A new method of biorefining that exploits agricultural and industrial lignin waste

A new method of biorefining that exploits agricultural and industrial lignin waste

Researchers from Northwestern University – Illinois have developed a sustainable, inexpensive two-step process that can recycle organic carbon waste, including lignin, a substance that is difficult to break down and is involved in the structural makeup of plants. عملية المعالجة التي طورها الباحثون تشمل التكرير الحيوي المدعوم بالميكروبات؛ This is to convert lignin into other carbon sources that can be used in high-value plant-derived pharmaceuticals, antioxidant nutritional supplements, as well as carbon-based nanoparticles. لتوصيل الأدوية أو المواد الكيميائية (Drug Delivery).

Lignin (Lignin) is a heterogeneous and highly complex chemical compound, which is primarily responsible for the mechanical rigidity of cell walls. وبالتالي النبات ككل، حيث يعمل باعتباره المادة الرابطة للهيكل البنائي للنبات. To simplify, we can liken lignin and plant cells to cement and bricks, respectively; Therefore, lignin is extracted mainly from wood, where it represents a percentage ranging between 25 – 35% of the total dry mass.

Chemically speaking, “embryo” does not have a fixed chemical composition, but it can be described as a group of aromatic rings linked together. It is a very strong natural polymer that is slow to decompose, and is mainly composed of carbon. It is also highly resistant to bacteria and mold, and is characterized by shades of black and brown. ومن الناحية الصناعية، يتم استخراج وفصل اللجنين من الخشب باعتباره مخلَّفًا؛ This is for the manufacture of various paper products. Without lignin, the hard brown wood turns into flexible white coils.

But the question that arises here: What happens to the huge amounts of lignin waste resulting from agricultural lands, brewing factories, and paper products? للأسف الشديد يتم حرق أو دفن معظمها! ما يؤدي إلى التلوث وإهدار مورد متجدد محتمل.

Converting waste into a source of value

Fortunately, Northwestern University researchers have developed a sustainable, inexpensive two-step process that can recycle organic carbon waste, including lignin, by treating these wastes with microbial-assisted biorefining. These researchers were able to convert lignin into carbon sources that can be used in high-value plant-derived pharmaceuticals, in antioxidant nutritional supplements, as well as in carbon-based nanoparticles. To deliver drugs or chemicals. The study appeared on the cover of the January issue of the Journal of Sustainable Chemistry and Engineering (ACS).

The biorefining process is similar in itself to the petroleum refining process, except that it is concerned with converting biomass into energy and useful secondary compounds.

Kimberly Gray of Northwestern University, who led the research, said: “The fetus should have enormous value, but it is generally viewed as a waste product that needs to be disposed of. Lignin makes up 20-30% of biomass, which is a large amount, but difficult to utilize. Nature has made lignin so resistant to processing that people have not figured out how to use it, and researchers have been trying to solve this problem for decades. But by imitating the way petroleum refining units work, we have developed a biorefinery unit that takes organic waste and produces high-value products.”

It is worth noting that Kimberly Gray is the head of the Department of Civil and Environmental Engineering at Northwestern University, in addition to being a professor of chemical and biological engineering.

Lignin is a natural building material

Lignin is one of the most abundant natural organic polymers in the world, as it is found in all vascular plants. Lignin, found between the cell walls of plants, provides strength and mechanical durability to their structures. Without lignin, wood and bark would become too weak to support trees, and we would not be able to use wood to build houses, or even to make furniture.

Most industries that use plants – such as paper making and brewing industries – remove lignin; This is to obtain “cellulose” (a type of sugar), and instead of using this highly resistant natural material, it is burned as a cheap fuel.

Gray said: “Humans want to get rid of this substance to access sugars. They ferment cellulose to make alcohol, or process it to make pulp and paper, and then what do they do? “They burn lignin as a low-quality fuel, which is a real waste of a potential resource.”

Bacteria-powered fuel cell

To develop the biorefining process to be able to break down carbon waste, researchers first designed a microbial electrolysis cell (MEC). Similar to a fuel cell, a microbial analysis cell exchanges energy between the anode and cathode, but instead of using an anode made of metal, Northwestern’s bioanode is made of a special type of bacteria (exoelectrogens), which naturally generate electricity by devouring (oxidizing) organic materials.

Study co-author George Wells said: “The microbes act as a catalyst, rather than using chemical catalysts, which are often expensive and require high temperatures.”

The revolutionary nature of this microbial electrolysis cell lies in its ability to treat any type of organic waste, whether human, agricultural, or industrial. MEC also treats waste-filled water through carbon-eating bacteria, where organic carbon decomposes into carbon dioxide, and then the bacteria breathe out electrons naturally.

During this process, electrons extracted from the bioanode flow to the cathode, which is made of carbon cloth; To reduce oxygen and generate water. This process consumes protons, raising the pH of the water, turning it into a caustic solution that can then be used in a number of applications, including wastewater treatment.

Wells said: “Another benefit of this process is that it effectively treats wastewater to remove harmful organic carbon. Therefore, clean water is one of the main products of this process.”

The researchers then took the caustic material resulting from the previous process and turned their attention again to lignin. Lignin compounds are durable because they contain complex interconnected chains of aromatic carbons, which have a special bonding pattern based on hexagonal aromatic rings, each ring consisting of alternating double and single bonds, making them incredibly difficult to break.

Breaking Unbreakable Bonds

When the researchers exposed lignin to a biocaustic, its polymers broke down in a way that preserved the aromatic rings. They found that about 17% of the processed lignin was transformed into carbon rings called flavonoids, a nutrient rich in antioxidants, often found in nutritional supplements. These resulting aromatic rings are also commonly used in medicinal chemistry, and can be used as plant derivatives and sustainable alternatives to inexpensive drugs and supplements.

Gray said: “The innovative method breaks the polymer bonds between the rings, but selectively preserves the structure of the rings themselves. If you can preserve these aromatic rings, then you can make high-value materials. Before that, chemists had developed catalysts that degraded all of the lignin, and then had to rebuild the aromatic rings to take advantage of them, but we were able to selectively degrade the lignin; To preserve these rings.”

The remaining percentage of the processed lignin (about 80%) has been transformed into carbon-based nanoparticles, which can be used to include targeted drug delivery materials for humans, or targeted nutrient delivery in plants. Nanoparticles could also provide a sustainable, plant-derived alternative to sunscreens and cosmetics.

Wells said: “It is exciting to identify and explore a path to sustainably recover resources from waste. We have huge amounts of wastewater and lignin waste that require high costs to treat. So we are trying to reimagine these wastes as sources of value.”

Resource recovery without hazardous chemicals

Although the researchers could have used any commercially available caustic to treat the lignin, their approach using caustic from a microbial electrolysis cell has several advantages. On the one hand, the resulting caustic is considered a green chemical, since it is recovered from a waste product. On the other hand, this caustic material is safer and less expensive, and it can be generated when needed.

Wells added: “There are many caustic materials, such as sodium hydroxide, which are commonly used in many industrial processes and wastewater treatment, but relying on them will necessarily mean shipping and storing large quantities of toxic chemicals. Not only is this expensive, it also poses a public health risk; Therefore, bio-generated caustic from waste is considered safer and more sustainable. Another advantage is avoiding dependence on supply chains to secure the chemical needs of this process, as the innovative method gives us flexibility and the ability to adapt. To generate the necessary chemicals when they are needed.”