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CLL 733: Industrial multiphase reactors

ANISLOE AND GUAIACOL

HYDRODEOXYGENATION

REACTION

SUBMITTED BY

SONU KUMAR 2020CH101 33

HARSHIT AGARWAAL 2020CH 10087

Table of Contents

1. Abstract......................................................................................................................................... 2
2. Introduction ................................................................................................................................. 2
3. Literature survey .......................................................................................................................... 3
4. Materials Required................................................................. Error! Bookmark not defined.
5. Different conditions affecting HDO ............................................................................................ 8
6. Future Prospects ........................................................................................................................ 12
7. Conclusion .................................................................................................................................. 13

when processing fast pyrolysis bio-oils at high temperatures. These difficulties include reactor blockage and the formation of heavy tar and coke. In order to overcome these difficulties, scientists have investigated hydroprocessing at lower temperatures (<300°C), which can cut the oxygen concentration of the bio-oil to about 20% and produce a more stable product that can be processed further at higher temperatures. This process has shown to produce hydrocarbons in the petrol range while drastically lowering the liquid product's total oxygen concentration. Reactor clogging is still a worry, though, and trials are only allowed to run for fewer than 100 hours. Chemical Reactions in HDO HDO reactions involve a series of complex steps that cleave C-O bonds and remove oxygen in the form of water. The basic chemical equation for HDO can be represented as follows: R-O-X + H 2 → RH + HX + H 2 O where R represents a hydrocarbon chain, X can be hydrogen (H), another hydrocarbon fragment, or a carbonyl group (C=O), and HX represents the corresponding product after hydrogenation (e.g., H2O, CH4). The specific reaction mechanisms depend on the type of oxygenated compound being processed and the catalyst employed. However, some general pathways are commonly observed:

1. Hydrogenolysis: This pathway involves the cleavage of a C-O bond by hydrogen, resulting in the formation of a C-H bond and a molecule of water. For example, the conversion of ethanol (C2H5OH) to ethane (C2H6) can be represented by: C 2 H 5 OH + H 2 → C 2 H 6 + H 2 O
2. Dehydration: This pathway involves the removal of a water molecule from the feedstock, leading to the formation of an alkene (C=C double bond) or an aromatic ring. For instance, the dehydration of cellulose (C6H10O5) to form furan (C4H4O) can be depicted as: C 6 H 10 O 5 → C 4 H 4 O + 3H 2 O
3. Hydrodecarboxylation: This pathway involves the removal of a carboxyl group (COOH) as carbon dioxide (CO2) along with hydrogenation. For example, the hydro decarboxylation of lactic acid (C3H6O3) to form propane (C3H8) can be written as: C 3 H 6 O 3 + H 2 → C 3 H 8 + CO 2 + H 2 O

These are just a few examples, and the actual reaction network in HDO is often more intricate. Understanding these pathways is crucial for designing catalysts that can selectively promote the desired oxygen removal reactions while minimising unwanted side reactions.

3. Literature Review

3.1 The study looks into how well various catalysts work in the hydrodeoxygenation of anisole and guaiacol, including catalysts based on Ni, Fe, and FCC. The studies were carried out in fixed bed reactors with different catalyst loadings and temperatures. Reactants, hydrogen, and nitrogen made up the feed gas mixture. Argon was added as an internal standard for measurement. The study's main conclusions include a comparison of the catalytic activities of the various catalysts, which indicate that Ni-based catalysts have the most promising hydrodeoxygenation activity. At varied temperatures and reaction periods, the conversion rates of guaiacol over the different catalysts were reported. A Pfeiffer Vacuum Thermostar residual gas analyzer was used to continuously analyse the reactor effluent composition as one of the analytical techniques used in the investigation. The RGA made it easier to quantify the constituents of the reactor effluent by allocating calibration factors to each chemical compound. Overall, the work sheds light on the anisole and guaiacol hydrodeoxygenation reaction pathways over a range of catalysts, emphasising the significance of catalyst choice and reaction conditions for maximising energy recovery and carbon yield in bio-oil conversion processes. Mechanism

