EP0674689A1

EP0674689A1 - Middle petroleum distillate composition containing a paraffin settling speed limiter.

Info

Publication number: EP0674689A1
Application number: EP94902004A
Authority: EP
Inventors: Despina Vassilakis; Robert Leger; Alain Forestiere; Jean Gaillard
Original assignee: Elf Antar France; IFP Energies Nouvelles IFPEN
Current assignee: Elf Antar France; IFP Energies Nouvelles IFPEN
Priority date: 1992-12-17
Filing date: 1993-12-08
Publication date: 1995-10-04
Anticipated expiration: 2013-12-08
Also published as: DE69310766D1; CA2146573A1; WO1994013758A1; EP0674689B1; JPH08507315A; NO952393L; KR100287514B1; KR950704453A; NO952393D0; ATE153053T1; NO309729B1; JP3650781B2; FR2699550A1; FR2699550B1; DK0674689T3; DE69310766T2; ES2105607T3; CA2146573C; GR3023626T3

Abstract

A middle petroleum distillate composition containing a major proportion of middle petroleum distillate and a minor proportion of an additive in a sufficient amount to limit the settling speed of paraffins contained in said middle distillate. Said additive consists of a product resulting from a reaction between at least one aliphatic dicarboxylic compound and at least one primary amine functional compound of general formula (I), wherein R<1> is a monovalent saturated aliphatic radical, Z is selected from -NR'- groupings in which R' is a hydrogen atom or a monovalent saturated aliphatic radical, n is an integer between 2 and 4, and m is an integer between 1 and 4; said primary amine functional compound being used in a ratio of 0.3-0.8 mols per mol of said dicarboxylic compound.

Description

MEDIUM OIL DISTILLATE COMPOSITION CONTAINING AN AGENT LIMITING THE SPEED OF SEDIMENTATION OF PARAFFINS.

The invention relates to middle hydrocarbon distillates (fuel oils, gas oils), in which the decantation of paraffins is slowed down by the addition of nitrogenous additives. It also relates to a method for slowing the decantation or sedimentation of paraffins of a middle hydrocarbon distillate by adding a minor proportion of at least one nitrogenous additive.

The petroleum distillates concerned by the invention consist of middle distillates (fuel oils, gas oils) containing paraffins whose distillation range (ASTM D 86-67 standard) is between 150 ° C and 450 ° C. The gas oils considered more particularly have a distillation interval ranging from an initial temperature between 160 ° C and 190 ° C to a final temperature between 350 ° C and 390 ° C.

There are a large number of products on the market recommended to improve the limit filterability temperature and the pour point of petroleum fractions rich in paraffins, such as for example:

- polymers based on long chain olefins

- copolymers based on alpha-olefins,

- ethylene-vinyl acetate copolymers,

- N-acylaminoethyl esters of polymers containing acids, or also:

- halocarbon compounds.

These products act on the kinetic phenomena of crystallization and modify the size of the crystals, allowing the use of the suspension at a lower temperature without clogging of the pipes and filters.

There are also additives on the market which lower the cloud point of petroleum cuts, by modifying the temperature at which the first paraffin crystals appear.

Lowering the cloud point of middle distillates (especially diesel) by an additive, is of great interest to refiners, because it allows without modifying the distillation scheme, to meet the specifications, which are currently evolving in the direction of greater severity. Furthermore, when the paraffin crystals whose formation is caused by cooling have appeared, their natural tendency is to gather by gravity in the lower part. This phenomenon, generally known as sedimentation, causes clogging of pipes and filters and is detrimental to the proper use of middle distillates and in particular diesel at low temperature.

The class of chemical compounds described in patent EP-B-71513 as additives making it possible to lower the cloud point of middle hydrocarbon distillates and having a significant action on the limit filterability temperature and on the flow temperature are also described as having an action on the rate of sedimentation of paraffins formed by cooling of gas oils and other middle distillates.

The additives considered in the present application and defined below are close to the additives described in patent EP-B-71513 and belong to the same class of chemical compounds. Surprisingly, it has been discovered that in the class of chemical compounds described generically in patent EP-B-71513, some of them, which have not been described in this document, have much superior properties in with regard to their action on the sedimentation rate of paraffins and are so-called anti-sedimentation additives which are more effective under more severe test conditions.

