Hydrotreating catalysts

Several in-situ catalytic approaches for thermochemical upgrading have been suggested to convert the pyrolysis oil into fungible fuels including catalytic cracking, hydrogenation, and aqueous reforming. Catalytic cracking (equation 2) modifies the decomposition pathways through the use of heterogeneous acid catalysts to partially or fully deoxygenate the pyrolysis oil.

Catalytic Cracking: (2)

Catalytic pyrolysis has been recently studied as a method to produce partially deoxygenated pyrolysis oils. Catalytic cracking does not require external hydrogen and operates at atmospheric pressure, but high levels of coke (unwanted carbon deposits on the catalysts) may be formed during reaction. However, catalyst regeneration is a mature technology in fluid

C6H8O4 + H2 4.6CH12 + 1.4CO2

catalytic cracking (FCC) processes used in the petroleum industry, and could be applied to reduce the coking problem. Partial deoxygenation should improve the stability of pyrolysis oils by reducing the concentration of reactive oxygenated functional groups which improves downstream hydroprocessing. This also reduces coke formation and thereby improves catalyst life.

The type of catalyst used for hydrotreation processes is mainly dependent on the specific reaction and process requirements. In general, catalysts for hydrotreating reactions consist of mixed sulfides of CoMo, NiMo, or NiW supported on high surface area carries, like γ-alumina.

CoMo sulfide catalysts are preferred for hydrodesulphurization (HDS) reactions, while NiMo sulfide catalysts are excellent in hydrodenitrogenation (HDN) and hydrogenation (HYD). NiW sulfide catalysts are very promising for hydrocracking, aromatics hydrogenation at low H2S concentrations and conversion of alkylated dibenzothiophenes, although the high costs of these catalysts make industrial applications less attractive. However. These catalysts are sensitive towards poisoning by sulfur compounds. Interestingly, CoW sulfide catalysts seem somehow not to be a good combination for application in industrial hydrotreation processes. ^{41, 52}

Figure 1-19. The layout for a new method for processing agricultural waste ⁵³

Figure 1-19 shows the layout for a new method for processing agricultural waste and any available biomass into biofuels.⁵³ Researchers at Purdue University are proposing the creation of mobile processing plants that would rove the Midwest to produce the fuels using the technique, called fast-hydropyrolysis-hydrodeoxygenation. Biomass along with hydrogen will be fed into a high-pressure reactor and subjected to extremely fast heating, rising to as hot as 900 degrees Fahrenheit in less than a second. The new method would produce about twice as much biofuel as current technologies when hydrogen is derived from natural gas and 1.5 times the liquid fuel when hydrogen is derived from a portion of the biomass itself. Biomass along with hydrogen will be fed into a high-pressure reactor and subjected to extremely fast heating, rising to as hot as 500 degrees Celsius, or more than 900 °F in less than a second. The hydrogen containing gas is to be produced by "reforming" natural gas, with the hot exhaust directly fed into the biomass reactor. The biomass will break down into smaller molecules in the presence of hot hydrogen and suitable catalysts. The reaction products will then be subsequently condensed into liquid oil for eventual use as fuel. The uncondensed light gases such as methane, carbon monoxide, hydrogen and carbon dioxide, are separated and recycled back to the biomass reactor and the reformer.

1.9.1.2 Nickel loading Loy Yang brown coal char

Traditional desulfurization catalysts sulfidized Ni–Mo/Al2O3 and Co–Mo/Al2O3 have been most frequently used in the above processes.⁵⁴ However, because of a low sulfur content of the starting raw material of plant origin, these catalysts are rapidly deactivated as a result of the reduction and subsequent carbonization of an active component.⁵⁵ Catalysts based on Pd, Pt, Ru, and Rh noble metals have been used in the hydrocracking and hydrodeoxygenation of esters.^{50, 51} However, the use of these catalysts in large scale processes is not promising because they are expensive. Thus, it seems reasonable to develop catalysts free of noble metals for the mild hydrocracking of lipid derivatives of plant origin. As found previously ^56-58, the deoxygenation

of aromatic and aliphatic oxygen containing compounds to corresponding hydrocarbons can be efficiently performed on nickel catalysts.

In this study, the authors used Nickel-loaded Loy Yang brown coal (Ni/LY) char prepared with the ion-exchange method to obtain high quality bio-oil with the use of an inexpensive catalyst in the hydropyrolysis of biomass due to the fact that the catalyst with highly dispersed active site is more effective for biomass conversion. Brown coal or lignite is low rank with high moisture content of around 60%, low heat value and high oxygen content. Therefore, it is hard to use for converted to useful energy. However, it is concluding many outstanding features such as less ash and sulfur content, and especially, including abundant of oxygen-containing function groups such as carboxyl and phenol groups which are available for ion-exchange with metals.⁵⁹ The Schematic diagram of nickel-loaded brown coal char with structure unit of Ni/LY char is showed in Figure 1-20.

Li et al. ⁶⁰ reported that the metallic Ni dispersed well on the support in Ni/LY char with large specific surface area when the catalyst was prepared through ion-exchanged method. The authors ⁶¹ have studied the effects of gas atmosphere and catalyst on bio-oil with relatively low content of oxygen. The results reported that the pyrolysis of rice husk under hydrogen atmosphere using Ni/LY char can reduce the oxygen content of bio-oil and that bio-oil became increasing aromatic as more oxygenated compounds was removed. In this study, the hydropyrolysis of rice husk using inexpensive catalyst was investigated in a fluidized bed reactor.

Rice husk was pyrolyzed in hydrogen atmospheric pressure using Ni/LY char as the fluidizing particle. The effects of catalyst and temperature on the catalytic hydropyrolysis, on product yields, and the composition of bio-oil were investigated. Since the hydropyrolysis does not require high pressure gas atmosphere and a complicated system, these advantages in turn reduce the cost to a great extent.

Figure 1-20. The Schematic diagrams of nickel-loaded brown coal char with structure unit of Ni/LY char Brown coal

Ion-exchange

Ni-loaded brown coal

Ion-exchange