Beer aroma recovery and dealcoholisation by a two-step pervaporation process

Pervaporation with a polydimethylsiloxane membrane (PDMS) has previously been used for the recovery of aroma compounds or to dealcoholise beer. This work considers two PDMS pervaporation processes and associated operating conditions. In addition to ethanol, two esters and one higher alcohol were chosen as key beer aroma compounds. The effects of feed flow rate and temperature on aroma recovery were studied, with feed temperature and permeate pressure evaluated with regard to beer dealcoholisation. The required membrane areas for a given alcoholic beer flow rate were simulated by mass balance to achieve a non-alcoholic product. With aroma recovery, no concentration polarisation was observed with Reynolds numbers above 1520 and the optimal temperature was 10°C. For alcohol removal, the best operation conditions were 65°C and 1400 Pa. With such conditions, the required membrane surface to recover 50% of ethyl acetate from the original beer was 13.8 m² in the first pervaporation unit, whereas 4.4 m² was needed in the second one to achieve an alcohol content of 0.05% (v/v). The mixed final product was defined as an alcohol-free beer with significant aroma compounds, showing the feasibility of pervaporation for both beer aroma recovery and dealcoholisation. © 2019 The Institute of Brewing & Distilling     

A combined complete pore blocking and cake filtration model during ultrafiltration of polysaccharide in a batch cell

Ultrafiltration experiments of polysaccharide macromolecule have been performed in a batch, stirred as well as unstirred membrane cell using a fully retentive membrane over a wide range of operating conditions. A model based on Hermia’s approach for constant pressure dead-end filtration laws is proposed to analyze the flux decline behavior during ultrafiltration in a batch cell. Two model parameters, namely complete pore blocking coefficient and cake filtration coefficient are obtained by minimizing the error involved between calculated and experimental flux data. These parameters along with known operating conditions, membrane permeability and physical properties of feed enable one to predict the transient permeate flux decline. The effect of various operating conditions, such as feed solute concentration, stirrer speed and transmembrane pressure on the flux decline is studied. Experimental results show that operating conditions have significant effect on the onset of cake formation as well as on the flux decline behavior. Model predicted results are successfully compared with the experimental data.     

Recovery of volatile fruit juice aroma compounds by membrane technology: Sweeping gas versus vacuum membrane distillation

The influence of temperature (10–45 °C), feed flow rate (300–500 L/h) and sweeping gas flow rate (1.2–2 m³/h) on the recovery of berry fruit juice aroma compounds by sweeping gas membrane distillation (SGMD) was examined on an aroma model solution and on black currant juice in a lab scale membrane distillation set up. The data were compared to recovery of the aroma compounds by vacuum membrane distillation (VMD). The flux of SGMD increased with an increase in temperature, feed flow rate or sweeping gas flow rate. Increased temperature and feed flow rate also increased the concentration factors (C_permeate/C_feed) of the aroma compounds. At 45 °C the most volatile and hydrophobic aroma compounds obtained the highest concentration factors: 12.1–9.3 (black currant juice) and 17.2–12.8 (model solution). With black currant juice a volume reduction of 13.7% (vol.%) at 45 °C, 400 L/h, resulted in an aroma recovery of 73–84 vol.% for the most volatile compounds. Compared to VMD, the aroma recovery with SGMD was less influenced by the feed flow rate but more influenced by the temperature. Higher fluxes were achieved during concentration by VMD and this reduced the operation time, which in turn reduced the degradation of anthocyanins and polyphenolic compounds in the juice.

Industrial relevance

High temperature evaporation is the most widely used industrial technique for aroma recovery and concentration of juices, but membrane distillation (MD) may provide for gentler aroma stripping and lower energy consumption. This study gives important clues about the fate of berry juice aroma compounds and polyphenols during concentration by MD, and identifies the main factors influencing the aroma recovery efficiency with MD. Both SGMD and VMD are promising techniques for gentle stripping of berry juice aroma compounds and deserve further consideration as alternative techniques for gentle aroma stripping in industrial fruit juice processing.     

Prediction of Permeate Flux During Ultrafiltration of Polysaccharide in a Stirred Batch Cell

Ultrafiltration of polysaccharide macromolecule has been carried out in a stirred batch cell using a fully retentive membrane over a wide range of operating conditions. An unsteady state mass transfer model in conjunction with resistance-in-series model is developed using film theory. The proposed model is used to predict the transient permeate flux decline behavior in gel controlled ultrafiltration. This model is also able to quantify the variation of bulk volume as well as the bulk concentration of solute with time. The variation of viscosity as a function of solute concentration is included in the model. A model parameter is used in this model and is evaluated by optimizing the experimental flux profiles with calculated flux profiles. The model predictions are successfully compared with the experimental data. A parametric study has been performed to observe the effect of different process parameters on the filtration performance in terms of transient permeate flux decline behavior. The proposed model in general will provide a better understanding of gel controlled ultrafiltration.     

Aroma compound recovery with pervaporation — Temperature effects during pervaporation of a muscat wine

A muscat wine, in which eight aroma compounds had been identified, was pervaporated through a poly(dimethyl siloxane) membrane at four different feed temperatures, 6, 15, 25 and 35 °C. Marked effects were observed in the partial fluxes of aroma compounds as the temperature was increased, a phenomenon which could be described by Arrhenius expressions in the equations used to mathematically describe the pervaporation process. Different aroma compounds were differently affected by the temperature changes, and this resulted in changes in concentrations in the permeate, both total and relative, of the aroma compounds studied and in their aroma values in the permeate. Knowledge of the temperature dependence of different aroma compounds is therefore of great importance in the optimization of the pervaporation process for aroma compound recovery.     

Experimental study of water and salt fluxes through reverse osmosis membranes

Water flux and salt rejection rate, which are the two most important parameters in evaluating the performance of a reverse osmosis membrane process, are desirable to be directly related to the membrane properties and operating conditions. However, the membrane transport theories in their general forms are unable to describe the membrane performance satisfactorily. In this study, water and salt fluxes through reverse osmosis membranes were carefully examined with a cross-flow filtration cell under various operating conditions. Experimental results showed that a notable permeate flux was detected when the driving pressure was smaller than the feed osmotic pressure. Water flux increased with the driving pressure nonlinearly before approaching a linear relation with the pressure. In addition, salt transport was highly dependent on both operating pressure and feed salt concentration. A power relationship between salt flux and concentration was correlated well with the experimental data. The equations for water and salt fluxes obtained from this work would provide a facile and accurate means for predicting the membrane performance in design and optimization of reverse osmosis processes.     

Separation of Sucrose and Reducing Sugar in Cane Molasses by Nanofiltration

Recovery of sugars from cane molasses is a promising approach to increase the added value of molasses and reduce its environmental pollution. In this work, for the first time, nanofiltration (NF) was used for the separation of sucrose and reducing sugar in cane molasses by a cascade diafiltration-concentration process. The retention difference between sucrose and reducing sugar by all the tested NF membranes was not distinct at 25 °C, while due to the thermal-induced pore size change and enhanced solute diffusivity, the NF retention behavior changed significantly at 60 °C, and the DL membrane with a sucrose retention of 96% and a reducing sugar retention 5% was selected for the process optimization and modeling. High temperature (55–60 °C), low permeate flux (below 15 Lm^?2 h^?1), and high sugar concentration resulted in a low retention of reducing sugar due to the dominant diffusive mass transfer, which was desirable for the molasses separation by NF. Mathematical modeling could well predict the diafiltration and concentration processes if using right sugar retention data. The deviations between prediction lines and experimental data in the cross-flow filtration of real solution were mainly caused by the permeate flux variation rather than membrane fouling. After diafiltration, the ratio of sucrose in total molasses sugar increased from 76.1 to 87.9%, while in the permeate of the second concentration step, the ratio of sucrose was only 2.4%. Thus, the retentate of diafiltration could be directly used for sucrose crystallization to avoid the accumulation of reducing sugar and salts, and the permeate of the second concentration step could be concentrated by NF270 at room temperature to produce syrup drinking.     

