Detergents 127
To calculate the base number of monovalent metal-derived sulfonates, one must use only (w – v) in
Equation 4.2. For divalent metal-derived carboxylate, salicylate, and phenate detergents, Equation 4.3
is to be used.
TBN (mg KOH/g)
()
effective formula weight
2 w , 56 100
(4.3)For monovalent metal salt of this type, the numerator will be w × 56,100. As mentioned earlier, the
percent sulfated ash is the quantity of solid metal sulfate that results when the detergent is treated
with sulfuric acid and the mixture ignited. Theoretical sulfated ash for divalent and monovalent
metals can be calculated using the following equations. Equation 4.4 is for divalent metals, and
Equation 4.5 is for monovalent metals.
Percent sulfated ash
molecular weight of M SO 100
atom w^24
iic weight of metal M effective formula weight (4.4)Percent sulfated ash
molecular weight of M SO 100
ato^05 .w^24
mmic weight of metal M effective formula weight (4.5)4.4 DETERGENT SUBSTRATES
Various organic acids are used to synthesize detergents. These include alkylaromatic sulfonic acids,
alkylphenols, alkylsalicylic acids, fatty carboxylic acids, and alkenylphosphonic acids. Alkylaro-
matic sulfonic acids, such as alkylbenzenesulfonic acids and alkylnaphthalenesulfonic acids, are
made by reacting the respective alkylbenzenes and alkylnaphthalenes with a sulfonating agent. The
alkylaromatic starting materials are made through alkylation of aromatics—benzene and naph-
thalene [29–33]. To make synthetic sulfonates, benzene or naphthalene is fi rst alkylated and then
sulfonated. The alkylating agent is either an alkyl halide or an olefi n. The olefi ns can be α-olefi ns,
internal olefi ns, or olefi n oligomers such as polypropylene and polyisobutylene. An acid catalyst is
usually required. One may choose from many acids. These include mineral acids such as sulfuric
acid and phosphoric acid, Lewis acids such as aluminum chloride and boron trifl uoride, organic
acids such as methanesulfonic acid, and mixtures thereof [32,33]. Some of the inorganic acids such
as sulfuric acid are also available on a solid support, such as Fuller’s earth or silica. Unlike other
catalysts that require neutralization at the end of the reaction, these catalysts just require fi ltration
to remove them. Zeolites and related mixed-metal oxides also enjoy the same advantage as the solid
alkylation catalysts [30,31]. Another class of catalysts, exemplifi ed by Amberlysts®, is aromatic
polymer-derived sulfonic acids [31,34]. Although they have the advantages of being insoluble, hence
easier to remove, and of multiple use, they have the disadvantage of being expensive. It is important
to note that not all catalysts have equal effectiveness in all alkylations.
Alkylaromatic sulfonic acids are derived either from the sulfonation of alkylaromatics, such as
alkylbenzenes and alkylnaphthalenes, or from petroleum refi ning. The alkylbenzenes and alkyl-
naphthalenes are converted into respective sulfonic acids by reacting them with a sulfonating agent.
The acids thus obtained are called synthetic sulfonic acids. Alkylbenzenesulfonic acids are also
available from petroleum refi ning. These are referred to as natural sulfonic acids. Detergents made
from synthetic sulfonic acids are called synthetic sulfonates and those made from natural sulfonic
acids are called natural or petroleum sulfonates.
The steps involved in making synthetic sulfonic acids are shown in Figure 4.3. The degree of
branching in alkylbenzenes and alkylnaphthalenes, commonly called the alkylate, increases as we
go from α-olefi ns to internal olefi ns to olefi n oligomers. More branching of the alkylate implies