Döngüsel ekonomi yaklaşımıyla kullanım ömrü dolan seramik membranların iç ortam havasından co2 giderimi için yeniden kullanımı
The re-use of end-of-life ceramic membrane for co2 removal from indoor air with a circular economy approach
Yazar: ELÇİM KARATAŞ
Danışman: DOÇ. DR. DERYA YÜKSEL İMER
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Bilimleri Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Sürdürülebilirlik konusu son yıllarda küresel olarak ön plana çıkmış ve başta Avrupa Birliğindeki ülkeler olmak üzere birçok ülke bu konuyu ele almaya başlamıştır. Sürdürülebilirlik kavramı, çevresel bir yaklaşımla doğal kaynak tüketimini azaltmaya odaklanırken, aynı zamanda kaynakları tasarruflu kullanmayı hedeflemektedir. Bu bağlamda, döngüsel ekonomi ve sürdürülebilirlik ayrılmaz bir şekilde bağlantılıdır. Son zamanlarda, membran proseslerinin birçok alanda kullanımının artması buna karşın hızlı kirlenme problemi nedeniyle membranların sık değişim gerekliliği ve atık oluşturma potansiyeli bu alanda kullanım ömrünü tamamlamış membranların yeniden kullanımı, atık membranlardan enerji geri kazanımı veya başka bir membran türüne dönüştürme ve yeniden kullanma (örneğin, ultrafiltrasyon veya nanofiltrasyon olarak ters osmoz membranlarının kullanılması) ile ilgili çalışmalara ihtiyaç artmaktadır. Membranlar son yıllarda su ve atıksu arıtımı ve madde geri kazanımı alanında oldukça fazla kullanılmaktadır. Ortalama verimli kullanım ömürleri ve değişim periyotları düşünüldüğünde çok ciddi bir atık yüküne sahiptir. Bu alanda sürdürülebilirlik çözümü için bilim ve teknoloji çerçevesinde yeni yaklaşımlar ortaya koymak gelecek için çok ciddi bir adımdır. Yapılan çalışmaların büyük bir çoğunluğu TO polimerik membranların döngüsel ekonomi yaklaşmıyla UF veya NF olarak tekrar kullanımını içermektedir. Polimerik membranların ömrünün yeni membran üretim stratejileri ve modül tasarımları ile en az 6 yıl, seramik membranların ise çok fazla çalışma olmamasına rağmen ömrünün 20 yıla yakın olduğu belirtilmektedir. Seramik membranların veya filtrelerin yeniden kullanımı veya geri kazanımı ile ilgili çalışmaları araştırdığımızda şu anda literatürde veya endüstriyel uygulamada bununla ilgili bir çalışmaya rastlanmamış ve kabul görmüş sistematik bir yaklaşımdan bahsedilmemiştir. Genel olarak seramik atıklarının tekrar değerlendirilmesi ile ilgili literatürde yer edinmesine rağmen seramik membranların tekrar kullanımı ile ilgili bir çalışma mevcut değildir. Tez kapsamında endüstriyel atıksu arıtımında kullanılmış ve ekonomik ömrünü tamamlamış seramik membranların CO2 gideriminde kullanılabilirliğini incelemek, bu amaçla membran temas reaktör dizayn etmek ve işletmek ve böylelikle döngüsel ekonomi yaklaşımını membranların yeniden kullanımı için uygulayarak ön bir çalışma niteliğinde ortaya koymaktır. Tez çalışmasının amacı son yıllarda kullanımı gittikçe artan membran proseslerin temel malzemesi olan membranların faydalı kullanımları sonrası ekonomiye yeniden kazandırılması için yöntemler geliştirmektir. Bu bağlamda membran temas reaktörün CO2 giderimde verimliğini değerlendirebilmek amacıyla kullanılan sıvı absorbentin (NaOH çözeltisi) CO2 tutma kapasitesinin farklı NaOH konsantrasyonlarında ve farklı sıvı ve gaz sirkülasyon debisinde test edilerek optimum koşulu belirlemek amaçlanmıştır.

Abstract:
The issue of sustainability has come to the forefront globally in recent years and many countries, particularly European Union, have begun to address the issue. The concept of sustainability focuses on reducing the consumption of natural resources with an ecological approach, but also aims to use resources sparingly. In this context, the circular economy and sustainability are inextricably linked. Recently, studies on the reuse of used membranes, energy recovery or conversion to another type of membrane (e.g. the use of reverse osmosis membranes as ultrafiltration or nanofiltration) have come to the fore as the lifetime of membranes is short and they need to be replaced by a new one due to rapid fouling. There is an increasing need for studies on the use of reverse osmosis membranes as ultrafiltration or nanofiltration. Membranes have been widely used in the field of water and wastewater treatment and material recovery in recent years. Considering their average lifetime and replacement intervals, they have a very high waste load. The introduction of new approaches in science and technology to solve sustainability in this field is a very serious step for the future. The vast majority of studies deal with the reuse of RO polymeric membranes as UF or NF with a circular economy approach. It is stated that the lifetime of polymeric membranes with new membrane production strategies and module designs is at least 6 years, and the lifetime of ceramic membranes is almost 20 years despite the lack of much work. The purpose of direct membrane recycling is to regenerate used membranes that can compete with commercial membranes in terms of cost, effectiveness, durability, energy requirements, and maintenance.

