Question

Calculate the amount \((\mathrm{kg})\) of \(\mathrm{H}_{2}\) needed per \(\mathrm{kg}\) product for complete deoxygenation of pyrolysis oil and discuss the economics of the process based on this number.

Short answer

Short Answer: About 0.02976 kg of hydrogen is needed per kg of product for the complete deoxygenation of pyrolysis oil. The economic viability of this process depends on the cost of hydrogen production, which can range from \(1.50 - \)6.00 per kg of hydrogen. Therefore, the hydrogen cost for deoxygenating 1 kg of pyrolysis oil could range from \(0.04464 to \)0.17856. The overall economics should be evaluated by taking into account the price of the final product and other costs involved in the production process. Moreover, the future development and commercialization of renewable hydrogen production technologies might lower the cost of hydrogen production, improving the economics of this process.

Step-by-step solution

Determine the stoichiometric ratio for the reaction

Pyrolysis oil typically has a composition containing oxygen, carbon, and hydrogen. For this exercise, we will assume that all oxygen in pyrolysis oil is present as C-OH (hydroxyl) groups. The overall reaction for complete deoxygenation can be simplified as: Oxygen in the form of C-OH + H2 -> H2O + Carbon residue Since we are dealing with pyrolysis oil, empirical formulae can be used to represent its composition. A common empirical formula is CH1.8O0.27, representing the oxygen content of 27% in the oil. We will now balance the equation: CH1.8O0.27 + H2 -> 0.27H2O + CH1.53 The balanced equation has a stoichiometric ratio of 1 mole pyrolysis oil to 0.27 moles of H2.

Calculate the molar mass of pyrolysis oil and hydrogen

To convert the stoichiometric ratio into a mass ratio, we need the molar mass of pyrolysis oil and hydrogen. Molar mass of H2 = 2 g/mol (since there are 2 hydrogen atoms per H2 molecule) Molar mass of CH1.8O0.27 (pyrolysis oil) = (12.01 × 1) + (1.01 × 1.8) + (16 × 0.27) = 12.01 + 1.818 + 4.32 = 18.148 g/mol

Calculate the mass ratio of hydrogen to pyrolysis oil

Using the balanced equation from Step 1 and the molar masses from Step 2: mass of H2 per 1 mol pyrolysis oil = 0.27 mol × (2 g/mol) = 0.54 g mass of pyrolysis oil = 18.148 g Thus, the mass ratio of hydrogen to pyrolysis oil is: 0.54 g H2 / 18.148 g pyrolysis oil

Calculate the amount of hydrogen needed per kg product

To calculate the amount of H2 needed per kg of product, we will use the mass ratio calculated in step 3: (0.54 g H2 / 18.148 g pyrolysis oil) * (1 kg pyrolysis oil / 1000 g) = (0.54 / 18.148) kg H2 = 0.02976 kg H2 Therefore, 0.02976 kg of hydrogen is needed per kg of product for complete deoxygenation of pyrolysis oil.

Discuss the economics of the process

Based on our calculations, 0.02976 kg of hydrogen is needed per kg of product to completely deoxygenate pyrolysis oil. The cost of hydrogen production varies depending on the method used, but it is generally in the range of \(1.50 - \)6.00 per kg of hydrogen. Thus, the hydrogen cost for deoxygenating 1 kg of pyrolysis oil could range from \(0.04464 to \)0.17856. This cost should be compared with the price of the final product and other costs involved in the production process to determine the economic viability of this deoxygenation process. It is important to consider that the cost of hydrogen production may decrease in the future as renewable hydrogen production technologies are developed and commercialized, which may improve the economics of this process.

Key concepts

Pyrolysis Oil

Pyrolysis oil is a type of bio-oil derived from the thermal decomposition of organic materials, such as biomass, in the absence of oxygen. This process is called pyrolysis. The resulting liquid, known as pyrolysis oil, is a renewable energy source that can be used to produce biofuels and biochemicals.
Pyrolysis oil is composed of various chemical compounds, including oxygen, carbon, and hydrogen. The presence of oxygen in the form of functional groups like hydroxyl (C-OH) affects its energy content and stability. For chemical reactions or further refinement, it is often essential to remove this oxygen content through processes like deoxygenation.
By utilizing pyrolysis oil, industries aim to transition towards more sustainable energy solutions. It not only has the potential to replace fossil fuels but also helps in reducing waste by converting organic material into valuable products.

Stoichiometric Ratio

Understanding the stoichiometric ratio is crucial for chemical reactions, including the deoxygenation of pyrolysis oil. A stoichiometric ratio is a fixed ratio between reactants and products in a balanced chemical equation. It ensures that all reactants are consumed without any leftover atoms or molecules, optimizing the efficiency of the reaction.
In our scenario, the stoichiometric ratio is established by balancing the deoxygenation reaction equation: CH1.8O0.27 + H2 → 0.27H2O + CH1.53. This equation informs us that 0.27 moles of hydrogen (H2) are required per mole of pyrolysis oil to complete the deoxygenation.
Achieving the correct stoichiometric ratio in any chemical process is vital. It minimizes reactant wastage and ensures the desired output is obtained, highlighting its importance in industrial chemical processes.

Molar Mass Calculation

Molar mass calculation converts the stoichiometric ratio from a molar basis to a mass basis, making it more practical for real-world applications. The molar mass is the sum of the atomic masses of all atoms present in a molecule and is expressed in grams per mole (g/mol).
To perform the molar mass calculation for our scenario, we first determine the molar mass of hydrogen (H2), which is 2 g/mol, since hydrogen consists of two atoms with an atomic mass of approximately 1 g/mol each.
Next, the molar mass of pyrolysis oil with an empirical formula CH1.8O0.27 is calculated by considering:

• 1 Carbon (C) atom: 12.01 g/mol
• 1.8 Hydrogen (H) atoms: 1.01 x 1.8 = 1.818 g/mol
• 0.27 Oxygen (O) atoms: 16.00 x 0.27 = 4.32 g/mol

Adding these gives a molar mass of 18.148 g/mol for pyrolysis oil. This calculation is essential for adjusting chemical processes and determining material needs accurately.

Economics of Hydrogen Production

The economics of hydrogen production are a key consideration when evaluating processes such as the deoxygenation of pyrolysis oil. Hydrogen can be produced through various methods, including steam methane reforming, electrolysis, and biomass gasification. The method chosen significantly impacts the cost.
Typically, the cost of hydrogen production can range from around $1.50 to $6.00 per kilogram, depending on the production technology and scale. In our exercise, we require 0.02976 kg of hydrogen per kg of pyrolysis oil, resulting in a cost range for hydrogen alone from $0.04464 to $0.17856 per kg of pyrolysis oil.
To assess the economic feasibility, this cost must be compared with the market price of the final product and other operational costs. As technological advancements continue, particularly in green hydrogen production, costs are expected to drop, making these processes more financially accessible and sustainable in the long term.