(219d) Training Our Upcoming Chemical Engineers By Simulating an Industrial Setting: A Classroom Case-Study on Waste Cellulose Valorization

Chemical engineers are trained in a broad, multidisciplinary environment.
This is necessary since they are typically employed in an industrial
environment in which not only (chemical) engineering is key, but also knowledge
of informatics, mechanics, economics and even human psychology. At Ghent
University, in Belgium, our chemical engineering students are trained in every
aspect of their future professional career. One of the more prominent, truly
multidisciplinary courses in this respect is the ‘cross-course project’ in the
third bachelor year.  This is a mandatory, project-based course in which a
group of students tackle a real-life industrially relevant engineering problem.
Each year, new project topics are defined, based either on the actual need of
an industrial partner or on a more fundamental problem encountered by a
research institute. By simulating such an industrial setting, the students get
a clear picture of their future professional career.

Figure 1: a schematic
representation of a typical wastewater treatment plant [1]

One of the project topics was put forward by an industrial
partner specialized in wastewater treatment. Apart from organic matter, domestic
wastewater contains small, solid particles, mostly composed of cellulose fibers
originating from toilet paper. Without specific actions, these fibrous
particles would reach the aeration basin resulting in an extra load for the
sludge in the basin. Aiming at creating added value, an extra fine-meshed sieve
was installed upstream of the aeration basin, allowing the recovery of these
solid particles. As a result, an additional solid stream was obtained, almost
entirely composed of wet cellulose fibers. The challenge for the students was
to propose and design a solution to valorize this cellulosic waste stream. As a
result, not only the scientific feasibility of their solution needed to be evaluated,
but also the economic and industrial feasibility.

Figure 2: cellulose
conversion measured at specific time intervals in a batch reactor. Solid lines
represent the Michaelis-Menten kinetic model

After an initial brainstorm session, a two-stage conversion
process was developed. In a first step, the cellulose fibers are hydrolyzed to
glucose after which the glucose is fermented to bioethanol. The cellulose hydrolysis
was performed using a mixture of commercially available cellulase enzymes in a
lab-scale batch reactor. The reactant cellulose was provided by dissolving fresh
toilet paper in water by stirring. During reaction, samples were drawn from the
reactor mixture at well-defined time intervals and the unreacted cellulose was
filtered from the mixture. For analytical purposes, sulfuric acid was added to the
samples, which converted the glucose into hydroxymethylfurfural of which the
concentration can be measured by UV-VIS absorbance [2]. By varying the reaction conditions, such as
temperature and enzyme concentration, the kinetics of the enzymatic
transformation could be mapped experimentally. These data were subsequently
used to construct a Michaelis-Menten kinetic model. In the second stage of the
process, glucose was converted into ethanol by the addition of baker’s yeast.
To determine the enzymatic kinetics of the glucose, a similar approach was
followed as in the first step. A second Michaelis-Menten kinetic model was
constructed which could simulate the experimentally measured ethanol production
rates quite well. In order to measure reliable kinetic data with a minimal
experimental error, a critical mindset of the students in the lab was proven to
be essential. Through trial-and-error, the students got aware of a number of
potential sources of unreliability, e.g., cellulose fibers still present in the
sample, poor cellulose solubility in water, undesired oxygen during fermentation.

Figure 3: Aspen Plus®
model of an industrial plant for the conversion of cellulose into glucose and further
fermentation to ethanol

Using both kinetic models and industrial wastewater
capacities, several preliminary commercial configurations were designed and
evaluated via the process modelling software Aspen Plus®. Although this
valorization step was feasible on the laboratory scale, some key challenges
remain for its industrial application, e.g., the limited solubility of the
cellulose and the loss of the homogeneous enzymes after reaction. Overall, the
project resulted in a critical evaluation by the students of biomass as raw
material in the chemical industry, expressing both opportunities and challenges
of a bio-based society.

From a management perspective, the students worked as a
synergetic team by appointing specific roles to every team member. They learned
to be critical but also appreciated each other’s contributions. Apart from field
work and reporting, the students had weekly meetings with the responsible
professors and, sometimes, the industrial partner from which they received
valuable feedback. Finally, their presentation skills were trained by having to
present their progress twice, orally, for a broad audience of chemical engineers
and students. The students also participated in an international Student
Research Conference where they gave a presentation of their work, which earned
them the first prize from both the jury as well as the audience.

[1]           W. Noorderzijlvest. Available: www.noorderzijlvest.nl

[2]           A. A. Albalasmeh, A. A. Berhe, and T. A.
Ghezzehei, "A new method for rapid determination of carbohydrate and total
carbon concentrations using UV spectrophotometry," Carbohydrate
polymers, vol. 97, no. 2, pp. 253-261, 2013.

Acknowledgement

The authors would like to thank Bert Biesemans, Christophe
Naessens, Laura De Saedeleer and Laura Truyens for their commitment and hard
work during the project.