By Dr. Bernard Cooker, Chemical Processing Solutions, Lee Enterprises Consulting
Special to The Digest
The use of catalysts, both living entities, such as microorganisms, and otherwise inert synthetic and biologically-derived materials, such as supported transition metals and enzymes, are frequently key to the development of technically efficient and low cost commercial processes to biochemicals and biopolymers. The articles in Chemical Engineering Progress (CEP) and Chemical and Engineering News (CEN) on new or improved catalysts or catalytic systems in 2015 and 2016 have been entered in a spreadsheet database. The most noteworthy items in catalytic biotechnology, are presented here and summarized in Table 1. The articles were selected if 1. They use biomass to produce a specific renewable product and/or 2. Convert a biomass-derived chemical intermediate to a higher added value product. Due to limited space, the processes with potentially greater added value are discussed and the remainder noted.
Methane Raw Material Utilization
Methane from biological sources, usually through anaerobic digestion of biomass, is a renewable resource. Five projects using CH4 in catalyzed conversion to chemical intermediates or final products are listed in Table 1. The products were 1. Syngas (CO/H2), from dry reforming, 2. Methanol (two processes), 3. BTX (Benzene, toluene, xylene) and 4. Polyhydroxyalkanoate.
Ref. 4 reports CH4 conversion to BTX through non-oxidative methane dehydroaromatization (MDA). See Table 1. CoorsTek Membrane Sciences and two academic institutions developed a coionic ceramic membrane for a continuous catalytic MDA reactor. The membrane is a dense film of barium zirconate, doped with cerium and ytterium, on a porous support. The CH4 feed, activated on the metal sites of a bifunctional zeolite catalyst, reacts with the acidic zeolite sites, selectively forming aromatics and hydrogen. Selective separation of the H2 from the aromatics by the membrane displaces the product mix from the thermodynamic equilibrium state which would otherwise occur. H2 is preferentially transported through the membrane, which converts some of the H2 to steam, by reaction with oxygen ions in the membrane, on an interior electrode. The steam reacts with coke, forming CO and H2, preventing coke buildup and consequent membrane and catalyst deactivation. In experimental trials, a maximum yield of 12% was obtained, with a twofold increase in the cumulative yield relative to that of a conventional fixed bed reactor.
Ref. 5 discloses Newlight Technologies’ biocatalytic process making PHA from sequestered CH4 and CO2. The methane could, in principal, be from an anaerobic biomass process. The proprietary bacterial polymerase enzyme couples CH4 and CO2 with O2 from air to yield PHA, termed AirCarbon by Newlight. The enzyme activity is unhindered by the product, a previous challenge, and the reaction is conducted at near ambient conditions. Ref. 5 reports that it was commercialized in 2013.
Ethanol Raw Material Utilization
There are three processes in Table 1 where ethanol, as a chemical intermediate, was converted to added value products. The ethanol can, in principal, be bioethanol.
Ref. 6 describes research at U Rochester and U Ottawa, using an iridium-based catalyst in a one pot synthesis, based on the Guerbet process, to converting ethanol to 1-butanol. See Table 1.
Acrylic Acid, Polypropiolactone, Succinic Anhydride and Derivatives
Ref. 7 reports Novomer’s consideration of commercial scale manufacture of acrylic acid at 160,000 tons/yr in Europe, starting 2019. The acrylic acid would be derived via beta-propiolactone, obtained through homogeneous catalysis from ethanol-derived ethylene oxide and CO from gasified agricultural waste or natural gas. The beta-propiolactone can be polymerized to polypropiolactone, which breaks down at high temperatures to acrylic acid. Novomer is reported in ref. 7 as exploring other longer term applications for the beta-propiolactone intermediate. High MW polypropiolactone has good barrier properties and is biodegradable, having potential application in packaging. Beta-propiolactone can also be converted over a second Novomer catalyst to succinic anhydride, by reaction with CO. The succinic anhydride, in turn, can be converted to 1,4-butanediol, succinic acid or THF. Ref. 7 reports that Novomer has piloted the process to acrylic acid for two years.
Natural Oils Raw Material Utilization
Dicarboxylic Acids, Nylon
Ref. 8 reports Verdezyne’s yeast-utilizing process, converting vegetable oils to renewable diacid nylon intermediates; dicarboxylic acids from sugars or vegetable oils are increasingly important renewable chemicals. Verdezyne engineered genetically modified yeast and developed aerobic fermentation-based technology to produce adipic acid, sebacic acid and dodecanoicdioic acid (DDDA). They employed a Candida yeast strain, originally isolated from petroleum-contaminated soil, sequenced the genome and made genetic modifications. This changed the yeast biochemistry from consuming alkanes to consuming lauric acid, present in palm fruit and coconut oils. The optimized yeast uses a three step enzyme-mediated fermentation process from lauric acid to DDDA, at an exit concentration of 140 gm/liter. Ref. 8 discloses a lower carbon footprint for the subject process than the petrochemical-based one. It uses ambient conditions, not high temperature or pressure. Verdezyne have demonstrated the technology on the pilot scale and are reported in ref. 8 as building a 9,000 metric ton/year plant in Malaysia.
DDDA can be copolymerized with hexamethylene diamine to make Nylon 6,12 and Nylon 12,12; it has other applications in paints, adhesives and coatings.
Lactic Acid Raw Material Utilization
Polylactic Acid Polymer
Ref. 9 describes recent catalytic work on lactic acid conversion. Polylactic acid (PLA) has been produced from lactic acid, made from renewable raw materials, including starch and sugars. It is biodegradable and compostable and finds application in 3D printing, as reported in ref. 9. A new application of zeolite catalysis may streamline lactic acid to PLA conversion. The established route to PLA polymerizes lactic acid in vacuum and at high temperatures to a prepolymer, which must then be converted to a cyclic lactide. The cyclic lactide is then polymerized to PLA.
Researchers at Katholieke Universiteit, Leuven, Belgium have a laboratory scale process which catalytically converts the lactic acid directly to the cyclic lactide dimer, at 130C and ambient pressure. They employed commercially available zeolite catalysts in a condensation reaction. The controlled size of the zeolite micropores constrains the product dimensions. Consequently, the catalyst produces cyclic lactide dimers, for polymerization to PLA, but not the higher MW lactic acid oligomers of the current process. This new direct conversion of lactic acid to cyclic lactide dimer has the added features of not consuming metal salts and it produces less waste. It also has less than 1% (D,L)-lactide in the intermediate, compared with 5 to 15% of the (D,L)-lactide in the current process.
Lignin Raw Material Utilization
BTX (Benzene, Toluene, Xylene)
Refs. 10 and 11 disclose a recent potential upgrade in lignin use to produce BTX. Lignin, a tough, recalcitrant polymer, from lignocellulosic biomass, contains no sugar units but is rich in benzene rings. It has been consumed as low value fuel in pulp mill boilers. Ongoing research aims to chemically upgrade the lignin to higher value added products, including BTX and derivatives. An iridium hydroxylcyclopentadieneyl catalyst was used in the laboratory to deoxygenate lignin fragment model compounds without benzene ring reduction, advancing the goal of producing more valuable BTX from lignin.
This article has shown that methane, ethanol, lactic acid and lignin, derived from biomass, and vegetable oil biomass itself, can be converted catalytically to useful renewable chemicals with potential added value. These catalyzed chemical products include dry reforming gas, methanol, BTX, PHA, n-butanol, acrylic acid, succinic acid, 1,4-butanediol, THF, dodecanedioic acid, adipic acid, sebacic acid, polylactic acid. These products may offer more added value and more attractive economics than the intermediates on which they are based.
1 Chemical and Engineering News, 4/25/16, p. 30
2 Chemical Engineering Progress, 8/1/15, p. 11
3 Chemical Engineering Progress, 7/1/16, p. 5
4 Chemical Engineering Progress, 10/1/16, p. 4
5 Chemical and Engineering News, 6/20/16, p. 22
6 Chemical Engineering Progress, 1/1/16, p. 4
7 Chemical and Engineering News, 11/21/16, p. 29
8 Chemical and Engineering News, 6/20/16, p. 23
9 Chemical Engineering Progress, 8/1/15, p. 6
10 Chemical Engineering Progress, 4/1/15, p. 10
11 Chemical and Engineering News, 3/2/15, p. 29
Category: Thought Leadership