4. Phenol Formation : Phenol is a key intermediate in the HDO process of both Anisole and Guaiacol. It is formed through the decomposition of the methoxy group and subsequent deoxygenation steps. 5. Benzene Production: Benzene is the desired end product of the HDO reaction, resulting from the complete deoxygenation of phenolic compounds like phenol and catechol. It is a valuable compound for various industrial applications. 6. Deactivation and Product Distribution: The catalyst deactivation occurs over time on stream due to various factors, such as coke deposition or poisoning of active sites. This can lead to changes in product distribution, with a decrease in fully deoxygenated products and an increase in partially deoxygenated intermediates. 7. Transalkylation Pathway : Apart from the direct deoxygenation process, there is also a possibility of transalkylation, which is the transfer of alkyl groups from aromatic molecules to other aromatic molecules, resulting in the creation of alkylated phenolic compounds and ultimately benzene. The ultimate objective of the HDO mechanism of Anisole and Guaiacol is to selectively deoxygenate phenolic chemicals to produce valuable hydrocarbons like benzene. This is achieved by a sequence of intricate processes that are catalysed by bimetallic catalysts. The importance of temperature and hydrogen pressure in the Ru/HZSM-5 catalyst- mediated selective hydrogenolysis of lignin-derived substituted phenols—that is, in the generation of benzene—was recently brought to light by Zhao et al. While the author's previous research focused on phenol hydrodeoxygenation (HDO) over Ni2P and Ni2P@Pd supported catalysts, cyclohexane and cyclohexanol were the primary byproducts of this process. The current work investigates the effects of varying HDO reaction conditions on product distribution over base metal phosphide catalysts in a fixed bed reactor. The paper discloses the reaction paths for highly selective HDO of phenol, anisole, and guaiacol to benzene by integrating reaction evaluation with physiochemical characterization of the Ni2P catalyst. There are several advantages to using this method instead of traditional ones. These include the capacity to selectively produce cyclohexane or benzene by adjusting reaction conditions, the demonstration of high stability of phosphide-supported catalysts when significant amounts of benzene are present, the identification of intrinsic activation energy to understand the catalytic performance of Ni2P, and the clarification of reaction pathways for the efficient conversion of lignin model compounds into benzene over Ni2P-supported catalysts.

The experimental specifics include the use of analytical-grade materials and the manufacture of Ni2P/SiO2 catalysts using a methodology similar to previous studies. The procedure involved dissolving urea and Ni (NO3)2·6H2O in deionized water and combining them with a precursor solution of tetraethoxysilane (TEOS). After that, it was reduced in an H2 atmosphere, dried, calcined, impregnated with NH4H2PO solution, and passivated at room temperature in a 0.5% O2/N2 flow. The goal of this work is to create high yields of benzene by hydrodeoxygenating (HDO) phenol, guaiacol, and anisole using Ni2P/SiO2 catalysts. The benzene selectivity increased significantly from 5.8% to 60.6% as the reaction temperature rose from 573 K to 673 K. Furthermore, reducing the hydrogen pressure results in a 96.0% yield of benzene from anisole or phenol HDO, suggesting that higher temperatures and lower H2 pressures promote the conversion of anisole to benzene while hindering the hydrogenation of the benzene ring. The determined intrinsic activation energy of 58. kJ mol−1 at 573–673 K highlights the significant catalytic activity of nickel phosphide. The long-term evaluation of anisole HDO reveals that there was very little variation in catalytic performance over a 36-hour period. Guaiacol has a low conversion because of steric effects, but in the same conditions, its HDO exhibits characteristics akin to those of anisole and phenol. This work highlights Ni2P assisted catalysts as efficient substitutes for HDO in industrial applications and offers significant insights for the development of catalysts for the conversion of lignin model compounds into benzene.

were tested on Inconel monoliths coated in carbon nanofibers (CNFs) to increase surface area and anchoring sites for the active species (Pt and Sn). The bimetallic Pt- Sn catalysts showed higher activity and stability when compared to monometallic Pt and Sn catalysts. At 400 degrees Celsius at atmospheric pressure, both Guaiacol and Anisole were deoxygenated. The main byproducts of these feeds on the monolithic catalysts were phenol and benzene. The most effective Pt-Sn catalyst for fully deoxygenating Anisole and Guaiacol was the bimetallic Pt-Sn catalyst based on CNF-coated monoliths. The CNFs increased the surface area of the monoliths, increasing metal absorption and catalytic activity. The study tested the catalysts' reactivity and deactivation with guaiacol and anisole. It was demonstrated that guaiacol was more reactive and produced a faster rate of catalyst deactivation than anisole. As time went on, the distribution of the products shifted, with the main outputs from Guaiacol and Anisole being phenol and benzene, respectively. Methane was produced as a gaseous byproduct of the breakdown of the methoxy group. During the deoxygenation process, methane underwent many chemical conversions to phenol and benzene. In the end, the investigation demonstrated that Pt-Sn catalysts supported on CNF- coated monoliths could efficiently deoxygenate compounds produced from lignin in bio-oil, highlighting the importance of improving catalyst design and surface area in biomass conversion processes.

