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Three items in this section:
1-cd-book. Biobased polyols for industrial polymers
2-Naturally POM
3-Total PU synthesis from non petrochemical sources


Biobased polyols for industrial polymers
From chemistry to marketing
ISBN: 9789078546276

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ALL PUBLICATIONS ARE REVIEWED AND UPDATED CONTINUOUSLY
THEY ARE RE-EDITED, BEFORE SHIPMENT
GEM-Chem's PUBLICATIONS ARE ALWAYS NEW
GEM-Chem's TITLES ARE NEVER OBSOLETE


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For information contact Deny Kyriacos, President & CEO, GEM-Chem,
E-mail: dk@GEM-Chem.net, phone: +32-2-7710649

Dr.Kyriacos has worked at Upjohn, GE and ICI in international TS, Sales and Marketing.
He holds a B.Sc.(Distinction, Honours, University award in Chemistry) from Alexandria,
a M.Sc.course,(ICI scholarship award) in Polymer Technology and, a Ph.D. from
Loughborough in the UK.
D. Kyriacos is the founder of DK Business Group and GEM-Chem.

Deny Kyriacos: LinkedIn profile

Naturally POM

A-Introduction
The origin of commercial thermoplastics, thermosets and elastomers is automatically linked to the petrochemicals industry. The main reason is that the source of the monomers, which constitute their building blocks, are derivatives of chemicals either isolated from the distillation of crude oil or obtained from the combustion of natural gas. Examples of such basic petrochemicals include aromatics as well as alkenes.
B-POM from natural sources
However among the engineering thermoplastics exceptions exist or, more precisely, they can be made to exist if some modifications are introduced to their production methods.
In this article the polymer in question is polyacetal or polyoxymethylene (POM).
As everybody knows, polyacetals are commercialised in two forms, the homopolymers, first developed by DuPont in the nineteenfifties and the copolymers which were marketed a few years later by Celanese and Hoechst through their joint venture, Ticona. The very basic difference between homopolymers and copolymers lies in the method used to stabilise the heat sensitive polyformals which are produced by the polymerisation of formaldehyde.
A quick glance at the synthesis of polyacetal homopolymer, will give some insights on the possibilities of converting its current production to an environmentally friendly one.
1-CH4 from natural gas is converted to syngas by steam reforming
          CH4 + H2O (steam) ---------> CO + 3H2
In this step natural gas is subjected to the effect of large quantities of energy for the sake of producing carbon monoxide and hydrogen.
Letting aside nature and the financial interests involved in ripping it off, methane can also be generated from biomass. Microorganisms digesting buried organic waste produce landfill gas composed of methane (50-55%), carbon dioxide (40-45%), and trace levels of volatile organic compounds. At least the investments in such technologies will be beneficial to the environment.
2-The syngas components are reacted in the presence of a catalyst (Cu/ZnO/Al2O3)at 50–100 atm and 250 °C to give methanol
          CO + 2H2 --------> CH3OH
Hydrogen can be generated from the electrolysis of water. However the energy input required is tremendous and it can most advantageously be provided by nuclear power plants, which at the moment constitute the cleanest and most reliable source of bulk energy.
On the other hand carbon dioxide, the whole world in not in short supply of, can be converted to carbon monoxide through the good old reduction reaction we have all been taught at the preparatory school.
          CO2 + H2 -------->CO + H2O
The wonders of chemical engineering have provided us with methods of transforming carbon dioxide to methanol.
          CO2 + 3 H2 -------->CH3OH + H2O
3-Methanol is oxidised to formaldehyde (Formox or BASF processes for example)
          CH3OH + œ O2 --------> HCHO + H2O
The oxygen required for this oxidation reaction can be conveniently obtained from the electrolysis of water
          H2O --------> H2 + 1/2O2
4-Formaldehyde is polymerised anionically or cationically in a solvent (cyclohexane, toluene,...etc...)to a heat sensitive, hemiacetal terminated, polyacetal ( Mn = 20 000 to 100000)
          HCHO + catalyst (R) ----Cyclohexane----> R(CH2O)n-CH2OH
Unfortunately, this synthetic step includes a solvent, which is sourced from the petrochemicals industry.
To discard the manufacturing routes which involve solvents scientists and engineers must solve the technical problems associated with the gas polymerisation of formaldehyde.
The alternative of converting HCHO to trioxane, , and polymerising the latter in bulk to polyacetal avoids the use of a solvent. However the manufacture of trioxane itself involves a benzene extraction process.
5-The hemiacetal end groups are stabilised by acetylation
  R(CH2O)n-CH2OH + (CH3CO)2O ---CH3COONa------> R(CH2-O)n-CH2OCOCH3

6-Copolymers which involve the copolymerisation of trioxane with a small amount of dioxolane or ethylene oxide, will be more difficult to manufacture in a green way since both monomers are synthesised from ethylene
CH2=CH2+ 1/2O2--------> ethylene oxide---H2O----> HO-CH2-CH2-OH
HO-CH2-CH2-OH + HCHO --------> dioxolane,.

The problem can be solved in an environmentally attractive way if ethylene can be isolated from a recycling process involving thermooxidation or cracking
C-Conclusions
A green method for the manufacture of POM hopolymers and copolymers can be achieved if
-Methanol is produced in an environmentally friendly way from biomass or carbon dioxide and hydrogen. The technical problem to be solved is the gas phase polymerisation of formaldehyde unless the recycling of the polymerisation medium is not regarded as a sin the environment finds it difficult to forgive. Furthermore, formaldehyde can also be partly generated from the depolymerisation of polyacetals
-Trioxane is isolated through methods other than extraction with benzene. Here again, by recycling benzene efficently, the damages caused to the environment are minimal
-Ethylene, which is used in the manufacture of the comonomers is isolated from a cracking operation performed on polyolefins or some rubbers.
-Energy is generated from clean sources, the most viable of which is, until now, of nuclear origin.
April 2007.



Total PU synthesis from non petrochemical sources

For all those who have been involved, even briefly, in PU, the following few lines are a reminder of some basics on the chemistry and technology of this very interesting industry.
Polyurethanes or polymers with repeated urethane groups, are produced from the reaction of diols or/and polyols, usually polyesters or polyethers of various molecular weights, with di and/ or poly isocyanates.
To proceed in practically acceptable rates, at room temperature, the reaction has to be catalysed. Amines are the most common catalysts.
Solid (unexpanded), essentially aromatic PU's, either linear or crosslinked require the presence of additives such as light stabilizers and antioxidants in their formulations. PU, rigid foams very often include flame retardants.
PU foams can be flexible, semi rigid and rigid. The foaming of flexible and semi rigid foams aims at tailoring the properties, reducing the weight and thus the price of the final product which is mainly constituted of open cells.
The effectiveness of rigid foams, used for insulation purposes, relies mainly on the heat conductivity of the blowing agent. The latter is uniformly dispersed in the polymer matrix through the presence of small quantities of a surfactant.
Irrespective of the physical phenomena involved in the transport of heat, the K-factor of solid polyurethanes, such as a thermoplastic elastomers (TPU), is 0.14 W/m.K. On the other hand the K-factor of a blowing agent with almost zero ozone depleting potential such as 1,1,1,3,3-pentafluoropropane is 0.014 W/mK. A foam containing 24% of the cited fluoro compound has a K factor of 0.021 W/mK.
The isocyanate and the polyol components, being liquid at temperatures up to 50șC are processed by high (impingement) or low pressure (rotor blade) mixing. The products are formed by pouring or injection in an open or closed mould. The reactive extrusion of thermoplastic elatomers, on the other hand results in granulates which can be processed by extrusion and injection
. (Ref: D.Kyriacos. Thermoplastic polyurethanes. From chemistry to marketing).
With the emerging trend to step away from petrochemicals and shift towards products sourced from plant components, polyols have been produced from triglycerides by several routes a couple of which are shown below:
(Ref: D. Kyriacos. Biobased polyols. From chemistry to marketing)
1-Epoxidation followed by hydrolysis
2-Ozonolysis followed by reduction
Dimerization of vegetable oleic acid or tall oil fatty acid yields dimer acids. Originally introduced in the 1950s, this is a complex reaction resulting in a mixture of aliphatic branched and cyclic C36-Diacids (Dimer acid) and of other acids.
Hydrogenation of dimeracid methylester or dimerization of oleyl alcohol leads to dimer alcohols (dimer diols).
Their structure clearly indicates that they have a positive influence on the hydrolysis resistance of elastomers or other CASE family products.
Biobased, initiators for the production of polyether polyols by ethoxylation/epoxylation several initiators even triglycerides, have been known since long.
Ethylene oxide and, especially, propylene oxide are still produced from petrochemical sources, for economical reasons. Those chemicals can be synthesized from green sources.
Except sucrose, other initiators as well as low molecular weight diols can be made available from green sources as well.
There exist simple ways to convert biobased dicarboxylic acids into fully biobased polyester polyols.
The synthetic methods are undoubtedly very simple tasks to good and imaginative chemists.
From the above it follows that one of the two main components of polyurethanes, namely the polyols, can be produced from green sources.
A more difficult project however is the production of di and poly isocyanate components from green sources. The synthesis of aliphatic di and poly isocyanates should not pose any problem to organic chemists
Aromatic isocyanates from green sources, seem to be, at least on paper, not very difficult to produce.
However, the financial viability of a project is, quite sensibly, much more important than the commitment to green policies, which in the case of many industrial products mean primarily drifting away from the dependence on oil cartels rather than respecting speculative green concepts.
(Article published in November 2009)


For information contact Deny Kyriacos, President & CEO, GEM-Chem,
E-mail: dk@GEM-Chem.net, phone: +32-2-7710649

Dr.Kyriacos has worked at Upjohn, GE and ICI in international TS, Sales and Marketing.
He holds a B.Sc.(Distinction, Honours, University award in Chemistry) from Alexandria,
a M.Sc.course,(ICI scholarship award) in Polymer Technology and, a Ph.D. from
Loughborough in the UK.
D. Kyriacos is the founder of DK Business Group and GEM-Chem.

Deny Kyriacos: LinkedIn profile

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