(58ai) Novel Technique for the Separation of Foam Creators from Industrial Lean Amine Solutions for Identification Purposes

In this paper, a new technique based on the concept of foam fractionation is developed for the identification of foam creators in alkanolamine gas sweetening solvents. The developed foaming technique was used to identify the foam creators existing in industrial amine solutions (lean amine from the regeneration column outlet) obtained from a gas sweetening plant. The developed approach in this technique is based on inducing a lean amine sample to foam, allowing three samples to be collected: 1) A sample from the lean amine before foam (main amine sample) 2) A sample from the collected foam (foamate) 3) A sample from the remaining amine after collecting the foam. Liquid chromatography mass spectrometer (LC ToF MS) and direct sample analysis time of flight (AxION® 2 TOF) instruments were used to analyze the collected samples. A comparison was made between the three spectra obtained from a mass spectrometer for the three samples. The compounds that increased in concentration in the foamate sample and decreased in the remaining amine in the foaming column are believed to be responsible for generation of the foam. The obtained mass/charge from the mass spectrometer can be used to identify these compounds. Identification of foaming creators in industrial lean amine samples is provided as a proof of the capabilities of the proposed method. The results of this study introduce the foaming technique as a promising laboratory scale technique for the identification of foam creators in amine absorption solvents.

Keywords: Amine foaming; foam fractionation; foam creators
Introduction

Alkanolamine absorption processes are widely used to remove acid gases i.e. CO₂ and H₂S from Natural gas and flue gases Mokhatab;, POE; et al. (2012), Alhseinat, Pal et al. (2014). Foaming is one of the most severe operational problem in acid gas absorption process. Foaming has severe impact on plant operation, causing excessive loss of absorption solvents, premature flooding, reduction in plant throughput, and off-specification of products Thitakamol and Veawab (2009). Foaming problem can be induced by several contaminants including fine particulate, condensed liquid hydrocarbon, heat stable salts (HSS) and amine degradation products (Alhseinat, Pal et al. 2014, Alhseinat, Pal et al. 2015, Alhseinat, Keewan et al. 2017). Due to the closed loop nature of amine processes, foam creators can accumulate to reach their effective concentrations without being noticed by the unit operators (Pauley 1991, Chen, Freeman et al. 2011). Unfortunately, there is no method for foam source identification; despite the fact that identification of foam sources is key to troubleshooting the problem of amine foaming (Dhafeeri 2007){Al-Dhafeeri, 2007 #105}.

Adsorptive bubble separation is used for partially separating or concentrating dissolved material by adsorption at the surface of bubbles based on the difference of surface activity (Darton, Supino et al.),(Swain 2005). The compounds responsible for foaming in gas sweetening unit tend to accumulate in the foam itself, it is therefore possible to concentrate them by inducing the amine to foam in an experimental foam fractionation setup; this ultimately facilitates their identification and removal.

Phul et.al (Phul 2003) proposed a method and apparatus for removing foaming contaminates from solvents using the concept of foam fractionation. The proposed apparatus was designed and manufactured to clean all circulated lean amine or at least a significant portion of it in order to be effective in preventing foaming at amine gas sweetening processes. The major drawbacks of this apparatus, however, can be summarized as: 1) the size of the foam fractionation apparatus is too large to accommodate the solvent and the foam 2) it requires close monitoring with an operator 3) The lost solvent removed along with the foam is significant. These are the main reasons for this apparatus not being adopted in the majority of gas sweetening plants. Indeed, nothing is mentioned in the work of Phul et.al (Phul 2003) about the monitoring of solvent foaming behavior and no methodology is proposed for the identification of foam creators. There is a clear lack of scientific research investigating and optimizing the foam fractionation technique for amine gas sweeting solvent cleaning and the identification of foam creators. Therefore, to enhance our knowledge about the use of foam fractionation for amine solvents cleaning and foam creators’ identification, a first attempt for optimizing batch foam fractionation column using laboratory synthesized amine solutions from analytical grade amine was performed and published in Journal of Natural Gas Science and Engineering (Alhseinat, Amr et al. 2015). These efforts led to the development and optimization of a foam fractionation setup for the identification of foam creators in industrial lean amine. This paper introduces for the first time, an experimental technique and approach based on foam fractionation for the identification of foam creators in industrial lean amine solution. In this study, a continuous foam fractionation set-up was designed and used to concentrate the foam creators from industrial lean amine. Liquid chromatography mass spectrometry (LC ToF MS) and direct sample analysis time of flight (AxION® 2 TOF) instruments were used to analyze the collected foam, the main amine solution and the remaining liquid following foaming. A comparison between the concertation of the species existing in the collected foam, the initial amine solution prior to foaming and the amine solution following foaming (named the remaining liquid) is the key to identifying the foam source, which will be explained in detail later in the paper. The results of this study highlight, for the first time, the ability of foam analysis to identify foam creators using a simple experimental setup. This research enhances the understanding of the contributing factors to the foaming problem and will facilitate the tracking of the sources of foaming and facilitate their alleviation or impact reduction.
Materials and Methods

