FIELD

The present disclosure relates to a process for the preparation of 1 -chloro- 1,1- difluoroethane. Particularly, the present disclosure relates to a process for catalyzed liquid phase fluorination of vinylidene chloride to produce 1 -chloro- 1,1- difluoroethane (hydrochlorofluorocarbon- HCFC 142b).

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

1 -chloro- 1,1 -difluoroethane (HCFC 142b) belongs to hydrochlorofluorocarbon (HCFC) family of synthetic compounds and is primarily used as a refrigerant. HCFC 142b is also used as a blowing agent for foam plastic production, and as feedstock to make polyvinylidene fluoride (PVDF).

Various methods for the preparation of 1 -chloro- 1,1 -difluoroethane (HCFC 142b) are reported in the art. The current commercial route for the production of HCFC 142b, is based on catalyzed or un-catalyzed liquid phase fluorination of 1,1,1 -tri chloroethane. However, the conventionally used feedstock, ‘1,1,1 -trichloroethane’ is accountable for ozone depletion at higher rate and therefore, the supply of 1,1,1 -trichloroethane is expected to be regulated. Hence, 1,1,1 -trichloroethane is becoming short in supply. Hence, there is a need for identifying commercially available new feedstock to manufacture HCFC 142b.

An alternative feedstock is Vinylidene chloride (VDC). Conventionally, fluorination of VDC is carried out in a gas phase and a liquid phase, in the presence of a homogeneous catalyst, or a heterogeneous catalyst. Mostly, these conventional processes are non-selective, producing other fluorinated products such as 1,1- dichloro-1 -fluoroethane (R141b), 1,1,1 -trifluoroethane (R143a), 1,1, 1,3, 3- pentafluorobutane (365mfc), and the polymeric material polyvinylidene chloride (PVDC). The formation of other fluorinated products is disadvantageous as such products coat the active catalyst thereby leading to the catalyst deactivation. Hence, a continuous purging of the deactivated catalyst and feeding a fresh load of catalyst is needed during these processes. In addition, the feedstock VDC tends to produce polymeric material, which is not desirable. Further, the liquid phase processes cited in the prior art are related to batch processes, which is not suited for industrial applications.

Therefore, there is felt a need to provide a process for a catalyzed liquid phase fluorination of vinylidene chloride that mitigates the drawbacks mentioned hereinabove or at least provides a useful alternative.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

Another object of the present disclosure is to provide a process for the preparation of 1 -chloro- 1 , 1 -difluoroethane.

Still another object of the present disclosure is to provide a process for a catalyzed liquid phase fluorination of vinylidene chloride to produce 1 -chloro- 1,1- difluoroethane (HCFC 142b).

Yet another object of the present disclosure is to provide a simple, efficient and economical process for the preparation of 1 -chloro- 1,1 -difluoroethane (HCFC 142b). Still another object of the present disclosure is to provide a process for the preparation of 1 -chloro- 1,1 -difluoroethane that is environment friendly.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure relates to a process for the preparation of 1 -chloro- 1,1- difluoroethane. The process comprises hydrofluorinating vinylidene chloride by using an anhydrous hydrogen fluoride in the presence of a catalyst at a first predetermined temperature and a predetermined pressure for a predetermined time period to obtain a product mixture comprising 1 -chloro- 1,1 -difluoroethane and by-products. The product mixture comprising 1 -chloro- 1,1 -difluoroethane and the by-products is collected in a receiver maintained at a second predetermined temperature. The byproducts are separated from the product mixture to obtain a pure I -chloro- 1,1- difluoroethane.

The catalyst is selected from the group consisting of titanium tetrachloride (TiCh), tin chloride (SnCU), zirconium(IV) chloride (ZrCU), antimony pentachloride (SbCh), bismuth chloride (BiCh), boron trifluoride (BF3), aluminium chloride (A1C13), tritylium ions, gallium trichloride (GaC13), silver bis(trifluoromethanesulfonyl)imide (AgNTf2), trimethylsilyl trifluoromethanesulfonate (TMSOTf), and bis(trifluoromethanesulfonyl)amide (HNTf2).

In an embodiment of the present disclosure, the catalyst is selected from SnCU and TIC1 ₄ . In an embodiment of the present disclosure, the reaction of vinylidene chloride with the anhydrous hydrogen fluoride is carried out in the presence of a polymerization inhibitor.

The polymerization inhibitor is selected from the group consisting of para methoxy phenol, catechol, 4-tert-butyl catechol, butylated hydroxy toluene, hydroquinone and quinone. In an exemplary embodiment of the present disclosure, the polymerization inhibitor is para methoxy phenol.

In an embodiment of the present disclosure, an amount of the polymerization inhibitor is in the range of 200 ppm to 300 ppm.

In an embodiment of the present disclosure, a molar ratio of vinylidene chloride to the anhydrous hydrogen fluoride is in the range of 1:1 to 1:10. In an exemplery embodiment of the present disclosure, the molar ratio of vinylidene chloride to the anhydrous hydrogen fluoride is 1:3.

The first predetermined temperature is in the range of 70 °C to below 90 °C.

The predetermined pressure is in the range of 10 kg/cm ² to below 15 kg/cm ²

The predetermined time period is in the range of 10 minutes to 15 minutes.

The second predetermined temperature is in the range of -90 °C to -60 °C.

In an embodiment of the present disclosure, the by-products comprises 1 -fluoro- 1,1- dichloroethane, trifluoroethane, hydrogen chloride and unreacted hydrogen fluoride (HF).

The by-products are separated by passing the product mixture through at least one distillation column. In an embodiment of the present disclosure, a conversion of vinylidene chloride is greater than 99%.

DETAILED DESCRIPTION

The present disclosure relates to a process for the preparation of 1 -chloro- 1,1- difluoroethane. Particularly, the present disclosure relates to a process for catalyzed liquid phase fluorination of vinylidene chloride to produce 1 -chloro- 1,1- difluoroethane (HCFC 142b).

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well- known apparatus or structures, and well known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

Various methods for the preparation of 1 -chloro- 1,1 -difluoroethane (HCFC 142b) are reported in the art. The current commercial route for the production of HCFC 142b, is based on catalyzed or un-catalyzed liquid phase fluorination of 1,1,1 -tri chloroethane. Because of the high ozone depletion potential of 1,1,1 -trichloroethane, it is expected to be regulated and becoming in short supply. Hence there is a need for identifying commercially available new feedstock to manufacture HFC142b.

An alternative feedstock is Vinylidene chloride (VDC), wherein fluorination of VDC is carried out in a gas phase and a liquid phase, in presence of a homogeneous catalyst, or heterogeneous catalyst is reported in the literature. In most cases, the process is non-selective, producing other fluorinated products such as 1,1 -dichloro- 1- fluoroethane (R141b), 1,1,1-trifluoroethane (R143a), 1,1, 1,3, 3 -pentafluorobutane (365mfc), and the polymeric material polyvinylidene chloride (PVDC), wherein these other fluorinated products coat the active catalyst thereby leading to the catalyst deactivation. Hence, a continuous purging of the deactivated catalyst and feeding a fresh load of catalyst is needed during these processes. In addition, the feedstock VDC tends to produce polymeric material which is not desirable. Further, the liquid phase processes cited in the prior art are related to batch processes, which is not suited for industrial applications. The present disclosure provides a simple, economical and environment friendly process for the preparation of 1 -chloro- 1,1 -difluoroethane.

Particularly, the present disclosure provides a process for catalyzed liquid phase fluorination of 1 , 1 -dichloroethylene (vinylidene chloride) to produce 1 -chloro- 1,1- difluoroethane (hydrochlorofluorocarbon- HCFC 142b).

The process for the preparation of 1 -chi oro-1,1 -difluoroethane comprises the following steps: a. hydrofluorinating vinylidene chloride by using anhydrous hydrogen fluoride in the presence of a catalyst at a first predetermined temperature and a predetermined pressure for a predetermined time period to obtain a product mixture comprising 1 -chi oro-1,1 -difluoroethane (HCFC 142b) and byproducts; b. collecting the product mixture comprising 1 -chloro- 1 , 1 -difluoroethane and the by-products in a receiver maintained at a second predetermined temperature; and c. separating the by-products from the product mixture to obtain a pure 1 -chloro- 1,1 -difluoroethane (HCFC 142b).

In an embodiment of the present disclosure, the schematic representation of the process for the catalyzed liquid phase fluorination of vinylidene chloride to produce 1 -chloro- 1,1 -difluoroethane (hydrochlorofluorocarbon- HCFC 142b), is given below as Scheme 1 :

Scheme 1

The catalyst is selected from the group consisting of titanium tetrachloride (Ti C 1 ), tin chloride (SnCl ₄ ), zirconium(IV) chloride (ZrCl ₄ ), antimony pentachloride (SbCl ), bismuth chloride (BiCh), boron trifluoride (BF3), aluminium chloride (A1C13), tritylium ions, gallium trichloride (GaC13), silver bis(trifluoromethanesulfonyl)imide (AgNTf2), trimethylsilyl trifluoromethanesulfonate (TMSOTf), and bis(trifluoromethanesulfonyl)amide (HNTf2). In an exemplary embodiment of the present disclosure, the catalyst is SnCl ₄ . In another exemplary embodiment of the present disclosure, the catalyst is TiCl ₄ .

In an embodiment of the present disclosure, the catalyst, SnCl ₄ is activated by using the stable Lewis acid HF as represented below;

SnCl ₄ + 4HF -A SnF ₄ + 4HC1 SnF ₄ + HF -A H ⁺ [SnF ₅ ]’

In an embodiment of the present disclosure, the reaction of vinylidene chloride with an anhydrous hydrogen fluoride is carried out in the presence of a polymerization inhibitor.

The polymerization inhibitor is selected from the group consisting of para methoxy phenol, catechol, 4-tert-butyl catechol, butylated hydroxy toluene, hydroquinone and quinone. In an exemplary embodiment of the present disclosure, the polymerization inhibitor is para methoxy phenol. In an embodiment of the present disclosure, the commercial-grade anhydrous liquid HF and vinylidene chloride is used. The commercial grade vinylidene chloride contains 290 ppm to 300 ppm of para methoxy phenol as the polymerization inhibitor. The commercial-grade vinylidene chloride when subjected to drying by using molecular sieves 4A0, the moisture content of vinylidene chloride reduces up to 40 ppm to 50 ppm. During the drying process, in case there is a loss of inhibitor, the loss is compensated by adding more inhibitors dissolved in 1 -fluoro- 1,1- di chloroethane (141b), to bring the total inhibitor level in the feed to 290 ppm.

In accordance with an embodiment of the present disclosure, the by-products comprises 1 -fluoro- 1,1 -di chloroethane (141b) and trifluoroethane (143 a), HC1 and unreacted hydrogen fluoride (HF).

In an embodiment of the present disclosure, a molar ratio of vinylidene chloride to the anhydrous hydrogen fluoride is in the range of 1:1 to 1:10. In an exemplery embodiment of the present disclosure, the molar ratio of vinylidene chloride to the anhydrous hydrogen fluoride is 1:3.

The first predetermined temperature is in the range of 70 °C to below 90 °C. In an exemplary embodiment of the present disclosure, the predetermined temperature is 70 °C. In another exemplary embodiment of the present disclosure, the predetermined temperature is 80 °C.

At lower temperatures, selectivity of 1 -fluoro- 1,1 -dichloroethane (141b) is higher, and at higher temperatures, the selectivity of fluorinating product 143 a is higher. Therefore, it is recommended to carry out the catalyzed liquid phase fluorination at a temperature in the range of 70 °C to below 90 °C to obtain the desired product 1- chloro- 1,1 -difluoroethane (HCFC 142b). The predetermined pressure is in the range of 10 kg/cm ² to below 15 kg/cm ² . In an exemplary embodiment of the present disclosure, the predetermined pressure is in the range of 10 kg/cm ² . In another exemplary embodiment of the present disclosure, the predetermined pressure is in the range of 15 kg/cm ² .

A higher pressure will favour the formation of 143a with higher selectivity, and lower selectivity of 142b. Therefore, it is recommended to carry out the catalyzed liquid phase fluorination at a pressure in the range of 10 kg/cm ² to below 15 kg/cm ² .

The predetermined time period is in the range of 10 minutes to 15 minutes. In an exemplary embodiment of the present disclosure, the predetermined time period is 10 minutes. In another exemplary embodiment of the present disclosure, the predetermined time period is 15 minutes.

The second predetermined temperature is in the range of -90 °C to -60 °C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is -78 °C.

In an embodiment of the present disclosure, the product mixture is passed through a first distillation column to remove HC1 from the top and a bottom stream is chilled and organics are removed from HF layer; organics are then distilled in three distillation columns to remove non-condensable gases (NCG) and high boilers from the product. The product is then circulated in the alumina absorber to get desired level of acidity and moisture.

In an exemplery embodiment of the present disclosure, a two litre reactor is arranged (Hastelloy-C autoclave) with mechanical stirrer, interconnected to a cold condenser kept at -20 °C, pressure gauge, raw material liquid inlet, HF liquid inlet, catalyst liquid inlet and nitrogen gas inlet. The outlet of the condenser is interconnected to a 5 litre water scrubber, followed by 2 litres CaSCk solution, drying tower and 5 litres SS receiver kept at -78 °C using dry ice acetone bath.

TiCU is charged into the reactor along with anhydrous hydrogen fluoride and the temperature is raised to 80 °C and maintained for 1 hour. HF and vinylidene chloride (VDC) containing para methoxy phenol (200-300 ppm) (molar ratio of HF to VDC is maintained at 1 :2 to 1:4) are fed into the reactor. The feeding of HF and VDC is continued till the reaction pressure reached to 10 Kg/cm ² to obtain a product mixture comprising 1 -chloro- 1,1-difluoroethane (R-142b) and by-products such as 1-fluoro- 1,1 -dichloroethane (R-141b), trifluoroethane (R-143b), hydrogen chloride and unreacted hydrogen fluoride.

Then the product mixture is slowly collected into SS receiver (which is maintained at -78 °C using dry ice acetone bath) from the top of the condenser through water scrubber and calcium sulphate dryer. During the collection of product mixture the temperature of 80 °C and the pressure of 10 Kg/cm are maintained in the reactor.

The composition of the product mixture after running the reaction for 15 hours is VDC-0.8%, R-141b-6.1%, R-142b-91.5%, R-143a-1.9%. After complete collection of the product mixture, the reactor is evacuated with dry nitrogen purging. The polymeric residue is collected by methylene dichloride (MDC) flushing. The MDC washings are concentrated to isolate the polymeric residue.

The product mixture comprising 1 -chloro- 1,1-difluoroethane (R-142b) and byproducts is subjected to distillation column to remove the by-products to obtain a pure 1 -chloro- 1,1 -difluoroethane (R-142b).

The process of the present disclosure is based on the catalyzed liquid phase fluorination of vinylidene chloride which is a commercially available feedstock, to produce very high selectivity of the desired product HCFC 142b with >90% selectivity, at a very high conversion of about > 99%. The process of the present disclosure can run continuously for thousands of hours without deactivation or deterioration of the catalyst.

The present disclosure provides a method of producing HCFC 142b using environmentally acceptable vinylidene chloride. Using the stable Lewis acid HF activated SnCl catalyst, in the presence of optimum level of the polymerization inhibitor - para methoxy phenol, in presence of 141b as a solvent, the process provides desired products with high purity.

R- 141b is generated in the process as intermediate, and in the continuous process, R- 141b is present in the reaction mass and acts as a solvent.

The present disclosure, therefore, aims to provide a preparation process for HCFC 142b which no longer has the disadvantages of

• using 1,1,1 -tri chloroethane which has high ozone depletion potential, and

• reactor plugging due to polymerization of vinylidene chloride.

The process of the present disclosure can run continuously for more than 100 hours without deactivation or deterioration of the catalyst and hence, the process is feasible on a large/commercial scale.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure. The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the experiments should not be construed as limiting the scope of embodiments herein. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.

EXPERIMENTAL DETAILS:

Example 1:

A two litre reactor was arranged (Hastelloy-C autoclave) with mechanical stirrer, interconnected to a cold condenser kept at -20 °C, pressure gauge, raw material liquid inlet, HF liquid inlet, catalyst liquid inlet and nitrogen gas inlet. The outlet of the condenser was interconnected to a 5 litre water scrubber, followed by 2 litres CaSCL solution, drying tower and 5 litres SS receiver kept at -78 °C using dry ice acetone bath.

TiCl (18.5 g) was charged into the reactor along with anhydrous hydrogen fluoride (100 gm) and the temperature was raised to 80 °C and maintained for 1 hour. HF and vinylidene chloride (VDC) containing para methoxy phenol (200-300 ppm) (molar ratio of HF to VDC was maintained at 1:2 to 1:4) were fed into the reactor. The feeding of HF and VDC was continued till the reaction pressure reached to 10 Kg/cm ² to obtain a product mixture comprising 1 -chloro- 1 , 1 -difluoroethane (R-142b) and by-products such as 1 -fluoro- 1,1 -dichloroethane (R-141b), trifluoroethane (R- 143 b), hydrogen chloride and unreacted hydrogen fluoride. Then the product mixture was slowly collected into SS receiver (which was maintained at -78 °C using dry ice acetone bath) from the top of the condenser through water scrubber and calcium sulphate dryer. During the collection of product mixture the temperature of 80 °C and the pressure of 10 Kg/cm ² were maintained in the reactor.

The composition of the product mixture after running the reaction for 15 hours was VDC-0.8 %, R-141b-6.1%, R-142b-91.5%, R-143a-1.9% (Example-1). After complete collection of the product mixture, the reactor was evacuated with dry nitrogen purging. The polymeric residue was collected by methylene dichloride (MDC) flushing. The MDC washings were concentrated to isolate the polymeric residue (0.2 % w/w w. r. t. VDC).

The product mixture comprising l-chloro-l,l-difluoroethane (R-142b) and byproducts was subjected to distillation column to remove the by-products to obtain a pure 1 -chloro- 1,1 -difluoroethane (R-142b).

Examples 2 to 10 and comparative example:

The same procedure of Example 1 was carried out by varying the process parameters/conditions. In example 10, polymerization inhibitor was not used. The details of the various process parameters/conditions and the results are summarized in Table 1 below.

Similar to examples 1 to 10, other examples were also carried out by using different catalysts such as zirconium(IV) chloride (ZrC14), antimony pentachloride (SbC15), bismuth chloride (BiC13), boron trifluoride (BF3), aluminium chloride (A1C13), tritylium ions, gallium trichloride (GaC13), silver bis(trifluoromethanesulfonyl)imide (AgNTf2), trimethylsilyl trifluoromethanesulfonate (TMSOTf), and bis(trifluoromethanesulfonyl)amide (HNTf2) and by using different polymerization inhibitors such as catechol, 4-tert-butyl catechol, butylated hydroxy toluene, hydroquinone and quinone. The results obtained were comparable with the results obtained for example 1.

Table 1:

* 365 fmc: 1,1, 1,3, 3 -pentafluorobutane

From the above table, it is observed that in the reaction with a high mole ratio of HF/VDC. the formation of undesired R-143a is more (Example - 5) i.e. 20.2% and the % selectivity for R-142b (desired product) is 76.6%, whereas, if the ratio of HF/VDC is low the % selectivity for R-142b (desired product) is very low (Example - 4) i.e. 16.4%.

Further, if the temperature and pressure are high, the formation of R-143a (undesired product) is high (Example -9). If the contact time is high the formation of R-143a is also high (Example - 2) which is not desired. If the VDC is used without the polymerization inhibitor the formation of polymeric residue is more (Example -10) i.e. 1.6%.

It is observed that, the temperature of 80 °C with a mole ratio of HF/VDC of 3 and a contact time of 0.25 hour, gives VDC conversion > 99 %, best selectivity of R-142 (>90%) with the lower formation of R-143a and polymeric residue (Example - 1).

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for a catalyzed liquid phase fluorination, that:

• produces 1 -chloro- 1,1 -difluoroethane (HCFC 142b) with >90% selectively over 1- fluoro- 1,1 -dichloroethane (141b) and trifluoroethane (143a);

• can run continuously for more than hundred hours without deactivation or deterioration of the catalyst;

• is simple, efficient and environment friendly;

• is feasible on a large/commercial scale; and

• avoids using 1,1,1 -trichloroethane which has high ozone depletion potential.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The foregoing description of the specific embodiments 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.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation..