyl chloride previously mixed with the ethylene (90-95mole % purity). 43

44. The catalyst complex consisting of heavy organics and solid anhydrous aluminum chloride is separated and recycled after mixing with needed fresh AlCl 3 . An approximate composition is: 44   Percent AlCl 3 (combined with hydrocarbons) 26 AlCl 3 (free) 01 High-molecular-weight hydrocarbons 25 Benzene and ethylbenzene 46

45. In the alkylation, the benzene is converted to ethyl- and polymethyl benzenes (Figure a) at 93-94 C and a pressure slightly above atmospheric. As the reaction is exothermic, heat must be removed by evaporation or cooling. The crude alkylate is separated from the catalyst complex, cooled, and washed with water and then with caustic soda solution. This crude product contains 40-45% benzene, 15-20% polymethyl benzene, and a small amount of tar, the rest being ethylbenzene 45 Figure a: Equilibrium relation in the ethylation of benzene at 95 C

46. Separation is effected by a train of conventional columns, with the third one operated at a head pressure of about 50mmHg absolute, furnishing an overhead of the polymethyl benzenes which is charged to the dealkylator-realkylator (using AICh and excess benzene at higher temperature and different catalyst ratio). Ethylbenzene and dimethyl benzene result. 46

47. Tetraethyllead (TEL)[ Pb (C 2 H 5 ) 4 ] Tetraethyllead is widely used for the prevention of knocking in high-compression gasoline engines, 0.04% TEL being as efficient in this respect as 25% benzene. In order to prevent the deposition of lead in the exhaust sections of the engine, 3-parts by volume of TEL are mixed with 2-parts of ethylene bromide (CH 2 BrCH 2 Br) or a mixture of ethylene bromide and ethylene chloride. The ethylene halide converts the lead oxide formed during the combustion into the volatile lead halide. 47

48. Manufacture The mechanism of reaction is not known but the following is a simplified representation of the main reaction. 4PbNa + H 3 C-CH 2 Cl → Pb (C 2 H 5 ) 4 + 3Pb + 4NaCl In the commercial production of tetraethyllead , lead-monosodium alloy is placed in a jacketed autoclave equipped with an agitator; nitrogen and ethyl chloride are then added. As the reaction between the ethyl chloride and the alloy begins, heat is evolved and the pressure of the system begins to rise because of the vapor pressure of the ethyl chloride. 48

49. At optimum reaction conditions, about 65-75 C and about 50-65psi, a cooling medium is introduced to the autoclave jacket and condenser. About this time the autoclave, condenser, liquid-gas separator, and connecting pipes are filled with ethyl chloride vapor. The ethyl chloride in the condenser is condensed and flows back into the autoclave. This condensation causes a decrease in pressure, drawing more vapors into the condenser so that the side reaction gases may be removed . 49

50. As the ethyl chloride is added, the pressure should be about 60-75psi and should not rise over 80psi. This is done by regulating the feed rate . When all the ethyl chloride is added, the pressure will decrease rapidly to 50psi. At this point, the flow of the cooling media is stopped and the reaction is permitted to go to completion . 50

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52. The product from the autoclave reactor is discharged to a batch-type steam still, partly filled with water, where the ethyl chloride and the TEL are distilled off and fractionated from the solution of NaCl and the unreacted lead. The yield of TEL is 85-90% based on sodium used; approximately 10% of the sodium is involved in side reactions, leading to the formation of C 2 H 6 , C 2 H 4 and C 4 H 10 . 52