Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

In a chemical plant, 40%–60% of energy and capital cost is tied to separation processes. As such, these processes must be selected carefully. Separation process can classified as thermal or non-thermal. Recent literature suggests that such distillation are inherently intensive relative their non-thermal counterparts membrane separation. The reasons for this claim traced back the success reverse osmosis water desalination perception when separating mixtures components with close boiling points. We demonstrate pitfalls in sweeping generalizations. argue recovery need not typical all industrial show efficient even points close. More specifically, we elaborate efficacy depends on following: (1) mixture being separated, (2) purity products, (3) source energy, (4) interactions between separations unit remaining (5) scale use, among others. develop framework accounts effects optimize each ascertain its best achievable performance concrete examples. believe our structured comparison will invigorate research into processes, resulting selection operation more reduce overall carbon footprint. At level, variety predominantly carried out by thermally driven distillation. Nevertheless, current seems suggest much gained replacing alternative methods, which potentially require fraction used This primarily due widespread particularly those involve vaporization, highly intensive. However, belief well founded, because it based extrapolation from comparisons literature, many make ad-hoc assumptions result incorrect conclusions. Our analysis shows confusion arises utilize different types energy: heat electricity. Here, present consistent enables fair consume forms energies. Using framework, refute general most conclusively through examples two challenging constituting low volatilities, run properly, remarkably lower fuel than alternatives, have often been touted efficient. Molecular needed across industries, including oil gas, food, pharmaceutical, industries. Among available technologies, (see Note S1 Supplemental Information), distillation, entail traditionally preferred petrochemical plants. Just U.S., estimated over 90%–95% fluid plants refineries performed distillation.1United States Department EnergyMaterials technologies: emission reduction opportunities.https://www1.eere.energy.gov/manufacturing/industries_technologies/imf/pdfs/separationsreport.pdfDate: 2005Google Scholar recent claims methods involving vaporization (simply referred hereafter) and, if replaced lead huge savings various mixtures.1United Scholar, 2Sholl D.S. Lively R.P. Seven change world.Nature. 2016; 532: 435-437Crossref PubMed Scopus (1613) Google 3National Academies Sciences, Engineering, MedicineA Research Agenda Transforming Science. National Press, 2019https://doi.org/10.17226/25421Crossref 4Koros W.J. Evolving beyond age processes: membranes way.AIChE J. 2004; 50: 2326-2334Crossref (175) 5National CouncilSustainability Chemical Industry: Grand Challenges Needs. 2006Google 6Lively Sholl From organics separations.Nat. Mater. 2017; 16: 276-279Crossref (239) For example, agenda published Engineering Medicine,3National ranked rationale provided "thermal they enthalpy at least one component." intensity solely determined vaporization. actual number factors quality used, availability suitable source, possible use rejected heat, possibility work via pumping temperature use. requires careful system draw proper conclusion regarding high drawn basis classes first one, has extensively studied optimized seawater desalination.4Koros Depending how plant accounted, net consumption found up ten times higher (RO) plant.4Koros Scholar,7Darwish M.A. Al Asfour F. Al-Najem N. Energy equivalent desalting methods: case study Kuwait.Desalination. 2003; 152: 83-92Crossref (56) Scholar,8Nassrullah H. Anis S.F. Hashaikeh R. 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(1991). oxygen-lean argon air, US Patent 4,994,098, filed 2 February, 1990 granted, 19 1991.Google Furthermore, factor unsubstantiated.2Sholl Scholar,11Koros Water beyond: expanding spectrum large-scale processes.AIChE 2012; 58: 2624-2633Crossref (115) oxygen ∼20%12Mallapragada Singh N.R. Curteanu V. Agrawal Sun-to-fuel assessment routes fixing CO2 liquid fuel.Ind. Eng. Chem. Res. 2013; 52: 5136-5144Crossref (44) about 26%13Agrawal Woodward Efficient generators: exergy analysis.Gas 139-150Crossref (30) energy-intensive thermodynamically infeasible. second class alkanes alkenes propane/propylene, ethane/ethylene, etc. non-aqueous ortho para xylenes. duties distillations high, thus, cited processes.4Koros Scholar,14Xomeritakis G. Lai Z. Tsapatsis M. xylene isomer vapors oriented MFI made seeded growth.Ind. 2001; 40: 544-552Crossref (219) To large extent, originates challenges associated comparing work, comprehensive allows then test generally Toward end, analyzed relevant separations, p-xylene/o-xylene propylene/propane, both process. determine intensive, evaluate optimal-minimum consumption. results always well-founded. that, absence thorough likely appear Therefore, technology significantly sub-optimal implementation, adversely affect needs, but consuming fuel, increase footprint Frequently, energy. Non-thermal membranes, whereas distillations, usually wide range temperatures. understand intensity, sufficient compare electricity consumed candidates. Observe energies typically derived law thermodynamics, amount certain markedly same heat. better way calculate primary strategy requirements process.8Nassrullah Scholar,15Wade N.M. Distillation development update.Desalination. 