Propylene oxide (PO), a commodity chemical used for making antifreeze and plastics, has long been manufactured using technologies that make co-products that influence process economics and environmental footprint. In contrast, the hydrogen peroxide propylene oxide (HPPO) process (commercialized by Dow-BASF) uses titanium silicate as a catalyst and hydrogen peroxide (H2O2) as an oxidant to selectively produce PO without a co-product. Another alternate process (CEBC-PO) uses a homogeneous methyltrioxorhenium (MTO) catalyst and H2O2 to exclusively produce PO. This chapter compares the economics and environmental footprint of three technologies for making PO: HPPO, CEBC-PO and LyondelBasell that makes tertiary butyl alcohol (TBA) as a co-product. While the HPPO and CEBC-PO processes are profitable, the profitability of the LyondellBasell process depends on the demand and value for TBA. Cradle-to-gate LCA reveals that the environmental impacts of all three processes are similar, with most of the adverse impacts caused by using fossil-based sources (natural gas and transportation fuel) for producing the raw materials (isobutane, propylene and hydrogen peroxide).

Ethylene oxide (EO) is a commodity chemical made by treating ethylene with oxygen over a silver-based catalyst. One of its major applications is for making polyethylene terephthalate (PET) plastics used in water bottles. In the conventional process, up to 15% of the ethylene is simply burned as CO2. This chapter discusses an alternative process that employs methyltrioxorhenium (MTO) as a catalyst and hydrogen peroxide (H2O2) as an oxidant to produce EO with no CO2 as a byproduct. While the capital costs for both processes are similar, the EO production cost for the alternative process is competitive only if the MTO catalyst remains stable for at least one year and the Re leaching is <0.7 ppm. Unexpectedly, cradle-to-gate life cycle assessments (LCA) reveal that the overall environmental impacts on greenhouse gas emissions, air quality and water quality are similar for both processes. In the alternate technology, the carbon footprint associated with H2O2 production reduces the gains made in converting ethylene to EO avoiding CO2 as a byproduct. Direct H2O2 synthesis technology and effective H2O2 utilization are essential to reduce the environmental footprint of the alternate technology.

The 17 “Sustainable Development Goals” (SDGs) call for an equitable and sustained supply of basic needs such as food, water, electricity, clothing, medicines and shelter. Together, the SDGs represent a universal call to end poverty, protect the planet and ensure that all people live in peace and prosperity by the year 2030. Since the chemical industry produces so many everyday products such as fertilizers, medicines and materials for clothing and buildings, it must play a central role in meeting the SDGs. The demand for everyday products is expected to double by 2030 and the resulting boom in chemical manufacturing must not jeopardize the environment’s well-being and human health. The present-day chemical industry relies mostly on fossil-based carbon sources for raw materials and energy. If this dependence persists, the industry’s negative effects on the environment will continue to worsen. It is therefore essential that the chemical industry transition to renewable sources, both for its raw materials and energy. While the task may seem daunting, we are seeing the development of strategies and technologies that can lead the way to a more sustainable future.

Industrial propylene hydroformylation (PHF) to produce butyraldehyde uses polymer-grade propylene (99.99 wt% purity) obtained from propane dehydrogenation (PDH) followed by separation of the propylene/propane mixture by distillation. Recently, it was shown that the effluent from a PDH reactor (60–70% propylene in propane) can be directly used for PHF over Rh-based complexes, eliminating the energy intensive C3 distillation step. Because only propylene reacts in the PHF reactor, an enriched propane stream results and is recycled back to the PDH reactor. At industrial conditions (2.5 MPa, 90°C), hydroformylation with mixed propylene/propane feedstock occurs in a propane-expanded liquid (PXL) phase. The capital investment for the PXL process is approximately 20% lower than the conventional process. The production cost in the PXL process is also lower, resulting in an annual savings of nearly $12M for a 300 kt/y plant. Comparative gate-to-gate environmental impact analyses shows that the PXL process results in reduced environmental impacts (greenhouse gas emission by 20%, air pollutants emission by 22% and toxic release by 21%) compared to the conventional process.

Higher olefin hydroformylation with syngas to produce linear aldehydes uses cobalt-based catalyst complexes, which requires rather high temperatures (>180°C) and pressures (~20 MPa). Further, it entails substantial solvent usage to recover and recycle the cobalt complex. Rh-based catalysts are known to operate at milder conditions (<100°C and a few MPa) and are much more active and selective toward the linear aldehyde. However, Rh is three orders of magnitude more expensive than cobalt and requires near-quantitative recovery for economic viability. A new 1-octene hydroformylation process that uses carbon-dioxide expanded liquid (CXL) as solvent medium and a nanofiltration membrane to substantially retain the Rh-catalyst complex in the reactor was demonstrated by researchers at the University of Kansas Center for Environmentally Beneficial Catalysis to outperform the cobalt-based process, with capital investment being 30% lower than the Co-based process. Gate-to-gate life cycle assessments show that the CXL process is environmentally friendlier than the conventional process in most impact categories such as ecotoxicity, greenhouse gas emissions and smog formation.

