Optimization of Cellulose Dissolution Stage in Lyocell Process As Origin for Different Applications A

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FIBER RAW MATERIALS Optimization of cellulose dissolution stage in lyocell process as origin for different applications A. Diener, G. Raouzeos, List AG, Arisdorf/Switzerland

The worldwide interest to modify cellu- List technology in brief the List cellulose dissolving technology lose by means of lyocell process has in- preferably operates at temperatures low- creased strongly in the last 5 years. To- Scale of operation and features: er than 100 °C. A major advantage of the day raw cellulose, regardless of its origin, - Volume: 2.5-16,000 l low operating temperature and product - High interfacial renewal rate is available as low cost feed material. It - Large cross-sectional area temperature is the minimization of the can be processed into staple fibers, fila- - Large self cleaning heat exchange surfaces discoloration of NMMO and the maximi- ments and films. The core of the lyocell - Close temperature control zation of its recovery. processing technology is the dissolution - Narrow residence time distribution The large hold-up of the dissolver pro- - Operating pressure: 0.001 - ~150 bar besides the spinning step. - Processing viscosity: 40,000 Pas vides enough buffer capacity to regulate Parallel to viscose and cotton, lyocell fib- process fluctuation, if it should occur. ers show a progressive acceptance from Hence, the spinning solution is directly the market. The relatively simple adjust- the new List dissolution technology is discharged from the kneader in the filter ment of the properties of the lyocell fibers also available. This technology was de- and the spinning pump. ensures the provision of qualitative char- veloped in close collaboration with the A new development project between acteristics that previously could not be “Institute for Textile and Plastic Research TITK and List aims for further improve- reached with viscose fibers. The good (TITK, in Rudolstadt/Germany). In 1998 ments of the technology. It will result in skin compatibility as well as the high dry Alceru GmbH (Rudolstadt/Germany) and the 4th generation of the cellulose disso- and wet tear strength open new and Grasim Industries Ltd. (Nagda/India) im- lution by means of List technology. long-range future opportunities for the plemented the process on a pilot scale At present design work is being executed cellulose fibers. with a production capacity in the range of for production units with capacities 1000, List AG, Arisdorf/Switzerland further opti- 300-400 tons fibers/year. 5000, 10,000 and 15,000 t/year per line, mized the cellulose dissolution technolo- The cellulose dissolution in NMMO takes for the production of staple fibers, fila- gy, which was introduced in 1992. This place in a thick-layer kneader of the type ments and films. The spinning solution succeeded the production of excellent List Discotherm B Conti Fiber. The raw produced in the List cellulose dissolution spinning solution qualities, produced materials cellulose and NMMO are ho- unit can be used as a main stream for the from a variety of low cost raw materials. mogeneously mixed in the agitated production of fibers and as a secondary The technology fulfils the current high chamber of the kneader and processed stream for the production of filaments and safety standards. to the final cellulose spinning solution. films. TITK developed and defined the

In 2000 pilot units of the 3rd generation qualitative parameter “Filter Value (FP)” to Development and optimization were installed in the China Textile Uni- assess the spinning solution. This filter In order to increase the application of the versity (Shanghai/PR China) and in value is derived from the particle analysis lyocell process, it seems necessary to Fraunhofer Institut für Angewandte further optimize the dissolution step of Polymerforschung (Golm/Germany). Cellulose in NMMO. The optimization Both units have a processing capacity of aims to improve the economy of the pro- 50 tons cellulose/year. cess through the application of a cost-ef- The dissolution technology of the 3rd gen- ficient technology. eration aimed mainly for the optimization Reviewing the known processing tech- of the quality of the spinning solution (Fig. nologies to date, it is apparent that be- 1). In the foreground were the following: sides the industrially implemented spe- - use of raw cellulose of different origin cialized thin film processing technology, - production of spinning solution of con- stant and high quality - minimization of the gel formation in the spinning solution filter. Fig. 2 P & F diagram of the List cellulose soluti- For safety reasons ons-step

Cellulose solution in NMMO

✳ shaft speed (rpm) ● A (m2) ✛ Qmech. (kW)

Unit Index No.

Fig. 3 Process simulation: functions of the process conditions and the Fig. 1 Dissolving unit of the 3rd generation apparatus know number

260 CHEMICAL FIBERS INTERNATIONAL Volume 51, September 2001 FIBER RAW MATERIALS of the spinning solution. It is defined as the graded. Additionally the low operating uct properties and equipment specific quotient of the largest particle diameter Xm temperature ensures high safety levels. geometric characteristics. and the logarithm of the number of parti- Up to 80 % of the necessary energy for The worth of this cellulose cles N10 with sizes equal to 10 µm. the dissolution process is supplied by dissipation. dissolution technology The operating temperature should prefer- Taking into account the stringent process ably be under 100 °C. The large hold-up safety demands, which are fulfilled