136: 3-12Crossref (146) also include approach identify given candidates analyzing sources sinks site. form essential fossil strongly supplied obtained, utilized. Figure 1 depicts consider. When consumes could come steam directly generated burning (line 1) co-generation 2). operated pressure. Alternatively, required waste another 3) within plant. On hand, electricity, typically, produced 4). Another route extract 5). feasible, supply 6) generate 7). Distillation, some integrated units Tools pinch analysis16Linnhoff B. Hindmarsh E. design method exchanger networks.Chem. Sci. 1983; 38: 745-763Crossref (1220) Scholar,17Smith Linnhoff separators context processes.Trans IChemE ChERD. 1988; 66: 195-228Google employed integrations demand. seen 1, total combustion distributed entire distribution direct physically divided sent indirect cascaded along processing units. Henceforth, refer utilized indirectly provide effective fuel. following example illustrates importance evaluating level. p-xylene/o-xylene. p-xylene valuable feedstock manufacturing important polymers. Currently, simulating moving bed crystallization major technologies mixtures. co-production o-xylene needed.18Canella Xylenes Ethylbenzene.Kirk-Othmer Encyclopedia Technology. John Wiley & Sons, Inc., 2000: 1-30Crossref researchers.14Xomeritakis Scholar,19Koh D.Y. McCool B.A. Deckman H.W. Reverse molecular differentiation organic liquids sieve membranes.Science. 353: 804-807Crossref (142) 20Kim D. Jeon M.Y. Stottrup B.L. Para-xylene ultra-selective zeolite fabricated nanosheet monolayers air-water interface.Angew. Int. Ed. Engl. 2018; 57: 480-485Crossref (86) 21Schleiffelder Staudt-Bickel C. Crosslinkable copolyimides membrane- p-/o-xylene mixtures.React. Funct. Polym. 49: 205-213Crossref (35) These researchers (with 50% 90% p-xylene) case. studies motivated bring separation.22Lively Carbon aim cut hydrocarbon separations.Membr. Technol. 2017: 9-10Crossref shall later, expectation optimistic since selective membranes. next section, discuss detail before carefully review simulate p-xylene/o-xylene, consider 50 p-xylene. Since downstream purity,23Tsai T.-C. Liu S.-B. Wang I. Disproportionation transalkylation alkylbenzenes catalysts.Appl. Cat. A. 1999; 181: 355-398Crossref (336) set final equal value 99.5 99% respectively S2 definition recovery). analysis, assumed part co-generated situated nearby analyze under scenarios were identified 1. brevity avoid cases favor assume does (lines 3 5), 6 column input, reboiler 1; 1). 2A flowsheet simulated scheme alternately 2; case, extraction saturated bar pressure, saturation 159°C, perform transfer (Treb=146°C). reuse condenser (Tcond=138°C) One aid pump. 2B variant pump Under approach, rather comes 4; Table summarizes evaluated scenarios. See Experimental Procedures calculation details. Scenario burned extremely Not surprisingly, very inefficient Treb=146°C. 2, efficiently moderate temperature. synergy lowers turn reduces effectively 59%, although transferred remains unchanged Scenarios 2. 3, Interestingly, nearly on-tenth once again, exchanged same. benefit understood difference temperatures (138°C 146°C, respectively). small, compression ratio compressor, therefore, small quantity upgrade reboiler.Table 1Energy Requirements (kWhr/lb p-Xylene Feed) Distill 99.5% Mole Purity Recovery 50%/50% Mixture p-Xylene/o-XyleneSimulated ScenariosΔHvap ReboilerSupplied HeatSupplied ElectricityEffective Fuel HeatScenario 1: burn0.6310.63100.742Scenario 2: steam0.6310.63100.303Scenario 3: distillation0.63100.0180.036 Open table new tab addition previous calculations, calculated separate RO, method. note separation, insufficient meet specifications. considered multistage similar shown 3. formulated solved optimization model find optimum configuration operating conditions minimize Procedures). six-stage cascade values permselectivity, defined permeabilities (p-xylene) permeable (o-xylene) components. While highlight accounted auxiliary equipment irreversibilities, originating finite differences exchangers, drop, compressor inefficiencies. If incorrectly conclude true where scenario while picture emerges corresponding Even 2.9 point knowledge, permselectivity highest exhibited lab 130.19Koh discussed 21% impossible demand one-tenth implied literature.2Sholl ScholarTable 2Energy Permeate p-Xylene/o-Xylene Six-Stage Membrane CascadePermselectivitySupplied Heat1000.0730.1461,0000.0560.11110,0000.0530.107 so far clearly disprove emphasize misperception exists considering unattractive standpoint.2Sholl points, yet Certainly, involved makes just value.24Agrawal Herron D.M. Optimal thermodynamic ideal binary mixtures.AIChE 1997; 43: 2984-2996Crossref now nuances vis-a-vis versus Clearly, 0.053 kWhr/lb should 0.631 overcome problem, conversion suggested common unit.4Koros 50%,4Koros 0.32 lb p-xylene, six Same reached was converted 0.107 correct line level supplying wasted environment. low-level low-pressure S2, turbine 24%. Thus, 0.151 2.8 electric