On the use of ultrafiltration for the concentration and desalting of phosvitin from egg yolk protein concentrate

An ultrafiltration‐based approach was integrated in the preparation of phosvitin (PVs) from delipidated egg yolk proteins. An attempt was made to concentrate PVs as well as to desalt by means of the diafiltration technique. Primary experiments were devoted to optimise the ultrafiltration performance as function of parameters such as the effects of pH, feed concentration and transmembrane pressure on permeate flux with the 10‐kDa molecular weight cut‐off (MWCO) polyethersulfone membrane at laboratory scale. Higher permeate flux values were observed at low concentration and at alkaline pH, whatever transmembrane pressure studied. Then, desalting of PVs was carried out at 50 °C with 10‐ and 30‐kDa MWCO membranes. The results showed that desalting of PVs was obtained with both the 10‐ and 30‐kDa MWCO membranes and with a few loss of protein in the permeate side.     

Separation of non-sucrose compounds from syrup as a part of the sugar-beet production process by ultrafiltration with ceramic membranes

Non-sucrose compounds having intensive colour tend to build into the sucrose crystals during the crystallization. Their removal, or decrease of their concentration in sugar syrup, is a very important operation. The subject of this laboratory investigation was a separation process performed by ceramic tubular membrane in two modes of operation: with static mixer (SM) and without static mixer (NSM). In order to compare two alternatives as well as to determine optimal operating conditions, in both modes, solution flow rate, temperature, transmembrane pressure and process duration were varied independently and their influence on the permeate flux as well as on the efficiency of decolourization and purification were examined. The cross-flow filtration was carried out on ceramic tubular membrane with pore diameter of 20 nm. The obtained results have shown that permeate flux increased approximately 30%, at 80 °C, and 65%, at 70 °C, when static mixer was used. Significant part of coloured compounds—45% in average, determined by the absorbance measurement of permeate/feed, was separated from the raw sugar syrup. Decolourization in SM-mode is greater than the decolourization in NSM-mode (30% after 0.5 h and 55% after 2 h). Purity was eliminated with an efficiency of 80% in average compared to the feed, with the similar success when NSM-mode and SM-mode of operation were applied, particularly at the end of ultrafiltration.     

Influence of feed properties on membrane fouling in crossflow microfiltration of particulate suspensions

The effects of the feed concentration (C_feed) and particle size distribution (PSD) on the crossflow microfiltration (CFMF) of suspensions containing lactalbumin particles were investigated. Experiments were carried out in constant transmembrane pressure (TMP) mode using tubular ceramic membrane modules. All the important parameters: permeate flux, internal and surface fouling, cake mass, height, porosity, and PSD were estimated. The steady-state flux (J_ss) decreased, and internal as well surface fouling and cake mass and height all increased with an increase in C_feed from 0.65 to 2.5 gL⁻¹. This was due to the availability of more particles to foul the membrane at higher C_feed. However, above 2.5 gL⁻¹ there was no significant effect of C_feed on any of these parameters. The overall observed behaviour is attributed to steady-state membrane fouling resulting from the availability of sufficient particles for maximum possible deposition under the experimental conditions reached at 2.5 gL⁻¹. The larger the feed particles, the higher was the J_ss. However, the cake mass, height and porosity were not affected by the feed PSD. Significantly, addition of larger feed particles at the steady state increased the flux by about 6%. This behaviour is attributed to the scouring effect of the large particles on the cake surface. There is scope for looking at the possibility of using the scouring effect of large particles to improve the CFMF process performance.     

超滤法浓缩鳀蒸煮液的数学模型

采用切向流超滤技术浓缩鳀鱼蒸煮废弃液中蛋白质,在前期对超滤压力、进样流速、样品pH 值、操作温度等操作条件研究的基础上,建立超滤数学模型,通过实验获得拟合参数。结果表明：模型理论值曲线与实验值曲线拟合良好,各曲线的相关系数均在0.99 左右,且膜通量理论值和实验值之间的误差较小,范围在0.44%～10.00% 之间。在工业化设计和实践中,可以根据该数学模型预测超滤条件的变化对超滤过程的影响,根据该模型选择最佳的操作条件,有效地控制浓差极化和膜污染。     

Effect of the operating variables on the extraction and recovery of aroma compounds in an osmotic distillation process coupled to a vacuum membrane distillation system

The coupled operation of osmotic distillation (OD) and vacuum membrane distillation (VMD) for concentration of fruit juices and simultaneous recovery of their aroma compounds was studied. The simulated aqueous fruit juices containing four common aroma compounds were concentrated using osmotic distillation where the feed solution was in contact with a brine solution of CaCl₂, through a hydrophobic macroporous membrane contactor. Aroma compounds absorbed in the extraction brine were extracted using a membrane evaporator under vacuum and collected into a cold trap. This way, both concentration and aroma recovery of fruit juices were achieved simultaneously using two hollow fiber membrane modules. The transfer of the aroma compounds was evaluated by using different operating variables such as hydrodynamic conditions, brine concentration and vacuum pressure. The experiments show that the loss of aroma compounds during the concentration processes can be avoided by means of extraction of the aroma compounds from the brine separately, resulting in an average of 75% recovery in aroma compounds. In general, the process of aroma removal and recovery is faster than the concentration process of the fruit juices by osmotic distillation at a technical and commercial level (higher than 45°Brix). Thus, the simultaneous operation of these two membrane processes can be used to decrease the energy requirements for a given production capacity.     

超滤+纳滤回收甘薯淀粉加工废水中多糖的中试研究

为了探究超滤（UF）+纳滤（NF）组合工艺回收甘薯淀粉加工废水中多糖的技术可行性,通过UF+NF双膜法中试实验,研究了操作压力、进水流量、运行时间对NF膜分离效果的影响,采用正交实验优化了NF膜清洗参数。结果表明:当操作压力为0.2 MPa、进水流量为550 L/h时,UF（60 ku）对蛋白截留率为94.1%。NF最佳运行条件为操作压力0.3 MPa、进水流量450 L/h,运行时间3 h,透过液多糖浓度低于4.8 mg/L,多糖、化学需氧量（COD）截留率分别为98%、85.2%。清洗剂种类、清洗剂浓度、清洗时间对NF膜清洗效果影响显著（p<0.01）,而清洗温度对NF膜清洗效果影响不显著（p>0.05）,影响程度大小顺序为清洗时间>清洗剂种类>清洗剂浓度>清洗温度;最优清洗参数时（温度30℃、清洗时间15 min、碱性蛋白酶浓度0.06%）,NF膜通量恢复率为92.1%。      

酵母溶液超滤渗滤分离研究

采用MWCO为5000的超滤膜对酵母溶液进行超滤渗滤研究。结果表明，超滤通量随操作压力和温度的升高而增大，且在较高操作压力下的通量衰减较快，推导出超滤通量和料液溶质浓度的对数呈线性关系，可以对超滤通量变化情况作较好预测；随超滤和渗滤的进行，浓缩液中蛋白质主体浓度逐渐升高至20mg／mL，而超滤液和渗滤波中蛋白质最终浓度仅为0．3mg／mL，蛋白质被去除率达90％以上；浓缩液和渗滤液中海藻糖浓度几乎相同，最终浓度下降到0．9mg／mL左右，总回收率达到80％以上。     

Composition of Some Organic and Inorganic Compounds in Reverse Osmosis-Concentrated Citrus Juices

Orange, grapefruit and lemon juices were concentrated over twofold in a pilot scale reverse osmosis (RO) process using a commercially available membrane system. Major sugars, acids, vitamin C, aroma volatiles and over 20 minerals were examined in feed, concentrate and permeate streams. Typically, 15–20 aroma compounds were identified in feed juices and concentrates. Compared with less volatile compounds (e.g., ethyl butyrate, limonene), poorer retention during processing was noted for more volatile molecules (methanol, acetaldehyde, ethanol). °Brix of membrane concentrates were orange (25.3°B), grapefruit (25.1°B) and lemon (22.5°B). Vitamin C was rejected efficiently by the membrane. Mineral analyses showed similar elemental contents in feed and concentrate and insignificant concentration in permeate streams.     

The effect of ultrasound waves on the efficiency of membrane clarification of pomegranate juice

Pomegranate juice has a turbid appearance, which poses difficulties in its concentration process. Membrane clarification can be used to clarify pomegranate juice; however, membrane fouling reduces the permeate flux, limiting its effectiveness. Ultrasound at 30 kHz was used to reduce membrane fouling. Results were compared with the data obtained for membrane clarification without ultrasonic treatment at the same temperature. Results showed that permeate flux increased with ultrasonic treatment. Evaluation of different membrane fouling characteristics showed that the total membrane resistance fell due to the reduction in irreversible fouling and cake resistance. However, ultrasound did not affect the thick caking produced in membrane processing at low feed‐flow rates. Evaluation of the physicochemical properties of pomegranate juice showed that ultrasound can decrease antioxidant activity due to the reduction in total anthocyanin content. Also, total soluble solid content and acidity of pomegranate juice changed with ultrasonic treatment.     

