Universidad San Francisco de Quito
INQ-4202E Unit Operations II
Integrants: Pamela Bermúdez (328092) | Augustina Cepeda (328650) Date: April 9, 2025
Erick Cordero (327994) | Mateo Valencia (330116)
Adsorption Isotherms
Crude palm oil (CPO) contains a high concentration of carotenoid pigments, with βcarotene being the most abundant, responsible for the oil’s intense reddish color. While
these compounds are known for their antioxidant properties and as a source of provitamin
A, their presence is often considered undesirable in edible oils due to market preferences
for lighter yellow hues.
To remove these pigments, a bleaching process is commonly applied—among the most
efficient techniques is adsorption. Among various adsorbents tested, activated carbon
stands out due to its high surface area, porosity, and affinity for organic compounds such as
carotenoids. In particular, activated carbon derived from organic waste such as tea waste
provides a sustainable, low-cost, and effective solution.
The study by Harahap et al. (2018) focused on evaluating the efficiency of β-carotene
removal from CPO using activated carbon produced from tea waste (ACTW). An
isothermal approach was used to model the adsorption behavior and predict operating
conditions for optimal pigment removal.
Experimental Method
The activated carbon was produced from used tea leaves collected from local restaurants.
The tea waste was dried, ground, and sieved (50 mesh), then activated using 85%
phosphoric acid (H₃PO₄) at a 1:2 ratio for 24 hours. It was then pyrolyzed at 500 °C for 15
minutes under nitrogen flow, washed with hot water, dried, and ground into a fine powder.
Adsorption experiments were carried out at 60 °C using different weight ratios of ACTW to
CPO: 1:3, 1:4, 1:5, and 1:6. Each mixture was stirred at 120 rpm for 2 hours. After
filtration, the remaining β-carotene concentration in the oil was analyzed using a UV-Vis
spectrophotometer.
Results: Adsorption Isotherms
To model the adsorption behavior, two common isotherm models were tested:
Langmuir Isotherm
This model assumes monolayer adsorption on a homogeneous surface. The linearized
Langmuir equation used was:
𝐶!
1
𝐶!
=
+
𝑞! 𝐾" 𝑞# 𝑞#
Where:
•
•
•
Ce = equilibrium concentration of β-carotene
qe = amount adsorbed per gram of ACTW
KL, qm = Langmuir constants
The experimental data yielded a correlation coefficient R² = 0.962, indicating a moderate
fit.
Freundlich Isotherm
This model is suitable for non-ideal, heterogeneous, multilayer adsorption. The linear form
used was:
1
log 𝑞! = log 𝐾$ + 𝑙𝑜𝑔𝐶!
𝑛
The constants obtained were:
•
•
•
Kf=1.002
n=1.3368
R² = 0.999
These results confirm that Freundlich isotherm best describes the adsorption of β-carotene
on ACTW.
References:
Harahap, S. A. A., Nazar, A., Yunita, M., Pasaribu, R., Panjaitan, F., Yanuar, F., & Misran,
E. (2018). Isothermal approach to predict the removal efficiency of β-carotene
adsorption from CPO using activated carbon produced from tea waste. IOP
Conference Series Materials Science And Engineering, 309, 012120.
https://doi.org/10.1088/1757-899x/309/1/012120