Aspen Plus Modelling for PTD

Process modelling tools such as Aspen Plus are indispensable in developing new unit operations like PTD and predicting how they will perform in the context of a chemical plant.

In 2016 Hayley Hayden Smestad wrote her Chemical Engineering Master’s thesis at Worcester Polytechnic Institute on the topic of applying PTD to ethanol/water separation.

She concluded  “Aspen Plus V8.8 was used for the determination of parameters to use with the eNRTL­RK property method to accurately model the mixed solvent electrolyte system of ethanol, water and lithium bromide. These parameters can be implemented for a variety of applications especially the pass­through distillation application considered here. The accurate modeling of the ternary system was critical to the development of a foundation for the modeling of pass­through distillation with the specific application of separating bioethanol from a fermentation broth using a combination of evaporation, absorption, stripping and condensing to provide a low pressure, low temperature separation that does not damage temperature sensitive components present in a fermentation broth while at the same time minimizing energy required to achieve the separation. The simulation developed in Aspen Plus V8.8 to model this system will prove useful for future studies, as a teaching tool for how the process works, as well as a platform to test out variations in the system quickly with little associated risk”

There are presently efforts underway at two Universities to extend PTD Aspen modelling.


Institution: McMaster University,   Hamilton, Ontario Canada

Title:  Aspen Plus Modelling of Generation 1 and 2 Biofuel Plants Equipped with Pass-through Distillation

The Team:  Danilo Salas Ramirez, Zicong Zou, ViVek Patel, and Salim Kairulla.

Supervisor:  Professor Amin Rajabzadeh


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Institution: The University of Manchester, Manchester UK

Title:   Modelling of the In Situ Separation of Ethanol from a Fermentation Broth Using     Pass-Through Distillation

Student: Scott Bromley

Supervisor: Prof. Anton Kiss



Pass-through Distillation Pilot Plant

In 2014 two Canadian Companies collaborated to test Pass-through distillation experimentally.

One of the companies,Fielding Chemical Technologies Inc., is Canada’s foremost chemical recycler. Fielding wanted to learn through the pilot plant whether or not PTD could offer advanced treatment of hazardous industrial waste.

The other company, Drystill Holdings Inc., is a start-up technology company that has invented and patented equipment specifically for PTD, including the Stripper/Absorber Module (SAM) described in the fifth and sixth lectures of PTD 101. The pilot plant featured a mid-sized SAM capable of boiling 50 Kg of water per hour.

The pilot plant operated successfully for many months before being dismantled to make way for another project. For Drystill it furnished proof of concept for their proprietary technology. Fielding learned that the technology may be applied to the processing of industrial wastes, but has decided not to implement it for the time being.

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This is a picture of Drystill’s prototype SAM. It contains 100 heat pipes 25 mm in diameter and 550 mm in length.


Here is the same SAM installed on Fielding’s pilot plant framework.

Click here to see a video of SAM at work.

Click on the logos below to learn more about Fielding and Drystill.



About PTD

There are only so many unit operations known to chemical engineers, so it seems safe to say that every conceivable pair of them has been considered and, where appropriate, tested out in lab or plant. Some pairs exhibit such useful synergies that the combination becomes a unit operation in its own right, and it acquires a name of its own; witness evaporation + condensation = distillation.

I have searched the literature for references to current and previous attempts to combine evaporation and absorption. So far I have come up almost empty-handed. Yet this combination can provide low temperature distillations with half the energy used by current industrial practice. Has something been overlooked? As a community of professionals serving the world’s chemical engineering needs, we ought to talk.

To facilitate discussion, I have given combination of evaporation and gas absorption a name: “Pass-through distillation” and created this web site to serve as a clearing house for information on the topic. It is intended for the benefit of engineers and scientists in academia and industry world-wide.

If this field of enquiry ultimately generates wealth, some of it may rub off on Drystill and I will openly accept my share. In the meantime my activities relative to this web site will be directed toward shedding light on a topic that may benefit our planet.

Ian McGregor P. Eng.