| Biomass, due to its low sulfur, low nitrogen, zero emissions of carbon dioxide, renewability, and environmental benefits, has attracted interest as a potential alternative fuel resource. Biomass fast pyrolysis for bio-oil is one of the most potential and promising technologies. However, bio-oil needs to be further improved because of its chemical unstability. At present, the methods of bio-oil upgrading mainly include catalytic hydrogenation, catalytic cracking, catalytic esterification, steam reforming, and emulsifying technology etc. Thereinto, with catalytic hydrogenation bio-oil can be transformed to high-grade liquid fuels with low oxygen content, high heating value, low viscosity, low total acid value and low moisture. This paper focuses on key technologies of bio-oil catalytic hydrogenation for converting bio-oil to liquid hydrocarbon fuels.1. In this paper, the properties of bio-oil are investigated comprehensively, to provide reference data for the following study of upgrading of bio-oil. The main physical and chemical properties of bio-oil are as follows:The density is 1.1-1.2 kg L"1, viscosity is 19-25 mm2 s-1,moisture content is 20-30%, high heat value is 16-18 MJ kg-1, total acid number is 100-120 mg KOH g-1, pH is 2-3. With GPC analysis, the effects of solvent addition on the thermal stability of bio-oil were investigated. The results show that, under the same conditions (150℃,8 h), the polymerization reaction of bio-oil can be effectively inhibited by tetralin (30%) addition. Addition 30% of diesel/isopropanol (2:1) can achieve the same effect. However, when the temperature is increased to 180℃,the molecular weight distribution of bio-oil rapidly removes to above 100000. This shows that the improvement of thermal stability of bio-oil is limited if only addition of solvent into bio-oil. Catalyst is needed to improve the quality of bio oil.2. It is almost impossible that bio-oil is transformed to hydrocarbon liquid fuel by single upgrading process, since the polymerization reaction and coke formation take place easily in the process of upgrading bio-oil. In this paper, two-step catalytic hydrodeoxygenation of pyrolysis oil to hydrocarbon liquid fuels was realized successfully under the improvement of organic solvent. In the first process, various organic solvents were added into bio-oil for overcoming polymerization reaction, while, Ru/C catalyst was used under relatively mild reaction condition (300℃ and 10 MPa) for partial hydrodeoxygenation of bio-oil. The results show that, after reaction at mild condition, the solid coking rate is less than 2%, the oxygen content reducing to below 10%. the properties of bio-oil is improved obviously with calorific value increasing from 17 to 40 MJ kg-1, total acid number decreasing from 118 to 25 mg KOH g-1, moisture content reducing to 1.5%. In the second process, deep hydrodeoxygenation of intermediate products were carried out over traditional hydrogenation catalyst (NiMo/Al2O3) under relatively harsh condition (400℃,13 MPa). The results show that, the properties of deep hydrogenation product are improved significantly, such as, high heat value (HHV) up to 46 MJ kg-1, and low oxygen content less than 0.5%. GC/MS analysis shows that the components of product mainly include C6-27 aliphatic hydrocarbons and aromatic hydrocarbons.3. In order to overcome polymerization and coking of bio-oil, and further study on the role of solvent in the process of upgrading bio-oil. In this paper, we investigated upgrading of bio-oil using supercritical 1-butanol over Ru/C catalyst. The results show that the coke is reduced dramatically from 10% to 0.2%, and HHV increases from 28 to 32 MJ kg-1 compared with the blank experiment without solvent; the properties of upgraded bio-oil are also improved significantly compared with non-critical and subcritical conditions, such as, HHV from 29 to 32 MJ kg-1, oxygen content from 24.7% to 14.5%. GC/MS analysis shows that the components mainly include esters, ethers, alcohols, acids, aldehydes and the contents of acids, aldehydes, ketones, furans are decreased significantly. So the stability of upgraded bio-oil is enhanced significantly. Moreover, the roles of solvent and reaction pathways of bio-oil compositions were studied in the upgrading process. Solvent as reaction medium provides a homogeneous reaction environment to reduce the mass transfer resistance, at the same time, oxygenated compounds of bio-oil are dispersed and diluted. Thus, the polymerization reaction is inhibited significantly. As a reactant, l-butanol can react with acids, aldehydes of bio-oil to form esters and ethers, leading to reduce the corrosions and improve the stability of bio-oil. The main reaction pathways include:esterification, etherification, aldolization, hydrogenation, hydrodeoxygenation, ring opening reaction, demethylation and molecular isomerization reaction.4. According to the characteristics of bio-oil with high acids and water content, as well as high hydrogen consumption in the process of catalytic hydrogenation. With Pd/C and Ni-based reforming catalyst RZ409 as catalysts, Furfural and phenol were selected as model compounds of bio-oil, while formic acid and acetic acid were selected as hydrogen source for study of in situ hydrogenation; and then, the possibility of bio-oil in situ hydrogenation was investigated. The results show that furfural and phenol all can take place in situ hydrogenation reaction over Pd/C and RZ409catalysts with formic acid as a hydrogen source. When acetic acid was selected as a hydrogen source, the in situ hydrogenation reaction of furfural and phenol can be realized only under the RZ409 catalyst. Without additionoal external hydrogen, the composition of bio-oil can take place in situ hydrogenation reaction over Pd/C and RZ409 catalysts.By contrast, RZ409 catalyst has better performance for in situ hydrogenation. |
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