In searching for studies on the reuse or recovery of ceramic membranes or filters, no study was found in the literature or in industrial application, and no accepted systematic approach was mentioned. Although there is a post in the literature on the reuse of ceramic waste in general, there is no study on the reuse of ceramic membranes. 

The effect of CO2 emissions on the atmosphere has been considered a major concern in recent years due to global warming. The greenhouse gas effect that causes global warming is largely associated with the increased CO2 content in the atmosphere. Therefore, reducing CO2 emissions is a very important issue and one of the ways to achieve this goal is carbon capture and storage (Carbon Capture Storage) technologies. The absorption and desorption process is commonly used for CO2 removal, but this method has high capital and operating costs and some technological drawbacks. The gas-liquid membrane contact reactor, which can overcome the disadvantages of traditional methods in recent years, is a very suitable technological alternative to selectively retain CO2 from the mixed gas. In this technology, phase dispersion does not take place, so problems such as overflow, foam formation and/or drift are avoided. The membrane contact reactor is easy to scale and the gas and liquid flow rates can be controlled independently, allowing for high process flexibility. The driving force of the liquid absorbent in the membrane contact reactor depends on the concentration difference. The CO2 is separated from the gas phase along the membrane surface and transferred to the liquid absorbent. One of the main difficulties of the process is the penetration of the liquid absorbent into the membrane pores. Wetting of the membrane creates mass transfer resistance to CO2 and reduces separation efficiency. Ideally, the membranes to be used in this process should have high hydrophobic properties and the membrane pores should be filled with gas molecules in the feed stream to limit mass transfer resistance (Rosli et. al., 2019). CO2 absorption and removal is very important in terms of climate change and prevention of environmental damage, especially from fossil fuel consumption. In recent years, upstream contactors have proven to be more advantageous in CO2 absorption than conventional gas-liquid contactors with their large mass transfer and successful separation of gas-liquid phases. For this process to be successful, the membrane materials and absorbents must be very well selected. Although the gas separation ability of porous membranes is not permanent and selective, it was found in the studies that it is of great importance for stable and long-term operation due to the structure and properties of the membranes. Furthermore, in order for liquid absorbents to capture CO2 from the feed gas, they must have the property of having an appropriate proximity to CO2.

Polyvinylidene fluoride (PVDF) is the preferred material in membrane contactors, followed by poly(etherimide) (PEI) and polytetrafluoroethylene (PTFE) materials. In most studies, pure water and amine solution were used as sorbents. Liquid sorbents used in membranes occur naturally as hydrophilic or in aqueous form. Therefore, it is desirable for the membrane to be hydrophobic so as not to wet the pores of the membrane. Due to this requirement, polypropylene (PP), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and polyethylene (PE) are the most preferred hydrophobic materials in membrane fabrication. In addition to membrane selection, sorbent selection is also an important issue for CO2 capture efficiency (Chuah et al., 2020). If the sorbent selected has high CO2 solubility, it will allow the reduction of the required liquid volume in the membrane contact reactor and have lower operating costs with a smaller footprint of the plant. From an environmental point of view, the sorbent must be non-toxic to avoid the release of pollutants. At the same time, the CO2 absorption process must have a low viscosity characteristic, not only to minimize mass transfer resistance for CO2, but also to reduce pressure drop. Another consideration is that a sorbent with a high surface tension is generally preferred to minimize the membrane wetting problem.
The thesis aims to investigate the usability of ceramic membranes used in industrial wastewater treatment that have reached their economic life in CO2 removal, to design and operate a membrane contact reactor for this purpose, and thus to present the circular economy approach to membrane reuse as a preliminary study. The aim of the work is to develop methods to recycle membranes, which are the feedstock of the membrane processes that have been increasingly used in recent years, back into the economy after their economic use. In this context, we aim to determine the optimum condition by testing the CO2 holding capacity of the liquid absorbent (NaOH solution) used to evaluate the CO2 removal efficiency of the membrane contact reactor at different NaOH concentrations and different liquid and gas circulating flows. It is found that the liquid circulation rate is one of the most important operating parameters affecting the mass transfer for gas absorption into the liquid phase. Previous studies have shown that there is mass transfer resistance on the liquid side of the membrane during chemical absorption (Golkhar ve diğ.,2020). It was observed that the CO2 removal efficiency decreases with the increase of gas flow rate. This is because the gas phase boundary layer becomes thinner with increasing feed gas flow rate and the overall transfer coefficient increases until the gas resistance is neglected (Kong et al., 2020).al., 2020). Membrane channels have low mass transfer resistance and can increase the mass transfer coefficient of the channels with increasing NaOH concentration (Kong et al., 2020).