Lyocell 2.0

High viscosity mixing & kneading

All-phase processing

Safe handling of product phase changes which may typically occur during processes such as evaporations, drying, devolatilizations, crystallizations, (de)sublimations, polymerizations, polycondensations, chemical solid-liquid and solid-gas reactions, recycling and recovery.

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NMMO

The Lyocell process uses N-methylmorpholine-N-oxide (NMMO) as a solvent. NMMO is very hygroscopic and quickly and easily absorbs water and atmospheric moisture. It dissolves a pulp only within a certain concentration range, the so-called dissolving window, in which NMMO forms a monohydrate with water.

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Dissolving process

The usual manufacturing process of a Lyocell spinning solution from pulp starts with an excess of water, allowing the NMMO to strongly penetrate the pulp without dissolving it. Thus, the NMMO, the water and the pulp form a suspension. By adding energy, the water begins to evaporate until the dissolution window is reached. The pulp begins to dissolve, the suspension becomes a solution, and the viscosity increases sharply. During these processing steps, a good mixture of the components is essential for the success of the process ultimately targeting a high degree of homogeneity. LIST KneaderReactors are specialized in mixing highly viscous substances and evaporating volatile components. They are the key element of the LIST Dissolving Technology Platform and their use addresses the concerns for Safety and Quality.

Viscose vs Lyocell
The Lyocell process is fundamentally different from the viscose process: The viscose process includes a process step that converts the cellulose pulp into an intermediate called derivative, specifically a xanthogenate, through a chemical reaction (derivatization). Cellulose fibers are then obtained from a viscous solution of this derivative (not directly from a solution of the cellulose pulp like in the Lyocell process). The average chain length (DP) in the solution is shorter, which is a limitation of the derivatization reaction. In addition, unlike the Lyocell process, the viscose process of the derivatization to make the Xanthogenate uses CS2, a chemical which is highly harmful to humans and the environment. This is in particular not compatible with the sustainability goals of fibers from recycled textiles.

Dissolving Technology Platform
LIST specializes in KneaderReactors for various high-viscosity processes in the chemical industry. They include a wide variety of applications in all sizes - from laboratory kneaders to 100 ton heavy machines. Since about 2018, one of LIST's most dynamic business areas is in the textile industry. The process is a direct dissolving process, the most common of which is known as Lyocell.

With its KneaderReactors, LIST specializes in the mixing and kneading of viscous materials. For this purpose, LIST operates a pilot plant center in Switzerland, in Arisdorf nearby Basel, where the products of LIST customers are tested and process design data is collected. One of these applications is the production of a homogeneous high-viscosity solution of cellulose, which can be pressed through a spinneret to produce cellulose-based fibers. LIST provides the dissolving technology platform for fibers from any type of biomass from lab to world scale.

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Safety

NMMO in itself is harmless to humans and the environment. However, overheating of the solvent can, under certain circumstances, lead to an autocatalytic reaction with a sudden release of gases, i.e. an explosion. Water evaporation requires high heating temperatures. Constant temperature control is therefore very important. If a temperature rise is detected, the energy supply must be reduced immediately.

In LIST KneaderReactors, the energy input occurs largely through mechanical energy from the rotation of the shaft and interaction of the mixing elements. The high viscosity causes friction, which heats the product. This frictional heat is the predominant energy to evaporate the water compared to hot heating surfaces in other process technology. Thereby, the use of LIST KneaderReactor increases the process reliability and safety.

LIST KneaderReactor increases the process reliability and safety

The good mixing of the mass in the process chamber of the LIST KneaderReactor ensures that no hotspots are formed. Since the frictional heat is directly dependent on the rotational speed of the shaft, the product temperature can be precisely controlled. In an emergency, the shaft rotation can thus be quickly and greatly reduced or even stopped altogether, thus immediately stopping the energy input. This input of mechanical energy is an advantage over a thin-film evaporator, whose energy input is via heated surfaces that remain hot even after the heating energy has been stopped and can continue to heat the thin film of product.

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Quality

LIST KneaderReactors are specialized in mixing and kneading of viscous materials due to the following unique properties:

1. The unlimited mixing intensity and residence time range of the LIST KneaderReactor allows dissolving also high cellulose biomass and/or extra high homogeneities. The Lyocell producer can thus easily switch to other cellulose sources that may be cheaper, more sustainable or higher quality
2. Tight temperature control due to
   • mechanical energy input through shaft rotation speed, combined with a
   • high accuracy of the temperature measurement due to the good mixing of the product mass
3. No hotspots can be formed in the process chamber due to the good mixing of the product

This accurate temperature control heats the product just enough to evaporate the water without overheating the rest of the product while concurrently mixing it with a biomass-specific intensity to reach the required homogeneity. This makes it possible to dissolve pulps from alternative biomass, such as hemp or cotton from recycled textiles, to 100% and process them into fibers.

