Elsevier

Fuel

Volume 287, 1 March 2021, 119329
Fuel

Full Length Article
Upgrading of bio-oil from thermochemical conversion of various biomass – Mechanism, challenges and opportunities

https://doi.org/10.1016/j.fuel.2020.119329Get rights and content

Abstract

Bio-oil is being investigated as a plausible alternate to petro-crude due to its almost akin composition profile with crude oil. However, the extracted bio-oil from various biomasses revealed an intricate composition with majorly acids, phenols and aldehydes, which confers thermal instability and corrosiveness and bio-oil possesses nitrogen and oxygen heteroatoms. Therefore, handful of research attempts were undertaken to enhance the quality and composition of bio-oil to penetrate the bio-oil into petroleum refinery. With this in view, this article provides a broad and informative discussion on the mechanism of conventional and contemporary upgrading techniques for bio-oil quality improvement. The underlying principle and previous research works on the upgrading methods viz., emulsification, steam reforming, catalytic cracking, zeolite cracking, alcoholysis/esterification, supercritical fluids, hydrogenation, hydrotreating/hydrodeoxygenation, and molecular distillation on enhancing the bio-oil quality was elaborated.

Introduction

Over the years, demand and supply of energy in almost every sector are imbalanced as a result of economic development and population growth. Considering the world’s total final energy consumption by sector, significant increase in the energy consumption by transport sector from 23% in 1971 to 29% in 2017 is noticeable [49]. This high demand of energy (especially oil as dominate fuel) from the transport division are critical to manage in the subsequent years. Also, as per BP statistical review of world energy [100], the energy consumption and carbon emissions were found to increase at a rate of 2.9% and 2% respectively. Such urging energy demand due to inadequate supply from non-renewable fossil fuel sources can be fulfilled by renewable and sustainable biomass sources [4], [98]. In addition, biofuels from renewable sources decreases the level of pollutants in the atmosphere and helps in development of rural areas socio-economically [93]. In the pursuit of parent material for biofuels, algal biomass owing to its inherent properties such as higher biomass productivity, higher oil content, eco-friendly and carbon neutral nature [11], [78], [118]. In general, algae based biofuels consisting of solid, liquid and gaseous fuels are produced through i) lipid extraction followed by transesterification into biodiesel, ii) hydrothermal liquefaction (HTL) for bio-oil production, iii) pyrolysis for biochar, bio-oil and syngas [127] and anaerobic digestion, fermentation for biogas and biohydrogen production.

Among various fuel products from thermochemical processes, bio-oil is obtained through HTL and pyrolysis, which comprises of many non-identical molecules acquired from depolymerization and fragmentation of biological macromolecules [75]. Bio-oil is a highly preferred liquid fuel than solid (biochar) and gaseous (syngas) fuels because of its advantages of having higher energy density and its ease in transport and storage [53]. Examining the physical characteristics, bio-oil is a highly viscous black organic liquid with the pH ranging from 3.5 to 4.2, having typical smoky odour and near equivalent energy value of 70–95% to that of petro-crude [21], [92], [135]. However, the chemical constituents and physical properties of bio-oil slightly vary in quality and quantity depending on the operational conditions, types of biomass and conversion processes. To increase the yield of bio-oil through pyrolysis process, setting up certain operating conditions such as i) less than 3 mm particle size, ii) 0.5–2 s residence time, iii) 400–500 °C temperature would be favourable [82]. Bio-oil is claimed to be carbon neutral or greenhouse gas neutral with traceable or no zero SOX emissions because of the unsubstantial amount of sulfur content in the biomass [92]. Despite the fact of being carbon neutral, bio-oil has also certain limiting elements that are naturally unavoidable during conversion processes like acidic nature, oxidative instability, heteroatom existence, presence of water and oxygen content etc, which makes it unsuitable to be used as fuel [9], [85].

In view of the existing difficulties in utilizing bio-oil due to its invariable composition, upgradation is essential for its use in transportation. The above specified undesirable properties of bio-oil restrict its use in petroleum refinery for transportation application. Therefore, enhancing the quality of bio-oil with prerequisite characteristics is utmost important and in this regard, diverse physical and chemical upgrading methods are being investigated for upgrading bio-oil. These methods focused solely on reducing bio-oil viscosity, corrosiveness, oxygen, nitrogen, ash and water contents, phase separation, polymerization, coking and precipitation. Emerging bio-oil upgradation techniques that are widely practiced are i) Solvent addition for reducing viscosity, iii) Emulsification for improving ignition, iv) Supercritical fluids for increasing HHV, v) Hydrotreating for reducing N, S, O content in bio-oil, vi) Catalytic cracking for significant yield and better quality of bio-oil, vii) Steam reforming of bio-oil for H2 production [77], [135]. Considering the significance of the upgrading methods for bio-oil, this review aims to present all-inclusive upgrading methods for bio-oil improvement using copious literature survey.

Section snippets

Bio-oil composition and limitations

To make bio-crude to use in petroleum refinery, composition of bio-crude need to be analyzed. With this context, ultimate or elemental composition of bio-crude obtained from various algal strains has been given in Table 1. Carbon content of bio-oil occupied a predominant fraction in the vicinity of 63–78%. Oxygen is the second most predominant element that constitutes 7–26%. Further, Hydrogen, Nitrogen, Sulfur content of the bio-crude are in the range of 7.6–11.2%, 0.5–7.6% and 0.4–1.4%,

Bio-oil upgrading- a broad view on methods

Several physical and chemical methods are available for upgrading bio-oil [92]. The high water content and acidity lead corrosiveness of bio-oil when compare with fossil fuels make them not suitable for diesel locomotive engines. The combustion performance can be improved by upgrading process which enhances H/C rate and corrosion reduction. Numerous solutions in petrochemical industries with advanced machining technologies offer broad possibility of enhancement of bio-oil into petro crude level

Conclusion and recommendation

Biomass can be converted into liquid fuel or bio-oil by technical processes, though it is regarded as potential alternatives to petroleum fuels, direct application is limited due to unstable thermodynamic properties. In this review, upgrading techniques namely emulsification, steam reforming, catalytic cracking, zeolite cracking, alcoholysis/esterification, supercritical fluids, hydrogenation, hydrotreating/hydrodeoxygenation, and molecular distillation were discussed in detail on enhancing the

CRediT authorship contribution statement

Tharifkhan Shan Ahamed: Conceptualization, Data curation, Formal analysis, Writing - original draft. Susaimanickam Anto: Conceptualization, Data curation, Validation. Thangavel Mathimani: Supervision, Writing - original draft, writing - review & editing. Kathirvel Brindhadevi: Conceptualization, Data curation, supervision, Validation. Arivalagan Pugazhendhi: Validation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (136)

  • J.G. Dickinson et al.

    Deoxygenation of benzofuran in supercritical water over a platinum catalyst

    Appl Catal B Environ

    (2012)
  • P. Duan et al.

    Catalytic hydrotreatment of crude algal bio-oil in supercritical water

    Appl Catal B Environ

    (2011)
  • J. Feng et al.

    In situ catalytic hydrogenation of model compounds and biomass-derived phenolic compounds for bio-oil upgrading

    Renew Energy

    (2017)
  • M.U. Garba et al.

    Catalytic upgrading of bio-oil from bagasse: Thermogravimetric analysis and fixed bed pyrolysis

    Beni-Suef Univ J basic Appl Sci

    (2018)
  • J.R. García et al.

    Catalytic cracking of bio-oils improved by the formation of mesopores by means of Y zeolite desilication

    Appl Catal A Gen

    (2015)
  • M. Garcia-Perez et al.

    Production and fuel properties of fast pyrolysis oil/bio-diesel blends

    Fuel Process Technol

    (2010)
  • A.R.K. Gollakota et al.

    A review on the upgradation techniques of pyrolysis oil

    Renew Sustain Energy Rev

    (2016)
  • Q. Guan et al.

    Gasification of alga Nannochloropsis sp. in supercritical water

    J Supercrit Fluids

    (2012)
  • Z. Guo et al.

    Separation characteristics of biomass pyrolysis oil in molecular distillation

    Sep Purif Technol

    (2010)
  • Z. Guo et al.

    Separation of acid compounds for refining biomass pyrolysis oil

    J Fuel Chem Technol

    (2009)
  • K.L. Hew et al.

    Catalytic cracking of bio-oil to organic liquid product (OLP)

    Bioresour Technol

    (2010)
  • Y. Huang et al.

    Bio-oil production from hydrothermal liquefaction of high-protein high-ash microalgae including wild Cyanobacteria sp. and cultivated Bacillariophyta sp

    Fuel

    (2016)
  • M. Ikura et al.

    Emulsification of pyrolysis derived bio-oil in diesel fuel

    Biomass Bioenergy

    (2003)
  • M. Lavanya et al.

    Hydrothermal liquefaction of freshwater and marine algal biomass: A novel approach to produce distillate fuel fractions through blending and co-processing of biocrude with petrocrude

    Bioresour Technol

    (2016)
  • H. Li et al.

    Online upgrading of organic vapors from the fast pyrolysis of biomass

    J Fuel Chem Technol

    (2008)
  • S. Li et al.

    Coke formation in the catalytic cracking of bio-oil model compounds

    Environ Prog Sustain Energy

    (2015)
  • B.-J. Lin et al.

    Emulsification analysis of bio-oil and diesel under various combinations of emulsifiers

    Appl Energy

    (2016)
  • L. Liu et al.

    Hydrodeoxygenation of bio-oil model compounds over amorphous NiB/SiO2-Al2O3 catalyst in oil-water biphasic system

    J Fuel Chem Technol

    (2017)
  • N. Lohitharn et al.

    Upgrading of bio-oil: Effect of light aldehydes on acetic acid removal via esterification

    Catal Commun

    (2009)
  • D. López Barreiro et al.

    Hydrothermal liquefaction of microalgae: Effect on the product yields of the addition of an organic solvent to separate the aqueous phase and the biocrude oil

    Algal Res

    (2015)
  • Q. Lu et al.

    Overview of fuel properties of biomass fast pyrolysis oils

    Energy Convers Manag

    (2009)
  • T. Mathimani et al.

    Review on cultivation and thermochemical conversion of microalgae to fuels and chemicals: Process evaluation and knowledge gaps

    J Clean Prod

    (2019)
  • T. Mathimani et al.

    Optimization of direct solvent lipid extraction kinetics on marine trebouxiophycean alga by central composite design – Bioenergy perspective

    Energy Convers Manag

    (2017)
  • X. Miao et al.

    High yield bio-oil production from fast pyrolysis by metabolic controlling of Chlorella protothecoides

    J Biotechnol

    (2004)
  • P.M. Mortensen et al.

    A review of catalytic upgrading of bio-oil to engine fuels

    Appl Catal A Gen

    (2011)
  • S.R. Naqvi et al.

    The role of zeolite structure and acidity in catalytic deoxygenation of biomass pyrolysis vapors

    Energy Procedia

    (2015)
  • J.-Y. Park et al.

    Effects of supercritical fluids in catalytic upgrading of biomass pyrolysis oil

    Chem Eng J

    (2019)
  • L. Pastor-Pérez et al.

    CeO2-promoted Ni/activated carbon catalysts for the water–gas shift (WGS) reaction

    Int J Hydrogen Energy

    (2014)
  • P.D. Patil et al.

    Extraction of bio-oils from algae with supercritical carbon dioxide and co-solvents

    J Supercrit Fluids

    (2018)
  • J. Peng et al.

    Catalytic upgrading of bio-oil by HZSM-5 in sub-and super-critical ethanol

    Bioresour Technol

    (2009)
  • R. Prakash et al.

    Experimental investigation on a diesel engine fueled with bio-oil derived from waste wood–biodiesel emulsions

    Energy

    (2013)
  • C. Rioche et al.

    Steam reforming of model compounds and fast pyrolysis bio-oil on supported noble metal catalysts

    Appl Catal B Environ

    (2005)
  • M. Saber et al.

    A review of production and upgrading of algal bio-oil

    Renew Sustain Energy Rev

    (2016)
  • A.P. Saravanan et al.

    A comprehensive assessment of biofuel policies in the BRICS nations: Implementation, blending target and gaps

    Fuel

    (2020)
  • H. Shafaghat et al.

    Catalytic hydrodeoxygenation of crude bio-oil in supercritical methanol using supported nickel catalysts

    Renew Energy

    (2019)
  • Z. Shuping et al.

    Production and characterization of bio-oil from hydrothermal liquefaction of microalgae Dunaliella tertiolecta cake

    Energy

    (2010)
  • R. Singh et al.

    Optimization of biodiesel synthesis from microalgal (Spirulina platensis) oil by using a novel heterogeneous catalyst, β-strontium silicate (β-Sr2SiO4)

    Fuel

    (2020)
  • S. Alejandro-Martín et al.

    Influence of chemical surface characteristics of ammonium-modified chilean zeolite on oak catalytic pyrolysis

    Catalysts

    (2019)
  • T. Aysu

    Pyrolysis of isochrysis microalgae with metal oxide catalysts for bio-oil production

    J Turkish Chem Soc Sect A Chem

    (2017)
  • Y.-C. Bak et al.

    Production of bio-diesel fuels by transesterification of rice bran oil

    Korean J Chem Eng

    (1996)
  • Cited by (97)

    View all citing articles on Scopus
    View full text