4.Catalysts and their effect on HDO

The study examined the anisole and guaiacol hydrodeoxygenation (HDO) reaction pathways over a range of catalysts in a fixed bed reactor under variable circumstances. Three types of catalysts were tested: D, which was zeolite-based, C, which was Fe- based, and A and B, which were based on nickel. An overview of each catalyst's impact on the HDO reaction is provided below: Ni-based Catalysts A and B:

• When compared to Fe- and zeolite-based catalysts, both Ni-based catalysts demonstrated higher hydrodeoxygenation activity.

• Under all test conditions, guaiacol was completely converted using Ni-based catalysts A and B.
• As the temperature rose, the selectivity of the products shifted towards those that were entirely deoxygenated (benzene and toluene).
• Higher benzene and toluene selectivity was obtained by increasing the hydrogen concentration in the feed gas.
• As the concentration of hydrogen increased, less coke was formed.
• Compared to the other catalysts examined, the Ni-based catalysts demonstrated greater selectivity for fully deoxygenated products. Fe-based Catalyst C:
  • The conversion of guaiacol was less than that of catalysts based on nickel.
• The main products found were phenol and cresol.
• At lower temperatures, catalyst C produced the most coke. In addition, guaiacol conversion was lower with Zeolite-based Catalyst D than with Ni- based catalysts.
• The main products found were phenol and cresol.• The amount of coke formed was greater at lower temperatures but reduced as the temperature rose. Figure 5. Table of different catalyst in different conditions

On the other hand, partial guaiacol conversion at lower temperatures was seen in Fe- based and FCC catalysts, which demonstrated lesser activity in comparison to Ni- based catalysts. For these catalysts, guaiacol conversion increased with temperature; however, because of their low activity for secondary deoxygenation reactions, they primarily formed mono-oxygenated products. The FCC catalyst showed the highest coke formation at lower temperatures, whereas Ni-based catalysts showed an increase in coke formation with temperature and Fe- based catalysts showed a drop in it. With the exception of catalyst C, methane selectivity generally increased with temperature for all catalysts, suggesting that Ni- based catalysts exhibit greater methanation activity as temperatures rise. Figure 7. Effects of temperature at 60 bar H2, pressure at 200 °C, and solvent at 200 °C, 60 bar H2 on the dispersion of the product and the conversion of anisole across a mic-Ni/ZSM-5:50 mL mixture containing 100 mg of catalyst and 3.0 wt% anisole.

6. Future Prospects

Future prospects for specific catalysts in the HDO of anisole and guaiacol involve advancements in catalyst design, optimization, and application. By exploring innovative synthesis methods, incorporating promoters, designing bimetallic and multifunctional catalysts, modifying support materials, and enhancing catalyst recycling and stability, researchers can unlock the full potential of these catalysts for sustainable biomass conversion and renewable chemical production. Active Site Engineering: Tailoring the active sites of catalysts to enhance their performance in the HDO of anisole and guaiacol is crucial. This may involve controlling the morphology, composition, and surface properties of catalyst nanoparticles to optimize their interaction with reactants and intermediates. Future research could explore novel synthesis methods, such as templating or doping, to create catalysts with well-defined active sites and improved catalytic activity and selectivity. Promoter Addition: Incorporating promoters into catalyst formulations can enhance their catalytic activity and stability. Promoters such as transition metals, metal oxides, or phosphorus compounds can modify the electronic structure or acidity of catalysts, thereby influencing reaction kinetics and product distribution. Future studies may focus on identifying optimal promoter materials and concentrations to maximize the efficiency of anisole and guaiacol HDO catalysts. Bimetallic and Multifunctional Catalysts: Bimetallic catalysts, composed of two different metals, offer synergistic effects that can improve catalytic performance. By combining metals with complementary catalytic properties, such as hydrogenation and deoxygenation activities, bimetallic catalysts can enhance overall reaction rates and selectivity. Future research may explore the design and synthesis of bimetallic catalysts tailored specifically for anisole and guaiacol HDO reactions. Additionally, the development of multifunctional catalysts capable of simultaneously promoting multiple reaction steps, such as hydrogenation and deoxygenation, could streamline the HDO process and improve efficiency. Support Modification: Modifying the support material of catalysts can influence their textural properties, surface area, and acidity, thereby affecting catalytic performance.

The study underscores the importance of catalyst selection, process optimization, and understanding reaction pathways for enhancing bio-oil upgrading efficiency and energy conversion in hydropyrolysis processes. Overall, the research provides a foundation for future studies focusing on catalyst development, process optimization, and the advancement of biomass hydropyrolysis technologies for sustainable biofuel production. By further exploring and refining the HDO reactions of model compounds like anisole and guaiacol, researchers can work towards improving the carbon yield, energy recovery, and overall efficiency of biofuel production processes.

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