CLIAMS:1. A process for crystallizing polyester chips having amorphousness greater than 90 %, said process comprising the steps of:
? providing said polyester chips;
? introducing said polyester chips into an operative inlet of a conveying system on to a conveyor belt, wherein a plurality of infrared lamps is disposed in proximity to said conveyor belt, for heating said polyester chips; and
? collecting said infrared heated polyester chips from an operative outlet end of said conveying system;
? wherein at least one factor from a group consisting of:
a speed of conveyor belt;
a heat emission rate of said infrared lamps;
number of said infrared lamps; and
residence time of said polyester chips on said conveyor belt;
is controlled during transit of said polyester chips, from said operative inlet to said operative outlet of said conveying system, such that heating of said polyester chips by said infrared lamps transforms at least some of said polyester chips from amorphous to crystalline form with a degree of crystallization upto 50%.
2. The process as claimed in claim 1, wherein at least a part of heat emitted by said infrared lamps falls on said polyester chips conveyed on said conveyor belt.
3. The process as claimed in claim 1, wherein said polyester chips before being introduced in to said conveying system have amorphousness greater than or equal to 95 %.
4. The process as claimed in claim 1, wherein said polyester chips have a shape chosen from a group consisting of rectangular, planar, spherical, cylindrical and any other shape.
5. The process as claimed in claim 1, wherein said infrared lamps span entire length of said conveyor belt.
6. The process as claimed in claim 1, wherein said polyester chips are Polyethylene terephthalate (PET) chips.
7. The process as claimed in claim 1, wherein said polyester chips are heated by the infrared lamps in the temperature range from 120°C to 210°C. ,TagSPECI:FIELD OF THE DISCLOSURE
The present disclosure relates generally to a process of crystallizing polyester resins and chips made therefrom and more particularly to a process for crystallization of polyester resins and chips made therefrom using infrared heating lamps.
BACKGROUND
In today’s world, thermoplastic and products made therefrom have become essential part of our daily life. This is evident from the use of thermoplastics in clothes, vehicles, appliances etc. The significance gained by thermoplastics may be attributed to the properties like good mechanical strength, low density and high formability to name a few.
As the name indicates ‘thermoplastics’ are materials that flow upon heating and harden when cooled. Various useful goods including but not limited to containers for storing food, beverage, and other liquid as well as synthetic fibers may be manufactured using thermoplastics by using a wide variety of techniques, such as injection moulding, thermoforming, blow moulding and rotational moulding. Further, thermoplastics have the potential to be recycled by re-melting them to form new articles, or burnt and used to generate electrical energy.
In particular, thermoplastics like polyesters have become essential commodities whose manufacture is well known and established. Typical examples of polyesters are polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), and similar polymers and copolymers. The polyesters such as PET may exist both in amorphous and semi-crystalline forms, the amorphous PET being transparent whereas the crystalline PET is opaque.
In accordance with the conventional process, the PET is formed by the process of esterification of terephthalic acid and ethylene glycol in a reaction vessel to form a mixture. The step of esterification may or may not include catalyst. The mixture is then heated to increase polymerization. The resulting mixture is then subjected to poly-condensation in a melt at elevated temperatures in the presence of an appropriate catalyst. The polymer is extruded directly from the poly-condensation reactor into strands. The hot, extruded strands are contacted with cool water prior to chopping into chips, dried, and stored into silos prior to crystallizing.
In particular, in accordance with the conventional process, two major and distinct process steps are involved in the production of high molecular weight polyesters, namely, the steps of melt polymerization and solid-state polymerization (SSP). In the step of melt polymerization for producing polyester having high intrinsic viscosity (IV), a pre-polymer polyester having IV of about 0.4 dL/g to 0.65 dL/g is produced in form of chips. The pre-polymer polyester so obtained is amorphous in nature. This pre-polymer polyester is subjected to solid-state polymerization wherein the molecular weight of the polyester may be augmented further. In the step of solid-state polymerization, the polyester with desired intrinsic viscosity may be produced. However, before the step of solid-state polymerization the pre-polymer polyester has to be crystallized in a crystallizer. This step of crystallization is essential as direct solid-state polymerization of the pre-polymer polyester may led to sintering and/or lump formation and hence to avoid the sintering and/or lump-formation in the pre-polymer polyester during the solid-state polymerization step the pre-polymer polyester is subjected to crystallization.
