Final Report: Beneficial Reuse of PCBsEPA Grant Number: SU836782
Title: Beneficial Reuse of PCBs
Investigators: Lu, Mingming
Institution: University of Cincinnati - Main Campus
EPA Project Officer: Page, Angela
Project Period: August 1, 2016 through October 31, 2017
Project Amount: $14,985
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2016) RFA Text | Recipients Lists
Research Category: Sustainability , P3 Awards , P3 Challenge Area - Materials & Chemicals
Even though production of PCBs (polychlorinated biphenyls) has ceased due to their high toxicity and bioaccumulation, PCB contamination remains a challenging problem to solve worldwide. There has been a lot of progress made over the years in PCB treatment, via chemical, biological, and thermal desorption, etc.. However, there are challenges in adopting these technologies for the following reasons: high temperature, longer duration, and high initial cost, etc. Therefore, there is the constant need to seek low cost and yet effective technologies.
The overall objective of the research was to develop a low-cost technology for PCB decontamination. Phase I tested the feasibility of catalytic hydrodechlorination by converting select PCBs into non-chlorine containing chemicals. Parametric study was carried out to understand what factors and how the factors affect the reaction. Reaction kinetics also will be studied with the time remaining to prepare for future scale up. Phase I (this project) is a proof of concept of the proposed technology. In Phase II, the team planned to test with more complex PCBs, including some commonly used in the past, such as Aroclor 1254 and 1248 and Askarel. With the help of partners, we will modify the design based on test results as well as the real world oil or sediment matrices. If Phase II is successful, we will pursue SBIR or contract opportunities to do a pilot test with the actual site conditions. The possibility of patenting the technology also will be pursued, offering license opportunities to companies.
The proposal team has studied the effectiveness of catalytic de-coloration at low temperatures and atmospheric pressure under hydrogen environment. The catalyst responsible for dechlorination is palladium on carbon (Pd/C) with triethylamine (Et3N) serving as an electronic donor and acid neutralizer. Both 3-PCB and 2,3-PCB are being studied, with respect to the reaction time, catalyst dosage, hydrogen partial pressure, mixing effects, and temperature, etc. Reaction kinetics also are being investigated.
The experimental setup is designed as a batch process. 50 mg of reactants (AccuStandard), the catalyst Pd/C (with Pd content varying from 0.5% to 10% by weight), and Et3N and 50 ml toluene were placed in a flask. This flask was sealed with a cork that had a carrier gas tube passing through. Before reaction, N2 gas was passed into the flask for 15 minutes to eliminate any air inside the flask.
Then a mixture of N2 and H2 (with a H2 partial pressure varying from 0.41 to 0.5) was passed through the suspension at room temperature (25°C) and atmospheric pressure. The carrier gas has two functions. It both supplied the hydrogen and also mixes the suspension. After reaction, the products were washed with magnetic stirs, filtered using vacuum filtration, and an aliquot of the filtered liquid was diluted 50 times for GC-MS (gas chromatography and mass spectroscopy) analysis. Both 3-chlorobiphenyl (3-PCB) and 2,3-dichlorobiphenyl (2,3-PCB) were tested. The reaction time was varied from 0.5 hrs to 6 hrs.
The Phase I goal was divided into three specific aims: (1) study the optimum conditions for catalytic dechlorination; (2) research the optimum conditions for bipehneyl conversion; and (3) conduct public outreach—disseminate research results at various venues to educate the public about waste reuse in environmentally friendly ways.
For specific aim 1, studying the optimum conditions for catalytic dechlorination has been carried out, and may result in a journal publication. New findings include a better solvent than reported from literature, much lower temperatures and much shorter time used.
In our study, toluene was identified as a better solvent than methanol. It resulted in higher product recovery (not much difference with regard to dechlorination) and was more sensitive for instrumentation (peak area in toluene is 6.08 times larger).
SEM-EDS (Energy Dispersive X-ray Spectroscopy) studies indicated that the surface Pd rate on 10% Pd/C is much higher than the other two: Pd weights were 0.1%, 2.1% to 7.0% for 0.5%, 5% and 10% Pd/C. Given that hydrodechlorination (HDC) is heterogeneous surface reaction, the catalyst amount on the surface is important. Therefore, 10% Pd/C is considered the best catalyst condition.
The effective reaction time for 3-PCB was determined as 2 hours. Similarly, the reaction time for 2,3-PCB was determined as 6 hours, where >95% of dechlorination had occurred. Our findings indicate that the reaction time may be related to the number of chlorines on the PCB, which will be further investigated in Phase II.
Hydrogen partial pressure and the stirring intensity both affect the reaction. A balance of these factors will result in more effective reactions, and will affect the cost effectiveness. For example, for 3-PCB, a total flow rate of 150 cc/min (3 point all 99-100%) (hydrogen partial pressure of 0.483) seems to be the optimum condition. This also is supported by the highest biphenyl recovery rate (average of 79.6%, 3 repeats) at the same condition. More runs will be carried out for 2,3-PCB to ensure consistent results. The impacts associated with chlorine content will be further investigated in Phase II. Temperatures other than room temperature, such as 50°C and 80°C, also will be tested to obtain kinetic parameters, such as the activation energy and rate coefficient.
A few tests were performed on specific aim 2. After discussion with the ETSC (Engineering Technology Support Center) of the U.S. EPA and one of the executive secretaries of the PEN (PCB Elimination Network), however, we decided to terminate work on this aim because it is “not practical” based on the feedback from these experts.
Specific aim 3, student mentoring and outreach, is being carried out at a healthy pace. An interdisciplinary team of students has been formed, which consists of two graduate students (environmental and materials engineering) and three undergraduate students (one in chemical engineering and two in chemistry). Also a visiting faculty mentor, who is an expert in environmental catalysis, has been co-leading this project. The team developed best practices through working together. They made several binders to document experimental conditions, one for instrumental analysis, and another one for literature on sustainability and technology related publications. They also established a shared Google Drive for literature and results. Students developed effective management skills for documentation/research.
The PI has worked with partners to recruit students and make business connections, and will work with newly developed partners to guide the team through the Phase II project to accomplish what is needed to move the technology to a pilot demonstration. New partnership have been established with the ETSC of the U.S. EPA and the PEN (PCB Elimination Network) under the Stockholm Convention.
Overall, the Phase I project is on the right track, and will be completed by the time the project ends. A few experiments will be repeated in the next steps to ensure repeatability.
Preliminary results indicated that the catalytic hydrodechlorination can occur at room temperature and atmospheric pressure, which makes this technology promising as a low-cost and simple technology for real-world deployment. During the study, we also found an actual company that uses a similar technology, but with much higher temperature and pressure. This offers indirect validation of this technology.
An interdisciplinary student team has been formed and has become highly functional after 5 months of work together. Best practices have been developed for data collection, data processing, and results presentation. This project has been used as an educational tool to train students on sustainability, technology, and outreach.