Solutions with FP < 50 have excellent and the large contribution of the dissipa- through the selection of adequate con- spinning quality, while solutions with tion energy to the total thermal duty allow struction material and the limitation of the ≤ 50 FP < 100 designate adequate spin- for a simple automatic process control. operating temperatures, the technology ning quality. For the detailed optimization of the oper- was optimized to produce excellent spin- ating parameters, which would best ning solutions from practically any cellu- Particulars to the List NMMO match the solution of any raw cellulose, lose, regardless of its origin. cellulose dissolution technology List provides state-of-the-art pilot units in Through the optimization of the dissolu- The large volume kneader of the Disco- its test center in Arisdorf/Switzerland. tion process and of the kneader it is pos- therm B Conti Fiber has proved very flex- The same pilot units are also available sible to produce spinning solutions of ible with regard to adapting the process for rental and for purchase. very good quality without pre-treatment for different raw cellulose qualities, but (activation) of the raw cellulose. The also when variations in the spinning pro- Process simulation spinning solution can be used for the process occur. The large processing volume List developed a process simulation production of fibers, filaments and films. serves as a buffer tank for the spinning gram for supporting the design and opti- The really compact technology can opti- solution. The mixing/homogenization mization of the process. Furthermore, pi- mally be regulated and controlled. It is step, which is pertinent for the prepara- lot and full scale process data can be fit- characterized by its flexibility and easy tion of the cellulose dope, can be simulta- ted. Fitting and interpreting pilot-scale adaptation on process conditions and neously used for the addition of addi- data, the simulation leads to the optimum product compositions. Low operating tives. design of the full scale unit. Using full- temperatures and the short residence Due to the high flexibility of this dissolu- scale data the simulation delivers infor- time of the processed product minimize tion technology, an intermediate buffer mation about the flexibility of the process the recuperation and rectification costs of tank be avoided. Consequently, the filter and the reserves of the plant. NMMO and contribute to the maximiza- and the spinning unit would be installed Fig. 3 shows the influence of the speed of tion of the economy of this technology. downstream to the discharge nozzle of revolution of the kneader’s agitator on The integration of the continuous prepa- the Discotherm B Conti Fiber. It is appar- the generated dissipation energy. The ration of the cellulose dope in a List Co- ent that the equipment and the space re- combination of those two parameters en- Rotating-Processor Conti rounds off the quirements are reduced, which in turn ables the optimal selection of the optimization of this technology. grants economic benefits. processing machine. The basis for the The List cellulose dissolution technology process simulation are the mass and en- Outlook is clearly characterized by the low oper- ergy balance, equipment characteristic List is currently negotiating the extension ating temperature. This offers the advan- values, caloric properties of the compo- of the field of application of this technolo- tage that the product is not thermally de- nents, shear effects as function of prod- gy with new partners.

Complete spinning line for nonwovens viscose fibers Lenzing Technik GmbH & Co. KG, Len- regard to clean operations and easy logical scaleup and development are all zing/Austria, is currently focussing on a maintenance. factors which have had to be dealt with. construction of a new 35,000 t/year pro- As an essential part of the gas-recovery, Using this project, Lenzing Technik aims duction line for Lenzing AG at its head- a CS2 condensation plant will be installed to implement advanced technology in quarters. This project represents the in addition to the activated carbon plants. their own plant and gain experience. strategy of the plant’s continuous capaci- Another set of candle-filters will be added ty expansion. At the same time this is to the sluice circulation system. currently the biggest investment espe- While the overall concept of the single cially in the fiber spinning section. line high capacity will allow for economic Eastman PET business to be The project covers the complete spinning operations, the production will focus on called Voridian line from spinning machines to the dryer nonwoven fibers; the technical features Eastman Chemical has chosen Voridian and the required expansions of circula- have been especially designed with re- as the name for the new company that tion systems as well as gas and spinbath spect to this requirement. will incorporate its polyester, acetate fib- recovery. The complete equipment for the spinning ers, and polyethylene businesses. East- The new spinning line is based on the LT line has been manufactured in the LT man is scheduled to split into two compa- design and covers the latest innovations workshops and is being currently assem- nies at year-end. Its specialty chemicals to ensure the product properties and bled by the Lenzing Technik staff. and polymers business (including coat- highest quality standards for current and Regarding the specific challenges of this ings, adhesives, inks, specialty poly- future markets. With the new design for a project the very tight schedule has to be mers, intermediates) will continue oper- 4 m wide aftertreatment, Lenzing adjust- mentioned: one year from start of design ating as Eastman. Voridian will have 9 ing the technology to the changing re- till startup. The extremely limited space production sites in seven countries, with quirements. The drum-dryer has been of a plant, which has been growing over two contract manufacturing sites in Asia redesigned and improved especially with several decades, as well as the techno- and one in North America.

262 CHEMICAL FIBERS INTERNATIONAL Volume 51, September 2001