by Gary Shawhan and Dave Sikora Ph.D., Contributing Editors, The CHEMARK Consulting Group
This is Part 2 of a 3-part article on sustainability and challenges facing many markets including CASE in finding commercial sources of supply for bio-based polymer raw materials. In part 2 and 3, we will focus on the chemical options for manufacturing different resin/polymer categories that are derived from bio-based sources. The categories covered include the following:
Table 1: Polymer Families Covered
- Polyurethanes, Part 2
- Polyamides Part, 2
- Aromatic Polyesters, Part 3
- Aliphatic Polyesters, Part 3
- Acrylic Acid Derivatives, Part 3
- Epoxies and Epoxy Derivatives, Part 3
In the next two segments we will address the present situation with regard to the available sources for bio-based polymer raw materials in each category. We will also examine the potential chemical routes to commercial production of new bio-based polymer types. This includes an assessment of the current global efforts to bring new commercial products to market in each of the above polymer families from both the existing and new emerging sources of supply.
Background (from the Part 1 Article in November)
Renewable resources as raw materials, in place of petroleum derived raw materials, means plant biomass. What is biomass?
- Biomass is renewable organic materialthat comes from plants and animals.
- Biomass contains stored chemical energy from the sun. Plants produce biomass through photosynthesis. Biomass can be burned directly for heat or converted to renewable liquid and gaseous fuels through various processes.
The principle chemical families that comprise the renewable bio-based alternatives include those listed in Table 2. In general, bio-based chemicals originating from the last two items represent a much smaller portion of the four options and will not be considered in this article.
Table 2: Alternative Bio-based Chemical Families
(1) Carbohydrates such as starches, sugar, cellulose, and hemicellulose
(2) Plant oils, specifically triglycerides (commonly soya oil) and the hydrolysis/methanolysis products of triglycerides. These chemistries include fatty acids/methyl esters-particularly those containing carbon-carbon double bonds, the so-called unsaturated ones- oleic, linoleic, linolenic, along with the triol, glycerol (glycerin).
(3) Lignins
(4) Proteins
There are very few commercial products that are 100% derived from purely bio-based polymers. Most are hybrids of petrochemical-based and bio-based molecules. Within the chemical industry the current petrochemical derived-materials are recognized targets for hybridization with bio-based chemicals
Organic molecules containing carboxylic functionality and hydroxyl functionality are the key precursors to esters. Thus, many bio-based chemicals serve as monomers for aromatic, and aliphatic polyesters, and polymers containing polyester moieties such as the “soft” segment of polyurethanes. Bio-diols are also reactants for the synthesis of reactive vinyl monomers such as diol diacrylates and bis epoxides known as di-glycidyl ethers.
Significant steps are now being made by chemical companies to facilitate the production of hybrids intended to address the growing demand for greater bio-based content products. The big challenge in meeting this demand is in identifying commercially available options that can fulfill this task. Where do you look to find raw materials that will support commercially viable reactions to produce bio-based resins?
The following discussion explores some of the options that are being explored or can be explored for producing bio-based resin in each of the major resin categories used in the CASE markets.
Polyurethanes
For polyurethanes (PU), used for coatings, adhesives, sealants, and elastomers (CASE), bio-based chemicals serve as a formulator’s treasure trove of options. Modification of mechanical and physical properties via the soft polyester polyol segment, including polyether polyols, polycaprolactone polyols, and polycarbonate polyols provide a variety of alternative chemical pathways to make bio-based alternatives
The predominant area of effort and spending for development and commercialization for bio-based chemicals in the PU space has been for succinic acid, adipic acid, 1,4-butanediol, 1,3-propanediol and to a lesser extent, isosorbide, a sugar-based diol containing fused furan rings.
Since the early 2000’s there has been intense commercial activity for the production of bio-succinic acid and bio-1,4-butanediol. The purpose for this effort was to serve the ester derivative market with bio-based succinic particularly in PU as a polyester polyol component. Potentially it could also be used as a replacement for adipic acid whose commercialization is less progressed than succinic. Furthermore, succinic can be hydrogenated to bio-1,4-butanediol.
Petrochemically, succinic anhydride is manufactured via hydrogenation of butane-based maleic anhydride and hydrolyzed to succinic acid. 1,4-butanediol (BDO) is ultimately made from either acetylene, butadiene, propylene, or hydrogenation of butane-derived succinic acid.
This bio BDO could also serve as a chain extender for PU prepolymers. Most importantly it can serve as a raw material for bio-tetrahydrofuran (THF) which is transformed to poly-THF (polytetramethylene ether glycol, PTMEG) which serves as a bio polyether polyol.
MDI/TDI diisocyanates and bio-polytetramethylene ether glycol (PTMEG) form the PU from which Spandex fibers are made and then used in athletic apparel partially derived from a bio-based chemical.
Progress for creating bio-based chemistries for the workhorse diisocyanates, MDI and TDI, has been a greater challenge. The aliphatic, pentamethylene diisocyanate (PDMI) is available from Cathay Industrial Biotech Co. This material potentially enables the production of a 100% bio-PU when bio-1.4-butanediol and bio-succinic acid can be used either for making the polyester or polyether polyols.
Commercialization of bio succinic acid has been reported by many companies. The most prevalent companies in this field appear to be Roquette, Shandong Chemical, PTTGC Innovation America, and Succinity.
Rennovia, the Northern California company which developed adipic acid via the fermentation of sugar to glucaric acid and subsequent to adipic acid, discontinued operation in 2018. This bio-based adipic acid was also planned to be hydrogenated to bio-1,6-hexanediol (HDO).
Currently, there appears no near-term commercial plans for producing a bio-based adipic acid and hexanediol (HDO). Adipic acid, which is principally used for nylon 66, is made commercially via oxidation of benzene through various chemical steps. Commercial petrochemical-based HDO is obtained via adipic acid hydrogenation similar to the hydrogenation process of succinic acid to 1,4-butanediol (BDO).
Efforts for the commercialization of a direct route to bio-BDO (non-succinic acid intermediate) have been quite successful. This biotechnology, developed by Genomatica, makes 1.4 butanediol directly from sugar without the intermediate succinic acid.
The Genomatica process has been licensed. A plant has been built by Novamont, in Italy with a 30,000 mt/yr. capacity. Plans for a U.S. plant in Iowa, by a JV of Cargill and Helm (Qore) has been announced. Thus, bio-1,4-butanediol used as the hydroxyl-containing raw material for polyester polyols and polytetramethylene ether glycol (polyether polyol), and additionally as a PU prepolymer chain extender, represent possible routes for the production of bio-based PU.
Another successful commercialization of a bio-based (dextrose fermentation) diol is 1,3-propanediol (1,3 PDO) by DuPont and Tate & Lyle (DTL) called Susterra®. Like 1,4-butanediol (BDO) it can be transformed into its polyether glycol, namely, polytrimethylene ether glycol Cerenol®. Thus, 1,3-PDO like bio-BDO can be used in two different polyols for polyurethane manufacture. The route to PU manufacture: Reaction with a diacid to form a polyester polyol, and also via novel chemistry to form a polyether polyol.
Also noteworthy is bio-1,5-pentanediol (PDO), another odd carbon numbered diol like 1,3-PDO. This has been commercialized by Pyran, Inc. This process uses furfural as a starting material. Similarly, PDO’s can be esterified with a diacid yielding a polyester polyol. If the diacid were to be succinic acid, fully bio-polyester polyols could be made. Pyran has suggested the utility of PDO’s in PU-based coatings and adhesive markets not only as PU-containing polyester polyols, but also are used in polycarbonate polyols.
It seems that the polyether polyol from bio pentanediol (PDO), polypentamethylene ether glycol, has not been made. Unique to 1,3-PDO and 1,5-PDO is that they contain an odd number of carbons. Polyurethanes containing such polyester polyols may have different physical properties relative to their even numbered counterparts such as crystallization temperature which may be advantageous in processing.
All of the above bio-chemical routes have been derived from carbohydrates. Bio-based chemicals useful for polyurethanes also originate from plant oil triglycerides composed of high concentrations of fatty acids containing unsaturated carbon-carbon double bonds (oleic, linoleic, linolenic). Most notable among the plant oil sources is soybean oil referred to as soya oil.
Hydroxyl functionalization, as the route to produce soy polyols, is the most recognized path. A principal processing method is via expoxidization followed by hydrolysis to give polyols. While epoxidized soybean oil (ESBO) has been commercial for decades as a heat stabilizer for PVC, whereby the epoxide rings readily react with the fugitive decomposition product HCl, it has undergone a renaissance of interest due to its versatility as a bio-based raw material.
Similarly, the ESBO’s precursor, soya oil, contains a rich collection of carbon-carbon double bonds which serve as reactive sites beyond epoxidation. The hydroxyl functionalization method of hydroformylation of the double bond and the subsequent hydrogenation of aldehyde to yield -CH2OH moieties protruding from the triglyceride backbone, are available for making polyester polyols. The automobile industry has been quite interested in PU made from these bio-based soya polyols.
During the first decade of 2000, there was substantial effort to make biodiesel fuel. This was done by trans-esterifying unsaturated fatty acid-containing triglycerides with methanol resulting in biodiesel fuel known as fatty acid methyl ester (FAME) and glycerol. These efforts led to a dramatic interest in using glycerol as a bio-based chemical raw material. Two success stories arising from this work are bio-based processes for epichlorohydrin (discussed in later epoxide section) and propylene glycol. In the case of propylene glycol, it is polymerized to polypropylene glycol (PPG) where it finds vast use as its polyether polyol. Furthermore, as a diol, it can be reacted with various diacids such as succinic, to produce polyester polyols.
Polyamides
As noted above, Cathay Industrial Biotech has developed the aliphatic bio diamine, 1,5-pentamethylene diamine. This intermediate is then reacted with adipic acid to produce their commercial product, polyamide 56. This product is trade-named Terryl®, which is touted to be an alternative to polyamide 66 (nylon 66).
Polyamide 6 (nylon 6), produced via the ring-opening polymerization of cyclohexane-derived caprolactam now has a bio-based version due to Genomatica’s biotech production of caprolactam via sugar fermentation. In partnership with Aquafil, there are now plans to commercialize renewable nylon 6.
Part 3 of this article will continue this discussion to include aromatic polyesters, aliphatic polyesters, acrylic acid derivatives, epoxies, and epoxy derivatives.