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Prepared for dynamic Markets

Lyocell plants equipped with LIST KneaderReactors enable the plant owner to change the pulp source and adjust the relevant process parameters without having to rebuild the plant. Lyocell producers can thus confidently follow developments on the pulp side and react flexibly to them at any time whether they are striving for cost leadership with low-cost pulp or want to differentiate themselves on the market through high fiber quality using high-quality pulp.

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0 - 100% alternative Biomasses

LIST KneaderReactors have been specially developed for various high-viscosity processes in the chemical industry. Their strength lies in the continuous conversion and processing of highly viscous masses, whereby these can be kneaded at any intensity for any length of time. This technology allows to set a processing time and intensity specifically for any pulp. LIST KneaderReactor based plants have never faced any quality limitations and could easily dissolve alternative biomasses, such as 100% hemp-based pulp (Lyohemp^©). The use of LIST KneadingReactors gives you the option to switch your biomass any time from traditional dissolving wood pulp to 100% alternative biomasses  - or to any blends thereof - requiring more dissolving-homogenization time. 

Do you know, which pulp you want to process in the future?

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LIST Combo

In the 1990s, thin film evaporators were used in conjunction with the LIST KneaderReactor for the development of the manufacturing process for Lyocell spinning solutions. As the name suggests, a thin film evaporator is characterized as an efficient evaporator. Below a certain water concentration in the NMMO the cellulose dissolves and causes the product viscosity to increase. In this range of high product viscosities, thin film technology reaches its limits. However, it is precisely in this part of the process that the LIST KneaderReactor shows its strength. The LIST Combo System combines the strengths of both technologies, the thin film evaporator evaporates the water until the viscosities increase such that a LIST KneaderReactor can handle the product better. The process can then be completed to a homogeneous spinning solution without limiting the residence time or mixing intensity.

This combination of advantages has become more and more relevant in recent years, due to the increasing demand for

• High Capacities
• No Dissolving Limitation for alternative biomasses or extra high homogeneities
• Simple & Robust process that is especially suitable for newcomers to the market
• Safety AND efficiency
• Energy savings

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Why Now?

In recent years, the textile industry has recognized its lack of sustainability and the interest in producing sustainable cellulosic fibers grew quickly. The realization took hold that pulp sources for alternative biomasses must be developed to meet the raw material demand that could replace even a small portion of polyester fibers. This has since been reflected in several technology innovation initiatives. Hereto, more technological flexibility in processing time and intensity is needed - and LIST KneaderReactors provide this.

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High Capacities

The largest thin film evaporators do not require the largest LIST KneaderReactors. Conversely, this means that a large LIST KneaderReactor can be combined with more than one thin film evaporator in a LIST Combo system set-up. Further, all of the heating surface of a thin film evaporator can be used for heating and no areas need to be reserved for a dissolving section, where hot surfaces must be avoided for safety reasons. This increases the capacity of spinning solution production because the entire surface of a thin film evaporator is available for evaporation and several thin film evaporators can be connected in parallel to a LIST KneaderReactor (see also "Energy savings").

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Safety and Efficiency

As the highly viscous process section is shifted to the LIST KneaderReactor, less consideration has to be given to excessive shear and product overheating in the thin film evaporator. Without a LIST Combo System, this higher shear in the thin film evaporation could lead to product damage or autocatalytic decomposition (explosion).

In the LIST KneaderReactor, cellulose from any biomass can be dissolved and homogenized with any mixing intensity and for any length of time. Thanks to the exact temperature measurement and the energy input via the shaft rotation, the product temperature can also be controlled precisely and "fail-safe".

The division of evaporation and dissolving into two separate pieces of equipment avoids a compromise between efficiency on the one hand and safety and quality on the other. This makes the operation more robust and thus safer to operate.

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No Dissolving Limitations

The unlimited mixing intensity and residence time range of the LIST KneaderReactor allows dissolving also high cellulose biomass and/or extra high homogeneities. The Lyocell producer can thus easily switch to other cellulose sources that may be cheaper, more sustainable or higher quality.

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Energy Savings

In the LIST Combo mode, the thin film evaporator does not have a homogenization section in which it would have to cool the product due to consideration of product quality and process safety, which means avoiding a loss of energy.

