Polyurethanes

RECOVERY OF POLYOLS FROM FLEXIBLE POLYURETHANE FOAMS THROUGH GLICOLISIS.

Author: MOLERO CEREZO CAROLINA.
Year: 2006.
University: CASTILLA-LA MANCHA [www.uclm.es].
Place of defense: FACULTAD DE CIENCIAS QUIMICAS.
Place of preparation: FACULTAD DE CIENCIAS QUIMICAS.

Summary: Since its discovery in 1937 was the polyurethanes, this product has become one of the most important groups of polymers. La variedad de polioles y aditivos susceptibles de uso en la síntesis del poliuretano ha dado lugar a un amplio rango de productos con numerosas aplicaciones donde destacan las espumas flexibles de poliuretano, que abarcan el 29% de la producción total. However, as a direct consequence of commercial success there has been an increase in the amount of waste produced and to be managed. Traditionally these residues found in landfills their destiny, but environmental issues that comes running out to find solutions based on recycling through physical or chemical processes. Currently chemical processes described are based on treatments such as hydrolysis, aminólisis or glicólisis, producing a break of the link urethane by hydrolysis or transesterificación leading to the release of the structure of polymeric polyol. These treatments provide a liquid mixture of products which only allows its use mixed with virgin polyols obtained polyurethanes lower quality. The main objective of this work is to study and development of a recovery process chemistry polyols residues present in flexible polyurethane foams. For the development of the recovery process of polyol from waste polyurethane was selected for their special characteristics, the procedure glicólisis under heading. This process involves the treatment of polyurethane with glycols low molecular weight, so that the hydroxyl end groups glycol produced an exchange on the link urethane, freed polyol to the reaction medium. The act of using excessive polyol glycol and recover a high molecular weight provides separation of phases in the reaction products, where one of the phases is comprised mainly by the polyol recovered with low pollution. The glicólisis phase line has the important advantage over other processes glicólisis that the final product recovered presents greater purity than in homogeneous processes. To carry out the study process and the influence of the variables on it, it was a facility where laboratory to conduct experiments glicólisis, and were nearing the analytical techniques needed to monitor the response and characterization products. First, they conducted some preliminary experiments that helped establish the experimental procedure and obtain a preliminary analysis of the technical feasibility of the process with industrial waste foam to treat. In these experiments, conducted under conditions similar to those described in literature for a different kind of foam, was used as diethylene glycol (DEG) glicólisis agent and as a catalyst dietanolamina (DEA). Through them, we checked the suitability of the process and were selected conditions experimental basis to enable the obtaining of a biphasic product. It was noted that the upper stage consisted mainly by the polyol recovered and lower phase by excessive glycol and products of reaction. During these experiments, we studied the evolution of the concentrations of the species in the environment over time, the terms of repeatability and the basic mechanisms of reaction. It was proved the necessity of using a catalyst to carry out this process, as though the glycol is capable of producing some substitution of urethane on the links in the absence of catalyst, the activities of the temperature is not sufficient to obtain the complete decomposition the foam reaction times moderate. Later, we moved on to study different systems glycol / catalyst for the reaction, taking into account 8 the influ 1ff8 fer ence they had on the process. For the study were selected glycols monoetilenglicol (MEG), diethylene glycol (DEG), monopropilenglicol (MPG) and dipropilenglicol (DPG), and that due to its low molecular weight had expectations to produce a final product biphasic. As catalysts were selected from the literature DEA and n-butóxido titanium, as well as two new compounds, octoato potassium and calcium, not described previously in similar applications. First, we studied the catalytic role of the DEA, using different glycols above as agents glicoliticos. These experiments led to know how the glycols influence on the characteristics of the end products and on the time required to achieve complete conversion. There was an increased solubility between phases using glycols propilénicos, leading even to a product phase in the case of DPG. On the other hand, the biggest reaction times were obtained in the case of MPG. Taking into account both the similarities of polyol recovered with the departure of the concentration of this and the reaction times required, the SDR agent glicólisis seemed more appropriate to carry out this process. During the study of the system glycol / n-butóxido titanium, which was not included by