The ability to accurately model and simulate chemical processes has been paramount to the growing success and efficiency in process design and operation. These improvements usually come with increasing complexity of the underlying models leading to substantial computational effort in their use. It may also occur that the structure of the model is sometimes unknown making optimization and study difficult. To circumvent these issues, mathematically simpler models, commonly known as surrogate models, have been designed and used to successfully replace these complex, underlying models with much success. This technique has seen increasing use within the chemical process engineering field and this article summarizes some popular surrogates and their recent use in this area.

Different operational modes, various scales and complex phenomena make the design of a chemical process a challenging task. Besides conducting basic lab experiments and deriving fundamental kinetic and thermodynamic models, a crucial task within the entire process design is the synthesis of an optimal reactornetwork constituting the core of a chemical process. However, instead of directly up-scaling the process to large devices, it is wise to investigate process characteristics on miniplant-scale. For an existing miniplant for the hydroformylation of 1-dodecene using a rhodium catalyst and a thermomorphic solvent system for catalyst recovery, two optimized reactor designs are derived. Suitable reactor-networks were synthesized by applying the Flux Profile Analysis approach introduced in Kaiser et al. (2017). The combination of a first reactor with dynamic/distributed control options and a subsequent backmixed CSTR arose to be the most promising configurations. The technical design under miniplant conditions were carried out for two possible realizations of this network, namely (i) a continuous flow reactor and (ii) a periodically operated semibatch reactor, both followed by the existing CSTR which was originally operated in the miniplant. An optimization of the two optimal reactor configurations within an overall process including a Page 1 of 53 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research liquid-liquid phase separation for catalyst recovery and a distillation column for separating the solvents and reactant evinced a selectivity w.r.t. the linear aldehyde around 94 % and a conversion around 98 %. This is a large improvement of the process performance of 24 % linear aldehyde selectivity and 40 % conversion when using the existing CSTR.

Decreasing dietary N inputs into beef cattle feeding operations could potentially decrease environmental concerns relating to air and water quality. Previous studies with sheep suggest that oscillating dietary CP concentrations may improve N use efficiency and thereby decrease dietary N requirements. Therefore, two studies were conducted to determine the effects of oscillating dietary CP concentrations on performance, acid-base balance, and manure characteristics of steers fed high-concentrate diets. Steers were fed to a constant backfat thickness in both studies. In the first trial, 92 steers (mean BW = 408 +/- 2.8 kg; four pens/treatment) were fed the following diets: 1) constant 12% CP, 2) constant 14% CP, and 3) 10 and 14% CP oscillated at 2-d intervals. Steer performance and carcass characteristics were measured. In the second trial, 27 steers were individually fed the same three experimental dietary regimens (nine steers/treatment). Animal performance, arterial acid-base balance, plasma metabolites, and fecal characteristics were measured. In both trials, steers fed the 14% CP diet tended (P < 0.10) to have greater ADG and gain:feed than steers fed the 12% CP diet. Steers fed the oscillating CP regimen had intermediate performance. In Trial 1, steers fed the 14% CP diet tended (P = 0.09) to have smaller longissimus area and higher quality grades than steers fed the oscillating CP regimen. Protein retentions (g/d) calculated from NRC (2000) equations were greater (P = 0.04) for steers fed the 14% CP diet than steers fed the 12% CP diet. Steers fed the oscillating CP regimen tended (P = 0.08) to have greater calculated protein retention (g/d) than steers fed the 12% CP diet. Steers fed the 14% CP diet had greater (P < 0.05) calculated urinary N excretion than steers fed the 12% CP or oscillating CP regimens. Venous plasma concentrations of urea N were greater (P < 0.001) in steers fed the 14% CP diet than in steers fed the 12% CP diet; steers fed the oscillating CP regimen were intermediate but fluctuated over days. Based on arterial blood gas concentrations, acid-base balance was not significantly affected by dietary CP regimen. Results of these trials suggest that the CP requirement of steers in these studies was greater than 12% of the diet DM, and/or that the degradable CP requirement was greater than 6.3% of diet DM. However, the effects of oscillating dietary CP were minimal.

Emissions of ammonia, as well as other gases and particulates, to the atmosphere are a growing concern of livestock producers, the general public, and regulators. The concentration and ruminal degradability of CP in beef cattle diets may affect urinary and fecal excretion of N and thus may affect ammonia emissions from beef cattle feed yards. To determine the effects of dietary CP concentration and degradability on potential ammonia emissions, 54 steers were randomly assigned to nine dietary treatments in a 3 × 3 factorial arrangement of treatments. Treatments consisted of three dietary CP concentrations (11.5, 13, and 14.5%) and three supplemental urea:cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N). Steers were confined to tie stalls, and feces and urine excreted were collected and frozen after approximately 30, 75, and 120 d on feed. One percent of daily urine and feces

No abstract

Three dietary CP concentrations (11.5, 13.0, and 14.5% of DM) and 3 supplemental urea levels (100, 50, and 0% of supplemental N) were used in a completely randomized block design experiment conducted at 2 locations to determine N and P balance and serum urea N (SUN) concentrations of feedlot cattle. Crossbred steers [British and British x Continental; initial BW = 315.0 +/- 3.2 kg at location 1 (n = 27) and initial BW = 353.2 +/- 8.4 kg at location 2 (n = 27)] were used in 3 nutrient balance sampling periods (SP) at the beginning, middle, and end of the feeding period (154 d in location 1 and 159 d in location 2). Fecal N (g/d; P = 0.03), urinary N (g/d; P < 0.01), urinary urea N (UUN; g/d; P < 0.01), apparent N absorption (g/d; P < 0.01), and SUN concentration (mg/dL; P < 0.01) increased linearly as dietary CP concentration increased. Nitrogen retention (g/d) was not affected (P = 0.61) by dietary CP concentration. Phosphorus intake (g/d; P = 0.02), fecal P (g/d; P = 0.04), and urinary P (g/d; P = 0.01) increased linearly as dietary CP increased, reflecting changes in diet composition with increasing CP concentrations. As dietary urea levels increased, urinary N (g/d; P = 0.04), UUN (g/d; P = 0.01), and apparent N absorption (g/d; P = 0.04) increased linearly, but P intake (g/d; P = 0.10) and urinary P (g/d; P = 0.02) decreased linearly. No interactions were observed between SP and dietary treatments for most variables. Evaluation of SP means, however, showed that as days on feed increased, fecal N (g/d; P = 0.01), urinary N (g/d; P < 0.01), UUN (g/d; P < 0.01), apparent absorption of N (g/d; P < 0.01), SUN (mg/dL; P < 0.01), and urinary P (g/d; P < 0.01) increased linearly, whereas retained N (g/d) decreased linearly (P < 0.01) with increasing days on feed. These data suggest that changes in dietary CP and urea levels, as well as stage of the feeding period, markedly alter N and P utilization by feedlot cattle.

A new kind of solvent descriptor obtained from quantum chemical calculations is introduced. Group contributions to each solvent descriptor are regressed for 71 UNIFAC groups. A reaction kinetic model is built by correlating a set of experimentally determined reaction rate constants in various solvents with the corresponding theoretical solvent descriptors. Based on the kinetic model and the developed group contribution method, a computer-aided molecular design problem is formulated and optimal solvents to achieve highest reaction rates are identified. For considering the multiple and complicated effects of solvents on a chemical process, an integrated solvent and process design is performed. Solvent molecular structures and process operations are simultaneously optimized by the formulation and solution of a mixed-integer nonlinear program. The proposed design methodology is exemplified for a selected Diels-Alder reaction.

No abstract