Joint Formation of 1,2 Propylene Glycol and Isopropyl Alcohol from Biologically Derived Soketal.

[NNadir]

The paper I'll discuss in this post is this one: The Joint Synthesis of 1,2-Propylene Glycol and Isopropyl Alcohol by the Copper-Catalyzed Hydrogenolysis of Solketal (Vadim O. Samoilov,* Denis S. Ni, Georgiy S. Dmitriev, Leonid N. Zanaveskin, and Anton L. Maximov ACS Sustainable Chem. Eng. 2019, 7, 9330?9341)

I'm not all that much into - in fact I generally oppose - so called "renewable energy" because of its land use and material intensity is in my view, environmentally unacceptable. The failure of this strategy is recorded in the planetary atmosphere, CO2 concentration increases are accelerating, not falling, and in the fact that the use of dangerous fossil fuels and the resultant death toll are also rising not falling. Reliance on this strategy, while remaining popular in many places, is making things worse, not better.

It was not always so with me; I once thought - not all that long ago - that so called "renewable energy" was a good idea. In particular, I was very fond of the idea of biodiesel at one time, until, at least, little trivialities like the destruction of Indonesian rain forests to make palm oil plantations.

Driven by largely German "Renewable Energy Portfolio Standards" biodiesel was, for a time, a very popular fuel, although, according to the authors of this paper it no longer is, since they remark in their Russified English the following:

Over recent decades, much effort has been made by the world scientific community toward the development of efficient methods for bioglycerol valorization. Despite the so-called “biodiesel boom” being left in the past, the issue of bioglycerol usage for chemical synthesis of value-added products instead of petroleum-derived building blocks still stays relevant.

Glycerol is a by product of biodiesel production, and although it has always had some commercial value, prices for it fell so dramatically in the "biodiesel boom" that it ended up being dumped, which is a shame, as it has a significant amount of concentrated carbon removed from the atmosphere.

I personally believe that biomass offers something of a path to removing carbon dioxide from the atmosphere, something that will fall to future generations as we have screwed them - with our dangerous fantasies - out of their rightful inheritance of a clean planet, albeit one that will always remain minor, but I favor a brute force approach of high temperature reforming driven by nuclear heat rather than expensive and water intensive fermentation processes. This said, there are some applications where biological schemes might be utilized to obtain specialty chemicals without too much strain on the environment, and, as I have been interested in biodiesel in the past, and in glycerol, this paper caught my eye.

"Soketal" is a compound made by condensing acetone with glycerol. It's structure will be shown below. About half a century ago, industrial operations of the "ABE process," a fermentation process, (Acetone, Butanol, and Ethanol) operated in some countries commercially. Today most of the world's acetone is made from the oxidative decomposition of cumene, a product of the dangerous petroleum industry, butanol from the oxidation of butene from the dangerous fossil fuel industry, and ethanol from corn, albeit, in the United States, at the cost of the complete destruction of the Mississippi River Delta's ecosystem.

The paper before this one in this journal is about reviving the "ABE Process." (It's probably a bad idea.)

Anyway, from the paper, the full introductory paragraphs excerpted above:

Over recent decades, much effort has been made by the world scientific community toward the development of efficient methods for bioglycerol valorization. Despite the so-called “biodiesel boom” being left in the past, the issue of bioglycerol usage for chemical synthesis of value-added products instead of petroleum-derived building blocks still stays relevant. One of the most important options for bioglycerol valorization is its conversion into propylene glycols (PG).
Regarding the methods of production of propylene glycols (PG), scientific efforts are mainly aimed at (a) the development of new heterogeneous catalysts for glycerol conversion providing enhanced stability and selectivity toward 1,2-PG and (b) the development of approaches toward the selective hydrogenolysis of glycerol into valuable 1,3-propanediol.(1) While the noble metal-based catalysts have turned out to be the most promising for the latter purpose,(2,3) the copper-based catalysts seem to be the best choice for the hydrogenolysis of glycerol into 1,2-PG because of the relative low costs and efficient performance. High yields (up to 98%) and selectivities (up to 99.6%) in glycerol hydrogenolysis have been reported for Cu,(4?10) Cu–B,(11,12) Cu–Cr,(5,6,10,13) Cu–Mg,(14) Cu–Pd,(15) and Cu–Zn(16,17) catalysts.

At the same time, much attention has been recently paid to glycerol acetals and ketals, due to the relative ease of synthesis and intriguing prospects of application as fuel additives(18?20) and solvents.(21) The majority of the investigations are dedicated to solketal (2,2-dimethyl-4-(hydroxymethyl)-dioxolane-1,3), a ketal formed by the condensation of glycerol with acetone. For the synthesis of this compound, a few technological schemes have been proposed,(22?24) but one of the most interesting points about solketal is that it could be synthesized directly from crude bioglycerol.(25?27) A specific feature of the process (using sulfuric acid, sulfonic exchange-resins, or AlF3·3H2O as a catalyst) is the relative ease of the crude bioglycerol conversion and the product recovery (the boiling point of solketal is about 187 °C, which is approximately 100 °C lower than for glycerol). Upon the acidification of crude glycerol with H2SO4, a separate lipophilic phase (which mainly consists of fatty acids) is formed. During the ketalization, the major part (?80%) of the mineral impurities is separated as a solid, as well; in this manner, along with ketalization, some purification is conducted.

The authors investigate catalysts for the conversion of soketal into value added chemicals of possible industrial importance.

Some pictures:



The caption:

Scheme 1. Possible Routes for Obtaining 1,2-Propylene Glycol from Crude Glycerol

Almost of the chemicals shown in the following scheme are of some industrial importance, at least if purified, something which is energy intensive, but still...



The caption:

Scheme 2. Solketal Copper-Catalyzed Liquid-Phase Hydrogenolysis Reaction Network

Some yield and distribution information in differing conditions:



The caption:

Figure 1. Influence of the temperature and the hydrogen pressure of the solketal hydrogenolysis product yields (under standard conditions, p(H2) = 20 bar (a), 30 bar (b), and 40 bar (c)). White, the glycerol yield (YGly); gray, the overhydrogenation products (IPA and acetone) total yield (Yover); blue, the 1,2-PG yield (YPG); green, the 2,2,4-TMD yield (YTMD). The total bar height (the sum of all the yields) equals the solketal conversion (XSol). The propanol-1 yield YPrOH was <0.1% in all the experiments.

More yield information:




The caption:

Scheme 4. Conversion of the Potential Intermediate Products and the Probe Molecules (TMD (1), 1-Mono-GIPE (2), SIPE (3), and GPAs (4)) under Liquid-Phase Hydrogenolysis Conditions over 60% Cu/Al2O3 Catalyst (T = 240°C, NaOH (0.63 mol. % to Feed) Added, Standard Conditions)

Nothing here is going to be earth shattering, unless an attempt is made to overuse it, but I can certainly see niche applications for this sort of thing, and to the extent carbon is removed from the atmosphere, it's a good thing.

[RKP5637]

1. K&R!!! n/t