the DPG lead to a homogeneous product, were confirmed earlier trends in terms of speed and properties of the reaction products on the basis of glycols employees Check required a minor reaction time and got a polyol with better properties in the case of process conducted with SDR. There was also less by the catalytic activity of titanium with respect to the DEA, indicating reaction times and obtained a much higher polyol recovered with the worst properties. Once selected the SDR glycol as most appropriate to carry out the recovery of polyols, assessed the activity of octoatos potassium and calcium as a catalyst. These novel compounds presented excellent characteristics as a catalyst and pose a novel alternative to those described. The amount of octoato used to obtain a speed of decomposition similar to the one obtained with DEA, the catalyst of the more active studied, only accounts for 15% of it, being the characteristics of polyol recovered better than those obtained with the catalyst of titanium. Since the octoatos increased speeds degradation and led to some polyols with appropriate characteristics, we proceeded to study the influence of different process variables (concentration, temperature and mass reason) to employ them as catalysts. The results obtained from the study of the influence of the amount of catalyst noteworthy that although an increase in the quantity of catalyst accelerates decomposition, this increase is more pronounced at low concentrations because after a certain amount was noted that the increase the speed of decomposition was not significant. Moreover, the increase in the quantity of catalyst, carries a negative effect associated. The use of greater amounts resulted polyols most polluted because of the increased solubilization between phases surfactant prompted by the nature of octoatos. Así mismo se comprobó que el proceso era mucho menos sensible a cambios en la concentración de catalizador en el caso del octoato de calcio, siendo necesario un gran incremento en la concentración para obtener mejorías similares a las obtenidas con el compuesto de potasio. The temperature range in which it was noted that the glicólisis was feasible, includes a narrow margin work, because at temperatures lower than 170 ° C the speed of reaction is very slow and is not operational work over 200 ° C due to difficulties in the experimental setup and the promotion of secondary reactions of descarboxilacion. Within this range, there is a very strong dependence of the reaction rate with temperature, as well as an increase in oxidation of polyol recovered and a sustained increase in the concentration of pollutants in it. The reason mass foam treated regarding the agent of glicólisis is an important variable related to both the operability and with the economy in the process. For its study, we conducted a series of experiments in which Modified reason polímero-agente, keeping all other variables of the process fixed. Through them we determined the minimum proportion of glycol from which the two-stage process was carried out in the experimental configuration used. It was also noted that employ large excess agent glicólisis favored the operability of the system and increased the purity of polyol recovered by dilution of the products in phase glycol. Because after a certain excess of this improvement is not very representative and an increase in expenses associated with a large number of glicólisis agent, it was determined the most appropriate, with the latter reason to Mass foam glycol 1:1, 5. The octoatos used as catalysts showed excellent catalyst for the process, although it was found in the literature. In order to complete the study of their influence on the process of transesterificación and achieve a better awareness of the same, it conducted a series of experiments by changing both the anion part of the catalyst (carboxylate), as the cationic species of salt. To study the influence of the anion part of the catalyst was contrasted the use of acetate and benzoate versus octoato, all as potassium salt. The effect of changing the type of carboxylate on the characteristics of polyol recovered and the kinetics of decomposition was insignificant due to the same mechanism of action, the weak core carboxylate salts is responsible for its catalytic activity. The study of the influence of cationic species were used various preparations commercial octoatos of alkali metals and alcalino-térreos and Transition metal. For each of the octoatos studied different catalytic activities were obtained depending on the hardness and ability coordination cation. Based on the experimental results obtained ran a reaction mechanism with several steps, depending on the nature of cation: formation of a alcóxido metal coordinación-inserción of alcóxido in the group and transfer urethane polyol recovered from a molecule glycol. Among all salts studied, octoato lithium presented the best results in terms of speed decomposition and purity of polyol recovered. The biphasic process, but allows the obtaining of a polyol much more pure