Effects of paraffin chain size on the oil outflow investigated by a combination of thermal lens and laser-induced fluorescence spectrometries Yuji Nascimento Watanabe a,b,⇑ , Ângelo Marcos Vieira Lima c , Cristina Maria Assis Lopes Tavares da Mata Hermida Quintella b a Federal University of the Reconcavo of Bahia, Center for Teacher Formation, Av. Nestor de Melo Pita, 535, Centro, Amargosa, BA CEP: 45.300-000, Brazil b Institute of Chemistry, Federal University of Bahia, Rua Barão de Geremoabo, 147, Campus Universitário de Ondina, Salvador, BA CEP: 40.170-115, Brazil c Petróleo Brasileiro S.A. Rua Eteno, 2198 Complexo Petroquímico, Camaçari, BA CEP: 42.810-000, Brazil highlights  TLS-LIF-FI coupling was sensitive to variations in fluid composition.  LIF and TLS revealed different information, but complementary, about the sample.  Paraffin molecules tend to increase the fluorescent quantum yield of natural oil probes.  This increase is preferably in the vertically polarized fluorescence component.  Higher paraffin molecules tend to move to the boundary layer during the flow. article info Article history: Received 16 April 2015 Received in revised form 26 July 2015 Accepted 30 July 2015 Available online 10 August 2015 Keywords: Thermal lens spectrometry Laser induced fluorescence Flow injection Crude oil Waxing abstract We investigated the influence of three different paraffin chain sizes (C22, C28, and C36) on the outflow profile of oil dissolved in mineral oil using thermal lens spectrometry (TLS) coupled with laser-induced fluorescence spectrometry (LIFS). The data show that the presence of paraffin molecules leads to an increase in the fluorescent quantum yield of natural oil probes, as observed by the reduction of the pho- tothermal signal and the consequently increased fluorescent emission. We also observe that larger paraf- fin molecules such as C36 tend to move toward the bottom layer during the fluid outflow. This may be associated with the nucleation process and formation of paraffinic deposits in oil ducts. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The oil produced in the Reconcavo of Bahia Bay, Brazil, has a great commercial value owing to the presence of high levels of paraffin. The presence of large paraffin chains increases the oil value, because, when processed, other hydrocarbons can be obtained and sold to raw material industries for more attractive prices. However, what at first glance appears to be an economical advantage becomes a problem for the oil industry, because, under specific temperature and pressure conditions, paraffinic deposits can form [1] both in the tabulation used for raw oil extraction, pre- cluding the exploration of some mature fields, and in the transport ducts, obstructing the flow of the produced material. In the past, several research groups dedicated time and effort to investigate the physicochemical mechanisms that lead to the for- mation of paraffinic deposits, as well as to develop methods to pre- vent the formation of these crystals and the consequent stagnation of oil production and transport [2–5]. Several techniques have been used to determine the properties such as thermal diffusivity, heat capacity, (paraffin) molecular diffusion coefficient, and kinematic viscosity, with the aim of developing alternative methods to char- acterize the types of oil [6–8]. Through a combination of these properties with different chemical compositions such as paraffin http://dx.doi.org/10.1016/j.fuel.2015.07.103 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved. Abbreviations: TLS, thermal lens spectrometry; LIFS, laser-induced fluorescence spectrometry; FI, flow injection; C22, C 22 H 46 ; C28, C 28 H 58 ; C36, C 36 H 74 ; C, mechanical chopper; DF, dichroic filter. ⇑ Corresponding author at: Federal University of the Reconcavo of Bahia, Center for Teacher Formation, Av. Nestor de Melo Pita, 535, Centro, Amargosa, BA CEP: 45.300-000, Brazil. E-mail address: yuji@ufrb.edu.br (Y.N. Watanabe). Fuel 160 (2015) 568–576 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel