Understanding and taking advantage of your PVC Technology

During the time I have worked as a Consultant I have been asked on occasions what is the best Technology for the production of S-PVC (resins) or how Technology X compares to Technology Y.

I believe this is because a large number of today's S-PVC resin producers acquired their Technology from one of the few PVC licensors that existed at the time.

Below is a list of PVC resins Technologies obtained from a recent Internet search (some other renowned Technologies are no longer available):

Licensors are (or were) S-PVC producers who allocated resources to R&D more than 40 years ago to discover patentable innovations in PVC production, investing in prototyping, scale-up and eventually designing competitive processes that they first used for their own production and then decided to license to new entrants.

It is necessary to take into account that Chemical Process Technology can be defined as the integration of all the knowledge generated by various disciplines necessary for the design, construction and operation of a Plant that produces a desired chemical product while meeting the designed goals of productivity, quality and cost, as well as relevant requirements in safety, health and environmental protection.

Moulijn, Makkee and Van Diepen in their book “Chemical Process Technology” postulate that the different disciplines address different sizes and time (integration) scales: micro/nanolevel, mesolevel and macrolevel.

a. Micro/nanolevel

It refers to the Natural Sciences that deal with phenomena that occur on very small and rapid scales such as chemical reactions, catalysis, molecular and intermolecular interactions, etc.

Generally, the discovery of phenomena that result in new materials or products occurs accidentally or by systematic “trial and error”, and only later the phenomena is studied and understood resulting in further improvements.

In the case of PVC, we can identify the following milestones in its discovery as product:

- 1835, the anecdotal discovery of PVC by accidental vinyl chloride polymerization, by Regnault

- 1860, the first mention of a “metamorphosis” (polymerization) of vinyl bromide, by Hofmann

- 1872, the production of the white powder that is currently identified as PVC resin by vinyl chloride photopolymerization, by Baumann

Although natural phenomena at the micro/nano scale are not patentable and are not mentioned in any documentation provided with Process Technology, they are the cornerstone on which it is built. Their knowledge and mastery are necessary either to create process and/or product innovations that can be patented.

b. Mesolevel

It refers to Applied Sciences and Engineering disciplines that are related to the design of process equipment, process conditions and chemical additives that allow micro/nanoscale phenomena to form the target chemical product with defined characteristics.

The specific combination of equipment, conditions and additives of a licensed Process Technology is transferred to the Licensee through various documents such as specifications, diagrams, recipes, set-points, procedures, tolerances, etc.

Licensor expects Licensees to comply with all of these requirements to ensure the offered results of their Technology, but there is commonly little or no explanation as to the reasons or consequences that non-compliance may cause. Regardless of the underlying reason, this lays the foundation for Licensee's technological dependency on the Licensor.

In the case of PVC resins, both the 1913 Griesheim-Elektron patent (DRP 281,687) for the production of PVC from vinyl chloride by peroxide initiation and the 1935 Wacker patent (DRP 750,428) for the suspension polymerization of vinyl chloride served as basis for the subsequent development of new combinations of equipment, additives and conditions.

Among the equipment developed, the cases of large volume reactors, reflux condensers, washing/coating systems for closed-reactor operation, stripping columns, dryers and automated control systems stand out.

Among the additives, we can point to the development of secondary suspending agents to guarantee low levels of residual VCM after stripping, antifouling agents to increase productivity, and initiators with increasingly higher reactivity and dispersibility.

Most of these developments were once protected by patents of their inventors (S-PVC producers in the case of equipment and additive producers in the case of their products), but have now expired allowing their commercial exploitation without restrictions or license obligations.

However, given that there are potentially a large number of combinations of equipment, additives and conditions that have not been explored to obtain S-PVC resins with different characteristics or economic performance, some could still be patentable if they meet the requirements of novelty, non-obviousness and usefulness.

c. Macrolevel

It refers to Engineering disciplines, such as Design and Control, that allow different process equipment to be selected and interwoven into a rational whole ("Process Technology") that guarantees that a Plant installed, commissioned and operated according to the provided guidelines and documentation delivers the target chemical product complying with the offerings of quality, costs, productivity, consistency and safety.

Although there may be many combinations of equipment to configure a Plant, a Process can only be patentable when the steps are different from what previously exists (novelty).

In the case of S-PVC, all subsequent developments are based on the process designed by Wacker from his 1935 patent (DRP 750,428).

In fact, its first commercial plant was built with such design in 1935 for the production of PVC resins (VINNOL), having a sequence of operations (preparation/charge → polymerization → centrifugation → drying) that is still in use in S-PVC Plants (see figure in header).

Wacker's plant used 10 m3 batch reactors fitted with paddle stirrers rotating at 40 rpm with the following recipe:

o Vinyl chloride monomer - 5,000 Kg

o Water - 6,000 Kg

o Benzoyl peroxide - 4 Kg

o Polyvinyl alcohol (Sap. No. 100-130) - 1,000 Kg of aqueous solution

Reactor content was heated to a temperature between 40 and 60°C and maintained at such temperature for approximately 50 hours until reaching a final conversion between 65% and 95%. S-PVC resin was filtered, resuspended with water and then separated by centrifugation. Finally, it was dried in a hot air dryer at 80-100°C.

As you can see, S-PVC Process remains mostly the same as it was almost 90 years ago, so patent protection of the entire process is unlikely (but was possible when PVC mass polymerization was developed). What has essentially changed are equipment, additives and process conditions (mesolevel) to make S-PVC more thermally stable, easier of processing and with a low level of residual VCM, while process economics have improved with shorter polymerization and lower downtime.

Generally, the Licensee of a Technology can generate a lot of experience in the operation of said Technology. However, if process conditions change due to uncontrolled factors or if additives or equipment need to be changed to obtain/regain economic competitiveness, experience alone will not be enough to achieve changes in a fast, assertive, efficient and safe way.

Only when both micro/nanoscale and mesoscale phenomena involved in the different stages of the process are known and taken into account is it possible to realize the effects that can arise from any change in equipment, additives or process conditions, even without having first hand experience in them.

Let me help you master and innovate your PVC Technology so you get the best benefits from it.

caguilar063@hotmail.com

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