Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
2001-06-21
2003-10-28
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S129000, C528S256000, C430S627000, C430S495100, C250S339090
Reexamination Certificate
active
06639044
ABSTRACT:
The present invention relates to the use of a spectroscopic method (NIR (Near-infrared spectroscopy)) for monitoring an industrial process (production of resin bonded composites particularly formaldehyde resin bonded composites) from the analysis of raw materials and intermediate products (such as urea-formaldehyde concentrates) to the quality control of the final product.
The use of NIR spectroscopy to monitor various processes has been developed systematically during the last years and was assisted by the increase in speed and capacity of the computers available. This NIR technique has been applied to various industries such as the oil industry, pharmaceuticals, food industry, control of fermentation, and certain polymer manufacture. There has been the use of the system in on line and end point determinations and reaction coordination for homogeneous and heterogeneous reactions. The analysis has been carried out on liquid and vapor phase process streams. In line process monitoring on polymer systems by NIR spectroscopy is discussed by D. Fischer et al., Fresenius J. Anal. Chemistry, 359 (1997) page 74 and J. Dunkers et al, Fourier Transform-NIR monitoring of Reacting Resins Using an Evanescent Wave High Index Fiber optic Sensor, Applied Spectroscopy, 52 (4), 1998, page 552. In particular the use of the system has been described in particleboard (composite board) manufacturing for monitoring raw wood quality (B. Engstrom and Mona Hedqvist, Prediction of the Properties of board by using a spectroscopic method combined with multivariate calibration, U.S. Pat. No. 5,965,888).
The manufacturing of composite wood-based panels (particleboard, medium density fiberboard, etc.) originated from a market need to provide inexpensive wood product alternatives and relied originally on the use of urea-formaldehyde adhesives. At high formaldehyde to urea ratios (F/U≈1.5 molar), these water-based adhesives are easy to make and use, and give excellent bonding results to almost any kind of wood chip. Around 1978, environmental concerns for formaldehyde emission imposed lower F/U ratios (≈1) that brought up the need for a much more careful and systematic control of the adhesive production. Furthermore, it was proposed that urea-formaldehyde concentrate (UFC) be used instead of formalin as a raw material for the preparation of the adhesives, in order to reduce the costs and hazards of transportation and to avoid the application of vacuum for the distillation of the excess water at the end of resin production. Despite its merits, only very few manufacturers implement today the UFC approach, because of its chemical complexity and the lack of quick methods for its characterization. Formaldehyde-based adhesives are made reliably by relatively large companies that have developed semi empirical know-how and can afford occasional application of costly and time consuming off-line monitoring techniques (GPC, NMR, etc.).
UFC is an intermediate for the resin synthesis that is typically prepared, by a continuous process, in an absorption tower. During this process gaseous formaldehyde is absorbed by an aqueous solution of urea. Absorption involves both dissolution of formaldehyde as well as chemical reaction of formaldehyde with urea. The ratio of urea to formaldehyde and the total solids content, pH, and temperature vary along the absorption tower and are important for the quality of the final product and the safe continuous production. Irregularities in the process can result in insoluble precipitate formation along the length of the tower or even blocking of intermediate disks of the tower.
The final product is a complex mixture of at least fifteen different compounds. The precise determination of the urea and formaldehyde content in these compounds is essential for the subsequent formulation of the resin. Conventionally it is performed only off line by tedious methods. One such method involves the hydrolysis of the UFC to obtain formalin that is subsequently extracted and after numerous dilutions; its concentration is finally determined by titration. The concentration of urea is calculated independently by determining the total nitrogen concentration (Kjeldahl method). The overall determination of formaldehyde and urea content with these methods takes more than four hours. Faster chromatographic methods have been developed but they are less accurate and require precise sample weighting and specific equipment. Furthermore, they cannot be applied on line. The above methods can only determine the overall content of urea and formaldehyde and give no information on the existing chemical speciation.
The UFC produced is subsequently used for the resin production (conventionally performed in a batch process). (Alternatively, formalin, that does not contain any urea, can be used for the resin production). The process of resin production is influenced by the raw materials used and the conditions applied and particularly the pH and concentration of the various components at every particular time. Failing to terminate the reaction at the correct conversion level can result in crosslinking of the resin and formation of an insoluble network inside the reactor. Furthermore, variability of resin production can result in variations in resin's performance that are decreasing the reliability to the customers.
An objective of the invention is to provide a methodology for the control of all the raw materials and intermediate products (methanol, formaldehyde, urea, urea solutions, UFC, melamine, etc.) involved in formaldehyde based resin synthesis.
Particularly for the case of UFC the objective of the present invention is to provide a methodology for the fast and reliable determination of its content in urea and formaldehyde. Furthermore this methodology will be adaptable to on-line monitoring of the UFC production process. Therefore the urea and formaldehyde content will be measured continuously and at various points along the absorption tower in order to ensure regular production or detect irregularities.
Another objective of the invention is to provide a methodology for monitoring the resin production and for ensuring the reproducibility of the final product.
It has surprisingly been found that NIR can be used for the determination of the overall content of urea and formaldehyde in UFC even though the latter is a complex mixture of more than 15 different compounds containing urea and formaldehyde.
It has also been surprisingly found that NIR can be used for the monitoring of reactions of urea and formaldehyde in the production of a UF resin. This enables the monitoring of the start of methylolation through to the ending of polymerization so as to an evaluation of the various stages of the production. Again it was surprising to find that NIR could be used for the monitoring of such a polymerization despite the complex mixture of different compounds formed during the polymerization.
According to a first aspect of the invention there is provided a method for controlling the production of formaldehyde resin compositions in which formaldehyde takes part in a reaction with one or a combination of co resin forming material (of the type phenol, urea, melamine) the method comprising monitoring at least one of the formation of reaction mixture and the course of the reaction by near-infrared (NIR) spectroscopy and adjusting the course of the reaction (when necessary) in accordance with the results of the spectroscopy to obtain optimum conditions for the reaction.
According to the second aspect of the invention there is provided a method for controlling the production of formaldehyde resin compositions in which formaldehyde takes part in a reaction with one or a combination of co resin forming material, the method comprising monitoring at least one of the formation of the reaction mixture and the course of the reaction by near-infrared (NIR) spectroscopy, adjusting the course of the reaction (when necessary) in accordance with the results of the spectroscopy to obtain optimum conditions for the reaction wherein said monito
Chryssikos Georgios D.
Dessipri Eugenia
Gionis Vassilis
Kalousis George
Paipetis Alkiviadis
Enigma N.V.
Ladas & Parry
Truong Duc
LandOfFree
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