Making plastic : extracting raw material
In 2012, 4.6 million tons of plastic were used in France (44% of it was for packaging, a much higher percentage than construction or the car industry). This makes France the third biggest consumer of plastic in Europe, after Germany and Italy. Previously, a large portion of this waste (a little over 3 million tons) were sent to landfills (1.4M tons) or recovered for energy (1.1M tons), while the leftover 17% were sent for recycling, transformed into new plastic material. But before being sold, used, and recycled (by recycling companies such as Paprec), plastic has to be made using a various amount of raw materials. Let us review these materials, in order to have a better grasp on the manufacturing process, which will help us better understand the subsequent recycling processes.
Petroleum (crude oil)
Although plastic does not occur naturally, specialised manufacturers have techniques to use natural polymers (this terms describes the macromolecular substances at the core of all plastic material) such as cellulose, starch, natural gas, and various plant-based proteins to create it. Despite these various sources, most artificial polymers today are made from petroleum, using this method:
There are two steps in the drilling of oil. Because the drilling operations are the only ones capable of certifying that oil is present in the target location, teams of scientists are first sent to perform lengthy analysis of the geological structures surrounding the location. The extraction process can start once the scientists have given their assent.
Next, several wells are drilled, creating optimal networking for the reservoir. The crude oil is then extracted using water or gas pressure systems. At the well’s surface, specialised machinery separates liquids and gases.
Petroleum has been classified into two groups: ‘conventional’ oil, that is liquid and easy to pump; ‘unconventional’ oil, such as shale oil or extra heavy oil, which are extracted using more sophisticated methods.
2/ Oil refining
Once the oil has been prospected, targeted, and extracted from the newly-dug well by huge pumping stations, the crude oil is transported via a pipeline to an oil refinery. It is then heated up to hundreds of degrees, sent up a fractional distillation column, a tower that separates the oil’s thousands of components using condensation or boiling-point techniques (the higher the boiling point, the lower up the column the component stays). Several distinct oils are thus obtained at the end of distillation process, such as fuel (for heating), diesel fuel, kerosene, and naphtha, the primary component for plastic making which condenses between 180°C and 40°C. It is also used to make colorants, fertilizers, cosmetics, perfume, pharmaceuticals, and various household products. However, it is important to note than only 4% of Europe’s petroleum consumption is used to make plastic.
The collected naphtha needs to undergo an important transformation step before being used by the plastics engineers. Cracking is the fragmentation of naphtha’s big hydrocarbon molecules into smaller, and thus more easily processed, sections. First, the crude oil is mixed with water vapour. The melange is then heated to 800°C, then very quickly cooled down to 400°C. The tiny molecules obtained (molecules with 2 to 7 carbon atoms called monomer’s) will be used to make chains called polymers, plastic’s basic building blocks.
Natural gas is obtained by roughly the same methods of extraction and cracking as crude oil (sometimes on the same site), but the plastic industry uses it for its potentially high ethane content, a gas that, once it has been condensed at below 100°C, is another raw material for plastic making. When heated to 850°C, ethane molecules separate and create a hydrogen and ethylene mix. Only the purified ethylene is then used to create the future polymer solids, also called polyethylene. It can be noted that, to create 1 ton of plastic material, 1.25 tons of ethane are needed, and the chemical industry annually produces a little over 130 000 tons of ethylene.
Over half of plastic packaging (mainly plastic bags and films, but not bottles) are made from polyethylene (PE). Thanks to progress in package sorting, recycling of this type of material has greatly increased in France, of which PE is an important part. It is also important to note that the recuperation of plastic lids also leads to a lot more recycling, specifically the recovery of high-density PE (PEHD).
38% of a plastic bottle’s composition is recyclable PET (polyethylene terephthalate), another plastic compound from the petrochemical industry. Its recycling rate has greatly increased over the last decade (up to 51%), thanks to the sorting of household waste, but also thanks to the building of factories specialising in the recovery of plastic waste, such as the site France Plastique Recyclage in Limay. The chemical recovery of PET allows recyclers to create material that is almost identical to the original plastic. Today, about 30% of plastic bottles in circulation are made from recycled material.
The petrochemical industry makes three other recyclable plastics: polystyrene, PVC, and polypropylene.
Contrary to popular belief, coal usage is ever increasing (with a record increase of 37% between 2002 and 2008). Coal is currently used for generating electricity, or in the manufacturing of various products such as cast iron, fertilizers, medicine, and plastics (Plexiglas, nylon, polyester).
Depending on the deposit’s depth, coal can be extracted from underground mines (by a header machine, a machine with a giant cutting head that collects minerals, leaving the galleries to collapse behind it), or from surface mining (in which case huge excavation machinery is used). Once it has been measured and sifted, the collected material is distilled in an oxygen-free coke oven. This coke-making process is used to create quasi-pure carbon, but also creates volatile material that can be used to create gas for households (among others), benzole (used a lot in the cosmetics and pharmaceutical industries), or coal-tar which can be reused to make plastic material.
It is interesting to note that the heat of combustion for recycled plastic is equivalent to that of coal (and petrol), which is why energy recovery is an important part of the plastic recycling industry.
Soil is rich in organic molecules, and the most abundant one is cellulose. This naturally occurring homopolymer (i.e.: made up of one type of polymer) is the main component of plants’ cellular walls, making up between 15% to 99% of the cell walls. This raw material is particularly used by the plastic industry for making cellulose acetate, celluloid, cellophane, or Rhodoid, and is extracted using a sequence of various mechanical and chemical treatments that separate the cellulose (mainly by grinding and purification) from the plant’s other components (sap, lipids, wax, etc). Further plastic-treatment processes (whitening, drying, formatting) can then be applied, depending on the desired type of product or the client’s needs. Cellulose fibres are used in many industrial sectors, such as the textile and paper industry, farming, or construction (particularly for insulation material).
Bio plastics, also called PLA (PolyLactic Acid), are derived from renewable biomass sources, such as cereals (corn, wheat, peas), tubers (sugar beets, sweet potatoes), oleaginous plants (castor oil), sugar production plants (sugar canes), or protein rich plants. Most of these plant based plastics can replace petrochemical processes or be associated with petroleum based polymers (a bioplastic can contain as little as 40% organic plant material); they are biodegradable, do not use limited resources (as well as costly ones, due to market fluctuations), and help lower CO2 emissions. However, using a biomass source consumes a lot of water, and research is now looking for processes that would be drier, more cost effective, and thus more environmentally friendly. Consequently, some second generation bio plastics are biodegradable and compostable, created from food or wood waste, and leave an almost invisible carbon footprint. At this time, some common household products are made with bio plastics (packaging, bags, kitchen ware, water bottles, razors, cling film), but the use of this type of plastic is still too negligible.
Recycling of non biodegradable bio plastics (biomass sourced PET, ET, or PE for example) is increasing, and, if pre-existing plastic recycling industries continue to process these materials, could slowly reconcile plastic and environment. On the other hand, the sorting of some biodegradable polymers such as PLA and PHA is not sufficiently carried out to avoid upsetting the general plastic recycling process.
The plastic recycling cycle is a step-by-step process. Discover the different steps :
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