Polyphosphoric Acid (PPA)-Modified Bitumen: Disruption of the Asphaltenes Network Based on the Reaction of Nonbasic Nitrogen with PPA

Abstract

Relatively little is known about the effect of polyphosphoric acid (PPA) on bitumen chemistry and structure. In an effort to increase this understanding, the reaction of indole with PPA was studied by Fourier-transform infrared spectroscopy (FTIR). Indole contains a pyrrole functional group very common in bitumen. The results revealed that both the amine and the double bond of indole can be reactive, and that indole concentration affected the reaction pathway. All reactions began with the protonation of the indole double bond, which provided two reactive carbocation intermediates. When the concentration of indole was high, each carbocation coupled with unprotonated indole and two products were obtained. In one case two N-H groups produced a N-N bond, and in the other case two indole double bonds to produced a cyclobutane ring. When the concentration of indole was reduced by dilution, N-H coupling proceeded without double bonds coupling, and a reaction with the PPA anion was found to occur instead. These findings indicate that the effect of PPA in bitumen may be to raise molecular stiffness through N-N bridging, while at the same time disrupt the hydrogen bond network where the N-H function of pyrrole groups is involved and reduce the effective molecular weight of asphaltenes.

Bitumen and Bitumen Modification: A Review on Latest Advances

“…To date many chemical agents have been introduced for the target of bitumen modification, such as: organo-metallic compounds [113,114], sulfur (S) [66,[115][116][117][118][119][120][121], polyphosphoric acid (PPA) [122][123][124], sulfonic acid [125], carboxylic anhydrides [126][127][128], silanes [129,130], thiourea dioxide [131], nanocomposite-modified bitumen [132][133][134][135][136][137][138][139][140], and reactive polymers [141][142][143][144][145][146][147][148][149][150][151][152][153][154][155]. However, from the above-mentioned chemical compounds only a few of them have been used practically.…”

“…Among the different acids that can be used to improve bitumen properties through chemical modification, polyphosphoric acid (PPA) has been studied in numerous papers and patent publications [172][173][174][175][176][177][178][179][180][181][182][183][184][185]. From a chemical point of view PPA is an oligomer of phosphoric acid (H 3 PO 4 ), with no free water, which may have more than 10 repeating units [122].…”

Dynamical characteristics of asphalt binder containing Polyphosphoric acid modifiers

“…PPA modified asphalt binder and mixture have been successfully applied in construction field [4][5][6]. However, the effect of PPA additives on the pavement engineering performances is profound, and the mechanism of PPA affect bitumen is complex.…”

Reactions of Polyphosphoric Acid and Bitumen Model Compounds with Oxygenated Functional Groups: Where Is the Phosphorylation?

“…9 In efforts to verify this postulate and better establish the nature of the reaction between PPA and bitumen, we resorted to the use of bitumen model compounds. 10,11 In working with nitrogenated compounds, it was found that PPA could act as a simple acid to produce ionic-pairs 10 or facilitate intermolecular coupling, 11 and that it could also be a reactive catalyst that produces phosphorylated amines. 11 Here, we report on the reaction of PPA with four oxygenated bitumen model compounds, heated alone or together with PPA ( Figure 1).…”

“…10,11 In working with nitrogenated compounds, it was found that PPA could act as a simple acid to produce ionic-pairs 10 or facilitate intermolecular coupling, 11 and that it could also be a reactive catalyst that produces phosphorylated amines. 11 Here, we report on the reaction of PPA with four oxygenated bitumen model compounds, heated alone or together with PPA ( Figure 1). They are representatives of compounds with phenol, ether, ketone, and carboxylic acid functionalities.…”