than in the case of uniform, resulting in two phases product that presents a small mutual solubility. This raises the need for further purification to obtain a polyol that meets all specifications commercial product virgin, and therefore carried out the study of the purification stages obtained. To have a sufficient quantity and homogenous product with which to conduct studies purification stages were conducted an experiment in a pilot-scale reactor discontinuous. Compared with the processes at the laboratory scale of change alone resulted in slight variations in the speed of reaction and properties of the end products, mainly due to differences in system configuration, such as feeding solids. It tested well that the process was applied consistently and on a larger scale. After some preliminary tests, it was found the liquid-liquid extraction with water as the best option in the purification of polyol product as a higher stage. This or 8 eration 14d2 would glycol and the elimination of impurities through a second aqueous phase liquid, partially inmiscible with polyol. To determine the best operating conditions for the purification, it conducted a series of experiments of extracting polyol obtained a pilot scale. As process variables were taken temperature, why mass disolvente-poliol, pH of the aqueous solvent (neutro-ácido) and type of separation (decantation, centrifugation). The influence of the same was studied on the pH of the extract's departure, and decanting the tendency to phase separation as well as the concentrations of polyol, water and impurities in the refining and extract. Starting with the study conducted, defined the optimum operating conditions for the purification of polyol so as to increase its purity, minimizing losses in the extract. It is concluded that the best operating conditions involving the use of solvent pH slightly acidic, separation by decanting natural excess solvent front of the food and temperatures above room temperature. Given that the main application of polyols polieter is the manufacture of flexible polyurethane foam, the key parameter that defines its quality and usefulness is the ability to foam and reaction with isocyanate to give rise to such products. To consider reuse polyols once purified in the replacement of commercial products were tested foam from an original recipe of flexible polyurethane foam. As a result of the replacement at different percentages of polyol virgin recovered were obtained with foam profiles risométricos close to those obtained with polyol virgin, except for replacements of 100%. With respect to the mechanical properties, the introduction of a 25% polyol not recovered was a detriment in the physical properties of foams. Higher rates resulted in minor changes in the profiles and physical characteristics of the foam, thus requiring an adjustment in the recipe for preserving properties related to the characteristics of elastic and flexible foams comfort. On the other hand, lower phase obtained by glicólisis represents a residue which contains the large amount of glycol used in excess to produce separation of phases. Therefore, it designed a revaluation process for this phase, which included the recovery of excess glycol used for recirculation process glicólisis and implementation of waste distillation as a starter in the synthesis of new polyols rigid. To carry out the recovery of glycol was chosen by the vacuum distillation, so that it obtains a pure glycol capable of reuse. The glycol recovered retreated content catalyst was recirculó back to the processes of glicólisis, displaying behavior similar to fresh glycol. With the residue vacuum, and because of its high content in functional groups with proton labile likely to be initiators of anionic polymerization of epoxides, undertook a study of application as starter in the production of polyols polieter rigid. This synthesized varying degrees of a rigid polyol based waste and on the basis of a commercial originator, toluendiamina (TDA). The kinetic constants calculated for different polyols synthesized showed the same order of magnitude, demonstrating the suitability of the waste as a starter. Trials of foam polyols obtained on the basis of residue for obtaining rigid polyurethanes were also favorables.El treatment proposed for later phases obtained after glicólisis of foams get not only improve the quality of polyol recovered, but also take the products created. From conceptual design process integrated glicólisis was carried out the design and construction of a pilot unit to operate continuously, with a processing capacity of 5 kg / h cuts foam. A first approximation to the operation of a pilot scale prototype, not optimized conditions, showed that it was possible to carry out the process under stationary at low levels of recovery and a purity of polyol glycol recovered satisfactory. The slight differences observed with respect to the results obtained in the laboratory are justified by the change in scale and the move from batch to continuous operation in the pilot plant.

POLYURETHANES