Alkylation of 1-butene with isobutane is employed industrially to produce C8 alkylates (such as trimethylpentane) as high-octane motor fuel. Such alkylates supply roughly up to 15% of the U.S. gasoline pool. However, the process uses large quantities of sulfuric acid (as catalyst) generating acid waste whose handling poses health and environmental hazards. The main pollutants are sulfur dioxide (SO2) emissions (which causes acid rain) and acid leakage in the alkylation unit. This chapter presents an alternate process that uses a solid catalyst (Nafion® supported on silica) in dense CO2 media to produce C8 alkylates (solid acid/CO2 process). Although the environmental concerns with SO2 emissions and acid leakage are eliminated, the activity of the solid acid catalyst is lower than sulfuric acid resulting in an approximately 30% higher capital investment than the conventional process. For C8 alkylate productivity, capital investments and operating costs to be nearly identical, the required olefin throughput in the solid acid/CO2 process must be four-fold higher. Such analyses establish performance targets for the solid acid/CO2 process to be commercially viable.

Demand for chemicals is growing. The chemical industry’s global output is expected to double between 2017 and 2030. Lowering the carbon footprint of such growth requires sustainable alternative technologies. Fortunately, green chemistry and engineering research has made remarkable progress, laying the foundation for developing resource-efficient processes that conserve feedstock and energy as well as reduce adverse impacts on human health and the environment. Life cycle assessment (LCA) plays a key role for identifying environmental hotspots along the supply chain, either within the manufacturing plant (catalysts, solvents, reactors, separators) or upstream during raw material extraction or during the generation of energy at any stage. In concert with traditional techno-economic analysis, LCA is an essential tool for the rational development of sustainable chemical processes.

Solvents play a vital role in chemical processes such as solubilizing reactants, facilitating product/catalyst separation, increasing reaction rates, enhancing solubilities of gaseous reactants (such as O2, CO, H2) and providing heat capacity to manage the heat of reaction. However, solvent use can also cause adverse environmental impacts by increasing the carbon footprint and/or emitting harmful vapors. This chapter highlights such roles of solvents in multiphase catalytic processes such as hydroformylation, carbonylation, hydrogenation and oxidation through industrial examples. It also discusses how the pressure-tunable properties of supercritical fluids (SCFs) and gas-expanded liquids (GXLs) can be harnessed to develop greener chemical technologies through efficient feedstock utilization, process intensification, enhanced process safety and reduced use of volatile organic solvents. Emerging feedstocks, such as plant-based biomass, shale gas and sequestered CO2 offer excellent opportunities for using such tunable solvents.

Ethylene ranks among the top-20 chemicals, with nearly 200 million metric tons made globally in 2020. Its production requires much energy that is currently derived from fossil fuels. This chapter discusses environmental impacts for ethylene production from petroleum, natural gas and biomass sources, predicted using commercial software. Most of the predicted environmental impacts are within the same order of magnitude. For all feedstocks, the main sources of adverse environmental impacts are greenhouse gas emissions, acidification and air pollution stemming from the burning of fossil-based fuel; and for agricultural operations, production of fertilizers and pesticides needed for cultivation (in the case of ethanol), ocean-based transportation of crude oil and the chemical processing steps (for all feedstocks). An assessment of the environmental impacts of different fossil energy sources (coal, natural gas and fuel oil) reveals almost similar carbon footprints to produce a given quantity of energy. The predicted emissions agree well with the actual emissions data reported by coal-based and natural gas-based power plants to the U.S. Environmental Protection Agency (USEPA).

Terephthalic acid (TPA) is a commodity chemical made by treating p-xylene (pX) with oxygen (O2) via the so-called Mid-Century (MC) process. TPA is a key ingredient to make polyethylene terephthalate plastic used in water bottles. The MC process uses a stirred reactor in which O2 is dispersed through an acetic acid solution of pX and catalyst (Co/Mn/Br). However, O2 starvation in the liquid phase causes incomplete oxidation necessitating product purification in a catalytic hydrogenation unit that accounts for nearly 50%, 16% and 33% of the overall capital investment, operating costs and greenhouse gas emissions, respectively. To mitigate O2 starvation, an alternate reactor technology is presented wherein the continuous and dispersed phases are reversed by spraying the liquid phase as fine droplets into a vapor phase containing O2 to increase the gas–liquid interfacial area. As a result, the spray reactor produces polymer-grade TPA in one step, eliminating the hydrogenation unit. Life cycle assessment confirms that the spray process without the hydrogenation unit significantly lowers global warming, acidification and other harmful emissions when compared to the MC process.

Adiabatic combustion raises the temperature of the working fluid in a power cycle and provides the source of “high-temperature heat” to the heat engine. Analysis in the previous chapter showed that adiabatic combustion reactions are irreversible, and lead to entropy generation and hence loss of availability. Isothermal reactions that operate at equilibrium with the environment avoid this loss mechanism. If carefully executed, these can lead to more efficient use of the chemical energy. One practical way to directly convert chemical energy to electricity under nearly isothermal conditions is in a fuel cell, where reactions occur in the form of an electrochemical pair, or a redox pair.