Conversion Of Lactic Acid Research Articles

A Bifunctional CdS/MoO2/MoS2 Catalyst Enhances Photocatalytic H2 Evolution and Pyruvic Acid Synthesis

AbstractThe best use of photogenerated electrons and holes is crucial to boosting photocatalytic activity. Herein, a bifunctional dual‐cocatalyst‐modified photocatalyst is constructed based on CdS/MoO2/MoS2 hollow spheres for hydrogen evolution coupled with selective pyruvic acid (PA) production from lactic acid (LA) oxidation. MoS2 and MoO2 are simultaneously obtained from the conversion of CdMoO4 in one step. In a photocatalytic process, the MoS2 and MoO2 function as the reduction and oxidation centers on which photogenerated electrons and holes accumulate and are used for hydrogen evolution reaction (HER) and PA synthesis, respectively. By monitoring the intermediates, a two‐step single‐electron route for PA production is proposed, initiated by the cleavage of the α‐C(sp3)−H bond in the LA. The conversion of LA and the selectivity of PA can reach ca. 29 % and 95 % after a five‐hour reaction, respectively.

A Bifunctional CdS/MoO2/MoS2 Catalyst Enhances Photocatalytic H2 Evolution and Pyruvic Acid Synthesis

The best use of photogenerated electrons and holes is crucial to boosting photocatalytic activity. Herein, a bifunctional dual-cocatalyst-modified photocatalyst is constructed based on CdS/MoO2 /MoS2 hollow spheres for hydrogen evolution coupled with selective pyruvic acid (PA) production from lactic acid (LA) oxidation. MoS2 and MoO2 are simultaneously obtained from the conversion of CdMoO4 in one step. In a photocatalytic process, the MoS2 and MoO2 function as the reduction and oxidation centers on which photogenerated electrons and holes accumulate and are used for hydrogen evolution reaction (HER) and PA synthesis, respectively. By monitoring the intermediates, a two-step single-electron route for PA production is proposed, initiated by the cleavage of the α-C(sp3 )-H bond in the LA. The conversion of LA and the selectivity of PA can reach ca. 29 % and 95 % after a five-hour reaction, respectively.

Lactic acid fermentation of food waste at acidic conditions in a semicontinuous system: effect of HRT and OLR changes

Lactic acid production through fermentation is an established technology, however, improvements are necessary to reduce the process costs and to decrease its market price. Lactic acid is used in many industrial sectors and its market has increased in the last decade for its use as the raw material for polylactic acid product. Using food waste as a cheap and renewable substrate, as well as fermentation at uncontrolled pH, helps to make the production cheaper and to simplify the downstream purification process. Lactic acid production at acidic conditions and the role of varying organic loading rate (OLR) and hydraulic retention time (HRT) were tested in two different semicontinuous batch fermentation systems. Reactor performances indicated that lactic acid fermentation was still possible at pH < 3.5 and even up to a pH of 2.95. The highest lactic acid production was recorded at 14-day HRT, 2.14 g VS/L·day OLR, and pH 3.11 with a maximum lactic acid concentration of 8.72 g/L and a relative yield of 0.82 g lactate/g carbohydrates. The fermentation microbial community was dominated by Lactobacillus strains, the organism mainly responsible for lactic acid conversion from carbohydrates. This study shows that low pH fermentation is a key parameter to improve lactic acid production from food waste in a semicontinuous system. Acidic pH favored both the selection of Lactobacillus strains and inhibited VFA producers from utilizing lactic acid as primary substrate, thus promoting the accumulation of lactic acid. Finally, production yields tend to decrease with high OLR and low HRT, while lactic acid production rates showed the opposite trend.

High-rate conversion of lactic acid-rich streams to caproic acid in a fermentative granular system

Lactic acid-driven chain elongation enables upgrading low-value organic streams into caproic acid. Recently, volumetric production rates over 0.5 g L-1 h-1have been reported for carbohydrate-rich streams in expanded granular sludge bed (EGSB) reactors. However, many target streams contain mixtures of carbohydrates and lactic acid, and little is known about their impact on product profile and microbial ecology, or the importance of carbohydrates as substrate to achieve high rates. This manuscript investigated varying glucose-to-lactate ratios and observed that decreasing glucose-content eliminated odd-chain by-products, while glucose omission required acetic acid addition to support lactic acid conversion. Decreasing the glucose-content fed resulted in decreasing amounts of granular biomass, with the disappearance of granules when no glucose was fed. Lowering the HRT to 0.3 days while feeding only lactic and acetic acid likely triggered re-granulation, enabling the highest lactic acid-driven caproic acid production rates reported thus far at 16.4 ± 1.7 g L-1 d-1.

Neglected effect of transportation on the property of municipal biowaste and the subsequent biomethane potential

Long-distance transportation of municipal biowaste can influence its physio-chemical characteristics and the subsequent anaerobic digestion (AD) performance. However, the effect of whole transportation processes on the characteristics of municipal biowaste from upstream source separation/collection to downstream storage remains poorly documented. To this end, this study presented the relevant work by sampling in practical conditions. Results showed that transportation led to a high hydrolysis rate of 33.4%–35.5%, and an acidification rate of 15.8%–17.3%. Simultaneously, lactic acid was produced to a concentration of 18.1 g/L, occupying approximately 20% of dissolved organic carbon. Furthermore, the highest cumulative CH4 production was observed at the samples of source separation/collection (398 ± 52–519 ± 117 mL/gVS for FW, 276 ± 51–332 ± 41 mL/gVS for KW), and then accompanied by a decrease (299 ± 31 mL/gVS for FW and 285 ± 39 mL/gVS for KW) after downstream storage. The results indicated that the subsequent anaerobic digestion would be inclined to appear perturbation caused by the lactic acidification of the initial feed and it is imperative to avoid further conversion of lactic acid to propionic acid, which could provide vital guideline reference for the optimization of biogas production process. Moreover, the lactic acid-rich property also highlights other value-added pathways for the resource recovery of municipal biowaste.

Medium-chain carboxylates production from co-fermentation of swine manure and corn stalk silage via lactic acid: Without external electron donors

Environmental issues caused by untreated animal manure and crop straws require the development of resource recovery from waste through a circular economy approach. Swine manure and corn stalks as the main agricultural biomass can be a renewable resource to produce biofuels and chemicals, and they have been successfully converted into methane via anaerobic digestion. However, the revenue from methane has been relatively low. This study aimed to convert swine manure and corn stalk silage into a high-value medium-chain carboxylic acid (MCCA) through a temperature-phased two-stage bioprocess. The carbohydrates in these streams, which were first converted to lactic acid (LA) rich solution at thermophilic condition, were then fermented to MCCA by mesophilic chain elongation without addition of external e-donors. In this study, thermophilic condition enhanced the LA fermentation and shifted the dominant product spectrum from volatile fatty acid (VFA) to LA. The average LA concentration was 8.4 gCOD/L at thermophilic, which was improved by 3.4 times compared with that achieved at mesophilic condition. For the chain-elongating bioreactor, the LA-rich broth was successfully converted into MCCA. Moreover, the maximum productivities of MCCA and n-caproate were 1890 and 1290 mg COD/L/d, respectively, at pH 6.0 with an LA loading rate of 2.1 g COD/L/d. Maintaining an appropriate LA/VFA ratio and mild pH was necessary to overcome the acrylate pathway and drive LA conversion toward n-caproate instead of propionate. In addition, Pseudoramibacter and Caproiciproducens became the dominant community, with a relative abundance of 45.6% and 9.7%, respectively.

Co-valorization of corn cobs and dairy wastewater for simultaneous saccharification and lactic acid production: Process optimization and kinetic assessment

This study optimized the co-valorization of corn cob wastes (CCW) and dairy wastewater for simultaneous saccharification and lactic acid (LA) production (sDWW-SSF). Subsequently, the kinetics of Lactobacillus plantarum growth and LA production was assessed using the optimized conditions under microaerophilic (sDWW-SSFmicroaerophilic) and anaerobic (sDWW-SSFanaerobic) conditions, and thereafter compared to De Man, Rogosa and Sharpe (MRS) medium modified with pretreated CCW (mMRS-SSFmicroaerophilic). Optimized sDWW-SSF conditions produced maximum LA concentration and conversion of 11.15 ± 0.42 g/L and 18.90 ± 0.75%, respectively. Kinetic studies revealed that although the mMRS-SSFmicroaerophilic system obtained a higher maximum specific growth rate (μmax) and maximum potential LA concentration (Pm) compared to the wastewater-based bioprocesses, the data obtained for the latter were comparable when taking the resources and costs into consideration. These findings represent the potential to eliminate the use of valuable resources in lignocellulosic bioprocesses and provide insights on innovation towards driving a sustainable economy in line with the food-energy-water nexus.

Development of an enhanced chain elongation process for caproic acid production from waste-derived lactic acid and butyric acid

Medium chain carboxylic acids (MCCA), such as caproic acid, are high-value chemicals with many industrial applications. The development of a biological mixed culture chain elongation (CE) process, using waste-derived lactic acid offers an opportunity to sustainably produce MCCA, such as caproic acid. However, the nature of the biological conversions in mixed communities is still poorly understood. In particular, inhibition of methanogens and MCCA competitors for the development of a specialised inoculum and optimisation of lactic acid conversion and selectivity toward caproic acid are required. Here, the impacts of physical and chemical treatments of the inoculum (anaerobic granular sludge) on the efficiency of CE were evaluated. Additionally, the effects of lactic acid/butyric acid concentrations and ratio (r LA/BA) on selectivity and concentration of caproic acid were investigated. Blended and acidified (pH 3) granular sludge yielded the highest caproic acid concentrations. Moreover, using pH 3 acidified and blended granular sludge, substrate concentrations of 250 mM (r LA/BA = 1.5:1) and 300 mM (r LA/BA = 1:1) were optimal for efficient caproic acid accumulation with a selectivity ≥90 and a mole of lactic to mole of butyric acid consumption (C r LA/BA) of 2:1. However, a similar outcome was achieved when using an enriched caproic acid producing culture with a lower substrate concentration of 200 mM (r LA/BA = 1:1). We report a lactic acid to butyric acid threshold concentration, below and above which the selectivity toward caproic acid is reduced. With these optimum substrate concentrations and ratios, the feasibility for efficient caproic acid synthesis using lactic acid as electron donor and butyric acid as electron acceptor was established. Caproic acid synthesis was completely inhibited when the substrate concentrations were increased to 400 mM (r LA/BA = 1:1). Finally, species affiliated with Ruminococcaceae were likely involved in the caproic acid synthesis. These findings have strong potential for process-design applications in continuous reactor systems, thus allowing for continuous, efficient and sustainable caproic acid production from biomass-derived lactic acid and butyric acid.

Effect of Lotus Seed Resistant Starch on Lactic Acid Conversion to Butyric Acid Fermented by Rat Fecal Microbiota.

The aim was to investigate the effect of lotus seed resistant starch (LRS) on lactic acid (LA) conversion to butyric acid (BA) fermented by rat fecal microbiota to construct an acetyl CoA pathway. According to growth curves, the microbiota compositions at 10 and 36 h were further analyzed. The microbiota in the LRS group had higher richness and diversity compared to glucose (GLU) and high amylose maize starch (HAMS). Moreover, LRS and isotope LA promoted the growth of Lactobacillus and Bifidobacterium, promoted BA production, and inhibited the growth of Escherichia-Shigella. The BUT pathway played a dominant role in three groups. At 10 h, Escherichia-Shigella and Bifidobacterium showed a negative correlation with BUT and a positive correlation with BUK, whereas Escherichia-Shigella, Allobaculum, Bifidobacterium, and Ralstonia showed a positive correlation with BUT and BUK at 36 h. [3-13C] LA was converted to [4-13C] BA by the isotope labeling technique. Finally, LRS promoted LA conversion to BA mainly by the BUT pathway in intestinal microbiota, especially including Allobaculum, Bifidobacterium, and Ralstonia.

Efficient conversion of lactic acid to alanine over noble metal supported on Ni@C catalysts.

Alanine (Ala), regarded as the building block for protein synthesis, has been widely used in the field of food processing, pharmaceutical, and bio-based plastic industries. Containing plenty of oxygenic functional groups, biomass-derived chemicals are proper for Ala synthesis in an economic and green way via amination. In this work, lactic acid (LA) derived from renewable biomass and waste glycerol (the major by-product of biodiesel industry) was used to produce Ala. Here, a series of magnetic catalysts M/Ni@C (M = Ru, Pt, Pd, Ir, and Rh) were synthesized by ethylene glycol reduction of metal M supported on encapsulated Ni@C. Compared with catalysts based on other M metals, Ru/Ni@C catalysts exhibited extraordinary efficiency with 91.4% selectivity for Ala synthesis from LA (63.7% yield of Ala and 69.7% conversion of LA). The results of experiments and catalyst characterization indicated that the doping of M metals could improve the dehydrogenation ability of catalysts, as well as the ability of NH3 adsorption, facilitating the reaction towards Ala. Overall, this study provides an efficient chemo-catalytic way for the production of Ala from biomass-derived substrates.

Steam-assisted crystallization of highly dispersed nanosized hierarchical zeolites from solid raw materials and their catalytic performance in lactide production.

A solvent-free route based on solid raw materials affords higher product yield and lower waste production compared to the traditional hydrothermal synthesis. However, the as-made zeolites usually present blocky aggregation states, limiting their mass transfer and exposure of active sites in catalytic applications. Herein, highly dispersed nanosized hierarchical Beta zeolites with varied Si/Al ratios were prepared via steam-assisted crystallization from ball-milled solid raw materials. Thanks to the sufficient mixing of solid raw materials and favorable migration of solid mixture, nanosized Beta zeolites are obtained that are assembled from nanoparticles (∼15 nm) and possess abundant interconnected intraparticle mesopores. The strategy can also be extended to synthesize nanosized hierarchical ZSM-5 zeolites. The as-prepared Beta zeolite (Si/Al = 10) exhibits outstanding catalytic performance in conversion of lactic acid to lactide (as high as 77.5% in yield). This work provides avenues for simple and cost-efficient synthesis of highly dispersed nanosized hierarchical zeolites, promising their important catalytic applications.

Roles of micro-aeration on enhancing volatile fatty acids and lactic acid production from agricultural wastes

Micro-aeration was proven to be an environmentally friendly strategy for efficiently enhancing volatile fatty acids (VFAs) and lactic acid (LA) production. The roles of micro-aeration on mono-digestion of swine manure (SM) for VFAs production and co-digestion of SM with corn silage (CS) for LA production were investigated, respectively. In this study, micro-aeration increased the maximum VFAs concentration by 20.3% to 35.71 g COD/L, and shortened the time to reach the maximum from 18 days to 10 days. Micro-aeration limited the conversion of LA into VFAs, leading to LA accumulation effectively to be 26.08 g COD/L. Microbial community analysis suggested that Clostridium and Terrisporobacter were always the dominant bacteria with or without micro-aeration for VFAs production, but the relative abundance increased notably during the same period. However, Bifidobacterium, which could use the higher productivity metabolism pathway, i.e., Bifidum pathway to produce LA, increased from lower than 1% to 22.9% by micro-aeration.

Lactic acid conversion into acrylic acid and other products over natural and synthetic zeolite catalysts: theoretical and experimental studies

In the present study we are interested in designing theoretical and experimental approach for the production of acrylic acid (AA) from lactic acid (LA) over various zeolite catalysts: synthetic BEA and natural clinoptilolite CLI zeolites modified with metals (Sn, Co, Cu and Fe). The catalysts were prepared using an ion exchange method. In the theoretical studies the metal M-O-M dimers were found to be stable above oxygen bound with aluminium centres of BEA and CLI zeolites. The mechanism of direct lactic acid dehydration in Sn-, Co-, Cu- and Fe-BEA zeolites was found inside the zeolites pores and in the hierarchical/surface model. Experimentally, the investigated catalysts set trends in the following by-product formation: acrylic acid, pyruvic acid (PAC), 2,3-pentanedione (2,3-PD) or acetaldehyde (AC). Based on the collected results, the following types of LA conversion reactions can be proposed: dehydration to AA, decarboxylation to acetaldehyde, hydrogenation to 2,3-pentanedione, oxidation to acetic acid, reduction to propionic acid, oxidative dehydrogenation to pyruvic acid, condensation to 1,2-propanediol.

Synthesis and characterization of bio catalyst prepared from dairy waste for lactic acid esterification

Abstract Dairy byproduct is known for its valuable chemical and nutritional content possessing high market potential. Notwithstanding, it is tractable to exploit its utilization. The waste generated is organic and having huge energy potential. The objective of current research is to synthesize novel catalyst from a dairy based solid waste called Ghee Residue by chemical activation process and deploy it for the production of iso-butyl lactate. Surface identity of catalyst was furnished using Brunauer-Emmet Teller (BET) method and Fourier Transform Infrared Spectroscopy (FTIR). Effect of variables like reaction time, temperature of reaction and loading of catalyst on lactic acid conversion were studied. In addition to this, reaction kinetics modelling was performed using 2nd order pseudo-homogeneous approach. It was inferred that, both internal as well as external resistance of mass transfer could not offer any influence on overall rate of reaction in this esterification. Optimum condition for esterification reaction was at 368 K with 3% catalyst loading giving the highest conversion around 74%. The energy of activation for the present system using synthesized catalyst was 41.5 kJ/mol and found to be lower in comparison with the other catalysts. Although, the activity of GRC declined gradually less than 10% from the activity of the several reaction cycle.

Enhanced lactic acid production from P2O5-pretreated biomass by domesticated Pediococcuspentosaceus without detoxification.

Expensive cellulase and complex detoxification procedures increase the cost of biomass lactic acid fermentation. Therefore, it is of great significance to develop a robust method to ferment lactic acid using biomass by avoiding cellulase and detoxification. This study demonstrates the advantage of combining mechanocatalytic P2O5 pre-treatment and strain domestication. We show that an enzyme-free mechanocatalytic saccharification process by combining mix-milling of P2O5 with biomass and successive hydrolysis produces a fermentable hydrolysate with much less inhibitory compounds than the hydrolysates obtained by conventional methods; only 5-HMF, furfural and acetic acid were detected in the biomass hydrolysate, and no phenolic inhibitors were detected. Pretreatment of biomass with P2O5 not only avoided cellulase, but also obtained less toxic hydrolysate. Furthermore, the Pediococcuspentosaceus strain gained superior inhibitor tolerance through domestication. It could tolerate 17.1g/L acetic acid, 12.5g/L 5-HMF, 11.9g/L guaiacol and 11.5g/L furfural and showed activity in decomposing furfural and 5-HMF for self-detoxification, allowing efficient lactic acid fermentation from biomass hydrolysate without detoxification. The lactic acid concentration and conversion rate fermented by domesticated bacteria were increased by 113.5% and 22.4%, respectively. In addition, the domesticated bacteria could utilize glucose and xylose simultaneously to produce lactic acid selectively. The combination of P2O5 pre-treatment and strain domestication to ferment lactic acid is applied to several biomass feedstocks, including corn stalk, corn stalk residue and rice husk residue. Lactic acid concentrations of 29.8g/L, 31.1g/L, and 46.2g/L were produced from the hydrolysates of corn stalk, corn stalk residue and rice husk residue, respectively.

Production of medium-chain fatty acid caproate from Chinese liquor distillers’ grain using pit mud as the fermentation microbes

Chinese liquor distillers’ grain (CLDG) is an abundant industrial organic waste showing high potential as feedstock for biofuel conversion. In this study, CLDG was used as substrate by microbial community in pit mud to produce medium-chain fatty acids (especially caproate). Simulated and real fermentation were used to evaluate the effect of ethanol and lactic acid being the electronic donors (EDs) during the anaerobic chain elongation (CE). The caproate concentration was achieved at 449 mg COD/g VS, with the corresponding high carbon selectivity at 37.1%. Microbial analysis revealed that the domestication of pit mud increased the abundance of Caproiciproducens (converting lactic acid into caproate) and Lactobacillus (producing lactic acid), leading to enhanced caproate production. The lactic acid conversion facilitated in full utilization of ethanol through CE consumption. The coexistence of EDs benefited the CE system and that this green energy production can be a promising high-performance biofuel donor for sustainable industrial production development.

Conceptual design of a dual reactive dividing wall column for downstream processing of lactic acid

Methodologies for designing intensified processing units are necessary to enable the industrial application of process intensification concepts. This article presents a ruled-based systematic methodology for the synthesis and conceptual design of a dual reactive dividing wall column (dual R-DWC). A decomposition approach is used to identify the tasks required for the separation by introducing a reactive separating agent to exploit a reversible reaction to enhance the driving forces. A combination of shortcut and rigorous simulations led to the conceptual design of a novel dual R-DWC in which the forward and reverse reactions and the separation occur at once.The methodology was demonstrated in a case study for the separation of lactic acid from dilute aqueous streams and a reactive impurity that hinders the lactic acid conversion and its recovery, while the byproducts may bring new challenges for the desired separations.This study is the first to investigate the effect of reactive impurities on the reaction and the separation, hence adding a more realistic framework to the design. The flowsheet produced was evaluated against benchmark processes and showed a significant process improvement in terms of energy savings (ranging 13-27 %), material intensity (28-32 % reduction), and water consumption (22-36 % reduction), while the reactive impurities are effectively removed.

The Role of the Surface Acid-Base Nature of Nanocrystalline Hydroxyapatite Catalysts in the 1,6-Hexanediol Conversion.

Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid–base nature of hydroxyapatites containing sodium ions. We prepared nanocrystalline hydroxyapatite (Ca-HAP) catalysts with various Ca/P ratios and sodium contents by the hydrothermal method. The adsorption and desorption experiments using NH3 and CO2 molecules and the catalytic reactions for 2-propenol conversion revealed that the surface acid–base natures changed continuously with the bulk Ca/P ratios. Furthermore, the new catalytic properties of hydroxyapatite were exhibited for 1,6-hexanediol conversion. The non-stoichiometric Ca-HAP(1.54) catalyst with sodium ions of 2.3 wt% and a Ca/P molar ratio of 1.54 gave a high 5-hexen-1-ol yield of 68%. In contrast, the Ca-HAP(1.72) catalyst, with a Ca/P molar ratio of 1.72, gave a high cyclopentanemethanol yield of 42%. Both yields were the highest ever reported in the relevant literature. It was shown that hydroxyapatite also has excellent catalytic properties for alkanediol conversion because the surface acid–base properties can be continuously controlled by the elemental compositions, such as bulk Ca/P ratios and sodium contents.

Lanthanum phosphate: an efficient catalyst for acrylic acid production through lactic acid dehydration

In this work, biomass-based platform molecule lactic acid conversion to acrylic acid has been studied. A series of lanthanum phosphate (LaP) catalysts prepared by varying the lanthanum to phosphorus (La/P) mole ratio (i.e., 0.2, 0.35, 0.5, 1.0, and 2.0) and also prepared at different calcination temperatures (i.e., 400, 500, 600, and 800 °C) were investigated. The catalysts were characterized by using different techniques and tested in the dehydration of lactic acid (LA) to acrylic acid (AA) production. All the synthesized catalysts were characterized to analyze the physicochemical properties such as degree of crystallinity, total surface acidity, specific surface area, and morphology. The La/P mole ratio was found to be significant in designing the optimized catalytic system. The NH3-TPD results imply that all the catalysts exhibited varied amount of total acidity with phosphate loadings, which are mostly weak acid sites. The weak acid sites which are mainly Lewis acidity type played an important role in producing AA selectively and efficiently from the LA conversion. The most optimized reaction conditions were determined to obtain the highest LA conversion, selectivity, and AA yield. The catalyst with an La/P mole ratio of 0.35 and calcined at 500 °C exhibited the best performance with complete LA conversion, AA selectivity of ~ 74%, and a maximum yield of AA of ~ 74%. Furthermore, the LaP(0.35)[500] catalyst was successfully tested at three different time on streams and found to be stable.

Microcontroller Based Automated Reactor for Esterification of Lactic Acid: MATLAB Simulation

ABSTRACT: This paper deals with esterification of lactic acid using sulphonated carbon catalyst in a newly designed microcontroller based automated reactor (MBAR) and the simulation of process parameters using MATLAB programming. The reactor was accompanied with moisture sensor, temperature sensor and solenoid valves in the embedded system. The study of effect of process parameters such as silica gel weight, hot air temperature, molar ratio and conversion of lactic acid on the removal of water, generated during esterification reaction, was performed. Water removal by adsorption using silica gel at each stage of conversion was estimated experimentally as well as with the help of developed, simulated linear equations, using MATLAB. The experimental and MATLAB results were compared and found in close vicinity. The simulation results revealed that an increased water removal is achieved with increasing conversion and molar ratio. The results also validated that increasing the reaction temperature increases the conversion tremendously with a rapid decrease in hot air flow requirement. The uniqueness of newly designed reactor is that the silica bed is operated in rotation in such a way that when one is in operation another is regenerated during its idle time.