Finally, the products recommended in the present invention for their properties, in particular the anti-sedimentation properties mentioned above, also confer on diesel oils and other middle distillates to which they are added, anti-corrosion properties on metal surfaces.

In general, the compositions of middle petroleum distillates according to the present invention can be defined as comprising a major proportion of middle petroleum distillate and a minor proportion sufficient to limit the rate of sedimentation of the paraffins which it contains, at least one additive consisting of a product with an average molecular weight of approximately 300 to 10,000 resulting from the reaction of at least one aliphatic dicarboxylic compound chosen from anhydrides maleic and alkyl maleic, alkenyl succinic anhydrides having from 10 to 32 carbon atoms in the alkenyl radical, dicarboxylic acids and the corresponding light alkyl diesters, and at least one compound having a primary amino function corresponding to the general formula (I ):

where R ¹ represents a monovalent saturated aliphatic radical having from 1 to 32 carbon atoms, Z is chosen from the groups -NR'- in which R 'represents a hydrogen atom or a monovalent saturated aliphatic radical having from 1 to 32 atoms carbon, n is an integer from 2 to 4, m is an integer from 1 to 4; said compound with primary amine function being used in a proportion of 0.3 to 0.8 mole per mole of said dicarboxylic compound and said reaction being carried out at a temperature of 120 to 200 ° C, and being continued until the end of the release volatile products consisting of water and / or alcohol formed during the reaction. Most often the reaction is continued for a time sufficient to form the theoretical amount of volatile products consisting of water and / or alcohol, which are removed.

The present invention also relates to a method for reducing the rate of sedimentation of paraffins contained in a mixture of hydrocarbons comprising the introduction into this mixture of hydrocarbons of a minor amount sufficient to reduce the rate of sedimentation of paraffins, at least at least one additive consisting of a product with an average molecular weight of approximately 300 to 10,000 resulting from the reaction of at least one aliphatic dicarboxylic compound chosen from maleic and alkylmaleic anhydrides, alkenyl succinic anhydrides having from 10 to 30 carbon atoms in the alkenyl radical, the dicarboxylic acids and the corresponding light alkyl diesters, and of at least one compound with a primary amino function corresponding to the general formula (I):

in which Z, R1, n and m have the definition given above, said compound with primary amine function being used in a proportion of 0.3 to 0.8 mole per mole of said dicarboxylic compound and said reaction being carried out at a temperature from 120 to 200 ° C, and being continued until the end of the evolution of volatile products consisting of water and / or alcohol formed during the reaction.

The compounds of formula (I) can consist of polyamines derived from saturated aliphatic amines corresponding to the formula:

which corresponds to the general formula (I) in which Z represents the group -NH-; m can have a value of 1 to 4 and n a value of 2 to 4, preferably ma a value of 2 to 4 and n is equal to 3; R ¹ is preferably a linear monovalent saturated aliphatic radical having from 12 to 32 carbon atoms and more particularly from 16 to 24 carbon atoms.

As specific compounds, there may be mentioned: N-dodecyl diamino-1, 3 propane, N-tetradecyl diamino-1, 3 propane, N-hexadecyl diamino-1, 3 propane, N-octadecyl diami no-1, 3 propane, N-eicosyl diamino-1, 3 propane, N-docosyl diamino-1, 3 propane, N-hexadecyldipropylene triamine, N-octadecyl dipropylene triamine, N-eicosyldipropylene triamine and N-docosyldipropylene triamine. Most advantageously, N-docosyl-, N-eicosyl-, N-octadecyl, N-hexadecyl- or N-dodecyl-diamino 1, 3 propane are used, and preferably tripropylene d ipropylenes such as N-hexadecyl- or N-octadecyl-dipropylene-triamine.

The compounds of formula (I) can also consist of polyamines corresponding to the formula:

which corresponds to the general formula (I) in which Z represents the group -NR ² R ³ where R ² and R ³ , identical or different, have the same definition as R ¹ and are each preferably an alkyl radical having from 1 to 24 and preferably from 6 to 24

2 3 carbon atoms, R and R containing both of them preferably from 12 to 32 carbon atoms; n has a value of 2 to 4, preferably 3 and m a value of 1 to 4, preferably of 2 to 4.

As specific compounds, there may be mentioned N, N-diethyl-diamino-1, 2 ethane, N, N-diisopropyldiamino-1, 2 ethane, N, N-dibutyl-diamino-1, 2 ethane, NN- diethyl-diamino-1, 4 butane, N, N-dimethyl-diamino-1, 3 propane, NN-diethyl-diamino-1, 3 propane, N, N-dioctyl-diamino-1, 3 propane, N, N-didécyldiamino- 1, 3 propane, N, N-didodécyl-diamino-1, 3 propane, N, N-ditétradécyl-diamino- 1, 3 propane, N, N-dihexadécyldiamino-1, 3 propane , N, N-dioctadécyldiamino- 1, 3 propane, and as preferred specific compounds N, N-didodécyldipropylène triamine, N, N-ditétradécyl-dipropylène triamine, N, N-dihexadécyldipropylène triamine and N, N-dioctadécyldipropylène triamine.

It should be understood that, without departing from the scope of the invention, it is possible to bring into play one or more compounds corresponding to formula (I).

The dicarboxylic compounds on which the condensation of a compound of formula (I) is carried out as described above, are more particularly chosen from maleic anhydride, alkylmaleic anhydrides, for example methylmaleic anhydride (or citraconic) or also from alkenyl succinic anhydrides, for example those obtained by the action of at least one olefin, preferably linear, (for example having 10 to 32 carbon atoms) on maleic anhydride. There may be mentioned more specifically n-octadecenyl succinic anhydride or dodecenyl succinic anhydride. It is of course possible to use mixtures of two (or more) of these compounds Instead of the anhydrides mentioned above, it is possible to use the corresponding dicarboxylic acids, as well as the light alkyl diesters thereof (such as, for example, methyl, ethyl, propyl and butyl esters) .

The compounds with a primary amine function of formula (I) are usually used in an amount of 0.3 to 0.8 mole, preferably from 0.4 to 0.7 mole, per mole of dicarboxylic compound.

The condensation of the compounds of formula (I) on the dicarboxylic compounds (for example dicarboxylic acids, esters, or preferably anhydrides) can be carried out without solvent, but preferably a hydrocarbon solvent with a boiling point of between 70 ° C. will be used. and 250 ° C., more particularly consisting of an aromatic or naphtheno-aromatic hydrocarbon, for example: toluene, xylenes, diisopropylbenzene or alternatively a petroleum fraction having the appropriate distillation range.

To prepare the additive compositions considered in the invention, it is possible in practice to proceed as follows: in a reactor containing the dicarboxylic compound, and maintaining the temperature between 30 ° C. and 80 ° C., little is introduced at little the compound of formula (I). The temperature is then raised to 120 ° C-200 ° C by eliminating the volatile products formed (water or alcohols), either by entrainment with a stream of inert gas, or by azeotropic distillation with the chosen solvent; the dry matter concentration is for example 40 to 70%, most often close to 60%.

The reaction time, after addition of the reagents, is for example between 1 and 8 hours and preferably between 3 and 6 hours.

The additives considered in the invention are particularly advantageous for slowing down the settling of paraffins in middle petroleum distillates (in particular gas oils).

Although the mechanism of action of these additives on the rate of sedimentation of paraffin crystals in middle distillates has not yet been clearly elucidated, a marked slowing down of the decantation of paraffins in the middle distillates treated with these additives, when added at concentrations ranging for example from 20 to 2000 grams per tonne (g / t) of middle distillate. Preferred concentrations range from 100 to 2000 g / t.

In addition, it is remarkable to note that the additives considered in the invention which have the property of inhibiting the sedimentation of n-paraffins in middle distillates at rest, also inhibit the corrosion of metal surfaces in contact with these distillates.

In the concentration range of the additive, from 20 g to 2000 g / t, it is possible to observe a reduction in the proportion of sedimented paraffins of up to 100% under the conditions of the tests described in the patent EP- B-71513 but also under more severe temperature conditions of 5 to 10 ° C. In addition, a clear anticorrosion effect is observed in particular on ferrous metals.

To formulate the middle distillate compositions of the invention, it is possible to add the additives directly to the middle distillate by a simple mixing operation.

It is however often advantageous to introduce them in the form of "mother solutions" prepared beforehand in the solvents already mentioned above. The "mother solutions" can contain, for example, from 20 to 60% by weight of additives.

The compositions of middle petroleum distillates (for example gas oils) of the invention may also contain other additives, in particular other additives intended to improve the cold behavior, for example additives lowering the pour point and additives lowering the filterability limit temperature of middle distillates (for example diesel).

The present invention also relates to the use of at least one compound of formula (I):

in which Z, R ¹ , n and m have the definition given above, in a proportion of 20 to 2000 parts per million of the total weight of the composition, as an additive reducing the rate of sedimentation of paraffins in a hydrocarbon composition consisting of a major proportion of a middle hydrocarbon distillate containing paraffins. It also relates to the use of at least one compound of general formula (I) above in a proportion of 20 to 2,000 parts per million of the total weight of the composition, as an anticorrosion additive in a hydrocarbon composition consisting of a major proportion of a middle hydrocarbon distillate containing paraffins.

In this context, it is advantageous to use at least one compound of formula (I) consisting of at least one polyamine having one of the following formulas:

Rl -NH - [(CH) n-NH-] _m H

in which R1, R2, R3, n and m have the definition given above. The following examples illustrate the invention and should in no way be taken as limiting.

Example 1 (comparative)

2.700 g of a commercial polyamine (containing a mixture formed of approximately 27% palmityl 1,3-propane diamine and approximately 70% stearyl 1) are introduced into a 20 I reactor fitted with good stirring. 3 propanediamine, said mixture having an equivalent of 370 g for a primary amino group) and 2,700 g of xylene, the amine is dissolved at 50 ° C. and then cooled to 30 ° C., a solution of 699 g of maleic anhydride dissolved in 1.050 g of xylene while maintaining the internal temperature at 40 ° C; the addition lasts one hour, then heated for 3 hours at the reflux temperature of xylene, the internal temperature of the reactor is 144 ° C., 157 g of water are removed by distillation corresponding to 128 g of reaction water and 29 g of water contained in the starting amine; at the end of the reaction, 500 g of xylene are distilled to obtain a 50% by weight solution of the additive I in xylene.

Additive I was analyzed after evaporation of the solvent. Its number-average molecular mass, measured by tonometry, is 1800. The infrared spectrum in thin layer less than the im eid e x ist nce at 1700 e t

1 17. 80 cm ^-1 , secondary amide at 1635 and 1560 cm ^' and secondary amide at 3300 cm ^" 1

. This additive is that described in Example 1 of patent EP-B-71513.

Example 2

Example 1 is repeated using the amine N-stearyldipropylene triamine in a proportion of 0.75 mole of amine per mole of anhydride. The reactor is kept at the reflux temperature of xylene for 3 hours 30 minutes, at the end of which there is no longer any elimination of water. The amount of xylene is adjusted to obtain a 50% by weight solution of the additive II in xylene.

Additive II was analyzed after evaporation of the solvent. Its number average molecular mass measured by tonometry is 1600. The infrared spectrum in thin layer shows the existence of bands imides at 1700 and 1780 cm ^{- 1} , secondary amide at 1635 and 1560 cm - ¹ and secondary amine at 3300 cm ' ¹ .

Example 3

Example 2 is repeated using the amino N-stearyldipropylene triamine and the anhydride N-octadecenyl succinic anhydride in a proportion of 0.70 mole of amine per mole of anhydride. The reactor is maintained at the reflux temperature of xylene for 4 hours at the end of which there is no longer any removal of water. The amount of xylene is adjusted to obtain a 50% by weight solution of the additive III in xylene.

Additive III was analyzed after evaporation of the solvent. Its number average molecular mass measured by tonometry is 1700. The infrared spectrum in thin layer shows the existence of bands i mides at 1700 and 1780 cm ^{- 1} , secondary amide at 1365 and 1560 cm ^{- 1} and secondary amide at 3300 cm ^"1 .

Example 4

Example 2 is repeated, using the amine N-stearyldipropylene triamine and the anhydride N-octadecenyl succinic anhydride in a proportion of 0.5 mole of amine per mole of anhydride. The reactor is maintained at the xylene reflux temperature for 3 hours, at the end of which there is no longer any removal of water. The amount of xylene is adjusted to obtain a 50% by weight solution of the additive IV in xylene.

Additive IV was analyzed after evaporation of the solvent. Its number average molecular mass measured by tonometry is 1650. The infrared spectrum in thin layer shows the existence of bands i mides at 1700 and 1780 cm ^"1 , secondary amide at 1365 and 1560 cm ^{- 1} and amine secondary at 3300 cm ^{- 1} .

Example 5

The inhibitory action of the additive I and of the additives II to IV according to the invention is tested on the sedimentation of the n-paraffins crystallizing in two commercial winter gas oils, the characteristics of which are indicated in table I below:

BOARD

These commercial gas oils contain 500 ppm by weight of a pour point improver of the ethylene vinyl acetate (EVA) type.

Two 250 cm test tubes are filled with No. 1 diesel fuel. In the first test tube, no additive is introduced. In the second test tube, 0J% by weight of one of the additives is introduced. The 2 test pieces are hermetically sealed, then left to stand in a cold room at -15 ° C for 24 hours. After 24 hours, the degree of sedimentation of the paraffins that have precipitated is expressed by the volumes of the different phases (quantity of sediment, phase slightly cloudy, cloudy phase, clear or limpid phase) in the test tube.

The following results are noted given in Tables II, IV and VI below.

The same test is carried out with diesel No. 2, at -20 ° C for 24 hours. The results are shown in Tables III, V and VII below.

The quality of the upper phase is decisive for the anti-sedimentation efficiency of the product: when the upper phase is cloudy, a large proportion of paraffins has remained in suspension. When this phase is clear, almost all of the paraffins have sedimented. With a slightly cloudy upper phase, the anti-sedimentation efficiency is intermediate.

If we now consider the quantity of sedimented paraffins: the more the dewaxed upper phase, the denser the sedimented phase, which makes pumpability of diesel difficult. The quantities of sedimented paraffins can only be compared if they are of equivalent density, that is to say if the upper phases are of the same nature.

Tables II and III relate to the results obtained with additive I. Tables IV and V relate to the results obtained with additive II Tables VI and VII relate to the results obtained with additives III and IV.

TABLE II

BOARD

It is found that the additive I exemplified in EP-B-71513 for its anti-sedimentation efficiency at -10 ° C is less effective at -15 ° C and not effective at -20 ° C.

TABLE IV

TABLE V

Test tube N ° 1 Test tube N ° 2

Commercial diesel N ° 2 as is Commercial diesel N ° 2 -t-additive II

60 ml sedimented 80 ml sedimented

+ +

190 ml clear 170 ml slightly cloudy

The anti-sedimentation efficiency of additive II is higher than that of the additive, in particular at -20 ° C. TABLE VI

TABLE VII

A better dispersion of paraffins is obtained with additive III compared to additive 11, but the ratio of reagents is an important factor for the anti-sedimentation efficiency of the additives: additive IV manages to ensure the best homogeneity of the diesel fuel in cold storage.

Example 6

The anti-corrosion effect of the additives I to IV described above is tested.

The additive is used in the two gas oils No. 1 and No. 2 already described above at a concentration of 0.01% by weight.

The corrosion test consists in studying corrosion by synthetic seawater, of cylindrical steel or polished iron specimens according to standard ASTM D 665 modified as follows: the temperature is 32.2 ° C and the duration of 20 hours. The two non-additive diesel no. 1 and no. 2 give rusty test pieces at 100% of their surface and the two gas oils containing 0.01% by weight of one of the additives described above give 0% intact test pieces. rust.

Claims

1 - Composition of medium petroleum distillate comprising a major proportion of medium petroleum distillate and a minor proportion, sufficient to limit the rate of sedimentation of the paraffins contained in said medium distillate, of at least one additive consisting of a product of molecular mass average of approximately 300 to 10,000 resulting from the reaction of at least one aliphatic dicarboxylic compound chosen from maleic and alkylmaleic anhydrides, alkenyl succinic anhydrides having from 10 to 32 carbon atoms in the alkenyl radical, dicarboxylic acids and diesters corresponding light alkyls, and at least one compound with a primary amino function corresponding to the general formula (I):

where R ¹ represents a monovalent saturated aliphatic radical of 1 to 32 carbon atoms, Z is chosen from the groups -NR'- in which R 'represents a hydrogen atom or a monovalent saturated aliphatic radical having from 1 to 32 atoms of carbon, n is an integer from 2 to 4, m is an integer from 1 to 4; said compound with primary amine function being used in a proportion of 0.3 to 0.8 mole per mole of said dicarboxylic compound and said reaction being carried out at a temperature of 120 to 200 ° C, and being continued until the end of the release volatile products consisting of water and / or alcohol formed during the reaction.