Concentration of Skim Milk by a Cascade Comprised of Ultrafiltration and Nanofiltration: Investigation of the Nanofiltration of Skim Milk Ultrafiltration Permeate

In order to reach a high volume reduction ratio (VRR) prior to drying of skim milk, a membrane cascade comprising of an ultrafiltration (UF) coupled with a nanofiltration (NF) can be applied. The present study investigated the impact of processing (filtration temperature, transmembrane pressure (TMP)) and product (feed pH) parameters on the NF of skim milk UF permeate. It could be shown that a low filtration temperature of 10 °C is more advantageous in terms of flux stability and rejection of the solute fraction as compared to higher filtration temperatures up to 45 °C. The solution pH did not affect permeate flux and lactose retention. However, in order to avoid calcium losses, it is more favorable to conduct the concentration at a pH of 6.8 instead of at a lower pH of 5. The application of a higher TMP (up to 4 MPa) enhances permeate flux and VRR as well as solute rejection during concentration of UF permeate. It was also shown that the retention of solutes decreases towards the end of the concentration process. As a consequence, the achievement of high final VRR must be weighed against increased product losses at the end.     

REVERSE OSMOSIS CONCENTRATION of APPLE JUICE: FLUX and FLAVOR RETENTION BY CELLULOSE ACETATE and POLYAMIDE MEMBRANES

Apple juice was concentrated in a pilot scale reverse osmosis unit using two commercial spiral wound cellulose acetate membranes with 97% (CA-97) and 99% (CA-99) NaCl rejection ratings and an experimental polyamide (PA-99) membrane with 99% salt rejection rating. Flux and concentration rates were higher for the PA-99 membrane than for the CA membranes. Gas chromatographic analysis of feed, permeate, and concentrate samples was undertaken and a mass balance of odor-active volatiles was performed. the PA-99 membrane retained 45% of the total odor-active volatiles while the CA-99 retained 23 %. Acetates were not found to increase when apple juice was concentrated with the cellulose acetate membrane. Retention of individual aroma compounds for the CA-99 and PA-99 membrane was rationalized using polar, nonpolar, and steric parameters.     

Modeling of Sucrose Permeation through a Pectin Gel During Ultrafiltration of Depectinized Mosambi [Citrus sinensis (L.) Osbeck] Juice

Ultrafiltration of synthetic juice (mixture of sucrose and pectin with varying composition) as well as enzymatically treated mosambi [Citrus sinensis (L.) Osbeck] juice is performed in a batch, unstirred membrane cell. Thin‐film composite polyamide membrane of molecular weight cutoff 50000 was used. The flux decline mechanism is found to be controlled by the growth of a gel layer of pectin over the membrane surface. Using standard cake filtration theory, the flux decline and the growth of gel layer is quantified. The gel layer is characterized in terms of specific gel layer resistance, gel porosity, and gel density. A transient model is proposed and solved numerically to quantify the transport of sucrose through the pectin gel for the synthetic juice and enzymatically treated juice. The hindered diffusion coefficient of sucrose through the gel is calculated by comparing the results with the experimentally obtained permeate concentration profile of sucrose. The calculated permeate concentration profile agrees well with the experimental data.     

Application of nanofiltration models for the prediction of lactose retention using three modes of operation

The desal 5 DL membrane (Dow Chemical, USA) was used to recover lactose from whey ultrafiltration permeate. Lactose and ions rejection and permeate flux were measured using ultrafiltered sweet whey as feed solution. Three different operation modes (total recycle mode, concentration mode and continuous diafiltration mode) were considered. Lactose retention was predicted by means of the Donnan Steric Partioning model (DSPM) and the Kedem–Spiegler model (KSM). The best fit for the total recycle and concentration modes was obtained with the KSM. Moreover, the KSM predictions were worse for the CDM. These models contribute to a better understanding of the transport mechanisms involved in nanofiltration processes and to optimize the process at industrial scale. The two models can be considered as a useful tool to improve the recovery, demineralization and concentration of lactose.