In accordance with the conventional process, the pre-polymer polyester, which may have crystallinity of about 0 % to 5 %, is subjected to the process of crystallization wherein the crystallinity of the pre-polymer polyester is increased up to 45% before it is subjected to the solid-state polymerization.
In accordance with the conventional process, the pre-polymer polyester is subjected to crystallization wherein the temperature during the process of crystallization is in the range from 140°C to 210°C. The temperature depends on the co-monomer contents in the polyester resin.
In accordance with the conventional process, the residence time for achieving the desired crystallinity in the pre-polymer polyester is in the range of 45 minutes to 90 minutes. The pre-polymer polyester is required to be heated throughout this time interval at around the temperature of 140°C to 210°C.
Further, in order to crystallize the pre-polymer polyester it is necessary to provide a pre-crystallizer and crystallizer hardware that inevitably consumes huge plant space and incurs large capital expenditure and operating expense for the hardware.
Thus, it is apparent that the conventional crystallization process as described herein above is time consuming and along with being energy inefficient.
Further, it is observed that if the co-monomer content is increased for specialty application, the crystallization rate of the pre-polymer polyester is reduced and hence the crystallization time increases.
In summary, the overall output of the plant is affected by the crystallization process.
Hence, there is a need for improving the crystallization process and provide a process that is time and energy efficient. Further, there is a need for providing a crystallization process that enhances the overall plant output and hence is economically viable. Still further, there is a need for providing a crystallization process that substantially reduces plant space requirement and does not incur large capital expenditure and operating expense.
OBJECTS
Some of the objects of the present disclosure, aimed to ameliorate one or more problems of the prior art or to at least provide a useful alternative, are described herein below:
An object of the present disclosure is to provide a process for crystallization of polyester or polyester chips.
Another object of the present disclosure is to provide a process for crystallization of polyester that consumes less time.
Still another object of the present disclosure is to provide a process for crystallization of polyester that is energy efficient.
Yet another object of the present disclosure is to provide a process for crystallization of polyester that enhances the overall output of the plant.
Another object of the present disclosure is to provide an apparatus for crystallization of polyester that reduces the overall time for crystallization and at the same time is energy efficient.
Another object of the present disclosure is to provide an apparatus for crystallization of specialty polyesters containing higher co-monomer contents (like Isopthalic acid, higher DEG etc. which reduces the overall crystallization rate of the polyester resin) without increasing the crystallization time and at the same time is energy efficient.
Another object of the present disclosure is to provide a process and apparatus for crystallization of polyester that does not requires huge plant space.
Another object of the present disclosure is to provide a process and apparatus for crystallization of polyester that does not incur large capital expenditure and operating expense.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
DETAILED DESCRIPTION
The process for crystallization of polyester chip or the polyester of the present disclosure will now be described with reference to the embodiments disclosed herein. The embodiment does not limit the scope and ambit of the disclosure. The description relates purely to the example and preferred embodiment of the disclosed method and its suggested application.
The process for crystallization of polyester chip and the various features and advantageous details thereof are explained with reference to the non-limiting embodiment in the following description. Descriptions of well-known parameters and processing techniques are omitted so as to not unnecessarily obscure the embodiment herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiment herein may be practiced and to further enable those of skill in the art to practice the embodiment herein. Accordingly, the examples should not be construed as limiting the scope of the embodiment herein.
In accordance with the present disclosure a process of crystallizing polymer chips is disclosed and in particular a process for crystallization of polyester resins or polyester chips using infrared heating is disclosed.
In accordance with the present disclosure, the process of crystallization of the polymer polyester chips is carried out before the polymer polyester chips are sent to solid-state polymerization to avoid sintering and/or lump formation in the step of solid-state polymerization of the polymer polyester chips.
In accordance with the present disclosure, a process for crystallizing polyester chips having amorphousness greater than 90 % is disclosed; the process comprises the steps of:
? providing polyester chips;
? introducing the polyester chips into an operative inlet of a conveying system on to a conveyor belt, wherein a plurality of infrared lamps is disposed in proximity to the conveyor belt defining an infrared heating zone, for heating the polyester chips; and
? collecting the infrared heated polyester chips from an operative outlet end of the conveying system;
? wherein at least one factor from a group consisting of:
o the speed of conveyor belt, that is the speed at which the polyester chips are conveyed;
o the heat emission rate of the infrared lamps, that is, the intensity of the infrared lamps;
o the number of operative infrared lamps; and
o the residence time of the polyester chips on the conveyor belt in the infrared heating zone(s);
is controlled during transit of said polyester chips, from said operative inlet to said operative outlet of said conveying system, such that heating of said polyester chips by said infrared lamps transforms at least one of said polyester chips from amorphous to crystalline form with degree of crystallization upto 50%.
In accordance with the present disclosure, the chips are introduced into the conveying system at room temperature.
In accordance with the present disclosure, the polyester chips being introduced into the conveying system have shape chosen from a group consisting of rectangular, planar, spherical, cylindrical or any other regular or irregular shape.
In accordance with the present disclosure, the polyester chips are laid down on the conveyor belt in a single or at maximum 2 layers of the polyester chips.
In accordance with the present disclosure, conveyor belt is an endless conveyor belt, that is, a conveyor in the form of a continuous belt traveling around a set of pulleys.
In accordance with the present disclosure, the infrared lamps span the entire length of the conveyor belt.
In accordance with the present disclosure, the intensity of the infrared lamps may be varied as per requirement.
In accordance with the present disclosure, the length of the conveyor belt and span of infrared lamps is such that the crystallinity of the chips increases up to 50 %.
In accordance with the present disclosure, the polyester chips are Polyethylene terephthalate (PET) chips.
In accordance with the present disclosure, the polyester chips are heated by the infrared lamps in the temperature range from 120°C to 210°C depending upon the co-monomer content in the polyester chips.
In accordance with the present disclosure, the polyester chips are heated for a time span of few seconds subjected to the constraint that the crystallinity of the chips after heating reaches at most up to 50 %.
In accordance with the present disclosure, the crystallized polyester chips are sent to solid-state polymerization, wherein the sintering and/or lump formation is reduced and/or eliminated.
In accordance with the present disclosure, it is observed that the desired crystallinity of the chips may be achieved by heating the chips using the infrared lamps in just few seconds as compared to several minutes when heated in accordance with the conventional prior art process thereby reducing the process time substantially.
In accordance with the present disclosure, it is evident that the throughput of the plant increases substantially as the time required for crystallizing the chips before solid-state polymerization has shrunk to few seconds instead of several minutes. This reduction in time is further beneficial for better color retention and lower acetaldehyde generation in the polyester resin in the solid-state polymerization step along with decrease in the residence time in the solid-state polymerization step.
In accordance with the present disclosure, it is observed that the energy required for heating the chips by the infrared lamps is low as compared with the conventional prior art process.
In accordance with the present disclosure, it is observed that the plant space required to install the conveyance system with the infrared lamps is substantially low as compared with the conventional crystallization apparatus.
In accordance with the present disclosure, the capital expenditure and the operating expenses for operating the conveyance system with the infrared lamps is substantially low as compared with the conventional crystallization apparatus.
TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE
The technical advancements offered by the present disclosure include the realization of a process for crystallizing polyester and/or polyester chips that:
• is time and energy efficient;
• enhances the overall output of the plant;
• does not require huge plant space; and
• does not incur large capital expenditure and operating expense.
The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.