2 - Composition according to claim 1 in which the compound with primary amino function (I) consists of at least one polyamine of formula

R ¹ -NH ι * j <(αCHy - NNHH] | H m which corresponds to the general formula (I) in which Z represents the group -NH-, my a value of 1 to 4, n a value of 2 to 4, and R ¹ is a linear monovalent saturated aliphatic radical having from 12 to 32 carbon atoms.

3 - Composition according to claim 1 in which the compound with primary amino function (I) consists of at least one polyamine of formula

which corresponds to the general formula (I) in which Z represents the group -NR ² R ³ where R ² and R ³ , identical or different, are each an alkyl radical having from 1 to 24 carbon atoms, na has a value of 2 at 4 and m a value from 1 to 4.

4 - Composition according to one of claims 1 to 3 wherein the dicarboxylic compound is selected from the group formed by maleic anhydride, methylmaleic anhydride, n-octadecenyl succinic anhydride and dodecenyl succinic anhydride.

5 - Composition according to one of claims 1 to 4 wherein the reaction is carried out in a hydrocarbon solvent with a boiling point between 70 ° and

250 ° C and comprises mixing, at a temperature of 30 to 80 ° C, said dicarboxylic compound with said compound of formula (I) and heating the resulting mixture at a temperature of 120 to 200 ° C, for a period of 1 at 8 o'clock.

6 - Composition according to one of claims 1 to 5 wherein the middle distillate containing paraffins is a middle distillate having a distillation range between 150 and 450 ° C and preferably a fraction of diesel having a distillation range ranging from an initial temperature of 160 to 190 ° C to a final temperature of 350 to 390 ° C.

7 - Composition according to one of claims 1 to 6 wherein the proportion of said additive is from 20 to 2000 grams per ton (g / t) of middle distillate. 8- Method for reducing the rate of sedimentation of paraffins contained in a mixture of hydrocarbons comprising the introduction into this mixture of hydrocarbons of a minor amount sufficient to reduce the rate of sedimentation of paraffins of at least one additive consisting of a product of average molecular weight of approximately 300 to 10,000 resulting from the reaction of at least one aliphatic dicarboxylic compound chosen from maleic and alkylmaleic anhydrides, alkenylsuccinic anhydrides having from 10 to 32 carbon atoms in the alkenyl radical, dicarboxylic acids and the corresponding light alkyl diesters, and at least one compound with a primary amino function corresponding to the general formula (I):

where R ¹ represents a monovalent saturated aliphatic radical of 1 to 32 carbon atoms, Z is chosen from the groups -NR'- in which R 'represents a hydrogen atom or a monovalent saturated aliphatic radical having from 1 to 32 atoms of carbon, n is an integer from 2 to 4, m is an integer from 1 to 4; said compound with primary amine function being used in a proportion of 0.3 to 0.8 mole per mole of said dicarboxylic compound and said reaction being carried out at a temperature of 120 to 200 ° C, and being continued until the end of the release volatile products consisting of water and or alcohol formed during the reaction.

9 - Composition of middle hydrocarbon distillate containing a major proportion of a middle hydrocarbon distillate and a proportion of 20 to 2,000 parts per million of the total weight of said composition of at least one compound of general formula (I)

R ¹ -Z [- (CH ₂ ) n-NH-] _m H

wherein R ¹ , Z, n and m are defined as in claim 1, as an additive for reducing the rate of sedimentation of paraffins. 10 - Composition of middle hydrocarbon distillate containing a major proportion of middle hydrocarbon distillate and a proportion of 20 to 2,000 parts per million of the total weight of said composition of at least one compound of general formula (I)

R ¹ -Z [- (CH ₂ ) n-NH-] _m H

wherein R ¹ , Z, n and m are defined as in claim 1, as an anticorrosive additive.

11 - Composition according to one of claims 9 and 10 in which the compound of general formula (l) consists of at least one polyamine having one of the formulas below:

in which ma a value of 1 to 4, n a value of 2 to 4, R1 is a linear monovalent saturated aliphatic radical having from 12 to 32 carbon atoms and R2 and R3, identical or different, are each an alkyl radical having 1 to 24 carbon atoms.