Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 11: Problem 3

The concentration of acetic acid in pyrolysis oil varies between 1 and the \(8 \mathrm{wt} \%\). HAc is the most abundant acid in the oil. Can you explain the low (2-3) but hardly varying \(\mathrm{pH}\) of the oil?

Short Answer

Expert verified
Question: Explain the low but hardly varying pH of pyrolysis oil, given that the concentration of acetic acid in it varies between 1 and 8 wt%. Answer: The pH of pyrolysis oil depends on the square root of the product of the equilibrium constant (Ka) for acetic acid and the initial concentration of acetic acid. Due to the small Ka value of acetic acid, the overall pH is low. Additionally, small changes in the concentration of acetic acid have little effect on the pH due to the square root relationship. This leads to a low but hardly varying pH of pyrolysis oil.

Step by step solution

01

Write down the equilibrium constant (Ka) for acetic acid

Acetic acid is a weak acid and its dissociation in water can be written as: HAc \(\rightleftharpoons\) H\(^+\) + Ac\(^-\) The equilibrium constant, Ka, for this reaction is given by: Ka = \(\frac{[\mathrm{H}^+][\mathrm{Ac}^-]}{[\mathrm{HAc}]}\)
02

Use the Ka value to determine the concentration of hydrogen ions (H\(^+\))

The Ka value for acetic acid is around \(1.75 \times 10^{-5}\). To determine the concentration of hydrogen ions (H\(^+\)), we can use the approximation that the concentration of HAc decreases by x, while the concentration of H\(^+\) and Ac\(^-\) increase by x. Then: Ka = \(\frac{(x)(x)}{([\mathrm{HAc}]_0 - x)}\) Where \([\mathrm{HAc}]_0\) is the initial concentration of HAc, and x is the concentration of H\(^+\) and Ac\(^-\) at equilibrium.
03

Simplify the equation and determine the relationship between the concentration of acetic acid and the pH of the oil

In most cases, x is relatively small compared to the initial concentration of acetic acid (HAc), so we can approximate that \([\mathrm{HAc}]_0\) - x \(\approx [\mathrm{HAc}]_0\). This simplifies the equation: Ka \(\approx \frac{x^2}{[\mathrm{HAc}]_0}\) Now, we can solve for x, which represents the concentration of H\(^+\) ions: x \(\approx \sqrt{Ka \times [\mathrm{HAc}]_0}\)
04

Calculate the pH of the solution

The pH of a solution is defined as the negative logarithm of the hydrogen ion concentration: pH = \(- \log_{10} [\mathrm{H}^+]\) Using the relationship found in step 3, we have: pH \(\approx -\log_{10} \sqrt{Ka \times [\mathrm{HAc}]_0}\)
05

Explain the low but hardly varying pH of pyrolysis oil

As we can see from the equation found in step 4, the pH of the oil depends on the square root of the product of the equilibrium constant (Ka) and the initial concentration of acetic acid. The value of Ka for acetic acid is very small, thus the overall pH value will be low. Moreover, since the pH value is affected by the square root of the product, small changes in the concentration of acetic acid will not have a significant impact on the pH of the oil. This explains the low but hardly varying pH of pyrolysis oil.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

For the case where sand is circulated between a hot utility and the pyrolysis reactor, derive an equation that gives the required sand flow (in \(\mathrm{kg}\) ) per \(\mathrm{kg}\) biomass fed as a function of the temperature differences between the pyrolysis reactor and the hot utility and the energy requirement of the reactor.

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.

a. Explain why the observation of larger oligomers during the pyrolysis of a cellulose particle contradicts an unzipping mechanism. b. Argue how these large oligomer anhydrosugars \((D P=9)\) leave the particle.

a. Derive an expression that relates the loss of vapors due the homogeneous vapor cracking reaction in the hot zone above a fluidized bed as a function of temperature and vapor residence time. b. Consider a fluidized bed pyrolysis reactor that contains ideally mixed biomass particles that are producing vapors. In the fluidized bed reactor, also, vapor cracking proceeds, which can be described by a first-order reaction in vapors. Derive an expression to calculate the fraction of the vapors that is cracked relative to the amount produced in the pyrolysis reactions as a function of temperature and residence time. You may assume that the gas/vapors show plug flow behavior.
See all solutions

Recommended explanations on Environmental Science Textbooks

Energy Resources

Read Explanation

Pollution

Read Explanation

Physical Environment

Read Explanation

Biological Resources

Read Explanation

Environmental Research

Read Explanation

Environmental Policy

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free