Characterisation of aliphatic chains in vacuum residues (vrs) of asphaltenes and resins using molecular modelling and ftir techniques

Centro de Tecnologia Mineral Ministério da Ciência e Tecnologia Coordenação de Apoio Tecnológico a Micro e Pequena Empresa - CATE

CHARACTERIZATION OF ALIPHATIC CHAINS IN VACUUM RESIDUES (VRS) OF ASPHALTENES AND RESINS USING MOLECULAR MODELLING AND FTIR TECHNIQUES

Rio de Janeiro, RJ, Abril de 2006

Roberto Rodrigues Coelho Ian Hovell Marisa B. de Mello Monte Antonieta Middea André Lopes deSouza

Rio de Janeiro Abril/2006

CT2006-034-00 - Comunicação Técnica publicada na Revista Fuel Processing Technology, 87, 325-333 (2006)

Fuel Processing Technology 87 (2006) 325 – 333 www.elsevier.com/locate/fuproc

Characterisation of aliphatic chains in vacuum residues (VRs) of asphaltenes and resins using molecular modelling and FTIR techniques
Roberto Rodrigues Coelho *, IanHovell, Marisa B. de Mello Monte, Antonieta Middea, Andre Lopes de Souza
Centro de Tecnologia Mineral, CETEM, Avenida Ipe, N- 900, Cidade Universitaria, Ilha do Fundao, Rio de Janeiro, RJ 21941-590, Brazil ˆ ´ ˜ Received 1 February 2005; accepted 1 October 2005

Abstract Asphaltenes are the main components of crude oil, and their chemical structures are very difficult to be analysed andcharacterised. Fourier Transform Infrared Spectroscopy (FT-IR) is one of the available analytical methods for interpreting the structure of asphaltenes and it has been used to characterise functional groups in these compounds. In the present work, FT-IR spectra of alkyl-benzenes, obtained both experimentally and theoretically (by quantum mechanic modelling), were studied using a semi-empirical software AM1.Based on these spectra, the linear relationship between the intensity ratios at 2927 and 2957 cmÀ 1, and the ratios nCH2 / mCH3 from carbon chains of alkyl-benzenes, have been analysed to determine the terminal aliphatic chains of asphaltenes. This methodology was satisfactorily evaluated using molecular average structures found in the literature. Also, using both theoretical IR and experimentalDRIFTS spectra, with deconvolution, the relationship between methylene and methyl groups, which are part of the aliphatic chains, were calculated for three types of Brazilian vacuum residue asphaltenes. D 2005 Elsevier B.V. All rights reserved.
Keywords: Quantum mechanic modelling; Spectroscopy FT-IR; DRIFTS; Deconvolution; Intensity; Vacuum residual; Asphaltene; Resins; Aliphatic chains; Alkyl-benzenes

1. Introduction Asphaltenes are components of crude oil and they are present in all the petroleum processing phases. Due to their precipitation and flocculation properties, these compounds become a serious problem to a variety of processes in the petroleum industry [1]. Vacuum residue (VR) is a product resulting from the refining process where the resulting asphaltenes have a lowhydrogen to carbon (H / C) ratio due to dealkylation and increase in the number of condensed aromatic structures [2,3] with the consequent reduction in branching and aliphatic chain length [2]. The characterisation of molecular average structures of asphaltenes and resins is fundamental to the understanding of their functional properties and their capacity to form aggregates and reverse micellesaccording to the experimental conditions. The elucidation of the average structures of the asphaltenes,
* Corresponding author. E-mail address: coelho@cetem.gov.br (R.R. Coelho). 0378-3820/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2005.10.010

includes [4], besides the inorganic atoms (O, N, S), aromatic groups, Methyl Terminated Aliphatic Chains (MTAC) andmethylene chains [4]: consisting of naphthenic rings, of aliphatic chains that unite the aromatic groups, including the a, h, m, and y methyl terminals. The characterisation of these methylene structures in the average structure of asphaltenes is still an open question. Nomura et al. [5] studied the structural composition of coal using analytical methods such as Ruthenium Ion Catalysed Oxidation...