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Simple & Robust

The division of evaporation and dissolving into two separate equipment avoids the compromise between efficiency on the one hand and safety and quality on the other. This makes the process more robust and easier to operate. Ideal for Newcomers in the industry.

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High Tenacities

Due to RePulp’s high cellulose content Lyocell fibers from 100% RePulp have higher tenacities than from traditional dissolving wood pulp.

Why high tenacities?
Cotton has cultivated for thousands of years to obtain fibers. Their cellulose-based structure makes them moisture absorbing and comfortable to wear. Cotton-based pulp has a higher cellulose content than wood-based pulp – but also requires more kneading-mixing intensity during the process to also dissolve the long polymer chains. In a direct dissolution process, as used in the Lyocell process, the cellulose is physically dissolved and the polymer chain lengths (measured in DP - Degree of Polymerization) are largely retained. If cellulose with long polymer chains (like RePulp) is used in the Lyocell process, they remain and increase the tensile strength of the Lyocell fibers.

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Specific Qualities

The unlimited kneading mixing intensity allows to process

• pulp with integrated additives for functional fibers,
• pulp for spinning solutions for filaments

to increase the product value.

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Lyocell from 100% Recycled Textiles

Today's Lyocell plants are built to process wood pulp. They cannot process 100% recycled pulp. Typically, only proportions on the order of 30% RePulp are possible in pulp blends. 70% is still virgin wood-based pulp so that the process is similar to that of pure wood pulp. LIST KneaderReactors do not have this limitation. The high cellulose content of RePulp requires a higher mixing intensity and LIST KneaderReactors make it possible to obtain Lyocell fibers from 100% RePulp.

• High Tenacities
• Integrated Pulp-Fiber Plants

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Integrated Pulp-Fiber Plants

Lyocell made from 100% RePulp or from other cellulose rich biomass has a very substantial strategic implication. It enables fully closed supply chains in the fashion industry. A limitation of only 30% RePulp would mean that a production plant for Lyocell from used clothing would in fact still have to process an additional 70% pulp from virgin wood. In other words, in order to recycle used clothing, twice as many trees would have to be felled - measured in cellulose equivalents.

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Textile Recycling Process

Recycled pulp is obtained from textiles containing cotton fibers. Most of them are blended fabrics. Most are polycotton, namely blended fabrics made of cotton and polyester fibers. Here, the polyester must first be separated from the cotton. Most easy is the processing of pre-consumer (pre-use) cuttings from pure cotton textiles, which are produced by textile processors. Their composition is known, and the textiles are not contaminated. Most costly are used (post-use or post-consumer) polycotton fabrics. Like with wood-based pulp, they must meet a specific requirement profile. These requirement profiles are different for viscose and Lyocell and vary from fiber manufacturer to fiber manufacturer.

Various manufacturing processes are currently being developed and launched on the market for this purpose. They are at different stages of development. They all go through several process steps, typically starting with a pre-selection in the supply logistics through cooperation with the textile collection organizations, then start with mechanical process steps followed by chemical processes to produce a RePulp with the required specifications.

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Re-Recycling

As soon as Lyocell textiles made from recycled cotton textiles come on the market, the question of their further recycling arises immediately. Lyocell fibers can be recycled at least five (5) times.

Since cotton fibers account for just over one-fifth of the total fiber market, using cotton fibers for the first time followed by recycling them four more times would equal the total biomass to produce all synthetic and natural cellulose-based fibers combined - without cutting down a single tree.

This consideration is not about how much of the polyester fiber market could be replaced by cellulosic fibers. It is simply about showing the potential that lies in re-recycling.

Closing the textile loop not only improves sustainability, but also reduces dependence on raw materials and shortens transport distances.

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Establish New Supply Chains

Other than wood-based pulp, the raw material of RePulp (textile waste) occurs locally in the middle of the end-user market. This enables

1. completely new, local supply and value chains with shorter transport routes,
2. less dependence on foreign countries
3. involvement of the end consumer – enabling completely new branding strategies.
4. better control the supply chain
5. more credibly guarantees of sustainability of their value chain
6. greater customer awareness through the use of recycled pulp.

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Compete on Cost

The capabilities for high capacities, low energy costs and a wide range of type of biomasses allow the reduction of production cost per ton of fiber by low specific staff cost, low specific capital cost, low energy cost and by low raw material cost.

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Compete on Product Differentiation

The unlimited kneading mixing intensity allows to process

• unblended biomass with a high cellulose content for high tenacity fibers,
• pulp with integrated additives for functional fibers,
• pulp for spinning solutions for filaments

to increase the product value.

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