The identification and detection of foam creators was carried out for lean MDEA solution obtained from GASCO (A gas sweetening company in the United Arab Emirates). A continuous foam fractionation column was used to concentrate the foam creators existing in industrial lean amine. Direct sample analysis time of flight mass spectrometry (DSA-ToF MS) instrument and Liquid chromatography mass spectrometry (LC ToF MS) were then used to detect and identify the foam creators.
Materials

Industrial lean MDEA was obtained from GASCO, Habshan, Abu Dhabi.
Experimental Setup

As illustrated in Figure 1, the experimental setup was composed of a foam fractionation column with a cross sectional area of 0.0022 m², and a flow meter. Nitrogen gas (N₂) was used to generate bubbles in the tested amine solution. A peristaltic pump was used to compensate the lean amine solution level in main column; in addition to a vacuum pump that was used to withdraw the foamate sample.

Figure 1: Schematic diagram for Continuous foam fractionation setup
Experimental Procedures and Conditions
Foam Fractionation

In the foam fractionation experiments, three samples where collected from each experiment and tested using Direct sample analyzer Time of Flight mass spectrometry (DSA-ToF MS) and Liquid Chromatography Time of Flight mass spectrometry (LC-ToF MS): the main solution sample (before foaming treatment): the foamate sample and the liquid sample (remaining MDEA solution in the foam fractionation column). For the foaming treatment, foam was collected until no further foam was accumulated.

Several samples were analyzed to evaluate the repeatability of the results. Selected experiments were repeated to test the reproducibility of the results. Selected foam and breaking time experiments were repeated three times. The results from the repeated experiments demonstrated almost exact readings for foam volume with less than 1% deviation and 2% deviation in the breaking time readings.
Direct Sample Analysis (DSA) Time of Flight (ToF) Mass Spectrometry (MS) (AxION 2 ToF) Instrument

A DSA ToF MS (AxION 2 ToF MS, Perkin Elmer) instrument was used to analyze the collected samples and to identify foam creators in lean amine samples. DSA, which is integrated with a (TOF- MS), is one of the most recent and development ambient ionization techniques; these techniques enable the investigation of a variety sample types across the molecular weight range. Accurate peak intensity can be recorded across the complete mass range, mass (m)/charge (z), by AxION 2 ToF MS (PerkinElmer) instrument; it records ions and time, which is particularly important to identify and quantify all contaminant components in the sample. The DSA LC ToF MS was used previously for the identification of MDEA degradation products with high concentrations [8]. Small quantities of prepared sample without any dilution or further treatment were sent to the DAS instrument via disposable mesh; (10 µL of prepared sample), rapid screening of samples was then conducted. The obtained full spectrum measurement captured the complete composition of every sample tested. These spectra were used to identify the foam creators collected in the samples tested. The identification of compounds in this study was based on the previous degradation studies and proposed degradation mechanisms of amine by the research group using the DSA TOF MS database provided by the supplier (Perkin Elmer).
Sample Preparation for LC ToF MS

5 µL from the foamate, liquid or main solution sample were added to 1500 µL of water (particular water supplied to LC ToF MS Instrument), then 10 µL of this diluted sample was introduced to the LC ToF MS.