Prof. Songbo He was invited as a speaker

何松波研究员应邀担任演讲嘉宾

Title: Microplastics in the paper sludge and chemical recycling via fast pyrolysis

口头报告题目：造纸污泥中的微塑料及其快速热解化学回收研究

ABSTRACT:

       Paper sludge is the largest waste stream in the paper and pulp industry, which recycles the post-consumer paper, accounting for 4-5 wt.% of the global paper production. Paper sludge is currently incinerated or landfilled. It is well-known that paper sludge contains fillers (such as calcium carbonate, dolomite, kaolin, and talc) and fibers (such as cellulose and hemi-cellulose), which can be utilized for circular bioeconomy. A few emerging technologies, such as the enzymatic process (to generate fertilizers and produce bio-based natural gas) and the fast pyrolysis process (to recycle minerals and produce bio-based fuels and chemicals), have been demonstrated in the biorefinery. However, the wastepaper recycling process cannot completely separate paper and plastics (in the form of rejects), which are related to the papermaking and packaging processes that use various plastic coatings, such as polypropylene (PP), polylactic acid (PLA), and polyethylene terephthalate (PET). The remaining plastics enter the pulp and papermaking processes and ultimately end up in the wastewater treatment process. Microplastics in the wastewater of the paper and pulp industry and their removal have been widely reported. Nevertheless, the wastewater treatment process cannot remove microplastics effectively. Therefore, a few microplastics remained in the paper sludge, which has not been brought to the public’s attention. In this contribution, our latest study on microplastics in the paper sludge and the chemical recycling via fast pyrolysis will be presented. Three paper sludge samples collected from the pulp and paper companies in China, Germany, and the Netherlands were analyzed not only by routine analyses (thermogravimetric analysis, moisture analysis, ash analysis, CHNS elemental analysis, powder X-ray diffraction, and X-ray fluorescence spectrometry) to characterize the biomass and minerals but also by additional analyses (micro-Fourier transform infrared (μ-FTIR) spectroscopy and pyrolysis-gas chromatography-mass (Py-GC/MS) spectrometry) to characterize the microplastics. Besides the qualification and quantification analyses of microplastics, their removal (or valorization) via fast pyrolysis to produce circular hydrocarbons (such as paraffins, olefins, and aromatics) was also considered. Pyrolysis experiments were performed on different units, including a tandem micro-reactor (mg-scale, batch), a fixed bed reactor (10-g scale, batch), a staged free-fall pyrolysis reactor (50-g scale, semi-continuous), and a conical pyrolysis reactor integrated into the Pyros pilot plant (feeding 9.2 kg/h, continuous). The liquid products were analyzed by GC-FID/TCD, GC×GC-FID, gel permeation chromatography (GPC), elemental (CHN) analysis, Karl Fischer titration, and total acid number (TAN) to qualify and quantify the bio-based chemicals. Microplastics analysis results show that different types of microplastics (PE, PP, PET, PS, and cellophane) with different shapes (fiber, thread, particle, fragment, foam, and film), sizes (<0.02 mm, 0.02-0.05 mm, 0.05-0.1 mm, 0.1-0.2 mm, 0.2-0.5 mm, 0.5-1.0 mm, 1.0-2.0 mm, 2.0-3.0 mm, 3.0-4.0 mm), and colors (transparent, semitransparent, white, grey, black, red, yellow, blue, and green) are present in the paper sludge samples. The concentrations of MPs are 7.0-17.3 μg/g and 1800-71200 pieces/kg in the three paper sludge samples. Pyrolysis experiments show that microplastics are converted to hydrocarbons, which improves the quality of the paper sludge pyrolysis bio-liquid (also known as biooil) product. These results show the advantages of chemical recycling of microplastic-containing paper sludge (e.g., via fast pyrolysis) compared to the enzymatic process, in which the microplastics cannot be converted and end up in the digestate solid.

摘要：

       造纸污泥是纸浆造纸工业中最大的废物流，该行业对消费后废纸进行回收，其污泥量约占全球纸张产量的4-5wt.%。目前，造纸污泥主要通过焚烧或填埋处理。众所周知，造纸污泥中含有填料（如碳酸钙、白云石、高岭土和滑石）和纤维（如纤维素和半纤维素），这些成分可用于循环生物经济。一些新兴技术，例如酶法工艺（用于生产肥料和生物基天然气）和快速热解工艺（用于回收矿物质和生产生物基燃料与化学品），已在生物精炼中得到验证。然而，废纸回收过程无法完全分离纸张和塑料（以废料形式存在），这些塑料与使用各种塑料涂层（如聚丙烯、聚乳酸和聚对苯二甲酸乙二醇酯）的造纸和包装工艺相关。残留的塑料进入制浆和造纸过程，最终进入废水处理环节。纸浆造纸工业废水中的微塑料及其去除已得到广泛报道。然而，废水处理过程无法有效去除微塑料。因此，少量微塑料残留在造纸污泥中，这一问题尚未引起公众关注。本报告将介绍我们在造纸污泥中微塑料及其快速热解化学回收方面的最新研究。我们对来自中国、德国和荷兰造纸企业的三种造纸污泥样品进行了分析，不仅采用常规分析（热重分析、水分分析、灰分分析、CHNS元素分析、粉末X射线衍射和X射线荧光光谱）来表征生物质和矿物质，还通过额外分析（显微傅里叶变换红外光谱和热解-气相色谱-质谱）来表征微塑料。除了对微塑料进行定性和定量分析外，还考虑了通过快速热解将其去除（或高值化转化）以生产循环碳氢化合物（如烷烃、烯烃和芳烃）。热解实验在不同装置上进行，包括串联微反应器、固定床反应器、分级自由落体热解反应器以及集成在Pyros中试装置中的锥形热解反应器。液体产物通过GC-FID/TCD、GC×GC-FID、凝胶渗透色谱、元素分析、卡尔费休滴定和总酸值进行定性和定量分析，以鉴定生物基化学品。微塑料分析结果表明，造纸污泥样品中存在不同类型、形状、尺寸和颜色的微塑料。三种造纸污泥样品中微塑料的浓度分别为7.0-17.3微克/克和1800-71200个/千克。热解实验表明，微塑料可转化为碳氢化合物，从而改善了造纸污泥热解生物液体产物的质量。这些结果表明，与酶法工艺相比，对含微塑料的造纸污泥进行化学回收（例如通过快速热解）具有优势，因为在酶法工艺中微塑料无法被转化，最终残留在消化固体中。