3.3 The oxidation products analysis and oxidation mechanism
study
Since the base oils without antioxidants show slight change of color
number, this paper focus on the oil samples with antioxidants. The
oxidation reactions carried out in the paper could divided as four
series experiments (each series has two categories depends on Cu sheet
is applies in experiment or not): the PAO and T501
(P501, the total ions chromatograms shown in Figure 3s),
PAO and Tz516 (P516, the total ions chromatograms shown
in Figure 4s), PAO T501 and Tz516 (P501+516, the total
ions chromatograms shown in Figure 5s), DIOS and T531
(D531, the total ions chromatograms shown in Figure 6s).
The total ions chromatograms shown in SI give a rough sense of the
oxidation products.
After careful analysis, the evidences from Figure 3s-6s show the species
of base oils, antioxidants and Cu sheet catalyst could significantly
change the color number of the oxidized oil samples. There are demands
for identifying the oxidation products’ species and antioxidants to
determine the yield of oxidation products and consumption of
antioxidants. The oxidation products are too many to list, otherwise a
large amount of oxidation chemicals would be resulting in confusion.
After extraction, separation and analysis, the
typical
color materials existing in the oil samples can be distinguished as two
categories: color- related-oxidation-products (CORP) from antioxidants
(CORPA) and CORP from base oil (CORPB).
According to the molecular analysis of the typical color related
oxidation products with or without Cu sheet, the typical CORPA and CORPB
have considerable amount (have larger peak area) and highly repeatedly
shown in their total ions chromatograms could be concluded as follows
(Table 1). The listed chemicals (Table 1) that shown as the typical
color related oxidation products are the representative substances
detected in the oil samples after extraction and separation. It’s
reasonable that the content of the typical CORPA and CORPB might reflect
the color variation of the oxidized oil samples. Generally, the CORPA
mainly have the basic molecular structure that similar to the
antioxidants and the CORPB have longer alkane chain.