Table 4.

Comparison and evaluation of all routes and sub‐routes based on atom economy, RME, sustainability based on green chemistry principles, and maturity.

Primary pathway	Process step	Atom economy[a] [%]	RME[b] [%]	Sustainability[c] (1–5)	Maturity[d]
direct conversion of CO2	classic electrochemistry	152	137	3.50	bench
	metal‐complex electrochemistry	152	146	3.65	lab
	sacrificial ascorbate reduction	61	49	3.93	lab
formate coupling	carbonate reduction	79	78	4.21	bench
	photochemical reduction	73	69	4.21	pilot
	photochemical reduction	73	47	3.87	bench
	enzymatic production	–	–	4.14	bench
	caustic CO reduction	100	97	3.93	commercial
	formate coupling	99	98	4.36	commercial
CO to oxalic acid	Boudouard reaction	100	80	2.00	commercial
	coal gasification	33	8	3.29	commercial
	steam reforming	93	75	1.86	commercial
	partial oxidation	92	74	2.21	commercial
	biomass gasification	X	X	4.14	pilot
	reverse water‐gas shift	61	33	4.14	commercial
	electrochemical reduction	61	52	4.07	bench
	photochemical reduction	61	61	4.14	lab
	electrolysis (solid oxide electrolyzer cell)	64	51	4.14	commercial
	dialkyl oxalate process	98	96	3.00	commercial
direct biomass conversion	alkali fusion	27	22	2.79	commercial
	oxidation	92	60	3.79	commercial
	fermentation	X	X	3.86	bench
EG oxidation	ethylene oxide hydrolysis	100	90	1.96	commercial
	glycerol oxidation	69	59	3.93	pilot
	catalytic EG oxidation	71	67	3.71	commercial
	electrochemical EG oxidation	71	67	4.22	bench
propylene oxidation	steam cracking	90	90	1.93	commercial
	fossil on‐purpose processes	X	X	1.85	commercial
	bioethanol dehydrogenation	53	48	3.14	pilot
	Fischer‐Tropsch to olefins	67	64	3.12	lab
	direct hydrogenation	36	33	3.21	lab
	catalytic propylene oxidation	32	36	3.07	commercial
oxalate acidification	classic acidification	44	44	4.29	commercial
	paired electrodialysis	85	84	4.71	bench

X=could not be calculated. [a] Atom economy=(mass of all products/mass of all reactants)×100. [b] Reaction mass efficiency=actual yield of all process steps combined×(mass of all products)/(mass of all reactants). [c] Sustainability rating is a rating on the overall sustainability of the process on a 1–5 scale, where 1 is the worst and 5 is the best achievable rating. The rating considers seven categories for which different impacts were attributed and are listed with descending impact: feedstock sustainability (Impact: 5), production of waste and greenhouse gases (Impact: 3), use of precious materials or solvents (Impact: 2), energy source process toxicity and safety concerns (Impact: 2), intensity of downstream separation (Impact: 1), energy efficiency and process conditions (Impact: 1). For all sub‐categories, a rating from 1 (worst) to 5 (best) was given. The overall rating reflects the average of the sum of grades for all categories weighted by their impact factors. [d] Maturity reflects scale at which a process is proven: lab‐scale includes non‐automized or optimized systems at low or sub gram scale (TRL 1–2); bench‐scale includes processes that are performed at a high g or kg scale with upscaling and optimization in mind (TRL 3–5); pilot‐scale includes processes that are performed at a large kg or low ton scale to demonstrate the process (TRL 5–7); commercial‐scale includes processes that have been used successfully commercially.